Experimental investigation on flow boiling characteristics in offset strip fin channels under different sloshing conditions

Abstract

In order to reveal the effects of sloshing movement on the performance of the plate-fin heat exchangers applied in floating liquefied natural gas platforms and environment control system of aircrafts, the flow boiling characteristics in offset strip fin channels of plate-fin heat exchangers under different sloshing conditions were investigated experimentally, covering rolling, pitching and swaying movements. The results show that, the rotational type movements enhance the transient heat transfer coefficient by a maximum of 21.1% at low vapor quality condition and weaken the transient heat transfer coefficient by a maximum of 27.7% at high vapor quality condition, while the transitional type movements enhance the heat transfer at high vapor quality. Fast Fourier transform method was used in the spectrum analysis of flow instabilities, and there are two peak frequencies caused by the inlet fluctuations, the distribution of the liquid phase and the enhanced turbulence. The time-average factors were proposed to evaluate the average heat transfer performance during the sloshing period. The ranges of sloshing time-average factors for rolling, pitching, and swaying conditions are 0.861 ∼ 1.079, 0.923 ∼ 1.061, 0.834 ∼ 1.064 and 0.994 ∼ 1.090, respectively. As the mass flux and sloshing period increase, the time-average factors trend to 1.0, and increase at the transitional sloshing movement. With the increasing amplitude, the time-average factors increase from 1 to a maximal value of 1.093. The correlations to predict the time-average two-phase heat transfer coefficients under rolling, pitching, swaying, and heaving conditions for offset strip fins have been developed, and the deviations are within ± 10 %.