Abstract:
A liquid-vapor separating method and a liquid-vapor separating type evaporator, the method includes the following steps: (i) provide a partition device ( 3 ) in the upper portion of the evaporated liquid pipe, the partition device ( 3 ) divides the evaporated liquid pipe into a superheating section ( 12 ) and an evaporating section ( 13 ); (ii) a liquid-vapor separating pipe ( 4 ) is connected to the superheating section ( 12 ) near the partition device ( 3 ), an evaporated liquid feeding pipe ( 6 ) is connected to the evaporating section ( 13 ) near the partition device ( 3 ), several vapor guiding pipes ( 5 ) are respectively provided in the pipe of the evaporating section ( 13 ), the vapor guiding pipes ( 5 ) are respectively connected with the liquid-vapor separating pipe ( 4 ); vapor inside the pipe can flow out, and is separated into vapor and liquid in the liquid-vapor separating pipe ( 4 ), then the vapor enters the superheating section ( 12 ) and is superheated; the superheated vapor is discharged from a vapor outlet ( 11 ); (iii) the residual liquid separated from the liquid-vapor separating pipe ( 4 ) and the residual liquid in evaporating section ( 13 ) are together sent to the evaporated liquid feeding pipe ( 6 ) through a return pipe ( 14 ), and back to the evaporating and heat-exchanging process of evaporated liquid.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a series of new evaporators with liquid-vapor separation, and specially, to liquid-vapor separation technologies/devices associated with these new evaporators. 
       BACKGROUND OF THE INVENTION 
       [0002]    As a type of thermal engineering equipment, evaporators are widely employed in power, chemical, air-conditioning and refrigeration engineering in two types, one of which is liquid-heating, such as commonly used tube-in-tube or shell-tube evaporators, and the other type is air-heating, generally in-tube-evaporation, such as those employed in domestic air-conditioning, large scale refrigerators, chemical engineering and power plants. 
         [0003]    As shown in  FIG. 1 , generally, the evaporator of a domestic split air conditioner belongs to air-heating evaporators. A traditional vertical serpentine tube evaporator  9  is composed of heat exchange tubes  91  and fins  92  positioned outside the heat exchange tubes  91 . The evaporated liquid (generally referred to as refrigerant of a refrigeration system of the air conditioner) enters the heat exchange tube  91  from the inlet  93  of heat exchange tube  91 , and exchanges heat with the air flowing through the evaporator  9  via heat exchange tubes  91  and fins  92  outside the heat exchange tubes  91 , which makes evaporated liquid in heat exchange tubes  91  boil and evaporate into vapor which vents from the outlet  94  of heat exchange tube  91 . 
         [0004]    As shown in  FIGS. 2 and 3 , a traditional spiral tube-in-tube evaporator  10  is composed of outer tube  101  and inner tube  102  which can be a single tube or a bundle of tubes. The inlet  103  and outlet  104  arranged at the both ends of the outer tube  101  are used to transport heat source liquid (being cooled), and the inlet  105  and outlet  106  arranged at the both ends of the inner tube  102  are used to transport evaporated liquid. In such a spiral tube-in-tube evaporator, heat transfers between the heat source liquid (being cooled liquid, between the outer tube  101  and the inner tube  102 ) and the evaporated liquid (in the inner tube  102 ), which makes the evaporated liquid boil, and completely evaporate into vapor. The traditional spiral tube-in-tube evaporator  10  also can employ a serpentine tube (as shown in  FIG. 1 ) without a fin structure outside of the tube, and instead, the structure composed of an outer tube and inner tube is employed. In such an evaporator, the evaporated liquid may flow through the outer tube, and the heat source liquid may flow through the inner tube, which shares a similar principle but is rarely employed in practice. 
         [0005]    In the tube evaporator described above according to the prior art, pure liquid flows through the inlets  93 ,  105  and evaporates while flowing through the entire tube, and pure vapor discharges from the outlet  94 ,  106  for evaporated liquid. In order to improve the efficiency of heat transfer, the heat exchange tube will be subjected to surface enhancement processing, such as adding inner threads, inner groove pipe, micro-fin tubes of the inside surface, etc., which provides an extended heat exchange area while enhancing the surface. During the evaporation of the liquid in the heat exchange tube, the efficiency of heat exchange will be improved by the increase of the vapor quality to a limited extent. But the evaporation in the tube of the prior art can result in a more complex two-phase flow which disadvantages the formation of modality with efficient heat exchange. At the same time, a tube-in-tube evaporator employs a horizontal spiral structure, in which the flow will be inevitably layered, although there is a disturbance effect of secondary flow in the tube. The layered flow will result in local dryout and congregating of liquid at the bottom of the tube, thus the surface of the inner wall of the tube can not be well wetted by the liquid. Therefore uneven boiling or surface evaporation will be formed, or non-perfect boiling or surface evaporation will be formed, and as a result, the effect of surface enhancement will be weakened and the heat exchange efficiency will be reduced. Annular flow and thin liquid film have advantages in heat exchange, but they account for a limited percentage in the whole flow process, and thus have a limited effect on heat transfer. On the other hand, evaporation and boiling in a single tube flow process will result in a complex two-phase flow of vapor and liquid. When a two-phase flow occurs, bubbling, vapor blocking, annular flow, or stratified flow may occur in the flow depending on local vapor quality, thus substantially increasing the flow resistance and instability. As a result, the system stability, flow resistance and system adjustment are adversely affected. 
       SUMMARY OF THE INVENTION 
       [0006]    Based on the description above, the present invention is directed to an evaporator which can realize the auto separation of vapor and liquid, and improve the heat exchange performance. 
         [0007]    In order to realize the object above, the present invention employs a liquid-vapor-separation method and associated technologies in evaporators. The vapor-liquid separation is reached by the following steps: (1) setting a separation device for partitioning the tube into a superheat segment and an evaporation segment on the top of the tube through which the evaporated liquid flows; (2) connecting a separation tube for separating vapor and liquid to the superheat segment nearby the separation device, and connecting an incoming tube for circulating evaporated liquid to the evaporation segment nearby the separation device, setting a plurality of steam drainage tubes to the tube of the evaporation segment, each of the steam drainage tube connects to the liquid-vapor-separation tube respectively, thus the evaporated vapor can be vented at each segment and enter the superheat segment for superheating after separating vapor and liquid, and then the superheated steam vents via the steam outlet; (3) conveying the residual liquid from the liquid-vapor-separation tube and the residual liquid (not completely evaporated) from the evaporation segment to the incoming tube for the evaporated liquid through tubes and returning to the process for heat exchange of the liquid to be evaporated. 
         [0008]    The tube through which the evaporated liquid flows through a tube between an outer tube and an inner tube, and the separation device is an annular separation plate installed between the outer tube and the inner tube, and the heating liquid (fluid) flows through the inner tube. 
         [0009]    The evaporated liquid flows through a single row inner tube arranged with fins outside of the tube and the heating air flows outside of the inner tube. 
         [0010]    The evaporated liquid flows through an inner tube, outside of which is arranged an outer tube, and the heating liquid (fluid) flows through between the outer and the inner tube. 
         [0011]    A liquid-vapor-separation evaporator comprises a tube through which the evaporated liquid flows, a tube through which the heating liquid (fluid) flows or a space through which the heating vapor flows, the evaporator is characterized by: setting a separation device for partitioning the tube into a superheat segment and an evaporation segment on the top of the tube through which the evaporated liquid flows; connecting a separation tube for separating vapor and liquid to the superheat segment nearby the separation device, and connecting an incoming tube for circulating evaporated liquid to the evaporation segment nearby the separation device, setting a plurality of steam drainage tubes to the tube of the evaporation segment, each of the steam drainage tube connects to the liquid-vapor-separation tube respectively; connecting the bottom port of the liquid-vapor-separation tube to the inlet of the incoming tube for circulating evaporated liquid via tubes. 
         [0012]    The tube through which the evaporated liquid flows is a tube composed of an outer tube and an inner tube, the separation device is an annular separation plate positioned between the outer tube and the inner tube, and the heating liquid (fluid) inlet is positioned at the bottom port of the inner tube, and the heating liquid (fluid) outlet is positioned at the top port of the inner tube. 
         [0013]    The shapes of the outer tube and inner tube are spiral or vertical serpentine. 
         [0014]    The tube through which the evaporated liquid flows is a single row tube with fins arranged outside the tube. 
         [0015]    The tube through which the evaporated liquid flows is an inner tube outside which an outer tube is arranged, the separation device is a circular separation plate positioned inside the inner tube, the bottom port of the outer tube is the heating liquid (fluid) inlet, and the top port of the outer tube is the heating liquid outlet. 
         [0016]    The shapes of the corresponding outer tube and the inner tube are spiral or vertical serpentine. 
         [0017]    The inner flow passage can be an inner tube bundle composed of a plurality of spiral inner tubes. 
         [0018]    The inner tube can also be a single tube. 
         [0019]    The inner wall of the inner tube is designed having inner threads or micro-grooves, and the surface of a smooth inner wall or the inner threads or micro-grooves is covered by a porous layer formed by sintering a plurality of layers of screen and metal or non-metal particles. 
         [0020]    The inner wall of the outer tube is covered by a porous layer formed by sintering a plurality of layers of screen and metal or non-metal particles. 
         [0021]    The present invention is characterized by the following advantages due to the above technical measures: 1) the present invention employs a separation device to partition the heat exchange tube into a liquid evaporation segment and a steam superheat segment in a non-seal manner, thus preventing the incoming liquid from entering the superheat segment directly-which will influence the operation of the evaporator, while enabling the control of the superheat degree of the leaving steam-which is difficult to be implemented by traditional evaporators. The present evaporator can control the temperature of superheat steam according to the requirements to specified superheat degrees. Compared to adding the length of tube in the prior art, the separation device of the present invention has advantages in reducing the consumption of materials, improving the efficiency of energy conversion and utilization, and decreasing the power of the compressor of a refrigeration system. 2) By employing a reflux tube filled with porous core for the drainage and recirculation of residual evaporated liquid, which has dual functions in drawing and blocking liquid by capillarity, thus making the residual liquid gathering at the main body of the flow of the evaporation liquid, the present invention can realize recycling of the residual liquid, thus having advantages for auto-recycling residual liquid and re-evaporating the residual liquid, and eliminating the problem of accumulation and discharge of residual liquid. At the same time, the present invention can prevent the main body of the liquid flow from entering into the main heat exchange and evaporation section, which may result in degraded operation of the evaporator. Thus the efficiency and adaptability of the evaporator can be improved. 3) The present invention provides a novel liquid-vapor-separation device which can fast discharge the vapor from evaporation via a discharge tube thus reducing the pressure drop in the system helping to reach a higher efficiency of the evaporation process. 4) The present invention utilizes an inner tube bundle structure to circulate evaporated liquid (refrigerant) between an outer tube and an inner tube, with the complex inner features of the structure, and the present invention not only enhances the disturbance to the liquid flow, but also reduces the liquid by transferring it into vapor. Reducing the liquid is helpful to the wetting of liquid film, and the evaporation of a thin liquid film with better heat exchange effect is formed, thus the heat exchange is enhanced. 5) The evaporation surface is designed with micro-threads, grooves, and a porous layer, where the micro-threads or grooves covered with a porous layer are formed by sintering a plurality of screen and metal or non-metal particles. By the capillarity of the porous structure, the inner wall of the tube can be wetted by the liquid and the evaporation of a thin liquid film with a better heat exchange effect can be reached and the effect of surface enhancement can be further improved. Moreover, the porous layer can improve venting of the vapor of the surface area inside the tube and supplying of liquid to the surface area; a similar effect can be made to the outer surface of the heat exchange tube by similar measures. 6) The present invention has advantages for better efficiency of evaporation, high exchange transfer coefficient, small heat exchanger size, and low consumption of metal. Compared with prior art, the present invention can save more than 20% in materials, and provide lower manufacturing and operation costs, and a more simple manufacturing process. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0022]      FIG. 1  is a schematic view of the structure of a prior art air-heat evaporator. 
           [0023]      FIG. 2  is a prior art spiral tube evaporator. 
           [0024]      FIG. 3  is a side view of  FIG. 2 . 
           [0025]      FIG. 4  is a schematic view of a liquid-vapor-separation-outside-spiral-tube evaporator structure according to embodiment 1 of the present invention. 
           [0026]      FIG. 5  is a schematic view of a tube bundle of inner tubes in spiral configuration. 
           [0027]      FIG. 6  is a schematic view of liquid-vapor-separation-outside-vertical-serpentine-tube evaporator structure according to embodiment 2 of the present invention. 
           [0028]      FIG. 7  is a schematic view of liquid-vapor-separation-inside-vertical-serpentine-tube evaporator structure according to embodiment 3 of the present invention. 
           [0029]      FIG. 8  is the schematic view of the structure of the inner wall of serpentine tube of  FIG. 7 . 
           [0030]      FIG. 9  is the sectional view of  FIG. 8 . 
           [0031]      FIG. 10  is a schematic view of a liquid-vapor-separation-inside-serpentine-tube evaporator structure according to embodiment 4 of the present invention. 
           [0032]      FIG. 11  is a schematic view of liquid-vapor-separation-inside-spiral-tube evaporator structure according to embodiment 5 of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    The present invention will be described in detail in the following in connection with the drawings and embodiments. 
       Embodiment 1 
     A Liquid-Vapor-Separation-Outside-Spiral-Tube Evaporator 
       [0034]    As shown in  FIG. 4 , the present embodiment comprises a spiral outer tube  1 , and an inner tube  2  positioned in the outer tube  1 , the inner tube  2  of present embodiment is an inner tube bundle with spiral configuration (as shown in  FIG. 5 ), which can effectively improve the wetting and disturbance of the liquid while enhancing the heat exchange and the evaporation of the thin liquid film. As shown in  FIG. 4 , both ends of the outer tube  1  connect the outer wall of the inner tube  2  hermetically, the bottom port of the inner tube  2  is used as the inlet  21  of heating fluid, the top port of the inner tube  2  is used as the outlet  22  of heating fluid, and the steam outlet  11  of the outer tube  1  is positioned at the tube wall of the top port of the outer tube  1 . Between the upmost outer tube  1  and the inner tube  2 , an annular separation plate is set as a separation device  3  which partitions the outer tube  1  into a superheat segment  12  and an evaporation segment  13 . A liquid-vapor-separation tube  4  is set near the superheat segment  12  of separation device  3 , each layer of outer tube  1  of evaporation segment  13  is designed having a steam drainage tube  5  respectively, and connects the other ends of steam drainage tube  5  to liquid-vapor-separation tube  4 . An evaporated liquid incoming tube  6  is set (from the evaporation segment  13  downward) near the separation device  3 , the bottommost outer tube  1  is connected to the incoming tube  6  near its end via a recycling tube  14  for the residual liquid, thus the unevaporated liquid can be conveyed to the top of evaporation segment  13  again. 
         [0035]    In the above embodiment, the separation device  3  may also be positioned at the second or third layer of tube  1 , that is to say, the length of the superheat segment  12  can be adjusted based on the demand to meet the requirement of vapor superheat. Further, the steam drainage tube  5  of liquid-vapor-separation tube  4  connected to the outer tube  1  is set every two or three layers, instead of set at each layer, which can provide flexibility in design. 
         [0036]    When the device of the embodiment is used, as shown in  FIG. 4 , the heating fluid flows upward from the bottom of the inner tube  2 , and the evaporated liquid entering into the evaporation segment  13  between the upmost layer of outer tube  1  and inner tube  2  via the incoming tube  6  of the evaporated liquid, then flows downward via the spiral outer tube  1  and absorbs energy emanated by the heating fluid in the inner tube  2 , the steam from each layer enters into the liquid-vapor-separation tube  4  via steam drainage tube  5 . In the liquid-vapor-separation tube  4 , vapor flows upward, and flows to the steam outlet  11  after being superheated at the upmost layer of superheat segment  12 , while the liquid flows downward by gravity and flows into the bottom of the evaporation segment  13  together with the residual unevaporated liquid, and then returns to incoming tube  6  via the recycling tube  14  of the downmost layer of outer tube  1 , and then returns to evaporation segment  13  at the upper section of the outer tube  1  for heat exchange and evaporation. At this point, the incoming tube  6  will supply liquid continuously. During the circulation and supplement of the evaporated liquid, the steam in the tube will be vented at each segment, thus the flow of vapor and liquid can be kept without blocking, and the liquid can wet and form thin liquid film for evaporation and a good refrigerating effect can be realized. 
       Embodiment 2 
     A Liquid-Vapor-Separation-Outside-Vertical-Serpentine-Tube Evaporator 
       [0037]    As shown in  FIG. 6 , the main difference between this embodiment and the embodiment 1 lies in that the present embodiment employs a vertical serpentine outer tube  1  and a corresponding inner tube  2  as a separation device  3  positioned between the layer  1  and layer  2 , and makes the first layer of outer tube  1  a superheat segment  12  and the downstream of the second layer of outer tube  1  an evaporation segment  13 . Alternatively, the separation device can be positioned between the third layer and the fourth layer, and the actual position of the separation device can be determined according to requirement of the superheat degree. A liquid-vapor-separation tube  4  is connected to the superheat segment  12  near the separation device  3 , and a steam drainage tube  5  connects the liquid-vapor-separation tube  4  with each layer of outer tube  1  at the evaporation segment  13 . An incoming tube  6  for evaporated liquid connects to the evaporation segment  13  near the separation device  3 . The outer tube  1  of the downmost layer connects to the incoming tube  6  near its end via a recycling tube  14  for the residual liquid, thus the unevaporated liquid reenters into the top of evaporation segment, the bottom port of the inner tube  2  is the heating fluid inlet  21 , the top port of which is the heating fluid outlet  22 . 
         [0038]    In the embodiment 1 and 2, the outer wall of the inner tube  1  can be covered by a porous layer  15  (as shown in  FIG. 5 ) formed by sintering a plurality of screen and metal or non-metal particles. By the capillarity of the porous structure, liquid can wet the wall of the inner tube to form and maintain the evaporation of a thin liquid film with better heat exchange effect, thus the surface enhancement effect can be further improved. The principle of the embodiment is similar to that of embodiment 1 and the description of which will be omitted here. 
       Embodiment 3 
     A Liquid-Vapor-Separation-Inside-Vertical-Serpentine-Air-Heating Evaporator 
       [0039]    As shown in  FIG. 7 , the present embodiment has a vertical serpentine tube similar to that of embodiment 2, but a single layer tube referred to as inner tube  2  is employed due to air used as heating fluid. Outside fins  7  are set between each layer of inner tube  2  via expanded joints, and the separation device  3  partitions the outer tube  2  into superheat segment  23  and evaporation segment  24 . The exact position of separation segment  3  can be determined according to the requirement of the superheat degree. The top port of the inner tube  2  is steam outlet  25 , and the bottom port is closed, and the inner tube  2  is connected to the lower portion of the incoming tube  6  via a residual liquid recycling tube  14  positioned on the surface of the port. The top of the incoming tube  6  is connected to the evaporation segment  24  near the separation device  3 . The top end of the liquid-vapor-separation tube  4  is connected to the superheat segment  23  near the separation device, and each steam drainage tube  5  connected to the evaporation segment  24  is connected with the liquid-vapor-separation tube  4 , and the downmost inner tube  2  is connected to the bottom portion of the liquid-vapor-separation tube  4 . 
         [0040]    As shown in  FIGS. 8 and 9 , in the present embodiment, the inner wall of the inner tube  2  can be designed with inner threads or micro-grooves  16 , and the surface of the inner threads or micro-grooves  16  is covered with a porous layer  15  for forming and maintaining a thin liquid film with good wettability on the inner wall of the inner tube  2 , keeping a best evaporation status for the thin liquid film in the tube. 
         [0041]    In the embodiment, the heating fluid is air which exchanges heat with the inner tube  2  and the fin  7  outside the tube. The liquid flows into the evaporation segment  24  for evaporating or boiling via the incoming tube  6 , and the vapor resulted from the evaporation continuously flows into the superheat segment  23  of the inner tube  2  for superheat via the steam drainage tube  5  and the liquid-vapor-separation tube  4 , then flows out through the steam outlet  25  of the inner tube  2 . The residual liquid separated by the liquid-vapor-separation tube  4  and the residual liquid from the evaporation segment  24  flow into inner tube  2  together, and then into the incoming tube  6  via the recycling tube  14  for residual liquid, and then into the evaporation segment  24  at the upper portion of the inner tube  2  by the drive of a pump at one end of the incoming tube  6  for a new heat exchange cycle. 
       Embodiment 4 
     A Liquid-Vapor-Separation-Inside-Vertical-Serpentine-Tube Evaporator 
       [0042]    As shown in  FIG. 10 , the embodiment comprises a vertical serpentine inner tube  2  which is a single tube. A steam outlet  25  is set at the top port of the inner tube  2 , and the bottom port is closed. An outer tube  1  is positioned outside the inner tube  2  and seals the horizontal section of each layer of inner tube  2 , and the outer tube  1  of the horizontal sections of each layer are connected to the next layer of outer tube  1  via an independent vertical linking tube  8 . A heating fluid inlet  17  is set at the end of the downmost layer of outer tube  1 , and a heating fluid outlet  18  is set at the end of the upmost layer of outer tube  1 . The separation device  3  is an annular plate positioned at the corner between the first layer of inner tube  2  and the second layer of inner tube  2  (which can be positioned at another position according to requirement of the design, and is not limited). The separation device  3  partitions the inner tube  2  into a superheat segment  23  and an evaporation segment  24 , and a liquid-vapor-separation tube  4  connects to the superheat segment  23  near the separation device  3 , and the steam drainage tube  5  of each layer is connected to the inner tube  2  of the evaporation segment  24  and the liquid-vapor-separation tube  4  respectively, and the liquid-vapor-separation tube  4  is connected to the downmost port of the inner tube  2 , then connected to the incoming tube  6  via the recycling tube  14  for residual liquid. The top outlet of the incoming tube  6  is connected to the evaporation segment  24  of the inner tube  2  which is near the separation device  3 . 
         [0043]    In the embodiment, the heating fluid media enters through inlet  17  of the outer tube  1 , and flows out through the outlet  18  after cooled in each layer of inner tube  2 , and the liquid entering from the incoming tube  6  flows to the evaporation segment  24  of the inner tube  2  near the separation device  3  at the upper part, then exchanges heat with the heating fluid in the outer tube  1  through each layer of inner tube  2 , then the steam resulted from the process flows into the liquid-vapor-separation tube  4  via the steam drainage tube  5 , and then flows out through the steam outlet  25  after being superheated by the superheat segment of the inner tube  2 . The residual liquid and the unevaporated liquid from the evaporation segment  24  enter into the bottom of the inner tube  2  together, then into the evaporation segment  24  at the upper part of the inner tube  2  after flowing into the incoming tube  6  through the residual liquid recycling tube  14 . 
       Embodiment 5 
     A Liquid-Vapor-Separation-Inside-Spiral-Tube Evaporator 
       [0044]    As shown in  FIG. 11 , the present embodiment is similar with embodiment 4, both inside-tube evaporation, but the tube configuration of the embodiment employs a spiral configuration, which comprises a spiral inner tube  2 . In the present embodiment, the inner tube is a single tube, on the top port of which is a steam outlet  25  and the bottom port is closed. An outer tube  1  is set outside the inner tube  2 . A heating fluid inlet  17  is set at the bottom end of the downmost layer of outer tube  1 , and a heating fluid outlet  18  is set at the top end of the upmost layer of outer tube  1 . The separation device  3  is a circular plate positioned at the corner between the first layer and the second layer of inner tube  2  (which can be positioned at an other position according to requirement of the design, and is not limited), the separation device  3  partitions the inner tube  2  into a superheat segment and an evaporation segment. The liquid-vapor-separation tube  4  goes through the outer tube  1  and is connected to the superheat segment near the separation device  3 . The steam drainage tube  5  of each layer goes through the outer tube  1  and is connected to the inner tube  2  of the evaporation segment  24  and the liquid-vapor-separation tube  4  respectively, and the liquid-vapor-separation tube  4  goes through the outer tube  1  and is connected to the downmost port of the inner tube  2 , then connected to the incoming tube  6  via the recycling tube  14  for residual unevaporated liquid. The top outlet of the incoming tube  6  goes through the outer tube  1  and is connected to the evaporation segment of the inner tube  2  near the separation device  3 . 
         [0045]    The present embodiment is utilized in a similar way as that of embodiment 4, and the description of which is omitted here. 
         [0046]    Based on the above description, the method for separating vapor and liquid of the liquid-vapor-separation evaporator of the present invention includes the followings: 
         [0047]    setting a separation device at the upper part of tube through which the liquid in the vapor liquid separator flows in order to partition the tube into a superheat segment and evaporation segment; 
         [0048]    connecting a liquid-vapor-separation tube to the superheat segment nearby the separation device, and connecting an incoming tube for circulating evaporated liquid to the evaporation segment nearby the separation device, setting a plurality of spaced steam drainage tubes at the tube of the evaporation segment, each of the steam drainage tubes is connected to the liquid-vapor-separation tube respectively, thus the evaporated vapor can be vented at each segment and enter into the superheat segment for superheating after separating vapor and liquid, and the superheated steam can be vented via the steam outlet; 
         [0049]    conveying the residual liquid from the liquid-vapor-separation tube and the incompletely evaporated residual liquid from the evaporation segment to the incoming tube for the evaporated liquid through tubes and returning to the process for heat exchange of the liquid to be evaporated. 
         [0050]    The embodiments disclosed above are directed to illustrate the particular structure of present invention, not limiting the scope of the present invention, and those skilled in the art will appreciate that various equivalents based on the principles and technical solutions of the present invention will fall into the scope and spirit of the invention as disclosed in the accompanying claims.