Patent Application
20080148754
None
Not Applicable
Not Applicable
1. Field of Invention
The present application generally relates to the cooling systems, and in particular, the present invention relates to an electrical energy-generating cooling system and to a cryogenic cooling system.
2. Prior Art
Modern microelectronic devices generate substantial amounts of heat during their operation. This presents both the problem and the opportunity.
The problem is the need to remove the heat from the device to avoid overheating. Usually the heat has to be dissipated into the ambient air with the temperature 20-30K below the temperature of the device. This calls for massive heat exchangers with developed surfaces, pumps or fans for the forced convection. Many attempts have been made to cool the microelectronic device with the media colder than the ambient air. This requires a cooler or heat pump that consumes energy and generates even more heat in the vicinity of the device.
The opportunity is to convert the heat back into electric energy and thus reduce the energy consumption from the outer source like battery or power network. For example, in U.S. Pat. No. 6,877,318 to Tadayon et al. (2005) a system is described that uses the micro-machined turbine in the Rankine cycle. The maximum (Carnot) efficiency of the cycle with the worker fluid cooled by ambient air is 9%. Because of the lower efficiency of the Rankine cycle and the losses inherent to the miniature turbines the real efficiency of the system is about 1%. The better efficiency cannot be achieved without introduction of the cryogenic coolants.
Meanwhile significant progress has been made in using the cryogenic liquids and the liquid nitrogen (LN2) in particular for energy storage and generation. It is proven that the specific energy of the liquid nitrogen storage is more than the specific energy of electric batteries. The U.S. Pat. No. 5,390,500 to White et al (1995) describes a multipass heat exchanger that eliminates frost buildup harmful to electronics. The research has concentrated on the systems generating several kilowatts of power for car locomotion, as described for example in U.S. Pat. No. 3,681,609 to Boese et al (1972). No systems are known to use the cryogenic power cycle for micro-power generation.
In accordance with the present invention a two stage cooling system with electric energy-generating capability is described. A heat from a heat source, in particular an electronic chip, is converted into electric energy by a first stage conversion device. The residual heat is sunk by the cryogenic liquid that is thus evaporated, heated further by the ambient air heat exchanger and directed into a second stage expander turbine that drives a second stage electric generator.
I propose a system that uses a vessel with cryogenic liquid for energy storage, cools the microelectronic device with the liquid and generates electric energy by utilizing the heat from the device and from the environment.
The main components of the system are shown on
Since only the residual heat from the first stage (heat engine) reaches the cryogenic liquid the specific energies in this binary cycle are very high. For example the available work Q for the liquid nitrogen (LN2) in the Rankine cycle is 769 kJ/kg. The specific energies of LN2 in the open Rankine cycle may reach 300 kJ/kg, which is already comparable with the best available battery technology and is well above the specific energy of the lead-acid or Ni—Cd batteries at 110 kJ/kg. Given Etha1 is the thermal efficiency of the heat engine and Etha2 is the thermal efficiency of the Rankine cycle the specific energy of LN2 “fuel” in binary cycle is
Qe=Q(Etha1/(1−Etha1)+Etha2)
Assuming the thermal efficiency of the heat engine is the same as that of the Rankine cycle the specific energy of LN2 in the binary cycle is 792 kJ/kg.
To reduce the complexity, size or cost of the system at the expense of giving up some thermal efficiency, one of the “hot” heat exchangers may be placed outside the heat engine and deliver heat directly to the cryogenic liquid.
When the microelectronic device is connected to the power grid it is desirable to have an option to conserve the cryogenic liquid “battery” and switch to the main power supply. When the system switches from generation mode to mains powered mode the pump 201 is shut off. As a result turbine 500 and generator 600 halt. Generator 400 is connected to the mains power as a motor and delivers mechanical energy to the reversible heat engine 300 which now operates as a cooler. The heat from the microelectronic device is sunk at the heat exchanger 301 and dissipated from the heat exchanger 302. When the peak cooling performance is required the system may switch back to generating mode.
The mechanical energy is converted to electricity by means of the linear generator. The acoustic wave drives the flexible membrane 410 with the magnet 411 attached to it. Motion of the magnet induces an electric current in the coil 412.
The heat absorbed by the cold heat exchanger causes the liquid to evaporate. The vapor is then directed into the multiple pass heat exchanger 302. The exchanger design prevents frost buildup. The vapor heated to the ambient-air temperature is directed into the expander type microturbine 500 combined with the electrical generator. The expanded vapor (gas) is then released into the ambient air.
In the mains powered mode the alternating electric current in coil 412 causes the magnet 411 and membrane 410 to vibrate. The resulting acoustic wave cools the microchip device.
In the design depicted on
The generator/heat exchanger combination can be used in many different types of heat engines.
The coil windings may also be used as a regenerator type heat exchanger for example as a thermoacoustic engine stack.
Exposure of the coil windings to the cryogenic temperatures makes possible to use the high temperature superconducting wire and further improve generator efficiency.
One more distinctive feature of the device on
On
The high expansion ratio typical for cryogenic vapors will normally require a multitude of micro-turbines connected sequentially. The gas is warmed in between the expansions and the ambient air heat is sunk at every stage. The curve 603 describing the actual process is in between the lines 601 and 602.
The power generating unit is compact and well suited for the mobile applications. It is capable of adjusting the power output to the demands of the microelectronic device. When the power consumption increases the amount of heat sunk at the cold heat exchanger of the engine increases as well. More liquid is evaporated increasing the amount of gas available for the second stage operation. The throughput of the second stage increases and so is the power generated by the second stage. The drop in the power consumption will decrease the throughput of the second stage and conserve the cryogenic liquid.
The fact that the unit generates power by sinking the ambient heat allows for using it in the personal cooling system.
