The single-blow transient test technique using pulse change inlet condition with optimized pulse width and matching time

摘要

Compact heat exchanger is a kind of advanced heat transfer equipment with small size and high efficiency. It has wide application prospects in industry. However, due to the highly compact structure, it is difficult to measure the wall temperature of heat transfer surface by traditional test methods. For measuring the thermal performance of compact heat transfer surfaces more accurately, a single-blow transient test technique using pulse change inlet condition with optimized pulse width and matching time is developed. By turning on and off the electric air heater, the pulse change in the inlet temperature can be realized and is fitted as the superposition of a positive and a negative exponential function with a time shift. In order to reduce the effect of the uncertainty of temperature measurement, the optimum pulse width and optimum matching time is obtained by numerical calculations. By means of the newly extended test method, the heat transfer performance of a parallel-plate test core is measured and compared with the results from the literature. The analysis shows that the present pulse change technique considering the optimal pulse width and matching time have to be considered for the heat transfer surfaces with NTU > 4.5 to reduce the uncertainty in temperature measurement. The experimental results are in good agreement with those given in the literature.