Experimental testing of a new solar dryer

Drying of agricultural products is an energy-intensive operation. High prices and shortages in fossil fuels increase the emphasis on using solar energy as an alternative energy source, especially in developing countries. In this respect, a new solar dryer, which consisted of a solar air heater and a drying chamber, was developed and used for drying various fruits and vegetables, i.e., sultana grapes, green beans, sweet peppers and chilli peppers and was successfully tested. In order to make a comparison, the traditional sun-drying experiments were employed. Results showed that the solar dryer reduced the drying time significantly and prevented mass losses, and essentially provided better product quality.     

Experimental investigation of a solar dryer with natural convective heat flow

A direct type natural convection solar dryer is designed. It is constructed in local materials (wood, blades of glass, metals) then tested experimentally in foodstuffs drying (cassava, bananas, mango). It is about an experimental approach which consists in analyzing the behavior of the dryer. The study relates mainly kinetics and establishment of drying heat balances. The influence of significant parameters governing heat and mass transfers, such as solar incident radiation, drying air mass flow and effectiveness, is analyzed in order to evaluate its thermal performances. Experimental data can be represented by empirical correlations of the form M(t)=M_iexp(−kt) for representation of drying process. The resolution of these drying equations makes-possible to predict total drying time of each product. Moreover, this drying process allows to reduce the moisture content of cassava and sweet banana approximately to 80% in 19 and 22 h, respectively to reach the safety threshold value of 13%. This value permits the conservation of these products about one year without deterioration. The determination of parameters, like ambient temperature, drying chamber temperature, drying air mass flow and incident heat fluxes, allow to predict the drying effectiveness for modeling and refining the dimensioning of the elaborate prototype.     

Design and measured performance of a solar chimney for natural-circulation solar-energy dryers

The design and construction of a solar chimney which was undertaken as part of a study on natural-circulation solar-energy dryers is reported. The experimental solar chimney consists of a 5.3 m high and 1.64 m diameter cylindrical polyethylene-clad vertical chamber, supported structurally by a steel framework and draped internally with a selectively absorbing surface. The performance of the chimney which was monitored extensively with and without the selective surface in place (to study the effectiveness of this design option) is also reported.     

Design and performance studies of a solar dryer suitable for rural applications

This research paper is aimed at investigating means for food preservation using processes suitable for implementation in rural areas, where energy resources are scarce. Bearing in mind the low cost of capital investment and utilization possibilities, mainly agricultural drying, we have fabricated different types of solar dryers. Air flow in the drying system is by natural convection. The performance of the various types of solar dryers, along with a preliminary heat transfer analysis, is presented.     

Design, development and testing of a portable parabolic solar kitchen

In this project we describe the design, manufacture and testing of a new portable solar kitchen with a large, parabolic solar reflector that folds up into a small volume. Technical trials carried out with a prototype have determined that the solar kitchen reaches an average power scale of 175 W, with an energy efficiency of 26.6%. This power scale provides sufficient energy to cook a simple meal for two people in an average time of 2 h. Improvements in the design have reduced the weight of the solar kitchen to less than 5 kg and the assembly and disassembly times to 2 and 1 min, respectively. Moreover, its competitive price (48.62 €) encourages the substitution of solar energy for conventional energy. The parabolic solar kitchen described here thus provides a portable, inexpensive, environmentally friendly food heating system that can improve the quality of life of needy people in the Third World and reduce consumption of conventional energy.     

Design,development and testing of a novel non-tracking solar cooker

A novel solar cooker that does not require any tracking, has been designed, fabricated and tested and its performance has been compared with the hot-box solar cooker. The performance of the novel solar cooker is almost similar with the hot-box solar cooker though it is kept fixed while the hot box is tracked towards the sun every hour. The overall efficiency of the novel solar cooker has been found to be 29·5%. The payback period varies between 1·30 and 3·29 years depending upon the fuel it replaces. The payback periods are in the increasing order with respect to fuels such as firewood, coal, electricity, kerosene and LPG. The short payback period shows that the use of the novel non-tracking solar cooker is economical. © 1998 John Wiley & Sons, Ltd.     

Design and experimental evaluation of a solar dryer for commercial high-quality hay production

Design, experimental functional performance and economic evaluation of an energy efficient commercial-type solar energy dryer for production of high-quality hay, especially for the export market, are presented. The newly developed solar hay dryer consists of a solar collector with aluminum absorber plate and spaced fins, a drying shed with perforated metal grate floor above the ground level, swing-away plywood frames and polyethylene curtains for effectively sealing the hay stack during drying operations, an insulated duct, and a crawl space below the floor where a 3-hp in-line centrifugal fan is housed for air circulation by suction. In late August and in early September, 1996, 160 small rectangular bales of alfalfa hay with about 25% bromegrass were successfully dried from 33% initial moisture content to 13% moisture and from 25% to 11% moisture in 4 and 3 days, respectively, under average weather conditions in Saskatoon, Canada. The air temperature rise above ambient was 13–15 °C during peak bright sunshine hours in August and 10–13 °C in September. Ambient relative humidities ranged from 30–90%. Unlike field-cured hay, the hay produced by the dryer was of high-quality and remained green in colour and attractive after drying. Compared to field drying or conventional natural gas drying system, the payback period on investment in full-scale solar hay drying system may be just one to two years.     

Simulation, construction and testing of a two-cylinder solar Stirling engine powered by a flat-plate solar collector without regenerator

In this research, a gamma-type, low-temperature differential (LTD) solar Stirling engine with two cylinders was modeled, constructed and primarily tested. A flat-plate solar collector was employed as an in-built heat source, thus the system design was based on a temperature difference of 80 °C. The principles of thermodynamics as well as Schmidt theory were adapted to use for modeling the engine. To simulate the system some computer programs were written to analyze the models and the optimized parameters of the engine design were determined. The optimized compression ratio was computed to be 12.5 for solar application according to the mean collector temperature of 100 °C and sink temperature of 20 °C. The corresponding theoretical efficiency of the engine for the mentioned designed parameters was calculated to be 0.012 for zero regenerator efficiency. Proposed engine dimensions are as follows: power piston stroke 0.044 m, power piston diameter 0.13 m, displacer stroke 0.055 m and the displacer diameter 0.41 m. Finally, the engine was tested. The results indicated that at mean collector temperature of 110 °C and sink temperature of 25 °C, the engine produced a maximum brake power of 0.27 W at 14 rpm. The mean engine speed was about 30 rpm at solar radiation intensity of 900 W/m² and without load. The indicated power was computed to be 1.2 W at 30 rpm.     

Feasibility study of a solar chimney power plant in Jordan

A solar chimney power plant system is theoretically designed for future erection in Jordan. Analytical analysis of the system is simulated by mathematical software. The actual values of solar irradiation in Jordan are used in the simulation to predict the power output of the solar chimney power plant. The output results of the maximum (inlet) values of velocity, pressure, and mass flow rate of air versus the chimney height variation are obtained. Furthermore, the electrical power output and the efficiency of chimney versus chimney height variation were determined. For a solar collector diameter of 40 m and a chimney diameter of 3.5 m, the maximum power output (85 kW) was obtained for a chimney height of 210 m.     

Modelling and simulation of a wood solar dryer in a Moroccan climate

We present a numerical simulation of the functioning of a wood solar dryer in atmospheric conditions of Moroccan climate. A comparison of our numerical results with experimental measurements carried out on a wood solar dryer shows a good agreement. Results show that drying period is closely linked to glass partitions and timber thickness. The type of ventilation has no effect on the drying period (initial timber humidity lower than 40%). The substitution of east and west glass faces by concrete walls has practically no effect on drying period.     

Design, development and testing of a large-size solar cooker for animal feed

A large-size solar cooker for animal feed has been designed, developed and tested. The cooker employs locally available materials of low cost, e.g. pearl-millet husk and horse excreata. The commercial materials required for its fabrication are plain glass, mild steel angle and sheet, wood and aluminium sheet cooking utensils. The solar cooker is capable of boiling 10 kg of animal feed, sufficient for five cattle per day. The efficiency of the solar cooker is 21·8%. The cost of the cooker is only Rs 1200, which can be recovered in 0·45-1·36 years depending upon the fuel it replaces. The short payback periods suggest that the use of the solar cooker is economic. The use of the cooker will save a lot of firewood, cowdung cake and agricultural waste which are presently used for the boiling of animal feed.     

Enhancement of natural ventilation in a solar house with a solar chimney and a solid adsorption cooling cavity

This paper presents a parametric analytical study on the enhancement of natural ventilation in a solar house induced by a solar chimney and a solid adsorption cooling cavity. Some details on sizing such a system are also provided. Theoretical analyses are carried out to investigate the ventilation in the solar house with solar chimney alone, cooling cavity alone or with combined solar chimney and solar adsorption cooling cavity, without considering the wind effects. It is found that on a typical day, the solar house comprising of a 2.5 m² solar chimney, is able to create an airflow rate of more than 150 kg/h for the studied house. In addition, the ventilation rate at night is also increased by about 20% with the solar adsorption cooling cavity. It is expected that the proposed concept is useful to be incorporated with a stand-alone building or with a cluster of buildings for some favorable climates.     

Design of a new solar dryer system with swirling flow for drying seeded grape

In this study solar energy supported, swirling flow new drying system is designed and artificial drying of grapes grown around Elazığ/Turkey is investigated. With the developed swirling flow dryer with airy solar collector it is examined that drying occurs homogenously and lower moisture values are obtained in when compared with classical drying system. Also it is found that with an increase in the drying air velocity decreases drying time. When air directing elements are placed inside drying chamber and rotating element to the entrance, it is examined that drying time gets shorter compared to that of natural drying. Thus, drying time which is 200 h in natural conditions decrease to 80 h with an air velocity of 1.5 m/s with the developed solar energy supported swirling flow dryer.     

Experimental study of temperature field in a solar chimney power setup

A pilot experimental solar chimney power setup consisted of an air collector 10 m in diameter and an 8 m tall chimney has been built. The temperature distribution in the solar chimney power setup was measured. Temperature difference between the collector outlet and the ambient usually can reach 24.1 °C, which generates the driving force of airflow in the setup. This is the greenhouse effect produced in the solar collector. It is found that air temperature inversion appears in the latter chimney after sunrise both on a cool day and on a warm day. Air temperature inversion is formed by the increase of solar radiation from the minimum and clears up some time later when the absorber bed is heated to an enough high temperature to make airflow break through the temperature inversion layer and flow through the chimney outlet.     

Energy and exergy analyses of drying of red pepper slices in a convective type dryer

In this paper, the energy and exergy analyses of the drying process of thin layer of red pepper slices are investigated. Drying experiments were conducted at inlet temperatures of drying air of 55, 60 and 70 °C and at a drying air velocity of 1.5 m/s in a convective type dryer. Using the first law of thermodynamics, energy analysis was carried to estimate the ratios of energy utilization. However, exergy analysis was accomplished to determine type and magnitude of exergy losses during process by applying the second law of thermodynamics.     

Simulation and optimisation of the ventilation in a chimney-dependent solar crop dryer

As published earlier on the performance of a chimney-dependent solar crop dryer (CDSCD) designed by the authors, the solar chimney can be combined with an appropriately inclined roof of drying chamber for ventilation improvement in the dryer. Mathematical models and a computer code are now developed to simulate the ventilation in relation to the design of the CDSCD. This is done for situations without any crop (no-load) in the dryer, to relate the ventilation to the external dimensions. The pressure-loss and bulk-fluid-temperature coefficients are deduced empirically from trials on the physical model. The simulation code predicts the ventilation to within 5% and the temperatures to within 1.5% of observed data, confirming the validity of the code as an effective design tool for the CDSCD. Results of parametric studies performed with the code indicate that, maximum airflow can be achieved when the inlet-exit area ratio is around 4:1, above which the system then approaches saturation without any real variation. The drying-chamber roof inclination and the chimney height are critical for the design in the geographical regions far from the equator, whereas the decisive parameters in the regions close to the equator are the drying chamber height and the area ratio of the dryer floor to chimney cross section. A high drying chamber with a short solar chimney is generally favoured at locations close to the equator, whereas a short drying chamber with a high solar chimney is suitable for regions far away from the equator.     

Design and testing of a solar photovoltaic operated multi-seeds oil press

Oil expression tests were conducted to evaluate the performance of a novel oil expeller designed and fabricated to operate on a 200 W solar photovoltaic (PV) power system as a sole power source. The oil press was designed to press oilseeds meal with intermediate moisture content of 12±1% (w.b.) and 0.5–2 mm particle sizes. Freshly grated coconuts and ground peanuts were used to determine the oil expression efficiency of the press. The oilseed samples were pressed for 12 min with a maximum pressure of 3.0 MPa being reached at 6 min of pressing for peanuts and 8 min of pressing for coconuts. The pressure was then held for the rest of the pressing time. The press attained an average oil expression efficiency of 73% for coconuts and 70% for peanuts. The force-vs.-deformation studies indicated that peanut press meal was compacted at a higher rate as compared to coconuts. The observation on the energy consumption indicated that there was a significant increase (P<0.05) in the specific energy requirement for both coconuts and peanuts after 6 min of pressing, which resulted from the solidification of the press cake. An average specific energy of 36.55 and 20.35 Wh/kg was recorded for peanuts and coconuts, respectively, after 12 min of pressing.     

Design and construction of a residential solar heating and cooling system

The first integrated system providing heating and cooling to a building by use of solar energy has been designed and installed in a residential-type building at Colorado State University. Solar heated liquid supplies heat to air circulating in the building and to a lithium bromide absorption air conditioner. Service hot water is also provided. Approximately two-thirds of the heating and cooling loads are expected to be met by solar energy, the balance by natural gas. The paper contains details of design and principles of operation. A breakdown of actual costs of the equipment and its installation is also provided.     

Design and testing of Sudanese solar box cooker

This study aimed at developing a solar box cooker to be used in Sudan. The cooker was designed and fabricated in the workshop of Centre for Energy Studies, Indian Institute of Technology (IIT), Delhi. A series of tests were carried out during nine days to determine the two factors of merits F1 and F2 in order to make comparison of the cooker against the other Indian designs. The results obtained verified acceptability of the cooker and found successful.