Patent Publication Number: US-2020299892-A1

Title: Washing machine and controlling method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0032203, filed on Mar. 21, 2019 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to a washing machine capable of drying laundry and a controlling method thereof. 
     2. Description of the Related Art 
     In general, a washing machine is an apparatus configured to wash laundry inside of a tub retaining water by rotating a drum rotatably installed in the tub to accommodate the laundry. The washing machine may perform a washing cycle using water to separate pollutants from the laundry, a rinsing cycle rinsing the laundry, a spin-dry cycle removing water from the wet laundry, and a drying cycle drying the laundry. 
     In particular, the drying cycle may use a heat-drying method which dries the laundry by heating the air inside of the tub and the drum. To perform the drying cycle as mentioned above, the washing machine requires a drying duct configured to heat the air inside of the tub and the drum. 
     Typically, the drying duct is located above the tub. In addition, the drying duct is connected to the front upper part of the tub and the rear upper part of the tub, and can suck in wet air from the rear upper part of the tub and discharge the heated and dried air to the front upper part of the tub. 
     As such, as the drying duct is connected to the top of the tub, the flow of air is mainly generated at the top of the tub. Thereby, the drying time of the washing machine can be increased. 
     SUMMARY 
     In order to overcome this problem, one aspect of the present disclosure is to provide a washing machine that can shorten the drying time by improving the drying efficiency of the washing machine. 
     One aspect of the present disclosure is to provide a washing machine capable of improving the drying efficiency by heating air inside a tub during a drying stroke and at the same time rotating a drum at high speed. 
     One aspect of the present disclosure is to provide a washing machine that can improve the drying efficiency by providing a condensing duct extending from the bottom to the top of the rear of the tub and connecting the condensing duct with a drying duct. 
     In accordance with an aspect of the present disclosure, a washing machine includes a tub; a drum rotatably installed inside of the tub; a condensing duct formed on an inner wall of the tub; a heating duct provided outside the tub; a duct heater provided inside the heating duct; a fan configured to circulate air in the drum, the condensing duct, and the heating duct; and a controller configured to rotate the drum at a first rotational speed so as to tumble laundry contained in the drum while controlling the duct heater to heat air circulated by the fan. The controller may rotate the drum at a second rotational speed, which is higher than the first rotational speed, to separate water from the laundry contained in the drum while controlling the duct heater to heat the circulating air. 
     In accordance with an aspect of the present disclosure, a controlling method of washing machine including a tub, a drum provided to rotate inside the drum, comprising: rotating the drum at a first rotational speed so as to tumble laundry contained in the drum while controlling the duct heater to heat air circulated by the fan, rotating the drum at a second rotational speed to separate water from the laundry contained in the drum while controlling the duct heater to heat the circulating 
     In accordance with an aspect of the present disclosure, a washing machine, includes a tub; a drum rotatably installed inside of the tub; a condensing duct formed on an inner wall of the tub; a condensation conduit to connect an external water source to the condensing duct; a condensation valve provided on the condensation conduit to adjust supply of water to the condensing duct; a heating duct provided outside the tub; a duct heater provided inside the heating duct; a fan circulating air in the drum, the condensing duct, and the heating duct; and a controller electrically connected with the drum motor, the condensation valve, the duct heater, and the fan; and wherein the condensing duct includes a rear groove formed inside the rear wall of the tub having a cylindrical shape, and a cover for partitioning the inside of the rear groove from the inside of the tub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates an appearance of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 2  is a side cross-sectional view of a configuration of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 3  is an exploded perspective view of a drying duct of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 4  is a perspective view of a tub rear part of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 5  shows a cross-sectional view along line AA′ shown in  FIG. 4 ; 
         FIG. 6  shows a cross-sectional view along line BB′ shown in  FIG. 4 ; 
         FIG. 7  shows a cross-sectional view along line C-C′ shown in  FIG. 4 ; 
         FIG. 8  shows a rear outer side of a tub of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 9  shows a cross-sectional view along line DD′ shown in  FIG. 8 ; 
         FIG. 10  shows a flow of water and air in a condensing duct according to one embodiment; 
         FIG. 11  shows a flow of water and air in a condensing duct according to another embodiment; 
         FIG. 12  shows a configuration of a washing machine in accordance with an embodiment of the present disclosure; 
         FIG. 13  shows an operation of a washing machine according to one embodiment; 
         FIG. 14  shows a drying cycle performed by a washing machine according to one embodiment; 
         FIG. 15  shows operations of each of the components of as washing machine by the drying cycle shown in  FIG. 14 ; 
         FIGS. 16 and 17  show residual moisture by a heating/dehydration operation shown in  FIG. 14 ; 
         FIG. 18  shows the drying time according to a tub temperature; 
         FIG. 19  illustrates a filter cleaning operation of a washing machine according to one embodiment; 
         FIG. 20  shows the amount of water entering a drum during filter cleaning according to a rotational speed of the drum; 
         FIG. 21  is a side cross-sectional view of a washing machine according to one embodiment; and 
         FIG. 22  illustrates a configuration of a washing machine according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. The progression of processing operations described is an example; however, the sequence of and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of operations necessarily occurring in a particular order. In addition, respective descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
     Additionally, exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings. The exemplary embodiments may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the exemplary embodiments to those of ordinary skill in the art. Like numerals denote like elements throughout. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” or “directly coupled,” to another element, there are no intervening elements present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     The expression, “at least one of a, b, and c,” should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c. 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like components throughout. 
       FIG. 1  illustrates an appearance of a washing machine in accordance with an embodiment of the present disclosure.  FIG. 2  is a side cross-sectional view of a configuration of a washing machine in accordance with an embodiment of the present disclosure.  FIG. 3  is an exploded perspective view of a drying duct of a washing machine in accordance with an embodiment of the present disclosure. 
     Referring to  FIGS. 1, 2 and 3 , a washing machine  100  includes a cabinet  101 , a tub  110 , a drum  120 , a drum motor  130 , a water supplier  140 , a water drain  150 , a detergent supplier  160 , and a drying duct (dryer)  200 . 
     The cabinet  101  may accommodate components included in the washing machine  100 . For example, the cabinet  101  includes the tub  110 , the drum  120 , the drum motor  130 , the water supplier  140 , the water drain  150 , the detergent supplier  160 , and the drying duct  200 . 
     At the center of the front surface of the cabinet  101 , an inlet  101   a  is formed to which laundry is put into or taken out of. 
     The tub  110  includes a tub front part  111  having an opening  111   a  formed at a front surface thereof, and a tub rear part  112  having a cylindrical shape with a closed rear surface thereof. 
     The front of the tub front part  111  is provided with the opening  111   a  for injecting laundry into the drum  120  provided in the tub  110  or withdrawing laundry from the drum  120 . 
     A diaphragm  113  is provided in the opening  111   a  of the tub front part  111 , and the diaphragm  113  connects the opening  111   a  with the inlet  101   a  of the cabinet  101 . In the upper portion of the diaphragm  113 , a discharge port  113   a  is provided for discharging air dried by the drying duct  200  into the tub  110 /the drum  120  during a drying cycle. 
     The lower portion of the tub front part  111  is connected with a drain conduit  151  extending to a drain pump  152 . 
     A rear wall  112   a  of the tub rear part  112  is provided with a bearing  112   d  and a bearing housing  112   e  for rotatably fixing the drum motor  130 . 
     A tub heater  114  is provided below the tub rear part  112 . The tub heater  114  may heat water accommodated in the tub  110 . The tub heater  114  may be operated so that the temperature of the water accommodated in the tub  110  is heated to a temperature set by a user. 
     An upper side of the tub rear part  112  is provided with a suction port  112   c  for suctioning air inside the tub  110 /the drum  120  into the drying duct  200  during the drying cycle. A sidewall  112   b  is formed with a condensing duct  240  which guides air inside the tub  110 /the drum  120  to the suction port  112   c  during the drying cycle. 
     The condensing duct  240  is described in more detail below. 
     The drum  120  is rotatably provided in the tub  110  and may accommodate laundry. 
     The drum  120  includes a cylindrical drum body  121 , a drum front part  122  provided at the front of the drum body  121 , and a drum rear part  123  provided at the rear of the drum body  121 . 
     The inner surface of the drum body  121  provides a through hole  121   a  connecting the inside of the drum  120  and the inside of the tub  110  and a lifter  121   b  for raising the laundry to the upper portion of the drum  120  during the rotation of the drum  120 . The drum front part  122  is provided with an opening  122   a  for injecting laundry into the drum  120  or withdrawing laundry from the drum  120 . The drum rear part  123  may be connected to the shaft  131  of the drum motor  130  that rotates the drum  120 . 
     The drum motor  130  is provided outside the rear wall  112   a  of the tub  110  and is connected to the drum  120  through the shaft  131 . The shaft  131  penetrates the rear wall  112   a  of the tub  110  and is rotatably supported by the bearing  112   d  and the bearing housing  112   e  provided in the rear wall  112   a  of the tub  110 . 
     The drum motor  130  includes a stator  132  fixed to the outside of the rear wall  112   a  of the tub rear part  112 , and a rotor  133  rotatably provided and connected to the shaft  131 . The rotor  133  may rotate through magnetic interaction with the stator  132 , and the rotation of the rotor  133  may be transmitted to the drum  120  through the shaft  131 . 
     The drum motor  130  may include, for example, a BrushLess Direct Current Motor (BLDC Motor) or a Permanent Synchronous Motor (PMSM). 
     The water supplier  140  is provided above the tub  110  and may supply water to the tub  110 /the drum  120 . 
     The water supplier  140  includes a water supply conduit  141  connected to an external water supply source for supplying water to the tub  110 , and a water supply valve  142  provided on the water supply conduit  141 . 
     The water supply conduit  141  may extend from an external water supply source to a detergent compartment  161  and guide water to the tub  110  via the detergent compartment  161 . 
     The water supply valve  142  may allow or block the water supply from the external water source to the tub  110  in response to an electrical signal. The water supply valve  142  may include, for example, a solenoid valve that opens and closes in response to the electrical signal. 
     The water drain  150  is provided below the tub  110  and may discharge the water contained in the tub  110 /the drum  120  to the outside. 
     The water drain  150  includes the drain conduit  151  extending from the tub  110  to the outside of the cabinet  101  and the drain pump  152  provided on the drain conduit  151 . The drain pump  152  may pump water from the drain conduit  151  outside the cabinet  101 . 
     The detergent supplier  160  may be provided at the upper side of the tub  110  and may supply detergent to the tub  110 /the drum  120 . 
     The detergent supplier  160  includes the detergent compartment  161  for storing the detergent and a mixing conduit  162  connecting the detergent compartment  161  with the tub  110 . 
     The detergent compartment  161  is connected to the water supply conduit  141  and the water supplied through the water supply conduit  141  can be mixed with the detergent in the detergent compartment  161 . The mixture of the detergent and water may be supplied to the tub  110  through the mixing conduit  162 . 
     The drying duct  200  is provided on the rear wall  112   a  of the tub  110  and provided above the tub  110 , and may dry laundry contained in the drum  120 . 
     The drying duct  200  includes a heating duct  210 , a filter housing  220 , a connecting conduit  230  and the condensing duct  240 . 
     The heating duct  210  is provided above the tub  110 , and the air sucked from the tub  110  may be heated while passing through the heating duct  210 . 
     The heating duct  210  extends from the rear of the tub  110  to the front of the tub  110 . The front of the heating duct  210  is connected to a discharge port  111   b,  and the rear of the heating duct  210  is connected to the filter housing  220 . 
     The heating duct  210  has a tubular shape extending from the rear of the tub  110  to the front of the tub  110 . A duct upper plate  211  and a duct lower plate  212  may be included. However, the shape of the heating duct  210  is not limited to that shown in  FIG. 3 . 
     A fan  213 , a fan motor  214 , and a duct heater  215  are provided inside the heating duct  210 , that is, between the duct upper plate  211  and the duct lower plate  212 . 
     The fan motor  214  may be connected to the fan  213  through a rotation shaft, and may provide rotation to the fan  213 . 
     The fan  213  may be provided in an opening  212   a  of the duct lower plate  212 , and the fan  213  may circulate air between the tub  110  and the heating duct  210  by rotation. For example, the fan  213  sucks the internal air of the tub  110 /the drum  120  from the rear of the tub  110  to the heating duct  210  and exhausts the air of the heating duct  210  to the front of the tub  110 . 
     The duct heater  215  may heat air passing through the heating duct  210 . The air of the tub  110  is sucked into the heating duct  210  by the fan  213  and may flow into the heating duct  210 . The duct heater  215  may heat the air flowing through the heating duct  210 . The heated air may be discharged to the tub  110  by the fan  213 . 
     The filter housing  220  is provided between the heating duct  210  and the tub  110 , and guides air sucked from the tub  110  to the heating duct  210  through the connecting conduit  230 . 
     The filter housing  220  is connected to the heating duct  210 . In addition, the filter housing  220  is connected to the tub  110  through the connecting conduit  230 . 
     The filter housing  220  has a shape in which two cylinders are combined. The upper cylinder is connected to the heating duct  210 , and the lower cylinder is connected to the connecting conduit  230 . The upper cylinder and the lower cylinder have different diameters. The central axis of the upper cylinder does not coincide with the central axis of the lower cylinder, and the central axis of the upper cylinder may be disposed parallel to the central axis of the lower cylinder. However, the shape of the filter housing  220  is not limited to that shown in  FIG. 3 . 
     In the filter housing  220 , a filter  221  is provided to separate dust contained in the air sucked from the tub  110 . For example, the filter  221  may be provided at a portion where the upper cylinder and the lower cylinder are connected. 
     The filter housing  220  is provided with a washing water nozzle  222  for spraying water to clean the filter  221 . The washing water nozzle  222  is connected to an external water source through a washing water conduit  223 , and a washing water valve  224  is provided on the washing water conduit  223 . The washing water valve  224  may allow or block the supply of water to the washing water nozzle  222  in response to the electrical signal. The washing water valve  224  may include, for example, a solenoid valve that opens and closes in response to the electrical signal. 
     The connecting conduit  230  may be provided between the filter housing  220  and the tub  110  to guide the air sucked from the tub  110  to the heating duct  210 . 
     The connecting conduit  230  has one end connected to the condensing duct  240 . In more detail, the connecting conduit  230  may be connected to the suction port  112   c  of the tub  110 . The connecting conduit  230  is also connected at the other end to the filter housing  220 . 
     The connecting conduit  230  may have a bellows shape to prevent vibration of the tub  110  from being transmitted to the filter housing  220 . However, the shape of the connecting conduit  230  is not limited to that shown in  FIG. 3 . 
     Hereinafter, the condensing duct  240  will be described. 
       FIG. 4  is a perspective view of a tub rear part of a washing machine in accordance with an embodiment of the present disclosure.  FIG. 5  shows a cross-sectional view along line A-A′ shown in  FIG. 4 .  FIG. 6  shows a cross-sectional view along line B-B′ shown in  FIG. 4 .  FIG. 7  shows a cross-sectional view along line C-C′ shown in  FIG. 4 .  FIG. 8  shows a rear outer side of a tub of a washing machine in accordance with an embodiment of the present disclosure.  FIG. 9  shows a cross-sectional view along line D-D′ shown in  FIG. 8 . 
     Referring to  FIGS. 4, 5, 6, 7, 8 and 9 , the condensing duct  240  is provided inside the rear wall  112   a  of the tub  110 . 
     Water vapor contained in the air may be condensed while the air of the tub  110  passes through the condensing duct  240 . Air heated from the heating duct  210  is supplied to the inside of the tub  110  and the drum  120  during the drying cycle, and the heated air may absorb the moisture of wet laundry contained in the drum  120 . 
     When hot and humid air comes into contact with cold water, the water vapor contained in the hot and humid air may condense. 
     The condensing duct  240  may be provided at the rear wall  112   a  of the tub  110 , and water for condensation may be supplied to the condensing duct  240 . Therefore, the high temperature and high humidity air inside the drum  120  may contact with water flowing along the outer wall of the condensing duct  240 , and the water vapor contained in the high temperature and high humidity air may be condensed. 
     Referring to  FIGS. 4, 5, 6 and 7 , the condensing duct  240  may be provided integrally with the tub rear part  112 . For example, the condensing duct  240  may be provided along the sidewall  112   b  of the tub rear part  112  inside the rear wall  112   a  of the tub rear part  112 . 
     A stepped recessed along the sidewall  112   b  of the tub rear part  112  may be formed at the rear wall  112   a  of the tub rear part  112 . A part of the edge portion of the rear wall  112   a  of the tub rear part  112  is retracted further rearward than the center portion of the rear wall  112   a  of the tub  110 . As a result, a rear groove  241  having a substantially horseshoe shape may be formed at the edge portion inside the rear wall  112   a  of the tub rear part  112 . For example, the rear groove  241  is formed along the sidewall  112   b  of the tub rear part  112 , as shown in  FIG. 7 , and a first center angle a of the rear groove  241  is approximately between 180 degrees 360 degrees. 
     As illustrated in  FIG. 8 , ribs  112   f  and  112   g  may be provided outside the rear wall  112   a  of the tub rear part  112  to improve rigidity of the tub  110 . 
     The first rib  112   f  is provided at an approximately center portion of the rear wall  112   a  of the tub rear part  112 . The second rib  112   g  is provided at an approximately edge portion of the rear wall of the tub rear part  112 . The depth of the first rib  112   f  and the depth of the second rib  112   g  are different from each other. Specifically, since the rear groove  241  is formed at the edge portion of the rear wall  112   a  inside the tub rear part  112 , the depth of the second rib  112   g  provided at the approximately edge portion of the rear wall  112   a  of the tub rear part  112  is shallower than the depth of the first rib  112   f  provided at the approximately center portion of the rear wall  112   a  of the tub rear part  112 . 
     As shown in  FIGS. 4 and 7 , a cover  242  may be provided on the substantially horseshoe-shaped rear groove  241  formed inside the rear wall  112   a  of the tub rear part  112 . 
     The cover  242  has an approximately horseshoe shape to correspond to the shape of the rear groove  241 . For example, the cover  242  is provided along the sidewall  112   b  of the tub rear part  112  at the rear wall  112   a  of the tub rear part  112 , as shown in  FIG. 7 , and a second center angle β of the cover  242  may be between approximately 180 degrees and 360 degrees. 
     In addition, the second center angle β of the cover  242  may be smaller than the first center angle a of the rear groove  241 . Therefore, at least a part of the rear groove  241  may not be covered by the cover  242 , and at least a part of the rear groove  241  may be exposed to the outside. 
     Portions exposed to the outside due to not being covered by the cover  242  may form inlets  243   a  and  243   b.  As shown in  FIG. 7 , the inlets  243   a  and  243   b  may be formed at both ends of the rear groove  241 . For example, the first inlet  243   a  may be formed at the left end of the rear groove  241 , and the second inlet  243   b  may be formed at the right end of the rear groove  241 . Water or air inside the tub  110  may be introduced into the rear groove  241  through the first inlet  243   a  and the second inlet  243   b.  For example, the first inlet  243   a  may be formed at the left end of the rear groove  241 , and the second inlet  243   b  may be formed at the right end of the rear groove  241 . Water or air inside the tub  110  may be introduced into the rear groove  241  through the first inlet  243   a  and the second inlet  243   b.    
     The cover  242  may be spaced apart from the rear groove  241  in front of the rear groove  241 . For example, the cover  242  may be provided on the same plane as the inner surface of the rear wall  112   a  of the tub rear part  112 . 
     Since the cover  242  is spaced apart from the rear groove  241 , a space in which water or air can flow is formed between the cover  242  and the rear groove  241 , and the space between them forms the condensing duct  240 . 
     The condensing duct  240  is formed by the rear wall  112   a  and the cover  242  of the tub rear part  112 . The condensing duct  240  may be provided along the sidewall  112   b  of the tub rear part  112  at the rear wall  112   a  of the tub rear part  112  having a closed cylindrical bottom surface. 
     The condensing duct  240  may have an approximately horseshoe shape in the same manner as the cover  242  and the rear groove  241 . The first and second inlets  243   a  and  243   b  are respectively provided at both ends of the condensing duct  240  having a substantially horseshoe shape. 
     The cross section of the condensing duct  240  may have a substantially rectangular shape as shown in  FIGS. 5 and 6 . 
     A width w of the condensing duct  240  and a depth d of the condensing duct  240  may be determined depending on the stiffness of the tub  110  and the amount of air passing through the condensing duct  240 . 
     As the width w of the condensing duct  240  and the depth d of the condensing duct  240  increase, the amount of air passing through the condensing duct  240  increases, and the drying efficiency of the washing machine  100  may increase. 
     On the other hand, as the depth d of the condensing duct  240  increases, the depth of the second rib  112   g  provided outside the rear wall  112   a  of the tub rear part  112  is reduced. In order to match with other furniture or home appliances, the overall size (horizontal, vertical and height) of the washing machine  100  may be a predetermined value. Therefore, as the depth d of the condensing duct  240  increases, the size of the second rib  112   g  decreases, and the rigidity of the tub  110  may decrease. 
     In addition, as the width w of the condensing duct  240  increases, the size of the first rib  112   f  provided outside the rear wall  112   a  of the tub rear part  112  is reduced and the size of the second rib  112   g  is increased. Since the depth of the second rib  112   g  is shallower than the depth of the first rib  112   f,  the rigidity of the tub  110  may decrease as the width w of the condensing duct  240  increases. 
     The width w and the depth d of the condensing duct  240  affect the stiffness of the tub  110  and the amount of air passing through the condensing duct  240 , and the stiffness of the tub  110  and the air passing through the condensing duct  240  can be determined depending on the amount. For example, the width w of the condensing duct  240  may be determined so that the area of the condensing duct  240  is about 20% or more of the total area of the rear wall  112   a  of the tub rear part  112 . 
     The condensing duct  240  is provided with condensing nozzles  244   a  and  244   b  for injecting water for condensation of water vapor into the condensing duct  240 . The first condensing nozzle  244   a  is provided on the left side of the condensing duct  240 , and the second condensing nozzle  244   b  is provided on the right side of the condensing duct  240 . 
     The first condensing nozzle  244   a  and the second condensing nozzle  244   b  are connected to an external water source through a condensate conduit  245  (see  FIG. 3 ), and a condensation valve  246  is provided on the condensate conduit  245 . The condensation valve  246  may allow or block the supply of water to the first condensing nozzle  244   a  and the second condensing nozzle  244   b  in response to an electrical signal. The condensation valve  246  may include, for example, a solenoid valve that opens and closes in response to the electrical signal. 
     The condensing duct  240  may extend from the first inlet  243   a  and the second inlet  243   b  formed at both ends thereof to the suction port  112   c  formed at the upper side of the tub  110 . 
     In order to extend the condensing duct  240  provided inside the rear wall  112   a  of the tub rear part  112  to the suction port  112   c,  in the vicinity of the suction port  112   c  of the tub rear part  112 , a side groove  247  in which the sidewall  112   b  of the tub rear part  112  is recessed outward may be formed. 
     The side groove  247  may be provided above the tub  110 . For example, as illustrated in  FIGS. 4 and 7 , the tub  110  may be provided at an upper right side of the tub  110 . The center of the tub  110  may be provided at approximately 1 o&#39;clock to 2 o&#39;clock. 
     The side groove  247  may have a substantially triangular pillar shape. Therefore, when viewed from the outside of the tub  110 , the side groove  247  can be seen as a stepped protrusion  247   a.  For example, as shown in  FIG. 4 , the side groove  247  may be formed inside the stepped protrusion  247   a  formed on the sidewall of the tub rear part  112 . However, the shape of the side groove  247  is not limited to this. 
     The side groove  247  may extend from the rear groove  241  to the suction port  112   c.  For example, the side groove  247  may extend from the rear surface of the rear groove  241  to the suction port  112   c.    
     The cover  242  may include a protruding portion to cover the side groove  247 . The protruding portion of the cover  242  may extend to the lower side of the suction port  112   c  to partition the side groove  247  from the inside of the tub  110 . 
     As such, the condensing duct  240  may extend from the first inlet  243   a  and the second inlet  243   b  formed inside the rear wall  112   a  of the tub  110  to the suction port  112   c  formed above the sidewall  112   b  of the tub rear part  112 . The condensing duct  240  may be connected to the heating duct  210  through the suction port  112   c.  Air passing through the condensing duct  240  may be introduced into the heating duct  210  through the suction port  112   c.    
     As such, the condensing duct  240  may be provided at the rear wall  112   a  of the tub rear part  112 . Since the condensing duct  240  is provided, water vapor contained in the internal air of the tub  110 /the drum  120  may be condensed while passing through the condensing duct  240 . In addition, the condensing duct  240  increases the time for the internal air of the tub  110 /the drum  120  to contact with the water vapor, thereby increasing the amount of water vapor condensed. Therefore, the drying efficiency of the washing machine  100  is improved. 
     The condensing duct  240  may be integrally formed with the tub rear part  112  inside the rear wall  112   a  of the tub rear part  112 . Thereby, the condensing duct  240  can be provided without attachment of additional structures (e.g., conduits for forming condensation ducts) behind the tub  110 . 
     Furthermore, the increase in the size of the washing machine due to the additional structure can be prevented, and also the decrease in the size (washing capacity) of the tub and the drum due to the additional structure can be prevented. 
     Since the condensing duct  240  is formed by the cover  242 , the assembly structure for forming the condensing duct  240  can be simplified. 
     Since the condensing duct  240  is integrally formed with the tub rear part  112 , leakage of the condensing duct  240  may be prevented. 
     The condensing duct  240  includes the first inlet  243   a  and the second inlet  243   b,  thereby forming two flow paths from the first inlet  243   a  and the second inlet  243   b  to the suction port  112   c.  Thereby, the resistance of the airflow passing through the condensing duct  240  can be reduced, and the amount of air passing through the condensing duct  240  can be increased. 
     By configuring the cover  242  to form the condensing duct  240  made of a metal material, it is possible to further improve the condensation efficiency of the condensing duct  240 . 
       FIG. 10  illustrates a flow of water and air in a condensation duct according to one embodiment. 
     As shown in  FIG. 10 , sidewalls of the condensing duct  240  are provided with the first condensing nozzle  244   a  and the second condensing nozzle  244   b  for injecting water for condensing water vapor into the condensing duct  240 . 
     Water sprayed from the first condensing nozzle  244   a  and the second condensing nozzle  244   b  may flow down the sidewalls of the condensing duct  240 . For example, water may flow along the rear wall  112   a  of the tub rear part  112  forming the condensing duct  240  or along the cover  242 . 
     The internal air of the tub  110 /the drum  120  may be sucked into the condensing duct  240  through the first inlet  243   a  and the second inlet  243   b  formed under the rear wall  112   a  of the tub  110 . 
     The air sucked through the first inlet  243   a  and the second inlet  243   b  may flow along the condensing duct  240  to the suction port  112   c  provided at the upper portion of the tub  110 . Hot and humid air may contact water flowing along the sidewalls of the condensing duct  240  while flowing along the condensing duct  240 . Water vapor contained in the hot humid air may condense while the hot humid air comes into contact with the water of the condensing duct  240 . 
       FIG. 11  illustrates a flow of water and air in a condensation duct according to another embodiment. 
     In order to improve the condensation efficiency of the water vapor contained in the air, a portion of the cross-sectional area of the internal flow path of the condensing duct  240  may be reduced. 
     For example, to reduce the cross-sectional area of the internal flow path of the condensing duct  240 , protrusions  248   a  and  248   b  are formed on the inner wall of the condensing duct  240  as shown in  FIG. 11 . In addition, the protrusions  248   a  and  248   b  are provided with the condensing nozzles  244   a  and  244   b  for injecting water. The first protrusion  248   a  and the second protrusion  248   b  are formed in the condensing duct  240 , the first condensing nozzle  244   a  is provided in the first protrusion  248   a,  and the second condensing nozzle is provided in the second protrusion  248   b.    
     The air flowing through the condensing duct  240  increases in flow rate at a portion where the cross-sectional area is reduced by the first protrusion  248   a  and the second protrusion  248   b.  In addition, the air may contact the water sprayed from the first condensing nozzle  244   a  and the second condensing nozzle  244   b  respectively provided in the first protrusion  248   a  and the second protrusion  248   b.  For example, water is injected into the rapidly flowing air through the first condensing nozzle  244   a  provided in the first protrusion  248   a.    
     Thereby, the contact of water with the air is increased, and the amount of water vapor condensed by the water may be increased. In other words, the condensing efficiency in the condensing duct  240  can be improved and the drying time can be reduced. 
       FIGS. 1 to 11  describe the flow of air during the drying cycle. The internal air of the tub  110 /the drum  120  may be condensed and heated while passing through the condensing duct  240  and the heating duct  210 . 
     After dehydration, the laundry still contains a lot of moisture, and the amount of water vapor contained in the air inside the drum  120  may increase due to the wet laundry. 
     The air inside the drum  120  may be sucked into the condensing duct  240  by the operation of the fan  213 . For example, humid air inside the drum  120  may move to a space between the drum  120  and the tub  110  through the through hole  121   a  of the drum  120 . While passing through the through hole  121   a  of the drum  120 , the air inside the drum  120  passes through the wet laundry, thereby increasing the amount of water vapor contained in the air. 
     The air passing through the through hole  121   a  may be sucked into the condensing duct  240  through the first inlet  243   a  and/or the second inlet  243   b  provided at the rear wall  112   a  of the tub  110 . Water sprayed from the first condensing nozzle  244   a  and the second condensing nozzle  244   b  may flow on the sidewall of the condensing duct  240 . 
     The air entering the condensing duct  240  passes through the condensing duct  240  and is sucked into the heating duct  210 . While the humid air passes through the condensing duct  240 , it can come into contact with water flowing through the sidewalls of the condensing duct  240 , and it may condense during contact with cold water contained in the humid air. As a result, the amount of water vapor contained in the air during the passage of the condensing duct  240  may decrease. 
     The air which lost steam in the condensing duct  240  is sucked into the heating duct  210  through the suction port  112   c  by the fan  213 . Air passes through the filter housing  220 , and particles such as dust included in the air may be caught while passing through the filter housing  220 . Air passes through the fan  213  and may be discharged to the heating duct  210  by the fan  213 . 
     The air may be heated by the duct heater  215  while passing through the heating duct  210 . Due to the heating of the air, the capacity (amount of saturated steam) in which the air can receive water vapor may increase. In other words, the amount of saturated water vapor in the air may increase. 
     The air heated in the heating duct  210  may be discharged into the drum  120  through the discharge port  111   b.    
     The air inside the drum  120  may absorb water vapor from the wet laundry and circulate through the condensing duct  240  and the heating duct  210 . 
     As such, the washing machine  100  may dry the laundry through the absorption of water vapor in the drum  120 , condensation of water vapor in the condensing duct  240 , and heating of air in the heating duct  210 . 
     Hereinafter, a control configuration and a control operation of the washing machine  100  for drying laundry will be described. 
       FIG. 12  shows a configuration of a washing machine in accordance with an embodiment of the present disclosure.  FIG. 13  shows an operation of a washing machine according to one embodiment. 
     Referring to  FIGS. 12 and 13 , the washing machine  100  includes a user input  171 , a display  172 , a water level sensor  173 , a tub temperature sensor  174 , a duct temperature sensor  175 , a motor driving circuit  180 , the drum motor  130 , the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224 , the condensation valve  246  and a controller  190 . In addition, the washing machine  100  may perform an amount of laundry  1010 , a washing cycle  1020 , a rinsing cycle  1030 , a dehydration cycle  1040 , and a drying cycle  1050 . 
     The drum motor  130 , the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224  and the condensation valve  246  shown in  FIG. 3  may be the same as described. 
     The user input  171  is provided on the control panel  103  of the cabinet  101 , and includes a dial  171   a  (see  FIG. 1 ) capable of obtaining the user input by rotation and an input button  171   b  capable of obtaining the user input by reciprocating movement. 
     The user can select any one of the plurality of laundry courses by rotating the dial  171   a.  The washing machine  100  may include a plurality of different washing courses for washing different kinds of laundry, for example, the different washing courses may include different washing times, different rinsing times and different dehydration times. 
     The input button  171   b  may include a washing button for adjusting the washing time in which the washing machine  100  washes laundry, a rinsing button for adjusting the number of rinses of the washing machine  100  to rinse the laundry and, a dehydration button for adjusting the dehydration time for dehydrating the laundry. In addition, the input button  171   b  may include a power button for allowing or cutting off power supplied from an external power source, and an operation button for starting or stopping an operation of the washing machine  100 . 
     The dial  171   a  and the input button  171   b  may transmit an electrical signal (voltage or current) corresponding to the user input to the controller  190  in response to the user input received from the user. 
     The display  172  is provided on the control panel  103  of the cabinet  101  and may display an operation state of the washing machine  100  and a control command of the user. For example, the display  172  may display the washing course selected by the user, and display the time remaining until the completion of the operation while the washing machine  100  is in operation. 
     The display  172  may include a light emitting diode (LED) panel, an organic light emitting diode (OLED) panel, a liquid crystal display (LCD) panel, or the like. 
     The display  172  may adopt a touch screen panel (TSP) that receives a control command from the user and displays operation information corresponding to the received control command. 
     As such, the display  172  may receive a display control signal from the controller  170  and display an image corresponding to the display control signal. 
     The water level sensor  173  may be installed at the end of a connection hose  173   a  (see  FIG. 2 ) connected to the bottom of the tub  110 . 
     The water level of the connection hose  173   a  may be the same as that of the tub  110 . As the water level of the connection hose  173   a  increases, the pressure inside the connection hose  173   a  increases, and as the water level of the connection hose  173   a  decreases, the pressure inside the connection hose  173   a  decreases. 
     The water level sensor  173  may measure the pressure inside the connection hose  173   a  and output an electrical signal corresponding to the measured pressure to the controller  190 . The controller  190  may identify the level of the connection hose  173   a,  that is, the level of the tub  110 , based on the pressure of the connection hose  173   a  measured by the water level sensor  173 . 
     The tub temperature sensor  174  may be provided below the tub  110 . For example, the tub temperature sensor  174  may be installed near the tub heater  114 . 
     The tub temperature sensor  174  may measure the temperature of the water accommodated in the tub  110  or measure the temperature of the internal air of the tub  110 /the drum  120 . For example, the tub temperature sensor  174  may measure the temperature of the water contained in the tub  110  during the wash cycle and/or the rinse cycle. In addition, the tub temperature sensor  174  may measure the temperature of the internal air of the tub  110 /the drum  120  during the drying cycle. 
     The tub temperature sensor  174  may include a thermistor. An electrical resistance value of the thermistor is converted according to the temperature, and the tub temperature sensor  174  may transmit an electrical signal (voltage or current) corresponding to the electrical resistance value of the thermistor to the controller  190 . 
     The duct temperature sensor  175  may be provided inside the heating duct  210 . For example, the duct temperature sensor  175  may be installed in the vicinity of the duct heater  215 . Specifically, the duct temperature sensor  175  may be located downstream of the duct heater  215  based on the flow of air during the heating cycle. 
     The duct temperature sensor  175  may measure the internal temperature of the heating duct  210 . For example, the duct temperature sensor  175  may measure the temperature of the air heated by the duct heater  215  during the drying cycle. 
     The duct temperature sensor  175  may include a thermistor. An electrical resistance value of the thermistor is converted according to the temperature, and the duct temperature sensor  175  may transmit an electrical signal (voltage or current) corresponding to the electrical resistance value of the thermistor to the controller  190 . 
     The motor driving circuit  180  may be mounted on a printed circuit board installed near the drum motor  130 . 
     The motor driving circuit  180  may supply a driving current to the drum motor  130 . 
     The motor driving circuit  180  may convert AC power of an external power source into driving power for driving the drum motor  130 . 
     The motor driving circuit  180  may have various topologies according to the type of the drum motor  130 . 
     For example, when the drum motor  130  is a DC motor, the motor driving circuit  180  may convert AC power supplied from an external power source into DC power and intermittently supply DC power to the drum motor  130 . When the drum motor  130  is a non-commutator DC motor, the motor driving circuit  180  converts AC power into DC power, and thereafter, the DC power may be converted into AC power in the form of a square wave, and the AC power in the form of a square wave may be supplied to the drum motor  130 . When the drum motor  130  is a permanent magnet synchronous motor, the motor driving circuit  180  converts AC power into DC power, and then converts the DC power into AC power in the sine wave form, and converts the AC power in the sine wave form into a drum to supply to the motor  130 . When the drum motor  130  is an induction motor, the motor driving circuit  180  may intermittently supply AC power supplied from an external power source to the drum motor  130 . 
     In addition, the motor driving circuit  180  detects a first driving current supplied to the drum motor  130  in order to prevent damage of the drum motor  130  due to an overload, and the information about the first driving current (for example, driving current value) can be output to the controller  190 . 
     The controller  190  may be mounted on, for example, a printed circuit board provided at the rear of the control panel  103 . 
     The controller  190  is electrically connected to the user input  171 , the tub temperature sensor  174 , the duct temperature sensor  175 , the display  172 , the motor driving circuit  180 , the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224 , and the condensation valve  246 . 
     The controller  190  may control the display  172 , the motor driving circuit  180 , the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224 , and the condensation valve  246  based on the output of the user input  171 , the tub temperature sensor  174  and the duct temperature sensor  175 . 
     The controller  190  includes a processor  191  for generating a control signal for controlling the operation of the washing machine  100 , and a memory  192  for memorizing or storing a program and data for generating a control signal for controlling the operation of the washing machine  100 . The processor  191  and the memory  192  may be implemented as separate chips or as a single chip. In addition, the controller  190  may include a plurality of processors or a plurality of memories. 
     The processor  191  may process data and/or signals according to a program provided from the memory  192 , and provide a control signal to each component of the washing machine  100  based on the processing result. 
     The processor  191  receives an electrical signal related to the user input from the user input  171 , receives an electrical signal related to the temperature of the tub  110  from the tub temperature sensor  174 , and receives an electrical signal related to the heating duct  210  from the duct temperature sensor  175 . The processor  191  may process an electrical signal related to the user input, an electrical signal related to the temperature of the tub  110 , and an electrical signal related to the temperature of the heating duct  210 . 
     The processor  191  provides an image signal to the display  172 , a driving signal to the motor driving circuit  180 , a water supply signal to the water supply valve  142 , a drain signal to the drain pump  152 , a blow signal to the fan motor  214 , a tub heating signal to the tub heater  114 , a duct heating signal to the duct heater  215 , a filter wash signal to the washing water valve  224  and a condensation signal to the condensation valve  246 , based on the user input and the temperature of the tub  110  and the temperature of the heating duct  210 . 
     For example, the processor  191  may identify the washing course selected by the user based on the user input. The processor  191  determines the rotational speed and the operating cycle (e.g., on time and off time) of the drum  120  depending on the washing course selected by the user. According to the determined rotational speed and operation period, a motor signal for rotating the drum motor  130  may be provided to the motor driving circuit  180 . 
     The processor  191 , during the drying cycle, may provide a blowing signal to the fan motor  214  to suck the internal air of the tub  110 /the drum  120  into the drying duct  200 , provide a duct heating signal to the duct heater  215  for heating the air in the heating duct  210 , provide a condensation signal for injecting water into the condensing duct  240  to the condensation valve  246 , and provide a driving signal for rotating the drum  120  to the motor driving circuit  180 . 
     The processor  191  may include an operation circuit, a memory circuit, and a control circuit. The processor  191  may include one chip or may include a plurality of chips. In addition, the processor  191  may include one core or may include a plurality of cores. 
     The memory  192  may memorize or store a program and data for controlling the operation of the washing machine  100  according to the washing course. For example, the memory  192  may memorize or store the rotational speed of the drum  120  according to the washing course and the washing time/rinsing frequency/dehydration time according to the washing course. 
     The memory  192  may store a program and data for controlling the operation of the washing machine  100  according to the washing course. For example, the memory  192  may memorize or store the rotational speed of the drum  120  according to the washing course and the washing time/rinsing frequency/dehydration time according to the washing course. 
     The memory  192  stores the user input received through the dial  171   a  and the input button  171   b,  or information on the operation of the washing machine  100  (for example, a cycle in progress, remaining time until the operation of the washing machine is completed). 
     The memory  192  may include a volatile memory such as static random access memory (S-RAM), dynamic random access memory (D-RAM), and read only memory (ROM), or a non-volatile memory, such as Erasable Programmable Read Only Memory (EPROM). 
     The memory  192  may include one memory device or may include a plurality of memory devices. 
     As illustrated in  FIG. 13 , the controller  190  may control each component of the washing machine  100  to wash/rinse/dehydrate/dry laundry. The controller  190  may measure the amount of laundry  1010 , sequentially perform the washing cycle  1020 , the rinsing cycle  1030 , the dehydration cycle  1040 , and the drying cycle  1050 . 
     The controller  190  measures the amount of laundry  1010 . 
     By increasing the amount of laundry, the current supplied from the motor driving circuit  180  to the drum motor  130  may increase. The controller  190  controls the motor driving circuit  180  to rotate the drum  120  in the forward or reverse direction to measure the amount of laundry, and the current supplied from the motor driving circuit  180  to the drum motor  130  may be measured. 
     The controller  190  may estimate the amount of laundry based on the current supplied from the motor driving circuit  180  to the drum motor  130 . 
     The controller  190  performs the washing cycle  1020 . 
     The controller  190  may supply water and detergent to the tub  110 . The controller  190  may open the water supply valve  142  to supply water to the tub  110  depending on the amount of laundry measured. By opening the water supply valve  142 , water may be supplied to the tub  110  via the detergent compartment  161 . Thereby, the detergent may be supplied to the tub  110  with water during the first water supply for washing. 
     The controller  190  may rotate the drum  120  at low speed for washing. The controller  190  may control the motor driving circuit  180  to rotate the drum  120  at low speed (e.g., rotational speed between approximately 45 rpm and 60 rpm). The controller  190  may control the motor driving circuit  180  to alternately rotate the drum  120  in a first direction and in a second direction. While the drum  120  rotates alternately in the first direction and the second direction, the laundry inside the drum  120  may be rolled along the inner wall of the drum  120  or dropped after being lifted. Foreign matter attached to the laundry can be separated from the laundry by the physical action of tumbling and falling of the laundry and the chemical action of the detergent. 
     The controller  190  may discharge the water from the tub  110 . The controller  190  may operate the drain pump  152  to discharge the water from the tub  110 . The water in the tub  110  may be pumped out by the drain pump  152 . 
     The controller  190  may rotate the drum  120  at high speed for intermediate dehydration. The controller  190  may control the motor driving circuit  180  to rotate the drum  120  at high speed (e.g., rotational speed of approximately 1000 rpm to 1100 rpm). While the drum  120  rotates at high speed, the laundry inside the drum  120  is located along the inner wall of the drum  120 , and the water absorbed by the laundry may be separated from the laundry by centrifugal force. The water separated from the laundry may be discharged to the outside through the tub  110  and the drain conduit  151  through the through hole  121   a  of the drum  120 . 
     Thereafter, the controller  190  performs the rinsing cycle  1030 . The controller  190  may supply water to the tub  110  and rotate the drum motor  130  at low speed for rinsing. The controller  190  may discharge the water from the tub  110  and rotate the drum  120  at high speed for intermediate dehydration. 
     Thereafter, the controller  190  performs the dehydration cycle  1040 . The controller  190  may rotate the drum  120  at high speed. 
     Thereafter, the controller  190  performs the drying cycle  1050 . 
     The controller  190  may operate the duct heater  215  to heat the air inside the tub  110 /the drum  120 . When the temperature of the internal air of the tub  110  reaches a predetermined temperature, the controller  190  controls the motor driving circuit  180  to operate the duct heater  215  and to rotate the drum  120  at high speed. The controller  190  may open the condensation valve  246  to supply water to the condensing duct  240 . 
     As described above, the controller  190  may sequentially perform the washing cycle  1020 , the rinsing cycle  1030 , the dehydration cycle  1040 , and the drying cycle  1050  to wash laundry. 
       FIG. 14  shows a drying cycle performed by a washing machine according to one embodiment.  FIG. 15  shows operations of each of the components of a washing machine by the drying cycle shown in  FIG. 14 .  FIGS. 16 and 17  show residual moisture by a heating/dehydration operation shown in  FIG. 14 .  FIG. 18  shows the drying time according to a tub temperature. 
       FIGS. 14, 15, 16, 17 and 18  describe the drying cycle  1050  of the washing machine  100 . 
     After the dehydration cycle  1040  is finished, the washing machine  100  continuously heats the inside of the tub  110 /the drum  120  ( 1110 ). (Hereinafter referred to as “heating operation.”) 
     After stopping the rotation of the drum  120  for the dehydration cycle  1040 , the controller  190  may operate the duct heater  215  provided inside the heating duct  210  to heat the tub  110 /the drum  120 . For example, the controller  190  may provide a duct heating signal to the duct heater  215  to turn on the duct heater  215  as shown in  FIG. 15 . 
     During the heating operation, the controller  190  may operate the fan  213  provided inside the heating duct  210  to circulate air between the tub  110 /the drum  120  and the drying duct  200 . For example, the controller  190  can provide a blowing signal to the fan motor  214  for rotating the fan  213  during continuous heating as shown in  FIG. 15 . 
     During the heating operation, the controller  190  may rotate the drum  120  at a first rotational speed (for example, 40 rpm to 100 rpm) as shown in  FIG. 15 . While the drum  120  rotates at the first rotational speed, the laundry inside the drum  120  may be rolled inside the drum  120  by centrifugal force and gravity. For example, while the drum  120  rotates at low speed, the laundry may be lifted along with the drum  120  to approximately the center height of the drum  120  by centrifugal force and gravity. When the laundry is lifted to approximately the center height of the drum  120 , the direction of the centrifugal force is opposite to the direction of gravity and the laundry falls to the lower portion of the drum  120  by the gravity. As such, the laundry repeatedly enters the rotational direction of the drum  120  and falls to the bottom of the drum  120 , and this operation is hereinafter referred to as “tumbling.” 
     During the heating operation, the controller  190  may alternately rotate the drum  120  counterclockwise (CCW) or clockwise (CW) as shown in  FIG. 15 . The time for the controller  190  to rotate the drum  120  counterclockwise (CCW) may be different from the time for the controller  190  to rotate the drum  120  clockwise (CVV). For example, the ratio between the time when the controller  190  rotates the drum  120  counterclockwise (CCVV) and the time when the controller  190  rotates the drum  120  clockwise (CW) may be 5:1. 
     During the heating operation, the controller  190  may not supply water for condensation to the condensing duct  240 . For example, as shown in  FIG. 15 , the controller  190  may provide an off signal to the condensation valve  246  to close the condensation valve  246 . 
     Before the internal air of the tub  110 /the drum  120  is sufficiently heated, the water condensation efficiency may be low. In addition, the rate of increase of the internal temperature of the tub  110 /the drum  120  of the condensing duct  240  is lowered, thereby increasing the drying time. For this reason, the water for condensation may not be supplied to the condensing duct  240  while heating the internal air of the tub  110 /the drum  120 . 
     Optionally, the controller  190  may operate the tub heater  114  provided inside the tub  110  during the heating operation. For example, the controller  190  may provide a tub heating signal to the tub heater  114 . 
     The washing machine  100  determines whether the internal temperature of the tub  110  is equal to or greater than a first reference temperature ( 1120 ). 
     While heating the internal air of the tub  110 /the drum  120 , the controller  190  may measure the internal temperature of the tub  110 . For example, the controller  190  may receive an electrical signal (voltage or current) indicating the internal temperature of the tub  110  from the tub temperature sensor  174  at every predetermined time (per sampling period). 
     In addition, the controller  190  may compare the internal temperature of the tub  110  with the first reference temperature to determine whether the internal temperature of the tub  110  is greater than or equal to the first reference temperature. The first reference temperature may be set experimentally or empirically, and the first reference temperature may be, for example, approximately 90 degree Celsius. 
     If the internal temperature of the tub  110  is not greater than the first reference temperature (NO in  1120 ), the washing machine  100  continues to heat the internal air of the tub  110 /the drum  120 . 
     If the internal temperature of the tub  110  is equal to or greater than the first reference temperature (YES in  1120 ), the washing machine  100  intermittently heats the internal air of the tub  110 /the drum  120  and simultaneously heats the drum  120  and rotates at high speed ( 1130 ). (Hereinafter referred to as “heating/dehydration operation.”) 
     If the internal temperature of the tub  110  is greater than or equal to the first reference temperature, the controller  190  may intermittently operate the duct heater  215  to maintain the internal temperature of the tub  110 /the drum  120  at the first reference temperature. For example, if the internal temperature of the tub  110  is less than the first reference temperature, the controller  190  operates the duct heater  215 , and when the internal temperature of the tub  110  exceeds the first reference temperature, the controller  190  may stop the duct heater. 
     During the heating/dehydration operation, the controller  190  may operate the fan  213  provided inside the heating duct  210  to circulate air between the tub  110 /the drum  120  and the drying duct  200 . For example, the controller  190  can provide a blowing signal to the fan motor  214  for rotating the fan  213  during intermittent heating, as shown in  FIG. 15 . 
     During the heating/dehydration operation, the controller  190  may rotate the drum  120  at a second rotational speed (for example, 1000 rpm to 1600 rpm) for dehydration. While the drum  120  rotates at the second rotational speed, the laundry may be attached to the inner wall of the drum  120  by centrifugal force. In addition, the water absorbed in the laundry may be separated to the outside of the drum  120  through the through hole  121   a  of the drum  120 . 
     As the temperature of the laundry absorbing water increases or decreases, the amount of water separated from the laundry may increase. Specifically, the surface tension decreases with the increasing water temperature. For example, the surface tension of water at 25 degrees Celsius may be approximately 0.0712 Nm (Newton-meter), and the surface tension of water at 55 degrees Celsius may be approximately 0.0671 Nm. 
     Due to the reduction in the surface tension, water can be easily separated from the laundry. For example, the residual moisture content (RMC) of laundry after rinsing is approximately 45% as shown in  FIG. 16A , and the residual moisture content (RMC) of the laundry after dehydration may be approximately 38% as shown in  FIG. 16B . After dehydration at the same time as heating, the residual moisture content (RMC) of the laundry may be 33% as shown in  FIG. 16C . 
     Further, as shown in  FIG. 17 , as the temperature of the laundry increases or decreases, the residual moisture content (RMC) of the laundry changes. For example, if the temperature of the laundry is approximately 65 degrees Celsius, the residual moisture content (RMC) of the laundry is approximately 35.5%. If the temperature of the laundry is approximately 75 degrees Celsius, the residual moisture content (RMC) of the laundry is approximately 34%. If the temperature of the laundry is approximately 80 degrees Celsius, the residual moisture content (RMC) of the laundry may be approximately 33%. 
     As such, by simultaneously performing heating and dehydration, the washing machine  100  may improve the dehydration efficiency for drying, thereby reducing the time for drying. 
     During the heating/dehydration operation, the controller  190  may not supply the condensing duct  240  with water for condensation. For example, as shown in  FIG. 15 , the controller  190  may provide an off signal to the condensation valve  246  to close the condensation valve  246 . 
     The washing machine  100  determines whether the heating/dehydration time is greater than or equal to a first reference time ( 1140 ). 
     The controller  190  may determine a time when the heating/dehydration operation is performed during the heating/dehydration operation, and compare the heating/dehydration time with the first reference time (for example, any one of 5 minutes to 10 minutes). The first reference time can be set experimentally or empirically and can vary depending on the amount of laundry. For example, as the amount of laundry increases, the first reference time may increase. In other words, as the amount of laundry increases, the heating/dehydration time may increase. 
     If the heating/dehydration time is not greater than or equal to the first reference time (NO in  1140 ), the washing machine  100  may continue the heating/dehydration operation. 
     If the heating/dehydration time is greater than or equal to the first reference time (YES in  1140 ), the washing machine  100  intermittently heats the internal air of the tub  110 /the drum  120  and the interior of the tub  110 /the drum  120 , and condenses water vapor contained in the air ( 1150 ). (Hereinafter referred to as “heating/condensing operation.”) 
     After the end of the heating/dehydrating operation, the controller  190  may intermittently operate the duct heater  215  to maintain the internal temperature of the tub  110 /the drum  120  at the first reference temperature or a second reference temperature. For example, as shown in  FIG. 15 , the controller  190  may intermittently operate the duct heater  215  to maintain the internal temperature of the tub  110 /the drum  120  at the second reference temperature greater than the first reference temperature after completion of heating/dehydration. As shown in  FIG. 18 , the internal temperature of the tub  110 /the drum  120  increases during the drying operation, thereby reducing the time of the drying cycle of the washing machine  100 . Thus, in order to reduce the time of the drying cycle, the controller  190  maintains the internal temperature of the tub  110 /the drum  120  higher than the internal temperature of the tub  110 /the drum  120  during heating/dehydration during the drying operation after heating/dehydration. 
     However, the present invention is not limited thereto, and the controller  190  may set the internal temperature of the tub  110 /the drum  120  to be equal to the internal temperature of the tub  110 /the drum  120  during heating/dehydration after the heating/dehydration is completed. The duct heater  215  may be intermittently operated to maintain the reference temperature. 
     During the heating condensation operation, the controller  190  may operate the fan  213  provided inside the heating duct  210  to circulate air between the tub  110 /the drum  120  and the drying duct  200 . 
     During the heat condensation operation, the controller  190  may rotate the drum  120  at the first rotational speed (e.g., low speed, for example, 40 rpm to 100 rpm).While the drum  120  rotates at the first rotational speed, the laundry inside the drum  120  may be tumbling inside the drum  120  by centrifugal force and gravity. The controller  190  may alternately rotate the drum  120  counterclockwise (CCVV) or clockwise (CVV) as shown in  FIG. 15 . 
     During the heat condensation operation, the controller  190  can supply the condensing duct  240  with water for condensation for efficient drying. For example, as shown in  FIG. 15 , a condensation signal may be provided to the condensation valve  246  to open the condensation valve  246 . Due to the opening of the condensation valve  246 , the condensing duct  240  is supplied with water for condensation and water can flow along the inner wall of the condensing duct  240 . 
     The air heated by the heating duct  210  may absorb water vapor from the laundry passing through the tub  110  and the drum  120 . Water vapor absorbed by the air may be condensed by water flowing along the inner wall of the condensing duct  240  while the air passes through the condensing duct  240 . The air condensed with the water vapor may be heated again in the heating duct  210 . 
     As such, the internal air of the tub  110  and the drum  120  may be dried by condensation in the condensing duct  240  and heating in the heating duct  210 . 
     The washing machine  100  determines whether the condensation/heating time for drying is greater than or equal to the second reference time ( 1160 ). 
     The controller  190  may determine the time when the condensation/heating operation is performed during the condensation/heating operation, and compare the condensation/heating time with the second reference time. The second reference time can be set experimentally or empirically and can vary depending on the amount of laundry. 
     If the condensation/heating time is not greater than or equal to the second reference time (NO in  1160 ), the washing machine  100  may continue the condensation/heating operation. 
     If the condensation/heating time is greater than or equal to the second reference time (YES in  1160 ), the washing machine  100  cools the interior of the tub  110 /the drum  120  ( 1170 ). (Hereinafter referred to as “cooling operation.”) After the end of the condensation/heating operation, the controller  190  may stop heating the internal air of the tub  110 /the drum  120 . For example, as illustrated in  FIG. 15 , the controller  190  may provide the duct heater  215  with an off signal for stopping the duct heater  215 . 
     During the cooling operation, the controller  190  may operate the fan  213  provided inside the heating duct  210  to circulate air between the tub  110 /the drum  120  and the drying duct  200 . 
     During the cooling operation, the controller  190  may rotate the drum  120  at the first rotational speed (e.g., low speed, for example, 40 rpm to 100 rpm). The controller  190  may alternately rotate the drum  120  counterclockwise (CCW) or clockwise (CW) as shown in  FIG. 15 . 
     During the cooling operation, the controller  190  may supply water to the condensing duct  240  to cool the internal air of the tub  110 /the drum  120  more quickly. For example, as shown in  FIG. 15 , a condensation signal may be provided to the condensation valve  246  to open the condensation valve  246 . 
     The internal air of the tub  110 /the drum  120  may be cooled in contact with the water of the condensing duct  240 . 
     In addition, the washing machine  100  may discharge the water of the tub  110  to the outside intermittently during the drying cycle. For example, as shown in  FIG. 15 , the controller  190  may intermittently operate the drain pump  152  during the drying cycle. 
     As described above, the washing machine  100  may perform a heating operation, a heating/dehydrating operation, a condensation/heating operation, and a cooling operation during the drying cycle  1050 . In particular, during the heating/dehydration operation, the washing machine  100  maintains the internal air of the tub  110 /the drum  120  at high temperature, the internal air of the tub  110 /the drum  120  may be intermittently heated, and at the same time, the drum  120  may be rotated at high speed for dehydration. By the heating/dehydrating operation, the residual moisture content (RMC) of the laundry can be further reduced and the drying time can be reduced. 
       FIG. 19  illustrates a filter cleaning operation of a washing machine according to one embodiment.  FIG. 20  shows the amount of water entering a drum during filter cleaning according to a rotational speed of the drum. 
     Referring to  FIGS. 19 and 20 , a filter cleaning operation  1200  of the washing machine  100  is described. 
     The washing machine  100  performs the drying cycle  1050  after the dehydration cycle  1040  ( 1210 ). 
     During the drying cycle  1050 , the controller  190  may perform a heating operation, a heating/dehydrating operation, a condensation/heating operation, and a cooling operation. 
     The washing machine  100  determines whether the filter  221  is blocked during the drying cycle  1050  ( 1220 ). 
     Lint or dust is separated from the laundry by the rotation of the drum  120  during the drying cycle. The lint or dust can be filtered by the filter  221 . As the drying cycle progresses, the amount of lint or dust filtered by the filter  221  increases, and the filter  221  may be blocked by the filtered lint or dust. 
     The controller  190  may determine whether the filter  221  is blocked based on the internal temperature of the tub  110  and/or the internal temperature of the heating duct  210 . 
     For example, the controller  190  may determine whether the filter  221  is blocked based on the internal temperature of the tub  110  measured by the tub temperature sensor  174 . In detail, the controller  190  may determine whether the filter  221  is blocked based on the change in the internal temperature of the tub  110 . 
     During the drying cycle  1050 , the controller  190  can intermittently run the duct heater  215  and operate the fan motor  214  to allow air to circulate through the drying duct  200  and the tub  110 /the drum  120 . The internal temperature of the tub  110  may increase during the operation of the duct heater  215 , and the internal temperature of the tub  110  may decrease during the stop of the duct heater  215 . Therefore, the change of the internal temperature of the tub  110  measured by the tub temperature sensor  174  is large. On the other hand, if the filter  221  is blocked by lint or dust, the internal air of the tub  110 /the drum  120  does not circulate through the drying duct  200 . Therefore, the change of the internal temperature of the tub  110  by the start and stop of the duct heater  215  is small. 
     Therefore, if the change in the internal temperature of the tub  110  measured by the tub temperature sensor  174  is greater than or equal to the reference value, the controller  190  identifies that the filter  221  is not blocked, and the change in the internal temperature of the tub  110  is determined. If it is less than the reference value, the controller  190  may identify that the filter  221  is blocked. 
     Accordingly, when the change in the internal temperature of the tub  110  measured by the tub temperature sensor  174  is greater than or equal to the reference value, the controller  190  identifies that the filter  221  is not blocked, and when the change in the internal temperature of the tub  110  is less than the reference value, the controller  190  may identify that the filter  221  is blocked. 
     As another example, the controller  190  may determine whether the filter  221  is blocked based on the difference between the internal temperature of the tub  110  measured by the tub temperature sensor  174  and the internal temperature of the heating duct  210  measured by the duct temperature sensor  175 . 
     By the operation of the fan  213 , the air circulates through the heating duct  210  and the tub  110 /the drum  120 , and the difference between the internal temperature of the tub  110  and the internal temperature of the heating duct  210  measured by the duct temperature sensor  175  is small. On the other hand, if the filter  221  is blocked by lint or dust, air does not circulate through the heating duct  210  and the tub  110 /the drum  120 , therefore, the difference between the internal temperature of the tub  110  and the internal temperature of the heating duct  210  measured by the duct temperature sensor  175  is large. 
     Therefore, when the difference between the internal temperature of the tub  110  and the internal temperature of the heating duct  210  measured by the duct temperature sensor  175  is less than the reference value, the controller  190  identifies that the filter  221  is not blocked, and when the difference between the internal temperature of the tub  110  and the internal temperature of the heating duct  210  measured by the duct temperature sensor  175  is greater than or equal to the reference value, the controller  190  may identify that the filter  221  is blocked. 
     If blocking of the filter  221  is identified (YES in  1220 ), the washing machine  100  rotates the drum  120  at a third rotational speed ( 1230 ). 
     Once the blockage of the filter  221  is identified, the controller  190  may spray water into the filter  221  as described below. The injected water may flow into the tub  110  through the suction port  112   c  and flow along the sidewall of the tub  110 . Water flowing along the sidewall of the tub  110  may be introduced into the drum  120  by the rotation of the drum  120 . 
     The controller  190  is configured to rotate the drum  120  at the third rotational speed so as to prevent water from flowing into the drum  120  to clean the filter  221 . The driving current supplied to the drum motor  130  may be controlled. 
     As previously described with reference to  FIG. 14 , the controller  190  controls the driving current supplied from the motor driving circuit  180  to the drum motor  130  to rotate the drum  120  at the first rotational speed during the condensation/heating operation. 
     The third rotational speed during filter cleaning may be greater than the first rotational speed during the condensation/heating operation. As shown in  FIG. 20 , when the rotational speed of the drum  120  is approximately  120  rpm, the amount of water injected to clean the filter  221  that is introduced into the drum  120  is minimized. For example, the third rotational speed may be set to approximately 120 rpm, and the third rotational speed may be greater than the first rotational speed, which is approximately 40 rpm to 100 rpm. 
     The washing machine  100  washes the filter  221  ( 1240 ). 
     The controller  190  may control the washing water valve  224  to spray water for washing with the filter  221  while rotating the drum  120  at the third rotational speed. For example, the controller  190  can provide a filter wash signal to the washing water valve  224  to open the washing water valve  224 . 
     The washing machine  100  restores the rotational speed of the drum  120  ( 1250 ). 
     The controller  190  may restore the rotational speed of the drum  120  to the rotational speed before cleaning the filter  221 . For example, when the filter  221  is cleaned during the condensation/heating operation, the controller  190  may rotate the drum  120  at the first rotational speed (for example, 40 rpm to 100 rpm). 
     As described above, when the filter  221  is blocked by lint or dust, the washing machine  100  may control the rotational speed of the drum  120  and inject water for washing into the filter  221 . Therefore, the inflow of water for cleaning the filter  221  into the drum  120  may be minimized. 
       FIG. 21  is a side cross-sectional view of a washing machine according to one embodiment.  FIG. 22  illustrates a configuration of a washing machine according to one embodiment. 
     As shown in  FIG. 21 , the washing machine  100  includes the cabinet  101 , the tub  110 , the drum  120 , a pulsator  125 , a first motor  130   a,  a second motor  130   b,  the water supplier  140 , the water drain  150 , the detergent supplier  160  and the drying duct  200 . 
     The cabinet  101 , the tub  110 , the water supplier  140 , the water drain  150 , the detergent supplier  160 , and the drying duct  200  may be the same as illustrated in  FIG. 2 . 
     The drum  120  is rotatably provided in the tub  110 . The drum  120  may accommodate laundry therein. 
     The pulsator  125  is provided inside the rear of the drum  120  and is rotatably provided with respect to the drum  120 . The pulsator  125  may be provided to be rotatable independently of the drum  120 . In other words, the pulsator  125  may rotate in the same direction as the drum  120  or in a different direction from the drum  120 . The rotation axis of the pulsator  125  may be provided on the same axis as the rotation axis of the drum  120 . 
     The pulsator  125  may generate water flow in the front-rear direction inside the drum  120  during washing. The washing performance of the washing machine  100  may be improved by the pulsator  125 . 
     The first motor  130   a  is connected to a first drive shaft  131   a  and may provide rotation to rotate the drum  120  to the first drive shaft  131   a.  The first drive shaft  131   a  may provide rotation of the first motor  130   a  to a first pulley  136   a  through a first belt  135   a.  The first pulley  136   a  may be connected to the drum  120  through a first driven shaft  137   a  and may provide rotation of the first motor  130   a  to the drum  120 . 
     The second motor  130   b  is connected to a second drive shaft  131   b  and may provide rotation to rotate the pulsator  125  to the second drive shaft  131   b.  The second drive shaft  131   b  may provide rotation of the second motor  130   b  to a second pulley  136   b  through a second belt  135   b.  The second pulley  136   b  is connected to the pulsator  125  through a second driven shaft  137   b  and may provide rotation of the second motor  130   b  to the pulsator  125 . 
     The second motor  130   b  is connected to the second drive shaft  131   b  and may provide rotation to rotate the pulsator  125  to the second drive shaft  131   b.  The second drive shaft  131   b  may provide rotation of the second motor  130   b  to the second pulley  136   b  through the second belt  135   b.  The second pulley  136   b  is connected to the pulsator  125  through the second driven shaft  137   b  and may provide rotation of the second motor  130   b  to the pulsator  125 . 
     The first driven shaft  137   a  is provided on the same axis as the second driven shaft  137   b.  For example, a hollow in which the second driven shaft  137   b  is inserted is formed at an approximately center of the first driven shaft  137   a.  Thereby, the first driven shaft  137   a  can rotate at a different direction and/or at a different speed than the second driven shaft  137   b  on the same axis as the second driven shaft  137   b.    
     As shown in  FIG. 22 , the washing machine  100  includes the user input  171 , the display  172 , the water level sensor  173 , the tub temperature sensor  174 , the duct temperature sensor  175 , a first driving circuit  181 , the first motor  130   a,  a second driving circuit  182 , the second motor  130   b,  the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224 , the condensation valve  246  and the controller  190 . 
     The user input  171 , the display  172 , the water level sensor  173 , the tub temperature sensor  174 , the duct temperature sensor  175 , the water supply valve  142 , the drain pump  152 , the fan motor  214 , the tub heater  114 , the duct heater  215 , the washing water valve  224  and the condensation valve  246  may be the same as described with reference to  FIG. 12 . 
     The first driving circuit  181  can provide the first motor  130   a  with the first driving current for rotating the drum  120 . The second driving circuit  182  may provide a second driving current to the second motor  130   b  to rotate the pulsator  125 . For example, each of the first driving circuit  181  and the second driving circuit  182  may convert AC power of an external power source into driving power for driving each of the first motor  130   a  and the second motor  130   b.    
     The controller  190  may control the first motor  130   a  and the second motor  130   b  to rotate the drum  120  and the pulsator  125  during the washing cycle  1020 , the rinsing cycle  1030 , the dehydration cycle  1040 , and the drying cycle  1050 . In detail, the controller  190  may control the driving current supplied from the first driving circuit  181  and the second driving circuit  182  to the first motor  130   a  and the second motor  130   b.    
     The controller  190  controls the driving current supplied from the first driving circuit  181  and the second driving circuit  182  to the first motor  130   a  and the second motor  130   b  to rotate the drum  120  and the pulsator  125  during the heating operation, the heating/dehydrating operation, the heating/condensation operation, and the cooling operation of the drying cycle  1050 . The driving current supplied from the first driving circuit  181  and the second driving circuit  182  to the first motor  130   a  and the second motor  130   b  may be controlled. 
     The controller  190  controls the first motor  130   a  and the second motor  130   b  to rotate the drum  120  and the pulsator  125  in the same direction during the heating operation, the heating/condensing operation, and the cooling operation of the drying cycle  1050 . 
     During the heating operation, the heating/condensing operation and the cooling operation of the drying cycle  1050 , the controller  190  rotates the first driving circuit  181  so that the drum  120  rotates at the first rotational speed (e.g., approximately 40 rpm to 100 rpm) to control the first motor  130   a.    
     In addition, during the heating operation, the heating/condensing operation, and the cooling operation of the drying cycle  1050 , the controller  190  controls the second motor  130   b  through the second driving circuit  182  to rotate the pulsator  125  at a fourth rotational speed. The fourth rotational speed may be equal to or greater than the first rotational speed. For example, the ratio of the fourth rotational speed to the first rotational speed may be approximately 1:1 to 5:1. 
     As such, during the heating operation, the heating/condensing operation, and the cooling operation, the pulsator  125  may rotate at a rotational speed different from that of the drum  120  in the same direction as the rotation direction of the drum  120 . 
     As the pulsator  125  rotates in the same rotational direction as the drum  120 , the twisting of the laundry may be reduced during the drying cycle  1050 . In addition, the drying efficiency of the laundry may be improved because the twisting of the laundry is reduced. 
     A washing machine includes a tub; a drum rotatably installed inside of the tub; a condensing duct formed on an inner wall of the tub; a heating duct provided outside the tub; a duct heater provided inside the heating duct; a fan configured to circulate air in the drum, the condensing duct, and the heating duct; and a controller configured to rotate the drum at a first rotational speed so as to tumble laundry contained in the drum while controlling the duct heater to heat the air circulated by the fan. The controller may rotate the drum at a second rotational speed to separate water from the laundry contained in the drum while controlling the duct heater to heat the circulating air. 
     Because of this, the washing machine can perform heating and dehydration at the same time. Since the surface tension of the water is reduced by heating, the washing machine can reduce the amount of moisture contained in the laundry by simultaneously performing heating and dehydration. In addition, the washing machine can reduce the drying time for drying the laundry. 
     The washing machine may further include a condensation conduit extending from an external water source to the condensing duct; and a condensation valve provided on the condensation conduit to allow or block the supply of water to the condensing duct. 
     For this reason, the washing machine can prevent that water in the condensation duct impedes dehydration. 
     The controller may control the duct heater to heat the circulating air, and may control the condensation valve to block the supply of water to the condensing duct while rotating the drum to separate the water from the laundry contained within the drum. 
     As a result, the washing machine may dry the laundry through heating and condensation. 
     The controller may rotate the drum alternately in a first direction and a second direction so that the laundry contained in the drum tumbles, and the time for rotating the drum in the first direction may differ from the time for rotating the drum in the second direction. 
     As a result, the washing machine can effectively guide the air inside the drum to the condensation duct, and further reduce the drying time. 
     The condensation duct may include a rear groove formed inside a rear wall of the tub having a cylindrical shape, and a cover for partitioning the inside of the rear groove from the inside of the tub. 
     As a result, the condensation duct can be integrally formed with the tub. In addition, the condensation duct can be prevented from increasing the overall size of the washing machine or decreasing the size of the drum. 
     The condensing duct may be formed along a portion of a sidewall of the tub having the cylindrical shape. 
     The condensing duct may have a horseshoe shape. 
     Both ends of the condensing duct may be formed with inlets for connecting the condensing duct with the inside of the tub. 
     The washing machine may further include a filter for filtering foreign substances contained in the air sucked into the heating duct; a washing water nozzle for spraying water on the filter; a washing water conduit extending from an external water source to the washing nozzle; and a washing water valve configured to allow or block the supply of the water to the washing nozzle provided on the washing water conduit; and the controller may rotate the drum at a third rotational speed which is faster than the first rotational speed and slower than the second rotational speed while controlling the washing water valve to allow the supply of the water to the washing nozzle. 
     As a result, the washing machine can minimize the inflow of water for cleaning the filter into the drum. 
     The washing machine may further include a pulsator provided inside the rear of the drum having a cylindrical shape and rotating independently of the drum, and the controller may rotate the drum at the first rotational speed, and rotate the pulsator the same as the drum at a fourth rotational speed while controlling the duct heater and the fan to heat the air circulating in the drum and the condensing duct and the heating duct, and the fourth rotational speed may be greater than the first rotational speed. 
     Therefore, the washing machine can prevent the laundry inside the drum from being twisted by the pulsator. 
     A controlling method of a washing machine including a tub, a drum rotatably provided inside the drum, may include rotating the drum at a first rotational speed so as to tumble laundry contained in the drum while controlling a duct heater to heat air circulated by a fan, and rotating the drum at a second rotational speed to separate water from the laundry contained in the drum while controlling the duct heater to heat the circulating air. 
     Because of this, the washing machine can perform heating and dehydration at the same time. Since the surface tension of the water is reduced by heating, the washing machine can reduce the amount of moisture contained in the laundry by simultaneously performing heating and dehydration. In addition, the washing machine can reduce the drying time for drying the laundry. 
     Rotating the drum at the first rotational speed may include allowing the supply of water to the condensing duct while heating the heating duct and circulating the air and rotating the drum at the first rotational speed so as to tumble the laundry contained within the drum. 
     Rotating the drum at the first rotational speed may include rotating the drum alternately in a first direction and a second direction so that the laundry contained in the drum tumbles, and wherein the time for rotating the drum in the first direction differs from the time for rotating the drum in the second direction. 
     As a result, the washing machine can effectively guide the air inside the drum to the condensation duct, and further reduce the drying time. 
     Rotating the drum at the second rotational speed may include blocking the supply of water to the condensing duct while rotating the drum at the second rotational speed to separate the water from the laundry contained within the drum. 
     A washing machine includes a tub; a drum rotatably installed inside of the tub; a condensing duct formed on an inner wall of the tub; a condensation conduit extending from an external water source to the condensing duct; a condensation valve provided on the condensation conduit to allow or block the supply of water to the condensing duct; a heating duct provided outside the tub; a duct heater provided inside the heating duct; a fan circulating air in the drum, the condensing duct, and the heating duct; and a controller electrically connected with the drum motor, the condensation valve, the duct heater, and the fan; and the condensing duct may include a rear groove formed inside a rear wall of the tub having a cylindrical shape, and a cover for partitioning the inside of the rear groove from the inside of the tub. 
     As a result, the condensation duct can be integrally formed with the tub. In addition, the condensation duct can be prevented from increasing the overall size of the washing machine or decreasing the size of the drum. 
     The condensing duct may be formed along a portion of a sidewall of the tub having the cylindrical shape. 
     Both ends of the condensing duct may be formed with inlets for connecting the condensing duct with the inside of the tub. 
     The controller may rotate the drum to separate water from laundry contained within the drum while controlling the condensation valve to block the supply of water to the condensing duct and controlling the duct heater to heat the air circulated by the fan. 
     The controller may rotate the drum to tumble laundry contained within the drum while controlling the condensation valve to block the supply of water to the condensing duct and controlling the duct heater to heat the air circulated by the fan. 
     According to the embodiments of the disclosure, a washing machine that can shorten the drying time by improving the drying efficiency of the washing machine is provided. 
     According to the embodiments of the disclosure, a washing machine capable of improving the drying efficiency by heating the air inside the tub during the drying stroke and at the same time rotating the drum at high speed is provided. 
     According to the embodiments of the disclosure, a washing machine that can improve the drying efficiency by providing a condensing duct extending from the bottom to the top of the rear of the tub and connecting the condensing duct with the drying duct is provided. 
     Exemplary embodiments of the present disclosure have been described above. In the exemplary embodiments described above, some components may be implemented as a “module”. Here, the term ‘module’ means, but is not limited to, a software and/or hardware component, such as a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium and configured to execute on one or more processors. 
     Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The operations provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules. In addition, the components and modules may be implemented such that they execute one or more CPUs in a device. 
     With that being said, and in addition to the above described exemplary embodiments, embodiments can thus be implemented through computer readable code/instructions in/on a medium, e.g., a computer readable medium, to control at least one processing element to implement any above described exemplary embodiment. The medium can correspond to any medium/media permitting the storing and/or transmission of the computer readable code. 
     The computer-readable code can be recorded on a medium or transmitted through the Internet. The medium may include Read Only Memory (ROM), Random Access Memory (RAM), Compact Disk-Read Only Memories (CD-ROMs), magnetic tapes, floppy disks, and optical recording medium. Also, the medium may be a non-transitory computer-readable medium. The media may also be a distributed network, so that the computer readable code is stored or transferred and executed in a distributed fashion. Still further, as only an example, the processing element could include at least one processor or at least one computer processor, and processing elements may be distributed and/or included in a single device. 
     While exemplary embodiments have been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope as disclosed herein. Accordingly, the scope should be limited only by the attached claims.