Effect of helical coil orientation on flow boiling process

Abstract

The flow boiling process in helical coils is investigated experimentally to analyze the effects of the orientation of the helical coil on the local heat transfer distribution, pressure drop and critical heat flux. The literature review suggests that little information is available on the influence of the orientation on the heat transfer distribution, pressure drop and critical flux during flow boiling in helical coils. Experiments are performed on horizontal and vertical helical coils with R123 as the working medium. SS-304 tubes of 5.5 mm and 7.5 mm diameter with a coil diameter of 150 mm are chosen in this study. Non-intrusive thermal imaging technique is used to measure the wall temperature. The differential pressure transmitter is used to measure the pressure drop across the test section. The two-phase pressure drop is not affected significantly by the orientation of the helical coils. The wall temperature, heat transfer distribution and the critical heat flux are affected by the orientation of the helical coil. The local and average heat transfer coefficient is higher in vertical oriented helical coils than the horizontal oriented helical coils. The value of heat flux at the burnout is higher in vertical orientation compared to horizontal orientation in both the coils.