Boundary condition influences on the effective area of a local heat flux probe

Active heat flux probes are used to quantify the convection boundary condition in heat transfer environments. In previous studies, the probe response has been documented under ideal conditions, namely an isothermal sensor surface mounted in an isothermal body of equal temperature. In this paper, the influence of the thermal boundary conditions around the perimeter of an active isothermal heat flux probe is examined during steady state operation while one surface of the sensor is exposed to an imposed convection boundary condition. A two-dimensional numerical model is developed and used to simulate the behaviour of the local thermal field. The results show that the influence of the perimeter boundary conditions alters the static calibration of the probe. These effects decrease as convection heat transfer is increased and are predictable and linear. However, design geometry changes known to increase the sensitivity of the probe to the convection boundary conditions also are found to increase the sensitivity to the perimeter boundary conditions. This sets up a design trade-off. Under high-convection conditions, such influences are negligible and the probe calibration remains essentially constant.