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# HEAT TRANSFER COEFFICIENT MEASUREMENT INSTRUMENT

IP.com Disclosure Number: IPCOM000005919D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-15
Document File: 2 page(s) / 100K

Motorola

## Related People

James Andrews: AUTHOR

## Abstract

A heat transfer coefficient measurement instrument is used to directly measure the average surface heat transfer coefficient h for electronic packages that are cooled by convection and radiation. The equation below is typically used to define h which is equal to the sum of the convection and radiation heat transfer coefficients.

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MOTOROLA Technical Developments Volume 10 March 1990

HEAT TRANSFER COEFFICIENT MEASUREMENT INSTRUMENT

by James Andrews

A heat transfer coefficient measurement instrument is used to directly measure the average surface heat transfer coefficient h for electronic packages that are cooled by convection and radiation. The equation below is typically used to define h which is equal to the sum of the convection and radiation heat transfer coefficients.

q = h A (Tw - Ta). (wan@

q is the surface heat loss. (watts) A is the surface area normal to direction of heat flow. (cm? Tw is the wall temperature.

Ta is the local adiabatic fluid temperature. {;I;

The instrument consists of two equally powered electronic components mounted on a printed circuit (PC) board or other flat fixture as shown in FIG. 1. A flat electrical heater is attached to the PC board. Each of the components contains both a means for applying electrical power to be dissipated as heat, such as a resistor and a diode whose forward voltage has been calibrated at a constant current as a function of its temperature.

Thermocouples, Tbl and Tb2, are attached to the PC board in the center of each component package foot print on the side that the components are mounted. Thermocouples, Tel and Tc2, are attached externally to the center of each component case on the side facing away from the PC board. A single thermocouple, Ta, is positioned to measure the adiabatic air temperature. Therefore, it must be located such that its reading is not affected by heat from either of the two component packages.

Both components along with thermocouples or other temperature sensors can be formed from thin film depositions and enclosed along with the board and board heater into a thin flat measurement head. Both components can be ex- posed to the same side of the board, or the components can be exposed to opposite sides of the board with the require ment that both sides see the same cooling conditions.

The instrument is oriented such that both components are exposed to identical rates of air flow. Constant sense currents are applied to the temperature sensing diodes in packages 1 and 2...