Review: Observation on CFD Analysis of ZnO and TiO2 Nanofluid with Oil and Ethylene Glycol in Square and Helical Coil Heat Exchanger

Helically coiled heat exchangers are globally used in various industrial applications for their high heat transfer performance and compact size. Nanofluids can provide the excellent thermal performance in helical coil heat exchangers. Research studies on heat transfer enhancement have gained serious momentum during recent years and have been proposed many techniques by different research groups [1]. A fluid with higher thermal conductivity has been developed to increase the efficiency of heat exchangers. The dispersion of 1-100nm sized solid nanoparticles in the traditional heat transfer fluids, termed as nanofluids, exhibit substantial higher convective heat transfer than that of traditional heat transfer fluids. Nanofluid is a heat transfer fluid which is the combination of nanoparticles and base fluid that can improve the performance of heat exchanger systems. In this present paper the efforts are made to understand that how to compare the heat transfer rate in Copper helically coiled tube and squared coiled tube heat exchanger using Zinc Oxide and Titanium Dioxide Nano fluid by studying research papers of various authors. Keywords: Helical Coil, Nano-fluid, Heat Exchanger, CFD, Pressure Drop, Temperature Distribution.

THEORETICAL INVESTIGATION OF HEAT PRODUCTION FEASIBILITY BY MEANS OF WIND MECHANICAL PLANTS

A widespread use of wind turbines can fully or partly provide energy for the consumers, but with due regards to certain investments and instability of energy generation. Technologies of using wind energy imply the conversion of the mechanical energy of a wind flow into the electrical or heat energy. The work is concerned with the estimation of the amount of heat in the process of heating liquid coolants and heat-transfer fluids when using wind mechanical plants. In the paper was made a numerical analysis of the temperature rise of the liquid which circulates in a closed loop of a gear-type pump, whose productivity is 3 l/m and which is driven by a wind turbine 5 kW of power capacity under a nominal wind speed of 7 m/s and under cycle duration of 2 s. The analysis showed that the temperature increased by 0.290 °К/s. If such wind speed is observed during one hour, the temperature of 100 kg of water will increase by 8.1°С. Heating of a heat-transfer fluid with a supply of mechanical energy to a working part can be achieved by a centrifugal fan. Assuming that the given process occurs without supplying and removing heat energy (it is adiabatic), for the capacity of 1.5 kW and under the revolution in a range of 1000….3000 r/m, the changes in temperature will range from 0.38 to 0.87 °К/s, but for the capacity of 7.5 kW and under 750 – 1500 r/m, the changes in temperature will range from 0.56 to 1.23 °К/s.

Effects of Nanofluids in Improving the Efficiency of the Conical Concentrator System

Fossil fuels are being depleted, resulting in increasing environmental pollution due to greenhouse gases and, consequently, emerging detrimental environmental problems. Therefore, renewable energy is becoming more important; hence, significant research is in progress to increase efficient uses of solar energy. In this paper, the thermal performance of a conical concentrating system with different heat transfer fluids at varied flow rates was studied. The conical-shaped concentrator reflects the incoming solar radiation onto the absorber surface, which is located at the focal axis, where the collected heat is transported through heating mediums or heat transfer fluids. Distilled water and nanofluids (Al2O3, CuO) were used in this study as the heat transfer fluids and were circulated through the absorber and the heat storage tank in a closed loop by a pump to absorb the solar radiation. The efficiency of the conical concentrating system was measured during solar noon hours under a clear sky. The collector efficiency was analyzed at different flow rates of 2, 4, and 6 L/min. The thermal efficiency, calculated using different heat transfer fluids, were 72.5% for Al2O3, 65% for CuO, and 62.8% for distilled water. Comparing the thermal efficiency at different flow rates, Al2O3 at 6 L/min, CuO at 6 L/min, and distilled water at 4 L/min showed high efficiencies; these results indicate that the Al2O3 nanofluid is the better choice for use as a heating medium for practical applications.

Study and Feasibility of a Flat Collector Cooker using Vegetal Heat Transfer Fluid

Solar cookers currently produced are solar systems that use parabolic heat transfer to concentrate sun rays on a cooker. The new trend is focus on the cooker that uses a flat collector operating as a thermosiphon where the heat transfer fluid (oil) flows by natural convection. They are developed to address household needs at a lower cost, making them popular both in terms of research and use. Some of vegetable oils were previously investigated and which could be used as heat transfer fluids in such systems. A digital study using vegetable oil called "Kibi oil", an artisanal oil produced in Côte d’Ivoire, as a coolant, was conducted under poor weather conditions to calculate temperatures that could be reached in these cases. In the Sahelian zone, conditions are much better than these, and we can expect fairly excellent results. This study focused on temperature variation at different areas (1, 2, 3 and 4 specified in the diagram) of the cooker, on the mass flow of the fluid throughout the study day and to some quantities which enable to follow the performance of the solar collector of the stove. Sunlight measurements used are those of the city of Abidjan made in September, a very cloudy day with poor weather conditions. Temperature T3, very close to that of the hot plate, was around 110 °C between 10:30 am and 12:30 pm, which enables to cook certain dishes during this period. It should be noticed that at the exit of the flat panel collector, over the same period, the temperature is around 120 ° C. At that same time, the collector efficiency varies around 30%.

Theoretical investigation of the density and the heat capacity of [EMIM][BF4] and its MWCNTs ionanofluids: Effect of temperature and MWCNTs concentration

The density and specific heat capacity is an important parameter for heat transfer fluids (HTFs) specially which used for cooling or heating purposes. In this study the density of ethyle methyl imidazolium tetrafluoro borate ionicliquids ([EMIM][BF4]) measured experimentally. In addition, the density (ρ) and the specific heat capacity (Cp) of the ionanofluid (INF) were calculated theoretically. The studied INF composed of multi-walled carbon nanotubes (MWCNTs) dispersed in the ionicliquid (IL) [EMIM][BF4] in the concentrations (0.5%, 1%, 3%, 5%, 7% and 9%). Scanning electron microscopy and differential scanning calorimetry measured for the used MWCNTs. The density and the specific heat capacity of pure [EMIM][BF4] and its INFs were plotted versus temperature in a graphs. The results show that the density of [EMIM][BF4] and its INFs decreased linearly with temperature. The density increased by 0.243%-3.968% for 0.5%-9% MWCNTs concentration in INFs, reaching maximum value of 1.329 g.cm-3 at 20 °C. In contrast the specific heat capacity of [EMIM][BF4] and its INFs increased linearly with temperature with an enhancement of about 0.417%-7.99% for 0.5%-9% concentration of MWCNTs reaching maximum value of 1.812 J/g.K at 358.15K with 9%MWCNT concentration. That’s mean the addition of MWCNT cause increasing both of the density and the specific heat capacity of INF.

Utilization of Zinc-Ferrite/ Water Hybrid Nanofluids for enhancing thermal performance of a Flat Plate Solar Collector -An Analytical Study

Thermodynamic performance analysis is carried out on a flat plate solar thermal collector utilizing single and hybrid nanofluids. As heat transfer fluids, Fe2O4/water, Zn-Fe2O4/water hybrid nanofluids, and water are used, and its performance are compared based on the energy and exergy transfer rate. The thermo-physical properties are evaluated by regression polynomial model for all the working fluids. Developed codes in MATLAB solve the collector's thermal model iteratively, energy and exergetic performance are evaluated. The system was then subjected to parametric investigation and optimization for variations in fluid flow rate, temperatures, and concentrations of nanoparticles. The findings show that utilizing Zn-Fe2O4/water hybrid nanofluids with a particle concentration of 0.5 percent enhanced the solar collector's thermal performance by 6.6% while using Fe2O4/water nanofluids raised the collector's thermal performance by 7.83% when compared to water as the working fluid. While hybrid nanofluids give a better thermal alternative than water and single nanofluids, they have also produced a 5.36% increase in exergetic efficiency and an enhancement of 8.24 percent when used with Fe2O4/water nanofluids.

Effects of fluoride salt addition to the physico-chemical properties of the MgCl2-NaCl-KCl heat transfer fluid : a molecular dynamics study

Concentrated solar plants are promising solutions for electricity production. In these plants, the heat transfer fluid plays an important role, and finding systems with good thermal properties is very important. In this regard, molten salts, and more particularly molten chlorides, are currently investigated. Experimental studies of these melts are difficult and expensive, so complementing them with simulations would allow to test a wider range of compositions. In this work, we show that classical molecular dynamics simulations are suitable for predicting the properties of a ternary salt composed of MgCl2, KCl and NaCl by extensive comparisons with experimental data (and previous simulations) on the density, heat capacity, viscosity and thermal conductivity. We then study the effect of adding fluoride ions in the melt on these properties in order to investigate the suitability of mixed chlorides-fluorides for future heat transfer fluids studies.

Assessment and Perspectives of Heat Transfer Fluids for CSP Applications

Different fluid compositions have been considered as heat transfer fluids (HTF) for concentrating solar power (CSP) applications. In linear focusing CSP systems synthetic oils are prevalently employed; more recently, the use of molten salt mixtures in linear focusing CSP systems has been proposed too. This paper presents a comparative assessment of thermal oils and five four nitrate/nitrite mixtures, among the ones mostly employed or proposed so far for CSP applications. The typical medium-size CSP plant (50 MWe) operating with synthetic oil as HTF and the “solar salt” as TES was considered as a benchmark. In the first part of the paper, physical properties and operation ranges of different HTFs are reviewed; corrosion and environmental issues are highlighted too. Besides an extensive review of HTFs based on data available from the open literature, the authors report their own obtained experimental data needed to thoroughly compare different solutions. In the second part of the paper, the impact of the different HTF options on the design and operation of CSP plants are analyzed from techno-economic perspectives.