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.     

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.     

Solar cookers--part I: cooking vessel on lugs

A large number of papers have been published on the topic of solar cookers, but hardly any have discussed the role of the vessel inside the cooker. The heat has to penetrate the vessel and cook the food in a uniform pattern. The bottom surface of the cooking vessel and the lid are ineffective in the heat transfer process to the food. Raising the vessel by providing a few lugs will make the bottom of the vessel a heat transfer surface. This change improves the performance of the system by improving the heat transfer rates in both heating and cooling modes. The times for reaching saturation temperature and cooking were noticeably reduced. Raising the vessel above the base plate of the cooker is recommended for universal adoption.     

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.     

Experimental study of a double exposure solar cooker with finned cooking vessel

A comparative experimental study of a box type solar cooker with two different cooking vessels was conducted, the first one conventional and the second one identical to the first in shape and volume but its external lateral surface provided with fins. Fins are shown to improve the heat transfer from the internal hot air of the cooker towards the interior of the vessel where the food to be cooked is placed. This reduces the cooking time considerably. The tests were carried out on the experimental platform of the Research Unit in Renewable Energies in Saharan Medium of Adrar, located at 27°53′N latitude and 0°17′W longitude in the Algerian Sahara.     

沼气、太阳能生态海岛

提出了沼气、太阳能生态海岛模型.利用太阳池淡化海水,为官兵提供饮用水,在太阳池底铺设换热器,为官兵提供生活用热水,并对沼气池进行加热.利用海岛官兵的生活废弃物生产的沼气进行炊事,大约可以满足51%左右的炊事用能需求.     

Determining the heat flow through building walls under simulated actual weather patterns

We present a methodology for determining the transient heat flow through building walls. The methodology involves the use of a guarded hot box operating under a set of simulated conditions representative of actual weather patterns. Results validate the use of the guarded hot box for the measurement of heat flow through building constructions operating under different characteristic weather patterns. Outdoor heat flow measurements are made using an isothermal-heat-flux measuring plate and the same outdoor air temperature and solar radiation effects are simulated in a guarded hot box using the sol-air temperature. Finally, these heat flow values are compared with predictions made using the DOE-2 computer code. This comparison provides a means for validating computer predicted heat flows through building walls.     

Experimental studies on solar parabolic dish cooker with porous medium

The solar cooking is the alternate method of cooking to reduce consumptions of fossil fuels. An affordable, energy efficient solar cooking technology is much need due to the fossil fuels increasing cost and it is the hottest research topic in all over the world. This paper presents an experimental analysis of the heat transfer enhancement of solar parabolic dish cookers by a porous medium made of scrap material. Using the stagnation temperature test and water boiling test are conducted on the cooking vessel with and without porous medium. Experimental results are compared for both cases in terms of thermal performance, optical efficiency, heat loss factor and cooking power.     

应用于日光温室墙体的相变材料热物性优化研究

建立日光温室计算传热模型,以室内空气温度和墙体内表面温度为指标,通过实验方法验证了所建立的传热模型准确性,最后分析相变材料相变温度、相变焓、导热系数、密度等热物性对室内最低温度和相变蓄热率的影响规律,确定被动式相变蓄热墙体和主-被动式相变蓄热墙体的最佳相变材料热物性,阐明了实际应用时相变材料选择原则。研究结果表明,所建立的日光温室传热模型具有较高准确性,可用于日光温室墙体相变材料热物性优化;主-被动式相变蓄热墙体最佳相变材料的相变温度为27 ℃,相变焓为200 kJ/kg,导热系数为0.35 W/（m·K）,密度为440 kg/m³,被动式相变蓄热墙体最佳相变材料的相变温度为26 ℃,相变焓为200 kJ/kg,导热系数为0.35 W/（m·K）,密度为792 kg/m³;最佳相变材料热物性应用时,2种墙体室内最低温度均可达到15.0 ℃,但是被动式相变蓄热墙体的相变蓄热率较主-被动式相变蓄热墙体减小29.5%。本研究可为相变材料在日光温室的高效利用提供参考。     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

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.     

Experimental investigation of an indirect-type solar cooker for indoor cooking based on a parabolic dish collector

In the present research article, an indirect type solar cooking system has been developed for indoor cooking. In the proposed cooking system, a cooking pot has been placed at a distance of 5 m from the parabolic dish collector, and the heat has been transmitted from the collector to the cooking pot by means of heat transfer fluid. A gear pump of 40 W and insulated pipes have been used to circulate the fluid. A number of experiments have been performed to analyze the performance of the cooking system. During the investigation, the system achieved the temperature of the heat transfer fluid up to 175°C. The time taken for cooking the rice and the black grams has been observed 21 and 68min, respectively. The average thermal efficiency of the proposed system for the entire day has been achieved at 13.11%.     

Comportement thermique de differents types d'habitation soumis a un ensoleillement et à une température extérieure périodiques

This paper presents the response of different kinds of schematic dwellings under daily periodic variations of the solar flux and the external temperature. The influence of the parameters which are characteristic of coupled heat transfer is studied (thermal diffusion and heat storage in external and internal walls, heat loses or solar heat supply by windows or airing).Calculations show that for an idealised regulation: (i) The energetical consumption depends only on mean variations of external temperature and solar flux and does not depend on the insulation location. (ii) For a building with a regulated internal temperature, the thermal inertia for the internal walls does not play a role. (iii) For an unregulated building, the internal temperature variations depends of the insulation location. The best location is the external one. (iv) There is an optimal thickness of walls corresponding to the daily periodic variations.     

建筑墙体热、湿及空气耦合传递

为了研究建筑墙体的热质耦合传递规律，该文考虑了太阳辐射的影响，建立了在第三类边界条件下建筑墙体非稳态热、湿及空气渗透耦合传递的物理及数学模型，开发了相应的数值模拟计算软件。给出了墙体热、湿及空气耦合传递时各部位模拟计算温度随时间的变化曲线及不同使用年限湿容量沿墙体厚度的分布规律，并将墙体的模拟计算结果与现场实测热流及温度进行了对比分析。     

On-line recording of solar cooker use rate by a novel metering device: Prototype description and experimental verification of output data

A metering device for the determination of solar cooker use rate is presented. The device records food temperature, ambient temperature and irradiance. Automatic data evaluation yields the number of cooking cycles, cooking time, food “thermal mass”, as well as the impact on fuel consumption and GHG emission compared to other cooking techniques. Metering results are compared with actual conditions for box-type and concentrating solar cookers and found to be in agreement.     

Experimental and numerical model of wall like solar heat discharge passive system

The present work raises the use of solar energy as an aid for air conditioning by means of architectural envelope parts such as walls, basically as heat discharge systems. Using a thermal balance applied to these systems, an analytic model was formulated to simulate its behavior and to consider the time variation of the environmental temperature, solar radiation, heat storage in the wall and the temperature of the room to be ventilated. The analytical results were compared against experimental data, creating an experimentally validated model that gives confidence on the accuracy and trustworthiness of the analytic proposal. Six tests were carried out in the experimental model. In four of them, the heat flux simulation was performed with electrical resistors; in the other two, solar radiation was directly employed. The results show that the thermal performance of the system can be appropriately determined and described by the analytical model, within a small margin of error. The proposed analytic model can calculate the behavior of a heat discharge system in walls by simply knowing the dimensions of the prototype and the environmental conditions.     

Thermal performance of solar air heaters: Mathematical model and solution procedure

A mathematical model and solution procedure for predicting the thermal performance of single-pass solar air collectors is presented. By omitting or providing a top glass cover over a plane absorber plate, or by providing a bottom plate under the absorber plate and circulating air over one or both of the air channels so formed, four common types of flat-plate solar air collector designs were considered. The surface temperatures of the walls surrounding the air streams were assumed uniform whereas the air temperatures were assumed to vary linearly along the collector. In the mathematical model, the solar collector was assumed sufficiently short for which the assumptions were valid. By considering a steady state heat transfer using the thermal network analysis procedure, a set of simultaneous equations for the mean temperature of the walls and the air streams were obtained. Instead of solving the simultaneous equations for mean temperatures explicitly, a matrix inversion method was employed using a standard sub-routine programme. Because heat transfer coefficients were temperature dependent, a set of mean temperatures was approximated which allowed the heat transfer coefficients to be evaluated as a first guess. An iterative process was then created that enabled the mean temperatures for the collector to be calculated. The newly-calculated mean temperatures were then compared with the initially-guessed temperatures. The iterative procedure was repeated until consecutive mean temperature values differed by less than 0.01°C. After this, another section of collector with a length equal to the previous one was added to the end of the first collector. The temperature conditions at the inlet of the second section were assumed equal to the outlet temperature conditions of the previous section. The iterative procedure to determine the mean temperatures was repeated for the next section. Additional sections were added until the required overall length of collector was considered. By this procedure, predictions of mean wall and air streams temperatures for a collector of any length could be obtained. Although only four, common single-pass types of flat-plate solar collectors are considered here, the solution procedure could be extended to encompass most other collector designs.     

An improved solar cooker

An improved hot box type solar cooker (SC-2) has been designed, developed and tested. It is an improvement on the solar cooker SC-1 earlier developed at the institute. The cooking chamber has properly been optimized for cooking the food for a family of five persons. A rubber gasket has been provided at the boundary of the openable door to prevent the leakage of hot air, thus increasing the pressure in the cooking chamber. Different cooking trials like boiling, roasting and baking were successfully conducted and the cooker was found useful from 8.00 a.m. to 5.00 p.m., even during a winter month. The efficiency of the cooker was found to be 41.2 per cent.     

开放式热管中温太阳能空气集热装置的试验研究

设计一种使用简化CPC(非追踪式复合抛物线聚光板)集热板和新型开放式热管组合的全真空玻璃集热管中温太阳能空气集热装置。每个集热单元包括一个简化CPC集热板,一根全真空玻璃集热管,在玻璃集热管内安装一个铜管和外部的一个蒸汽包连接构成一个开放式热管结构。蒸汽包内安装螺旋换热管加热通过换热管的流动空气工质。分别使用水和CuO纳米流体作为热管工质,以空气作为集热工质,对热管式中温空气集热器的传热特性进行了实验研究。分析了不同工作压力、不同工质及纳米流体质量分数对热管集热传热特性的影响,详细比较了热管水工质和纳米流体工质在集热传热性能上的优劣。试验结果表明:本系统只使用2根玻璃集热管构成集热器,空气最大出口温度在夏天可达到200℃,在冬天可接近160℃,系统平均集热效率达到0.4以上,整个系统表现了良好的中温集热特性。以纳米流体为工质的热管热阻比以水为工质时平均降低了20%左右     

Solar thermal modelling of a non-airconditioned building: Evaluation of overall heat flux

This paper presents an investigation of the thermal behaviour of a non-airconditioned building with walls/roof being exposed to periodic solar radiation and atmospheric air while the inside air temperature is controlled by an isothermal mass, window and door in the walls of the room. The effects of air ventilation and infiltration, the heat capacities of the isothermal storage mass inside air and walls/roof, heat loss into the ground, and the presence/absence of the window/door have been incorporated in the realistic time dependent periodic heat transfer analysis to evaluate the overall heat flux coming into the room and the inside air temperature. A numerical computer model using typical weather data for Delhi has been made to appreciate the analytical results quantitatively. It is found that the heat fluxes through different walls have different magnitudes and phase lags w.r.t. the corresponding solair temperatures. The overall heat flux coming into the room as well as the room air temperature are sensitive functions of the number of air changes per hour, closing/opening of the window and the door ventilation. The effects of the heat capacity of the isothermal mass and the basement ground are found to reduce the inside air temperature swing and the presence of a window is found to increase the inside air temperature even when the window area is much smaller than the wall/roof area. The model presented would be an aid to a building architect for good thermal design of non-airconditioned buildings.