Evaluation of a Method for Heat Transfer Measurements and Thermal Visualization Using a Composite of a Heater Element and Liquid Crystals

Abstract

SUMMARYCommercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presentee.

Review of temperature measurement

“…Comparison of the hue values with calibration results gives the surface temperature for each pixel location. Descriptions of thermochromic liquid crystal techniques ͑ap-plication, calibration, the recording and measuring systems, and the analysis͒ have been given by Camci,118 by Hippensteele et al, 119 and by Baughn. 120 The data reduction technique for thermochromic liquid crystals was detailed by Ireland et al 121,122 The rate of thermal response of crystals, which is dependent of their viscosity, can be of the order of 5 ms to seconds.…”

Etude du transfert de chaleur convectif dans un four circulaire

“…A gold coated plastic sheet has been used as a heater in a number of recent investigations [5,17,37] to provide a nearly constant heat flux boundary condition at a test surface.…”

“…A. Hippensteele et al [17] were among the first to publish local convection heat transfer results using commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal and another sheet with a thin layer of conducting material (gold or carbon). Qualitative photographs of impingement cooling of a single jet on a flat plate, heat transfer at the end wall of a cascade, and film injection from a cylinder in cross flow were taken.…”

Preliminary Results of a Study of the Relationship Between Free Stream Turbulence and Stagnation Region Heat Transfer

“…As explained in Ref. 18 if the lighting angle and the viewing angle are not the same, there is a shift in color of the liquid crystal. Thus the simultaneous smoke and liquid crystal thermal visualization photographs can only be used to obtain qualitative heat transfer results.…”

“…18. Briefly, a heater element consisting of polyester sheet with a vapor deposited gold layer was fastened to the model surface with double sided tape.…”