Climate Of Delhi Research Articles

Technoeconomic optimization of a hybrid solar air-heating system

This paper presents a simple techno-economic model for a hybrid solar air-heating system based on water as the storage medium. The configuration of the system consists of a conventional solar air-heater, water tank for thermal storage, a unit which adjusts the higher air temperature (during peak sunshine hours) to the required limit (by mixing fresh air) and an arrangement for providing auxiliary energy if and when required. A thermostatically controlled electric heater is assumed to be the source of auxiliary energy, in the present calculations. In order to evaluate the performance of the system using the developed model numerical calculations have been made corresponding to the climate of Delhi, India. The calculations have been extended to obtain the optimized values of collector area and storage mass which correspond to the minimum value of useful energy. Numerical results show that the cost of useful energy obtained for optimized values of collector area and storage mass is much less than the cost of electrical heating.

Technoeconomic optimization of solar natural convection hybrid hot water systems

In this paper a techno-economic model for a hybrid domestic hot water system operating under natural convection mode is presented. Three modes of auxiliary energy supply viz. A electric heater fitted in the solar hot water tank. B electric heater fitted in a small water tank in series with the solar hot water tank, and C an instant electric heater fitted in the tap have been considered. Taking into account the life and the capital and maintenance costs of the solar and electrical equipments, the cost of useful energy (Rs/kWh) has been calculated for different values of the collector area and the tank capacity, and thereby the optimum collector area and tank capacity (for a given demand), corresponding to minimum cost of useful energy, has been determined. From numerical calculations made for the climate of Delhi, India (a representative composite climate) corresponding to the two cases of monthly hot water demand viz. (i) constant monthly demand, and (ii) variable monthly demand, it is seen that case (C) is the most economic design of the hybrid hot water system; numerical calculations have also been made for this case corresponding to the climates of Srinagar and Madras (representing cold and hot climates). The effect of government subsidy on the optimized values of collector area, tank capacity and cost of useful energy has also been investigated for the climate of Delhi.

Solar assisted biogas plants II: Energy balance of floating drum type biogas plants

In the present paper, a mathematical model is developed to predict i the heat losses and gains from various mechanisms in a KVIC-type biogas plant as a function of slurry temperature and other parameters, ii transient performance of the conventional KVIC-type biogas plants, and iii transient performance of KVIC-type biogas plants covered by a greenhouse. Numerical calculations have also been made to predict the monthly performance of biogas plants of different sizes having digester volumes ranging from about 4 to 220 m3 for the climate of Delhi, India. The heat losses from the digester to the ground through the sides have been evaluated following Sodha et al. (1980) by assuming the digester to be an infinite cylindrical cavity in the ground. Computations have also been made to study the effect of a greenhouse, its size and night curtains on the performance of biogas plants. Results indicate that the heat losses from the slurry to ambient through the annular space left between the gasholder and the digester are very significant for smaller plants, whereas charging represents the largest single component of heat losses for larger plants.

Optimization of a hybrid solar forced-convection water heating system

In this paper, a techno-economic model has been developed for a hybrid solar forced-convection water heating system. Two options of auxiliary energy use, viz. (A) an instant electric heater and (B) use of diesel as the auxiliary energy fuel, have been considered. Numerical calculations have been made for the climate of Delhi, India, corresponding to the two representative demand patterns, viz. (i) hot-water demand of big residential buildings and (ii) industrial hot-water demand. Taking into account the life, capital cost and the maintenance cost of the solar and auxiliary systems, the cost of useful energy has been calculated for different values of collector area and tank capacity. This exercise, thereby, yields the optimum values of collector area and tank capacity corresponding to the minimum cost of useful energy. The effect of government subsidy on the optimized values of collector area, tank capacity and cost of useful energy has also been investigated.

OPEN SUN DRYING : AN ANALYTICAL STUDY

ABSTRACT This communication presents a simple model of open sun drying to predict the hourly variation of product temperature and moisture constent under constant rate and falling rate regimes of drying. The model is based on the principle of simultaneous heat and mass transfer at the product surface and includes the effects of wind speed, relative humidity, product thickness and the heat conducted to the ground. The computations corresponding to the typical summer (June 1–2,1982) and winter (Dec. 6–8, 1982) days of New Delhi climate, have shown that the highly moistureous fruits/ vegetables having moisture content -80% (wet basis) may be dried to 13% moisture content in 24 and 34 sunshine hours in summer and winter climates respectively. It is also recommended that the layer thickness of the material should not be more than 5 cm for drying under open sun.

Solar assisted biogas digesters I: Thermal analysis

A thermal analysis has been made of a number of viable solar systems, namely (i) a solar canopy, (ii) a shallow solar pond (SSP) water heater, (iii) insulation and (iv) an SSP with a solar canopy around the digester, to boost the biogas production in conventional KVIC biogas plants during the winter months. Numerical calculations for a typical sunny winter day (17 January 1984) in the climate of New Delhi show that an SSP water heater on the top of the gas holder, covered with a solar canopy, is a good option from thermal point of view.

Thermal performance of a non-air-conditioned building for passive solar air-conditioning: Evaluation of roof cooling systems

A periodic heat transfer analysis has been presented to predict the dynamic thermal behaviour of a non-air-conditioned building with evaporative cooling systems over the roof. Three different cases of evaporative cooling systems, namely, open roof pond, moving water layer over the roof, and water spray over the roof, have been studied in detail to assess their effectiveness for passive space air-conditioning. The effects of air ventilation, furnishings and ground heat conduction have been incorporated in the present analysis. Numerical computations using typical data of a harsh summer day in the Delhi climate, have been made to assess the analytical results quantitatively. It was found that the maximum cooling is achieved by water spray over the roof. However, the roof pond system with stationary water is more effective in stabilizing the fluctuations of indoor temperature as well as heat flux entering through the roof. Furthermore, with the increase in the number of air changes per hour, the time variation of indoor air approaches to that of outdoor air in phase as well as in magnitude.

An analytical and experimental study of open sun drying and a cabinet tyre drier

This communication presents a simple analytical model of open sun drying and a cabinet type drier. Also, an extensive experimental study of the two methods of drying has been conducted on typical summer days (1–2 June) of the New Delhi climate during 1982. The analytical models are helpful in predicting the hourly variation of product temperature and moisture content under constant rate and falling rate periods of drying. These are based on the principle of simultaneous heat and mass transfer at the product surface and include the effects of wind speed, relative humidity, product thickness and heat conducted to the ground. The computations correspond to typical summer (1–2 June) and winter (6–8 December) days of the New Delhi climate during 1982. This analysis has been illustrated by specific examples of apples, peaches, cherries and mango flesh.

Thermal Performance of ‘Still-on-Roof’ System with Water Flowing through the Roof

In the present communication, authors propose and analyze a system which consists of a solar still kept over the roof of a room, and a water-flowing arrangement in the roof. The performance of the system is studied under two modes of heat extraction, viz., constant flow rate, and constant collection temperature, An analytical model has been developed which provides explicit expressions for various performance parameters of the system. The model is useful in evaluating the system performance under the variation of different parameters. In order to appreciate the proposed configuration, numerical calculations are carried out corresponding to the typical climate of Delhi, India. The calculations show that the system is effective in reducing the heat flux entering the room and provides warm water in addition to the distilled water.

Relative performance of walls

This communication presents the relative performance of different wall structures of a building in terms of the heat flux entering into the living space through the walls. Explicit expressions have been derived for the time dependent heat flux; the living space is assumed to be at constant temperature (corresponding to air-conditioning). Numerical calculations have been performed corresponding to the climate of Delhi (winter and summer). The seasonal studies from the point of view of load levelling show that cavity walls (brick-airgap-brick) (0.35-0.05-0.24 m) on all but the south side and a solid wall on the south side are desirable.

Letter to the Editor: THE IRON COLUMN AT DELHI

SIR, The occasion of the Corrosion and Metal Finishing Exhibition appears to have aroused fresh interest in the remarkable iron column at Delhi that is still, after nearly 1,700 years, in an excellent state of preservation. The Observer published a good photograph of it when alluding to the exhibition, and Sir Alexander Fleck in his speech when opening the exhibition made some interesting references to it as reported in your issue for December. Its preservation has puzzled many mineralogists and Sir Alexander did not offer an explanation, although he mentioned that he was not impressed by the suggestion that the so‐called mild climate of Delhi is an important factor in its preservation, and he referred to Desch's statement that there is a coating or fine adherent layer of slag, and to the suggestion that these metals may have been forged on stone anvils.