Solar Drying Process Research Articles

Determination of Air Flow Pattern During Solar Drying of Fruits Using a Low Range Air Speed Sensor

The solar drying is an attractive drying method in a sense of low temperature dehydration process which is useful for the dry product quality and energy saving including the environmental issues. Moreover, it can be applied in small scale (family size farms) which is in accordance with the distributed resource approach of the sustainable development. In the course of the recent research numerous drying experiments were elaborated with the solar drying of biomaterials, mainly with fruits. Beside the measurements, the modelling of the drying process was also investigated. Special attempt was carried out developing a low range air speed sensor (for measuring natural ventilation during the solar drying process) which can be used with a usual data logging system. After choosing the working principle a one dimensional prototype of the sensor was developed and constructed. Based on the measurements the optimal setting of the sensor was determined. Additionally, the set-up of a two-dimensional sensor prototype is also presented, along with its first measurement results.

Study of the solar drying of grapes by three different processes

The objective of this work is to analyse the drying of the Sultanine grape variety by three different solar processes. Three drying kinetics have been established respectively in a natural convection solar drier, under a tunnel greenhouse and in open sun. These tests show that the solar tunnel greenhouse drying is satisfactory and competitive to a natural convection solar drying process.

Influence of different treatments on dehydrated cauliflower quality

SummaryFresh cauliflower was cut into florets, blanched, treated and spread in trays to dry by means of a solar drying process. The influences of packaging materials, blanching time, and potassium metabisulphite (KMS) concentration levels on the quality of solar dehydrated cauliflower up to 6 months of storage were studied. Ascorbic acid (vitamin C) present in fresh cauliflower was 74.61 mg (100 g)−1. Results revealed that ascorbic acid concentration decreased with an increase in blanching time but its retention was high in cauliflower dehydrated by solar drying. Dehydrated cauliflower had 581.37 mg (100 g)−1 of ascorbic acid in samples treated with 0.5, 1.0 and 1.5% of KMS with 3 min blanching at day zero. Washing cauliflower florets in tap water reduced the microbial load as compared with the unwashed sample. Processed and dehydrated cauliflower, packed in three types of packaging materials did not show presence of fungi even after storage for 6 months. In almost all samples, permissible levels of bacterial counts were observed after 6 months of storage. All the samples were also found to be free from Escherichia coli. It was found that blanched samples (blanching done for 7 min) treated with 0.5% KMS, dehydrated and then packed in laminated aluminium foil (LF) were the best in regard with nutritional and microbiological quality of dehydrated cauliflower.

Simulation model for a solar drying process

The aim of this paper is to study the thermal behaviour of a solar air heater as a source of energy for drying agricultural products. The output temperature and velocity of the drying air were first evaluated, and a mathematical formulation of the physical process of solar drying based on conventional heat and mass transfer equations is then presented and simulated.

Energy and exergy analyses of drying of apricots in a rotary solar dryer

This paper presents the energy and exergy analyses of the drying process of apricots in a rotary column cylindrical drying (RCCD) cabinet. For these purposes, all stages of the drying process, considered as a steady-flow thermodynamic system, were analysed. Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air collectors and the ratios of energy utilisation. However, exergy analysis was accomplished to determine the type and magnitude of exergy losses during the solar drying process by applying the second law of thermodynamics. It was observed that the apricot samples sufficiently dried in the range 38-57.8°C drying air temperature and 20.5-49.7% relative humidity, at 2.3 ms-1 of drying air velocity and 2.25 rpm rotary speed of column in 76 h despite exergy losses of 0.1370-0.5612 kJkg-1.

03/01784 Energy and exergy analyses of solar drying process of pistachio: Midilli, A. and Kucuk, H. Energy, 2003, 28, (6), 539–556

03/01784 Energy and exergy analyses of solar drying process of pistachio: Midilli, A. and Kucuk, H. Energy, 2003, 28, (6), 539–556

Energy and exergy analyses of solar drying process of pistachio

This paper is concerned with the energy and exergy analyses of the drying process of shelled and unshelled pistachios using a solar drying cabinet. Using the first law of thermodynamics, energy analysis was carried to estimate the amounts of energy gained from solar air collectors and the ratios of energy utilization. However, exergy analysis was accomplished to determine the location, type, and magnitude of exergy losses during the solar drying process by applying the second law of thermodynamics. It was deduced that the exergy losses took place mostly in the 15th shelf where the available energy was less utilized. Moreover, the shelled and unshelled pistachios are sufficiently dried in the ranges between 40 and 60 °C and 37 and 62% of relative humidity at 1.23 m s −1 of drying air velocity in 6 h despite the exergy losses of 0.15–3.08 kJ kg −1.

PEAR DRYING PROCESS ANALYSIS: DRYING RATES AND EVOLUTION OF WATER AND SUGAR CONCENTRATIONS IN SPACE AND TIME

ABSTRACT Dried pears are produced in Portugal by a traditional solar drying process and, because they represent unquestionable regional economic interest, some studies are being conducted in order to convert their production to industrial drying methods. In this work the main mass transfer phenomena occurring during drying of pears are investigated. Experiments were carried out to determine the time evolution of the radial profiles of water and sugar content. The drying rates were also studied at constant drying temperatures of 30, 40 and 50°C. The results enable to conclude that the concentration profiles of water and sugar, both in space and time, follow an expected pattern if one takes into account the rates of water removal and the diffusion mechanisms. These also allow to explain why the sugar concentration increases in the periphery of the fruit. The drying rate curves obtained are typical, with the drying process at 30°C being more gradual but also much slower than that at 50°C.

Thermodynamic method for designing dryers operated by flat-plate solar collectors

In this work a thermal performance analysis of the solar drying process is presented. It describes semi-empirical models for the thermal characterization of an experimental indirect solar dryer device. A procedure for designing drying equipment, which takes into account the varying operating conditions given by the variations of the environmental conditions is also presented. On the other hand, a simplified method to design solar collectors based on the determination of minimum entropy generation during the thermal conversion of solar energy, is described. Finally, the results of the preliminary design of the solar dryer are presented using the thermal analysis procedure and the method derived from the Second law of thermodynamics.

Mathematical modelling of the thin layer solar drying of sweet potato slices

An indirect solar dryer was used to study the drying of sweet potato slices. The solar drying rates of sweet potato slices were affected by the fluctuating chamber temperature over the drying period. Solar drying rate curves exhibited a constant rate period and one linear falling rate period. A mathematical model for solar drying of sweet potato slices was derived based on the simplified form of the Fick's diffusion equation. The mathematical model could satisfactorily describe the solar drying of sweet potato slices to a moisture content below 20% dry basis. The mean effective drying chamber temperature and sample thickness were the main factors that affected the solar drying process for sweet potato slices.

Computerised control system for an experimental solar lumber dryer

The microcomputer based control system employed in an experimental highly efficient solar kiln and the advantages of using this approach in solar wood drying are discussed. The control system consisting mainly of a personal computer and a data acquisition unit, performs a number of measuring and control functions. The monitored drying variables are wood M.C., collector's temperature, kiln's temperature, and R.H. The M.C. is monitored by recording the weight of the 3.2 m3 timber stack, resting on a weighbridge. The direct and continuous monitoring of timber moisture and equilibrium moisture employed by the control system, makes it possible to run the solar drying process to a target value formed from these two measured drying variables (drying gradient). The developed control system is compared with a semiautomatic system controlling the same solar klin.

A steady-state model for the forced convection solar cabinet dryer

The insufficient knowledge base for the design and optimization of solar dryer could be the obstacle to the unrealized promise of solar drying. By applying the lumped-parameter approach in the analysis of the transfer processes and utilizing known results from drying theory, this article demonstrates a methodology for the construction of a reduced mathematical model of the forced convection solar cabinet dryer. The model comprises only the variables directly involved in the energy and mass balance relationships for the drying process. The values of the variables determine the state of the processes in the dryer, and the model is a set of relationships that determines such a state. Specializing into thin product bed with sponge pieces constituting the product, this article describes an experiment carried out to verify the model. It also presents an assessment of the model parameter value from the experimental result and a simulation procedure with a result, which positively validates the model. The procedure used indentifies and quantifies the important mechanisms occurring in the solar drying process. This opens up a new dimension in the design and optimization of the solar dryer and the dryer operation. The article hopes to contribute towards the knowledge base and stimulate further interest in solar drying.

Utilization of Solar Energy for Sludge Drying Beds

The present work is aimed to assess experimentally solar heated sludge drying beds located in the New Orleans, Louisiana metropolitan area with an appropriately sized solar system designed to operate on a fiberglass-covered drying bed. Another open drying bed was left without solar heating for comparative purposes. Five experimental runs were conducted over a one-year period to account for all weather conditions utilizing aerobically digested waste activated sludge. Compared to conventional beds, the solar beds achieved an average reduction of 50 percent in the drying period required to obtain a total solids concentration of 30 percent and an average reduction of 60 percent in the drying period of sludge to reach a total solids concentration of 60 percent. Sludge of total solids content of more than 90 percent was produced in an average period of 20 days under the solar drying process. System energy effects and economic analysis were also discussed.

Food Drying with Direct Solar Augmented by Fossil Energy

ABSTRACT A24-h, two-stage batch solar-drying process was developed for fruits and vegetables. It involved use of an enclosed solar collector/hot-air dryer with trans-parent covers and planar reflectors mounted above and beneath to increase solar radiation to the food com-partment. The process was demonstrated in preliminary drying tests conducted in autumn (42 to 62 deg noon solar elevation, 28 deg N latitude) with diced carrots and sliced parsley. Most of the moisture was evaporated during the solar stage, and drying was completed over-night with a low flow of air heated by fossil energy sources. During the solar stage, drying rates were 30 to 40 percent greater when both upper and lower reflectors were used, compared with use of the upper reflector alone.