Sadik Dost

Performance analyses of sensible heat storage systems for thermal applications

In this paper, sensible heat storage (SHS) systems and performance evaluation techniques are studied. A detailed investigation is presented of the availability of SHS techniques for solar thermal applications, selection criteria for SHS systems, the economics of SHS systems, the main issues in evaluating SHS systems, the viability of SHS systems, the environmental impacts of SHS systems and criteria for SHS feasibility studies, as well as energy saving options. In addition to energy and exergy analyses, several definitions of energy and exergy efficiency for the performance of SHS systems are provided with an illustrative example.

A modelling study for moisture diffusivities and moisture transfer coefficients in drying of solid objects

This article presents an effective analytical model for determining the moisture diffusivities and moisture transfer coefficients for solid objects (namely, infinite slab, infinite cylinder, sphere; and also for irregularly shaped objects, by using a shape factor) subject to drying applications in a medium. The unsteady-state moisture diffusion analysis is used on the basis of two important criteria: 0.1 100. The drying coefficients and lag factors were employed. The analytical models are then verified using available experimental data taken from the literature. The results show that the method presented here can be used to determine the moisture diffusion coefficients and moisture transfer coefficients for such solid objects in a simple and accurate manner for a variety of drying applications.

A perspective on thermal energy storage systems for solar energy applications

The use of thermal energy storage (TES) systems is essential for solar power systems because of fluctuations in the solar energy input. Several classes of storage may be required for a single installation, depending on the type and scale of the solar power plant itself, and the nature of its integration with conventional utility systems. For heating and hot water applications, water and phase change materials (PCMs) constitute the principle storage media. Soil, rock and other solids are used as well. Water has the advantage of approximately 80% less volume than that of water for a temperature variation of 10°C, which is the difference between temperatures of a fully charged and a fully discharged storage tank. Some PCMs are viscous and corrosive, and must be segregated within the container in order to be used as a heat transfer medium. For heat storage, two PCMs must be available, unless heat pumping is employed. A variety of solids is also used; rock particles of 20 to 50 mm in size are most prevalent. Well-designed packed rock beds have several desirable characteristics for energy storage. The heat transfer coefficient between the air and the solid is high, the cost of the storage material is low, the conductivity of the bed is low when air flow is not present and a large heat transfer area can be achieved at low cost by reducing the size of particles. TES systems have also been suggested for storing thermal energy at medium (38–304°C) and high temperatures (120–566°C). For instance, systems in an oil-rock system for hot water and heat-recovery applications are examples of medium-temperature applications, while those in molten nitrate salt systems (an excellent storage medium) for steam production for process applications are for high temperatures. Oil-rock TES, in which the energy is stored in a mixture of oil and rock in a tank, is less expensive than molten nitrate salt TES, but is limited to low-temperature applications. However, this oil-rock TES has been proven successful for solar thermal applications. The selection of the type of TES depends on various factors such as the storage period (diurnal or seasonal), economic viability, operating conditions, etc. In this article, a study of TES systems (including materials) is presented particularly with solar thermal applications in mind. The evaluation of their performances, cost and economic viability, ease of installation, cleanliness, environmental impact, safety factors, technological usability and applicability are discussed.

Wave propagation in fluid filled nonlinear viscoelastic tubes

SummaryThe present work considers one dimensional wave propagation in an infinitely long, straight and homogeneous nonlinear viscoelastic tube filled with an incompressible, inviscid fluid. In order to include the geometric dispersion in the analysis, the tube wall inertia effects are added to the pressure-area relation. Using the reductive perturbation technique, the propagation of weakly nonlinear waves in the long-wave approximation is examined. In the long-wave approximation, a general equation is obtained, and it is shown that by a proper scaling this equation reduces to the well-known nonlinear evolution equations. Intensifying the effect of nonlinearity in the perturbation process, the modified forms of these evolution equations are also obtained. In the absence of nonlinear viscoelastic effects all the equations reduce to those of the linear viscoelastic tube.

Energy intensities for Canada

The gross domestic product (GDP) measures the value of goods and services produced in a country in one year. There is a close relationship between the GDP and energy supply (and consumption). This relationship is a good indication of the level of economic development of a country. The GDP per capita is often used to measure the living standard of a country. Measures of the total energy use are useful for addressing energy intensity issues. Energy use is a numerator in determinating energy intensities. A commonly used and frequently quoted measure of energy use is the ratio of energy expenditure to GDP. Two types of energy intensities, namely TPES/GDP and TFC/GDP, are useful tools in making comparisons for both energy and GDP projections for countries. In this article we present evaluations and future projections for energy resources and energy intensities for Canada. The total primary energy supply (TPES) and total final energy consumption (TFEC), and energy intensities for supply and consumption are analyzed. The energy data are presented and analyses of the differences in energy and GDP ratios are carried out at an aggregate level by examining differences in factors affecting the energy intensities. In order to provide accurate projections for the future, new correlations were developed between the GDP, TPES, TFEC, TPES/GDP, TFEC/GDP, and population of Canada.

Energy and GDP

Understanding of the role of energy use at the national level requires the understanding of the relationship of energy use to economic activity and social well-being. Gross domestic product (GDP) measures the value of goods and services produced in a country in one year. There is a close relationship between energy supply, energy consumption, and GDP, which indicates the economic development of a country. The living standard of a country is often measured by the per capita GDP. This article presents the evaluations and future projections of energy and energy resources of the Organization for Economic Cooperation and Development (OECD). The total primary energy supply, total final energy consumption, and energy intensities for supply and consumption are analysed. The energy data for all OECD countries are presented and analyses of the differences in energy and GDP ratios are conducted at an aggregate level by examining differences in the factors that affect the energy intensities. To provide accurate projections for the future, new correlations are developed between average GDP, total primary energy supply, total final consumption, total per capita primary energy supply, total per capita final consumption and total OECD population.

Convective transport and interface kinetics in liquid phase epitaxy

Abstract This paper presents a time-dependent, two-dimensional model which accounts for convective and diffusive transport, and surface kinetics in liquid phase epitaxial crystal growth. The governing equations are solved numerically and the model is applied to investigate the roles of natural convection and interface kinetics during growth under constant cooling rate. During the initial phase, growth is found to proceed according to the diffusion-reaction rate model of Ghez and Lew. Thereafter, a complex, transient natural convection pattern develops predominantly in the upper region of the growth cell. Convection is found to enhance mass transport considerably along the top substrate, and results in the formation of wavy, irregularly shaped upper substrates with up to twice the thickness of the lower ones. Another remarkable consequence of convection is a change in the process at large times from what would be, in the case of pure diffusion, a bulk transport limited process, to one where interface kinetics becomes an important rate-limiting mechanism.

Modeling Transient Heat Transfer Using SPH and Implicit Time Integration

In this article, a two-dimensional transient heat conduction problem is modeled using smoothed particle hydrodynamics (SPH) with a Crank-Nicolson implicit time integration technique. The main feature of this work is that it applies implicit time stepping, an unconditionally stable Crank-Nicolson approach, in the thermal conduction simulation of liquid-phase diffusion (LPD) semiconductor crystal growth. This SPH simulation is compared with the equivalent finite-volume results. As well, two transient thermal conduction test problems are simulated using both explicit and Crank-Nicolson schemes, and their results compared with the analytical solutions. One of the current drawbacks of SPH is that explicit time-stepping algorithms, such as predictor-corrector methods or leapfrog methods, require extremely small time steps for a stable simulation. Using implicit time integration opens SPH up to a much larger class of practical problems in applied mechanics.

A continuum model for liquid phase electroepitaxy

Abstract This paper presents a macroscopic continuum model for liquid phase electroepitaxial growth of single crystal semiconductors. The governing equations and associated boundary and interface conditions of the model are obtained from the fundamental principles of electrodynamics and thermomechanics of continua. The constitutive equations of the substrate/source and the liquid phase are derived from an irreversible rational thermodynamic theory. By means of systematic simplifications, special forms of the governing equations and associated interface conditions are presented in order to obtain tractable equations and gain physical insight for various thermoelectric effects involved in the process. The formulation presented here is valid for general LPEE growth processes with any configuration, and takes into account electromigration and the well-known thermoelectric effects such as Joule, Peltier, Thomson, Dufour, and Sorel. The fundamental equations derived here can also be used to model the growth process of ternary compound semiconductors, either directly or with modifications depending on the type of compositions considered.

The effect of applied magnetic field on the growth mechanisms of liquid phase electroepitaxy

Abstract Binary (GaAs) and ternary (InGaAs) single crystals were grown by the growth process of liquid phase electroepitaxial (LPEE) under an applied static magnetic field. The effect of the applied magnetic field on two main growth mechanisms of the LPEE growth process, namely the “electromigration” and “natural convection” in the liquid zone, were examined numerically and experimentally. Numerical results show that the flow and concentration patterns exhibit three distinct stability characteristics: stable structures up to the magnetic field level of 2.0 kG, transitional structures between 2.0 and 3.0 kG, and unstable structures above 3.0 kG. In the stable region, the applied magnetic field suppresses the flow structures, and the intensities decrease with the increasing magnetic field level. In the transitional region, the flow intensity increases dramatically with the magnetic field strength, and concentrations show very different patterns leading to a wavy growth interface. Under strong magnetic field levels, the flows cells are confined to the vicinity of the vertical wall and exhibit significant non-uniformity near the growth interface. Experiments performed under various magnetic field levels show that the growth process at the 4.5 kG field level yields satisfactory growths. However, the growth experiments at higher field levels were unsatisfactory and unstable. Although the crystals were still grown, large wholes were observed in the grown crystals. This observation was attributed to the strong interaction of the applied electric and magnetic fields, making the convective flow in the solution very strong and unstable. However, lower magnetic field and electric current levels had very beneficial effects, namely flat growth interfaces and prolonged growth due to weak convection in the liquid zone, and a substantial increase in the growth rate (about 5–10 times higher) due to the effect of magnetic field on the mechanisms of “electromigration”. Such positive developments give the LPEE growth process the potential of becoming a commercial technique.