Transient and analytical solution of suspended flat-plate solar air heater

Based on a simple transient analysis, an explicit expression for the temperature of air, flowing through the channel of a suspended flat-plate solar air heater, has been developed as a function of time and space co-ordinates. Investigations regarding the effect of various parameters, such as air velocity, air channel depth and inlet air temperature, on the performance of the system have been carried out under two modes of operation; (1) the time is kept constant while the space co-ordinate along the flow direction is varied, and (2), the latter is kept constant while the former is varied.     

Performance study of forced circulation solar water heaters using packed-bed collectors

A performance study of forced circulation solar water heaters using packed-bed solar collectors is presented. Iron chips, gravel and stones have been used as packing materials. Thermal energy stored in the tank, system overall efficiency and pay-back capital for these solar water heaters are compared with those for solar water heaters using a plane collector. It is observed that the performance of the solar water heater is improved appreciably by packing its collector with packing material. A solar water heater using an iron chip, packed-bed collector shows the best performance.     

Transient analysis of a solar air heater of the second kind

This paper presents a theoretical analysis along with the experimental validation study of a solar air heater of the second kind. The heater consists of a flat passage between two metallic plates through which the heat transfer fluid air is made to pass by some auxiliary means. Study of the periodic response of different parameters of this solar air heater is attempted. The heat balance equations governing the behaviour of the system are solved explicitly. The results obtained from the analytical expressions for the transient variation of outlet air temperature compare well with experimental data. Predictions are also made regarding effects of different performance parameters of the air heater with variations of air mass flow rate and plate emissivity with the hope of optimizing the collector configuration.     

Transient analysis of rock bed air heaters for intermediate temperature applications

This paper deals with the transient analysis of rock bed air heaters in three different configurations. The analysis has been carried out for both summer and winter weather conditions to explore the feasibility of their use in summer for crop-drying applications and in winter for space-heating and water-heating applications. A parallel study has also been performed on the conventional empty channel air heater to compare its performance with that of rock bed air heaters.     

Transient analysis of a cylindrical solar water heater

An unsteady analysis of a cylindrical solar water heater has been performed. The physical parameters which govern the physical system are identified. The governing equations have been solved using the fourth order Runge-Kutta method for different values of the parameters. A good agreement between the numerical and experimental results has been obtained.     

Analysis of a glass solar air heater

A matrix solar collector fabricated from broken glass pieces is being supposed to be a thermally efficient and economically cheap system for heating air. In this communication, we develop an analysis to study the performance of such a system. Typical cases considered are (i) top surface blackened, (ii) all glass pieces blackened and (iii) bottom surface blackened. Numerical calculations have been performed to study the effect of single and double glazing and insulation at the bottom, besides the effect of other physical parameters.     

A mathematical model of thermal performance of a solar air heater with slats

A mathematical model for computing the thermal performance of a single pass flat-plate solar air collector is presented. Air channels were formed by providing metal slats running along the circulated air passage linking the absorber plate by the bottom one in an endeavor to enhance the thermal efficiency of the solar air collector. A mathematical model, therefore, is developed by which the influence of the addition of the metal slats on the efficiency of the solar collector is studied. A computer code that employs an iterative solution procedure is constructed to solve for the governing energy equations to estimate the mean temperatures of the collector. The effect of volume airflow rate, collector length, and spacing between the absorber and bottom plates on the thermal performance of the present solar air heater was investigated. Furthermore, a numerical comparison of the present design with the most common type of solar air heaters is conducted. The results of the comparison have indicated that better thermal performance was obtained by the modified system.     

Analyses of single and double exposure solar air heaters

This paper presents an investigation of the performance of single and double exposure solar air heaters. A conventional solar air heater consist of a flat passage between two metallic plates through which heating fluid (air) is made to pass. the conduction loss along the lengths of the plates in the direction of the air flow and the radiation loss of heat from the absorbing plate to the bottom plate have been incorporated in the analyses. the analyses consist of the exact solutions of the heat balance equations for the absorbing plate, bottom plate and the air stream. Analytical expressions for the plate and the air stream temperatures as a function of distance along the direction of air flow and some other parameters have been derived. It is found that the heat conduction effects are negligible in both the air heaters and the reradiation of heat from the absorbing plate to the bottom plate is also insignificant.     

Performance of a solar crop dryer under PNG climatic conditions

A small solar crop dryer, consisting of a drying unit, thermal storage and solar collector, was designed for the climatic conditions of Papua New Guinea, and was constructed and tested at the Energy Research site of the University of Papua New Guinea. Detailed experimental studies were carried out for drying of tapioca, as well as the testing of the drying unit with and without thermal storage. Based on economic analysis, it is observed that the annual cost per kilogram of dried tapioca is about K0.27 ≠.     

An experimental study on a finned type and non-porous type solar air heater with a solar simulator

The results of experiments performed on two non-porous solar absorber solar air heaters with and without fins have been reported in this communication. The experiments were performed under laboratory conditions. Air heaters with fins are seen to be more efficient in comparison to the air heater without fins for air flow rates ≤0.0388 kg/sec per m². The experimental results have been used to validate a simple theoretical model.     

Single and double pass solar air heaters with wire mesh as packing bed

The thermal performances of single and double pass solar air heaters with steel wire mesh layers are used instead of a flat absorber plate are investigated experimentally. The effects of mass flow rate of air on the outlet temperature and thermal efficiency were studied. The results indicate that the efficiency increases with increasing the mass flow rate for the range of the flow rate used in this work between 0.012 and 0.038 kg/s. For the same flow rate, the efficiency of the double pass is found to be higher than the single pass by 34–45%. Moreover, the maximum efficiencies obtained for the single and the double pass air collectors are 45.93 and 83.65% respectively for the mass flow rate of 0.038 kg/s. Comparison of the results of a packed bed collector with those of a conventional collector shows a substantial enhancement in the thermal efficiency.     

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

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.     

Influence of channel depth on the performance of solar air heaters

In the design of solar air heaters (SAHs), channel depth is a principal variable to be fixed. In this paper, the effect of the channel depth on the energy gain of type I and type III SAHs has been investigated by computational fluid dynamics (CFD) simulations. Laminar model and k–ω turbulence model of Wilcox are used for the prediction of flow and temperature field in SAHs. Our study shows that the heat transfer corresponding to the temperature distribution across the channel in SAH varies greatly with the change of channel depth. Based on the first and second laws of thermodynamics, the optimal channel depths for type I and type III SAHs with black-painted absorber are suggested as 10 mm. It is found that with selective coating, the absorber plate should be further from the cover glazing in order to prevent excessive convective heat loss, the distance is better of no less than 20 mm. In type III SAH, air flows in two channels above and below the absorber plate, the depth ratio of up channel to down channel should be no less than 1.     

A review on roughness geometry used in solar air heaters

The use of an artificial roughness on a surface is an effective technique to enhance the rate of heat transfer to fluid flow in the duct of a solar air heater. Number of geometries of roughness elements has been investigated on the heat transfer and friction characteristics of solar air heater ducts. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heaters in order to improve the heat transfer capability of solar air heater ducts. The correlations developed for heat transfer and friction factor in roughened ducts of solar air heaters by various investigators have been reviewed and presented.     

Transient performance of closed loop solar water heating system with heat exchanger

The present paper deals with an analysis of a forced circulation closed loop solar water heating system; withdrawal of hot water of constant flow rate from a storage tank through a heat exchanger is considered. The effect of flow rate and heat exchanger length on the performance has also been discussed for a typical set of parameters and for a typical cold day in Delhi (26 January 1980).     

A review of the performance of double pass solar air heater

Improvement of the thermal performance of a solar air heater can be obtained by enhancing the rate of heat transfer. The thermal efficiency of double pass solar air heater is higher in comparison to single pass with the concept involved of doubling the heat transfer area without increase in the system cost. Numbers of studies have been carried out on the performance analysis of double pass solar air heater provided with heat transfer augmentation techniques viz. using extended surfaces, packed bed, corrugated absorber were reported in the literature and found more increase in the thermal efficiency in comparison to conventional double duct solar air heater. These studies includes the design of double pass solar air heater, heat transfer enhancement, flow phenomenon and pressure drop in duct. This paper presents an extensive study of the research carried out on double pass solar air heater. Based on the literature review, it is concluded that most of the studies carried out on double pass solar air heater integrated with porous media and extended surfaces. Few studies were carried out with corrugated absorber. Further no study has been reported so far on double pass solar air heater with absorber plate artificially roughened from both the sides. Mathematical models based on energy analysis of some configurations of solar air heater have been discussed.     

Performance evaluation of photovoltaic thermal solar air collector for composite climate of India

The objective of present study is to evaluate the performance of the photovoltaic (PV) module integrated with air duct for composite climate of India. In this case, thermal energy is produced along with electrical energy generated by a PV module with higher efficiency. An analytical expression for an overall efficiency (electrical and thermal) has been derived by using energy balance equation for each component. Experimental validation of thermal model of hybrid photovoltaic/thermal (PV/T) system has also been carried out. It has been observed that there is a fair agreement between theoretical and experimental observations. Further it is concluded that an overall thermal efficiency of PV/T system is significantly increased due to utilization of thermal energy in PV module.     

Capital cost and economic viability of thermosyphonic solar water heaters manufactured from alternate materials in India

Many companies in India manufacture solar water heaters but these are not becoming popular in the domestic sector because of their high cost. The Ministry of Non-Conventional Energy Sources (MNES), New Delhi is recommending flat-plate collectors with copper (Cu) risers, headers and plate. Therefore, their cost is high. Long term studies have been carried out at the Central Arid Zone Research Institute, Jodhpur, to reduce the cost by replacing copper tubes with galvanised steel (G.S.) tube and copper plate with aluminium (Al) plate. The aluminium plate is wrapped over the G.S. tube by a special wire wound technique so that good contact of plate with risers and headers has been maintained. In this paper performance and testing of solar water heaters having G.S.–Al fin, Cu–Al fin and Cu–Cu fin in flat-plate collectors have been compared. It has been found that performance of all the three heaters is almost similar. The heater can provide 100 litres of hot water at an average temperature 62.0°C at 4 pm that can be retained to 50.4°C when average tap water temperature was 23.9°C. The efficiency of the heater is 51.9%. The cost of the heater with G.S.–Al collector is only Rs. 8,000.00 while it is Rs. 10,250.00 for solar water heaters with Cu–Cu collectors. The payback period of a solar water heater with G.S.–Al collector has been worked out by considering 10% compound annual interest, 5% maintenance cost, 5%, inflation in fuel prices and maintenance cost. The payback period varies between 2.92 years to 4.53 years depending upon which fuel it replaces. The payback periods are in increasing order with respect to fuels: electricity, firewood, LPG, charcoal, and kerosene.     

Exergy‐based performance analysis of packed‐bed solar air heaters

This paper presents an experimental investigation of the thermal performance of a solar air heater having its flow channel packed with Raschig rings. The packing improves the heat transfer from the plate to the air flow underneath. The dimensions of the heater are 0.9 m wide and 1.9 m long. The aluminium‐based absorber plate was coated with ordinary black paint. The characteristic diameter of the Raschig rings, made of black polyvinyl chloride (PVC) tube, is 50 mm and the depth of the packed‐bed in flow channel is 60 mm. Energy and exergy analyses were applied for evaluating the efficiency of the packed‐bed solar air heater. The rate of heat recovered from the packed‐bed solar air heater varied between 9.3 and 151.5 W m^?2, while the rate of thermal exergy recovered from the packed‐bed solar air heater varied between 0.04 and 8.77 W m^?2 during the charging period. The net energy efficiency varied from 2.05 to 33.78%, whereas the net exergy efficiency ranged from 0.01 to 2.16%. It was found that the average daily net energy and exergy efficiencies were 17.51 and 0.91%, respectively. The energy and exergy efficiencies of the packed‐bed solar air heater increased as the outlet temperature of heat transfer fluid increased. Copyright © 2004 John Wiley & Sons, Ltd.     

A review on methodology of artificial roughness used in duct of solar air heaters

In order to enhance rate of heat transfer to flowing air in the duct of a solar air heater, artificially roughened surface of absorber plate is considered to be an effective technique. Investigators reported various roughness geometries in literature for studying heat transfer and friction characteristics of an artificially roughened duct of solar air heaters. In the present paper an attempt has been made to categorize and review the reported roughness geometries used for creating artificial roughness. Heat transfer coefficient and friction factor correlations developed by various investigators for roughened ducts of solar air heaters have also been reported in the present paper.