Heat transfer of spray falling films over horizontal tubes with counter current airflows in an evaporative condenser

Abstract

The spray film evaporative cooling equipment is useful to circumvent the scaling with expanded liquid coverage for attaining good thermal performance and energy efficiency. This paper examines the evaporative heat transfer phenomena of falling spray films over the horizontal circular tube array. In the experimental study, a high-speed camera with a LED fiber optic light source is implemented to capture the optical images for illuminating the distributions of spray films over the tube array under the counter current airflows. The average wall temperature, outlet temperature of spray nozzle and heat flux regulated by a programmable DC power supply are measured to determine the heat transfer coefficient. Moreover, the computational simulation is conducted using the CFD software ANSYS/ Fluent® in conjunction with a user defined function (UDF) to investigate the evaporative heat transfer of liquid spray films over the tubes. The calculated liquid film thicknesses and average heat transfer coefficients around the upper and lower tubes agree reasonably with the measured data to validate the numerical model. To explore the development of falling spray film dispersion and thermal performance over the tubes, the measurements and simulations are then extended to examine the characteristics of film thickness and heat transfer of splashed water sprays on the tube array at varying water flow rates of 3–7 l/min, heat fluxes of 10–50 kW/m2, tube placement positions of 0–142.5 mm (i.e. w1-w6) and counter current airflow velocities of 0.8–2.0 m/s, respectively. In measurements, the average heat transfer coefficients of four positions for the tubes at an upward airflow velocity of 2 m/s can reach 5.0 kW/m2 K for the water flow rate of 5 l/min and a heat flux of 30 kW/m2K.