Heat flux measurement devices (heat flux meters) are designed to obtain experimental information about the heat flux.
The majority of heat flux meters is based on the method of an extra wall which was first formulated by E. Schmidt at the beginning of the present century. Its essence is that the extra wall is located on the path of a measured heat flux. When this wall is permeated by the flux to be measured, temperature gradients and differences appear whose values are proportional to the flux. By measuring these gradients or differences, the flux can be determined.
The most successful group of sensing element designs, the functions of the extra wall material and temperature difference meter are combined. Thus, in the design of the heat flux meter with a three-layer extra wall, the intermediate layer is the intermediate thermoelectrode of a differential thermocouple whose e.m.f. is measured across the end layers.
To increase the sensitivity, separate thermometric elements contain in series a generated thermometric signal and in parallel a measured heat flux. The modern technology allows up to 2000 elements to be placed per 1 cm2. Means are available to increase the packing density in order to elevate the sensitivity. Battery devices with an area of about 100 cm2 allow effective measurement of heat fluxes, as low as 10−3 W/m2. The upper limit of the measured heat flux density exceeds 107 W/m2. Heat flux meters are thus available to cover the range 10−3 to 107 W/m2 for temperatures 4-1000 K. At room temperature, the standard error is not beyond ±1.5% of the measured quantity. The error can approach ±7% at the boundaries of the mentioned temperature range.