The sono-PCM reactors: A new approach for recovering the heat dissipated from ultrasonic reactors using a phase change material

Abstract

To keep sonochemical reactors at a constant temperature, cryothermostat systems (equipped with a pump, cooling fluids and tubing) are commonly used. The cryothermostat serves a dual purpose, supplying both heating and cooling as needed to keep the temperature stable. However, this device is an energy consumer, especially when the sonochemical reaction is carried out over an extended period of time (hours to days). As a result, alternative systems are required to reduce the operating cost of sonosystems. The present work introduces a new approach of incorporating phase change materials (PCMs) for the recovery and storage of heat dissipated from ultrasonic reactors (i.e. the sono-PCM reactor approach). The purpose of the project is to go as far as replacing the circulating fluid-based cooling system with a small PCM unit capable of absorbing the generated heat flux and storing it in the form of latent heat (with phase change). The analysis was made on sonicated water (300 mL) in a standing wave ultrasonic reactor operating at 300 kHz, where the dissipated heat flux was measured calorimetrically. After that, using a computational fluid dynamics (CFD) model (implemented in ANSYS Fluent® software), the energetic performance of the PCM unit was assessed by tracking the system (i.e. the sono-PCM reactor) response (i.e. average and spatial evolutions of temperature, enthalpy, total energy, velocity and PCM-melting kinetics) to the imposed acoustic energy. Paraffin RT31 was selected as PCM because of its suitable characteristics such as low melting point (27–31 °C) and high thermal energy storage capacity (165 kJ kg−1). Despite the relatively low thermal conductivity of the used PCM (0.2 W m− 1 °C − 1), promising results have been obtained in terms of thermal energy management and storage using a phase change material (PCM) instead of a water-cooling system.