The performance of a box-type solar cooker with auxiliary heating

In Bangladesh it is very difficult to use solar cookers during the months when the days are generally cloudy and at times solar cooking becomes impossible. To overcome such problems for a box-type solar cooker, we have used an auxiliary source of energy inside it. This is done with the help of a built-in heating coil inside the cooker or a retrofit electric bulb in a black painted cylinder. It is found that the use of auxiliary sources allows cooking on most cloudy days.     

A novel advanced box-type solar cooker

An advanced version of the box-type solar cooker is presented: a fixed cooking vessel in good thermal contact with a conductive absorber plate is set into the glazing; the results are improved thermal performance, easier access to the cooking vessel and less frequent maintenance due to protection of all absorbing and reflecting surfaces. Outdoor tests show that 5 L of water per sq m of opening surface can be brought to full boiling in less than one hour. A finite element simulation model of the advanced box cooker is presented. It is shown that the most decisive parameters are absorber-to-pot heat transfer and absorber conductivity. Field tests in Ethiopia and India are under way, local production in India has started.     

Estimation of design parameters for thermal performance evaluation of box-type solar cooker

The paper presents a simple test procedure for determination of design parameters to predict the thermal performance of a box-type solar cooker. A series of out-door experiments were performed on the double-glazed solar cooker of aperture area 0.245 m² with a fibre body to obtain two figures of merit, F₁ and F₂. The necessary design parameters—optical efficiency, F′η_o and heat capacity, (MC)′ of the cooker are calculated using the linear regression analysis of experimental F₂ data for different load of water. Based on the experimental results, a correlation for F₂ as a function of quantity of water (load) is proposed. The close agreement between experimental and calculated F₂ indicates the validity of the correlation. The proposed procedure is then applied to predict the heating characteristic curves of the solar cooker for different load of water. The predicted heating characteristic curves are validated by comparing with the experimental data from a series of cooker testing experiments. The results of present study reveal that F′η_o and (MC)′ are the critical design parameters required for the prediction of thermal performance of the solar cooker.     

Natural convective heat transfer in trapezoidal enclosure of box-type solar cooker

This paper presents simple thermal analysis to evaluate the natural convective heat transfer coefficient, h_c12 for a trapezoidal absorber plate-inner glass cover enclosure of a double-glazed box-type solar cooker. Several indoor simulation experiments in steady state conditions have been performed to measure the temperatures of absorber plate, inner and outer glass covers, ambient air, electrical input supply and wind speed. The experimental data has been correlated by an equation of the form, Nu = CRaⁿ. The values of the constants C and n, obtained by linear regression analysis are used to calculate the convective heat transfer coefficient. The heat transfer analysis predicts that h_c12 varies from 4.84 to 6.23 W m^{−2 o}C⁻¹ for the absorber plate temperature from 54 to 141 ^oC. The results of h_c12 are compared with those of rectangular enclosure for the same absorber-inner glass cover temperatures and gap spacing. The study reveals that the values of convective heat transfer coefficient and top heat loss coefficient for rectangular enclosure are lower by 31–35% and 7% respectively.     

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

The top heat-loss factor (U_t) of a box-type solar cooker varies with plate temperature, wind heat-transfer coefficient and ambient temperature. A method for correlating U_t 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.     

Experimental investigation of a box-type solar cooker with a finned absorber plate

This article provides the results and finding of an experimental work undertaken in the desert of Algeria. That aimed to compare experimental performance of a box-type solar cooker equipped with a finned absorber plate to a similar box-type cooker which absorber plate without fins. Tests have been carried out on the experimental platform of the Renewable Energies Research Unit in Saharan Environment of Algeria at Adrar. Adrar is located at a latitude 27° 53′ North and a longitude 0° 17′ West. Fins that have been used in solar air collectors enhanced heat transfer from absorber plate to air. Experimental tests have been undertaken as part of this project where was applied this phenomenon to a box-type solar cooker. The results of the experimental investigation have been rigorously analysed and showed that the stagnation temperature for box-type solar cooker equipped with a finned absorber plate was about 7% more than box-type solar cooker equipped with an ordinary absorber plate. The time required for heating water up to boiling temperature in both box-type solar cookers was reduced with about 12% when a finned absorber plate was used.     

Numerical heat transfer studies of PCMs used in a box-type solar cooker

Theoretical investigations on the phase change materials (PCMs) used as the heat storage media for box-type solar cookers have been conducted in this study. The selected PCMs are magnesium nitrate hexahydrate, stearic acid, acetamide, acetanilide and erythritol. For a two-dimensional simulation model based on the enthalpy approach, calculations have been made for the melt fraction with conduction only. Different materials such as glass, stainless steel, tin, aluminum mixed, aluminum and copper are used as the heat exchanger container materials in the numerical calculations. The large value of thermal conductivity of heat exchanger container material did not make a significant contribution on the melt fraction except for at very low thermal conductivities. Based on the theoretical results, stearic acid and acetamide are found to be good compatibility with latent heat storage system. It is also found that the initial temperature of PCM does not have very important effects on the melting time, while the boundary wall temperature plays an important role during the melting and has a strong effect on the melt fraction. The results also show that the effect of thickness of container material on the melt fraction is insignificant. The results obtained in this paper show that in a box-type solar cooker, acetamide and stearic acid should be used as a latent heat storage materials.     

Experimental testing of a box-type solar cooker using the standard procedure of cooking power

A box-type solar cooker with one (Model I) or four (Model II) cooking pots was constructed and tested under Tanta prevailing weather conditions. Experiments were performed during July 2002 using the cooker with or without load. The obtained results were employed to calculate the two figures of merit, F₁ and F₂, as well as the utilization efficiency η_u and the specific t_s and characteristic t_c boiling times. The obtained values of F₁ indicate that the cooker can be used twice a day for consecutive cooking. F₂ was found to increase almost linearly with the mass of the cooking fluid M_f. The cooker is able to boil 1 kg of water in 15 min when its aperture area equals 1 m². Furthermore, experiments also considered the requirements for the international standard test procedure for solar cookers. The cooking power P was correlated with the temperature difference ΔT between the cooking fluid and the ambient air. Linear correlations between P and ΔT had correlation coefficients higher than 0.90 satisfying the standard. The obtained values of the initial cooking power, heat loss coefficient and the cooking power at a temperature difference of 50 °C agree well with those obtained for small solar cookers. The present cooker is able to cook most kinds of food with an overall utilization efficiency of 26.7%.     

Parametric model of solar cooker performance

This paper presents a model for prediction of the cooking power of a solar cooker based on three controlled parameters (solar intercept area, overall heat loss coefficient, and absorber plate thermal conductivity) and three uncontrolled variables (insolation, temperature difference, and load distribution). The model basis is a fundamental energy balance equation. Coefficients for each term in the model were determined by regression analysis of experimental data. The model was validated for commercially available solar cookers of both the box and concentrating types. The valid range of model application includes most of the feasible design space for family-sized solar cookers. The model can be used to estimate the cooking capacity of existing box type and concentrating type solar cookers. It can also be used to find the combinations of intercept area and heat loss coefficient required to cook a given quantity of food in a given climate.     

Mathematical modeling of a box-type solar cooker employing an asymmetric compound parabolic concentrator

A novel design of solar cooker is introduced. The cooker is of box-type equipped with an asymmetric compound parabolic concentrator (CPC) as booster-reflector. It consists of an insulated box equipped with a vertical double glazing cover on a side, and a vertical absorber plate laid out just behind the transparent cover. The booster-reflector is fixed on the glazed side of the box. The absorber plate and the glazing form a vertical channel, open at the top and bottom, and enclosed at the sides. The two openings allow the inside air circulation. A mathematical model of the heat transfer processes involved with this solar cooker, containing a cooking pot loaded with water and deposited on the box floor; was developed and the effects of various parameters, such as solar radiation, load of water and clouds on the dynamic behavior of the cooker are studied.     

Design and measured performance of a plane reflector augmented box-type solar-energy cooker

The design philosophy, construction and measured performances of a plane-reflector augmented box-type solar-energy cooker are presented. The experimental solar cooker consists of an aluminum plate absorber painted matt black and a double-glazed lid. The bottom and sides are lagged with fibreglass wool insulator. The reflector consists of a wooden-framed commercially available specular plane mirror which is sized to form a cover for the box when not in use. Provision is made for four cooking vessels, each capable of holding upto 1 kg of water. Results of thermal performance tests show stagnation absorber plate temperatures of 138°C and 119°C for the cooker with and without the plane reflector in place respectively. Boiling times of 60 min (3600 s) and 70 min (4200 s) for 1 kg of water, for the cooker with and without the plane reflector in place, respectively, were recorded. The solar cooker performance has been rated using the first figure of merit (F₁) on the no-load test and the second figure of merit (F₂) on the sensible heat tests. Predicted water boiling times using the two figures of merit compared favourably with measured values. The performance of the cooker with the plane reflector in place was improved tremendously compared to that without the reflector in place.     

Mathematical model of the thermal performance of box-type solar cookers

A mathematical model of the heat transfer processes involved with a box-type solar cooker, containing food, was developed. Solar radiation, including that from a flat reflector, enters the box and heat transfer within and out of the box was considered. Using small increments of time, the computer model finds the temperature of the air, food, interior walls and top cover as the solar flux varies throughout the cooking period. Sample results are presented, giving the food temperature as affected by latitude, month, wind, clouds, mass of food, thermal resistance of the box walls and adjustment of the box while cooking.     

The performance of a solar cooker in Egypt

A simple, efficient solar cooker was designed and its performance in the Egyptian climate was evaluated. The cooker is of the hot box type with a plane booster mirror reflector. The performance of the cooker was measured experimentally for over two years under different working conditions. The test conditions included experiments with and without adjusting the cooker's position for maximum solar radiation and the tilt angle of the booster reflector for maximum concentration. Formulas for calculating the orientation angle of the oven and tilt angle of the reflector were deduced. The shadow effect caused by the sides of the oven was also calculated. The solar cooker proved to be reliable, trouble free and efficient. All kinds of food were cooked including meat, chicken, rice, peas, beans, potatoes, soup, eggs and cakes. A good meal for a family of four was cooked in 3–4 h. It was established that better heat transfer occurred when the cooking pot was covered with an airtight plastic transparent cover rather than using an ordinary metallic cover. The energy balance of the cooker from heat transfer considerations enabled estimates of both over and food temperature to be made. Calculated values agreed well with the experimental measurements.     

Enhancement the solar box cooker performance using steel fibers

The use of fossil fuel and wood for cooking poses health, environmental, and economic challenges, especially with the growing population. This has led to an increase in the trend towards the use of clean and sustainable cooking sources, including solar cookers. This experimental study aims to contribute by enhancing the performance of a solar box cooker (SBC) according to the concept of porous media via adding steel fibers inside the box as a modified SBC and comparing it with a conventional SBC. The stagnation test to determine the first figure of merit and the load test to determine the second figure of merit, standard boiling time, and cooker optothermal ratio were conducted under the outdoor conditions of Baghdad city. Also, an energy and exergy efficiency analysis, and calculating the rate of heat loss by three water loads heating and cooling tests. The results revealed that the modified SBC has a higher thermal performance than the conventional SBC.     

Thermal performance of a solar pressure cooker based on evacuated tube solar collector

This paper presents the thermal performance of a community type solar pressure cooker based on evacuated tube solar collector. The developed design of solar pressure cooker has separate parts for energy collection and cooking unit and both are coupled by heat exchanger. The paper has presented the performance results of experimental study conducted on solar pressure cooker and a simulation model has been developed for predicting the cooker performance under a variety of operating and climatic conditions. The theoretical model is validated against the experimental results. The obtained results have suggested a possibility of several batches of solar cooking on a clear sunny day under typical conditions of Delhi.     

The performance of a low cost clay solar cooker

This paper reports the development of a low cost clay solar cooker. The main features of this cooker are that it is made from cheap, locally available materials, and needs no skilled labour. One of the new design features of the solar cooker is the replacement of the absorber plate with locally available black sontes. The effects of using the black stones instead of the abrosber plate resulted in solar cooker capable of storing solar energy, hence making late cooking possible.     

Design theory and performance analysis of paraboloidal solar cooker

A paraboloidal collector having aperture diameter 1.3 m, depth 0.30 m, and focal length 0.35 m was designed and fabricated. The paraboloidal solar cooker was tested under no-load conditions at a recorded maximum temperature of 326°C. The analysis was made from the sensible heating and cooling curves. The values of the overall heat loss factor (F′ UL) obtained from the sensible cooling curve were smaller on different days. The minimal heat loss was due to the wind shield provided at the paraboloidal receiver. Analysis of the sensible heating curve gave the values of the optical efficiency factor (F′ η₀). The performance of the paraboloidal collector was determined, and the thermal efficiency was found to be 26%. The performance curve was plotted to predict the approximate time required to boil a known amount of water under given climatic conditions. The solar cooker was found to be useful in cooking a variety of foods.     

太阳灶性能测试国际标准简介

〔第三届国际太阳灶学术会议于1997年1月6日至10日在印度哥印拜陀举行,会议提出了太阳灶测试和性能评估的国际标准。之后,美国农业部农业研究中心的科学家P.A.范克(Funk)利用实验数据对该标准进行了评估,认为该标准不仅易于使用,而且所提供的数据可很好的预测太阳灶的热性能。详细报道可见SolarEnergy(Vo1.68,No.1,2000)。—编译者〕     

Evaluation of solar cooker thermal performance using different insulating materials

This paper summarizes very briefly the thermal performance of solar cookers with four different insulations readily available in rural areas. A comparison of each one of these is made with the performance of glass wool. This experiment is performed to minimize the cost of the cooker with a view to enhance its widespread application in the rural Indian environment.     

Design optimization of solar cooker

Various designs of solar cookers have been theoretically investigated with a view to optimize their performance. Starting from a conventional box type cooker, various combinations of booster mirrors have been studied to arrive at a final design, aimed at providing a cooker, which can be fixed on a south facing window (for countries of northern hemisphere, mainly situated near the tropic of Cancer). This cooker, with a rear window opening, may provide higher cooking temperature for a fairly large duration of the day. Two or three changes in positions of the side booster mirrors, without moving the cooker as a whole has been proposed. The new design has been experimentally implemented and compared with a conventional box type solar cooker. Besides the convenience of a rear window opening, the cooker provides temperatures sufficiently high to enable cooking two meals a day.