Heat flux measurement techniques

Heat flux measurement is used in the field of fluid mechanics and heat tran sfer to quantify the transfer of heat within systems. Several techniques ar e in common use, including: differential temperature sensors such as thermo pile, layered resistance temperature devices or thermocouples and Garden ga uges; calorimetric methods involving a heat balance analysis and transient monitoring of a representative temperature, using, for example, thin-film t emperature sensors or temperature sensitive liquid crystals; energy supply or removal methods using, for example, a heater to generate a thermal balan ce; and, finally, by measurement of mass transfer which can be linked to he at transfer using the analogy between the two. No one method is suitable to all applications because of the differing considerations of accuracy, sens itivity, size, cost and robustness. Recent developments including the widespread availability and application o f thin-film deposition techniques for metals and ceramics, allied with adva nces in microtechnology, have expanded the range of devices available for h eat flux measurement. This paper reviews the various types of heat flux sen sors available, as well as unique designs for specific applications. Critic al to the use of a heat flux measurement technique is accurate calibration. Use of unmatched materials disturbs the local heat flux and also the local convective boundary layer, producing a potential error that must be compen sated for. The various techniques in common use fbr calibration are describ ed. A guide to the appropriate selection of a heat flux measurement techniq ue is provided according to the demands of response, sensitivity, temperatu re of operation, heat flux intensity, manufacturing constraints, commercial availability, cost, thermal disturbance and acceleration capability for vi brating, rotating and reciprocating applications.