Thin-film thermocouples for rapid measurement of transient surface temperature in cryogen spray cooling
Pulsed cryogen spray cooling (CSC) has become an effective method to protect the epidermis from non-specific thermal injuries in laser treatments of vascular malformation such as port wine stains. Cooling experiments with a skin phantom are usually conducted to quantify the heat transfer of CSC from a skin surface. Due to the high cooling ability of CSC and poor thermal conductivity of the skin phantom, the skin surface usually experiences a fast variation of the surface temperatures during CSC. It is therefore desirable to have a fast response surface thermal sensor to measure such temperature change. In traditional methods, commercial thermocouples of round or plate-shaped joints are buried on the surface or within the skin phantom in the experiments and usually give a poor response of the surface temperature. In this study, a fast response, thin film thermocouple (TFTC) of type T on a skin phantom made of epoxy or plastic glass is developed. The thin film thermocouple is manufactured by the Magnetron Spurting technique with a precise control of the compositions of Cu and Ni as well as the film thickness from 0. 5 to 2 microns. A 0. 05 micron thick of SiO2 protection layer is deposited on the TFTC as protection. Careful calibrations of TFTCs indicate that the thermoelectric property of the TFTCs agrees well with that of standard T-type thermocouples. The time constant of the TFTCs is about 1. 2 ms, determined by pulsed laser heating experiments. Due to its small thermal capacity, the TFTC is sensitive to environmental fluctuations and the original temperature data show large noises. A low pass Butterworth (BW) filter is then introduced in the data acquisition system to remove such noises. Effect of the cut-off frequency and sample rate on the filtered temperature data has also been investigated and optimal cut-off frequencies and sample rates are recommended. A typical result for the temperature variation of the epoxy phantom surface during CSC is presented to illustrate the effectiveness of our TFTCs.
flashingcryogen spray coolingthin film thermocouplesurface temperature measurement
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