D.P. Rao

Solar box-cooker: Part I—Modeling

Thermal models for the solar box-cookers loaded with one, two, or four vessels have been presented. The method of Taha and Eldighidy has been utilized to estimate the enhanced solar irradiance on the cooker due to the flat reflector fitted to the cooker. The coupling of the Taha and Eldighidy method with the thermal models yielded the models for the box-cookers. A great many transfer coefficients and view factors are required as the model inputs. The methods for their estimation are given. Analysis of the transfer processes, computer simulation of the cooker, and experimental data on some of the coefficients, which are peculiar to the cooker and not available in the literature are presented in the companion paper.

Performance of flat plate solar collector with fluid undergoing phase chance

Abstract The experimental set up for evaluating the performance of a solar collector with a fluid undergoing phase change is described. The effect of insolation and the liquid level on the collector performance has been studied with acetone and petroleum ether 40–60°C. The Hottel-Whillier equation, when modified to include the fraction of liquid level, correlates the experimental data. The collector efficiency increases linearly with liquid level.

Solar water pump for lift irrigation

Two types of solar water pumps for lift irrigation have been developed and tested. In this paper the thermodynamic and design aspects of the pumps are discussed. The pumps have no moving parts except for the check valves. No auxilliary power source or technical skill is required to run the pumps making both designs extremely suitable for rural lift irrigation. The running cost is nil except for the occasional use of an inexpensive organic fluid. Feasibility studies of the pumps indicate that they are economically viable and are within the means of an Indian farmer.

Solar box-cooker: Part II-analysis and simulation

Abstract Based on the model proposed in the companion paper (Part I), a method is outlined for simulation of the solar box-cookers loaded with one, two, or four vessels. The relative importance of various heat-exchange rates in the cooker were examined. The effect of parameters such as the thickness and size of the absorber plate, emissivity of the vessel, insulation thickness, and cooking time were studied. Cookers of three sizes were simulated to assess their adequacy in cooking. The studies indicate that the black paint on the vessels could be avoided if weathered stainless steel or aluminum vessels are used. The cooker with inner dimensions of 0.6 × 0.6 × 0.1 m 3 was found to be adequate to cook lunch and dinner on a clear day even in the winter months. Experimental studies carried out to obtain the heat-transfer coefficients, required for simulation, are presented.

Analysis and simulation of a solar water pump for lift irrigation

Abstract A solar water pump for lift irrigation, which was shown to be economically viable, was proposed by Rao and Rao [5]. A “modified pump” is suggested, which is suitable for village water supply. The thermodynamic analysis of the pumps is presented. Though the solar water pump is intended to be operated with flat-plate collectors, it is analysed whether the pump could be run more efficiently when coupled with concentrating collectors. The analysis is also applicable for bellow actuated solar water pumps. Preliminary experimental studies showed that the heat losses are 2–3 times the theoretical energy requirement and the losses to the water tank shell accounted for a major part of the total heat losses. To reduce these losses, it is proposed that the inner surface of the water tank shell be lined with a resin bonded cork insulation. A method to evaluate the heat losses to the shell with insulation by solving the unsteady state heat conduction equation for a composite cylindrical body with time varying convective boundary conditions is presented. The heat losses are reduced to 5–15 per cent of the theoretical energy requirement with the use of the internal insulation. The major problem encountered in operating the pump was the inadequate condensation of the working fluid, which resulted in failure of the suction of water into the water tank. To ensure proper suction of water, the conditions to be maintained are analysed. The presence of water vapor and air in the spent vapor has to be taken into consideration while designing the condenser. An algorithm to evaluate the year round performance of the water-cooled pump for any location, given the lift and collector area, is presented. The cost of the water-cooled pump is compared with the costs of other types of solar water pumps and it is shown that the pump under consideration costs several times less than the other ones. The conditions at which the pump will be economical vis-a-vis diesel and electrical pumps are presented.

Process intensification in duplex pressure swing adsorption

Abstract As an alternative to the Pressure Swing Adsorption (PSA) based on the Skarstrom cycle or its variants, a novel two-bed PSA – called duplex PSA – has been proposed by Hirose and independently by Leavitt to get both products of high purities. A modified duplex PSA has been presented to achieve process intensification, that is, to enhance the product purities and productivities. Simulation studies were carried out to explore the attainable product purities and possible process intensification for CO2 capture with the original and modified duplex PSA. The volume reduction of beds that can be realized with modified duplex PSA is about 100–50 times the original duplex PSA depending upon the product purities.

Ditigal simulation of indoor temperatures of buildings with roof ponds

Abstract A theoretical model is presented to predict the thermal performance of a building with roof ponds. Equations have been derived for the estimation of steady periodic heat fluxes through the roof slab and the outer walls. Energy storage and release by the partition walls and the floor has been considered. The other cooling loads have been estimated using the methods recommended in the ASHRAE Guide and Data Book . Hourly indoor temperatures are obtained by the numerical solution of the energy balance equation for the building. The algorithm that has been developed for digital simulation of the indoor temperatures is presented. The effectiveness of different kinds of roof-pond systems, i.e. shaded ponds, “Sky-therm”, etc. for passive coolings have been examined. The studies indicate that the indoor temperatures of a building located in Delhi can be maintained below 30°C in summer while the maximum dry-bulb temperatures are above 40°C.

NUMERICAL SIMULATION OF THE GAS FLOW AND MASS TRANSFER BETWEEN TWO COAXIALLY ROTATING DISKS

This paper deals with the study of the effect of rotation on the gas-side controlled mass transfer between two rotating disks. The velocity and concentration distribution in the gap between the disks have been determined from the solutions of the parabolized Navier?Stokes and species concentration equations. A satisfactory match between the numerical values of mass transfer coefficient with their experimental counterpart supports the efficacy of the numerical model to predict the mass transfer performance of the centrifugal contractor.This paper deals with the study of the effect of rotation on the gas-side controlled mass transfer between two rotating disks. The velocity and concentration distribution in the gap between the disks have been determined from the solutions of the parabolized Navier?Stokes and species concentration equations. A satisfactory match between the numerical values of mass transfer coefficient with their experimental counterpart supports the efficacy of the numerical model to predict the mass transfer performance of the centrifugal contractor.

Process Intensification in a “Simulated Moving-Bed” Heat Regenerator

The solid-gas contacting for thermal storage and thermal recovery is generally carried out in fixed-bed regenerators. Compared to a fixed bed, higher thermal recovery can be achieved in a moving bed with countercurrent flow of gas and solids. However, the moving beds have not been widely used due to difficulties in solid handling. The relative movement of the bed to the gas flow can be simulated in a fixed bed by moving the inlet and outlet ports of the gas along the length of the bed. Similar simulated moving beds are already in use for adsorptive separation of liquid mixtures in chemical industries. A novel moving-port system is proposed to achieve simulated moving-bed operation in a fixed bed. We have carried out studies to evaluate the relative performance of the fixed and the simulated moving-bed heat regenerators. We have examined the feasibility of replacing a set of three blast furnaces and thermal regeneration of an adsorption bed with the simulated moving-bed regenerator. It is found that high-heat transfer intensification can be achieved. The results indicate that three blast-furnace stoves can be replaced by a simulated moving-bed regenerator of volume of about 100 times smaller than the stoves. The heat-transfer intensification is high enough to carry out thermal regeneration of the adsorption beds in a cycle time that is in the range of the pressure swing adsorption, which is favored for its faster rate of regeneration.

Feasibility studies on the enhancement of energy storage in the ground beneath solar ponds

Abstract The salt used in a solar pond accounts for a significant fraction of the cost of the pond if it is located far away from the source of the salt, and if seasonal energy storage is required. However, if the energy storage in the ground beneath the pond is enhanced, the thickness of the lower convective layer, and hence the salt requirement, can be reduced. A method is proposed for the enhancement of ground storage. It requires formation of deep trenches at the bottom of the pond, in which the salt solution can circulate either heating or cooling the ridge (i.e., “fin-like” projection of the ground in between trenches) to affect the energy storage. Studies on the feasibility of the method are presented. The results show that the method of enhancement of energy storage is feasible if the depth of water table is more than 10 m. Also, it is found that the heat loss to the ground is lower in the case of the pond with trenches compared to the one with a flat bottom.