Subhash C. Mullick

Testing of box-type solar cooker: Second figure of merit F2 and its variation with load and number of pots

The performance of a box-type solar cooker can be represented in terms of two figures of merit, F1 and F2. The second figure F2 is a controlling factor in the sensible heating of a load. The present work validates F2 by computing this figure from experimental data by two different procedures and comparing the results. An attempt has also been made to provide some guidelines for selecting a suitable temperature interval for determination of F2. The results of some experiments to study the effect of number of pots and the load on F2 have also been presented. It is recommended that for standardization tests should be conducted at full load.

Wind induced heat losses from outer cover of solar collectors

The top cover of a flat plate solar collector is generally exposed to wind. In indoor experiments it is necessary to simulate this wind. Correlations have been developed for the wind heat transfer coefficient over flat horizontal surfaces exposed to forced air flow, produced by industrial fans in indoor experiments.

Heat losses from a paraboloid concentrator solar cooker: Experimental investigations on effect of reflector orientation

The thermal performance of any focussing-type solar cooker, where an unglazed/uuninsulated cooking pot is often used, depends to a great extent on wind conditions. Moreover, these cookers need frequent adjustments to track the Sun in order to keep the focus always at the bottom of the cooking pot. The present paper reports experimental investigations on heat losses from such cooker for different orientations of the paraboloied reflector. Values of the heat loss factor for the tilted reflector are compared with those obtained with the reflector in a horizontal position. The heat loss factore for a cooker with/without reflector is determined for no-wind conditions. It is suggested that a paraboloid reflector is not required for heat loss determination in this case.

Financial feasibility analysis of box-type solar cookers in India

A framework for financial evaluation of a box-type solar cooker, using cost functions for its capital cost, has been developed. The annual benefits accrued to the user are quantified in terms of number of meals cooked per year and monetary worth of the fuel saved per meal. Expressions for some financial performance indicators have been derived and results of typical numerical calculations are briefly presented.

Effect of wind on the thermal performance of a parabolloid concentrator solar cooker

Thermal performance of a parabolloid concentrator solar cooker depends greatly on the wind speed. Experiments have been conducted to study the effect of wind speed on heat loss parameter F′UL and hence on thermal performance of the cooker under simulated wind conditions. Correlations have been developed to express the F′UL as a function of wind speed and pot water temperature. Heating characteristic curves have been also developed with the variable values of F′UL and compared with those obtained from constant F′UL.

Top heat-loss factor of double-glazed box-type solar cooker from indoor experiments

The top heat-loss factor (Ut) of a box-type solar cooker varies with plate temperature, wind heat-transfer coefficient and ambient temperature. A method for correlating Ut with these variables is presented for a cooker with double glazing. A set of equations is developed for correlating data obtained in indoor experiments at different plate temperatures and wind speeds.

Solar thermal power generation in India: effect of potential incentives on unit cost of electricity

ABSTRACT For large-scale dissemination of solar thermal power plants, in countries identified with huge potential, governments are offering various incentives. In an attempt towards studying the effectiveness of various incentives in reducing the levelised cost of electricity (LCOE) delivered by solar thermal power plants in India, this paper presents simple mathematical frameworks that facilitate the determination of the required level of an incentive so as to ensure that the LCOE is within a pre-specified limit. For example, for a 50 MW solar thermal power plant at Barmer (Rajasthan), LCOE of Rs. 9.75 per kWh can be achieved by providing 6.3% viability gap funding or an interest subsidy of 3% or provision of 32% investment tax credits to the equity investor or provision of production tax credits to the equity investor at the rate of Rs. 0.81 per kWh for first 10 years of operation of a plant.

Comparison of solar radiation data sources for design and performance appraisal of CSP systems in India

ABSTRACT The choice of a solar radiation data source is expected to have a significant impact on the predicted performance of a concentrating solar power (CSP) system and consequently on its technical and financial feasibility. In the present study, an attempt has been made to analyse the effect of choice of various solar radiation data sources on the predicted performance of a CSP system at 13 different locations in 5 different climatic zones of India. It was observed that there is significant variation in the amount of annual electricity output obtained for various locations using different solar radiation data sources resulting in variations in levelised cost of electricity. For a 50-MW parabolic trough-based CSP plant located in Jaisalmer, the estimated value of annual electricity output varies from 63 to 124 GWh. For a CSP plant based on the central tower receiver technology, the corresponding range is from 106 to 145 GWh.

Wind Induced Heat Transfer Coefficient From Flat Horizontal Surfaces Exposed to Solar Radiation

Upward heat losses have strong effect on the performance of flat plate solar collectors under different operating conditions. Suitable equations for estimation of top heat loss coefficient have already been proposed [1,2]. The top heat loss coefficient is a function of wind induced convective heat transfer coefficient in a flat plate solar collector. It is, therefore, important to choose appropriate values of this convective heat transfer coefficient for correct estimation of the top heat loss coefficient. Researchers [3–6] have suggested different wind speed based correlations for estimation of the wind induced convective heat transfer coefficient. These correlations give different values of wind heat transfer coefficient thus resulting in variation in values of the top heat loss coefficient of a solar collector under same operating conditions. In present study, an attempt has been made to measure and study the wind induced convective heat transfer coefficient from exposed flat horizontal surfaces in real wind. For this purpose, three unglazed test plates of similar construction and different sizes were employed. Experiments were conducted on the three test plates over rooftop of a building in built environment. From experimental data of the test plate, of size 925mm × 865mm × 2mm, a correlation between wind heat transfer coefficient and wind speed has been obtained by linear regression. The obtained correlation has also been compared with work of other researchers [3–6]. Results obtained from experimental data of the three test plates provide some interesting information about wind induced convective heat transfer coefficient.Copyright

Assessment of utilisation potential of direct evaporative cooling for India

SYNOPSIS Hourly ambient temperature and humidity of 60 major cities of India were analysed to assess the utilisation potential of direct evaporative cooling for comfort conditioning. The hours with ambient wet-bulb temperature below 25°C, and tropical summer index above 25°C were considered as potential hours which can utilise direct evaporative cooling for achieving thermal comfort. The percentage utilisation potential was calculated for each city with the help of a simple computer spreadsheet. It was found convenient to divide the country into four zones (high, moderate, low and poor potential zones) from the viewpoint of evaporative cooling. It was observed that the central and north western regions of the country have high potential of evaporative cooling, while the coastal region, eastern and northern regions have poor potential.