DESIGNING WITH LOW-TEMPERATURE PHASE CHANGE
MATERIALS (PCM's)

For  PCM Prices check: www.pcm-solutions.com

MJM Engineering can design low-temperature applications using phase change materials (PCM).  These materials allow to keep low temperatures (from 240 K to 270 K) easily and at reasonable costs.   Transient power dissipation thermal management is substantially improved if a PCM is used to store "cold" at down times (with a undersized cryocooler), and then use "it" during power on situations. In other words, the user can install a smaller-capacity cryocooler if the power usage is transient.

MJM Engineering Co also sells bulk low temperature PCM's.   Please see below for a list of the PCM's available.

Bulk PCM, with additives for long life, for all types of applications can be purchased in bulk or we can design systems that will incorporate them such as a cryo-cooled High Speed PC. The following table shows general information about the PCM available for Bulk purchase:

E-mail us at:  info@mjm-engineering.com for prices and more info.

ELECTRONIC CHIP (CPU) APPLICATIONS

The cooling of CPU chips such as the Pentium^TM and ALPHA^TM chips to cryogenic temperatures has been proposed and demonstrated to increase substantially their speeds. By cryogenic temperatures is meant temperatures from around -40 C all the way down to 270 K; depending on the level of power dissipation and complexity desired by the supercomputer system designer. Different technologies have been proposed to implement cryogenic cooling such as pool boiling of MCM modules where high power chips are housed close together using liquid cryogens, direct cooling of chips using micro-sterling based cryocoolers such as pulse-tube refrigerators, thermoelectric coolers such as those used in the cooling of infrared sensors, and others. All of these technologies have in common complex cooling delivery systems in addition to the modification of the target chip in order to be properly cooled.

One further challenge to the thermal management of high power electronics to cryogenic temperatures is the density or number of heat generation sources to be cooled. When the designer is faced with cooling one or two 50W chips to 80 K, the equipment available, despite its costs and complexity, is being manufactured by a few companies around the world and are specifically tailored to low heat removal rates. In cases when the power dissipations are approaching 500 to 1000 W, cryogenic systems to generate the cooling load are approaching industrial size systems such as gas liquefaction systems for 70-80 K temperature range and industrial vapor-compression refrigeration systems for the -30 to -50 C temperature range.

The limitations are not confined to heat removal capacities. Volume restrictions are a very important consideration. The push for MCM packaging for cryogenically cooled computer chips is just one manifestation of the problem. MCM packaging reduces the distance between the CPU chip and its peripherals, thus increasing the speed of the system. Furthermore, reduction in the space between components also reduces signal propagation delays and distortion --a fact very important in telecommunication systems. Unfortunately, reduced volume packaging imposes very stringent requirements on the cooling system at room temperatures, and extraordinary requirements at cryogenic temperatures. Cryocooling systems take up space when existing technology is applied to single chips.

MJM Engineering Co has developed novel technologies to cryogenically cool high power computer chips such as the Pentium^TM and ALPHA^TM chips in an efficient, low cost, low volume manner. This involves the unique combination of individual technologies that separately have been proven to be effective in the thermal management of electronic systems, but together might solve the problem of cooling high power components to cryogenic temperatures . We have developed and designed a cryogenic thermal management system capable to remove high heat loads (from 500 W to 1500 W) in relatively small volumes (1 cubic foot or less) that feature Pentium^TM and ALPHA^TM CPU chips.

Typical Requirements:

Power Dissipation: 20 W (nominal) per chip or 50 W (max) per chip

Total System Power Dissipation: As many chips as needed (12 typical)

Temperature of Operation:

a) High Temperature : 233 K (-40 C)

b) Low Temperature: 50 K (-223 C)

TELECOMMUNICATIONS APPLICATIONS

In many telecommunications applications, switching/signal processing equipment is commonly placed in outdoor cabinets. The housed equipment generates heat that must dissipated while keeping the air temperature inside the cabinets within prescribed limits for optimum performance. Furthermore, the enclosure, being outdoors, receives full solar irradiation, creating an extra heat load that must be handled.

In many cases the temperature inside the cabinets can remain higher than ambient, but in many applications, such as cable TV and cellular phones, the temperature inside the cabinets must be kept between 20 to 30° C to maintain high reliability. This clearly demands refrigeration units to be installed as part the equipment. However, air conditioning equipment is bulky, expensive to maintain and, must be ozone friendly.

Thus, the push for higher processing speeds and capabilities in electronics and telecommunications systems with increasing clarity and reduced distortion and noise are making equipment designers look for highly innovative technologies. Higher speeds mean higher power dissipation densities; and cooling equipment (especially superconductors) to cryogenic temperatures appears to be one of the promising technologies. However, achieving cryogenic cooling is not simple and requires sophisticated, special equipment

Novel refrigeration systems derived from currently used low-temperature cryogenic cycles are being proposed and developed. These new systems will in all likelihood occupy less space than currently installed units, and some may use air as the working fluid --which will eliminate all environmental concerns. These systems are brought about by a push in installing equipment that works best at low temperatures down to cryogenic levels (0 C to -100/200 C) since reliability and power consumption reductions are enhanced.

MJM Engineering has developed systems to satisfy the current and future needs for cooling telecommunications equipment at low temperatures for indoor and outdoor applications, and the corresponding design and development issues related to successful building of thermal management systems. A typical cryocooler system development is outlined below.

Typical Development Plan of a Cryocooler System for an Outdoor Telecommunications Cabinet

The work proposed for the development of the proof of concept of the Cryocooler System for telecommunication applications can be broken down into two general categories: system level and detailed (individual) calculations. A general list of items needed to execute for the completion of this part are shown below.

SYSTEM LEVEL ACTIVITIESM

System level studies will be conducted on at least 2 different concepts. These concepts will be based on open cycle systems using air (cabinet gas) as the working fluid. These studies will allow for proper cost calculation by the client. Close coordination will allow modeling of equipment that is available in the market at competitive costs and/or can be manufactured at competitive costs. These will be parametric (which will include permutation of system components such as number of heat exchangers, etc.) studies which will comprise:

DETAILED FLOW AND HEAT TRANSFER STUDIES (INDIVIDUAL)

Detailed studies on each individual component will be conducted on the 2 concepts described above. These concepts will be based on open cycle systems using air (cabinets gas) as the working fluid. These studies will include literature search, literature analysis, analysis, parametric computer modeling of individual components, and some design and development. These studies will allow for proper cost calculation. Close coordination will allow modeling of equipment that is available in the market at competitive costs and/or can be manufactured at competitive costs.

OUTLINE OF THE PLAN

0.0 Outline Cryocooler Project--Development Plan Creation, Preliminary Literature Search and Review, and Miscellaneous Preparatory Work.

1.0 Cryocooler System/Component Analysis--Part (Literature Review and Analysis)

1.1 First Law Thermodynamic System Studies

1.1.1 Regenerative, Closed Cycles (i.e. Stirling, etc)

1.1.2 Recuperative, Closed Cycles (i.e., Linde-Hampson, etc.)

1.2 Second Law Thermodynamic System Studies (irreversibility and entropy generation)

1.2.1 Regenerative, Closed Cycles (i.e. Stirling, etc)

1.2.2 Recuperative, Closed Cycles (i.e., Linde-Hampson, etc.)

1.3 Thermodynamic Studies of Cabinet and Cryocooler Systems

2.0 Cryocooler System/Component Analysis--Part II (Literature Review and Analysis)

2.1 Thermodynamic Component Analysis and Modeling for:

a) Heat Exchangers
b) Pressure Expanders (exchangers)
c) Compressors
d) Flow Delivery Systems (piping, ducting, nozzles, etc.)

2.1.1 First Law Analysis

2.1.2 Second Law Analysis

2.2 Heat Exchanger Analysis and Modeling

2.3 Pressure Expanders (exchangers) Analysis and Modeling

2.4 Compressors Analysis and Modeling

2.5 Flow Delivery Systems (piping, ducting, nozzles, etc.) Analysis and Modeling

2.6 Design Review #1

3.0 Cryocooler System Definition--Part I

3.1 Definition of Cryocooler System--Outline

3.2 Design, Development, and Specification of Heat Exchangers

3.3 Design, Development, and Specification of Pressure Expander

4.0 System Definition--Part II

4.1 Design, Development, and Specification of Flow Delivery System and Devices

4.2 Design Review #2

5.0 Prototype Construction Supervision and Oversight

5.1 Individual Components

5.2 System

6.0 Prototype Testing

6.1 Testing of Individual Components

6.2 System Testing

7.0 Prototype Evaluation

7.1 Evaluation of Individual Components

7.2 Evaluation of Cryocooler System

7.3 Prototype Review #1

8.0 Final Design Recommendation/Design Completion

8.1 Recommendations of Changes

8.2 Final Design

9.0 Pilot Production

10.0 Field Testing

10.1 Design Review #3

11.0 Production Evaluation from Field Testing

Some References

Bar Cohen, A., (1991), "Thermal Management of Electronic Components with Dielectric Liquids," in 3^rd ASME/JSME Thermal Engineering Joint Conference, Reno, NV, pp. 15-38

Bland, T.J, Ciaccio, M.P., Downing, R.S., and Smith, W.G., (1990) "The Development of Advanced Cooling Methods for High Power Electronics," SAE Paper 901962, Proc. Aerospace Technology Conf. and Expo., Long Beach, CA, October 1-4.

Herold, K.E., Sridhar, S., and Hu, S., (1992) "Cooling of Electronics Boards Using Internal Fluid Flows," Proceedings for the First Joint ASME/JSME Conference on Electronic Packaging, Milpitas, CA, April 9-12, 1992, pp. 285-290

Howard, A.H., and Peterson, G.P, (1995) "Investigation Of A Heat Pipe Array For Convective Cooling," Journal of Electronic Packaging, Transactions of the ASME, vol. 117, nr. 3, (Sep, 1995)

Marongiu, M.J., Kusha, B., and Watwe, A., (1997) " Studies On The Enhancement Of Microchannel Heat Sinks With Heat Pipes," 2nd Pan Pacific Microelectronics Symposium, January 29-31, 1997, Maui, Hawai'i.

Marotta, E.G., Lambert, M.A., and Fletcher, L.S., (1994), "Evaluation of Nonmetallic Coatings and Films for Thermal Control Applications," J. of Thermophysics and Heat Transfer, vol. 8, nr. 2, April-June 1994, pp.349-357

Peterson, G. P.; Wu, D. (1990) " Investigation of a Tapered Artery Micro Heat Pipe for Cooling Ceramic Chip Carriers," Texas A&M University, Mech. Engineering Dept., Final Report, Jan 89-Feb 90

Silverstein, C.C., (1992) Design and Technology of Heat Pipes for Cooling and Heat Exchange, Hemisphere Publishing, Washington DC

Schrage, D.S., (1990) "On The Use Of A Small-Scale Two-Phase Thermosiphon To Cool High-Power Electronics," Presented at AIAA/ASME Thermophysics and Heat Transfer Conference Seattle, WA, USA, Jun 18-20 1990

Yamamoto, H. (1991), "Multichip Module Packaging for Cryogenic Computers", IEEE paper CH 3006-4/91/0000, pp. 2296-2299.IVITIES