Heat flux measurement techniques

Abstract

Heat flux measurement is used in the field of fluid mechanics and heat transfer to quantify the transfer of heat within systems. Several techniques are in common use, including: differential temperature sensors such as thermopile, layered resistance temperature devices or thermocouples and Gardon gauges; calorimetric methods involving a heat balance analysis and transient monitoring of a representative temperature, using, for example, thin-film temperature sensors or temperature sensitive liquid crystals; energy supply or removal methods using, for example, a heater to generate a thermal balance; and, finally, by measurement of mass transfer which can be linked to heat transfer using the analogy between the two. No one method is suitable to all applications because of the differing considerations of accuracy, sensitivity, size, cost and robustness. Recent developments including the widespread availability and application of thin-film deposition techniques for metals and ceramics, allied with advances in microtechnology, have expanded the range of devices available for heat flux measurement. This paper reviews the various types of heat flux sensors available, as well as unique designs for specific applications. Critical 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 compensated for. The various techniques in common use for calibration are described. A guide to the appropriate selection of a heat flux measurement technique is provided according to the demands of response, sensitivity, temperature of operation, heat flux intensity, manufacturing constraints, commercial availability, cost, thermal disturbance and acceleration capability for vibrating, rotating and reciprocating applications.

New Heat Transfer Correlation for an HCCI Engine Derived from Measurements of Instantaneous Surface Heat Flux

“…As long as the size of the hot junction is small enough, in this case its diameter is only 1.52 mm, the temperature between the ends of the center wire and the outer tube may be neglected [24]. The penetration of the thermal pulse into the surface is small in comparison with the relevant surrounding dimensions (αt/L 2 <<1) and a one-dimensional transient heat flux analysis can be used [21,22,23,24]. Theoretical analysis based on finite element method [22], and experiments in the dynamic test rig [16] indicate high-accuracy of instantaneous temperature measurements (~98%), good ability of the probe to capture instantaneous rise of heat flux, but also the potential for overpredicting the peak heat flux due to dynamic phenomena within the probe i.e.…”

“…Many previous papers have suggested their own formulas derived using different equilibrium programs applied to the specific fuel-air mixture composition [28,32,37]. As an example, the linear relationship proposed by Gatowski et al [21] is shown in Figure A-2. However, previously proposed correlations for typical SI engine conditions are not suitable for application to HCCI because the engine runs very lean with the fraction of internal residual up to 50%.…”

“…Ignoring the effect of A/F for our operating range results in an error of up to +/-0.005 for gamma, or only 1.0% of final gross heat release. Thus, a third-order polynomial curve-fit is found at the median A/F point and applied to the whole range: The difference between the curve fit and the classic linear correlation from literature [21] is quite significant, hence mandating the use of the new correlation for HCCI engine analysis. The third term of equation a2shows the heat transfer rate between gas and wall.…”

Online Tempercurve Analysis of Praline Products with the Objective of Cooling Process Optimization

“…,b; Childs et al . ). The additional term describes the crystallization event approximately by combining a simple kinetic factor with a temperature effect.…”

Theoretical Stability Analysis for Inverse Heat Conduction Problems Using the Condition Number

“…Knowledge of the surface heat flux density is a crucial factor in design and development of the respective thermal protection system. Common state-of-the-art commercial heat flux density sensors require installation on the measured surface [1]. Thus, their operating range is limited by environmental loads and surface interaction effects.…”