Thin Cavity Cooling of Electronic Circuitry

June 1, 2012

Anovel tested technology for cooling electronic circuitry is also useful in many other industries. The method is called “Thin Cavity Fluidic Heat Exchanger”(TCFHE). Technology details can be viewed at the U.S. Patent and Trademark Web site, at application 20100078155.

The TCFHE is a simply constructed, small-volume, high-performance, and effective method for cooling critical electronic devices at the chip, board, module, and system levels. Its high thermal performance originates from a very-high-velocity air flow, a very thin boundary layer, and high air utilization. It can efficiently and reliably cool critical regions in electronics at very low cost, in a small space, with high design flexibility, and with no concern for air leakage causing damage. The TCFHE resolves the conflict in high-speed electronics to completely seal a compact enclosure for shielding and packaging purposes while also removing high heat loads. It is technically positioned between fan and heat sink cooling methods and water cooling methods. When fan and heat sink methods or packaging constraints cannot obtain the needed thermal performance, the TCFHE is the next best choice over water cooling.

Figure 1 shows the cross-section of a basic TCFHE for a simple planar structure. It consists of a thermal load, heat transfer plate, a cavity spacer, a cover plate, a gas inlet, and a gas outlet. The cavity spacer can be a feature of the heat transfer plate or the cover plate instead of a separate item. Heat produced by the thermal load is conducted to a heat transfer plate, which can be planar, tubular, or another shape. Compressed air or other gas passes by the plate through a thin gap (

Figure 3. Exploded top view of prototype

Test data for a prototype TCFHE was taken using cavity gap thicknesses of 3, 5, 10, and 20 mils (using paper). The prototype is shown in Figure 2 through Figure 4, consisting of three main pieces. A set of graphs was produced to measure cooling performance using a load power of 3.6 Watts and an ordinary shop compressor for an air source. The cooling area was 1 inch long by 1.25 inches wide and air inlet temperature was about 29°C. The prototype was thermally insulated for worse-case test purposes using bubble wrap. Electronic pressure gauges (plenum located), flow meter, and temperature sensors (not shown) were used for air measurements.

Figure 4. Exploded bottom view of prototype

The lowest thermal resistance of 2.8°C/Watt was obtained for a cavity gap thickness of 3 mils, an air flow rate of 0.24 CFM, and an air inlet pressure of 23 PSI. This corresponds to an air velocity within the cavity of about 9,100 feet per minute (104 MPH), which is about 10 times faster than the fastest air velocity of fan and heat sink combinations. This required about 1.25 Watts of pneumatic power in the cavity. The decreasing difference between the outlet air temperature and the load temperature indicates that the incoming air heats up quickly from the load heat source. A longer cavity length or higher flow rate would not improve performance significantly. Thinner air gaps will result in even lower thermal resistance at the expense of higher required air pressure. Other prototype experiments have been close to Mach 1 with thermal resistance less than 1°C/Watt.

TCFHE technology is applicable from a micro to macro scale in power generation and distribution, defense, automotive, electronic, chemical, biomedical, and other industries. TCFHE structures can be used for air conditioning, refrigeration, combustion heaters, engines, motors, transformers, lighting, supercomputers, telecom, server farms, integrated circuits, and other devices. Building infrastructure capital and energy costs can be reduced when such products are used, due to remote location of the gas flow source and heat exhaust. The gas used could be air, nitrogen, oxygen, Freon, or similar gases at hot, room, or cold temperatures, and can be direct or alternating pressure. It could be hot gas produced by internal or external fuel combustion, or cool Freon gas from refrigeration systems. The gas flow could originate from a gas compressor, compressed gas tank, ducted fan or blower, combustion chamber, or other pneumatic source. The technology also works well with liquids.

This article was written by Dr. Steve Morra, President, Third Millenium Engineering (Plano, TX). For more information, contact Dr. Morra at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info.hotims.com/40434-401 .