Subcooled flow boiling heat transfer of ethanol aqueous solutions in vertical annulus space

The subcooled flow boiling heat-transfer characteristics of water and ethanol solutions in a vertical annulus have been investigated up to heat flux 132kW/m2. The variations in the effects of heat flux and fluid velocity, and concentration of ethanol on the observed heat-transfer coefficients over a range of ethanol concentrations implied an enhanced contribution of nucleate boiling heat transfer in flow boiling, where both forced convection and nucleate boiling heat transfer occurred. Increasing the ethanol concentration led to a significant deterioration in the observed heat-transfer coefficient because of a mixture effect, that resulted in a local rise in the saturation temperature of ethanol/water solution at the vapor-liquid interface. The reduction in the heat-transfer coefficient with increasing ethanol concentration is also attributed to changes in the fluid properties (for example, viscosity and heat capacity) of tested solutions with different ethanol content. The experimental data were compared with some well-established existing correlations. Results of comparisons indicate existing correlations are unable to obtain the acceptable values. Therefore a modified correlation based on Gnielinski correlation has been proposed that predicts the heat transfer coefficient for ethanol/water solution with uncertainty about 8% that is the least in comparison to other well-known existing correlations

Performance index improvement of a double-pipe cooler with MgO/water-ethylene glycol (50:50) nano-suspension

A series of tests was conducted to unlock the potential application of MgO/water-EG (ethylene glycol) nanofluids (NF) in a double-pipe heat exchanger (HEX). The overall heat transfer coefficient (HTC), the inlet temperature of the working fluid, the fluid pressure drop (FPD), friction factor (FF) and the hydraulic performance index of the NF within the HEX were experimentally measured. Fouling of nanoparticles (NPs) within the Hex was also studied and modelled using asymptotic particulate fouling model. Results showed that MgO NPs can enhance the HTC by 39% at Re=10,500 and wt.% = 0.3 in the turbulent regime. Also, the presence of MgO NPs augmented the FF and the FPD values. The former was enhanced 33.8%, while the latter was augmented by 37% both at wt.% = 0.3 and at Reynolds number = 10,500. Results also revealed that the formation of porous particulate fouling layer on the internal wall of the inner tube creates a fouling thermal resistance which changes asymptotically with time. Overall, MgO/water-ethylene glycol shows a great potential to be used as a coolant within a HEX.H. Arya, M.M. Sarafraz, O. Pourmehran, M. Arjomand

Thermal assessment of nano-particulate graphene-water/ethylene glycol (WEG 60:40) nano-suspension in a compact heat exchanger

In the present study, we report the results of the experiments conducted on the convective heat transfer of graphene nano-platelets dispersed in water-ethylene glycol. The graphene nano-suspension was employed as a coolant inside a micro-channel and heat-transfer coefficient (HTC) and pressure drop (PD) values of the system were reported at different operating conditions. The results demonstrated that the use of graphene nano-platelets can potentially augment the thermal conductivity of the working fluid by 32.1% (at wt. % = 0.3 at 60 °C). Likewise, GNP nano-suspension promoted the Brownian motion and thermophoresis effect, such that for the tests conducted within the mass fractions of 0.1%–0.3%, the HTC of the system was improved. However, a trade-off was identified between the PD value and the HTC. By assessing the thermal performance evaluation criteria (TPEC) of the system, it was identified that the thermal performance of the system increased by 21% despite a 12.1% augmentation in the PD value. Furthermore, with an increment in the fluid flow and heat-flux applied to the micro-channel, the HTC was augmented, showing the potential of the nano-suspension to be utilized in high heat-flux thermal applications.M. M. Sarafraz, Mohammad Reza Safaei, Zhe Tian, Marjan Goodarzi, Enio Pedone Bandarra Filho, and M. Arjomand

Experimental investigation on the pool boiling heat transfer to aqueous multi-walled carbon nanotube nanofluids on the micro-finned surfaces

Abstract not availableM.M. Sarafraz, F. Hormoz

Heat transfer, pressure drop and fouling studies of multi-walled carbon nanotube nano-fluids inside a plate heat exchanger

Abstract not availableM.M. Sarafraz, F. Hormoz

Demonstration of plausible application of gallium nano-suspension in microchannel solar thermal receiver: Experimental assessment of thermo-hydraulic performance of microchannel

The present study experimentally investigates the potential application of a liquid metal enriched with aluminum oxide nanoparticles in a microchannel, which can have further applications in designing the next generation of solar thermal receivers equipped with microchannel fluid passages. The gallium nano-suspensions were prepared at mass fractions of 5%, 10% and 15% of aluminum oxide in gallium and were utilized in a copper-made rectangular microchannel liquid block at 200 °C. Effects of different operating parameters such as heater heat flux, mass fraction of nanoparticles and peristaltic flow rate on the overall heat transfer coefficient, value of the pressure drop and thermo-hydraulic performance index of the microchannel were experimentally investigated. Results showed that gallium nano-suspension offers a great potential for cooling the surface of the microchannel at high heat flux condition. The highest thermal performance index of 3.5 and 2.9 were achieved for the flow in laminar and turbulent regimes at mass fraction of 10%. Likewise, heat flux and peristaltic flow rate plausibly enhanced the heat transfer coefficient, however, for the mass concentration, the thermo-hydraulic performance was decreased at wt% = 15, due to the augmentation in the viscosity and agglomeration of aluminum oxide nanoparticles within the gallium, which was attributed to the increase in friction forces between layers of gallium.M. M. Sarafraz, M. Arjomand

Filtration of per- and poly-fluoroalkyl from water and recycling of fluorine: a thermochemical equilibrium analysis

In the present work, a process concept is proposed and assessed for the separation of per- and poly-fluoroalkyl components referred to as “PFAS” from the activated carbon used in the process of water filtration and further utilization of fluorine as sodium fluoride. PFAS components are highly toxic materials, which have been spread in soil and water over past decades due to the use of fire-fighting foams and via different industrial processes. The current commercially available technology to separate PFAS from water is to use activated carbon to adsorb the chemical compounds, while transferring the pollution from water or soil into activated carbon and combust the activated carbon using an air-blown combustor which transfers the PFAS components to environment in form of chlorofluorocarbon materials. So, the current technology only transfers the pollution from soil or water into atmosphere. However, the proposed process consists of drying process, combustion and chemical reaction, which ultimately converts PFAS into a product with hygienic applications. The drying process removes a large portion of water from the activated carbon proving a better condition for the combustion of remaining carbon. The combustor breaks the long chain of fluorocarbons into smaller molecules of CF₄ using oxy-blown combustion. The exhaust gases from the combustor react with sodium in a sodium reactor to produce high-purity NaF compound which has further applications in hygienic industries such as toothpastes, cleaning agents and disinfectants. The proposed method destructs the composition of PFAS into very small molecules without transferring it to the environment.M.M. Sarafraz, M. Arjomand

Comparatively experimental study on the boiling thermal performance of metal oxide and multi-walled carbon nanotube nanofluids

Abstract not available.M.M. Sarafraz, F. Hormoz