Evaporative cooling solution for handheld electronic devices

An apparatus and method of the disclosure provides a cooling mechanism for a handheld electronic device. The cooling mechanism includes a heat sink and an evaporative cooling mechanism. The evaporative cooling mechanism includes liquid retaining structures. The liquid retaining structures are located in proximity to the at least one IC of the handheld electronic device. Each liquid retaining structure is coated with a temperature sensitive polymer that act as hydrophilic when the temperature of the surface of the handheld electronic device is below a threshold temperature. To maintain the temperature of the surface of the handheld electronic device below the threshold temperature, the temperature sensitive polymer act as hydrophobic and evaporates the liquid stored in the liquid retaining structures to the atmosphere surrounding the handheld electronic device when the temperature of the surface of the electronic device is above the threshold temperature.

FIELD

The present disclosure relates generally to thermal management of devices, and more particularly, to an evaporative cooling solution for electronic devices such as handheld electronic devices.

BACKGROUND

The external temperature of a handheld electronic device, for example, a smart phone, a smart watch, a virtual reality device, a tablet, etc., may be skin temperature limited for a user's comfort level and safety. In a handheld electronic device, the heat generated by the electronic chips located inside the handheld electronic device is distributed across the handheld electronic device's surface to reduce hot spots at the surface of the handheld electronic device. Natural convection is used to dissipate the heat generated in the handheld electronic device to the ambient environment. However, in some cases, natural convection may not provide sufficient heat dissipation to maintain the surface temperature of the handheld electronic device at or below skin temperature without impacting the performance of the handheld electronic device, e.g., due to reducing clock rate to reduce heat generation in the handheld electronic device. Therefore, there is a need for a cooling mechanism for a handheld electronic device which may be used in conjunction with natural convection to provide additional cooling capacity during an extended high power operation of the handheld electronic device that may maintain the handheld electronic device's surface temperature at or below skin temperature for a longer period of time before device performance is reduced. In particular, there is a need for a cooling technique that may increase the power envelope of a handheld electronic device by providing increased cooling capability for thermal mitigation for extended high power operation.

SUMMARY

In a handheld electronic device, the heat generated by the electronic chips located inside the handheld electronic device is distributed across the handheld electronic device's surface to reduce hot spots at the surface of the handheld electronic device. Natural convection is used to dissipate the heat generated in the handheld electronic device to the ambient environment. However, in some cases, natural convection may not provide sufficient heat dissipation to maintain the surface temperature of the handheld electronic device at or below skin temperature without impacting the performance of the handheld electronic device. In an aspect, an evaporative cooling mechanism for the handheld electronic device which may be used in conjunction with natural convection is provided. The evaporative cooling mechanism is used to provide additional cooling capacity during an extended high power operation of the handheld electronic device that may maintain the handheld electronic device's surface temperature at or below skin temperature for a longer period of time before device performance is reduced.

In an aspect of the disclosure, an electronic device, e.g., a handheld electronic device, is provided. The electronic device includes at least one integrated circuit (IC). The at least one IC is located between a first surface and a second surface and between a first side and a second side of the electronic device. The electronic device also includes a cooling mechanism. The cooling mechanism includes a heat sink. The heat sink extends in a first direction between the first side and the second side of the electronic device. A first side of the heat sink is adjacent to the second surface of the electronic device and a second side of the heat sink is in proximity to the at least one IC. The heat sink distributes heat generated from the at least one IC across the second surface of the electronic device to maintain temperature of the first surface and the second surface of the electronic device below a threshold temperature. The cooling mechanism also includes an evaporative cooling mechanism. The evaporative cooling mechanism includes a plurality of liquid retaining structures. The plurality of liquid retaining structures extend in parallel to each other in a second direction. The second direction is perpendicular to the first direction. The plurality of liquid retaining structures are located in proximity to the at least one IC on the second surface of the electronic device. Each liquid retaining structure of the plurality of liquid retaining structures is coated with a temperature sensitive polymer. In an aspect, the temperature sensitive polymer is hydrophilic and absorbs liquid from atmosphere surrounding the electronic device to store the absorbed liquid in the plurality of liquid retaining structures when the temperature of the second surface is below the threshold temperature. In another aspect, the temperature sensitive polymer is hydrophobic and repels the liquid stored in the plurality of liquid retaining structures when the temperature of the second surface exceeds the threshold temperature. In an aspect, to maintain the temperature of the first surface and the second surface of the electronic device below the threshold temperature, the evaporative cooling mechanism evaporates the liquid stored in the plurality of liquid retaining structures to the atmosphere surrounding the electronic device, when the temperature of the second surface exceeds the threshold temperature.

DETAILED DESCRIPTION

FIG. 1illustrates a handheld electronic device100. The handheld electronic device100may be a smart phone, a smart watch, a virtual reality device, a tablet, etc. The handheld electronic device100may include a first surface114(e.g., a front surface) and a second surface112(e.g., a back surface). A liquid crystal display (LCD)118may be embedded in the first surface114of the handheld electronic device100. The second surface112of the handheld electronic device100may be covered with a cover120made of plastic, glass, metal, or the like. The handheld electronic device100may also include a printed circuit board (PCB)116extending in a first direction and may be located between the LCD118and the second surface112and between a first side122and a second side124of the handheld electronic device100. A first side of the PCB116may be adjacent to the LCD118. The handheld electronic device100may also include one or more ICs or chips. For example, a first electronic chip102and a second electronic chip104may be embedded on a second side of the PCB116. The first electronic chip102and the second electronic chip104may be enclosed within an enclosure106located on the second side of the PCB116. The handheld electronic device100may further include a battery108extending in the first direction and may be located between the LCD118and the second surface112, and between the PCB116and the second side124of the handheld electronic device100. A first side of the battery108may be adjacent to the LCD118. The handheld electronic device100may additionally include a heat sink110(e.g., graphite sheets, thermal interface material, etc.) extending in the first direction between the first side122and the second side124of the handheld electronic device100. A first side of the heat sink110may be adjacent to the second surface112and a second side of the heat sink110may be adjacent to the enclosure106and a second side of the battery108.

The first electronic chip102and the second electronic chip104may generate heat during operation. The heat generated from the first electronic chip102and the second electronic chip104located inside the handheld electronic device100may be distributed across the handheld electronic device's100surface (114,112) to reduce hot spots at the surface114of the LCD118and/or the cover120of the handheld electronic device100. For example, the heat sink110may spread the heat generated from the first electronic chip102and the second electronic chip104across the second surface112of the handheld electronic device100to reduce hot spots at the surface114of the LCD118and/or the cover120of the handheld electronic device100. Natural convection may be used to dissipate the heat generated inside the handheld electronic device100into the ambient environment surrounding the handheld electronic device100. Natural convection may depend on the ambient temperature. The cooling capacity of natural convection may be represented as follows:

Natural convection to air=f(Tamb, hconvection), where Tambis the ambient temperature and hconvectionis the convection coefficient.

However, during an extended high power operation of the handheld electronic device100(for example, during a video conference call, when capturing a video clip using a camera module of the handheld electronic device100, etc.), the natural convection cooling mechanism may not maintain the desired surface temperature of the LCD118and/or the cover120of the handheld electronic device100at or below skin temperature without reducing the performance of the handheld electronic device100(e.g., by reducing the clock rate to reduce power dissipation/heat generation by various components in the handheld electronic device100). Therefore, there is a need for a cooling mechanism for handheld electronic devices100which may be used in conjunction with the natural convection cooling mechanism to provide additional cooling capacity for a handheld electronic device100to maintain the surface temperature of the LCD118and/or the cover120of the handheld electronic device100at skin temperature during an extended higher power operation. In particular, there is a need for a cooling technique that may improve the cooling capability of a handheld electronic device100by increasing the power envelope of the handheld electronic device100and thermal mitigation during extended high power operation, e.g., an additional 5 to 10 minutes of higher power operation. The additional operating time at higher power may allow a video conference to be completed or a video clip to be captured with reducing device performance, e.g., reducing video frame rate or video resolution.

FIG. 2Ais a diagram illustrating a plan view of a handheld electronic device200with an evaporative cooling mechanism226, according to an aspect.FIG. 2Bis a diagram illustrating a plan view of a configuration with two consecutive parallel channels of the evaporative cooling mechanism226, according to an aspect.FIG. 2Cis an example diagram illustrating a plan view of another configuration of two consecutive parallel channels of the evaporative cooling mechanism226, according to another aspect.

The handheld electronic device200may be the handheld electronic device discussed with respect toFIG. 1. The handheld electronic device200may be a smart phone, a smart watch, a virtual reality device, a tablet, etc. The handheld electronic device200may include a first surface214(e.g., a front surface) and a second surface212(e.g., a back surface). A LCD218may be embedded in the first surface214of the handheld electronic device200. The second surface212of the handheld electronic device200may be covered with a cover220made of plastic, glass, metal, or the like. The handheld electronic device200may also include a PCB216extending in a first direction which may be located between the LCD218and the second surface212and between a first side222and a second side224of the handheld electronic device200. A first side of the PCB216may be adjacent to the LCD218. The handheld electronic device200may also include one or more ICs or chips. For example, a first electronic chip202and a second electronic chip204may be embedded on a second side of the PCB216. The first electronic chip202and the second electronic chip204may be enclosed within an enclosure206located on the second side of the PCB216. The handheld electronic device200may further include a battery208extending in the first direction and may be located between the LCD218and the second surface212, and located between the PCB216and the second side224of the handheld electronic device200. A first side of the battery208may be adjacent to the LCD218. The handheld electronic device200may additionally include a heat sink210(e.g., graphite sheets) extending in the first direction between the first side222and the second side224of the handheld electronic device200. A first side of the heat sink210may be adjacent to the second surface212and a second side of the heat sink210may be adjacent to the enclosure206and a second side of the battery208.

The handheld electronic device200may further include an evaporative cooling mechanism226incorporated into the second surface212of the handheld electronic device200. However, in some embodiments, the evaporative cooling mechanism226may be incorporated into the cover220of the handheld electronic device200. The evaporative cooling mechanism226may include one or more micro-channels236extending in parallel to each other in a second direction, where the second direction is perpendicular to the first direction. In one embodiment, the one or more micro-channels236may cover the entire cover220of the handheld electronic device200. In an aspect, as depicted inFIG. 2B, each micro-channel236of the one or more micro-channels may include a bottom surface232and two side surfaces (228,230). The two side surfaces (228,230) may be separated from each other via the bottom surface232. The dimensions of each micro-channel236may be from a few microns to hundreds of microns (e.g., the depth/width of each micro-channel236may be in the range of 20 to 250 microns). The dimensions of each micro-channel236may be smaller or larger in other aspects depending on cooling capacity needed. In one embodiment, the length of each micro-channel236may be approximately equal to the width of the handheld electronic device200. In one embodiment, the cooling capacity provided by the evaporative cooling mechanism226may depend on an amount of water stored in each micro-channel236of the one or more micro-channels, which may depend on the length and depth of the each micro-channel236of the one or more micro-channels. For example, the depth of each micro-channel236may be 100-250 microns. The length of each micro-channel236may be smaller or equal to the length or the width of the second surface212(e.g., a back surface) of the handheld electronic device200. The length and depth of each micro-channel236may be small or larger in other embodiments depending on the desired amount of cooling capacity needed.

The bottom surface232of each micro-channel236may be coated with a temperature sensitive polymer having a surface property that changes based on temperature, switching between hydrophobic and hydrophilic (e.g., Poly(N-isopropylacrylamide) (PNIPAAm)). In an aspect, 50% to 75% of each of two side surfaces (228,230) of each micro-channel236may be coated with the temperature sensitive polymer. The polymer may not extend all the way up the sides of each micro-channel236to prevent the second surface212or cover220of the handheld electronic device200from feeling wet when touched by a user of the handheld electronic device200. In some aspects, the one or more micro-channels236on the cover220of the handheld electronic device200may be replaced with a plurality of cylinders where the bottom surface of each cylinder and half of the side surface of each cylinder are coated with the temperature sensitive polymer to implement the evaporative cooling and to prevent a user of the handheld electronic device200from feeling wet when touching the second surface212or cover220of the handheld electronic device200. In some aspects, as shown inFIG. 2C, one or more fins234coated with the temperature sensitive polymer may be attached to the bottom surface232of each micro-channel236to increase the surface area of the temperature sensitive polymer coating exposed to the surrounding environment. The additional temperature sensitive polymer surface area may increase the water absorption and evaporation by each micro-channel236. In one embodiment, the height of each fin234of the one or more fins is approximately equal to the height of the temperature sensitive polymer coating in the side surfaces228,230of each micro-channel236.

In one embodiment, the temperature sensitive polymer may be a simple sponge like cotton fabric which may collect and release water from the surrounding environment based on temperature variations of the handheld electronic device's200second surface212. (e.g., a combination of cotton and Poly(N-isopropylacrylamide) (PNIPAAm)). In an aspect, the temperature sensitive polymer changes from hydrophilic below skin temperature to hydrophobic at or above skin temperature. Therefore, water may be absorbed from the surrounding environment and released (evaporates) into the surrounding environment depending on the temperature of the temperature sensitive polymer. For example, the temperature sensitive polymer may be hydrophilic when the temperature of the handheld electronic device200is below a threshold and may absorb water from surrounding environment (e.g., the atmosphere) of the handheld electronic device200. The water may be stored in each micro-channel236coated with the temperature sensitive polymer by attaching to the surface of the temperature sensitive polymer. However, when the temperature of the handheld electronic device200is above the threshold, the temperature sensitive polymer may become hydrophobic and repel the absorbed water stored in each micro-channel236. When the water is repelled by the temperature sensitive polymer, the water in each micro-channel236may evaporate to the atmosphere surrounding the handheld electronic device200, thus cooling the handheld electronic device200. The threshold temperature at which the surface property of the temperature sensitive polymer changes between hydrophilic and hydrophobic may be about 35 degree centigrade or skin temperature.

In an aspect, the first electronic chip202and the second electronic chip204of the handheld electronic device200may generate heat during operation. The heat generated from the first electronic chip202and the second electronic chip204located inside the handheld electronic device200may be distributed across the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200to reduce hot spots at the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200. The heat sink210may be used to spread the heat generated from the first electronic chip202and the second electronic chip204across the second surface212of the handheld electronic device200to further reduce hot spots at the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200. Natural convection may be used to dissipate heat generated inside the handheld electronic device200into the ambient environment surrounding the handheld electronic device200. The amount of cooling provided by natural convection may depend on the ambient temperature. In some embodiments, when the temperature of the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200reaches the skin temperature, the performance of the first electronic chip202and/or the second electronic chip204of the handheld electronic device200may be reduced to reduce power consumption/heat generation to maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below skin temperature. In some cases, during an extended high power operation of the handheld electronic device200, the natural convection cooling mechanism may not be enough to maintain the desired surface temperature of the LCD218and/or the cover220and to maintain the performance of the handheld electronic device200.

In an aspect, during the extended high power operation of the handheld electronic device200(for example, during a video conference call or a capture of a video segment lasting 5 to 10 minutes, etc.), when the temperature of the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200reaches the skin temperature, the evaporative cooling mechanism226may maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below the skin temperature by evaporating water stored in each micro-channel236of the one or more micro-channels incorporated into the second surface212of the handheld electronic device200. For example, the temperature sensitive polymer covering the bottom surface232and the side surfaces228and230of each micro-channel236of the one or more micro-channels may be hydrophobic when the temperature of the handheld electronic device200is above the skin temperature and may repel the absorbed water stored in each micro-channel236of the one or more micro-channels. When the water is repelled by the bottom surface232and the side surfaces228and230of each micro-channel236of the one or more micro-channels coated with the temperature sensitive polymer, the water in each micro-channel236may evaporate into the atmosphere surrounding the handheld electronic device200, thus in turn cool the handheld electronic device200. As such, the performance of the handheld electronic device200may not be reduced during high power operation while there is water evaporation. Once the water in each micro-channel236of the one or more micro-channels is evaporated, the performance of the handheld electronic device200may be reduced to maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below skin temperature. Thus, by using the evaporative cooling mechanism226, the handheld electronic device200may be operated at a higher power for a longer period of time.

FIG. 3is a diagram illustrating a graphical representation of the relationship between the depth of each micro-channel236or water thickness in each micro-channel236incorporated into the second surface212or the cover220of the handheld electronic device200and the cooling capacity in Watts from the handheld electronic device200. As discussed supra, the cooling capacity of the evaporative cooling mechanism226may depend on the amount of water stored in each micro-channel236of the one or more micro channels, which may depend on the length and depth of each micro-channel236. The cooling capacity of the evaporative cooling mechanism226may also depend on the water evaporation rate, which may depend on the ambient temperature, the humidity of the air surrounding the handheld electronic device200, the ambient air pressure, elevation, etc. For example, as shown inFIG. 3, in one embodiment, for a 20 micron thickness of water in the one or more micro-channels (236), 1 W extra cooling may be achieved for 5 min using the evaporative cooling mechanism226. In another configuration, for a 40 micron thickness of water in the one or more micro-channels (236), 1 W extra cooling may be achieved for 10 min using the evaporative cooling mechanism226. In some configurations, for a 20 micron thickness of water in the one or more micro-channels (236), 2.5 W extra cooling may be achieved for 2 min using the evaporative cooling mechanism226. In some configurations, if the depth of each micro-channel236of the one or more micro channels is 30 micron and the width of each micro-channel236of the one or more micro channels is 60 micron, each micro-channel236may provide 1 W of additional cooling at 25° C. for 5 minutes with the evaporation rate of 0.3 Kg/hr/m2.

FIG. 4is a diagram illustrating a graphical representation of an increase in cooling capacity of the handheld electronic device200utilizing the evaporative cooling mechanism226that may be provided according to an aspect. InFIG. 4, the solid line shows the temperature increase with time at the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200. As shown inFIG. 4, at t1, when the temperature of the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200reaches the skin temperature, the performance of the first electronic chip202and the second electronic chip204of the handheld electronic device200may be reduced to reduce power and maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below skin temperature when cooling is provided by natural convention. However, with the evaporative cooling mechanism226in conjunction with the natural air convection, the performance of the handheld electronic device200may not be reduced during the additional cooling capacity provided by water evaporation. During the extended high power operation of the handheld electronic device200(for example, during a SKYPE call last 5 to 10 minutes, viewing a YOUTUBE video, etc.), at t1when the temperature of the surface (e.g., the first surface214) of the LCD218and/or the cover220of the handheld electronic device200reaches the skin temperature, the evaporative cooling mechanism226may maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below the skin temperature by evaporating the water stored in the plurality of micro-channels236incorporated into the second surface212or cover220of the handheld electronic device200. The performance of the handheld electronic device200may not be reduced between t1and t2, while additional cooling capacity is provided by water evaporation. Once the water in each micro-channel236of the one or more micro-channels is evaporated, at t2, the performance of the handheld electronic device200may be reduced to maintain the surface temperature of the LCD218and/or the cover220of the handheld electronic device200at or below skin temperature. Thus, by using the evaporative cooling mechanism226, the handheld electronic device200may be operated at high power for a longer period (up to t2, which is greater than t1) of time. For example, in one configuration, as shown inFIG. 3, for a 20 micron thickness of water in the micro-channels (e.g.,236), 1 W extra cooling may be achieved for 5 min using the evaporative cooling mechanism226. In another configuration, for a 40 micron thickness of water in the micro-channels (e.g.,236), 1 W extra cooling may be achieved for 10 min using the evaporative cooling mechanism226. In some configurations, for a 20 micron thickness of water in the micro-channels (e.g.,236), 2.5 W extra cooling may be achieved for 2 min using the evaporative cooling mechanism226.

FIG. 5is a flowchart500of a method of cooling a handheld electronic device. The handheld electronic device may be the handheld electronic device (100,200) ofFIGS. 1 and 2A. In one configuration, the flowchart500described inFIG. 5may be the method of cooling a handheld electronic device (100,200) described above with respect toFIGS. 1-2C.

At502, heat generated from at least one IC (102,202,104,204) of a handheld electronic device (100,200) is distributed by a heat sink (110,210). For example, as discussed with respect toFIGS. 1-2A, the heat sink (110,210) may distribute the heat generated from the first electronic chip (102,202) and the second electronic chip (104,204) located inside the handheld electronic device (100,200), across the surface (e.g., the first surface114/214) of the LCD (118,218) and/or the cover (120,220) of the handheld electronic device (100,200) to reduce hot spots at the surface (e.g., the first surface114/214) of the LCD (118,218) and/or the cover (120,220) of the handheld electronic device (100,200).

At504, liquid is evaporated to the atmosphere surrounding the handheld electronic device (100,200), when the temperature of the second surface (112,212) of the handheld electronic device (100,200) exceeds the threshold temperature. For example, as discussed with respect toFIGS. 2A-2C, when the temperature of the second surface (112,212) of the handheld electronic device200reaches the skin temperature, the evaporative cooling mechanism226evaporates the water stored in the one or more micro-channels236incorporated into the second surface (112,212) or the cover220of the handheld electronic device200to maintain the surface temperature of the LCD (118,218) and/or the cover (120,220) of the handheld electronic device200at or below the skin temperature. The evaporation of liquid continues until there is no more water to evaporate in the micro-channels236. Once all the water in the micro-channels236are evaporated, then the device200performance is scaled back.

Next, at506, when the temperature of the second surface (112,212) of the handheld electronic device (100,200) comes down at or below the threshold temperature, due to the evaporation of the liquid, liquid is absorbed from the atmosphere surrounding the handheld electronic device (100,200) by the temperature sensitive polymer covering the bottom surface232and the side surfaces228and230of the one or more micro-channels (236) until the capacity of the temperature sensitive polymer is reached. For example, as discussed with respect toFIGS. 2A-2C, when the temperature of the second surface (112,212) of the handheld electronic device (100,200) is at or below the threshold temperature, water is absorbed from the atmosphere surrounding the handheld electronic device (100,200) by the temperature sensitive polymer covering the bottom surface232and the side surfaces228and230of the one or more micro-channels (236) until the capacity of the temperature sensitive polymer is reached.

In an aspect, a handheld electronic device (100,200) is provided. The handheld electronic device (100,200) includes at least one IC (102,202,104,204). The at least one IC (102,202,104,204) is located between a first surface (114,214) and a second surface (112,212) and between a first side (122,222) and a second side (124,224) of the handheld electronic device (100,200). The handheld electronic device (100,200) also includes a cooling mechanism (110,210,226). The cooling mechanism (226) includes a heat sink (110,210). The heat sink (110,210) extends in a first direction between the first side (122,222) and the second side (124,224) of the handheld electronic device (100,200). A first side of the heat sink (110,210) is adjacent to the second surface (112,212) of the handheld electronic device (100,200). A second side of the heat sink (110,210) is in proximity to the at least one IC (102,104,202,204). The heat sink (110,210) distributes the heat generated from the at least one IC (102,202,104,204) across the second surface (112,212) of the handheld electronic device (100,200) to maintain temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device below a threshold temperature. The cooling mechanism (110,210,226) also includes an evaporative cooling mechanism (226). The evaporative cooling mechanism (226) includes a plurality of liquid retaining structures (236). The plurality of liquid retaining structures (236) extend in parallel to each other in a second direction. The second direction is perpendicular to the first direction. The plurality of liquid retaining structures (236) are located in proximity to the at least one IC (102,104,202,204) on the second surface (112,212) of the handheld electronic device (100,200). Each liquid retaining structure (236) of the plurality of liquid retaining structures (236) is coated with a temperature sensitive polymer. In an aspect, the temperature sensitive polymer is hydrophilic and absorbs liquid from an atmosphere surrounding the handheld electronic device (100,200) to store the absorbed liquid in the plurality of liquid retaining structures (236) when the temperature of the second surface (112,212) is below the threshold temperature. In another aspect, the temperature sensitive polymer is hydrophobic and repels the liquid stored in the plurality of liquid retaining structures (236) when the temperature of the second surface (112,212) exceeds the threshold temperature. In an aspect, to maintain the temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) below the threshold temperature, the evaporative cooling mechanism (226) evaporates the liquid stored in the plurality of liquid retaining structures (236) to the atmosphere surrounding the handheld electronic device (100,200), when the temperature of the second surface (112,212) exceeds the threshold temperature.

In one configuration, the liquid retaining structure (236) is a channel (236) that includes a bottom surface (232) and two side surfaces (228,230). The two side surfaces (228,230) are separated from each other via the bottom surface (232). The bottom (232) surface of the channel (236) and half or three fourth of each of the two side surfaces (228,230) of the channel (236) are coated with the temperature sensitive polymer. In an aspect, the threshold temperature is 35 degree centigrade. In another aspect, a dimension of the channel (236) ranges from few microns to hundreds of microns. In one configuration, a cooling capacity provided by the evaporative cooling mechanism (226) depends on an amount of water stored in the plurality of liquid retaining structures (236). In another configuration, the amount of water stored in the plurality of liquid retaining structures (236) depend on depth of each of the plurality of liquid retaining structures (236). In an aspect, one or more fins (234) coated with the temperature sensitive polymer are attached to the bottom surface (232) of the channel (236). In a configuration, a height of each fin (234) of the one or more fins (234) is approximately equal to the height of the temperature sensitive polymer coating in the two side surfaces (228,230) of the channel (236). In an aspect, the handheld electronic device (100,200) is one of a smart phone, a smart watch, a virtual reality device, a tablet. In another aspect, the temperature sensitive polymer is a combination of cotton and Poly(N-isopropylacrylamide) (PNIPAAm). In a configuration, the liquid is water. In another configuration, each of the plurality of liquid retaining structure (236) is an open cylinder that includes a bottom surface and a side surface, wherein the bottom surface and half of the side surface of the open cylinder are coated with the temperature sensitive polymer.

In an aspect, a method of cooling a handheld electronic device (100,200) is provided. The method of cooling includes distributing, by a heat sink (110,210), heat generated from at least one IC (102,202,104,204) located between a first surface (114,214) and a second surface (112,212) and between a first side (122,222) and a second side (124,224) of the handheld electronic device (100,200). The heat generated from the at least one IC (102,202,104,204) is distributed across the second surface (112,212) of the handheld electronic device (100,200) to maintain temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) below a threshold temperature. The heat sink (110,210) extends in a first direction between the first side (122,222) and the second side (124,224) of the handheld electronic device (100,200). A first side of the heat sink (110,210) is adjacent to the second surface (112,212) of the handheld electronic device (100,200) and a second side of the heat sink (110,210) is in proximity to the at least one IC (102,202,104,204). The method of cooling also includes evaporating liquid to an atmosphere surrounding the handheld electronic device (100,200), when the temperature of the second surface (112,212) of the handheld electronic device (100,200) exceeds the threshold temperature. The liquid is evaporated to maintain the temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) below the threshold temperature. The method of cooling further includes absorbing liquid from the atmosphere surrounding the handheld electronic device (100,200) when the temperature of the second surface (112,212) is at or below the threshold temperature.

In one configuration, performance of the handheld electronic device (100,200) is reduced when temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) is above the threshold temperature. The threshold temperature is 35 degree centigrade. The absorption of the liquid and evaporation of the liquid is performed by a temperature sensitive polymer with a surface property that switches from hydrophilic to hydrophobic at the threshold temperature. In an aspect, a cooling capacity provided by the evaporation of the liquid depends on an amount of water stored in a plurality of liquid retaining structures (236) in the second surface (112,212) of the handheld electronic device (100,200). Each liquid retaining structure (236) is coated with a temperature sensitive polymer with a surface property that switches from hydrophilic to hydrophobic at the threshold temperature. In one configuration, the handheld electronic device (100,200) is one of a smart phone, a smart watch, a virtual reality device, a tablet. In another configuration, the temperature sensitive polymer is a combination of cotton and Poly(N-isopropylacrylamide) (PNIPAAm). In an aspect, the liquid is water.

In an aspect, a means for auxiliary cooling a handheld electronic device (100,200) is provided. The means for cooling includes a means for distributing heat (110,210) generated from at least one IC (102,202,104,204) located between a first surface (114,214) and a second surface (112,212) and between a first side (122,222) and a second side (124,224) of the handheld electronic device (100,200). The heat generated from the at least one IC (102,202,104,204) is distributed across the second surface (112,212) of the handheld electronic device (100,200) to maintain temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) below a threshold temperature. The means for distributing heat (110,210) extends in a first direction between the first side (122,222) and the second side (124,224) of the handheld electronic device (100,200). A first side of the means for distributing heat (110,210) is adjacent to the second surface (112,212) of the handheld electronic device (100,200) and a second side of the means for distributing heat (110,210) is in proximity to the at least one IC (102,202,104,204). The means for cooling also includes evaporating liquid to an atmosphere surrounding the handheld electronic device (100,200), when the temperature of the second surface (112,212) of the handheld electronic device (100,200) exceeds the threshold temperature. The liquid is evaporated to maintain the temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) below the threshold temperature. The means for cooling further includes absorbing liquid from the atmosphere surrounding the handheld electronic device (100,200) when the temperature of the second surface (112,212) is at or below the threshold temperature.

In one configuration, performance of the handheld electronic device (100,200) is reduced when temperature of the first surface (114,214) and the second surface (112,212) of the handheld electronic device (100,200) is above the threshold temperature. The threshold temperature is 35 degree centigrade. The absorption of the liquid and evaporation of the liquid is performed by a temperature sensitive polymer with a surface property that switches from hydrophilic to hydrophobic at the threshold temperature. In an aspect, a cooling capacity provided by the means for evaporating liquid depends on an amount of water stored in a plurality of liquid retaining structures (236) in the second surface (112,212) of the handheld electronic device (100,200). Each liquid retaining structure (236) is coated with a temperature sensitive polymer with a surface property that switches from hydrophilic to hydrophobic at the threshold temperature. In one configuration, the handheld electronic device (100,200) is one of a smart phone, a smart watch, a virtual reality device, a tablet. In another configuration, the temperature sensitive polymer is a combination of cotton and Poly(N-isopropylacrylamide) (PNIPAAm). In an aspect, the liquid is water.