Abstract:
A water heater includes a combustion device, a primary heat exchanger, and a secondary heat exchanger. The combustion device burns gas to generate high-temperature air. The primary and the secondary heat exchangers are provided sequentially above the combustion device. When the high-temperature air passes through the primary heat exchanger, part of thermal energy is absorbed by exchange plates and a water pipe therein. When the high-temperature air continues to pass through the secondary heat exchanger, part of the rest thermal energy is absorbed by a heat tube set therein to preheat water flowing through the heat tube set. The preheated water then flows into the water pipe of the primary heat exchanger. The secondary heat exchanger includes a case and a cover board which detachably seals a bore on the case. Whereby, it&#39;s convenient for a user to clean pipes inside the secondary heat exchanger.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates generally to a water heater, and more particularly to a water heater having a secondary heat exchanger. 
         [0003]    2. Description of Related Art 
         [0004]    A conventional water heater has a burner and a heat exchanger. Gas is supplied to the burned and burned to heat the heat exchange above the burner. The heat exchange includes a water pipe and a plurality of exchange plates. The exchange plates are arranged in parallel, and the water pipe repeatedly passes through the exchange plates. The water pipe has an inlet and an outlet. Cold water enters the water pipe via the inlet, and hot water leaves the water pipe via the outlet. The exchange plates are heated by the burner, and the heat is transferred to the water pipe via conduction to heat the water therein. According to the laws of thermodynamics, the always is heat not transferred to the water pipe to heat the eater, therefore, high-temperature gas will be exhausted out of the water heater while heating water. In other words, the conventional water heater has a low efficiency in transfer of thermal energy. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In view of the above, the primary objective of the present invention is to provide a water heater having a secondary heat exchanger, which is able to use the thermal energy in high efficiency. 
         [0006]    The secondary of the present invention is to provide a water heater having a secondary heat exchanger, which can clean the secondary heat exchanger in an easy way. 
         [0007]    The present invention provides a secondary heat exchanger, which is mounted on a water heater having a primary heat exchanger, including a case having an enter opening, a second exit opening, and a bore, wherein the enter opening is communicated with the primary heat exchanger; a heat tube set received in the case, and having an inlet and an outlet for water entering the heat tube set via the inlet and leaving via the outlet; a cover board detachably connected to the case to seal the bore; and a collecting member received in the case under the heat tube set. 
         [0008]    The present invention also provides a water heater, including a combustion device where gas is burned to generate heat; a primary heat exchanger above the combustion device, and having a first case and a water pipe, wherein the first case has a first exit opening, and the water pipe is received in the first case; the water pipe has an inlet and an outlet; and a secondary heat exchanger. The secondary heat exchanger is above the primary heat exchanger, and includes a second case having an enter opening, a second exit opening, and a bore, wherein the enter opening is communicated with the first exit opening of the primary heat exchanger; a heat tube set received in the case, and having an inlet and an outlet for water entering the heat tube set via the inlet and leaving via the outlet; a cover board detachably connected to the case to seal the bore; and a collecting member received in the case under the heat tube set. 
         [0009]    With the design of above, water will be heated twice in the water heater to increase the heat transfer efficiency. The present invention also provides the cover board, which is helpful to the user to clean the secondary heat exchanger. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The present invention will be best understood by referring to the following detailed description of some illustrative embodiments in conjunction with the accompanying drawings, in which 
           [0011]      FIG. 1  is a schematic diagram of the water heater of a preferred embodiment of the present invention; 
           [0012]      FIG. 2  is a perspective view of the secondary heat exchanger of the preferred embodiment of the present invention; 
           [0013]      FIG. 3  is an exploded view of the secondary heat exchanger of the preferred embodiment of the present invention; 
           [0014]      FIG. 4  is a sectional view along the  4 - 4  line of  FIG. 2 ; 
           [0015]      FIG. 5  is a partial sectional view of the secondary heat exchanger of the preferred embodiment of the present invention; and 
           [0016]      FIG. 6  is a partial top view of inside of the secondary heat exchanger of the preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    As shown in  FIG. 1 , a water heater of the preferred embodiment of the present invention includes a base  10 , a main case  12 , a combustion device  14 , a primary heat exchanger  26 , and a secondary heat exchanger  34 . The combustion device  14 , the primary heat exchanger  26 , and the secondary heat exchanger  34  are mounted on the base  10 , and the main case  12  is detachably connected to the base  10  to receive these elements therein. 
         [0018]    The combustion device  14  has a housing  16 , a burner  18 , a gas valve  20 , and a blower  22 . The housing  16  has an opening at a top thereof, and the burner  18  is received in the housing  16  and under the opening. Gas is burned in the burner  18  to generate high-temperature air coming out via the opening of the housing  16 . The gas valve  20  is provided on a gas pipe  24 . The gas pipe  24  provides gas to the burner  18 , and the gas valve  20  is operated to adjust a gas flow in the gas pipe  24 . The blower  22  supplies the burner  18  with an air flow to be mixed with the gas from the gas pipe  24 . The gas valve  20  and the blower  22  are controllable by a controller (not shown) to change the gas flow and the air flow to the burner  18 . Therefore, gas and air are mixed in a desired air-fuel ratio. 
         [0019]    As shown in FIGS. from  FIG. 2  to  FIG. 6 , the primary heat exchanger  26  includes a first case  28 , a water pipe  30 , and exchange plates  32 . The first case  28  is connected to the top of the case  16 , and the opening of the case  16  is communicate with inside of the first case  28 . In other words, the first case  28  has an opening at a bottom, which is attached to the top of the case  16 . The first case  28  has a first exit opening  282  at a top thereof. The water pipe  30  is a continuous U-shaped pipe mounted in the first case  28 . The water pipe  30  has several straight heating sections  302  in the first case  28  and several U-turn sections left out of the first case  28 . Opposite ends of the water pipe  30  extend out of the first case  28 , one of which is provided with a connector  304 , and the other of which is a water outlet  306 . The exchange plates  32  are parallel to each other and received in the first case  28 , and the heating sections  302  of the water pipe  30  pass through the exchange plates  32 . 
         [0020]    The secondary heat exchanger  34  is mounted on the top of the primary heat exchanger  26 , and has a second case  36 , a heat tube set  56 , a collecting member  58 , and a cover board  62 . 
         [0021]    The second case  36  has a plate  38  at a top thereof, on which a second exit opening  382  is provided. An exhausting pipe  40  is connected to the second exit opening  382 . The second case  36  has an enter opening  362  at a bottom thereof, which is communicated with the first exit opening  282  of the first case  28  of the primary heat exchanger  26 . The second case  36  further has four sidewalls, which are called a front board  42 , a rear board  44 , a left board  46 , and a right board  48 . The front board  42  has a bore  422  and a plurality of threaded holes  424  around the bore  422 . The front board  42  faces the main case  12 , and the rear board  44  faces the base  10 . The right board  48  is provided with a first bore  482  and a second bore  484 . A water input tube  50  is inserted into the first bore  482 , and a connecting tube  52  is inserted into the second bore  484 . The water input tube  50  extends out of the main case  12  for water flowing into the water heater. The right board  48  is provided with an exhausting bore  486  for a water exhausting tube  54  passing through. 
         [0022]    The heat tube set  56  is received in the second case  36  in an inclined condition, and includes an input box  562 , an output box  564 , and a plurality of continuous S-shaped tubes  566 . The input box  562  is lower than the output box  564 . The input box  562  is provide with an inlet  562   a , and the inlet  562   a  is aligned with the first bore  482  of the second case  36  for the input tube  50  passing through. The output box  564  is provided with an outlet  564   a , and the outlet  564   a  is aligned with the second bore  484  of the second case  36  for the connecting tube  52  passing through. The connecting tube  52  is connected to the connector  304  of the water pipe  30 . All the tubes  566  have opposite ends connected to the input box  562  and the output box  564  respectively. The tubes  566  are staggered to expose surfaces thereof as possible. Water from the input tube  50  flows into the input box  562 , and then flows through the tubes  566 , the output box  564 , and the connecting tube  52  before enters the water pipe  30  of the primary heat exchanger  26 . 
         [0023]    The collecting member  58  is received in the second case  36  under the heat tube set  56 , and has a top board  582  and a low board  584 . The top board  582  is stacked on the low board  584 , and kept a distance from it, therefore a space is formed between the top board  582  and the top board  582 . 
         [0024]    The collecting member  58  is provided with four walls  602 ,  604 ,  606 ,  608  at four sides thereof. The walls  606 ,  608  at left and right sides abut against the rear board  44 , the left board  46 , and the right board  48  of the second case  36 . The collecting member  58  has a front edge  586  facing the front board  42  of the second case  36 . The front edge  586  faces the bore  422 , and keeps a first distance L 1  from the front board  42  in a horizontal direction. The same as the heat tube set  56 , the collecting member  58  is inclined while the wall  606  is lower than the wall  608 . The collecting member  58  is provided with a round bore  608   a  on the wall  608  of the right side, and the round bore  608   a  is aligned with the exhausting bore  486  of the right board  48  to drain the water in the collecting member  58  out of the second case  36  through the round bore  608   a  and the exhausting bore  486 . Water will be collected in the collecting member  58  because of the walls  602 - 608 . The space between the top and the low boards  582 ,  584  to avoid vapor from condensation. 
         [0025]    The cover board  62  is beside the front board  42 , and has a flange  624  at a periphery thereof. The flange  624  is provided with several holes  424   a , and the front board  42  is provided with several threaded holes  424 , so that the cover board  62  is fixed to the front board  42  of the second case  36  by bolts  66 . A gasket  64  is provided between the flange  624  and the front board  42 . The gasket  64  also has several holes  642  for the bolts  66 . As a result, the bore  422  of the front board  42  is sealed by the cover board  62 . 
         [0026]    The cover board  62  has an inner side  622  facing the front board  42 . The inner side  622  of the cover board  62  keeps a second distance L 2  from the front edge  586  of the collecting member  58  in the horizontal direction, and the second distance L 2  is longer than the first distance L 1 . A separating board  68  is connected to the cover board  62 , and keeps a distance from the inner side  622  of the cover board  62 . The separating board  68  keeps a third distance L 3  from the front edge  586  of the collecting member  58  in the horizontal direction to form a passageway P. The third distance L 3  is shorter than the second distance L 2 , but longer than the first distance L 1 . In other words, the cover board  62  has a room therein to provide a space (the passageway P) in the second case  36  for high-temperature air passing through. 
         [0027]    When gas is burned in the burner  18  and generates high-temperature air, the high-temperature air goes up to the first case  28  of the primary heat exchanger  26 , and heats the exchange plates  32 . After that, the high-temperature air keeps going up to the second case  36  of the secondary heat exchanger  32 . In the second case  26  the high-temperature air goes through the passageway P and to the S-shaped tubes  566 , and then goes out of the second case  36  via the second exit opening  382 . As a result, cold water is heated in the S-shaped tubes  566  of the secondary heat exchanger  32 , and then is heated in the water pipe  30  in the primary heat exchanger  26  again, therefore the heat transfer efficiency in the water heater of the present invention is higher than the conventional water heater having single heat exchanger. 
         [0028]    In addition, burning in the burner  18  generates carbon dioxide, and carbon dioxide is reacted with vapor to form carbonic acid solution. The carbonic acid solution will be collected in the collecting member  58 , and drained out of the water heater via the exhausting bore  486  to prevent the elements in the water heater from being corroded by the carbonic acid solution. 
         [0029]    The cover board  62  is able to be taken off from the second case  36  to allow user to clean the S-shaped tubes  566  after the main case  12  is removed. When cleaning the S-shaped tubes  566 , the user may put a board (not shown) on the wall  602  of the collecting member  58  and extends out of the bore  422 , so that the waste cleaning water may be guided out of the water heater via the exhausting bore  486  instead of flowing into the first case  28 . 
         [0030]    In conclusion, the water heater of the present invention make the water be heated twice with one burner to increase the heat transfer efficiency. The present invention also provides the cover board  62 , which is helpful to the user to clean the S-shaped tubes  566  of the secondary heat exchanger  32 , and the collecting member to drain the carbonic acid solution out of the water heater. 
         [0031]    It must be pointed out that the embodiments described above are only some preferred embodiments of the present invention. All equivalent structures which employ the concepts disclosed in this specification and the appended claims should fall within the scope of the present invention.