Characterization of liquid refrigerant R-123 flow emerging from a flooded evaporator tube bundle

Abstract

The distribution of liquid droplets emerging from an evaporator tube bundle is characterized for lowpressure refrigerant R-123 with a triangular tube arrangement of pitch 1.167. The purpose of this research is to improve the understanding of the droplet ejection process to aid in the design of evaporators typically used in larger chiller systems. A laser and camera system in a shadowgraphy arrangement captured images of the evaporator headspace at varying conditions. Conventional shadowgraphy techniques were applied to recognize droplets and match droplets for velocity calculations. The evaporator conditions were varied with mass fluxes from 3.5 to 40.7 kg/s-m 2 (2250 to 30000 lb/hr-ft 2), top-rows heat fluxes from 5.3 to 31.5 kW/m 2 (1700 to 10000 Btu/hr-ft 2), and outlet saturation temperatures of 4.4 and 12.8 °C (40 and 55 F). Conditions ranged from flooded to dryout on the top rows. Particle number count, size distribution, and velocity are presented. The experimentaly measured liquid volume fraction in the headspace is also presented. Liquid distribution in the headspace is found to be a strong function of all varied properties, particularly mass flux, liquid level, and saturation temperature. The high liquid-vapor density ratio of R-123 and corresponding high velocities make it particularly difficult to separate liquid droplets before they escape the tube bundle.

Measurement Method and Experimental Analysis of Liquid Entrainment for a Flooded Evaporator of a Water-Cooled Centrifugal Chiller Based on Energy Balance

“…However, there is only limited research on liquid entrainment in the evaporator with refrigerant. Using a laser and camera system and shadow graphic technique, Asher and Eckels investigated the distribution characteristics of droplets generated by the evaporation of refrigerant in the headspace of a rectangular tube bundle with R123 [12], R134a [13], respectively. The effects of heat flux, mass flow rate, evaporation temperature and refrigerant level on the liquid distribution generated in the headspace were investigated and the refrigerant level, mass flow rate and evaporation temperature were found to have the greatest influence.…”