Patent Publication Number: US-2023156961-A1

Title: Two-phase immersion cooling device with movable second condenser

Description:
TECHNICAL FIELD 
     The present disclosure relates to temperature control, in particular to a two-phase immersion cooling device. 
     BACKGROUND 
     With the rapid improvement of power and heat flux density of computer chips, internet of things, batteries of new energy vehicles, electronic devices, home digital electrical equipment, digital medical treatments, chips and electronic devices of edge computing, quantum computing, heating components of mechanical equipment and heating components of electronic equipment, the cooling technology of the heating components has also experienced rapid development from generation to generation. After the continuous development of passive cooling, enhanced air cooling, thermosyphon loop heat pipe cooling, liquid cooling, and single-phase immersion cooling technology, a two-phase immersion cooling method is one of the most promising and effective server cooling technologies. 
     The existing two-phase immersion cooling device includes a box body, a heating element, a coolant, and a first condenser. The heating element is contained in the lower part of the box body and immersed in the coolant. The first condenser is disposed along at least one side wall of a plurality of inner walls on the upper part of the box body. The first condenser is far away from an upper cavity surrounded by one or a plurality of side walls for the heating element to pass up and down. The coolant in the bottom of the box body absorbs the heat generated by the heating element and is boiled and gasified, thereby cooling the heating element. The coolant vapor rises to the upper part of the box body and is condensed on the first condenser, and the coolant condensate on the first condenser falls back into the accommodating cavity in the bottom of the box body under the action of gravity, so as to achieve the effective cooling of the heating element. However, a large amount of extremely expensive coolant may be lost by the existing two-phase immersion cooling device, and the first condenser is large in size with low compactness and high cost. 
     Therefore, improvement is desired. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a two-phase immersion cooling device with a movable second condenser, which can reduce the loss of the extremely expensive coolant and has high compactness of a box body with low cost. 
     The present disclosure provides a two-phase immersion cooling device with a movable second condenser, the two-phase immersion cooling device with the movable second condenser includes a box body, a plurality of heating elements, a first condenser, and a cover body. The box body includes a plurality of side walls connected to each other from top to bottom and a bottom wall. The bottom wall is connected to one end of each of the plurality of side walls, the plurality of side walls and the bottom wall jointly form an accommodating cavity, and a bottom of the accommodating cavity is configured to contain a coolant. The plurality of heating elements are disposed in the accommodating cavity and adapted to be immersed in the coolant. The first condenser is disposed along at least one side wall, the first condenser is received in the accommodating cavity and located above the coolant and the plurality of heating elements, and the first condenser is far away from a cavity surrounded by the plurality of side walls. The cover body covers the box body to seal the accommodating cavity and the cover body is expandable on the box body to expose the accommodating cavity to the exterior environment. At least one movable second condenser is fixedly disposed on the cover body or a rear door located on an upper part of the box body, the at least one movable second condenser is received in the upper cavity, and the at least one movable second condenser leaves the accommodating cavity with movement of the cover body or the rear door. 
     According to an embodiment of the present disclosure, the first condenser and the at least one movable second condenser are combined into a third condenser, the third condenser is disposed on the cover body or the rear door. 
     According to an embodiment of the present disclosure, the cover body is detachably or reversibly connected to the box body, or the rear door is detachably connected to the box body. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises a power support or a power mover, the power support is connected to the cover body and used to drive the opening or closing of the cover body, and the power mover is connected to the rear door and used to drive the opening or closing of the rear door. 
     According to an embodiment of the present disclosure, the first condenser comprises a first cooling water system, the at least one movable second condenser comprises a second cooling water system, the first cooling water system of the first condenser and the second cooling water system of the at least one movable second condenser are operated independently, in series or in parallel, respectively. 
     According to an embodiment of the present disclosure, both the first condenser and the at least one movable second condenser comprise an inlet of the cooling water and an outlet of the cooling water. The inlet of the cooling water and the outlet of the cooling water pass through the upper part of the side wall of the box body, the cover body, or the rear door. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises at least one sensor disposed in the accommodating cavity, the at least one sensor comprises at least one of a temperature sensor, a humidity sensor, a pressure sensor, a flow sensor, and a liquid level sensor, the at least one sensor is configured for sensing at least one of a vapor temperature, a liquid temperature, vapor humidity, a vapor pressure, a liquid level height of the coolant, an inlet temperature of the cooling water, an outlet temperature of the cooling water, and a flow rate of the cooling water of each of the first condenser and the at least one movable second condenser in the accommodating cavity. 
     According to an embodiment of the present disclosure, the liquid level sensor is disposed on the box body or in the box body, the liquid level sensor is connected to the accommodating cavity, and the liquid level sensor detects a liquid level height of the coolant. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises a controller, the controller is electrically connected to the at least one movable second condenser, the at least one sensor, and the first condenser. When the at least one sensor senses the vapor temperature in the accommodating cavity is higher than a preset temperature or the vapor pressure in the accommodating cavity is higher than a preset pressure, the controller controls and adjusts the inlet temperature and the flow rate of the cooling water in the at least one movable second condenser or in the first condenser. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises an alarm and a coolant management system, the controller is electrically connected to the alarm, and the coolant management system. When the liquid level height of the coolant detected by the liquid level sensor is lower than a preset height, the controller controls the alarm to give an alarm, and controls the coolant management system to replenish the coolant into the accommodating cavity. 
     According to an embodiment of the present disclosure, the coolant management system comprises an overflow weir plate, a liquid storage tank, a pump, a pipeline, a valve, and a filter. 
     According to an embodiment of the present disclosure, the plurality of heating elements comprises a server applied to a data center, a battery or an electronic device applied to a new energy vehicle, an electronic chip or a device applied to a home intelligent digital appliance, an electronic chip or an electronic device applied to a digital medical treatment, an electronic chip or electronic device for digital medical treatment, a chip and an electronic device for edge computing, a chip for quantum computing, and a heating component applied to mechanical equipment or electronic equipment. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises at least one double-faced socket hermetically disposed on the box body or the cover body. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises an extracting valve, the extracting valve is disposed on the box body or the cover body, the extracting valve is connected to a vacuum device to extract non-condensable vapor in the accommodating cavity. The vacuum device places the accommodating cavity in a closed vacuum state before the operation of the heating elements or after the installation, removal, repair, and maintenance of the heating elements, so as to ensure the first condenser and the movable second condenser in the accommodating cavity can operate efficiently without non-condensable vapor. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises a handle disposed on the cover body or the rear door. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser further comprises a supporting member, the supporting member is disposed on the bottom of the box body, and the supporting member is a supporting frame or a roller. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser comprises a safety valve, when the vapor pressure in the accommodating cavity is higher than a preset vapor pressure, the safety valve is opened until the vapor pressure in the accommodating cavity is lower than the preset vapor pressure. 
     According to an embodiment of the present disclosure, the at least one movable second condenser is any one of a U-shaped tube condenser, a straight tube condenser, and a snake tube condenser. 
     According to an embodiment of the present disclosure, the two-phase immersion cooling device with the movable second condenser comprises a pressure balance valve, when the vapor pressure in the accommodating cavity is lower than an atmospheric pressure, the pressure balance valve is opened until the vapor pressure in the accommodating cavity is equal to the atmospheric pressure. 
     In the two-phase immersion cooling device with the movable second condenser provided by the present disclosure, due to at least one movable second condenser is disposed in a cavity, the coolant vapor located in the cavity can be condensed down, the contact area between the coolant vapor and the condenser is increased, and the heat transfer capacity of the condenser is effectively improved, the condensation rate and the evaporation rate of the coolant in the box body tend to be balanced which reduce the continuous increase of temperature and pressure in the box body caused by the condensation rate being lower than the evaporation rate, the pressure difference inside and outside the box body is reduced, the leakage loss of extremely expensive coolant vapor is reduced, the height of the first condenser is reduced, the volume of the two-phase immersion cooling device is reduced, and the two-phase immersion cooling device is more compact with low cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a two-phase immersion cooling device with a movable second condenser according to an embodiment of the present disclosure. 
         FIG.  2    is a schematic diagram of a cover body of the two-phase immersion cooling device of  FIG.  1    unfolded on a box body. 
         FIG.  3    is a sectional view along line of  FIG.  1   . 
         FIG.  4    is an exploded view of the cover body and the box body of the two-phase immersion cooling device of  FIG.  1   . 
         FIG.  5    is a schematic block diagram of a third condenser according to an embodiment of the present disclosure. 
         FIG.  6    is a schematic block diagram of some components of the two-phase immersion cooling device with the movable second condenser according to an embodiment of the present disclosure. 
         FIG.  7    is a schematic block diagram of a coolant management system according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is used to disclose the present disclosure so that those skilled in the art can implement the present disclosure. The preferred embodiments in the following description are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present disclosure defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present disclosure. 
     It can be understood that the height of the box body in the present disclosure refers to the vertically-upward direction and perpendicular to the bottom wall of the box body. 
     Some embodiments of the present disclosure are described in detail below in combination with the accompanying drawings. Without conflict, the following embodiments and features in the embodiments may be combined or can replace each other. 
       FIG.  1    to  FIG.  7    illustrate a two-phase immersion cooling device with a movable second condenser  100  in accordance with an embodiment of the present disclosure. 
     The two-phase immersion cooling device with movable second condenser  100  includes a box body  10 , a cover body  15 , a coolant  20 , a plurality of heating elements  30 , a first condenser  40 , and a moveable second condenser  60 . The box body  10  defines an accommodating cavity  101 . The cover body  15  is adapted to cover the box body  10  to seal the accommodating cavity  101 , and the cover body  15  can open the box body  10  to expose the accommodating cavity  101  to the outside. The cover body  15  is detachably or reversibly connected to the box body  10 . The cover body  15  can be detachably connected to the box body  10  by means of flange connection, hook connection, bite joint connection, clamp connection, screw connection, etc. 
     The box body  10  includes a plurality of side walls  12  and a bottom wall  13 , the side walls  12  are connected to each other from top to bottom, and the bottom wall  13  is connected to bottom ends of the side walls  12 . The plurality of side walls  12  and the bottom wall  13  together form the accommodating cavity  101 . 
     The coolant  20  is disposed in the accommodating cavity  101 . The coolant  20  may be, but is not limited to, a liquid having low boiling point and insulating properties. The low boiling point here may be, for example, between about  40 - 70  degrees or lower than the temperature of heat generated during the operation of the heating elements  30 . In other words, the coolant  20  is a substance suitable for direct contact with the heating elements  30 , and can effectively absorb the heat generated by the heating elements  30 , and boil and evaporate as a result, the present disclosure is not limited to the coolant  20  and its types and physical characteristics. The coolant  20  boils and gasifies rapidly by absorbing the heat generated by the heating element  30 , thus reducing the temperature of the heating elements  30 . 
     The heating elements  30  are disposed in the accommodating cavity  101  and are immersed in the coolant  20 . The heating elements  30  can be, but are not limited to, a server and components applied in a data center, a battery and an electronic device of a new energy vehicle, an electronic chip and device of a home intelligent digital appliance, an electronic chip and an electronic device applied to digital medical treatment, a chip and an electronic device of edge computing, a chip of quantum computing, a chip of a robot, and heat-generating components of a mechanical equipment or an electronic equipment. The present disclosure is not limited to the type, quantity, size, or scale of the heating element  30 . 
     The first condenser  40  is disposed along the side walls  12 . The first condenser  40  is accommodated in the accommodating cavity  101  and is located above the coolant  20  and the heating elements  30 . The first condenser  40  is far away from a formed cavity  401  surrounded by the plurality of side walls  12 . The cavity  401  is used for the moving up and down of the heating elements  30  during installation, removal, and maintenance. The cavity  401  is a part of the accommodating cavity  101 . In the embodiment, the first condenser  40  includes a plurality of condensing tube groups  41 , the condensing tube groups  41  are disposed at intervals on the upper part of the box body  10 , and at least one condensing tube group  41  is disposed around the circumference of the upper part of the box body  10 , or at least one condensing tube group  41  is disposed according to at least one wall surface of the upper part of the box body  10 . In other embodiments, the first condenser  40  may also include at least one row and one column of the condensing tube groups  41 . 
     The movable second condenser  60  are fixedly disposed on the cover body  15  and accommodated in the cavity  401 . The movable second condenser  60  is used to condense the coolant vapor rising into the cavity  401 . The movable second condenser  60  includes at least one row and one column of U-shaped tubular condensing tubes, straight tubular condensing tubes, or snake condensing tubes. When the coolant  20  is gasified to form coolant vapor, the coolant vapor with high thermal energy flows upward to the first condenser  40  and the movable second condenser  60  in the closed accommodating cavity  101 , and may be condensed on the first condenser  40  and the movable second condenser  60 . The coolant condensate on the first condenser  40  and the movable second condenser  60  falls back into the coolant  20  under the action of gravity, so as to achieve the effective heat dissipation and cooling of the heating element  30 . 
     The movable second condenser  60  enhances the heat transfer capacity of the condenser. If the movable second condenser  60  is not provided in the cavity  401 , due to the pressure difference between the coolant vapor located in the cavity  401  and the coolant vapor located at the first condenser  40  being very small, only a small part of the coolant vapor located in the cavity  401  would be condensed on the first condenser  40  disposed on the box body  10 , most of the coolant vapor would remain in the cavity  401  and not be condensed effectively, so that the evaporation rate and condensation rate of the coolant  20  in the box body  10  would not reach equality or equilibrium. With the continuous heating by the heating elements  30 , after a period of time, the overall temperature in the closed box body  10  gradually increases. The higher the temperature, the greater the pressure in the box body  10 . When the pressure in the box body  10  is higher than the pressure outside the box body  10  to form a pressure difference, the vapor in the box body  10  would leak out of the box body  10  under the action of the pressure difference or from the place where the box body  10  is not tightly sealed, or, in order to prevent the box body  10  from exploding, the pressure might be relieved by a safety valve, resulting in the loss of extremely expensive coolant. 
     In the present disclosure, the movable second condenser  60  can be disposed in the cavity  401  to condense the coolant vapor located in the cavity  401 , which effectively increases the heat transfer capacity of the condenser. One of the advantages is that the coolant vapor trapped in the hollow cavity is condensed, so that the evaporation rate and the condensation rate of the coolant  20  in the box body  10  tend to be balanced, the likelihood of a continuous increase of temperature and pressure in the box body  10  caused due to evaporation rate being higher than condensation rate is reduced, the pressure difference inside and outside the box body  10  is reduced, and the leakage loss of extremely expensive coolant vapor is reduced. Another advantage is that the movable second condenser  60  bears part of the condensing capacity of the first condenser  40 , which reduces the condensing area required for the first condenser  40 , thereby reducing the height of the first condenser  40 , reducing the height of the box body  10 , and reducing the volume of the two-phase immersion cooling device  100 . Such advantages make the two-phase immersion cooling device  100  more compact with low cost. 
     Referring to  FIG.  5    and  FIG.  6   , in one embodiment, the first condenser  40  includes a cooling water system  401 , the movable second condenser  60  includes a cooling water system  601 . The cooling water system  401  of the first condenser  40  and the cooling water system  601  of the movable second condenser  60  can be operated independently, in series or in parallel, respectively. 
     The first condenser  40  also includes a water inlet  402  and a water outlet  403  of the cooling water. The movable second condenser  60  also includes a water inlet  602  and a water outlet  603  of the cooling water. The water inlet  402  and the water outlet  403  of the first condenser  40  and the water inlet  602  and the water outlet  603  of the movable second condenser  60  pass through the upper part of the side wall  12  of the box body  10  or the cover body  15 , or pass through a rear door  14 . 
     The two-phase immersion cooling device with movable second condenser  100  further includes a controller  62 , a plurality of temperature sensors  63 , a humidity sensor  69 , a plurality of pressure sensors  64 , a liquid level sensor  65 , a flow sensor  61 , an alarm  66 , a safety valve controller  681 , a pressure balance valve controller  682 , and a coolant management system  67 . 
     The temperature sensors  63 , the humidity sensor  69 , and the pressure sensors  64  are disposed in the accommodating cavity  101  and are respectively used to sense the vapor and liquid temperatures, vapor humidity, and vapor pressures at different positions in the accommodating cavity  101 . The controller  62  is electrically connected to the first condenser  40 , the movable second condenser  60 , the temperature sensor  63 , the humidity sensor  69 , the pressure sensor  64 , the liquid level sensor  65 , the flow sensor  61 , the alarm  66 , the safety valve controller  681 , the pressure balance valve controller  682 , and the coolant management system  67 . The controller  62  can determine the working state of the accommodating cavity  101  according to at least one of the vapor and liquid temperature sensed by the temperature sensor  63 , the humidity sensed by the humidity sensor  69 , the inlet and outlet temperature of the cooling water in the first condenser  40  or the movable second condenser  60  sensed by the temperature sensor  63 , the flow rate of the cooling water in the first condenser  40  or the movable second condenser  60  sensed by the flow sensor  61 , and the vapor pressure sensed by the pressure sensor  64 . When the vapor temperature sensed by the temperature sensor  63  is higher than a preset temperature, the humidity sensed by the humidity sensor  69  is higher than a preset humidity, or the vapor pressure sensed by the pressure sensor  64  is higher than a preset pressure, the controller  62  controls and adjusts the inlet temperature or the flow rate of the cooling water in the first condenser  40  and/or the movable second condenser  60 , to control the condensation capacity of the condenser, so as to achieve the purpose of adjusting and maintaining the balance of operating temperature, pressure, evaporation, and condensation in the box body  10 . 
     The two-phase immersion cooling device with movable second condenser  100  further includes a safety valve  68 . The safety valve  68  is disposed on the box body  10  and is electrically connected to the controller  62  through the safety valve controller  681 . When the vapor pressure in the accommodating cavity  101  is higher than the preset pressure, the controller  62  is also used to control the safety valve  68  to open until the vapor pressure in the accommodating cavity  101  is lower than the preset pressure, so as to control the operation of the box body  10  under a safe pressure. 
     The two-phase immersion cooling device with movable second condenser  100  further includes a pressure balance valve  71 . The pressure balance valve  71  is disposed on the box body  10  and is electrically connected to the controller  62  through the pressure balance valve controller  682 . When the pressure in the accommodating cavity  101  is lower than the atmospheric pressure, in order to facilitate the opening of the cover body  15 , the pressure balance valve  71  can be opened manually or through the controller  62  to make the vapor pressure in the accommodating cavity  101  equal to the atmospheric pressure. 
     The liquid level sensor  65  is disposed on the side wall  12  of the box body  10 , and the liquid level sensor  65  is used to detect the liquid level of the coolant  20 . The liquid level sensor  65  is connected to the accommodating cavity  101  using the communicator principle. The liquid level of the coolant  20  in the accommodating cavity  101  can be known by observing the liquid level of the liquid level sensor  65 . 
     The controller  62  can control whether the alarm  66  is activated according to the liquid level of the coolant  20  detected by the liquid level sensor  65 . When the liquid level detected by the liquid level sensor  65  is lower than a preset height, the controller  62  controls the alarm  66  to give an alarm and controls the coolant management system  67  to replenish the accommodating cavity  101  with coolant  20 . 
     Referring to  FIG.  7   , the coolant management system  67  includes an overflow weir plate  671 , a liquid storage tank  672 , a pump  673 , a pipeline  674 , a valve  675 , and a filter  676 . The liquid storage tank  672  is separated from a coolant tank by the overflow weir plate  671  at the bottom of the accommodating cavity  101 . The pump  673 , the pipeline  674 , the valve  675 , and the filter  676  are disposed inside or outside the box body  10 . When the liquid level of the coolant  20  in the accommodating cavity  101  is lower than the preset height, the controller  62  controls the coolant management system  67  to start the pump  673  and control the valve  675  to open, and the coolant  20  can be pumped from the liquid storage tank  672  to the coolant tank at the bottom of the accommodating cavity  101 , to keep the coolant level constant, and the excessive pumped coolant  20  flows through the upper end of the overflow weir plate  671  into the liquid storage tank  672 . 
     It can be understood that the number of each of the movable second condenser  60 , the temperature sensor  63 , the humidity sensor  69 , the pressure sensor  64 , the liquid level sensor  65 , the alarm  66 , the coolant management system  67 , the safety valve  68 , the pressure balance valve  71 , and the first condenser  40  can be adjusted according to actual needs, and the number can be 1-24, etc. 
     The two-phase immersion cooling device with movable second condenser  100  further includes at least one double-faced socket  70 . The double-faced socket  70  is disposed on the side wall  12 , the cover body  15 , or the rear door  14 . The inner socket of the double-faced socket  70  is exposed to the accommodating cavity  101 , and the outer socket of the double-faced socket  70  is exposed to the outside of the box body  10 . 
     The inner socket of the at least one double-faced socket  70  is electrically connected to the heating element  30 , the temperature sensor  63 , the humidity sensor  69 , the pressure sensor  64 , the liquid level sensor  65 , and the coolant management system  67 . The outer socket of another double-faced socket  70  is electrically connected to the external connecting lines of the heating element  30 , the temperature sensor  63 , the humidity sensor  69 , the pressure sensor  64 , the liquid level sensor  65 , and the coolant management system  67 , so that the heating element  30 , the temperature sensor  63 , the humidity sensor  69 , the pressure sensor  64 , the liquid level sensor  65 , and the coolant management system  67  are electrically connected to the external elements. The double-faced socket  70  is hermetically connected to the box body  10  or the cover body  15  to seal the accommodating cavity  101 . 
     The two-phase immersion cooling device with movable second condenser  100  also includes a handle  80 , and the handle  80  is disposed on the cover body  15  to facilitate opening the cover body  15 . 
     The two-phase immersion cooling device with movable second condenser  100  also includes a power support  81 , the power support  81  is connected to the cover body  15  and is used to drive the cover body  15  to open or close. The cover body  15  can be opened to a maximum angle of 180°. The power support  81  can be opened, supported, and closed electrically or pneumatically. 
     The two-phase immersion cooling device with movable second condenser  100  also includes a power mover  82  (shown in  FIG.  2   ). The power mover  82  is connected to the rear door  14  and is used to move the opening or closing of the rear door  14 . The power mover  82  can be opened, supported, and closed electrically or pneumatically. 
     The two-phase immersion cooling device with movable second condenser  100  further includes a supporting member  90 , the supporting member  90  is disposed on the bottom of the box body  10 , to support the box body  10 . The supporting member  90  may be, but is not limited to, a supporting frame to stabilize the box body  10 , or a roller to facilitate the movement of the box body  10 . 
     The two-phase immersion cooling device with movable second condenser  100  further includes a liquid level window  125 , and the liquid level window  125  is disposed on the box body  10 . The operation state of the heating element  30  and the liquid level height of the coolant  20  can be observed through the liquid level window  125 . 
     The two-phase immersion cooling device with movable second condenser  100  further includes an extracting valve  50 , and the extracting valve  50  is disposed on the box body  10 . 
     Before the heating element  30  starts to operate, a vacuum device is used to extract air or other non-condensable vapor in the accommodating cavity  101  through the extracting valve  50 , the vacuum device places the accommodating cavity  101  in a closed vacuum state before the operation of the heating element  30  or after the installation, removal, repair, and maintenance of the heating elements  30 , so as to ensure the first condenser  40  and the movable second condenser  60  in the accommodating cavity  101  can operate efficiently without non-condensable vapor. In a PID control mode, the pressure or temperature in the accommodating cavity  101  is adjusted to reach a predetermined value by adjusting the flow or inlet temperature of the cooling water in the condenser. 
     In one embodiment, the two-phase immersion cooling device with movable second condenser  100  further includes a rear door  14 , and the rear door  14  is disposed on the box body  10 . The rear door  14  is disposed on one side wall  12 , and the position of the rear door  14  corresponds to the position of the movable second condenser  60 . The side wall  12  of the rear door  14  is not provided with the first condenser  40  when there is a movable second condenser  60  on the rear door  14 . The movable second condenser  60  is fixedly disposed on the rear door  14 , and the movable second condenser  60  is removed from the accommodating cavity  101  with the movement of the rear door  14 . In some embodiments, the rear door  14  is detachably disposed on the box body  10 . The rear door  14  can, but is not limited to, make a detachable connection with the box body  10  by means of flange connection, hook connection, bite joint connection, clamp connection, or screw connection. 
     In some embodiments, the water inlets and the outlets of the first condenser  40  and the movable second condenser  60  can pass through the rear door. In some embodiments, the handle  80  may also be disposed on the rear door. 
     When a user intends to replace, take, assemble, or repair the heating element  30 , the cover body  15  or the rear door  14  can be opened, the movable second condenser  60  is removed from the cavity  401  with the opening of the cover body  15  or the rear door  14 , then the heating element  30  can be taken out of the box body  10  or put into the box body  10  through the cavity  401 . The first condenser  40  and the movable second condenser  60  can also be combined into a third condenser  110 , the third condenser  110  is disposed on the cover body  15  or the rear door  14  and accommodated in the accommodating cavity  101 , and the third condenser  110  may be removed from the cavity  401  together with the opening of the cover body  15  or the rear door  14 . 
     Those skilled in the art can understand that the above embodiments are only examples, in which the features of different embodiments can be combined with each other to obtain implementations that are easily conceivable according to the disclosure of the present disclosure but are not clearly indicated in the drawings. 
     Those skilled in the art should understand that the above description and the embodiments of the present disclosure shown in the drawings are only examples and do not limit the present disclosure. The purpose of the present disclosure has been completely and effectively achieved. The functions and structural principles of the present disclosure have been shown and explained in the embodiments. Without departing from the principles, the implementation of the present disclosure may have any deformation or modification.