Mathematical modelling and simulation of multiphase flow in a flat plate solar energy collector

Non-conventional collectors where organic fluid or refrigerant experience a phase change have many advantages over conventional collectors which have either air or relatively high temperature boiling liquid. Increase in heat transfer coefficient and system efficiency, corrosion prevention and freeze protection are the main benefits of the first type. In this study, a detailed numerical model of a flat plate collector is developed to investigate the fluid mean temperature, useful heat gain and heat transfer coefficient along the collector tube. The refrigerant HFC-134a was used in the simulation as the working fluid of the collector. The model can both predict the location where the fluid undergoes a phase change in the tube and the state at the exit under given inlet conditions. The effect of boiling on the heat transfer coefficient of the fluid is also investigated. Simulations were performed at three different mass flow rates (0.001, 0.005 and 0.01 kg/s) and three different operating pressures (4, 6 and 8 bar) to be able to see the effect of mass flow rate and pressure on plate temperature, heat loss coefficient, efficiency of the collector and the heat transfer coefficient of the fluid. The simulation results indicate that the heat transfer coefficient of the fluid increases from 153.54 W/m2K to 610.27 W/m2K in multiphase flow region. In the liquid single phase region, the collector efficiency rises from 60.2% to 68.8% and the heat transfer coefficient of the fluid increases from 39.24 W/m2K to 392.31 W/m2K with an increased flow rate whereas the collector efficiency decreases from 72.5% to 62.3% as the operating pressure increases from 4 bar to 8 bar. In order to validate the simulation model an experimental test rig was built and the experiments were performed with HFE 7000 as working thermo-fluid. A new simulation model utilizing HFE 7000 has been developed and the outlet temperature of the fluid was compared with the measured outlet temperature. Both measured and simulated results have shown close conformity

Heat transfer through heat exchanger using Al₂O₃ nanofluid at different concentrations

This article reports an experimental study on the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and different volume concentrations of Al₂O₃ nanofluid (0.3–2)% flowing in a horizontal shell and tube heat exchanger counter flow under turbulent flow conditions are investigated. The Al₂O₃ nanoparticles of about 30 nm diameter are used in the present study. The results show that the convective heat transfer coefficient of nanofluid is slightly higher than that of the base liquid at same mass flow rate and at same inlet temperature. The heat transfer coefficient of the nanofluid increases with an increase in the mass flow rate, also the heat transfer coefficient increases with the increase of the volume concentration of the Al₂O₃ nanofluid, however increasing the volume concentration cause increase in the viscosity of the nanofluid leading to increase in friction factor

Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow

This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration

Exploratory evaluation of solar radiation and ambient temperature in twenty locations distributed in United Kingdom

Solar radiation and ambient temperature is a foundation resource programs of large-scale deployment of solar energy technologies. This paper summarizes the analysis of a weather station network in United Kingdom. Whistle 3 years (January 2015 – December 2017) of data from twenty weather stations distributed across the country. The data comprises of Global Horizontal Irradiance (GHI), Diffuse Horizontal Irradiance (DHI), Direct Normal Irradiance (DNI), ambient temperature, wind speed, and the humidity. Network design, implementation, and data quality assurance are described, in order to document the network extent and quality. From all observed datasets, it was found that Plymouth (located in southwest England) has the dominant GHI, and ambient temperature among all other 19 locations. The least GHI is observed for Aberdeen (located in northeast Scotland) estimated at 77.3 kWh/m2. However, the least average ambient temperature is equal to 9.1 °C, this data was detected from the weather station located in the capital of Scotland (Edinburgh). Although continued measurements are needed to understand the interannual resource variability, the current study provides significant guidance for preliminary technology selection, power plant modeling, and resource forecasting

Preliminary assessment of the solar resource in the United Kingdom

Solar radiation resources data are the foundation of knowledge for programs of large-scale deployment of solar energy technologies. This article summarizes the analysis of a new weather stations network in the United Kingdom. The analysis used three years (January 2015–December 2017) of data from 27 weather stations distributed across the country. The data comprises global horizontal irradiance (GHI), diffuse horizontal irradiance, direct normal irradiance and the ambient temperature. Network design, implementation and data quality assurance are described to document the network extent and quality. From all observed datasets, we found that Plymouth (located in southwest England) has the dominant GHI and ambient temperature among all other 26 locations. The least GHI is observed for Aberdeen (located in northeast Scotland) estimated at 77.3 kWh/m2. The least average ambient temperature is equal to 9.1°C; the data were detected by the weather station located in the capital of Scotland (Edinburgh). Although continued measurements are needed to understand the interannual resource variability, the current study should have significant applications for preliminary technology selection, power plant modeling and resource forecasting

Optimization of Thermal Conductivity of Al 2 O 3 Nanofluid by Using ANN and GRG Methods

Abstract: Commo

Experimental studies on the stability of CuO nanoparticles dispersed in different base fluids: influence of stirring, sonication and surface active agents

The main aim of this work is to investigate the influence of different parameters on the stability of spherical CuO nanoparticles dispersed in water, ethylene glycol and 50:50 water/ethylene glycol binary mixture as different base fluids for heat transfer applications. Nano-fluids were prepared using two-step method at weight concentration of 0.1–0.4 %. Time-settlement experiments were established to examine the stability of nano-fluids. Quality tests were also performed to investigate the morphology, purity and size of nanoparticles. In order to stabilize the nano-fluids, stirring, pH control and sonication were utilized. The criteria for assessing the stability of nano-fluids were zeta potential and time-settlement experiments. Results demonstrated that the ethylene glycol can be the best medium for dispersing the CuO nanoparticle in comparison with water and water/EG binary mixture. The best condition for achieving the most stable nano-fluid was also introduced. Role of sonication time, stirring time and addition of surfactant on the stability of nano-fluids were investigated and briefly discussed.M. Kamalgharibi, F. Hormozi, Seyed Amir Hossein Zamzamian, M.M. Sarafra

Study on Reaction Conditions in Whole Cell Biocatalyst Methanolysis of Pretreated Used Cooking Oil

Abstract: Biodiesel fuel (fatty acid methyl esters; FAMEs) can be produced by methanolysis of waste edible oil with a whole cell biocatalyst which is an attractive alternative to fossil fuel because it is produced from renewable resources. Utilizing whole cell biocatalyst instead of free or immobilized enzyme is a potential approach to reduce the cost of catalyst in lipase-catalyzed biodiesel production. Rhizopus oryzae (R. oryzae) PTCC 5174 cells were cultured with polyurethane foam biomass support particles (BSPs) and the cells immobilized within BSPs were used for the methanolysis of pretreated used cooking oil (UCO) for biodiesel production in this research. UCO is the residue from the kitchen, restaurant and food industries which promotes environmental pollution and human health risks. The inhibitory effect of undissolved methanol on lipase activity was eliminated by stepwise addition of methanol to the reaction mixture. The optimum conditions for the reaction were as follows: 50 BSPs, molar ratio of methanol to UCO 3:1, 15.54% (wt) water (in the form of buffer phosphate with pH= 6.8) based on UCO weight and temperature 35°C in three-step addition of methanol. The maximum methyl ester yield of 98.4% was obtained after 72 h of reaction in a shaken Erlenmeyer at mentioned conditions