US20090120618A1

US20090120618A1 - Cooling apparatus for a computer system

Info

Publication number: US20090120618A1
Application number: US12/264,796
Authority: US
Inventors: Christoph Konig
Original assignee: Fujitsu Technology Solutions GmbH
Current assignee: Fujitsu Technology Solutions GmbH
Priority date: 2007-11-06
Filing date: 2008-11-04
Publication date: 2009-05-14
Also published as: EP2059104A3; EP2059104A2; DE102007053219A1; CN101430590A

Abstract

The invention relates to a cooling apparatus for a computer system and a method for cooling at least one heat producing component of a computer system.

The cooling apparatus for the computer system features an evaporator (2) for a working medium, which can be thermally coupled to the at least one heat producing component of the computer system. In this connection, the cooling apparatus is constructed as a heat engine or as an absorption refrigerator in order to carry out a thermodynamic cycle.

Description

BACKGROUND OF THE INVENTION

The invention relates to a cooling apparatus for a computer system and to a method for cooling at least one heat producing component of a computer system.
Today's computer systems, for example, so-called server farms, can already feature up to several thousand processors. In light of increasing demand on network services, a continuing rise in the number of processors in future systems is foreseeable. In addition, the increasing capacity of individual processors is accompanied by a rise in the electric power required. Taken together, on the one hand this results in an enormous primary power requirement (power consumption) of large computer systems, and on the other hand in a large quantity of waste heat, which must be transported away from the computer system by means of suitable cooling apparatuses, wherein it is known to employ waste heat for heating purposes or for hot water production and thus to render this useful.

SUMMARY OF THE INVENTION

The purpose of the invention is to create a cooling apparatus for a computer system, and a method for cooling at least one heat producing component of a computer system, which enables an effective cooling and an efficient and versatile use of waste heat from a computer system.
According to a first aspect of the invention, the problem is solved by means of a cooling apparatus for a computer system which features an evaporator for a working medium, where the evaporator can be thermally coupled to the at least one heat producing component of the computer system, and the cooling apparatus is a heat engine.
For the cooling apparatus, evaporation of the working medium achieves an effective heat absorption, which brings about good cooling properties. In the cooling apparatus, the absorbed heat can be converted in a thermodynamic cycle of the heat engine into mechanical energy, which is usable in manifold ways. For example, a steam turbine having a generator for converting the mechanical energy into electrical power can be employed, and the electrical power can be used to cover a portion of the primary power requirement of the computer system. It also is possible to couple the steam turbine to cooling medium compressors that are used in an air-conditioning system. Air-conditioning systems frequently are used to provide climate control of rooms for computer systems. If a portion of the energy/power required for operating the air-conditioning system is supplied by making useful the waste heat of the computer system, this in turn leads to a decrease in the energy consumption connected with operation of the computer system.
In a preferred improvement of the cooling apparatus, the working medium is a mixture of ammonia and water. A thermodynamic cycle based on this working medium is also termed a Kalina process. This mixture evaporates at temperatures below the maximum possible operating temperature of electronic components, of processors in particular. For this reason, evaporation of this type of working medium is well-suited for cooling the components of a computer system. In addition, an ammonia-rich vapor phase and an ammonia-poor liquid phase arise during evaporation, by means of which the evaporating temperature of the yet liquid portion of the mixture increases during evaporation. The increase brings about good heat transfer properties in the evaporator. If after passing through the steam turbine the steam phase is combined afresh with the unevaporated liquid phase of the working medium, the boiling point is analogously likewise lowered, leading to a lowering of the temperature in the condenser. The greater temperature difference thus achieved between evaporator and condenser leads to a Carnot efficiency which is better than could be achieved with a working medium having a constant boiling point.
According to a second aspect of the invention, the problem is solved by means of a method for cooling at least one heat-producing component of a computer system, with the evaporator being capable of being coupled thermally to the at least one heat producing component of the computer system and the cooling apparatus being an absorption refrigerator.
Heat absorbed in the evaporator can be used for cooling purposes in the cooling apparatus by means of the thermodynamic cycle of the absorption refrigerator. For example, an air-conditioning system can be operated or supported in order to provide climate control for the rooms of the computer system, effectively lowering the primary power requirement connected with operation of the computer system.
According to a third aspect of the invention, the problem is solved by means of a method for which a working medium is at least partially evaporated in an evaporator by means of the generated heat, and a vapor phase of the working medium arising in the course of evaporation is expanded in a steam turbine with the delivery of a mechanical yield.
According to a fourth aspect of the invention, the problem is solved by means of a method for which a working medium is partially evaporated in an evaporator by means of the generated heat, a vapor phase of said working medium arising in the course of a partial evaporation is refrigerated and condensed and the condensed working medium is evaporated in an additional evaporator while absorbing evaporation heat.
The advantages of the third and fourth aspect of the invention correspond to those of the first and second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained in more detail on the basis of embodiments with the aid of three figures. Shown are:

FIG. 1 is a schematic depiction of a first embodiment of a cooling apparatus for a computer system,

FIG. 2 is the schematic depiction of a second embodiment of a cooling apparatus for a computer system, and

FIG. 3 is the schematic depiction of a third embodiment of a cooling apparatus for a computer system.

DETAILED DESCRIPTION OF THE INVENTION

For the cooling apparatus depicted in FIG. 1, a processor 1 is in direct thermal contact with an evaporator 2. The evaporator 2 is connected by means of a working medium circuit 3, to a separator 4. A first outlet of the separator 4 is connected to a steam turbine 5, which is coupled to a generator 6. A low-pressure outlet of the steam turbine 5 and a second outlet of the separator 4 are led to a condenser 7 that is tied to a cooling-water flow 8. The outlet of the condenser 7 is connected to the evaporator 2 by means of a condensate pump 9.
During operation of the cooling apparatus shown in FIG. 1, waste heat from a heat producing component of the computer system, here, by means of example, the processor 1, is absorbed by the evaporator 2. The evaporator 2 is in direct thermal contact with the processor 1 for this purpose. To this end, it works to advantage for the evaporator 2 to feature a contact surface with the processor 1 and mounting elements corresponding to the specifications of heat sinks or cooling elements for the processor 1.
Driven by means of the condensate pump 9, a working medium 3 flows through the evaporator 2. Said working medium is a liquid which evaporates or partially evaporates at relatively low temperatures at the prevailing pressure conditions within the working medium circuit 3. The working medium is evaporated in the evaporator 2, absorbing, in this connection, a quantity of heat dependent on its heat of evaporation and on the flow rate. For this reason, the lowest temperature to which the evaporator can be brought is the boiling temperature of the working medium in the evaporator 2 at the prevailing pressure in the working medium circuit 3. Due to temperature gradients between the processor 1 and evaporator 2, caused by heat conductance values of the materials employed as well as by heat transmission resistances, particularly at the transition from the processor 1 to the evaporator 2, the temperature of the processor 1 will be somewhat, e.g., several degrees, higher than the boiling temperature of the working medium. Since processors and electronic components in general must not exceed a certain maximum temperature, above which error functions and/or a reduction of the lifespan can result, the working medium is to be selected appropriately such that an acceptable operating temperature is reached at the component during operation.
A mixture of ammonia and water is particularly suited as a working medium. A thermodynamic cycle which is operated with such a working medium is also termed a Kalina process. A distinctive feature of the Kalina process is that an ammonia-rich vapor phase and an ammonia-poor liquid phase arise during evaporation. Changing the ammonia concentration in the liquid phase increases its evaporation temperature, leading to good heat transfer properties in the evaporator 2.
The liquid phase and the vapor phase are separated from one another in the separator 4. The vapor phase is supplied to the steam turbine 5 designed as a low-pressure turbine. It is expanded in the steam turbine 5 while delivering mechanical energy that is conveyed to the generator 6 to generate electrical power. The power generated by the generator 6 can be supplied again to the computer system, reducing the primary power requirement (energy consumption) of the computer system. Alternatively, mechanical energy furnished by the steam turbine 5 can be used in other ways, e.g., in order to operate compressors for air conditioners, which are frequently employed in combination with large computer systems for additional cooling by means of air circulation. The power requirement of a computer system also can be indirectly lowered in this way.
The expanded ammonia-rich vapor leaving the low pressure outlet of the steam turbine 5 is mixed with the ammonia-poor liquid phase isolated by the separator 4 and supplied to the condenser 7. Mixing lowers the boiling point of the working medium, which leads to a reduction in pressure. The pressure difference utilized by the steam turbine 5 consequently increases, which is advantageous for an effective energy conversion in the steam turbine 5. In addition, a lowering of the temperature in the condenser makes the temperature difference attainable between evaporator and condenser greater than could be achieved with a working medium having a constant boiling point. This leads to a correspondingly superior Carnot efficiency.
In the condenser 7, the working medium is chilled to the point of liquefaction and can in turn be supplied to the evaporator 2 by the condensate pump 9, closing the thermodynamic cycle. Alternatively, liquefaction can also occur not until, or during, compression by means of the condensate pump 9.
In order to dissipate condensation heat of the working medium, a cooling-water flow 8 passes through the condenser 7. Said cooling-water flow 8 can be part of a closed circuit in which absorbed heat is emitted, e.g. outside the building to ambient air by means of heat exchangers, or is supplied to a heating system. Alternatively, the cooling-water flow 8 can be a fresh water flow in which absorbed heat then serves, e.g., for hot water production.
For the sake of clarity, only one processor 1 is shown in FIG. 1 as a heat producing component of a computer system. In practice, a meaningful use of the waste heat of a computer system in the way shown is effective when a cooling apparatus is employed for a large computer system having a multitude of heat producing components, thus, for example, a multitude of processors or also power supplies. If so, a provision can be made to provide an evaporator 2 on every heat producing component, with the evaporators 2 then being arranged in parallel within the working medium circuit 3. A temperature-dependent controlled valve can be provided at each evaporator 2 in order to control the partial streams of working medium conducted through the individual evaporators 2. In addition, it is possible to provide, for each instance of several heat producing components, e.g., several processors arranged in spatial proximity to one another, one evaporator 2 that is connected to the individual heat producing components by means of heat conducting elements, e.g., heat pipes. Larger server farms customarily feature a multitude of server racks, which, in each case, are fitted with a number of individual servers, each of which can feature several processors 1. Then, for example, one evaporator 2 per server can be provided that is thermally coupled to the individual processors 1 of the server by means of heat pipes.
FIG. 2 shows an additional embodiment of a cooling apparatus for a computer system. In this connection, identical reference numbers in FIGS. 1 and 2 denote identical or equally acting elements.
For the cooling apparatus of FIG. 2, two processors 1 are in respective direct thermal contact with a first heat exchanger 10. The first heat exchangers 10 form, together with a second heat exchanger 11 and a cooling-medium pump 12, a closed cooling circuit 13. An evaporator 2 is in direct thermal contact with the second heat exchanger 11. The evaporator 2 forms a closed working medium circuit 3 with a steam turbine 5 that is coupled to a generator 6, a condenser 7, and a condensate pump 9. The condenser 7 features a cooling surface 14 that is exposed to a cooling-air flow 15.
As with the embodiment shown in FIG. 1, in the embodiment of FIG. 2 the evaporation heat of a working medium also is applied in an evaporator 2 as a thermodynamic cycle is completed in order to cool processors 1 of a computer system.
Unlike the embodiment of FIG. 1, the working medium circuit 3 does not feature a separator 4. It is therefore not a binary method for a thermodynamic cycle having a mixed working medium that undergoes a change in concentration during evaporation. In place of this, a working medium such as silicone oil or another organic compounds having an inherently low boiling point is suitable. A thermodynamic cycle implemented with such a working medium also is designated as an organic Rankine cycle (ORC).
The condenser 7 is likewise designed differently in the two embodiments. For the embodiment of FIG. 2, an air cooling of the condenser 7 by means of the cooling surface 14 and a cooling-air flow 15 is provided instead of a liquid cooling.
In the embodiment of FIG. 2, heat absorption from heat producing components of the computer system is carried out indirectly by means of the first heat exchanger 10 and the second heat exchanger 11, which together with the cooling-medium pump 12 form a cooling circuit 13. In this connection, the heat exchangers 10 are arranged in parallel in the cooling circuit 13. In order to ensure a sufficient flow rate of cooling medium through the individual heat exchangers 10, a control valve can be provided ahead of each heat exchanger. Said control valve can control, for example, the flow rate to a predetermined value. A provision also can be made to control the flow rate as a function of the temperature of the heat exchanger 10 or of the corresponding processor 1.
Such a construction can easily achieve a thermal coupling of several of the heat producing components to an evaporator 2. An additional advantage of this arrangement is that commercially available cooling elements for liquid cooling that are usually used in the server field can be employed as the first heat exchanger 10. This also enables a possibly aggressive working medium in the working medium circuit 3 to be spatially separated from the computer system, as indicated by a dashed line in FIG. 2. For example, one evaporator 2 mounted outside of the servers can be provided per server rack, with this being connected to the processors 1 of the server by means of one or several second heat exchangers 11 and one or several cooling circuits 13 and a corresponding number of first heat exchangers 10.
An additional embodiment of a cooling apparatus for a computer system is depicted In FIG. 3. Reference numbers identical to those in FIGS. 1 and 2 likewise denote identical or equally acting elements.
As in the embodiment of FIG. 2, two processors 1 are also in respective direct thermal contact with a first heat exchanger 10. The first heat exchangers 10 form, together with a second heat exchanger 11 and a cooling-medium pump 12, a closed cooling circuit 13. An evaporator 2 is directly thermally coupled to the second heat exchanger 11. The evaporator 2 forms, together with a condenser 7, an additional evaporator 16, an absorber 18 and a condensate pump 9, a closed working medium circuit 3. The condenser 7 and absorber 18 are thermally coupled to a cooling-water flow 8. The additional evaporator 16 is in thermal contact with a cooling circuit 17. Returns 19 are provided from the evaporator 2 to the absorber 18 and from the absorber 18 to the additional evaporator 16.
As in the aforementioned embodiments, in the embodiment of FIG. 3 evaporation heat of a working medium is also used in an evaporator 2 to drive a thermodynamic cycle using the waste heat of the processors 1 of a computer system. However, the thermodynamic cycle serves here not for mechanical energy production but for cold production by means of an absorption refrigerator. Employed for this purpose is a working medium having at least two components dissolved into one another, e.g., a mixture of ammonia and water or lithium bromide dissolved in water. With an absorption refrigerator, the evaporator 2 frequently is also designated as an ejector.
The working medium is partially evaporated in the evaporator 2, with one of the components of the working medium being concentrated in the vapor phase. Said component (ammonia for an ammonia/water mixture, water for a lithium bromide/water mixture) is also referred to as the cooling medium. In the remaining liquid phase the other component of the working medium will correspondingly be present in a concentrated manner. This liquid phase of the working medium is conducted back to the absorber 18 by means of the return line 19, depicted in FIG. 3 by a solid line. The cooling medium-rich vapor phase is subsequently cooled in the condenser 7 and liquefied. The heat accumulated in this connection is absorbed by the cooling-water flow 8 and can be used for heating purposes and/or for hot water production.
The cooling medium-rich working medium is then evaporated in an additional evaporator 16 at low pressure, wherein a choke element can be provided in order to lower the pressure. Due to the low pressure, evaporation heat is absorbed from the cooling circuit 17 at such a low temperature level that the cooling circuit 17 can be employed in order to air-condition a room. Waste heat of the computer system can be used in this way directly, i.e., without a detour via mechanical energy, in order to air-condition the rooms in which the computer system is operated. The overall primary energy requirement for operating the computer system can thus be lowered.
After evaporation, the cooling medium-rich working medium is in turn condensed in the absorber 18 and dissolved in the cooling medium-poor working medium conducted back from the evaporator 2. The condensation heat and heat of solution emitted in this connection is conducted away by the cooling-agent stream 8. In this connection, an auxiliary-medium cycle having an auxiliary medium, e.g., hydrogen gas in the case of an ammonia/water mixture as the working medium, can be additionally provided. The optional return 19 depicted in FIG. 3 with a dashed line then serves to return the auxiliary medium from the absorber 18 to the additional evaporator 16.
The working medium is subsequently again conducted to the evaporator 2 from the absorber 18 with the aid of the working medium pump 9, closing the cycle.
For all three embodiments, the selection of a suitable working medium and a suitable dimensioning of the components can be used to achieve an efficient utilization of waste heat even for a relatively low temperature of the evaporator 2 in the range of 60-100° C. At these temperatures, components of a computer system, processors in particular, can be operated without any danger of error functions and damage.
Features of the embodiments can, of course, be combined with one another in other ways. For example, an indirect heat transmission from the processors 1 to the evaporators 2 by means of the cooling circuit 13 also can be employed in combination with the Kalina cycle shown in FIG. 1, or an air-cooling of the condenser 7 indicated in connection with FIG. 2 also can be employed with the other embodiments.

List of Reference Numerals

1 Processor
2 Evaporator
3 Working medium circuit
4 Separator
5 Steam turbine
6 Generator
7 Condenser
8 Cooling-water flow
9 Condensate pump
10 First heat exchanger
11 Second heat exchanger
12 Cooling-medium pump
13 Cooling circuit
14 Cooling surface
15 Cooling-air flow
16 Additional evaporators
17 Cooling circuit
18 Absorber
19 Return

Claims

1. A cooling apparatus for a computer system, comprising an evaporator for a working medium, wherein the evaporator can be thermally coupled to at least one heat producing component of the computer system and the cooling apparatus is a heat engine.

2. The cooling apparatus according to claim 1, wherein the heat engine comprises a steam turbine.

3. The cooling apparatus according to claim 2, wherein a generator is coupled to the steam turbine for generating electricity.

4. The cooling apparatus according to claim 1, wherein the working medium comprises organic components and has a low boiling temperature.

5. The cooling apparatus according to claim 1, wherein the working medium comprises a mixture of ammonia and water.

6. The cooling apparatus according to claim 5, wherein a separator is provided downstream of the evaporator to separate a vapor phase and a liquid phase of the working medium, and the cooling apparatus is arranged such that the vapor phase is supplied to a steam turbine and, after expansion in the steam turbine, is again merged with the liquid phase.

7. A cooling apparatus for a computer system, comprising an evaporator for a working medium, wherein the evaporator can be thermally coupled to the at least one heat producing component of the computer system and the cooling apparatus is an absorption refrigerator.

8. The cooling apparatus according to claim 7, further comprising an additional evaporator that is thermally coupled to a cooling circuit of an air conditioning system.

9. The cooling apparatus according to claim 7, wherein the working medium comprises a mixture of ammonia and water.

10. The cooling apparatus according to claim 7, wherein the working medium contains lithium bromide.

11. The cooling apparatus according to claim 1, wherein the evaporator is directly connected to the at least one heat producing component through a contact surface.

12. The cooling apparatus according to claim 1, wherein the evaporator is connected to the at least one heat producing component through a heat conducting element.

13. The cooling apparatus according to claim 12, wherein the heat conducting element comprises a heat pipe.

14. The cooling apparatus according to claim 1, wherein the evaporator is connected to the at least one heat producing component through a heat transporting arrangement.

15. The cooling apparatus according to claim 14, wherein the heat transporting arrangement comprises at least a first heat exchanger and a second heat exchanger coupled thereto, wherein the at least one first heat exchanger is directly connected to the at least one heat producing component, and the second heat exchanger is thermally connected to the evaporator.

16. The cooling apparatus according to claim 7, wherein the evaporator is directly connected to the at least one heat producing component through a contact surface.

17. The cooling apparatus according to claim 7, wherein the evaporator is connected to the at least one heat producing component through a heat conducting element.

18. The cooling apparatus according to claim 17, wherein the heat conducting element comprises a heat pipe.

19. The cooling apparatus according to claim 7, wherein the evaporator is connected to the at least one heat producing component through a heat transporting arrangement.

20. The cooling apparatus according to claim 19, wherein the heat transporting arrangement comprises at least a first heat exchanger and a second heat exchanger coupled thereto, wherein the at least one first heat exchanger is connected directly to the at least one heat producing component, and the second heat exchanger is thermally connected to the evaporator.

21. A method for cooling at least one heat producing component of a computer system, wherein

a working medium is at least partially evaporated in an evaporator by the heat produced, and

a vapor phase, arising during evaporation of the working medium, is expanded in a steam turbine to produce an output of mechanical power.

22. The method according to claim 21, wherein the output from the steam turbine is used to drive a generator for generating electricity.

23. A method for cooling at least one heat producing component of a computer system, wherein

a working medium is partially evaporated in an evaporator by the generated heat,

a vapor phase of the working medium arising during the partial evaporation is cooled and condensed, and

the condensed working medium is evaporated in an additional evaporator while absorbing evaporation heat.

24. The method according to claim 23, wherein the evaporation heat is removed and used to air condition the surrounding air.