Thermal Energy Conservation Research Articles

Utilization of Basalt Stone as a Sensible Heat Storage Material

Thermal energy storage plays an important role in the conservation of thermal energy in many processes, such as waste heat recovery and load leveling at power plants, including those utilizing alternative energy sources. The objective of this study is to investigate many aspects of basalt stone as a material of heat storage. Belonging to gabbro volcanic group, magmatic basalt rock is a thin grained, dark colored (black), hard and durable material. Within the scope of the theory of sensible heat storage, heat and material properties of the basalt stone were studied, while comparisons were made with other materials of heat storage.

Assessment of the thermal performance and energy conservation opportunities of a cement industry in Indonesia

A simple model is presented to assess the thermal performance of a cement industry with an integrated view to improve the productivity of the plant. The model is developed on the basis of mass, energy and exergy balance and is applied to an existing Portland cement industry in Indonesia. The data obtained from industry show that the burning efficiency and the second law efficiency of the kiln system are 52.07% and 57.07% respectively. Cooler efficiency and heat recovery efficiency are 47.75% and 51.2% respectively. The unaccounted loss at kiln system was found to be 1.85% and that of cooler system was 19%. The high loss at cooler was mainly due to the convection and radiation losses from the uninsulated cooler. Irreversibility of the system was found to be about 20%, which is due to the conversion from chemical to thermal energy. The thermal energy conservation opportunities are identified. This study show that by replacing industrial diesel oil (IDO) with waste heat recovery from kiln and cooler exhaust for drying of raw meal and fuel, and preheating of combustion air, a cement industry in Indonesia can save about 1.264 × 10 5 US dollars per year.

A Model of Coupled Heat and Moisture Transport in an Annular Clay Barrier

The design of repository seals for deeply buried high-level radioactive wastes incorporates densely compacted clayey barriers around metallic waste canisters. In this paper, a mathematical model that is based on conservation of thermal energy and mass is developed to describe the locations of moisture and temperature fronts within a barrier, around a cylindrical waste canister of 1 m radius, containing radionuclides with half-lives that range from 100 to 10,000 years. The solution developed is axisymmetric: the moisture fraction w and temperature T vary only with time t, and radial distance r from the axis of the cylindrical waste canister. The model produces parabolic partial differential equations. The spatial domain is discretized such that ordinary differential equations that result are solved. Computations using a uniform mesh of 0.1 m and a cooling coefficient of 6.7x10\U-2\N with assumed but typical data on material properties, indicate that coupling of transport processes would be negligible in the case of radionuclides with long half-lives. Also, a quasisteady vaporization front can form and propagate outward over the course of several decades after waste emplacement. The evolution of the front is somewhat insensitive to the half-life used and the permeability of the clayey barrier material.

Computational fluid dynamics

The improvement in the quality of life together with thermal comfort, air quality, health, workplace security and energy conservation measures justify the integral education of environmental (outdoor and/or indoor) phenomena. Environmental education, through the appropriate tool, can play an important and vital role in this domain. Computational fluid dynamics (CFD) is the analysis of systems involving fluid flow, heat transfer and associated phenomena such as distribution of pollutants by means of computer‐based simulation. This technique, allowing the simulation and the visualization of environmental problems, represents a powerful tool to motivate, guide and educate on the environment. The main objective of this paper is to introduce this new advanced active tool in environmental education, directed to indoor‐environment quality, that permits the prediction and visualization of air movement, air temperature and air contaminant (such as tobacco smoke) distribution in rooms. With suitable mathematical models and boundary conditions, a computational code has been developed to predict and visualize these phenomena. In order to demonstrate its applicability, the simulation of air contamination distribution in an office room with a smoker was performed.

A Stefan Problem with Surface Tension as the Sharp Interface Limit of a Nonlocal System of Phase-Field Type

A model for the evolution of phase boundaries reminiscent of the phase-field model is considered. The equation related to conservation of thermal energy is diffusive and coupled to an equation for the order parameter, which contains a nonlinear convolution operator, related to the limit of an interacting particle model with Kac-potential. Under diffusive rescaling the solutions converge to solutions of the Stefan problem with kinetic undercooling and surface tension.

The finite element model of non-isothermal semi-solid fluid flow

A new general non-isothermal rheological model of metal alloys in the thixoforming processes has been derived. The model uses the two-phase approach to flow description with two momentum conservation equations buckled by common pressure and interface drag force. The thixotropy phenomena occurring in the globular structure of the alloy, is modelled by means of an extra kinetic equation describing agglomeration degree. The non-isothermal processes are governed by the thermal energy conservation equation coupled with a temperature–enthalpy and solid fraction relationship. The time evolution of the solid fraction is described by the mass conservation equation for the solid phase with a source term based on the Sheil equation. The mathematical model has been implemented in an original efficient finite element algorithm, which is tested against very well known benchmark problems as well as used in a real 3-D simulation of a thixoforming process.

Thermal behavior of masonry walls in Istanbul

This study is based on thermal performance analysis and evaluation of masonry wall configurations with respect to thermal comfort and energy conservation with the software doe -2.1E. The analysis comprises the comparison of the annual heating and cooling loads of the masonry wall alternatives of the sample building. Besides, the exterior and interior surface temperatures of the wall alternatives are computed for appraising dynamic temperature effects on their thermal behavior both in heating and cooling seasons under the climatic conditions in Istanbul having temperate humid climate.

Thermal behavior of masonry walls in Istanbul

This study is based on thermal performance analysis and evaluation of masonry wall configurations with respect to thermal comfort and energy conservation with the software doe-2.1E. The analysis comprises the comparison of the annual heating and cooling loads of the masonry wall alternatives of the sample building. Besides, the exterior and interior surface temperatures of the wall alternatives are computed for appraising dynamic temperature effects on their thermal behavior both in heating and cooling seasons under the climatic conditions in Istanbul having temperate humid climate.

New boundary constraints for elliptic systems used in grid generation problems

New boundary constraints for elliptic partial differential equations as used in grid generation problems in generalized curvilinear coordinate systems are proposed in this paper. These constraints, based on the principle of local conservation of thermal energy in the vicinity of the boundaries, are derived using the Green’s Theorem. They uniquely determine the so called decay parameters in the inhomogeneous terms of these elliptic systems. These constraints 1 Invention under US Patent application process. 1 are designed for boundary clustered grids where large gradients in physical quantities need to be resolved adequately. It is observed that the present formulation also works satisfactorily for mild clustering. Therefore, a closure for the decay parameter specification for elliptic grid generation problems has been provided resulting in a fully automated elliptic grid generation technique. Thus, there is no need for a parametric study of these decay parameters since the new constraints fix them uniquely. It is also shown that for Neumann type boundary conditions, these boundary constraints uniquely determine the solution to the internal elliptic problem thus eliminating the nonuniqueness of the solution of an internal boundary value grid generation problem with Neumann boundary conditions.

Experimental and Numerical Investigation on the Regeneration Process of Passive Solar Shading and Dehumidifying System for Hot-humid Areas

This paper presents an idea of passive solar shading and dehumidifying system to improve the indoor thermal environment and energy conservation in hot-humid areas. Elementary investigation on the regeneration of this passive system is undertaken. First, the test apparatuses are constructed for solar shading dehumidifier and silica gel is chosen as the desiccant material; the effects of internal surface color and the orientation of the test apparatus on the regeneration process are experimentally investigated. Then a mathematical model and valid Fortran program made to calculate the regeneration process are checked by the experimental results, it is used to analyze the influences of airflow rate, glass layer, the thickness of desiccant material and insulation material. The distribution and variation of moisture content and air temperature at different point in the apparatus are also obtained by numerical calculation. Experimental results and numerical results show that: lower airflow rate is beneficial to the regeneration of this passive system, the airflow rate influences the regeneration process greatly; thinner desiccant material layer can be quickly and fully regenerated, but adsorbs moisture easily; single glass layer and black internal surface are more affective of using solar energy to regenerate the desiccant material; insulation material has almost no effect on the regeneration process. The numerical results also show that desiccant material is more dehydrated when it is far from the inlet of air.

Internal heat integration – the key to an energy‐conserving distillation column

AbstractThis paper illustrates the thermal energy conservation potential of the so‐called heat integrated distillation column (HIDiC), which combines advantages of direct vapour recompression and diabatic operation at half of the normal column height. In a typical close boiling mixture separation, compared with a column utilising the usual vapour recompression scheme, HIDiC halved the consumption of exergy at approximately the same capital cost, indicating a strikingly short pay‐off time. The complexities of integrating the heat transfer equipment in the stripping section with proven gas/liquid contacting devices, which may work adversely to practical implementation of HIDiC concept, are also addressed.© 2003 Society of Chemical Industry

406 暖房便座の温熱快適性と省エネルギー

406 暖房便座の温熱快適性と省エネルギー

The limit U values for building envelope related to building form in temperate and cold climatic zones

The aim of this paper is to introduce a methodology which enables to revise the limit values of the heat transfer coefficient in accordance with the building form with respect to thermal comfort and energy conservation. In this study, the building form is represented by the ratio of the total façade area to building volume (A/V). As the building form and the heat transfer coefficient ( U value) of a building are the most important parameters affecting indoor climate, they have been taken into consideration in detail. The proposed methodology enables to determine the limit values of the building envelope heat transfer coefficients on the basis of A/V ratios and other design parameters affecting indoor thermal comfort and energy conservation such as orientation, window type, optical and thermophysical properties of the building envelope. The methodology has been applied for temperate and cold zones of Turkey and the results of the application are given by sample graphics in the paper.

In-flight oxidation of composite powder particles during thermal spraying

This paper presents a mathematical model of the in-flight thermal behavior and oxidation of powder particles during thermal spray deposition. In particular, stainless steel and Cr 3C 2–NiCr particles are investigated. The in-flight model accounts for the acceleration and deceleration of the particles during flight under variable fluid velocity, while the thermal model takes into account heating, melting, cooling and possible solidification as the particle travels towards the substrate. A finite difference method is used to solve the thermal energy conservation equation of the particles. The model includes non-equilibrium calculations of the phase change phenomena in the liquid–solid (mushy) zone and dissolution of the ceramic reinforcement in the composite particles. The growth of the oxide layer at the particle surface is represented by a modified boundary condition, which includes finite-rate oxidation. The results obtained give the interrelations between various process parameters and the oxidation phenomenon.

The adaptive model of thermal comfort and energy conservation in the built environment.

Current thermal comfort standards and the models underpinning them purport to be equally applicable across all types of building, ventilation, occupancy pattern and climate zone. A recent research project sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, RP-884) critically evaluated these assumptions by statistically analysing a large database of research results in building comfort studies from all over the world (n=22,346). The results reported in this paper indicated a clear dependence of indoor comfort temperatures on outdoor air temperatures (instead of outdoor effective temperature ET* used in RP-884), especially in buildings that were free-running or naturally ventilated. These findings encourage significant revisions of ASHRAE's comfort standard in terms of climatically relevant prescriptions. The paper highlights the potential for reduced cooling energy requirements by designing for natural or hybrid ventilation in many moderate climate zones of the world.

Optimization of the LENS Rapid Fabrication Process for In-Flight Melting of Feed Powder

A model for in-flight melting of feed-powder particles propelled through a laser beam in the Laser-Engineered Net Shaping (LENS) process has been developed. The model is next incorporated in an optimization analysis to determine optimum LENS process parameters (laser power, particle velocity, and the angle between the laser-beam axis and particle trajectory), which maximize the probability for in-flight particle melting while ensuring the absence of melting of the surface of the substrate. A simple model, based on solution of the thermal energy conservation equation, is also developed to determine the laser-power threshold for melting of the substrate surface. The optimization analysis is then applied to Inconel 625 Ni-Cr-Mo superalloy. The results show that by maximizing the laser power and the residence time of the particles in the laser beam (increases with reductions in particle velocity and particle trajectory angle), the probability for in-flight particle melting can be greatly increased, i.e. relatively coarse (−30/+40 mesh size) particles can be melted by propelling them through the laser beam.

A Numerical Analysis on the Freeze Coating of a Non-Isothermal Flat Plate with a Binary Alloy

A numerical analysis on the freeze coating process of a non-isothermal finite dimensional plate with a binary alloy is performed to investigate the growth and decay behavior of the solid and the mushy layer of the freeze coat and a complete procedure to calculate the process is obtained in this study. The continuously varying solid and mushy layers are immobilized by a coordinate transform and the resulting governing differential equations are solved by a finite difference technique. To account for the latent heat release and property change during solidification, proper phase change models are adopted. And the convection in the liquid melt is modeled as an appropriate heat transfer boundary condition at the liquid/mushy interface. The present results are compared with analytic solutions derived for the freeze coating of infinite dimensional plates and the discrepancy is found to be less than 0.5 percent in relative magnitude for all simulation cases. In addition the conservation of thermal energy is checked. The results show that the freeze coat grows proportional to the 1.2 square of axial position as predicted by analytic solutions ar first. But after the short period of initial growth, the growth rate of the freeze coat gradually decreases and finally the freeze coat starts to decay. The effects of various non-dimensional processing parameters on the behavior of freeze coat are also investigated.

Numerical simulation of dump combustor with auxiliary fuel injection

Solutions of the steady, two-dimensional Navier-Stokes, thermal energy, radiation flux, and species conservation equations have been computed for a dump combustor geometry with downstream constriction. The equations are solved in the conservative finite-difference form on a nonuniform rectilinear grid of sufficient resolution to capture the momentum/thermal boundary layers accurately. The numerical procedure, SIMPLEST, which is a variation of SIMPLE, is used to ensure more rapid convergence. A κ−e model is incorporated for the enclosure of turbulence with a wall function. The combustion model, ESCRS (extended simple chemically-reacting system) with eddy break-up model for the reaction rates of species conservation equation or energy equation is also used. For the good destruction of hazardous waste, it is effective that the waste is injected in the recirculation zone of high temperature with the condition not disturbing the combustion cavity. Excess oxygen from a lean core flame can be effectively utilized for waste destruction with the hydrocarbon waste injection as fuel-rich condition. The core flame has a significant impact on the structure of recirculation cell, in some cases completely changing the nature of the flow within the cavity. The optimum velocity of waste injection exists for the highest temperature at the recirculation zone. A premixed flame type for the auxiliary fuel is good for high temperature and long residence time to be large cavity in the recirculation zone.

One-dimensional thermal model for direct methanol fuel cell stacks

Using the one-dimensional thermal model for the direct methanol fuel cell (DMFC) (presented in Part 1), based on the differential thermal energy conservation equation, which describes the thermal behaviour of a DMFC stack comprised of up to 25 large (272 cm2) cells, temperature profiles are predicted along the stack length. The model is used to assess the effect of operating parameters (temperature gradient, current density, flow rate and pressure) on the temperature profile along the stack. In addition, it enables investigation of the stack thermal management and the effect of altering a number of systematic parameters such as the number of cells in the stack, the active and exposed area and the interactions between the physical properties of the various components. The model aids the fuel cell system designer to gain an insight in the stack structure and select materials and geometric configurations that are optimal from a thermal management point of view.

One-dimensional thermal model for direct methanol fuel cell stacks

A thermal energy model for the direct methanol fuel cell (DMFC) is presented, based on the differential thermal energy conservation equation. The model is used to predict the thermal behaviour of a DMFC stack comprising of many large cells in a bipolar arrangement. The model allows an assessment of the effect of operating parameters (feed and oxidant inlet temperature, flow rate and pressure, operating current density), and the system design (active area, material properties and geometry) on the temperature profile along the stack and the interactions between the various components in the cell stack. The model is designed to enable the fuel cell system designer to estimate, insulation requirements, auxiliary equipment sizing and required thermal duties and response. Furthermore, the model can be used to decide on the optimum set of operating conditions for an efficient thermal management of the whole process.