Patent Application
20120096871
This invention relates to a dynamic switching thermal management system and more particularly to a temperature controlling system using a thermoelectric module and an energy storage device.
For most heat generating systems, a large fraction of energy is dissipated as waste heat. As a result, the temperatures of the heat sources in the system are elevated. Most of these heat sources need passive or powered heat dissipation devices to extract the waste heat and maintain the critical components of the system within a desired temperature range. Moreover, the powered cooling devices need additional energy to operate.
Prior systems have used a fan driven heat sink assembly that includes a fan assembly mounted on a heat sink. The heat sink has a solid flat base and a plurality of spaced cooling fins, and the fan provides forced air convective heat transfer on the surfaces of the heat exchanger. Other systems have used a thermoelectric heat pump that is resistant to thermal stresses incurred during thermal cycling between cold and hot temperatures. Other alternative thermal management systems include water cooling circulation systems with pipes to spread the heat of a heat source.
The waste heat can provide a source of energy recovery as well. The temperature difference between the hot heat sources and the cold ambient makes thermoelectric power generation possible. The temperature difference can creates an electric potential difference in thermoelectric materials. If an external load is connected, the thermoelectric material can serve as a power source in the completed circuit. During thermoelectric power generation, the temperature of the heat source will be raised compared to its temperature without the power generation device. In certain scenarios, heat generating systems can work in elevated temperature ranges; eliminating the need to further cool the heat sources down. However, if the desired operating temperature range is exceeded, the performance of the system may be compromised.
It would be desirable to have a thermal management system that can recover energy from the waste heat of a system and that can control the heat source temperature to maintain the desired operating conditions for the system.
Thermoelectric effects include the direct conversion of temperature differences to electric potential differences (Seebeck effect) and electric potential differences to temperature differences (Peltier effect). The names are derived from the independent discoveries of French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck. In 1821, Seebeck found that if two dissimilar metals are connected and there is a temperature difference across the junction, a voltage will develop across the junction. The Seebeck effect forms the basis of the power generation function of a thermoelectric device. In 1834, Peltier discovered the inverse Seebeck effect where if a current is flowing through two dissimilar metals connected at a junction, a temperature gradient will develop across the junction, which leads to a heat flux. The Peltier effect forms the basis of the cooling function of a thermoelectric device. In the 1900's, researchers found efficient thermoelectric materials that possess large Seebeck coefficients (S), high electrical conductivity (σ) and low thermal conductivity (κ). The performance (i.e., efficiency of Seebeck or Peltier effect) of thermoelectric materials can be expressed in terms of a dimensionless figure of merit (ZT), where Z is given by Z=S2σ/κ, and T is temperature. Now, a thermoelectric device utilizing properly doped semiconductor materials can provide high performance either in Seebeck power generation or Peltier cooling. The device usually includes dozens of p and n type semiconductor legs connected electrically in series and thermally in parallel, sandwiched between two plates made of a material that is an electrical insulator with high thermal conductivity. It normally has two power wires, the “+” and “−” connectors. When applying a voltage on the wires, it works in Peltier cooling mode, which pumps heat from one side to the other. When connecting the two power wires to an energy storage device and applying a temperature difference across the two sides, it works in Seebeck power generation mode, which generates electricity.
A solid state dynamic switching thermal management system is described herein. An exemplary embodiment of the system includes a heat spreader, a thermoelectric module, a heat dissipation device, an energy storage device, two temperature sensors, and a programmable microchip. The heat spreader is coupled to a heat source that is under the thermal management of the dynamic switching system. The heat spreader carries heat away from the heat source. One of the temperature sensors detects the temperature of the heat source, and the other temperature sensor detects the temperature of the ambient environment around the heat dissipation device. One side of the thermoelectric module is thermally coupled to the heat spreader, and the other side of the thermoelectric module is thermally coupled to the heat dissipation device. The thermoelectric module switches between power generation (Seebeck power generation function) and cooling (Peltier cooling function). The programmable microchip is coupled to the thermoelectric module, the two temperature sensors and the energy storage device. The microchip periodically samples the two temperature sensors, controls the system temperatures and controls powering of the cooling function.
A dynamic switching thermoelectric thermal management system for coupling to a heat source is disclosed. This embodiment of the thermal management system includes a heat dissipation device, a thermoelectric module, first and second temperature sensors, an energy storage device and a controller. The thermoelectric module includes a first side thermally coupled to the heat source and a second side thermally coupled to the heat dissipation device. The first temperature sensor detects the ambient temperature of the environment surrounding the thermal management system, and the second temperature sensor detects a temperature for the heat source. The controller is coupled to the thermoelectric module, the first and second temperature sensors and the energy storage device. The controller periodically samples the first and second temperature sensors and dynamically switches the thermoelectric module between a power generation mode, a cooling mode, and an idle mode. In the power generation mode, the thermoelectric module uses the temperature difference between the heat source and ambient to charge the energy storage device. In the cooling mode, the thermoelectric module is powered to create a voltage difference across the thermoelectric module to cool the heat source. In the idle mode, the thermoelectric module neither generates nor consumes power. The thermal management system can be integrated into a portable electronic device, for example the thermal management system can be integrated into a portable computing device.
The thermal management system can include a heat spreader with a proximal end coupled to the heat dissipation device and a distal end coupled to the heat source, the first side of the thermoelectric module being coupled to the heat spreader. The controller can be a programmable microchip. The second temperature sensor can be coupled to the distal end of the heat spreader. The first temperature sensor can be coupled to the heat dissipation device. The energy storage device can be a battery. The energy storage device can power the thermoelectric module during cooling mode.
The heat dissipation device can be, for example, a heat sink having a plurality of fins or a liquid cooling device. The heat dissipation device can dissipate heat to the surrounding environment by conduction. The thermal management system can include a fan for forcing fluid over the heat dissipation device to dissipate heat to the surrounding environment by forced convection. The thermal management system can include a pump forcing liquid over the heat dissipation device to dissipate heat to the surrounding environment by forced convection.
A method is disclosed for controlling a dynamic switching thermoelectric thermal management system that includes a thermoelectric module having a first side thermally coupled to a heat source and a second side thermally coupled to a heat dissipation device. The method includes monitoring a temperature of the heat source; monitoring a temperature of the ambient environment surrounding the thermal management system; and dissipating heat from the heat source using the heat dissipation device. When the heat source temperature is greater than the ambient temperature and less than a critical working temperature, the method includes putting the thermal management system in a power generation mode for charging an energy storage device using the temperature difference across the thermoelectric module. When the heat source temperature is greater than the critical working temperature, the method includes putting the thermal management system in a cooling mode for cooling the heat source using a voltage difference across the thermoelectric module. The energy storage device can be used to create the voltage difference across the thermoelectric module when the thermal management system is in the cooling mode. The method can also include conducting heat from the heat source to the thermoelectric module through the heat spreader, where the heat spreader includes a proximal end coupled to the first side of the thermoelectric module and a distal end coupled to the heat source. The temperature sensor for monitoring the heat source temperature can be coupled to the distal end of the heat spreader. The temperature sensor for monitoring the ambient temperature can monitor the temperature near the heat dissipation device. The heat source temperature and ambient temperature can be monitored periodically.
For the purposes of promoting an understanding of the principles of the novel technology, reference will now be made to the embodiments described herein and illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, such alterations and further modifications in the illustrated devices and methods, and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates.
The temperature sensors 50 and 52 can be coupled the microchip 60 with signal cables. The ambient temperature sensor 50 can be connected to a surface of the heat dissipation device 30 that is exposed to the ambient environment where the ambient temperature sensor 50 can have convective heat transfer with the ambient working fluid, for example air. Alternatively, the ambient temperature sensor 50 can be coupled to another surface where the ambient temperature sensor 50 is exposed to the ambient temperature of the environment. The heat source temperature sensor 52 can be connected to the heat spreader 10 adjacent to the heat source 70, or can be connected to the surface of the heat source 70, or can otherwise be located within the generally isothermal area of the temperature of the heat source 70.
The arrow 80 indicates that a fluid, such as air or water, can be moved across the heat dissipation device 30 to dissipate heat using forced convection. Alternatively, conduction or other methods can be used to dissipate the heat.
The heat spreader 10 can be made of any heat conducting materials, heat pipes or other heat conducting devices with phase transformation mechanism. The temperature difference between the two ends of the heat spreader 10 should be smaller than the temperature of the heat source 70.
The heat dissipation device 30 is illustrated as a heat sink with a plurality of fins. Other configurations of heat dissipation devices can be used. The heat dissipation device 30 can be made of any type of heat conducting materials or liquid cooling devices. The interaction of the heat dissipation device 30 and the surrounding environment working fluid can be conduction, free convection or forced convection, for example forced air flow by a powered fan or forced water flow by a pump.
The thermoelectric module 20 can be connected by power cords to the microchip 60. The microchip 60 controls the temperature detection of the two temperature sensors 50 and 52, and also controls the switching between Seebeck power generation mode and Peltier cooling mode of the thermoelectric module 20.
The energy storage device 40 can be a battery, a capacitor or other energy storage mechanism that can store electrical energy temporarily or long term. The energy storage device 40 can be the main electrical power source of the heat generating system. The energy storage device 40 is under control of the microchip 60 to be charged by the thermoelectric module 20 or to power the cooling function of thermoelectric module 20.
The Seebeck power generation function can recover waste heat energy, and the solid state Peltier cooling function can enhance the cooling efficiency for heat sources. These will give an overall energy benefit for any thermal system, especially for portable electronic devices.
At block 210 the heat generating system starts which can signal the start of the thermal management system. As the heat generating system operates, the heat source 70 starts generating heat and raising its surface temperature. At block 220, the microchip 60 detects the heat source temperature Th and the ambient temperature Ta. The heat source temperature Th can be detected using the heat source temperature sensor 52, and the ambient temperature Ta can be detected using the ambient temperature sensors 50.
At block 230, the system determines whether Th is below a critical working temperature Tcw for the heat generation system 70. The critical working temperature is a temperature beyond which the system will need extra cooling to lower the operating temperature and maintain desired performance. The critical working temperature may be a temperature recommended by the manufacturer of the heat generating system 70. If Th is below the critical working temperature Tcw, control passes to block 240, otherwise control passes to block 250.
At block 240, the system determines whether Th is equal to or greater than Ta. If Th is equal to or greater than Ta, the process proceeds to block 260 where the Seebeck power generation function is implemented and Th will slowly increase. In the embodiment of
At block 230, if Th is equal to or above the critical working temperature then the process proceeds to block 250 to implement the Peltier cooling function. In this case, the heat source 70 needs extra cooling to lower its temperature and to maintain a desired performance. In the embodiment of
At block 240, if Th is less than Ta then the process proceeds to block 270 since the heat source 70 is still cool enough to operate without the Peltier cooling function and there is no temperature difference to generate power for the Seebeck power generation function. This usually happens when the heat source 70 is idle or during the initial start-up of the system.
From block 270, the system continues to block 280 where it determines whether to shutdown or to continue operation. At block 280, if the system receives a shutdown command then the system proceeds to block 290 and shuts down. If the system has not received a shut down command then, to realize the dynamic switching mechanism, control passes back to block 220 where the microchip 60 will sample the heat source and ambient temperatures, Th and Ta, from the temperature sensors 50 and 52 in a real-time or periodic manner. The sampling interval can range from substantially continuously, to seconds, to minutes, to hours, depending on the power of the heat source 70 and the heat capacity of the heat spreader 10.
As an example, a laptop or portable device application can utilize thin profile generators with relatively high heat transfer coefficients and the possibility of dynamic switching between Peltier and Seebeck modes. Because most electronic devices run within a certain temperature range, it is often not necessary to cool it down further. When a dynamic switching thermoelectric module as described above is installed on the heat pipes or heat exchanger surface near the processing units, the thermoelectric module can scavenge the waste heat to power a battery or a cooling device if the processing unit is idle and has an operating temperature higher than the ambient. If the processing unit is operating and generating a great amount of heat, the thermoelectric module can be used to cool the heat source. The response time of the system can be in the range from seconds to hours, thus the temperature of the processing units can be maintained below a maximum value as the laptop or portable device cycles in and out of computationally intense periods. The laptop or portable device with the thermoelectric module will have an overall energy saving benefit and can cool the device more efficiently and quietly.
An estimate can be made of the maximum power density a dynamic switching thermoelectric module can produce in a laptop. Assuming that the thermoelectric system has the properties shown in the following table, the power density versus thickness of the thermoelectric module is shown in FIG. 3\
The maximum power density is 1.9e3 W/m2, which means by using a 3 cm by 3 cm thermoelectric module, the power generation would be 1.71 W. If the dynamic switching system has 80% time in power generation mode and 20% in cooling mode, in principle, the 1.71 W should be enough to power a conventional cooling fan for laptops which consume approximately 1 W for all the operation time. The remaining energy may be enough for powering cooling mode power consumption which is approximately 1.4 W. The excessive energy produced would be approximately
1.71 W*80%-1 W*100%-1.4 W*20%=0.088 W.
This excess energy could be used to power LED indicators or to back charge to the main battery.
The dynamic switching thermoelectric system may enhance the efficiency and stability of a heat generating system. The thermoelectric thermal management system can be solid-state without moving parts, which can lead to a more reliable and quiet operation. It is apparent that various changes or modification can be made to the dynamic switching system without deviating from the original spirit of the invention. While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/405,891, filed on Oct. 22, 2010, entitled “Dynamic Switching Thermoelectric Thermal Management Systems and Methods” which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61405891 | Oct 2010 | US |
