Design and development of a simple solar dehydrator for crop drying

In this paper, a simple solar collector cum crop drying system is described. The categorical objectives of this paper are (1) to identify a suitable medium capacity solar drying system and (2) to study analytically and experimentally the performance characteristics of this newly fabricated solar drying system. The drying ratio, rehydration ratio, culinary and organoleptic characteristics, of Methi and Bhendi crops were studied and presented in this paper.     

Experimental and simulated performance of a PV-ventilated solar greenhouse dryer for drying of peeled longan and banana

This paper presents experimental and simulated performance of a PV-ventilated solar greenhouse dryer for drying of peeled longan and banana. The dryer consists of a parabolic roof structure covered with polycarbonate plates on a concrete floor. Three fans powered by a 50-W PV module ventilate the dryer. To investigate the experimental performances of the solar greenhouse dryer for drying of peeled longan and banana, 10 full scale experimental runs were conducted. Of which five experimental runs were conducted for drying of peeled longan and another five experimental runs were conducted for drying of banana. The drying air temperature varied from 31 °C to 58 °C during drying of peeled longan while it varied from 30 °C to 60 °C during drying of banana. The drying time of peeled longan in the solar greenhouse dryer was 3 days, whereas 5-6 days are required for natural sun drying under similar conditions. The drying time of banana in the solar greenhouse dryer was 4 days, while it took 5-6 days for natural sun drying under similar conditions. The quality of solar dried products in terms of colour and taste was high-quality dried products. A system of partial differential equations describing heat and moisture transfer during drying of peeled longan and banana in the solar greenhouse dryer was developed and this system of non-linear partial differential equations was solved numerically using the finite difference method. The numerical solution was programmed in Compaq Visual FORTRAN version 6.5. The simulated results reasonably agreed with the experimental data for solar drying of peeled longan and banana. This model can be used to provide the design data and is also essential for optimal design of the dryer.     

Development of a new type of solar dryer: Its mathematical modelling and experimental evaluation

A solar dryer fitted with a novel design of absorber having inbuilt thermal storage capabilities was designed, fabricated, simulated and also tested at Rajiv Gandhi College of Engineering Research & Technology, Chandrapur (MS) India. Thermic oil was used as a storage material. The main objective of the study was to reduce the drying period and enhance the quality of dried product mainly chillies and fenugreek leaves. The products were laid in a single layer. The dimensions of the dryer were arrived at using the well-defined procedure available in literature. The mass of thermic oil needed in the absorber and mass of product to be dried in trays were optimized using simulation techniques. The maximum drying air temperature required for drying agricultural products was around 65°C. The ambient conditions at the location were 25–40°C, 16–43% RH and solar radiation 105–1024 W m⁻². Experimental studies based on temperature and humidity measurements were performed on the dryer. The research concluded that the desired drying air temperature was achieved and maintained for a longer period. The length of operation of the solar air heater and the efficiency of the dryer were increased, and better quality of agricultural products in terms of colour value were obtained compared with open sun drying. Copyright © 2007 John Wiley & Sons, Ltd.     

A study of the drying effect on lemon slices using a closed-type solar dryer

An experimental closed-type dryer associated with a photovoltaic system (PV) was developed. The transparent drying cabinet was designed with high transmittance glass to decrease the reflection of direct sunlight and to offer extra direct solar heating on the raw material during drying. Parallel wiring with a local electrical grid was necessary for switching purposes if there is insufficient battery backup during peak operation. Lemon slices were dried using the closed-type solar dryer and results were compared with hot air drying at 60 °C. The results indicate that the dried lemon slices using a closed-type solar dryer has better general levels of quality in terms of sensory parameters.     

Performance evaluation of solar dryer system for optimal operation: mathematical modelling and experimental validation

An analytical moisture diffusion model which considers the influence of external resistance to mass transfer is developed. The methodology to determine constant and variable moisture diffusion coefficients, D_eff is proposed. A laboratory model of mixed-mode solar dryer is constructed to perform 16 experiments for different performance dependent variables under simulated indoor conditions. The potatoes (Solanum tuberosum) of Kufri Safed variety have been chosen as the test food product. The range of variables investigated is absorbed thermal energy (150–750 W/m²); air mass flow rate (0.009–0.022 kg/s); loading density (1.08–4.33 kg/m²) and sample thickness (5–18 mm). The efficiency results have been analysed to identify the value of each process variable leading to optimal operation of dryer. The study reveals that dryer with sample thickness of 8 mm and loading density of 4.33 kg/m² can operate optimally for absorbed energy of 450 W/m² and air mass flow rate of 0.017 kg/s.     

Experimental investigation of forced convection and desiccant integrated solar dryer

An indirect forced convection and desiccant integrated solar dryer is designed and fabricated to investigate its performance under the hot and humid climatic conditions of Chennai, India. The system consists of a flat plate solar air collector, drying chamber and a desiccant unit. The desiccant unit is designed to hold 75 kg of CaCl₂-based solid desiccant consisting of 60% bentonite, 10% calcium chloride, 20% vermiculite and 10% cement. Drying experiments have been performed for green peas at different air flow rate. The equilibrium moisture content M_e is reached in 14 h at an air flow rate of 0.03 kg/m² s. The system pickup efficiency, specific moisture extraction rate, dimensionless mass loss, mass shrinkage ratio and drying rate are discussed in this paper.     

Performance of a solar dryer using hot air from roof-integrated solar collectors for drying herbs and spices

A solar dryer for drying herbs and spices using hot air from roof-integrated solar collectors was developed. The dryer is a bin type with a rectangular perforated floor. The bin has a dimension of 1.0 m×2.0 m×0.7 m. Hot air is supplied to the dryer from fiberglass-covered solar collectors, which also function as the roof of a farmhouse. The total area of the solar collectors is 72 m². To investigate its performance, the dryer was used to dry four batches of rosella flowers and three batches of lemon-grasses during the year 2002–2003. The dryer can be used to dry 200 kg of rosella flowers and lemon-grasses within 4 and 3 days, respectively. The products being dried in the dryer were completely protected from rains and insects and the dried products are of high quality. The solar air heater has an average daily efficiency of 35% and it performs well both as a solar collector and a roof of a farmhouse.     

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 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.     

Mathematical modelling of thin layer drying process of long green pepper in solar dryer and under open sun

An experimental study was performed to determine the thin layer drying characteristics in a solar dryer with forced convection and under open sun with natural convection of long green pepper. An indirect forced convection solar dryer consisting of a solar air collector and drying cabinet was used in the experiments. Natural sun drying experiments were conducted for comparison at the same time. The constant rate period is absent from the drying curves. The drying process took place in the falling rate period. The drying data were fitted to 13 different mathematical models. Among the models, the logarithmic model for forced solar drying and the Midilli and Kucuk model for natural sun drying were found best to explain the thin layer drying behaviour of long green peppers. The performance of these models was investigated by comparing the coefficient of determination (R), reduced chi-square (χ²) and root mean square error (RMSE) between the observed and predicted moisture ratios.     

Design of a commercial solar hot water system

The paper critically evaluates the design and performance of a commercial hot water system. These systems are installed in IIT Delhi hostels mainly for cooking and washing utensils. In some of these systems, heat exchangers are also used. In specific terms, one can regard the thermal efficiency and the maximum hot water temperature as indicators of the performance of the system. Hence different parameters of the heat exchanger and the number of collector panels directly affect the performance of the system. In the paper, an energy balance for different components of the system under steady state conditions is primarily investigated. It is found that excellent agreement exists between experimental and theoretical results for the proposed design parameters.     

Performance of evaporator-collector and air collector in solar assisted heat pump dryer

A solar assisted heat pump dryer has been designed, fabricated and tested. This paper presents the performance of the evaporator-collector and the air collector when operated under the same meteorological conditions. ASHRAE standard procedure for collector testing has been followed. The evaporator-collector of the heat pump is acting directly as the solar collector, and the temperature of the refrigerant at the inlet to the evaporator-collector always remained below the ambient temperature. Because of the rejection of sensible and latent heats of air at the dehumidifier, the temperature at the inlet to the air collector is lower than that of the ambient air. Hence, the thermal efficiency of the air collector also increases due to a reduction of losses from the collector. The efficiencies of the evaporator-collector and the air collector were found to vary between 0.8–0.86 and 0.7–0.75, respectively, when operated under the meteorological conditions of Singapore.     

Valuation and development of the solar hydrogen production

This article considers Algeria as a case study for the evaluation of the solar hydrogen production potential. The study relates to the design of a hydrogen generating station by water electrolysis whose energy resources are solar. The electricity supply is done by a solar tower power plant. The numerical simulation of the hydrogen production for the installation proposed is made while being based on the characteristic equations governing the electrolysis of water, hydraulic pumping system and the solar tower. The hydrogen production rate is given for various values of the solar radiation and several sites of Algeria. The results obtained by the established computer code, and of which the required goal is the determination of the most favorable conditions for a better production of hydrogen, are presented and discussed.     

Technical feasibility assessment of a solar chimney for food drying

Solar dryers use free and renewable energy sources, reduce drying losses (as compared to sun drying) and show lower operational costs than the artificial drying, thus presenting an interesting alternative to conventional dryers. This work proposes to study the feasibility of a solar chimney to dry agricultural products. To assess the technical feasibility of this drying device, a prototype solar chimney, in which the air velocity, temperature and humidity parameters were monitored as a function of the solar incident radiation, was built. Drying tests of food, based on theoretical and experimental studies, assure the technical feasibility of solar chimneys used as solar dryers for agricultural products. The constructed chimney generates a hot airflow with a yearly average rise in temperature (compared to the ambient air temperature) of 13 ± 1 °C. In the prototype, the yearly average mass flow was found to be 1.40 ± 0.08 kg/s, which allowed a drying capacity of approximately 440 kg.     

Technical and economical evaluation of solar thermal power generation

This article presents a feasibilty on a solar power system based on the Stirling dish (SD) technology, reviews and compares the available Stirling engines in the perspective of a solar Stirling system.The system is evaluated, as a parameter to alleviate the energy system of the Cretan island while taking care of the CO₂ emissions. In the results a sensitivity analysis was implemented, as well as a comparison with conventional power systems.In the long-term, solar thermal power stations based on a SD can become a competitive option on the electricity market, if a concerted programme capable of building the forces of industry, finance, insurance and other decision makers will support the market extension for this promising technology.     

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.     

Investigation of hydrogen production performance of a reactor assisted by a solar pond via photoelectrochemical process

In this study, the hydrogen production performance of a reactor assisted by a solar pond by photoelectrochemical method is examined conceptually. The main components of the new integrated system are a solar pond, a photovoltaic panel (PV) and a hybrid chlor-alkali reactor which consists of a semiconductor anot, photocathode and cation exchange membrane. The proposed system produces hydrogen via water splitting reaction and also yields the by products namely chlorine and sodium hydroxide while consumes saturated NaCl solution and pure water. In order to increase the efficiency of the reactor, the saturated hot NaCl solution at the heat storage zone (HSZ) of the solar pond is transferred to the anot section and the heated pure water by heat exchanger in the HSZ is transferred to cathode section. The photoelectrode releases electrons for hydrogen production with diminishing the power requirement from the PV panel that is used as a source of electrical energy for the electrolysis. The results confirm that the thermal performance of the solar pond plays a key role on the hydrogen production efficiency of the reactor.     

Heat transfer analysis of thermal disassociation of ZnO for solar hydrogen production

Hydrogen production by the two-step solar thermochemical cycle has high cycle efficiency, low cost, and a great development space. Of special interest is the solar thermochemical cycle based on ZnO/Zn redox reactions since its high theoretical hydrogen yield and relatively low endothermic reaction temperature. In this paper, a steady heat transfer model for thermal ZnO dissociation in a solar thermochemical reactor is developed, coupling conduction, convection and radiation with chemical reaction. Accuracy was evaluated by comparison of results obtained from other references. Based on the new proposed reactor, the model is adopted to analyze the operating parameter effect on the conversion rate and fluid feature inside the solar reactor. The results show that the mass flow rate of ZnO and aperture gas temperature have a positive relation with ZnO conversion rate, however, the diameter of particles and aperture gas velocity has an inverse relation with ZnO conversion rate under specific condition. The results will provide useful foundation for improving the solar-to-fuel conversion rate in the near future.     

Design and performance evaluation of a Double-pass solar drier for drying of red chilli (Capsicum annum L.)

Performances of a new designed Double-pass solar drier (DPSD) were compared with those of a typical cabinet drier(CD) and a traditional open-air sun drying for drying of red chilli in central Vietnam. The drying times (including nights) to reach the desired moisture content of 10% (on a wet basis) were 32 and 73 h respectively. During open-air sun drying the desired moisture content of 10% (on a wet basis) could not be reached even after 93 h of drying (including nights). The overall drying efficiencies of DSPD and CD to reach the desired moisture content of 10% (on a wet basis) were 24.04% and 11.52% respectively while the overall drying efficiency of open-air sun drying to reach the desired moisture content of 15% (on a wet basis) was 8.03%. Further, ASTA colour value of the solar dried products from the DSPD was higher than those from CD and open-air sun drying. Similar results were obtained for mycotoxins occurrence. Contamination by aflatoxin B1 was significantly lower in dried chilli from DPSD (<0.250 μg kg⁻¹) when compared to traditional open-air drying technique (11.980 μg kg⁻¹). The drying cost per one kilogram of chilli was 39% lower in case of DPSD (0.077 US$/kg) as compared to CD (0.126 US$/kg). The Double-pass solar drier was found to be technically suitable and economically viable for drying of red chillies in central Vietnam.     

Dynamic modelling of a solar hydrogen system for power and ammonia production

A new configuration of solar energy-driven integrated system for ammonia synthesis and power generation is proposed in this study. A detailed dynamic analysis is conducted on the designed system to investigate its performance under different radiation intensities. The solar heliostat field is integrated to generate steam that is provided to the steam Rankine cycle for power generation. The significant amount of power produced is fed to the PEM electrolyser for hydrogen production after covering the system requirements. A pressure swing adsorption system is integrated with the system that separates nitrogen from the air. The produced hydrogen and nitrogen are employed to the cascaded ammonia production system to establish increased fractional conversions. Numerous parametric studies are conducted to investigate the significant parameters namely; incoming beam irradiance, power production using steam Rankine cycle, hydrogen and ammonia production and power production using TEGs and ORC. The maximum hydrogen and ammonia production flowrates are revealed in June for 17th hour as 5.85 mol/s and 1.38 mol/s and the maximum energetic and exergetic efficiencies are depicted by the month of November as 25.4% and 28.6% respectively. Moreover, the key findings using the comprehensive dynamic analysis are presented and discussed.