Heat Transfer Performance of a Glass Thermosyphon Using Graphene-Acetone Nanofluid

This study presents an enhancement in the heat transfer performance of a glass thermosyphon using graphene-acetone nanofluid with 0.05%, 0.07%, and 0.09% volume concentrations. The heat load is varied between 10 and 50 W in five steps. The effect of heat load, volume concentration, and vapor temperature on thermal resistance, evaporator and condenser heat transfer coefficients, are experimentally investigated. A substantial reduction in thermal resistance of 70.3% is observed for the maximum concentration of 0.09% by volume of graphene-acetone nanofluid. Further, an enhancement in the evaporator heat transfer coefficient of 61.25% is observed for the same concentration. Also from the visualization study the different flow patterns in the evaporator, adiabatic, and condenser regions are obtained for acetone at different heat inputs

Enhancement of heat transfer using nanofluids--An overview

A colloidal mixture of nano-sized particles in a base fluid, called nanofluids, tremendously enhances the heat transfer characteristics of the original fluid, and is ideally suited for practical applications due to its marvelous characteristics. This article addresses the unique features of nanofluids, such as enhancement of heat transfer, improvement in thermal conductivity, increase in surface volume ratio, Brownian motion, thermophoresis, etc. In addition, the article summarizes the recent research in experimental and theoretical studies on forced and free convective heat transfer in nanofluids, their thermo-physical properties and their applications, and identifies the challenges and opportunities for future research.Nanofluid Convective heat transfer Laminar flow Turbulent flow Nanoparticles Dispersion Thermal conductivity

Experimental Study on Forced Convective Heat Transfer with Low Volume Fraction of CuO/Water Nanofluid

The present work is an experimental study of steady state convective heat transfer of de-ionized water with a low volume fraction (0.003% by volume) of copper oxide (CuO) nanoparticles dispersed to form a nanofluid that flows through a copper tube. The effect of mass flow rate ranging from (0.0113 kg/s to 0.0139 kg/s) and the effect of inlet temperatures at 100C and 17 0C on the heat transfer coefficient are studied on the entry region under laminar flow condition. The results have shown 8% enhancement of the convective heat transfer coefficient of the nanofluid even with a low volume concentration of CuO nanoparticles. The heat transfer enhancement was increased considerably as the Reynolds number increased. Possible reasons for the enhancement are discussed. Nanofluid thermo-physical properties and chaotic movement of ultrafine particles which accelerate the energy exchange process are proposed to be the main reasons for the observed heat transfer enhancement. A correlation for convective heat transfer coefficient of nanofluids, based on transport property and D/x for 8 mm tube has been evolved. The correlation predicts variation in the local Nusselt number along the flow direction of the nanofluid. A good agreement (±10%) is seen between the experimental and predicted results

Air-side performance of a micro-channel heat exchanger in wet surface conditions

The effects of operating conditions on the air-side heat transfer, and pressure drop of a micro-channel heat exchanger under wet surface conditions were studied experimentally. The test section was an aluminum micro-channel heat exchanger, consisting of a multi-louvered fin and multi-port mini-channels. Experiments were conducted to study the effects of inlet relative humidity, air frontal velocity, air inlet temperature, and refrigerant temperature on air-side performance. The experimental data were analyzed using the mean enthalpy difference method. The test run was performed at relative air humidities ranging between 45% and 80%; air inlet temperature ranges of 27, 30, and 33°C; refrigerant-saturated temperatures ranging from 18 to 22°C; and Reynolds numbers between 128 and 166. The results show that the inlet relative humidity, air inlet temperature, and the refrigerant temperature had significant effects on heat transfer performance and air-side pressure drop. The heat transfer coefficient and pressure drop for the micro-channel heat exchanger under wet surface conditions are proposed in terms of the Colburn j factor and Fanning f factor

Absorption refrigeration system using engine exhaust gas as an energy source

A single-effect absorption refrigeration system that uses LiBr-water solution and engine exhaust gas is investigated. The generator is a spiral fin-and-tube heat exchanger, while the condenser, evaporator, and absorber are shell and coil heat exchangers. Experiments are conducted at engine speeds of 1000, 1200, 1400, and 1600 rpm; expansion valve opening percentages of 54.5%, 72.7%, and 90.9% at the separator outlet and 3.41%, 4.55%, and 5.68% at the condenser outlet; refrigerant temperatures at the condenser outlet of 25, 30, and 35 °C; and LiBr-water solution flow rates of 0.35 and 0.7 LPM. The results show that the system could work with an engine speed of 1200–1400 rpm. The cooling load and coefficient of performance (COP) increase with increasing engine speed. The highest COP of 0.275 is reached at an engine speed of 1400 rpm, opening percentage of 72.7% at the separator outlet and 4.55% at the condenser outlet, water temperature of 25 °C at the condenser outlet, and LiBr-water flow rate of 0.7 LPM. The decreased refrigerant temperature at the condenser outlet helps to increase both cooling load and COP. The increase of the LiBr-water solution flow rate helps to increase cooling load but decrease COP. Keywords: Absorption refrigeration, LiBr-water solution, Exhaust gas, CO