This paper describes a technique to obtain two-dimensional surface temperatures inside an insulating glazing (IG) unit. The method is based on the use of liquid crystal sheets that are photographed with a digital camera. The photographs are then processed using a calibrated computer program for conversion from color to temperature. The technique was used to measure temperatures on surface no. 3 of an IG unit (i.e., surface facing the air-filled cavity of the warm-side pane) with a vertical aspect ratio of 21.3. The IG unit was inserted in a wood-frame window and subjected to winterlike conditions in an environmental chamber with corresponding Rayleigh numbers of »14,500. The first part of the paper is devoted to the calibration procedure. Then it is shown that the proposed technique can give excellent qualitative two-dimensional thermal fields. In addition, it can give relatively accurate quantitative temperature measurements at the pixel level (1 mm x 1 mm in the present experiment) especially near the bottom of the IG unit where the uncertainty is ±0.25°C. The technique could potentially be employed, in conjunction with other measuring techniques, to evaluate inside film coefficients and to study condensation resistance.

Units: SI