Applied Mechanics and Materials Vol. 819

Abstract: Thermoacoustic refrigerator is an alternative cooling system, which is environmentally safe due to the absence of any refrigerants. The resonator tube of the system is of great importance; its design and dimensions influence the design and performance of the entire refrigerator. This work describes the design of the stack and the resonator along with the influence of its dimensions on the performance of the standing-wave thermoacoustic refrigerator. The resonator consists of two tubes, one larger than the other, characterized by the diameter ratio of the smaller over the larger diameter. A Lagrange multiplier method is used as a technique to optimize the coefficient of performance (COP) of the system. Results show that the resonator small diameter tube dissipates a minimum acoustic power at a diameter ratio of 0.46, which is 17 percent less than the published values. Moreover, the results show that the resonator length increases gradually with the increase of the mean design temperature which leads to the increase of the total acoustic power dissipated by the resonator, reducing the COP of the standing-wave thermoacoustic refrigerator.

Abstract: This project is conducted with aim to determine the thermal conductivity for mixture of rice husk fiber and gypsum. The thermal conductivity value for 100% gypsum is also determined in this project for comparison purpose. The experiment used the Guarded Hot Plate Method, single specimen apparatus. This method is based on one-dimensional heat flow through conduction and steady state technique. Four samples have been tested which are 100% gypsum with a mass of 1kg for sample 1, a mixture of 0.1kg of rice husk fiber and 1kg gypsum for sample 2, mixture of 0.2kg of rice husk fiber and 1kg gypsum for sample 3 and a mixture of 0.3kg of rice husk fiber and 1kg gypsum for sample 4. From the data of the experiment that have been carried out, the value of thermal conductivity is decreasing with the increasing of rice husk fiber in the sample. The value of thermal conductivity is 0.772W/mK for sample 1, 0.7574 W/mK for sample 2, 0.7469W/mK for sample 3 and 0.7368W/mK for sample 4. The rice husk fiber is a bio-waste material and the mixture of rice husk fiber and gypsum will add value to the material as gypsum are widely used in construction field such as for plaster ingredient and ceiling finishing because it is a good insulator. The mixture of rice husk fiber and gypsum improve the 100% gypsum thermal conductivity and therefore the mixing of these two materials should have bright application potential.

Abstract: Jet impingement is one of cooling method used in order to achieve high heat transfer coefficient and widely used in industry applications such as drying of textile and film, glass and plastic sheets, cooling of electronic equipment, and heat treatment of metals. In this research, it focused on the effectiveness of the jet impingement cooling system on the convex surface based on mass blowing rate and nozzle exit to surface parameters. The scope of experiment research encompasses are convex surface made of aluminum alloy and diameter 12.5cm. For mass blowing rate parameters, it use ʋjet = 1.98m/s, 3.03m/s, 4.97m/s and 6.00m/s which has Reynolds number range from 643 until 1946. Nozzle exit to surface distance,s/d = 4.0, 8.0 and 12.0. In this experiment model, a major components that involved are a compressor, nozzle, convex surface model, K thermocouple and heater. For the result of the experiment, it is based on the data obtain through a heat transfer coefficient and Nusselt number which the plotted graph focus on the space spacing and Reynolds number parameters. For the graph Nusselt number versus s/d at stagnation point c/d=0, it shown that when the Reynolds number increase, the Nusselt number also increase. In term of effectiveness, the s/d=12.0 has a good effectiveness jet impingement cooling system. For the graph of Nusselt number versus Reynolds at stagnation point, c/d=0, as Reynolds number increase, the Nusselt number increase too. From this experiment the better cooling effect is at Reynolds number, Re=1946. Thus, it can conclude that, effectiveness for jet impingement cooling system on the convex surface occurs at the highest Reynolds number.

Abstract: The purpose of this study is related to a numerical simulation of flows in a solar chimney. The mathematical modelling approach used is based on flows in an opened enclosure with two components: a cylinder and a disc. This analysis consists in developing a computer software with dimensionless variables, and in generalized coordinates, in order to simulate an air flow in a chimney, by taking into account different flow regimes. Thermo-hydrodynamic aspect of flows is also analysed by solving the governing equations numerically using the finite volume method with adequate boundary conditions. The results presented are related to air flow velocity and temperature distributions versus Rayleigh number and some geometrical and physical parameters, such as the height of the chimney and the solar radiation intensity. The approach undertaken in this paper is related mainly in analyzing a solar chimney power plant to produce a power of a few MW.

Abstract: Excessive water production is one of the main problems that occur during hydrocarbon production. During water injection, the less viscous water which has higher mobility than the reservoir fluid, tends to by-pass the oil. This phenomenon is normally called water fingering. Density difference between denser water and oil makes the water segregate to the bottom of layer, creating water tongue. Uncontrolled excessive water production will reduce oil production potential and increase the cost for water management and treatment. This phenomenon is economical unfavorable. Intelligent well integrated with monitoring systems and inflow control valve (ICV) has been applied in producing hydrocarbon. The excessive flow of water into well can be controlled using ICV. There are various methods and approaches been proposed to control water production. One of them is by measuring the spontaneous potential (SP) using permanent sensor outside the insulated casing. However, thermoelectric (TE) potential could also contribute to the measurement of the SP. The main objective of this experiment is to measure TE potential across sandstone rock sample at four different salinities which are 0.001M, 0.01M, 0.1M, and 1.0M of brine (NaCl). The core samples dimension is 7.62 cm in length and 3.81 cm in diameter. Temperature difference up to 80°C was applied to rock sample inducing different TE potentials at different salinities. Gradual heating technique was applied in creating temperature difference by using a temperature controller. Three different experiments were conducted for each salinity and real-time voltage (V) and temperature (T) were recorded using data acquisition system. Then the TE coupling coefficient can be determined by calculating the slope after plotting Voltage versus Temperature Difference. The result is as the salinity increases, TE coupling coefficient decrease and drop to zero around 0.1M. The result shows small but still measurable thermoelectric coupling coefficients.

Abstract: Optimization of energy-related systems with by-products that involve environmental degradation has never been so crucial today with depleting resources and global concerns over negative impacts on our environment. This paper reports the results of an optimization scheme on the coefficient of performance (COP) of a standing wave thermoacoustic refrigerator based on genetic algorithm. The environmentally friendly refrigerator operates without any CFCs, which has been associated with the depletion of ozone, a substance that prevents uv light from reaching the earth’s atmosphere. A single-objective optimization to maximize the COP of a thermoacoustic refrigerator has been completed. The variables investigated include the length of the stack, Lsn, center position of the stack, xsn, blockage ratio, B and drive ratio, DR. The results show that a COP of up to 1.64 is achievable which provides promise for future improvements in the present systems.

Abstract: Condensation heat transfer has been evaluated experimentally on the tube side of three different circular tubes with inner diameter of 6.2, 7.5 and 9.2mm, respectively. Two-phase fluid flow conditions include mass fluxes from 200 to 320kg/m²s, qualities between 0.1 to 0.9, and heat flus range of 5 to 20kW/m² at a fixed saturation temperature of 48°C. Results showed that the average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux, but decreased with inner diameter. The experiment results are compared with the existing heat transfer coefficient correlations, and a new correlation is developed with good prediction.

Abstract: In the present work, an experimental investigation has been made to analyze the performance of microchannel heat sink under transient operating conditions. The transient analysis has been made by estimating the response time for different input heat flux and coolant mass flow rate. Analysis has been made for rectangular cross-section microchannels fabricated on a copper block of size 25.7 × 12 × 10 mm³. Twelve (12) numbers of microchannels are fabricated in the copper block. The width and depth of individual channels are 400 μm and 750 μm respectively. Performance analysis has been made for both single phase and flow boiling conditions of the coolant flow using deionized water as coolant. Experiments have been performed for coolant mass flux (G) range of 90 - 250 kg/m²s and input heat flux (q) range of 20 - 300 kW/m² respectively. It has been observed that at constant input heat flux, response time decreases with the increase in coolant mass flux during single phase cooling. However this trend is not strongly followed during the two-phase or flow boiling cooling condition.

Abstract: Natural gas, from the environmental point of view, is the cleanest fuel after hydrogen. Widespread use of gaseous fuel is restricted by its storage problems in containers under high pressure (20-25 MPa) or liquefied gas at low temperatures (-163 °C). One of the most promising solutions to such problems (high pressure and low temperature) is to develop a vessel based on adsorption technology, designed for efficient storage of natural gas at relatively low pressures (3-3.5 MPa). Adsorbed natural gas (ANG) storage system provides reduction in compressor cost, tank manufacture cost and gas refueling cost (energy consumption of ANG is lower than that of compressed (CNG) and liquefied natural gas (LNG) storage systems) and improves environmental safety by transferring vehicles from gasoline to natural gas. This paper presents simulation results of charging of ANG vessel under the dynamic conditions where the heat effect is controlled by the fin and tube type heat exchanger.

Abstract: In the present study, mixed convection in a horizontal rectangular duct using Al₂O₃ is numerically investigated. The effects of different Rayleigh number, Reynolds number and radiation on flow and heat transfer characteristics were studied in detail. This study covers Rayleigh number in the range of 2 10⁶ ≤ Ra ≤ 2 10⁷ and Reynolds number in the range of 100 ≤ Re ≤ 1100. Results reveal that the Nusselt number increases as Reynolds and Rayleigh numbers increase. It was also found that the dimensionless temperature distribution increases as Rayleigh number increases.