Showing papers in "International Journal of Energy Research in 1993"

A multiobjective programming approach to energy resource allocation problems

Abstract: The optimal allocation of energy resources to various energy end uses is an important strategy for bridging the energy supply and demand gap in India. It has been recognized that the allocation should be guided by multiple criteria. A multiobjective programming model for such an allocation process is presented in the paper. The normative model has been applied for the households sector of Madras city. The model is solved using non pre-emptive goal programming. Variations in the original model have been made to build alternative scenarios. The results of the original model and the alternative scenarios indicate that the use of solar thermal energy, natural gas, LPG, fuelwood, kerosene and lignite should be promoted for cooking, and the use of grid electricity and diesel, should be promoted for meeting water pumping demands. They favour the use of electricity generated from diesel for lighting, and the use of solar photovoltaics for meeting the electricity demands of household appliances. The results also indicate that grid electricity and electricity generated from fuelwood should be promoted to meet the demands of all the four household end uses, and point to the need for more research into solar photovoltaics, which may become competitive for meeting household demands in the future.

Experimental verification of a heat pump assisted continuous dryer simulation model

Abstract: The experimental and predicted performance of a prototype heat pump assisted continuous dryer is reported. The dryer was shown to be capable of specific moisture extraction rates (SMERs) of between 1.5 and 2.5 kg/kWh using wetted foam rubber as the test material being dried. The results highlight the importance of maintaining conditions of high relative humidity within the air stream entering the evaporator; an increase in the relative humidity from 30 to 80% was shown to give a two‐fold increase in the SMER. An optimum evaporator bypass air ratio of between 60 and 70% was observed for this dryer. The effects on performance of deviations from this optimum condition were found to be less significant than had been indicated by earlier models. The predicted performance of the dryer using a simulation model developed previously by the authors was in good agreement with the corresponding measured values.

Effects of oil on output growth and inflation in developing countries: The case of Thailand from January 1966 to January 1991

Abstract: The paper reports the results of a simple cointegration analysis applied to bivariate causality models and quarterly data on crude oil consumption, GDP and inflation in Thailand to investigate the long-term relationships in the sense of Granger between oil and these two major macroeconomic aggregates. For the period from January 1966 to January 1991, the empirical evidence indicates that oil consumption, output growth and inflation rate, as formulated in our models, are not random walks. In addition, oil consumption is significantly cointegrated with economic growth and, unfortunately, inflation rate.

Steady‐state simulation of vapour‐compression heat pumps

Abstract: A vapour compression simulation model was developed. Simple mathematical models were employed for each component of the cycle. They resulted in a set of nonlinear equations, which was solved numerically. Heat losses from condenser to ambient were included. The model is capable of predicting the operating point of the system (including condensing and evaporating pressures) as a function of equipment characteristics (for example, compressor swept volume, speed and clearance ratio, and heat exchanger overall conductances) and prevailing thermodynamic conditions (such as heat source and heat sink temperatures with the mass flow rates of their fluids). The predicted performance was compared to that of an existing R-12 unit, showing good agreement. As an application, a comparative analysis is made on the thermodynamic performance of a domestic heat pump running on two different refrigerants: R-12 and R-134a.

Analytical and experimental investigation of thermal stratification in storage tanks

Abstract: An analytical and experimental investigation of transient turbulent two-dimensional charging and discharging of a sensible heat storage tank has been conducted. Parametric studies showed that the turbulent mixing factor due to hydrodynamic disturbances at the inlet ports is the most significant item in the performance of thermal stratification storage tanks. Furthermore, the effect of the aspect ratio and convection at the walls in promoting stratification have been studied. Comparison with experimental data showed the capability of the present analytic approach to accommodate, with a satisfactory degree of accuracy, such problems.

Computer analysis, design and simulation of horizontal ground heat exchangers

Abstract: This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77.

Free and forced convection boundary layer flow through a porous medium with large suction

Abstract: An analytical study is made of the free and forced convection boundary layer flow past a porous medium bounded by a semi-infinite vertical porous plate Locally similar solutions are then obtained by a perturbation method for large suction Solutions for the velocity and temperature distributions are shown graphically for various suction velocities and values of the driving parameter G r /R e 2 , where G r is the Grashof number and R e is the Reynolds number The corresponding values of the skin friction coefficient and the Nusselt number are finally shown in tabular form

Thermodynamic limits on the performance of a solar thermochemical energy storage system

Abstract: Use of closed-loop thermochemical energy storage systems for the storage of solar energy places fundamental limits on the amount of work which can be extracted from the recovered energy. These arise because of thermodynamic irreversibilities associated with the storage system itself and because of the need to degrade collected solar energy to the characteristic temperature of the reaction system chosen. General expressions for the exergetic and work recovery efficiencies of thermochemical storage systems have been developed by assuming that the reaction process is the only source irreversibility within the closed-loop system. These have been used to plot contours of constant efficiency for the ammonia-based thermochemical system. The effect of spontaneous separation of mixtures due to the preferential condensation of ammonia has been examined analytically and graphically. The analysis presented represents a necessary prerequisite for the optimization of system efficiencies by reactor design.

Degradation of a stratified thermocline in a solar storage tank

Abstract: The thermal stratification behaviour in a solar storage tank is simulated and analysed using a theoretical model based on an integral transform technique. A comparison with available experimental and theoretical data is used to validate the present theoretical results. The accuracy of the model in simulating the thermal behaviour of stratification is reasonably good, especially when consideration is given to the complexity of the physical mechanisms involved, and the relative simplicity of the model. The effect of the heat loss parameter is investigated and it is found that initially it is strongly spatially and temporally dependent. Therefore, a functional form that accurately represents the heat loss parameter is needed for closer agreement with experimental results. However, after a relatively long time, the assumption of a constant heat loss parameter is adequate to produce acceptable predictions.

Developing strategies for robust energy systems. I: Methodology

Abstract: Strategic energy planning is concerned with investments in energy technologies with long lead times and long life times. Of special interest are uncertainties about future developments that could lead to a major reappraisal of the cost-efficiency of different energy technologies. Decision making in this context is concerned, therefore, with finding a solution to the decision problem which is both low-cost and robust. Here, a method is described for using hedging to improve the robustness of the energy system. The method is applied using a standard energy systems model, MARKAL. It is shown how the model results can be used for a quantitative analysis of the robustness of the energy system. A study of the Swedish energy system is used as an example, where the uncertain factor is whether or not future restrictions on CO2 emissions will be imposed.

Space heating using small-scale fluidized beds: a technoeconomic evaluation

Abstract: The technical and economic feasibility of small-scale fluidized-bed furnaces (SSFBF) for providing residential space and domestic hot water heating in Nova Scotia is analysed. A model of the provincial housing stock is developed to estimate the residential energy consumption for domestic space and hot water heating. The number of dwellings in the province is estimated from available statistical data, and the heating equipment in these dwellings is classified by type, age, and principal heating fuel. Market share levels are assumed for the new and replacement residential housing markets, and the number of SSFBFs required for those levels is calculated. The amount of coal water slurry (CWS) fuel used by the SSFBFs is calculated, and the quantities of oil, wood, and coal displaced by the CWS, as well as the number of jobs created by the adoption of SSFBF technology, are estimated. A procedure is developed to design SSFBFs in the 15–250 kW capacity range. Computer programs are developed, based on this procedure, to calculate the furnace design and performance parameters. The manufacturing cost, and the annual fuel and maintenance costs of SSFBFs are estimated, as were the capital, and annual fuel and maintenance costs of various residential heating systems. From these estimated costs, economic analyses are carried out using the annualized cost and total present worth methods. The findings of this work indicate that SSFBF technology is technically feasible, and is economically superior to conventional oil, wood and coal fired systems for residential space and domestic hot water heating.

Analysis of the Lithuanian final energy consumption using fuzzy sets

Abstract: In the paper, the development of final energy consumption in Lithuania, on the basis of realistic economic scenarios, is investigated. The main parameters influencing the energy consumption are the gross national product (GNP) and the wholesale price of energy. Owing to the uncertainties in former socialist economies, these parameters are described as ‘fuzzy sets.’ The theory of fuzzy sets is used to study the influences that the prices of preceding periods have on the actual final energy consumption, with a quasidynamic model. In so far as this mechanism cannot be ascertained for Lithuania, experiences with other former centrally planned economies, which have already turned into a kind of market economy, are applied to give realistic projections for the transitory period. The underlying scenarios for the GNP and price developments are taken from official Lithuanian projections. The results of the fuzzy quasidynamic model are compared with the official final energy demand projections, to provide policy advice for a proper restructuring of the energy system.

Exergetic optimization of a solar thermochemical energy storage system subject to real constraints

Abstract: An approach to the optimization of a solar energy conversion system which involves treating the system as a series of subsystems, each having a single cost determining variable, is proposed. Optimization techniques can be used to determine designs for each subsystem for constant values of the cost determining variable. Subsequently, the allocation of a financial resource amongst subsystems to achieve an optimal performance can be determined. The application to an ammonia-based thermochemical system with direct work output is discussed and possible subsystems are identified. The subsystem consisting of the exothermic reactor has been studied in detail. For this subsystem, the ratio of available catalyst volume to thermal power level is held constant whilst the exergetic efficiency is maximized. Results are presented from a determination of optimized reaction paths using dynamic programming techniques.

Effects of multi-parameter changes on energy use of large buildings

Abstract: We describe the development of a methodology for predicting the effects of multi-parameter changes on the energy use of large buildings. The methodology is based on the third-order Taylor series expansion whose coefficients are evaluated for several key building parameters. The building was coded for energy performance simulation by the DOE-2 computer program. A database of simulation results was created from which the coefficients of the Taylor series expansion were derived. Test results using this energy predicting methodology provided reasonably accurate estimates of the total and cooling energy of a generic building in Singapore.

An exact heat transfer analysis of spherical products subjected to forced-air cooling

Abstract: The thermal analysis of forced-air cooling processes being of primary concern, an experimental and analytical study program was undertaken to investigate the heat transfer during the cooling of figs as spherical food products. The process conditions were analysed according to a mathematical model to gain a better understanding of the product's behaviour. The heat transfer between the product and air was influenced by conduction inside the product, convection outside the product, radiation, respiratory heat rate (internal heat generation), and moisture evaporation at the surface of the product. These situations were considered as three cases, such as h = hc, h = hc + hc, and h = hc, + hr + he. The four various air velocities of 1.1, 1.5, 1.75, and 2.5 m/s were applied in the experimental study. The results obtained by the mathematical model in the estimation of the heat transfer rates from the products were compared with the experimental data, and the best agreement was found for the third case (h = hc + hr + he). The fastest cooling was accomplished with the highest airflow velocity.

Studies on a stove for powdery biomass

Abstract: The sawdust stove, classically known for several decades, is considered here in a scientific study. The poor ignition characteristics and smoky start up are related to improper geometric dimensions. Based on a parametric study, the startup procedure and the dimensions of the stove were modified to achieve a smooth start up. Also, the range of acceptable fuels was enlarged to include tiny unprocessed dry twigs, weeds and wood sticks o the extent of about 50%, with the rest being sawdust-like material. The efficiency of the stove was measured to be 30–40%, depending on the relative size and shape of the vessel and the power level of the stove. A simple procedure for designing this class of stove for various power levels, as well as burning times, is presented. A new concept of multiport design is also discussed.

Micro-level energy planning in India - A case study of bangalore north Taluk

Abstract: Demand for energy in India is constantly on the rise and the conventional supply options available have failed to cope with this increase. The emergence of efficiency improvement, carrier substitution and renewable energy as alternative sources of energy supply, make adherence only to macro-level energy planning unrealistic. A micro-level (district/taluk) energy planning becomes pragmatic under these circumstances to pursue the goal of sustainable development and to harness locally available energy resources. This paper considers the energy consumption pattern in Bangalore North taluk in 1987-88 and projects the demand for energy in 1995-96. Taking into account the different energy sources used to provide different end-use services through different end-use devices, the paper presents a linear programming formulation for optimum allocation. The model considers the conventional and new alternative technologies for meeting the demand for energy service. The results show that substantial savings could be achieved by this optimal allocation. The cost savings could be to the tune of Rs 41.879 million in Bangalore North taluk during 1995-96 (terminal year of Eighth Five-Year Plan). Energy savings of about 27% and cost savings of 16% could also be achieved.

Solar absorption heat transformer applications to absorption refrigerating machines

Abstract: This paper concerns the study of a two-stage vapour absorption system (heat transformer and refrigerating machine) employing the refrigerant absorbent combinations of LiBr-H2O and NH3-H2O successively. The system consists of coupling the previous absorption cycles so that the first-stage absorber produces heating water to circulate in the generator of the second stage. The performances of a solar installation (two stage system plus solar collector) had been tested in Rabat (Morocco). It is found that the system can be operated at lower hot source temperatures and, thus, it can be supplied either from flat plate collectors or from thermal effluents.

Mixed free and forced convection in the incompressible boundary layer along a rotating vertical cylinder with fluid injection

Abstract: We examine the steady incompressible laminar boundary layer flow along a vertical cylinder with isothermal walls. The mixed free and forced convection regime is studied while injection/suction of fluid can take place through the cylinder surface. The two-dimensional boundary layer equations are solved using an efficient finite difference scheme, and velocity and temperature profiles, as well as skin friction, heat transfer and pressure coefficients, are calculated. It is proved that fluid injection can considerably reduce the skin friction and heat transfer at the wall. Also, significant differences are reported when the present results are compared with published results for the zero mass transfer case.

Application of absorption heat transformers for energy conservation in the oleochemical industry

Abstract: A comprehensive energy mapping of an oleochemical plant, for production of technical fatty acids and refined glycerol, was performed. Saturated water vapour is currently produced at 100°C from four flash vessels used to depressurize condensate streams emerging from different processing units in the plant. This vapour has a heat content of 314 kW and is currently condensed in a dump condenser and discharged. Incorporating an absorption heat transformer system would enable the recovery of almost half of this energy and a temperature lift of 34°C can be achieved. The heat transformer system delivers steam at 3 bar which can be fully reused in the plant. An economic analysis resulted in a pay-off period of less than 18 months based on a steam cost of 14.25 $/GJ, an installed equipment cost of 535 $/kW, an annual operation time of 7200 h, and a heat transformer efficiency of 0.45. However, the pay-off period depends on the estimated steam cost and heat transformer efficiency, and also on how much of the existing equipment can be utilized as components in the heat transformer. Installing the heat transformer would require minimum changes in the existing plant.

Simultaneous use of two reductants in a photogalvanic cell for solar‐energy conversion and storage

Abstract: Azur dyes were used with mannitol (MANN) and nitrilotriacetic acid (NTA) in photogalvanic cells for the purpose of solar energy conversion and storage. The photocurrents and photopotentials generated by cells containing azur A, mannitol and NTA systems were 80 μA and 347 mV, respectively. The effects of various parameters on the electrical output, the fill factor, the conversion efficiency and the performance of the cells in the dark were studied.

High‐temperature chemical heat pump based on reversible catalytic reactions of cyclohexane‐dehydrogenation/benzene‐hydrogenation: Comparison of the potentialities of different flow diagrams

Abstract: The authors compare various flow diagrams for high temperature chemical heat pumps (HTCHP) based on the reversible cyclohexane-dehydrogenation/benzene-hydrogenation reactions. A new technological flow diagram for HTCHP is suggested. The peculiarity of this diagram is a multipurpose use of hydrogen-permeable membranes. A comparative thermodynamic analysis of the flow diagrams under consideration is undertaken in order to examine the influence of various factors on the heat efficiency and coefficient of performance of the heat pump. It is shown that the use of the hydrogen-permeable membranes in principle allows one to improve the performance of the HTCHPs and to extend the field of their application in comparison with the HTCHPs based on the flow diagrams suggested earlier.

Development of an energy‐estimating equation for large commercial buildings

Abstract: We present the methodology used in developing an equation for estimating the cooling energy consumption of large commercial buildings. The equation was developed from a database of results generated from computer simulations using the DOE-2 program. Factors accounted for by the equation include: part-load performance of equipment, the number of cooling-degree days, diversity of building operation, and the overall thermal transfer value of the building envelope. Also, the equation has been generalized to take into account the oversizing of the chiller from 110% to 160% of the design capacity. Parametric analyses using single- and multiple-parameter variations validated the accuracy of the equation.

Developing strategies for robust energy systems. II: Application to CO2 risk management

Abstract: One of the most important determinants for the design of the future energy system is whether or not constraints on CO2 emissions will be imposed. Here, this issue is treated as a decision under uncertainty. Three strategies have been considered: immediate action to adapt to a future emission constraint (Commitment), business as usual (No Hedging), and hedging (Hedging). In the case of hedging, preparations are made outside the energy system, but the energy system itself is allowed to develop according to baseline assumptions until the uncertainty has been resolved. The IEA-MARKAL model has been used to show how efficient and robust the three strategies are under different developments. The development of the Swedish energy system has been studied for two rates of economic growth in combination with three nuclear policies and two CO2 policies. The value of preparations for meeting a possible restriction on CO2 emissions, i.e., following either the Commitment or the Hedging strategy, is considerably higher when the energy demand increases rapidly. In the low growth case, the choice of strategy is largely dependent upon the decision maker's estimate of the likelihood of an emission cap. In the high growth case, this likelihood must be considered to be very small in order to choose the No Hedging strategy, even with reinvestments in nuclear capacity beyond 2010.

An experimental investigation of fuel‐injection‐pressure and engine‐speed effects on the performance and emission characteristics of a divided‐chamber diesel engine

Abstract: An experimental study is conducted to investigate the fuel-injection-pressure and engine-speed effects on the performance and exhaust emissions of a naturally aspirated four-stroke indirect-injection (IDI) diesel engine with a swirl combustion chamber. The influence of the injection pressure and the engine rotational speed on fuel consumption, exhaust-gas temperature, exhaust smokiness and exhaust-gas emissions (nitrogen oxides and unburned hydrocarbons) is examined, following a detailed experimental investigation. Empirical easy-to-use correlations are produced, expressing the variation of the various parameters with injection pressure, by applying a regression analysis on the curves fitting the relevant experimental data. Theoretical aspects of diesel fuel spray progress (atomization, evaporation and mixing), combustion and emissions formation are used for the interpretation of the observed engine behaviour.

Sensitivity analysis for room thermal response

Abstract: The sensitivity theory is a suitable approach for assessing the room thermal response. It results in the ‘sensitivity coefficients’ (SCs) which, as derived here, evaluate the variation of the thermal load due to a fluctuation in a given design parameter around its nominal value. In this paper the general method is presented and a number of SCs are derived to evaluate the sensitivity of the building energy demand to the window surface area, to the overall transmittance and mass thermal capacity of a given wall, and to other structural data.

On the non-periodic unsteady heat transfer through walls

Abstract: Existing calculation methods of the transient heat flow through walls for air-conditioning applications, assume periodic outdoor conditions. Therefore, the effect of a temporary temperature rise on the indoor heat flow is usually neglected. In the present work an attempt is being made to model the related non-periodic transient problem. The method of approach is based on a finite-difference solution of the transient heat conduction equation within the wall. Outdoor air temperature deviation parameters are introduced, which characterize any temporary deviation of the outdoor air-temperature from periodicity. Indoor heat flow deviation characteristics are defined, which describe the deviation of the indoor heat flow from periodicity, provoked by the corresponding outdoor air temperature deviation. A parametric study is conducted, where the effects of the temperature deviation parameters on the indoor heat flow deviation characteristics are examined. It has been found that (a) the maximum heat flow deviation varies linearly with the mean temperature difference, (b) the restoration ratio is practically independent of the temperature amplitude difference, and (c) an increase in the wall thermal diffusivity results in a decrease of the maximum heat flow deviation. The practical importance of the present analysis is that it helps towards the estimation of peak loads under non-periodic outdoor conditions.

The effect of the downturn in oil prices on the external surpluses of the GCC countries

Abstract: The paper examines the impact of the downturn in oil prices on the performance of the external sectors of the members of the Gulf Co-operation Council (GCC). The paper also developes and tests a simultaneous-equations model to examine the interaction between the economies of the GCC and the rest of the world. The analysis shows that the slump in oil exports has reduced drastically the external surplus of the GCC and has resulted in structural shifts in the import and resource balance functions.

Effect of corrugation frequencies on natural convective heat transfer and flow characteristics in a square enclosure of vee‐corrugated vertical walls

Abstract: A numerical investigation has been carried out on natural convective heat transfer and fluid flow in a square cavity with vee-corrugated vertical surfaces. This study covers the range of corrugation frequency from 1 to 3 and Grashof number from 103 to 105. The corrugation amplitude has been fixed at 5% of the enclosure height. The vorticity stream function formulation with the control volume based finite element method has been used to analyse the effects of corrugation frequency and Grashof number. The investigation shows that the overall heat transfer through the enclosure increases with the increase of corrugation for low Grashof number; but the trend is reversed for high Grashof number.

Unsteady MHD flow of a dusty viscous liquid in a rotating channel with hall currents

Abstract: The unsteady magnetohydrodynamic flow of a dusty, viscous, incompressible liquid in a rotating channel, in the presence of a transverse magnetic field with Hall currents, is considered. Analytical expressions for the velocities of the liquid and the dust particles are obtained. The effects of Hall current m, and the rotation parameter K on the velocity are shown graphically, and are discussed.