Two-phase Frictional Pressure Drop Correlations Research Articles

Two-phase flow performance prediction for minichannel solar collectors

High thermal efficiencies reported in the literature for non-evacuated minichannel-based solar collectors open up the possibility to explore their operation under two-phase flow conditions for low-grade steam generation and energy storage. In this article, a mathematical model is developed to analyze the performance of a minichannel solar collector under two-phase flow conditions. Six published two-phase frictional pressure drop correlations and six two-phase heat transfer correlations are utilized, and the results compared against experimental two-phase flow data from the literature. The most accurate correlations are later on used for simulating the operation of the minichannel solar collector. Results show that for two phase flow conditions, the pressure drop is found to increase dramatically with mass flux, while the outlet quality is found to remain near saturated liquid at mass fluxes higher than 54.58 kg/m2s. In addition, inlet temperature at saturated liquid conditions and constant mass flux did not have a significant effect on outlet quality. Applications that require low-grade steam, such as food-drying, steam-cleaning, or sterilization, among others, could benefit from the two-phase flow operation of this type of collectors.

Evaluation of using two-phase frictional pressure drop correlations for normal gravity to microgravity and reduced gravity

The calculation of two-phase frictional pressure drop (TPFPD) is required by two-phase systems operating under microgravity and reduced gravity. There are a large number of correlations for the TPFPD in tubes under normal gravity. However, it is hard to find out a TPFPD correlation obtained from microgravity and/or reduced gravity conditions, and thus people have to use TPFPD correlations for normal gravity to calculate TPFPD under microgravity and reduced gravity. It is necessary to evaluate the feasibility of such practice. This paper offers a comprehensive review of the TPFPD correlations for normal gravity and an up-to-data survey of the TPFPD experimental study under microgravity and reduced gravity. There are 23 TPFPD correlations for normal gravity reviewed and 135 experimental data under microgravity obtained from the literature. These experimental data are used to evaluate the reviewed TPFPD correlations. It is found that the smallest mean absolute relative deviation (MARD) of the correlations is greater than 34%. Using TPFPD correlations for normal gravity to reduced gravity and microgravity may be acceptable for the first approximation, but correlations intended for microgravity and reduced gravity are needed and more experiments are desired to obtain more data with high accuracy.

Two-phase pressure drop in a horizontal thin annulus: Effects of channel vibration and wall gas injection

Two-phase pressure drop in a narrow horizontal annular test section was experimentally investigated, using air and water as the working fluids. The annular test section had inner and outer diameters of 7.93 mm and 9.53 mm, respectively. In one group of tests (constant quality tests) air and water were mixed before entering the test section. In another group (variable quality tests), gas was injected into the test section via the porous inner test section wall. The liquid Reynolds number varied in the Re L = 50–9000 range, and the test section exit qualities covered the 0–25% range. The measured total pressure drops were compared with the predictions of a one-dimensional model with several two-phase frictional pressure drop correlations. The pressure variations caused by flow acceleration were calculated based on the homogeneous flow assumption. The correlation of Beattie and Whalley [D.R.H. Beattie, P.B. Whalley, A simplified two-phase frictional pressure drop prediction method, Int. J. Multiphase Flow 18 (1982) 83–87] agreed reasonably well with results of both groups of tests. The effect of lateral mechanical vibrations, imposed at the center of the test section, on two-phase pressure drop was also studied, with vibration amplitudes in the 0.034–0.2 mm range, and frequencies in the range 5–400 Hz. These effects were generally small.