A mechanistic model for acoustically enhanced condensation heat transfer and pressure drop

Abstract

Enhancing low-quality condensation where thermal resistance is the highest is critical for size reduction and efficiency improvements for many power generation, HVAC&R, and chemical processing applications. Recently, acoustic actuation has been shown to enhance low-quality condensation by ∼30% by introducing a sound wave that oscillates between the condenser headers and resonates within the tube, agitating the liquid-vapor interface and significantly altering the distribution of the liquid phase towards the end of condensation, thereby increasing the heat transfer rate. This paper presents a multiple flow-regime model to predict the pressure drop and heat transfer during acoustically actuated condensation based on hydrodynamic changes induced by forced oscillation. Experimental results for R134a flowing through a horizontal tube across the entire quality range for mass fluxes ranging from 120 to 235 kg m−2 s−1, actuation frequencies from 2 to 20 Hz, header volumes from 150 to 1000 mL, and wall-to-refrigerant temperature differences ranging from 6 to 12 K are used for the development of the models. Enhancement mechanisms are discussed and heat-and-momentum analogy-based correlations are developed to accurately predict actuated and unactuated condensation pressure drop and heat transfer data simultaneously within 23% and 7% on average, respectively.