Uncertain price rise and rapid depletion of fossil fuels accelerated the development of renewable energy sources in the form of alternative power sources. Solar is an abundant, renewable and sustainable energy source that attracted many eminent researchers across the world to work in the field of solar energy applications. In developing countries, solar drying is capable of fulfilling the increasing demand of healthy, low cost natural foods and need for sustainable income. Solar dryers used for agricultural product drying can be proved to be most useful device from energy conservation point of view that not only save energy but also saves a lot of time, occupying less area, improves product quality and personnel life style. A solar crop drying system does not solely depends on solar energy for its functioning besides many recent advancements in drying process which combines other form of auxiliary heating source with sun energy are also in recent trends for reducing fuel consumption. In this paper, a review of various types of solar dryers namely, direct solar dryers, indirect solar dryers, hybrid solar dryers and their various drying applications are represented.

Progress in solar dryers for drying various commodities

This review paper is focused on the application of software in solar drying systems. The application of software is very important to develop and analyze the mathematical models and predicting the performance of different kinds of solar drying systems. It is also useful for predicting the crop temperature, moisture content and drying rate, drying kinetics, and color of the crop. Computational fluid dynamics can be used for the analysis and investigation of air flow and temperature distribution pattern through appropriate simulation with the help ANSYS and FLUENT. MATLAB and FORTRAN are very useful tools to develop mathematical models for prediction the crop temperature, air temperature, the moisture evaporated. It is also very useful for training and testing of various models. For statistical data analysis, statistical software SPSS, Sigma Plot V and Statistica. All recent employed software and their utility in solar drying systems are emphasized in this communication. This comprehensive review of the various software applications in different solar drying systems is useful for academician, scientist and researchers.

Applications of software in solar drying systems: A review

Drying of untreated Musa nendra and Momordica charantia in a forced convection solar cabinet dryer with thermal storage

This work optimises the collection of solar energy within the period of its availability in order to increase its utilisation and also to enhance performance of heating systems that depend on it through appropriate determination of optimum solar collector tilt angles. Buoyancy-induced flow equation in solar collector pipe was established by continuity, energy and Navier–Stokes equations in cylindrical coordinates. Fundamental solar radiation equations were programmed to determine optimum tilt angles in locations within latitudes 1° and 14°. A set of data recorded from a pryanometer located on latitude 6.45° north of the equator was used to generate average monthly radiation over the latitudes. Graphs obtained from latitude 6° and 13° data were analysed to investigate solar radiation on some tilt angles. The optimum tilt angles for solar heating for periodic tracking of the sun in the region within latitudes 1° and 14° were predicted as ∅ + 25° for November, December and January; ∅ + 15° for February, September and October; ∅ − 15° for August; ∅ − 25° for May, June and July; and ∅ for March and April. The results of this work confirmed that solar radiation on tilted surface increases with latitude.

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Determination of optimum tilt angles for solar collectors in low-latitude tropical region

In this paper, the solar radiation on diversely oriented surfaces and optimum tilts for solar absorbers were assessed. The KT solar radiation model was coded in the MATLAB-based environment to compute the monthly solar radiation values. Seven years data of monthly average daily solar radiation on a horizontal surface in Bangi, Malaysia (latitude = 3° N) was adopted as input in the simulation programme, and the results were compared with the local optimum tilt angle at solar noon and other solar radiation model. The contour mappings of solar irradiation at various orientations in 12 months were presented. Results showed that the surface tilted at ≤20° could intercept a relatively high solar intensity, which was less sensitive to the variation of azimuths with average insolation deviation of 11.82%. The monthly optimum tilt angle altered throughout the year, ranging from -24° (in equator direction) to +22° (in north direction). The estimated annual optimum slope, 1.4° facing to the equator, was close to local latitude. Based on the seasonal analysis, the north-facing surface was able to intercept higher daily average solar radiation energy compared to south-facing plane. The optimum angles for seasonal south- and north-facing surfaces were found to be 14.4° and 14.8°, respectively, with a tolerable slope deviation of ±5° from the optimal values in the present work.

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Assessment of solar radiation on diversely oriented surfaces and optimum tilts for solar absorbers in Malaysian tropical latitude

Based on preliminary investigations under controlled condition of drying experiments, a mixed-mode solar dryer with forced convection using smooth and rough plate solar collector was constructed. This paper describes the development of dryer considerations followed by the results of experiments to compare the performance of the smooth and the roughed plate collector. The thermal performance of solar collector was found to be poorer because of low convective heat transfer from the absorber plate to air. Artificial rib roughness on the underside of the absorber plate has been found to considerably enhance the heat transfer coefficient. The absorber plate of the dryer attained a temperature of 69.2°C when it was studied under no-load conditions. The maximum air temperature in the dryer, under this condition, was 64.1°C. The dryer was loaded with 3 kg of grapes having an initial moisture content of 81.4%, and the final desired moisture content of 18.6% was achieved within 4 days while it was 8 days for open sun drying. This prototype dryer was designed and constructed to have a maximum collector area of 1.03 m 2 . This solar dryer been be used in experimental drying tests under various loading

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Jiwanlal L Bhagoria

Papers

Development and performance evaluation of mixed-mode solar dryer with forced convection