Showing papers in "International Journal of Energy Research in 1982"

Heat transfer in flow through a porous medium bounded by an infinite vertical plate under the action of a magnetic field

Abstract: An analysis of steady two-dimensional flow, of an electrically conducting fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite, vertical and porous limiting surface under the action of a transverse magnetic field is considered. Approximate solutions have been derived for the velocity and temperature fields and the rate of heat transfer (Nusselt number). The variations of the velocity and Nusselt number are shown on graphs.

Calculating heat transfer through windows

Abstract: To calculate the energy performance of buildings, one must know the heat-transfer characteristics of the windows as functions of environmental variables, such as temperature and wind speed. Window designs are becoming more complex in response to the need for energy conservation. In this paper, we develop a general procedure for calculating the net energy flux through the glazed area of a window composed of an arbitrary number of solid layers. These layers, which may have thin-film coatings, can have any specified solar and thermal radiation properties and enclosed spaces between solid layers can contain either air or other gases. We verified our results by comparing them with experimental measurements of heat flow using a calibrated hot-box.

The potential for heat pumps in drying and dehumidification systems I: Theoretical considerations

Abstract: Drying is one of the most energy intensive unit operations. In many applications the drying temperatures required are low enough to make the inclusion of a heat pump in the system worthy of consideration. Five drying/dehumidification systems, including three with heat pumps, have been compared theoretically on the basis of specific power consumption (SPC), (i.e. the energy supplied per unit of moisture condensed) and primary energy consumption (PEC) which is (SPC) divided by the efficiency of primary energy conversion. The efficiency of each system is improved as the relative humidity of the air leaving the dryer is increased. The optimum is, however, very flat and a heat pump should be advantageous when a minimum relative humidity of 30 per cent is acceptable within the drying chamber. A closed cycle dryer is shown to be the most advantageous but requires careful matching.

Solar optical properties of windows

Abstract: To properly calculate dynamic solar gain in buildings, one must know the optical properties of the window in detail. In this paper, we develop a complete set of calculation procedures for determining the solar transmittance, reflectance, and absorptance of a window composed of an arbitrary number of partially transparent layers. Any layer may have a thin-film multilayer coating, such as an anti-reflection coating for increasing solar transmittance, a solar control film for reducing solar heat gain, or a transparent heat-reflecting mirror for improving thermal resistance. The results of sample calculations are given over the range of incidence angles for conventional and advanced energy conserving window designs.

The potential for heat pumps in drying and dehumidification systems II: An experimental assessment of the heat pump characteristics of a heat pump dehumidification system using R114

Abstract: An experimental heat pump dehumidifier is described. Actual coefficients of performance (COP)A are plotted against the gross temperature lift (TCO - TEV) for various bypass ratios and air velocities. Interpolated values of (COP)A for a specified temperature lift were obtained by fitting each set for various dry bulb temperatures of air leaving the humidifier using a linear equation. These values of (COP)A are plotted against the linear velocity of the air stream approaching the evaporator at different dry bulb temperatures. The curves show a maximum of (COP)A at approach velocities in the region of 1·6 ms−1.

Solar thermal modelling of a non-airconditioned building: Evaluation of overall heat flux

Abstract: This paper presents an investigation of the thermal behaviour of a non-airconditioned building with walls/roof being exposed to periodic solar radiation and atmospheric air while the inside air temperature is controlled by an isothermal mass, window and door in the walls of the room. The effects of air ventilation and infiltration, the heat capacities of the isothermal storage mass inside air and walls/roof, heat loss into the ground, and the presence/absence of the window/door have been incorporated in the realistic time dependent periodic heat transfer analysis to evaluate the overall heat flux coming into the room and the inside air temperature. A numerical computer model using typical weather data for Delhi has been made to appreciate the analytical results quantitatively. It is found that the heat fluxes through different walls have different magnitudes and phase lags w.r.t. the corresponding solair temperatures. The overall heat flux coming into the room as well as the room air temperature are sensitive functions of the number of air changes per hour, closing/opening of the window and the door ventilation. The effects of the heat capacity of the isothermal mass and the basement ground are found to reduce the inside air temperature swing and the presence of a window is found to increase the inside air temperature even when the window area is much smaller than the wall/roof area. The model presented would be an aid to a building architect for good thermal design of non-airconditioned buildings.

Thermal performance of a matrix air heater

Abstract: A periodic analysis of a matrix air heater has been carried out to study the capacity effect of various storage materials such as concrete, fire bricks, glass and coal. The storage effect is, however, not significant in such systems. Higher conducting and low heat capacity materials, such as iron, copper and aluminium used in the form of scraps, result in a good performance of the system. Coal is also found to give as good a performance as metallic materials. The efficiency of the system increases with increased mass flow rate but the rise in the inlet air temperature is correspondingly smaller. The temperature distribution inside the system is seen to be almost linear.

Theoretical analysis of ammonia‐water absorption cycles for refrigeration and space conditioning systems

Abstract: This paper presents an investigation of an ammonia-water absorption cycle for solar refrigeration, airconditioning and heat pump operations at higher heat supply temperatures. The system consists of a solar driven generator, rectifier, condenser, evaporator, absorber and heat exchangers for preheating and subcooling within the system. A steady state thermodynamic cycle analysis based on mass and heat balances along with the state equations for the thermodynamic properties of the ammonia-water mixture has been carried out. A numerical computer simulation of the system with input component temperatures, refrigerant concentration/mass flow rate and effectiveness of the heat exchangers has been made to evaluate the relative heat transfer rates (i.e. coefficients of performance) and the mass flow rates for the cooling/heating modes. It is found that unlike the low generator temperature behaviour the coefficients of performance for both cooling and heating modes are reduced at higher generator temperatures. However, an increase of condenser temperature for each mode of operation improves the performance of the systems at higher generator temperatures. A choice for keeping the absorber temperature equal to/lower than that of the condenser is also predicted at lower/higher generator temperatures, respectively. In general the results are more pronounced for the refrigeration mode than for the heat pump mode and are least effective for the airconditioning mode.

The performance of heat pumps in service—A simulation study

Abstract: A computer model is developed to simulate the performance of air-to-water heat pumps heating a house via a radiator system. The performance characteristics of the heat pumps are derived from laboratory measurements. Hourly weather observations are used to calculate the heat demand of the house and the performance of the heat pump. The effects of changes in heat pump characteristics, changes of radiator size, and changes in heat demand of the house due to insulation, are compared in terms of their effects on annual energy consumption.

Liquid phase thermochemical energy conversion systems - An application of Diels-Alder chemistry

Abstract: Thermochemical energy conversion at moderate or low temperature (> about 400°C) employing liquid phase components throughout a cycle is suggested as a promising concept for high-efficiency conversion of various energy sources (e.g. solar or industrial waste heat) to a convenient chemical form. In particular, we propose liquid phase Diels-Alder cycloaddition chemistry as an important class of reversible reactions for such low or moderate temperature thermochemical energy conversion systems. One of the important attributes of thermally driven Diels-Alder reactions is their concerted mechanism, with consequent high yields and efficiencies relative to liquid photochemical systems. Since the systems we propose involve organic species, with thermal stability concerns above about 400°C, it is important to demonstrate equilibrium shift capability for the highly energetic reactions sought. We have therefore carried out experimental studies with model liquid Diels-Alder systems that clearly demonstrate the degree of control over equilibrium available through substituent entropy effects. For example, Keq is unity at about 420°C (T*) for the anthracene/maleic anhydride system (in solvent) while a phenyl substituent on the anthracene or isopropyl substituent on the anhydride reduce T* to about 200°C at constant ΔH0. These results are of importance as regards subsequent systematic identification of Diels-Alder reactions having ideal thermochemical and physical properties. We also have developed a rapid NMR technique for qualitative screening of candidate reactions, and have applied this technique to the study of various bicyclic diene/fumaric acid ester systems. Our paper further points to the need for better understanding of the catalysis likely required for these liquid phase Diels-Alder reactions.

Solar energy storage using surfactant micelles

Abstract: The photogalvanic behaviour of iron-thionine and iron-methylene blue systems in the presence of surfactants has been studied. The data indicate that the surfactant micelles can be utilized for the storage of light energy.

An improved solar cooker

Abstract: An improved hot box type solar cooker (SC-2) has been designed, developed and tested. It is an improvement on the solar cooker SC-1 earlier developed at the institute. The cooking chamber has properly been optimized for cooking the food for a family of five persons. A rubber gasket has been provided at the boundary of the openable door to prevent the leakage of hot air, thus increasing the pressure in the cooking chamber. Different cooking trials like boiling, roasting and baking were successfully conducted and the cooker was found useful from 8.00 a.m. to 5.00 p.m., even during a winter month. The efficiency of the cooker was found to be 41.2 per cent.

Design and development of a solar conical concentrator

Abstract: A portable solar conical concentrator of 1 metre aperture and consisting of 63 triangular plane mirror strips has been designed and fabricated. This device has been tested using cylindrical receivers having radii of 7.5 cm and 3 cm, respectively. It required 2 h for 8 kg of water in a large cylinder to reach boiling point, whereas it required only 20 min for 1.25 kg of water to boil in a smaller cylinder. The steam formed can be utilized to sterilize medical instruments or for other purposes as desired. The paper includes a detailed analytical treatment of heat exchange at the surface of the absorber, an evaluation of the appropriate heat transfer coefficients, and solutions of the energy balance equation for cylindrical absorbers of the sizes noted. Efficiencies as high as 60 per cent have been observed.

Optimal geometries of plane mirror solar collectors

Abstract: This paper presents an analytical study of a stationary plane mirror solar concentrator. It is composed of an array of East-West oriented trapezoidal channels with two sided reflecting walls and a tubular absorber as a receiver at the base. We have analysed and identified the most practical design parameters for a trough like concentrator. The one- and two-faceted plane side wall configurations with tubular receiver at the base of the trough have been studied in detail. It has been concluded that large savings in reflecting surfaces are possible while sacrificing some reduction in concentration. A theoretical prediction for the dependance of absorber efficiency on temperature has been obtained.

Performance of an inexpensive rural solar collector

Abstract: In this paper we discuss an inexpensive solar collector in which the heat storage material is sand or sand mixed with iron filings. The heat is absorbed by the blackened portion of the heat storage material. The heat is withdrawn from the system by water flowing through a network of plastic pipes buried in the heat storage material at an appropriate depth. The large efficiency is obtained when the material is sand mixed with iron filings. It is shown that the efficiency of the system can be judged from the glass cover temperature. As the glass cover temperature decreases, the efficiency of the system increases.

A low cost collector-cum-storage type solar water heater

Abstract: A low cost collector-cum-storage type solar water heater has been developed. The cost of the heater is reduced by replacing window glass cover with 0.2 mm thick PVC film to avoid glass breakage in transportation and maintenance. In this paper the performances of solar water heaters having double glazing of PVC and glass have been compared. It was found that their performances are similar. Moreover, by providing an insulating cover in the night, the water remains warm till next morning for taking a bath etc. in the early hours when there is no sunshine.

Flavin mononucleotide (FMN)‐ethylenediaminetetraacetic acid (EDTA) photogalvanic cell

Abstract: The photovoltages and photocurrent in a photogalvanic cell containing flavin mononucleotide (FMN) and a reducing agent, ethylenediaminetetraacetic acid (EDTA) have been determined and found to be appreciable. The efficiency of the cell has been estimated to be ∼ 0-048 percent. The electrochemical behaviour of FMN in the presence of EDTA has been examined by cyclic voltametry.

Performance of a cylindrical parabolic trough using a fin receiver: Limb darkening effects

Abstract: The distribution of local concentration ratio on a fin receiver used with cylindrical parabolic solar concentrators has been calculated analytically considering the variation of intensity over the solar disc. The effect of the pointing error of the concentrator and that of the lateral shift and tilt of the fin receiver have also been studied. The results are plotted graphically and discussed.

Performance study of thermosyphonic circulation solar water heaters using packed bed collectors

Abstract: In the present investigation the performance behaviour of thermosyphonic circulation solar water heaters using packed bed collectors has been analysed. Iron chips, gravels and stones have been used as packing materials. Average tank water temperature, collector as well as system efficiency and mony pay-back for these packed bed solar water heaters are compared with those for solar water heater using a plane collector. Experimental results reveal that the performance of solar water heater improves appreciably by packing its collector with packing material. Among the packed-bed solar water heaters tested the iron chips packed-bed solar water heater gives the overall best performance.

Solar device for the candle industry

Abstract: A solar device has been developed for manufacturing candles from paraffin wax, utilizing solar energy. The design, operation and performance of the device have been described. It is concluded that the device can be used for saving fuel, minimizing the loss of wax due to the vaporization and labour.

Liquid collector efficiency in solar stills

Abstract: The paper deals with the results of preliminary studies on the effect of surface area on the performance of a solar still. Results on the effects of floating coal, compartmentalization and stirring of raw water are reported with respect to a reference still in terms of percentage increase in distillate output. The results show an increase in distillate output in all these cases especially at low water depths and in the presence of solar radiation. The stirring of raw water gave interesting results during daytime which have been explained on the basis of increased aquation of air within the system.

Design of electronic optimizer for solar electric drive system

Abstract: There has been considerable interest in the use of solar electrical converters for supplying electric drive motors in pumping schemes for rural areas. The optimum control of solar electric drive motors is desirable because it leads firstly, to higher apparent efficiency of solar energy conversion, and, secondly, to reduced cost per useful watt. Although the ‘fuel’ for solar drives is free, the cost of solar cells is high. Optimization means that smaller areas of solar panels are required, thus reducing the overall cost of the solar drive system. The present investigation has been directed towards the development of a reliable electronic controller, which would ensure stable and optimal performance characteristics of solar electric-powered pumping scheme over a broad range of operating conditions. The design goals are low cost, reasonable accuracy, control capability and efficient utilization of the electrically converted solar power. The developed electronic optimizer provides constant voltage operation of the solar generator so that maximum power can be delivered to the drive motor for any light intensity. The main part of the optimizer is a servo chopper. The chopper operation is automatically adjusted so that the overall system efficiency is always maintained at a maximum value. Details of the electronic optimizer circuits are given and the overall system performance is investigated. Valuable information for the design and operation of the solar electric drive system with the electronic optimizer is gained from this analysis.

Use of controlled water circulation in tap water heat pumps

Abstract: Condensers used in tap water heat pumps are either of the integrated passive immersion type or separate units with active water circulation. The use of the active circulation configuration together with a counter-flow condenser and water flow control has a number of advantages compared to passive immersion condensers. In particular, hot water temperatures above the saturation temperature of the condensing refrigerant are possible. The counter-flow arrangement also permits sub-cooling gains in cycle efficiency. These two features offset the pumping power penalty which would not be necessary in a system with a passive immersion condenser.

Seasonal constraints in management of alternative sources of energy in rural areas

Abstract: A plan for the management of alternative sources of energy, namely, wind, solar and biomass, available in a typical village of arid area has been formulated and it is found that the energy potential available in the village from mid February to mid September is much more than the energy requirement of the village; and during the remaining period the energy available is about 78.5 per cent of the energy requirement. Appropriate technologies for the effective and efficient use of these energies are earmarked so as to convert the energy potential available into useful energy.

Effect of non‐uniform hall parameter on the electrode voltage drop in Faraday‐type combustion mhd generators

Abstract: Following a simplified approach, we derive an expression for the gas-dynamic voltage drop in a finitely segmented Faraday-type combustion MHD generator, taking into account the non-uniform Hall parameter across the channel. Combining the electrical sheath voltage drop, discussed briefly, with the gas-dynamic voltage drop, the effect of a non-uniform Hall parameter on the electrode voltage drop is studied using the theoretical and experimental input parameters of the Indian MHD channel test. The condition for the validity of the usual assumption of uniform Hall parameter across the channel is pointed out. Analysis of the measured electrode voltage drop predicts the real gas conductivity in the core to be in the range of 60 to 75 per cent of the theoretically calculated core conductivity.

Spectral selectivity and accelerated life testing of Al‐PbS solar selective surfaces

Abstract: High absorptance and low thermal emittance selective surfaces have been formed by evaporating lead sulphide onto Al evaporated Al substrates. The dependence of selectivity, α/ϵ, on thickness has been studied. The maximum selectivity was obtained for PbS thickness of 400 A. The emissivity is found to increase with temperature. The coatings are stable up to a temperature of 240°C in air. Long term ultraviolet irradiation causes the photo-oxidation of PbS to PbSO4 which results in the increase of emittance and a decrease in absorptance. When cycled between 0°C and 200°C, the coatings do not show any signs of degradation.

Optimum placement/distribution of insulation/concrete in a heavily insulated multilayered roof/wall for best load levelling

Abstract: In this paper we investigate the optimum placement/distribution of insulation/concrete in a double hollow multilayered wall/roof for achieving the best load levelling in the thermal flux through the slab. It is seen that, of six possible configurations, for a given total thickness of insulation and given total thickness of concrete, the best load levelling is achieved when equal thicknesses of insulation are placed on outside and inside. Better load levelling is achieved in the insulation-air gap-concrete-air gap-concrete configuration when the thickness of the inner layer of concrete (facing room) is least, consistent with structural considerations. No, or the worst, load levelling is achieved in the concrete-air gap-insulation-air gap-insulation and insulation-air gap-insulation-air gap-concrete configurations.

The economics of comprehensive community energy planning

Abstract: This paper is the result of a survey of cities engaged in the Comprehensive Community Energy Program. It states the underlying themes of local energy analysis and summarizes methodology and conclusions reached in the various studies with special emphasis on economic methodologies.

Thermodynamic analysis of solar thermochemical energy absorption

Abstract: Thermochemical energy conversion is analysed on a thermodynamic basis with particular interest in obtaining guidance as to solar thermochemical absorber design at an early stage of development when technical and cost information is often unreliable. An earlier-used thermodynamic equivalence technique which is equally applicable to both the endothermic and exothermic reactions has been developed to the point where it gives a clear insight into all sources of heat and work. The method is applied in particular to separating endothermic reactions of which ammonia dissociation is a prime example. A reversibility ratio is defined as the ratio of irreversible to reversible work and it is shown that in a practical solar thermochemical absorber design the reversibility ratio should be minimized, corresponding to reaction temperature minimization and therefore to tower energy losses and to potential for use of lower cost reactor materials and more active catalysts. Values of reversibility ratio are calculated for the ammonia system and are discussed in relation to solar thermochemical absorber design. In a final analysis employing the thermodynamic equivalence technique, it is shown that the apparent paradox between liquid and alternative gas pump work requirements in a liquid/gas thermochemical system is thermodynamically consistent with the internal generation of effective work from the heat source used to drive the endothermic reaction system.