With the growing need for greater cooling capacity in electronic and heat exchange systems,significant attention has been directed toward improving the heat transfer by incorporating nanoparticles into the base fluid....With the growing need for greater cooling capacity in electronic and heat exchange systems,significant attention has been directed toward improving the heat transfer by incorporating nanoparticles into the base fluid.While the use of nanoparticles in spray cooling shows promise for enhancing heat transfer,additional clarification is required.The paper compiles empirical data from existing literature focusing on spray cooling using nanofluids.Its objective is to clarify how nanoparticles impact the efficiency of spray heat transfer and investigate the effects of factors such as spray Weber number,nanoparticle concentration and droplet spread.Gathered data reveal that when compared to water droplets,nanofluid droplets exhibited more extensive surface spreading at low impinging droplet Weber numbers.Data also show that the heat transfer effectiveness of nanofluid sprays at the critical heat flux and film boiling temperature decreases with the increase in the spray Weber number.At the critical heat flux temperature and for intermediate spray Weber numbers,sprays utilizing nanofluids are more effective than sprays utilizing pure water;however,the situation reverses when dealing with exceedingly high Weber numbers.The data indicate that for surfaces heated within the film boiling range,it remains unclear whether sprays containing nanoparticles demonstrate higher heat transfer efficiency compared to sprays using pure water alone.For surfaces heated to the critical heat flux temperature,there is a critical nanoparticle concentration below which spraying with pure water is more effective than spraying with a nanofluid.However,for surfaces heated to temperatures near the Leidenfrost point,there is no clear indication that nanoparticle concentration plays a role.With the introduction of nanoparticles into sprays,there is a tendency for both the critical heat flux and the Leidenfrost temperatures to shift to a higher temperature range and to increase with the increase in nanoparticle concentration.展开更多
A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between th...A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances,and for dilute mist conditions.Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio,and reach a limit for a critical loading.For these dilute spray conditions,complete evaporation of the droplets takes place.Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate.The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.展开更多
文摘With the growing need for greater cooling capacity in electronic and heat exchange systems,significant attention has been directed toward improving the heat transfer by incorporating nanoparticles into the base fluid.While the use of nanoparticles in spray cooling shows promise for enhancing heat transfer,additional clarification is required.The paper compiles empirical data from existing literature focusing on spray cooling using nanofluids.Its objective is to clarify how nanoparticles impact the efficiency of spray heat transfer and investigate the effects of factors such as spray Weber number,nanoparticle concentration and droplet spread.Gathered data reveal that when compared to water droplets,nanofluid droplets exhibited more extensive surface spreading at low impinging droplet Weber numbers.Data also show that the heat transfer effectiveness of nanofluid sprays at the critical heat flux and film boiling temperature decreases with the increase in the spray Weber number.At the critical heat flux temperature and for intermediate spray Weber numbers,sprays utilizing nanofluids are more effective than sprays utilizing pure water;however,the situation reverses when dealing with exceedingly high Weber numbers.The data indicate that for surfaces heated within the film boiling range,it remains unclear whether sprays containing nanoparticles demonstrate higher heat transfer efficiency compared to sprays using pure water alone.For surfaces heated to the critical heat flux temperature,there is a critical nanoparticle concentration below which spraying with pure water is more effective than spraying with a nanofluid.However,for surfaces heated to temperatures near the Leidenfrost point,there is no clear indication that nanoparticle concentration plays a role.With the introduction of nanoparticles into sprays,there is a tendency for both the critical heat flux and the Leidenfrost temperatures to shift to a higher temperature range and to increase with the increase in nanoparticle concentration.
文摘A theoretical model is developed to predict the upper limit heat transfer between a stack of parallel plates subject to multiphase cooling by air-mist flow.The model predicts the optimal separation distance between the plates based on the development of the boundary layers for small and large separation distances,and for dilute mist conditions.Simulation results show the optimal separation distance to be strongly dependent on the liquid-to-air mass flow rate loading ratio,and reach a limit for a critical loading.For these dilute spray conditions,complete evaporation of the droplets takes place.Simulation results also show the optimal separation distance decreases with the increase in the mist flow rate.The proposed theoretical model shall lead to a better understanding of the design of fins spacing in heat exchangers where multiphase spray cooling is used.
