A Novel Transient Heater-Foil Technique for Liquid Crystal Experiments on Film-Cooled Surfaces

Abstract

A novel transient measurement technique has been developed for determining the heat transfer characteristics in the presence of film cooling (heat transfer coefficient and adiabatic film-cooling effectiveness). The method is based on a transient heater foil technique, where a non-homogeneous surface heat flux is applied to the test surface. A regression analysis of multiple transient liquid crystal experiments is used to obtain the heat transfer characteristics. The method introduced here has the advantage that the (often not known) heat flux distribution at the surface is not needed for the analysis of the measured data. The method is used to study the influence of several heater foil configurations on a flat plate with film cooling, elucidating the effect of different thermal boundary conditions on film-cooling performance. The obtained data is also compared to results presented in literature and good agreement is found.

Flow and heat transfer of confined impingement jets cooling using a 3-D transient liquid crystal scheme

“…More complete procedures are employed in the three-temperature film cooling problem such as proposed by Vogel et al [18], and Chambers et al [19]. Theoretically, the following conditions need to be satisfied for employing the analytical 1-D transient solutions: (a) 1-D heat conduction, (b) imposing an instantaneous convective heating or cooling boundary condition on the surface, and (c) semi-infinite depth of the solid.…”

Accuracy improvement of the transient heater foil technique for heat transfer tests: preliminary results

“…The transient liquid crystal technique previously applied for impingement studies at GTT used mainly the heater mesh technique [7,8]. A variation in form of using the heater foil was developed and applied in various contexts [4,6,9]. At time t=0, instead of causing a step change in fluid temperature an electric current is passed through the heater foil, which generates a power Q that provides a constant local heat flux q=Q/A, where A is the foil area.…”

“…Heat is added to the system either by heating the flow (heater mesh technique) or by applying a heat flux via Joule heating with a thin conductive foil applied to the surface (heater foil technique). The latter is widely used in the frame of film cooling to determine the film cooling effectiveness [4], but has seen applications also for the determination of the heat transfer coefficient [5].…”

Thermocouple thermal inertia effects on impingement heat transfer experiments using the transient liquid crystal technique

“…If the thermal conductivity of the models, where the liquid crystals are sprayed, is sufficiently low, then the wall temperature response is limited to a very thin layer near the wall surface (semiinfinite body assumption), while the lateral conduction can be assumed negligible. These assumptions are accurate when the thickness of the model is chosen according to the following equation [25]:…”