Abstract
Disclosed herein is a heat transfer device (2), the heat transfer device comprising a heat exchanger (10) driven by movement of a fluid, a heat transfer cavity (6) and a fan (12) for creating a circulating gas flow between the heat exchanger and the heat transfer cavity. The heat transfer device (2) includes: a housing having an opening (14) for allowing an object to be inserted into the heat transfer cavity (6); an outlet valve (52) for exhausting gas and/or liquid from the heat transfer cavity (6); and a controller arranged to operate the outlet valve (52). The heat transfer device (2) may, for example, take the form of a cooling device for rapidly cooling a drinking vessel such as a beer glass.
Claims
1. A heat transfer device comprising: a heat exchanger driven by movement of a fluid therein, a heat transfer cavity and a fan for creating a circulating gas flow between the heat exchanger and the heat transfer cavity; a housing having an opening for allowing an object to be inserted into the heat transfer cavity; an outlet valve for exhausting gas and/or liquid from the heat transfer cavity; and a controller arranged to operate the outlet valve.
2. A heat transfer device according to claim 1, wherein the heat transfer cavity comprises an outlet flow path arranged to direct liquid towards the outlet valve.
3. A heat transfer device comprising: a heat exchanger, a heat transfer cavity and means for creating a circulating gas flow between the heat exchanger and the heat transfer cavity; a housing having an opening for allowing an object to be inserted into the heat transfer cavity; and an outlet valve for exhausting gas and/or liquid from the heat transfer cavity; wherein the heat transfer cavity comprises an outlet flow path arranged to direct liquid towards the outlet valve.
4. A heat transfer device according to claim 2, wherein the outlet flow path is inclined downwardly in a radial and/or circumferential direction so as to direct liquid towards the outlet valve.
5. A heat transfer device according to claim 2, wherein the outlet flow path provides a helical incline towards the outlet valve.
6. A heat transfer device according to claim 1, wherein the outlet valve comprises an outlet opening that is directed substantially tangential to the direction of the circulating gas flow.
7. A heat transfer device according to claim 6, wherein the outlet opening is substantially positioned at a periphery of the fan.
8. A heat transfer device according to claim 1, wherein the outlet valve comprises an outlet opening having a cross-sectional area of at least about 50 mm.sup.2.
9. A heat transfer device according to claim 1, further comprising a funnel arranged adjacent to the outlet valve to collect liquid.
10. A heat transfer device according to claim 1, wherein the heat transfer device is a cooling device and the heat exchanger is a thermal sink arranged to cool the circulating gas flow.
11. A heat transfer device according to claim 1, wherein the controller is further arranged to control the fan.
12. A heat transfer device according to claim 1, wherein in a (“defrost”) mode of operation the heat exchanger is no longer driven and the controller opens the outlet valve.
13. A heat transfer device according to claim 12, wherein in the (“defrost”) mode of operation the controller operates the fan at an increased speed so as to circulate the gas flow more rapidly.
14. A heat transfer device according to claim 12, further comprising a heater operating in the (“defrost”) mode of operation, and optionally wherein the heat exchanger acts as the heater.
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16. A heat transfer device according to claim 1, wherein the outlet valve is arranged to automatically drain liquid from the heat transfer cavity upon loss of electrical power to the heat exchanger, or the controller operates to open the outlet valve in response to a power cut detection signal.
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18. A heat transfer device according to claim 1, wherein the outlet valve is biased open but held closed by an electromechanical actuator.
19. A heat transfer device according to claim 1, wherein the outlet valve is actively opened upon loss of electrical power.
20. (canceled)
21. A heat transfer device according to claim 1, comprising means for storing electrical power and/or means for generating electrical power so that the outlet valve can be opened in response to a power cut.
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68. A method of drying a heat transfer device comprising a heat transfer cavity that can receive an object, the method comprising: creating a circulating gas flow in the heat transfer cavity; ceasing to cool or heat the circulating gas flow; and opening an outlet valve to exhaust gas and/or liquid from the heat transfer cavity.
69. A method according to claim 68, further comprising: increasing the rate of the circulating gas flow.
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Description
[0069] Some embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying figures, in which:
[0070] FIG. 1a is a cross-sectional view of a cooling device and FIG. 1b is a schematic illustration of the circulating airflow in such a device;
[0071] FIG. 2a is a top view of a sensor arrangement across the opening of such a cooling device and
[0072] FIG. 2b is a side cross-sectional view of the opening;
[0073] FIG. 3a and FIG. 3b show an infrared sensor arrangement to detect when a glass is inserted through the opening;
[0074] FIG. 4 shows a black and white image of passive thermal emission in the far infrared spectrum for a glass inserted through the opening;
[0075] FIG. 5a and FIG. 5b provide a side sectional view and a perspective sectional view of a capacitive sensor arrangement;
[0076] FIG. 6 is a side sectional view of a cooling device including an electrical connection to earth;
[0077] FIG. 7 is a schematic side sectional view of a cooling device including an outlet valve;
[0078] FIG. 8 is a top view of an outlet flow path in the base of the heat transfer cavity of a cooling device;
[0079] FIGS. 9a-9c provide perspective and side sectional views of the outlet valve in the base of a heat transfer cavity;
[0080] FIG. 10 is a side sectional view of a counter-top cooling device;
[0081] FIGS. 11a and 11b provide schematic side views of a counter-top cooling device connected to a refrigerant device by an umbilical cord; and
[0082] FIG. 12 provides a schematic overview of the components in a cooling device connected to a separate refrigerant device.
[0083] There is seen in FIG. 1a an exemplary cooling device 2 that may be used to chill and frost a beer glass 4 inserted into a heat transfer cavity 6 of the device 2. The heat transfer cavity 6 is defined by a double-walled, cylindrical ducting member 8 that is shaped to receive an inverted beer glass 4. The ducting member 8 may be removable and optionally interchangeable, for example to allow for different sizes and shapes of beer glass 4 to be positioned in the heat transfer cavity 6. Surrounding the ducting member 8 is a heat exchanger 10 in the form of a set of coils. In this example, the heat exchanger 10 is a heat sink comprising multiple copper coils that are cooled by a refrigerant fluid pumped there through. A fan 12 is positioned below the ducting member 8 and heat exchanger 10 so as to create a circulating airflow in the heat transfer cavity 6. The schematic inset of FIG. 1b illustrates how air, or any other gas inside heat transfer cavity 6, is circulated by the fan 12. As is described in WO 2011/042698, the ducting member 8 is shaped as a pseudo-negative of the glass 4 to be cooled such that there is a specified gap between the ducting 8 and the glass 4 that promotes turbulence in the airflow. When the fan 12 is operated at high speed, the circulating airflow is highly turbulent and this generates a high heat transfer coefficient so as to achieve rapid cooling. As seen in FIG. 1b, the airflow is drawn out of the heat transfer cavity 6 by the fan 12 at (1), driven across the coils of the heat exchanger 10 at (2) and circulated around the ducting member 8 at (3), with a restricted region between the glass 4 and the ducting member 8 acting to accelerate the airflow and create turbulence for optimal heat transfer with the glass at (4).
[0084] The cooling device 2 includes an outer housing defining an opening 14 that allows the glass 4 or other object to be inserted into the heat transfer cavity 6. The opening 14 may be closed by a flexible membrane 16 or other seal so as to help retain the cold air inside the heat transfer cavity 6. The housing provides a flange 17 extending circumferentially around the opening 14 and extending for a height above the opening. It has been found beneficial to make the flange at least 45 mm high. This helps to trap a static volume of air above the opening 14, which may be cooler than ambient and hence denser. The flange 17 surrounds the protruding base of a glass 4 while it is being frosted.
[0085] Various embodiments of such a cooling device will now be described with reference to the subsequent figures. Although the object inserted into the heat transfer cavity is described as a glass, it will be appreciated that other objects may of course be cooled instead. Furthermore, the heat exchanger may take the form of a thermal sink or thermal source and, in the latter case, the heat transfer cavity may be arranged to warm rather than cool an object inserted therein.
[0086] There is seen in FIGS. 2-5 some non-contact sensor arrangements for detecting when a glass is inserted into the heat transfer cavity of a cooling device. In the example of FIGS. 2a and 2b, an active radiation sensor arrangement is used to detect when a glass 4 is inserted through an opening 14 in the upper part of the heat transfer cavity 6. It may be seen with reference to FIG. 1a that the opening 14 is generally closed by a flexible membrane 16 that can be deformed so as to allow a glass 4 to be pushed through the opening 14 and down into the heat transfer cavity 6. The top view of FIG. 2a shows a flexible membrane 16 that is split into radial flaps providing a flexible seal around the glass 4. The flaps bend against the glass 4 when it is inserted, to provide an intimate seal and encouraging any air that is pulled into the heat transfer cavity 6 to curve down the sides of the glass 4. Once positioned in the heat transfer cavity 6, an upper end of the glass 4 protrudes above the opening 14 so as to enable the user to grip the glass when it is ready to be removed. The protruding base of the glass 4 is detected by a light gate arrangement indicated generally by 18 in FIGS. 2a and 2b. The light gate 18 is defined between an infrared light emitting diode (LED) 20 and a photodiode 22 arranged non-diametrically opposite the LED 20. The LED emitter 20 and photodiode receiver 22 may be filtered so as to be sensitive to the same wavelength range.
[0087] It can be seen from FIGS. 2a and 2b that the emitter/ray receiver pair 20, 22 and light gate 18 therebetween is offset by a distance 24 to one side of the centre of the glass 4, e.g. offset by 10 mm. The emitter/receiver pair 20, 22 is positioned so that the light gate 18 is at the same height as the thickened base of the glass 4. Lenses 26 that are clear to infrared light can be used to hide the emitter 20 and receiver 22 and protect them from frost growth. For each sensor reading, a controller turns the LED emitter 20 on and off 50 times and converts a detection signal from the receiver 22 at each step by a 10-bit ADC to eliminate ambient infrared from the reading. The on and off values are summed separately, and the off total is subtracted from the on total. It has been found that such an infrared sensor arrangement works best with a narrow beam LED with a half angle of 20° or less. For example, the emitter 20 may be an 8° half angle LED, for which typical sensor reading values are 3,000-4,000 without a glass present and 200-300 with a glass present, giving at least a 10:1 ratio, which allows a simple threshold for the detection signal to determine whether a glass 4 is present or not.
[0088] Another non-contact sensor arrangement is seen in FIGS. 3 and 4. This arrangement uses passive thermal emission in the far infrared spectrum to detect an ambient temperature glass 4 that is inserted through an aperture defined by the flexible membrane 16. As seen in FIGS. 3a and 3b, a far-infrared (FIR) thermopile sensor 28 is positioned to point down at an angle through the opening to the cold heat transfer cavity inside the device. The field of view 30 of the sensor 28 includes the less cold aperture seal 16 as well as the aperture itself. When a glass 4 is inserted (FIG. 3b), much of the field of view 30 is filled by the base of the glass 4, which is at ambient temperature. The thermal emission image shown in FIG. 4 shows that the ambient temperature glass 4 is clearly visible against the cold aperture and aperture seal 16. While typical temperatures sensed for the aperture may be −15° to −35°, the ambient temperature glass 4 gives about 40° C. swing in reading.
[0089] Another non-contact sensor arrangement is seen in FIGS. 5a and 5b. In this example the presence of a glass 4 in the heat transfer cavity 6 is detected by measuring changes in capacitance. Glass in particular provides for good detectability in air because it has a relative permittivity of between around 4 and 10. In this capacitive sensor arrangement, electrodes 32, 34 are arranged in the heat transfer cavity 6 on either side of the ducting member 8, so that an inner electrode 32 is positioned inside the inserted glass 4 and an outer electrode 34 is positioned outside the glass 4. To eliminate sensitivity to local ice build-up and improve glass protection capability, concentric annular (e.g. cylindrical/frustoconical) electrodes 32, 34 are used to increase surface area. Such an arrangement is less proximity-dependent so that the build-up of a thin ice or frost layer on the surfaces of the glass 4 does not affect sensor readings. It has been found that good glass detection sensitivity can be achieved with an electrode separation of several centimetres, even with two layers of plastic ducting member 8 in series. The electrodes 32, 34 may be provided as annular plates, or may take the form of conductive coatings applied to the plastic ducting member 8 or other suitable surfaces inside the housing of the device 2. Conductive paint (such as that used for EMC shielding), printed conductive tracks and chromed finishes are all appropriate methods of achieving sufficiently effective electrodes 32, 34. If the ducting member 8 carried the electrodes 32, 34 and it is removable, then a separable electrical connection may be required. As is seen most clearly from FIG. 5b, the ducting member 8 may be removably positioned over an inner moulding 36 that carries the capacitive sensing electrodes 32, 34. The inner moulding 36 may be permanently positioned inside the device housing. The inner moulding 36 includes an inner tube 38 that runs up the inside of the ducting member 8 to prevent fingers from reaching the fan (not shown) when the ducting member 8 is removed. The inner tube 38 is an ideal part to apply a coating for the inner electrode 32 so that it penetrates deep inside the glass 4 without any need for an electrical connection to the ducting member 8. The outer electrode 34 may be fitted inside the moulding 36, or alternatively a coating can be applied to an inner surface of the cylindrical moulding 36.
[0090] FIG. 6 provides a side sectional view similar to that seen in FIG. 1a, except that details of the fan 12 are visible. It can be seen that the electric fan 12 comprises a rotating arrangement of vanes or blades mounted on a hub 40. The hub 40 is driven by a rotating drive shaft 42 with bearings 44 arranged therebetween. The shaft 42 extends from a fan base 46 that has an electrical connection to ground 48. An impedance 50 may optionally be added to the grounding line so as to prevent any EMC emissions if electrical noise is present, by reducing the ability of the hub 40 to act as an antenna. It has been found that there may be sufficient electrical conduction through the bearings 44 that connect the fan base 46 to the hub 40, but other connection methods are also possible. Earthing of the fan hub 40 means that a metallic hub can be used instead of a plastic hub. It has been found that when ice crystals are ingested into the fan 12 it can cause a malfunction. This is often only momentary, but occasionally terminal for the fan motor and its control board. The cause of this malfunction is believed to be electrostatic charge separation seemingly caused by the high velocity (e.g. 30-50 mph) impact of ice crystals onto the fan hub 40, as generally indicated by the arrows in FIG. 6. It seems that sufficient charge may build up on the hub 40 to cause an electrical arc to the fan motor or drive electronics below, affecting operation of the fan controller.
[0091] Any of the non-contact sensor arrangements described above may be used, alone or in combination, to detect when an object such as a glass is inserted into the heat transfer cavity of a cooling device. A controller connected to the fan may then adjust the rate of circulating airflow in response to a detection signal from the sensor arrangement. Insertion of a glass or other object may trigger a rapid cooling mode in which the fan speed is increased. Readings from the sensor arrangement may also be used by the controller to decide when to switch the cooling device between peak and off-peak modes of operation, for example when it is determined that the cooling device has not been used for a certain period of time.
[0092] In addition to the modes of operation mentioned above, the cooling device may be operated in a defrost mode where the heat exchanger 10 is turned off and the heat transfer cavity 6 is allowed to defrost. As in seen in the schematic of FIG. 7, the heat transfer cavity 6 may be provided with an outlet valve 52 that enables fluid to leave the heat transfer cavity 6, for example to drain water produced during defrost. During a defrost mode of operation, the flow of refrigerant through the heat exchanger 10 may be stopped so that the coils begin to warm up under the thermal load. The fan 12 may be turned on to full power so as to circulate the air as it warms up and assist in drying out the heat transfer cavity 6. When the defrost mode is activated, the outlet valve 52 may be opened so that air is pulled through the heat exchange cavity 6 and liquid can drain out. As indicated by arrow 54, ambient air may be drawn in through the upper opening 14 and the circulating air movement helps to exchange heat and moisture with the outside world through the venting flow 55 provided by the outlet valve 52. The high air speed created by the fan 12 can act to quickly clear droplets of water created from condensation and melted frost. In addition, the increase in power dissipated by the fan 12 can help to warm up the inside of the cooling device 2, helping to melt and evaporate frost and increasing the capacity of the airflow to carry water vapour. The fan 12 may include potted or coated electronics so as to be unaffected by moisture ingress.
[0093] The flow path to the outlet vent 52 and its position will now be described in more detail with reference to FIGS. 8 and 9. As seen from the top view of FIG. 8, the heat transfer cavity includes an exit 56 to the outlet valve 52 is at a point near the periphery of the fan 12. The flow path indicated by the arrows 60 is arranged to run towards the exit 56 tangential to the direction of rotation 58 of the fan 12. This point in the air circuit is at relatively high pressure, whereas the opening 14 is at relatively low pressure, and so ambient air is drawn in through the top of the heat transfer cavity 6 and ejected through the outlet vent 52. The position of the exit 56, outside the fan 12 and angled tangentially, not only benefits the air pressure recovery—encouraging good flow—but also allows spray that is flung tangentially from the fan 12 to be collected effectively. Furthermore, the floor of the heat transfer cavity 6 around the fan 12 may slope downwards towards the exit 56 in the general direction of air flow, allowing water collected in the bottom of the cavity 6 to drain out through the vent 52. The arrows 60 in FIG. 8 indicate how the floor of the heat transfer cavity 6 slopes continually downwards towards the exit 56. Furthermore, the arrows 62 and 64 indicate how the floor of the heat transfer cavity 6 may be inclined in a radial direction, on both sides, so that liquid runs down onto the outlet flow path 60, which is then sloped downwardly in a circumferential direction towards the exit 56. In other words, the base of the heat transfer cavity 6 may be designed to provide a helical flow path that collects and drains liquid towards the exit 56.
[0094] The outlet valve 52 is seen in more detail in FIGS. 9a-9c. The outlet valve 52 comprises an outlet opening 66 leading out horizontally from the exit 56. A movable cover 68 is operated by a servo motor 70. The opening 66 is positioned above a funnel 72 designed to catch droplets of liquid as they drip out of the opening 66, which is provided with a pointed protrusion 74 that encourages any droplets remaining attached to collect directly into the funnel 72. The funnel 72 narrows to an exit tube 76 which is designed not to restrict airflow out of the valve 52 by having internal dimensions of 12.5 mm by 9 mm (95.1 mm.sup.2). The tube 76 passes through the bottom of the housing of the cooling device 2 so as to direct liquid into an external drip tray 78. As is seen in the cross-sectional view of FIG. 9b, the exit tube 76 has a pointed end 80 to clear drips more effectively. Melt water collected in the drip tray 78 can be left to evaporate or may be emptied out. The drip tray 78 may be removable for this purpose. It has been found that the exit opening 66 should ideally provide an unrestricted airflow path to promote circulation and dry out the heat transfer cavity quickly. For acceptable defrosting times, e.g. about 20 minutes (depending on ambient conditions), the exit 56 and flow path to the opening 66 may be made larger than 50 mm.sup.2 in cross-section along its length. The entire exit path may be more than 300 mm.sup.2 to provide for effective drying in a relatively short time period. The opening 66 may be a tube having an internal diameter of about 18.5 mm. From the cross-sectional view of FIG. 9c it can be seen how the opening 66 is at the end of a tube that extends generally horizontally through the housing from a periphery of the fan 12. Furthermore, comparing the left and right sides in FIG. 9c, it can be seen that the base 7 of the heat transfer cavity starts higher on the left side and then spirals downwardly, around the outside of the fan 12, to reach a low point at the exit 56 to the outlet opening 66.
[0095] The servo motor 7 operates to open the outlet valve 52 whenever the cooling device 2 enters a defrost mode. In addition, the device 2 may be designed to automatically enter a defrost mode in the event of a power cut. It is important that the glass froster i.e. cooling device 2 is able to drain if affected by a power cut, to avoid an unhygienic pool of water being trapped in the bottom of the device as it warms up. While it is not possible to operate the fan 12 to assist in defrosting without power, sufficient energy can be stored to open the outlet vent 52 just as the power is cut off, at least enabling the unit to drain. The controller may include an extra capacitance to store energy powering the logic and servo motor 70, as well as means of detecting a drop in the supply voltage. In an alternative system, the motor of the fan 12 may be turned into a generator by electric braking, thereby converting the remaining kinetic energy of the spinning fan into power to operate the motor 70 and open the vent 52. In some examples, the servo motor 70 may be replaced by a solenoid actuator with the cover 68 being sprung open but held closed by an electromagnet, such that when necessary, or when the power supply is cut, the electromagnet releases the spring and the cover 68 is opened.
[0096] FIG. 10 shows the cooling device 2 in the form of a countertop or bar top unit including an on-board controller 82 and a clamp 84 to mount the unit to a counter surface. An umbilical cord 86 is used to transfer refrigerant fluid and power to the cooling device 2. FIGS. 11a and 11b illustrate how the umbilical cord 86 may be connected to a separate refrigerant device 88 at 45 degrees, such that it can be bent either to lead vertically upwards or horizontally. A reversible cover plate 90 can then be attached in one of two orientations, depending on the direction of umbilical cord 86 that is required to fit different countertop arrangements.
[0097] Finally, it is seen with reference to FIG. 12 how the umbilical cord 86 may transfer coolant fluid e.g. refrigerant between the refrigerant device 88 and the bar top cooling device 2, as well as relaying control signals 92 and providing an electrical power supply 94. The cooler device 2 includes heat exchanger coils 10, fan 12, defrost valve 56, controller (e.g. PCB) 82, temperature sensor 96, glass detection sensor 98, display 100 and control interface 102. The refrigerant device 88 includes a mains power cable 104, a DC power supply 106 for the cooling device 2, a fridge control relay 108 and a condensing unit 110. Signals from the controller 82 in the cooling device 2 may be transmitted to the fridge control relay 108 so as to determine when the apparatus is operating in peak or off-peak mode. Any suitable coolant fluid may be used, for example a refrigerant such as R404A.
[0098] In peak mode, the condensing unit 110 may be constantly running and the sensor 96 used to monitor the temperature inside the cooling device 2 so as to maintain the heat transfer cavity in a desired temperature range e.g. −35° C. to −45° C. In off-peak mode, the heat transfer cavity may be maintained at a higher temperature by turning off the condensing unit 110 for some of the time, e.g. maintaining the cooling device in the temperature range of −25° C. to −35° C. Periodically turning off the condensing unit 110 results in a lower average heat transfer rate in the off-peak mode. The compressor in a typical condensing unit 110 cannot be turned back on for one minute (or more) after being turned off due to the back pressure, meaning there could be a significant rise in internal temperature of the cooling device 2. This would affect peak throughput, as the extra load of cooling glasses would worsen the rise while the compressor needs to stay off. In the off-peak mode, however, by not needing to frost a glass as quickly, such a temperature rise would be acceptable, so cycling the fridge compressor on and off is an effective way of lowering the power consumption significantly.
[0099] The higher internal temperature in the off-peak mode may be compensated by an increase in the time spent frosting a glass, which would be less significant to performance during off-peak times of use. The controllers 82, 108 may respond to glass detection signals from the sensor 98 to provide a faster cool down reaction to increased loads, e.g. frosting of multiple glasses in a series. This may be in addition to the controller 82 increasing the speed of the fan 12 when the glass sensor 98 provides a detection signal that causes the cooling device 2 to switch into rapid cooling mode. The system may include a time delay before switching into off-peak mode, to avoid cycling the condensing unit 110 (especially the compressor) too often, to prevent damage or excessive wear. If the condensing unit 110 was turned off more than e.g. two minutes ago, then inserting a glass may make it turn back on automatically. When responding to an inserted glass in off-peak mode, the rate at which the internal thermal mass warms will increase under the load of frosting a glass, but there will be a delay before this is detected by temperature measurement. Therefore turning on the condensing unit 110 when the glass is inserted can improve performance.
[0100] The fridge condensing unit 110 in the refrigerant device 88 may include, as is conventional, a compressor to pressurise the coolant fluid e.g. refrigerant returning from the cooling device 2, a condenser to remove heat from the fluid, and an expansion device to rapidly cool the fluid before it is supplied back to the cooling device 2. However, there is envisaged an embodiment in which the expansion valve is instead provided within the cooling device 2, so that warmer refrigerant is transferred from the refrigerant device 88 to the cooling device 2 via the umbilical cord 86. The umbilical cord 86 may then allow for energy regeneration, hot refrigerant flowing out transferring heat to the cold refrigerant returning. Additionally, the higher average temperature in the umbilical cord 86 may mean reduced heat gain through its insulation or even a reduced thickness of insulation required. The umbilical cord 86 may be a flexible tube containing cables to transfer power and control, and hoses to transfer refrigerant fluid between the refrigerant device 88 and the bar top glass froster 2. The umbilical cord 86 may have a quick disconnect on the hoses, as well as a separable electrical connector. This may make installation considerably easier, as the two parts of the system can be installed separately. To ensure correct connection, these connectors may be designed poka-yoke by having one female and one male connector on the umbilical and one of each to match on the refrigerant device 88, such that they cannot be connected the wrong way round.
