Applied Mechanics and Materials Vol. 819

Abstract: In this study, a typical kitchen having a standard dimension of 213cm × 243cm × 305cm was modeled with single open door exit. Steady state simulations were performed using three dimensional commercial CFD solver with appropriate boundary conditions. Two heat sources were used for modelling the kitchen that resembles the double burner gas stoves of urban residential kitchen in developing countries. In the earlier works, for the same model the predictions validated at an optimum grid resolution and the results have been presented for thermal comfort, carbon dioxide gas emission under natural, forced and no ventilation cases. The effect of kitchen hood system on the thermal comfort and emission has also been analyzed. In this present work, three different positions of the kitchen hood suction have been studied for the effect on thermal distribution and emission rate. The investigated positions of the kitchen hood are the Front, Top and Bottom with respect to the gas stove. It was observed that both front and bottom hood extraction method significantly reduces the emissions to well below the safe limit. They also can maintain thermal comfort quite well inside the kitchen space.

Abstract: Heat pipe is considered being used as a passive system to remove residual heat that generated from reactor core when incident occur or from spent fuel pool. The present research is aimed to studying the characteristics of straight heat pipe as passive residual heat removal system. As an initial step, a numerical simulation was conducted to simulate the best experimental design set up being prepared for the next step of the research. The objective is to get the thermal hydraulic characteristic due to variation of heat flux of heat source. The thermal hydraulic RELAP5 MOD 3.2 code is used to simulate and analyze the straight heat pipe characteristics. Variations of heat flux are 1567 Watt/m², 3134 Watt/m², 4701 Watt/m², 6269 Watt/m², and 7837 Watt/m². Water as working fluid is heated on evaporation section with filling ratio 60%. Environmental air with variation 5 m/s and 10 m/s of velocity are used as external cooler. Straight heat pipe used in the simulation is wickless with 0.1 m of diameter and 6 m of length. The results show that higher heat flux given to the evaporator section will lead to more rapid heat transfer and achievement of steady state condition. The increasing of heat flux leads to an increase of evaporation of the working fluid and of pressure built in the heat pipe affecting higher saturation temperature of working fluid. Heat flux loading must consider the velocity of air as heat removal in the condenser to prevent dry out phenomenon in the evaporator. Based on the results, given the experimental set-up, the optimum range of experimental parameters could be determined.

Abstract: The present study focuses on the numerical study of thermal and flow characteristics in a microchannel heat sink with alternating trapezoidal cavities in sidewall (MTCS). The effects of flow rate and heat flux on friction factor and Nusselt are presented. The results showed considerable improvement heat transfer performance micro channel heat sink with alternating trapezoidal cavities in sidewall with an acceptable pressure drop. The heat transfer rate has improved in the cavity area due the greater fluid mixing in fluid vortices and thermal boundary layer disruption. The slipping over the reentrant cavities and pressure gain reduces pressure drop appears as the reason behind of only minor pressure drop due to the cavities.

Abstract: A numerical model for determining the characteristics of flow and heat has been presented by modifying the eddy diffusivity equation of Sarma et al. The experimental data of thermo-physical properties determined using spherical particles in a wide range of concentration, particle size, materials and operating temperatures are available in the literature. The numerical analysis employed equations, which were developed using the experimental data of thermo-physical properties, friction factor and Nusselt number. Based on the agreement of the numerical results with the experimental data, the influence of concentration and temperature on the turbulent characteristics is presented. It is observed that SiO₂ nanofluid attained higher velocity and lower eddy diffusivity compared to Cu nanofluid at a concentration. The temperature gradient increases with concentration and decreases with temperature.

Abstract: Since topics like the greenhouse effect and the associated global warming issue are much more discussed in the past, automobile manufacturers have to become even more active in in two fields: reduction of fuel consumption and reduction of emissions. As the optimization of motor vehicles has reached a point at which significant additional fuel saving cannot be achieved by means of purely engine-internal measures alone, other systems must be found to improve the specific fuel consumption. One promising technology could be the use of engine waste heat contained in exhaust gas. Earlier studies have shown, besides systems like thermoelectric generators or a Turbo compounding system, an integrated Rankine Cycle offers a lot of potential to turn waste heat into mechanical or electrical power. The use of a suitable working fluid for this Rankine Cycle is required to achieve a maximum in system power output. The aim of this work is to investigate the suitability of working fluids for automotive Organic Rankine Cycle applications. The investigation is focused on the thermodynamic simulation on the one hand and the experimental evaluation of thermal stability of the fluids on the other hand. For the experimental evaluation of the stability a continuous cycle is used to achieve nearly equal process conditions. The stability tests start with a short time screening of all selected fluids, later on the most promising ones are tested in long time test runs. In the test runs, the substances of the categories alkanes, cycloalkanes, monoaromatics and fluorinated compounds show best results regarding stability. In contrast acetales, siloxanes and ethers are not stable under the selected conditions. The same applies to ethanol. With a temperature above 225 °C ethanol is not stable. Additional runs with ethanol show that the temperature has to be limited to below 250 °C at least to avoid a high decomposition. Also acetone reacting products can be found in the liquid phase leading to high boiling substances that then may lead to coke formation in the system. The validation of the tested and simulated fluids is done for two different condensation temperatures (CT) of 100°C and 40°C. Fluids acetone and ethanol (CT 100°C) show best overall results. In Addition fluids n-hexane, methylcyclohexane, cyclohexane and toluene show good upto very good results. For condensation temperature 40°C, cyclopentane and R1233zd is suggested.

Abstract: The increasing number of non-renewable energy and the rising need of energy caused some global issue. We always interested to discuss how human being could create and improve an instrument that can extract energy from renewable energy resources, which is clean and applicable. One instrument that can extract energy from the sun is solar water heater. Solar water heater, consist of two main components. The first one is storage tank, and the other is solar collector. The purpose of this research is to design, manufacture, determine the performance of the solar collector with vacuum tubes and dual heat pipe based on the wick length variation. This experiment used a 150 Watt halogen lamp as the simulator of the sun. A copper fin was utilized to collect heat from the sun and transfer the heat to heat pipes. Adiabatic walls made from Styrofoam and plywood were set to prevent heat transfer to the environment due temperature difference. The performance of the heat pipe was investigated based on the wick length inside the heat pipe. The flow characteristic inside of the heat pipe and the thermal resistance depend on the wick length. The study found that the full-length wick heat pipe has the best performance with 0.37 K/W thermal resistance, and the efficiency of the system reach 34.95%. This is the highest value compared to the half-length and three-quarter length wick heat pipe.

Abstract: Access to freshwater and energy resource management are two of the major concerns of the next decades. The global warming indicator, the decrease of rainfalls and the growing energy demand for cooling are correlated in the most populated agglomerations of the world. For industrial and social purposes, it seems vital to develop energy efficient systems for cooling and desalination. A heat pump can produce energy for space cooling and heat for desalination. Among the different desalination systems available, membrane distillation seems the most suitable solution to the condensing temperature level of a standard heat pump.This article presents the development of a model of heat pump for simultaneous cooling and desalination by air-gap membrane distillation. The model was first developed using EES software and validated with experimental results from our laboratory and from the literature. The desalination unit was then optimised by numerical means in terms of dimensions and operating conditions using a bi-dimensional model with Matlab. A coupled system with a heat pump was finally simulated. The objective is to estimate the freshwater production depending on the cooling loads of a refrigerator placed in a building submitted to the conditions given by a weather data file in the Trnsys environment. The energy consumptions are compared to those of a standard reverse osmosis plant producing the same amount of freshwater associated to a chiller of same cooling capacity as the heat pump. The results show that the heat pump for simultaneous cooling and desalination offers interesting perspectives.

Abstract: In this research, solar desiccant cooling cycles in ventilation and hybrid mode are simulated. To simulate cycles, at first a model for desiccant wheel simulation is presented and a computer code based on experimental correlations is used to solve equations. Then by TRNSYS software a model for solar hot water system is simulated, and eventually by representing a suitable algorithm, computer program for simulating solar desiccant cooling cycles by EES software is developed. For all components of desiccant cycle, the dynamic optimum were based on regeneration temperature and solar fraction, and after optimum, dynamic cycle performance in an office building with an area of 115 m² located in Bushehr city, capacity of cooling 3 ton refrigeration were analyzed. The results show that solar desiccant cooling cycles in comparison with compression refrigeration cycles with 40% saving in energy consumption and also during the day and in office buildings have a better performance.

Abstract: During the last three decades the concept of the traditional cooling systems was modified to include single, double, and multi-layer micro channels. The new studies, applications, fabrication, and research focus on four main areas: the geometrical shape of the micro channels, the number of stacked layers, the type of the coolants, and the heat performance optimization. The previous studies have shown a significant reduction in the power consumption as the optimization is accomplished. In this paper, a semi-review for the previous works is provided, an attempt to interpret the nature of the work done, and show another trial for optimization. In this study, water was used as coolant, stacked multi-channel was adopted, and thermal resistance network was calculated. The heat sink under consideration is a rectangle of width W and length L. The thickness Hsub of the base of the micro-channel is 100 [μ m] while the depth Hc of the micro-channel is 500[μ m], both kept constant for all future optimization cases.

Abstract: The heat transfer rate of an adsorbent embedded heat exchanger can be significantly improved by as much as three folds using powder adsorbent coated by binder on the fin surfaces of exchangers. The overall performance of such exchangers in an adsorption chiller, however, is determined both by the heat transfer and adsorption mass transport phenomena, which are also highly interlaced in the chiller operations. If a severe suppression on the latter is observed as a result of the binder, the heat exchanger may eventually underperform. This work evaluates the overall effect of the binder on the mass transport. It focuses on a common adsorbent-adsorbate pair utilized in the chiller, i.e. silica gel type 3A-water. A hydroxyethyl cellulose (HEC) is used as the binder. Experiment is conducted to measure the water equilibrium uptake of the pure and binder added silica gel at various temperatures. Based on the results, the net influence of the binder on the water uptake rate in the adsorption heat transfer process is determined.