MULTIPLE TEMPERATURE SENSITIVE DEVICES USING TWO HEAT PIPES
A heat pipe assembly comprises a first heat pipe having a condenser and a working fluid. A reservoir communicates with the condenser of the first heat pipe and contains a non-condensable gas which variably permits access of the working fluid to the condenser of the first heat pipe, depending on a pressure of the working fluid. A second heat pipe has an evaporator. At least a portion of the evaporator of the second heat pipe is contained inside of the condenser of the first heat pipe.
This application is a continuation of U.S. patent application Ser. No. 10/696,270, filed Oct. 29, 2003, which is a divisional of U.S. patent application Ser. No. 10/106,277, filed Mar. 26, 2002, now U.S. Pat. No. 6,675,887, issued Jan. 13, 2004.BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to heat transfer devices and, more particularly, to variable conductance heat pipes.
2. Description of Related Art
The reliability of electronic components decreases significantly as a result of high temperature extremes or large temperature swings, especially in circumstances where these swings or cycles are frequent. Causes of these temperature cycles include, for example, electronic loading or environmental temperature differences.
A heat pipe is a widely used device for transferring high rates of heat flow across large distances with negligible temperature drop. It generally includes a closed pressure vessel containing a working fluid (liquid and vapor) in saturated thermal equilibrium. External heat from a heat generating source is input to an evaporator section, and heat is rejected to and dissipated by an external heat sink from a condenser section. The evaporator section and condenser section are connected by a vapor flow volume and an internal capillary wick. A working fluid, such as ammonia, evaporates in the evaporator section, and the vapor flows to the condenser section and condenses, giving up its heat of vaporization to the heat pipe wall. The working fluid then returns in liquid form to the evaporator section via capillary pumping action within the wick.
The conventional heat pipe is effective in transferring a large amount of heat where a temperature difference between two places is small, but such a heat pipe can not execute a temperature control function. A Variable Conductance Heat Pipe (VCHP) is a device which provides better temperature control, i.e., maintains a heat source at a stable temperature within a few degrees of a set point, in situations where, for example, electronics equipment can either dissipate at different power levels, or the condenser or heat sink is exposed to varying environmental temperatures. With a VCHP, the amount of heat transferred is usually controlled by blocking part of the condenser area with a non-condensable gas. The non-condensable gas, which is stored in a gas reservoir fluidly connected to the condenser of the VCHP, displaces a controlled portion of the working fluid vapor in the condenser, rendering that portion of the condenser containing the non-condensable gas thermally inactive by blocking the interior condenser surface. Heat transfer is inhibited because the working fluid vapor must diffuse through the non-condensable gas in order to reach the condenser surface. Increasing condenser blockage effectively closes the heat pipe, reducing the area available for heat transfer. As the heat load from a heat generating source is increased, the vapor pressure of the working fluid increases causing the non-condensable gas to compress and expose more of the condenser area, resulting in a passively controlled heat transfer device.
Not only does a VCHP work to maintain a relatively constant temperature despite varying heat input from heat generating sources at the evaporator end of the VCHP, but it also is effective at maintaining the heat generating source at a relatively constant temperature where there is great variation in heat sink temperature due to varying environmental conditions.
The sensitivity or control level of the VCHP 300 is driven by the ratio of reservoir volume to condenser volume. As shown in
An improved VHCP is desired.SUMMARY OF THE INVENTION
The present invention is a heat pipe assembly comprising a first heat pipe having a condenser and a working fluid. A reservoir contains a non-condensable gas which variably permits access of the working fluid to the condenser of the first heat pipe, depending on a pressure of the working fluid. A second heat pipe has an evaporator that is in thermal contact with the first heat pipe.
It will be understood that the drawings are not scale drawings. One of ordinary skill in the art can readily select appropriate dimensions for a specific cooling application.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the description below, the terms top, bottom, left and right are understood to refer to the directions appropriate when the device is oriented in the manner shown in the figures. Such terms do not limit the possible orientations of the device, and it is understood that the device can be oriented in any manner, and such relational terms as top, bottom, left and right would automatically be changed.
In the various drawings, parts identified by the same reference numeral are the same.
VCHP 100 has an evaporator end 105 and a condenser end 110. VCHP includes a hollow envelope 120, a wick 130, a working fluid (not shown) and a gas reservoir 140, which may be external to the VHCP (as shown in
In the exemplary embodiment of
Envelope 220, like envelope 120, is typically comprised of a metal such as copper or aluminum. The structure and composition of the wick of the second heat pipe 200 and the composition of the working fluid, again, may vary depending on the application and may include any structure or composition known to those of ordinary skill in the art. Preferably, the envelope of second heat pipe 200 is made of the same material as the envelope of first heat pipe 100, and the working fluids are the same.
The exemplary assembly of
Evaporator end 205 of second heat pipe 200 is mechanically attached and sealed to condenser end 110 of VCHP and at least a portion of evaporator end 205 of second heat pipe 200 is contained inside of condenser end 110 of VCHP 100. Evaporator end 205 of second heat pipe 200 could be in thermal contact with the condenser end 110 of VCHP 100. Preferably, hear sink 240 or a plurality of individual fins are attached to an outside surface of envelope 210 of second heat pipe 200.
The embodiment of
A variable gas front 145 marks the separation point between the working fluid vapor and the non-condensable gas 142. The non-condensable gas 142 has a moving front 145 with a range of motion 146 within the condenser 110 of the first heat pipe 100. The non-condensable gas 142 variably permits access of the working fluid to the condenser 110 and evaporator 205. When the moving front 145 is at a first (right in
In prior art VCHP's, as shown in
As soon as the gas front 145 touches the evaporator 205 of the second heat pipe 200, heat pipe 200 transfers the heat load to the heat sink 140, from which the heat is dissipated. This in turn decreases the vapor pressure of the evaporator end 105 of the VCHP 100 causing the gas front to move back towards the evaporator end 105. This expansion of the non-condensable gas 142 again blocks access to the condenser end 110 of VCHP 100 and second heat pipe 200. In this state almost no heat can be rejected and the pressure will begin to increase where the heat source is generating heat. With this improved heat pipe assembly, as shown in
VCHP 100′ in the variation of
Second heat pipe 200′ has an evaporator end 205′ and a condenser end 210′. Second heat pipe 200′ includes a hollow envelope 220′, a wick (not shown), a working fluid (not shown) and evaporator fins 250. Second heat pipe 200′ may further include a heat sink 240′ attached to condenser end 210′. Such heat sink 240′ may be in the form of fins as shown in
In the embodiment as shown in
In the assembly 20] shown in
Although the exemplary conductive members are fins 250′, other shapes of conductive members may be used. For example, the conductive members may be radial columns or pins having a variety of shapes. Preferably, a shape that does not create significant resistance to movement of the vaporized working fluid is used.
VCHP 100″ has an evaporator end 105″ and a condenser end 110″. VCHP 100″ includes a hollow envelope 120″, a wick 130″, a working fluid (not shown) a gas reservoir 140″, and an insulator 150″. Gas reservoir 140″ contains non-condensable gas 142″. Insulator 150″ is preferably comprised of a ceramic material, but may be comprised of any thermally insulating material, such as a low conductivity metal.
In the first heat pipe 100″, the envelope 120″ has a section 150″ formed of a thermally insulating material at the condenser 110″, Insulating section 150″ provides continuity in the vapor seal of envelope 120″, while substantially reducing or eliminating the conductive couplings between the evaporator end 105″ of the envelope 120″ and the evaporator 205″ of second heat pipe 200″. Wick 130″ extends in the section between the thermally conductive portions of envelope 120″, and abuts the inside surface of insulator 150″. With an insulating section 150″ in the envelope 120″, heat transfer from the evaporator 105″ to the evaporator 205″ is essentially by way of the vaporized working fluid contacting the evaporator 205″.
The second heat pipe 200″ of
The heat pipe assembly 301 shown in
The improved heat pipe assemblies 101, 201 or 301 of
Another application for the heat pipe assemblies of
The proposed system can be used to couple multiple devices to an over-capacity heat sink operating at a constant temperature. The device operating temperatures will be maintained at a relatively constant temperature regardless of how many devices are operating at a given time.
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
1. A heat pipe assembly, comprising:
- a first heat pipe having a condenser and a working fluid;
- a reservoir containing a non-condensable gas which variably permits access of the working fluid to the condenser of the first heat pipe, depending on a pressure of the working fluid; and
- a second heat pipe having an evaporator that is in thermal contact with the first heat pipe.
2. The heat pipe assembly of claim 1, wherein the reservoir is internal to the first heat pipe.
3. The heat pipe assembly of claim 1, wherein:
- the first heat pipe has an envelope, and
- the second heat pipe has conductive members connecting the evaporator of the second heat pipe to an inside of the envelope of the first heat pipe at the condenser thereof.
4. The heat pipe assembly of claim 3, wherein the conductive members are a plurality of radial fins.
5. The heat pipe assembly of claim 3, further comprising a heat sink or a plurality of fins attached to the condenser of the second heat pipe, wherein the first heat pipe has no heat sink or fins attached directly thereto.
6. The heat pipe assembly of claim 1, further comprising an insulator that reduces heat transfer between an envelope of the first heat pipe and an envelope of the second heat pipe,
7. The heat pipe assembly of claim 6, wherein the envelope of the first heat pipe has a section formed of a thermally insulating material at the condenser of the first heat pipe.
8. The heat pipe assembly of claim 7, wherein the evaporator of the second heat pipe is located within the section formed of the thermally insulating material.
9. The heat pipe assembly of claim 7, wherein the non-condensable gas has a moving front with a range of motion within the section formed of the thermally insulating material.
International Classification: F28D 15/00 (20060101);