Investigation of Two-Phase Frictional Pressure Drop and Thermal Entrance Length in a Minichannel Helical Heat Exchanger

Experimental investigations are conducted to determine the two-phase frictional pressure drop of refrigerant R134a and the thermal entrance length for flow in a helically coiled mini-tube of 2mm inner diameter. The objective of this work is to study the effect of the tube curvature on the frictional pressure drop in two-phase flow as well as the thermal entrance length in laminar single phase flow. The two-phase frictional pressure drop is investigated through flow boiling of the refrigerant under uniform wall temperature boundary conditions. A generalized correlation is proposed to predict the single phase and two-phase frictional pressure drop through the coiled tube. A large set of experimental data is collected to evaluate the prediction performance of the proposed two-phase correlation. The results of the prediction are fairly good when compared with the measured pressure drop from experiments. A Computational Fluid Dynamics (CFD) analysis is also performed to compare with the thermal entrance length study from experiments. The results from the experimental analyses and CFD are seen to be in good agreement. It is found that the thermal entrance length for the coiled tube is 27–103.3% larger than a straight tube of equal length and cross-section.