Flow pattern maps, pressure drop and performance assessment of horizontal tubes with coiled wire inserts during condensation of R-600a

An experimental study is conducted to determine the pressure drop of refrigerant R-600a during forced convection condensation within a horizontal smooth pipe and spiral coil inserted pipes. Then, the system performance factor is calculated to evaluate the effectiveness of the inserts based on the pressure drop and heat transfer data. Test runs were done for varied vapor qualities between 0.05 and 0.79 and mass velocities between 115 and 365 kgm-2s-1. The test condenser was a pipe constructed from copper with the length and internal diameter of 1000 and 8.1 mm, respectively. Five coiled wires with varied wire thicknesses and coil pitches were utilized in the full length of the test section. Results revealed that the pressure drops in rough tubes were 1.51-11.97 times of those in the smooth tube. It was also observed that by decreasing the wire diameter and increasing the coil pitch, the pressure loss decreases. Results demonstrated that using inserts at higher mass fluxes results in higher performance factors. Based on the current empirical results, a new correlation is suggested for predicting the pressure drops of R-600a during condensation inside spiral coil inserted pipes. Furthermore, the flow pattern maps showed that inserting coiled wires postpones the transition from annular to intermittent.