Experimental investigation of the effect of ultrasonic waves on heat transfer enhancement and pressure drop for propylene glycol/water mixtures in a rectangular minichannel heat sink

In the recent era, ultrasound has gained significant prominence as a reliable technique for enhancing heat transfer, due to the growing demand to dissipate heat from various industrial applications. This study aims to experimentally investigate the effects of using ultrasound (27.8 kHz) on heat transfer and pressure drop in a rectangular minichannel heat sink with deionized (DI) water and propylene glycol/water mixtures at three different volume concentrations (20 %, 30 %, and 50 %) under laminar flow conditions. The experiment was conducted in a minichannel heat sink made of copper, consisting of 11 rectangular channels each with a hydraulic diameter of 2.8 mm. The influence of volumetric flow rate (0.2-0.72 lpm) and two heating powers (50 W and 60 W) on heat transfer characteristics and pressure drop with and without ultrasound was explored. The maximum heat transfer enhancement within the minichannel heat sink under ultrasonic waves, reaching approximately 11.3 %, was achieved with DI water at the lowest flow rate (0.2 lpm). The enhancement in heat transfer became less pronounced as the volume concentration of propylene glycol in the fluid mixture increased. Additionally, with an increase in flow velocity and heater power, the influence of ultrasound on enhancing heat transfer became less notable. Regarding temperature data, the measured results indicated a significant decrease in internal surface temperatures of the minichannel heat sink under ultrasound compared to the silent mode. The reasonable agreement between the experimental and the theoretical results demonstrates the validity of the measured pressure drop. Overall, the pressure drop across the minichannel heat sink increased with the application of ultrasound, but the effect of ultrasound decreased at high flow rates.