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.     

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.     

Performance of a two channel suspended flat plate solar air heater

In the present communication, an analytical model to study the performance of a two channel suspended flat plate air heater is presented. The effect of different parameters, e.g. spacing between the plates, plate length, same and different flow rates of air in the two channels of the air heater, on the air temperature has been studied. A comparison of single channel and two channel air heaters has also been made. Numerical calculations have been made for a typical cold day in Delhi, viz. Jan. 26, 1980.     

Investigation on double-glazed solar air heater connected in series with rock bed solar collector-cum-storage system

This paper presents an experimental investigation along with a theoretical model of a double-glazed flat plate solar air heater connected in series with an integrated rock bed collector-cumstorage unit. Predictions are made regarding the effects of heat transfer coefficient and number of glazings on the performance of the air heater. The model fits quite well with the experimental observations.     

Design and thermal performance evaluation of a novel solar air heater

In the present scenario, numerous applications perform on solar energy for cooking, heating and cooling, and power generation, globally. Solar air heaters are one of these applications purposely used for, drying, timber seasoning and space heating. In the present work, a solar air heater (SAH) has been designed to produce a good exhaust temperature for long hours especially in the case of poor ambient conditions or during off sunshine hours. A mixture of desert and granular carbon in the ratio of 4:6 has been used as thermal heat storage inside the SAH. Two halogen lights of 300 W are used to increase the exhaust temperature of the SAH by placing them in the inlet and outlet ducts. All the experiments have conducted on natural and forced convection for performance evaluation on two similar design solar air heaters (with and without heat storage). The comparisons are made with two similar design solar air heaters carrying desert and granular carbon, as an individual heat storing media, to find out an optimum design of a SAH with long term heating. The thermal efficiencies of the novel SAH range from 18.04% to 20.78% of natural convection and 52.21%–80.05% with forced convection.     

Performance of suspended flat plate air heater

In this communication, a heat transfer model to predict the transient behaviour of a suspended flat plate solar collector with constant flow of fluid (air) above the absorber has been presented. A reflecting sheet with an air gap between the absorber plate and bottom insulation to reduce heat loss has been used. The effect, on performance of the air heater, of the parameters viz, spacing between cover and plate, heat capacity of air and absorber plate, flow rate of fluid and collector length have been studied. The effect of changing the averaging inlet temperature with varying collector length has also been studied.     

A new type of solar water heater

This investigation reports a new type of solar water heating system without water pipes on the collector surface or a separate storage tank. The water to be heated continuously flows perpendicularly from an upper transparent cover to a porous absorber and is stored in a small volume beneath this assembly. Three different systems were designed, manufactured and tested but only one proved to be successful; this design indicated higher thermal efficiency compared to conventional collectors at high flow rates whereas at low flow rates the opposite is true.     

Refrigerant-charged integrated solar water heater

The performance of two R-11-charged integrated solar water heater collectors was investigated experimentally for forced and natural circulation water flows. The heat transfer from the refrigerant loop to the hot water storage tank took place through a condenser of novel design integrated within the collector frame. The effect of the condenser inclination on the system efficiency was remarkable for natural circulation water flow but had no significant effect for forced circulation flow. The difference in thermal response between the refrigerant and water loops caused buildup of stored energy in the condenser. This energy affected the buoyancy forces and generated flow pulsation that caused a harmonic-like variation of the system efficiency. This effect vanished with forced water circulation flow. The system efficiency varied between 20 and 50% depending on the solar insolation.     

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.     

The effect of plane booster reflectors on the performance of a solar air heater with solar cells suitable for a solar dryer

We present a theoretical study of a solar photovoltaic-thermal (hybrid) system consisting of a flat-plate solar air heater mounted with solar cells and a plane booster. A conventional flat-plate collector is converted into a hybrid system by mounting solar cells directly on the absorber plate. A hybrid system is self-sufficient in the sense that the electrical energy required by the pump is supplied by the panel. Such systems are well suited to applications such as solar drying. The combined system is analysed for the case when the radiative and absorptive properties of the cell surface and the absorber plate are nearly the same. The solar cell efficiency is a linearly-decreasing function of the absorber plate temperature. The performance of the system has been evaluated for various combinations of boosters. The minimum area of the solar cells required to run the pump at a given flow rate has been calculated as a function of time, with and without boosters. The minimum cell area required decreases with the use of boosters. High cost cells may be replaced by low cost reflectors. The solar air heaters presently available on the market are not suitable for direct conversion to hybrid systems.     

Thermal performance of a matrix air heater

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.     

Optimal thermohydraulic performance of a wire mesh packed solar air heater

This paper is concerned with thermohydraulic investigations on a packed bed solar air heater having its duct packed with blackened wire screen matrices of different geometrical parameters (wire diameter and pitch). The thermohydraulic performance of an air heater in terms of effective efficiency is determined on the basis of actual thermal energy gain subtracted by the primary energy required to generate power needed for pumping air through the packed bed. Based on energy transfer mechanism in the bed, a mathematical model is developed to compute effective efficiency. A design criterion is also suggested to select a matrix for packing the air flow duct of a solar air heater which results in the best thermal efficiency with minimum pumping power penalty. Resulting values of effective efficiency clearly indicate that the packed bed solar air heater investigated is thermohydraulically efficient as compared to flat plate collectors.     

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.     

Experimental investigation of thermal performance of solar air heater having different obstacles on absorber plates

This paper presents the results of an experimental investigation of the performance for a new flat plate solar air heater (SAH) with several obstacles (Type I, Type II, and Type III) and without obstacles (Type IV). The efficiencies, the heat gain factors and heat loss coefficients are determined for the collectors and comparisons were made among them. The experimental data along with the correlations obtained by linear regression are presented. The optimal value of efficiency was determined for the solar air heater with Type II absorbent plate in flow channel duct for all operating conditions and the collector supplied with obstacles appears significantly better than that without obstacles.     

On the boundary conditions applicable in the analysis of a matrix air heater

A dimensionless analysis of matrix air heaters has been developed to study the effect of different boundary conditions on its performance. The theoretical results have been compared with measurements of an experiment performed with one type of matrix solar air heater. For the fourth set of boundary conditions, the theoretical results agree fairly well with experimental data, thus providing confidence in particular boundary conditions. For this particular set of boundary conditions, the thermal performance of the system has been studied for different mass flow rates of air and as a function of other physical parameters.     

Year round performance of a cylindrical solar water heater

A cylindrical collector-cum-storage type solar water heater has been designed, developed and tested. Its year round performance has been carried out and reported in this paper. The heater can provide 50 litres of hot water at 50–60°C in the afternoon and a temperature of 35°C can be retained till the next day for early morning use. The heater receives approximately 30% more radiation as compared to a flat surface. The economics of the heater has been worked out and it has been found that the cost can be recovered within one year.     

Analysis of fluid flow and heat transfer in a rib grit roughened surface solar air heater using CFD

This paper presents the study of fluid flow and heat transfer in a solar air heater by using Computational Fluid Dynamics (CFD) which reduces time and cost. Lower side of collector plate is made rough with metal ribs of circular, square and triangular cross-section, having 60° inclinations to the air flow. The grit rib elements are fixed on the surface in staggered manner to form defined grid. The system and operating parameters studied are: e/D_h = 0.044, p/e = 17.5 and l/s = 1.72, for the Reynolds number range 3600-17,000. To validate CFD results, experimental investigations were carried out in the laboratory. It is found that experimental and CFD analysis results give the good agreement. The optimization of rib geometry and its angle of attack is also done. The square cross-section ribs with 58° angle of attack give maximum heat transfer. The percentage enhancement in the heat transfer for square plate over smooth surface is 30%.     

Optimized mass flux ratio of double-flow solar air heater with EHD

The numerical study of laminar forced convection inside double-flow solar air heater with electrohydrodynamic technique is investigated by finite difference method. The electric field is generated by the wire electrodes charged with DC high voltage. The mathematical modeling of computational fluid dynamics includes the interactions among electric field, flow field, and temperature field. It can be perceived that augmented heat transfer with presence of an electric field increases with the supplied voltage but decreases with the total mass flux. The optimized mass flux ratio is expressed incorporating with concerning parameter comprising of the electrode arrangement, the number of electrodes, the total heat flux at an absorbing plate, and the channel geometry.     

Thermal modeling of integrated roof air heater for passive solar space heating of a non-air-conditioned building

This communication presents the periodic heat transfer analysis for solar space heating of an unconditioned building with an integrated roof air heater. The system consists of an air duct within the roof such that the air is continuously or intermittently forced to circulate the cooler room air through the inlet of the air duct. Time dependence of the air flow is represented by a step function of time for daily operation and, hence, has been expressed as a Fourier series in time. The analysis takes into account air ventilation, ground heat conduction and furnishings. The effects of depth of the air duct from the outer surface of the roof and the magnitude and duration of air flow rate on indoor air temperature have been studied for a typical cold winter day in Delhi. It is seen that a time dependent air flow through the duct is desirable from the point of view of increasing the indoor air temperature in the case of a bare roof. However, in the case of a blackened and glazed roof, continuous air flow is needed for increasing the room air temperature. The results are desirable from the point of view of efficient space heating of solar passive buildings.     

Thermal performance optimization of a flat plate solar air heater using genetic algorithm

Thermal performance of solar air heater is low and different techniques are adopted to increase the performance of solar air heaters, such as: fins, artificial roughness etc. In this paper an attempt has been done to optimize the thermal performance of flat plate solar air heater by considering the different system and operating parameters to obtain maximum thermal performance. Thermal performance is obtained for different Reynolds number, emissivity of the plate, tilt angle and number of glass plates by using genetic algorithm.