Abstract
Thermal ice storage has gained a lot of interest due to its ability as cold energy storage. However, low thermal conductivity and high supercooling degree have become major issues during thermal cycling. For reducing the cost and making full use of the advantages of the graphene oxide–Al2O3, this study proposes heat transfer enhancement of thermal ice storage using novel hybrid nanofluids of aqueous graphene oxide–Al2O3. Thermal conductivity of aqueous graphene oxide–Al2O3 nanofluid was measured experimentally over a range of temperatures (0–70 °C) and concentrations. Thermal conductivity of ice mixing with the hybrid nanoparticles was tested. The influences of pH, dispersant, ultrasonic power and ultrasonic time on the stability of the hybrid nanofluids were examined. A new model for the effective thermal conductivity of the hybrid nanofluids considering the structure and Brownian motion was proposed. The results showed that pH, dispersant, ultrasonic power level and ultrasonication duration are important factors affecting the stability of the hybrid nanofluids tested. The optimum conditions for stability are pH = 11, 1% SDS, 375 W ultrasonic power level and 120 min ultrasonic application time. The thermal conductivity of hybrid nanofluids increases with the increase of temperature and mass fraction of nanoparticles. A newly proposed thermal conductivity model considering the nanofluid structure and Brownian motion can predict the thermal conductivity of hybrid nanofluids reasonably well.
Highlights
Thermal ice storage is a very important kind of phase change cold energy storage, which can be used in the solar and wind energy system to reduce the fluctuations in the energy flow
A high supercooling degree leads to reduced performance of the phase change material (PCM) thermal energy storage system because of the requirement of a large operating temperature range [3]
The pH of nanofluids is usually adjusted to increase the charges on the surface of the nanoparticles, which keeps the surface potential of the nanoparticles away from isoelectric point so as to enhance the electrostatic repulsion and stability of the nanofluids
Summary
Thermal ice storage is a very important kind of phase change cold energy storage, which can be used in the solar and wind energy system to reduce the fluctuations in the energy flow. Sci. 2020, 10, 5768 systems in centralized and decentralized environments [1]. The thermal ice storage is employed in heating, ventilation and air conditioning (HVAC) cooling, food processing, chemical reactions or pharmaceutical processing, inlet air cooling of turbine and district cooling plant [2]. As one type of phase change material (PCM), ice storage, has higher supercooling degree and lower thermal conductivity that reduce heat transfer performance. A high supercooling degree leads to reduced performance of the PCM thermal energy storage system because of the requirement of a large operating temperature range [3]. Many researchers found that addition of nanoparticles enhance the thermal conductivity, and reduce the supercooling degree, and improve the heat transfer performance greatly [4]. The stability of the nanoparticles suspended in base fluids during the thermal cycling is becoming a key problem
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