Natural Convection Solar Dryer Research Articles

Effects of Blanching and Natural Convection Solar Drying on Quality Characteristics of Red Pepper (Capsicum annuum L.).

The objective of this work was to determine the effects of blanching and two drying methods, open-sun drying and natural convection solar drying, on the quality characteristics of red pepper. A 2 × 3 factorial design with experimental factors as 2 drying methods (open-sun drying and use of solar dryer) and 3 levels of pepper blanching (unblanched, blanched in plain water, and blanched in 2% NaCl) was conducted. Dried pepper samples were analysed for chemical composition, microbial load, and consumer sensory acceptability. Blanching of pepper in 2% NaCl solution followed by drying in a natural convection solar dryer reduced drying time by 15 hours. Similarly, a combination of blanching and drying in the solar dryer improved microbial quality of dried pepper. However, blanching and drying processes resulted in reduction in nutrients such as vitamin C and minerals content of pepper. Blanching followed by drying in natural convection solar dryer had the highest consumer acceptability scores for colour and overall acceptability, while texture and aroma were not significantly (p > 0.05) affected by the different treatments. Therefore, natural convection solar dryer can be used to dry pepper with acceptable microbial and sensory qualities, as an alternative to open-sun drying.

Design of Fruits Solar Energy Dryer under Climatic Condition in Jordan

In this paper, a new design of a natural convection solar dryer used to dry fruits is presented; taking into account the local climatic conditions prevailed in Jordan during summer season. The dryer will have a capacity of 100 kg of sliced apples and the simulation is based on mass and heat balances. It is deemed that such new design will be able to reduce the original moisture content, of the final product, to 10% within two days. The special tailored program could be used to calculate drying parameters for similar products under different climatic conditions. The next step will be focused on constructing the solar dryer in order to conduct actual experiments in the field.

Moisture transfer modeling during solar drying of potato cylinders considering shrinkage

ABSTRACTIn the present work, the thin layer drying kinetics of potato during natural convection solar drying was investigated experimentally. Cylindrical potato samples with length 50 mm and varying diameter of 8, 10 and 13 mm were dried in an in-house designed and fabricated laboratory scale mixed-mode solar dryer. Thirteen different thin-layer mathematical models were fitted to the experimental moisture ratio (MR) data. The obtained results indicated that the Modified Page model could satisfactorily describe the drying curve of potato cylinders with higher value of R2 and lower values of RMSE and χ2. The shrinkage parameter is incorporated in the analytical diffusion model to study the moisture transfer mechanism of potato cylinders. It was observed that the values of effective diffusion coefficient (Deff) and convective mass transfer coefficient (hm) are overestimated in the range of 85.02–90.27% and 39.11–45.11% for the range of sample diameter examined, without considering the shrinkage effect in the mass transfer analysis. A Multiphysics approach was adopted in this study to get insight into the drying behavior of potato cylinders in terms of food-moisture interactions during the solar drying process. The predicted results of MR are in close agreement with the experimental data. Moreover, the anisotropic behavior of shrinkage as well as the moisture distribution inside the potato cylinder was very well described by Multiphysics model.

Experimental investigation of the drying characteristics of a mixed mode natural convection solar crop dryer with back up heater

A mixed mode natural convection solar crop dryer with a backup heater was designed and constructed from locally available materials and used to dry freshly prepared pineapples under four drying Scenarios for drying to correspond to specified drying periods for four typical seasons in Ghana. The experiments were devised for the material moisture content to be monitored continuously till the desired moisture content of between +106% and 184% (d.b) was achieved. In solar heating mode of operation, results show that the thermal mass was capable of storing part of the absorbed solar energy but the quantities involved are insufficient to sustain night drying. It was possible to dry a batch of pineapples in each mode of operation. The dryer reduced the moisture content of pineapple slices from about; 924% to 106% in 19 h; 1049% to 184% in 10 h; 912% to 155% in 7 h; and 1049% to 144% (d.b) in 23 h, for drying in Scenarios 1, 2, 3 and 4, respectively. The average moisture pickup efficiency values obtained were 27%, 24%, 11%, and 32% for drying in Scenarios 1, 2, 3, and 4, respectively.

EVALUATION OF POTATO SLICES DRYING USING SOLAR DRYER

The objective of the present study was to investigate the drying characteristic curves and the drying duration when drying potato slices using natural convection solar dryer. For that sake an experimental setup was developed. Measurements of total solar radiation on the plane of the collector, ambient air temperature, drying air temperature and moisture loss in weight were collected. A group of experiments were conducted using potato slices with thickness of 1 mm to study the effect of pretreatments on drying characteristics. The maximum temperature attained in the drying chamber is 52 oc at 13:00 and 14:00 pm and the maximum temperature attained in the collector is 75oc at 14:00 pm while the corresponding values of solar radiation and ambient temperature were 876.5 W/m2and 38oc, respectively. The final moisture contents were 7.15 and 4.48 db in B(blanch + calcium chloride) and C (blanch + citric acid) treatments, while in A (blanch), D (blanch + potassium meta sulphate) and E (blanch + acitric acid) were 14.20, 22.35 and 13.73 db. Consequently, citric acid solution and calcium chloride solution were more effective solutions in potato slices drying. The slices treated with citric acid (C), potassium meta sulphite (D) and acetic acid (E) provided better color for drying compared with the slices that treated with blanch only (A) and with calcium chloride (B) under which the colors were brown. The effective moisture diffusivities of pretreated with treatments (A, B, C, D and E) were (1.35×10-11, 1.39×10-11, 1.45×10-11 , 1.23×10-11and 1.40×10-11m2/s), respectively. Based on these results, pretreated samples with citric acid solution (C) had the highest effective moisture diffusivity compared with other samples.

Experimental Investigation on Indirect Mode Double Pass Natural Convection Solar Dryer with different Configurations of Absorber Plate (Radish)

An indirect mode double passnatural convection solar dryer was designed and fabricated with the loading capacity of 1kg to evaluate its performance using radish as a drying product. This paper presents the comparison ofthe performance of the collectors with different configurations of absorber plate of the collector. The different configurations of absorber plate are a flat plate, V-groove along the width (VAW), V-groove along the length (VAL), Sinusoidal along the width (SAW) and Sinusoidal along the length (SAL). The experiments were conducted during Feb-March 2016 in Salem, Tamil Nadu with the sample of 1 kg of radish having the initial moisture content of 95% wet basis from which 0.9 kg of water is required to be removed until it reaches the safe moisture content of 10% wet basis. The nominal surface area of all types of absorber plate is 0.5 m2 but effective surface area varies with configuration. The drying time was taken around 15.6 hours with the flat plate but it was taken only 10 hours and 11 hours with VAW and SAW respectively. Thus around 4 hours of drying time was reduced by using VAW and SAW than the flat plate and also the collector efficiency range was improved from 2.6–7.13% in the flat plate to 4.2–15.4% in VAW and SAW. Also, the quality of the dried radish was much superior compared to open sun drying.

Solar Drying Kinetics of Cass Ava Slices in a Mixed Flow Dryer

Abstract Drying characteristics of cassava slices was investigated in a mixed mode natural convection solar dryer to obtain a suitable mathematical model describing the drying. The average drying chamber temperature was between 34 ±2 °C and 50 ±1.8 °C, while 10 commonly used thin layer drying models were used for drying curve modelling. Coefficient of determination (R2) and root mean square error (RMSE) were used to determine the models performances. The drying curve of cassava slices showed a reduction of moisture content with increased drying time in the solar dryer, and the variation of moisture ratio exponentially decreased with increased drying time. The Midilli and Logarithmic models showed better fit to the experimental drying data of cassava slices. As compared with other models tested, there were no significant differences (p >0.05) in the R2 values obtained for the Midilli and Logarithmic models; hence, the Logarithmic model was preferable because of the lower RMSE. The diffusion mechanism could be used to describe the drying of cassava slices that was found to be in the falling rate period. A diffusion coefficient (Deff) of 1.22 × 10-8 m2 s-1 was obtained, which was within the established standard for food products.

Performance improvement studies in a solar greenhouse drier using sensible heat storage materials

Experiments were conducted in a natural convection solar greenhouse dryer using different sensible heat storage materials (concrete, sand and rock-bed) in order to study their thermal performance. For both sand and rock-bed, 4″ thickness was found to be optimum as it provides better drying environment both during day and night. The dryer reduced the moisture content of coconuts from 52 (w.b.) to 7 % (w.b.) using concrete as heat storage material in 78 h saving 55 % of drying time compared to open sun drying which takes 174 h for reducing the moisture content to the same level. The sand took 66 h saving 62 % of drying time whereas rock-bed took only 53 h thereby saving 69 % of drying time compared to open sun drying. The efficiency of the dryer was found to be 9.5, 11 and 11.65 % using concrete, sand and rock-bed respectively.

Performance of indirect through pass natural convective solar crop dryer with phase change thermal energy storage

A state-of-the-art solar crop dryer was developed with thermal energy storage to maintain continuity of drying of herbs for their colour and flavour vulnerability. The dryer consists of flat plate solar collector, packed bed phase change energy storage, drying plenum with crop trays and natural ventilation system. Dryer is designed with a maximum collector area of 1.5 m2, six crop trays with an effective area of 0.50 × 0.75 m2, can hold 12 kg of fresh leafy herbs. The dryer is attached with a packed bed thermal energy storage having capacity of 50 kg phase change material (PCM). The drying system works in such a manner that phase change material stores the thermal energy during sun shine hours and releases the latent and sensible heat after sunset, thus dryer is effectively operative for next 5–6 h. The temperature in drying chamber was observed 6 °C higher than the ambient temperature after sunshine hours till the mid night during the month of June at Jodhpur. Economic performance of the dryer was analysed with return on capital and simple payback period as 0.65 and 1.57 year respectively on optimum cost of raw material and product sale price.

Experimental study of drying techniques in retention of nutrients in aonla

This investigation deals with drying technique and proximate composition of aonla. The aonla was dried in natural and forced convection solar dryers and ground to obtain powder. Dried powder was analysed for its proximate composition and its nutritional characteristics on dry weight basis. It was found that crude fat, crude protein and crude fibre content were found to be highest in forced convection dryer (1.24 g, 1.74 g and 5.48 g). The ash content in natural convection dryer was found to be highest (1.95 g) in fresh aonla on dry weight basis. There was no significant difference (P > 0.05) in carbohydrate content in all three dried powders of aonla. The vitamin C content of natural convection dried aonla was 160.20 mg/100 g where as it was 175.60 mg/100 g for forced convection dried aonla powder and in fresh aonla vitamin C content was 195 mg/100 g. Thus, it can be inferred from the above results that forced convection solar drying is a superior technique of processing and for retaining maximum nutrients.

Experimental investigation of the performance of an indirect-mode natural convection solar dryer for drying fenugreek leaves

The main objectives of the present work are firstly to study and compare the thin layer drying characteristics of fenugreek leaves by open sun and solar drying methods, and secondly to select a mathematical model for describing the drying process under open sun and solar drying of fenugreek leaves using thin layer drying models available in the literature. Eight thin layer drying models, which are empirical or semi-empirical, are tested to validate the experimental data. A non-linear regression analysis using a statistical computer programme is used to evaluate the constants of the models. The performance of the models was investigated by comparing the coefficient of correlation (R2), sum of squares error (SSE), mean squared error (MSE) and root mean square error (RMSE) between observed and predicted moisture ratios. According to results, Wang and Singh model gives the highest value of R2 and the lowest values of SSE, MSE and RMSE. Therefore, Wang and Singh model is the best for explaining drying behaviour of fenugreek leaves in both the trays inside the solar dryer and in the tray under open sun.

Experimental investigation on energy and exergy analysis of coriander (Coriadrum sativum L.) leaves drying in natural convection solar dryer

This study deals with thin layer drying characteristics of Coriandrum sativum L. leaves in a natural convection solar dryer. The Coriandrum sativum L. leaves were dried from a moisture content of 88% (w.b.) to 4.5% (w.b.) in 7.5 hours. The obtained drying data were fitted to eight different drying kinetics models. Of these, the model suggested by Midilli et al. [20] had the best fit with the drying behavior of Coriandrum sativum L. leaves. In addition, the thermodynamic behaviour of a solar dryer was evaluated. The energy efficiency during the study varied from 7.81 to 37.93%. The exergy efficiency of the drying process ranged between 55.35 and 79.39%.

Development and Evaluation of Solar Tunnel Dryer for Commercial Fish Drying

The local practice of drying fish in open sun drying poses problems such as high moisture content, uncontrolled drying and contamination. These problems can be avoided by proper use of improved methods such as the solar tunnel dryer, which results in faster drying of fish. The semi cylindrical walk-in type natural convection solar tunnel dryer, having drying area of 37.5 m2 was developed and evaluated for the drying of fish products in comparison with the conventional method of open sun drying. The experiments were conducted without fish and with fish to evaluate the performance of solar tunnel dryer. The average rise in temperature inside the solar tunnel dryer was found to be 11.24 °C and 18.29 °C over the ambient temperature during no load test in winter and summer respectively. The average 28 % saving in time was observed for selected fish drying using solar tunnel dryer over open sun drying method with average drying efficiency of 19 %. The economics was calculated for drying of prawns (Parapaeneopsis stylifera) by solar tunnel dryer and open sun drying system on the basis of business as a whole. The economics of the solar tunnel dryer is presented in term of Net present worth, Benefit–Cost Ratio, Payback period, Profitability index and Internal rate of return. The pay back period for solar tunnel dryer was found to be 2.84 years.

Development of solar drying model for selected Cambodian fish species.

A solar drying was investigated as one of perspective techniques for fish processing in Cambodia. The solar drying was compared to conventional drying in electric oven. Five typical Cambodian fish species were selected for this study. Mean solar drying temperature and drying air relative humidity were 55.6°C and 19.9%, respectively. The overall solar dryer efficiency was 12.37%, which is typical for natural convection solar dryers. An average evaporative capacity of solar dryer was 0.049 kg·h−1. Based on coefficient of determination (R 2), chi-square (χ 2) test, and root-mean-square error (RMSE), the most suitable models describing natural convection solar drying kinetics were Logarithmic model, Diffusion approximate model, and Two-term model for climbing perch and Nile tilapia, swamp eel and walking catfish and Channa fish, respectively. In case of electric oven drying, the Modified Page 1 model shows the best results for all investigated fish species except Channa fish where the two-term model is the best one. Sensory evaluation shows that most preferable fish is climbing perch, followed by Nile tilapia and walking catfish. This study brings new knowledge about drying kinetics of fresh water fish species in Cambodia and confirms the solar drying as acceptable technology for fish processing.

A Mathematical Model of Indirect Solar Drying of Dairy Products (Jameed)

A Mathematical modeling of indirect natural convection solar dryer was designed for drying one of the famous dairy product in Jordan called Jameed. The intended solar dryer system is environmentally friendly and consumes zero electricity. The dryer consists of a flat plate solar collector having dimensions of 0.1 m height, 0.8 m width and 1.2 m length. A drying chamber consisting of four trays separated equally from each others at a distance of 0.2 m. The chamber is 1 m long made of wood. Each tray has a cross section of 0.8 m x 0.4 m. The solar collector is studied separately to establish the effect of changing its width or length on the air outlet temperature and mass flow rate. The drying chamber is used to dry 4 kilograms of jameed, each 1 kilogram is distributed on each tray. The total solar irradiation on the collector surface and chamber walls at each hour of the day was also calculated at the 21 st of May in Jordan. At these specific solar irradiation, the flat plate solar collector efficiency was almost constant having an average efficiency of 37% and a maximum outlet temperature of 41 °C at 1p.m. The drying time for trays 1, 2, 3 and 4 were 16.4, 19.14, 22.6 and 25.71 hours, respectively.

Performance Evaluation of an Adjustable and Collapsible Natural Convection Solar Food Dryer

The performance evaluation of an adjustable and collapsible natural convection solar food dryer, capable of taking 14,688 pieces equivalent to 16.52kg of fresh groundnut with maximum moisture content of 35%, at maximum capacity of 3.39m 2 , and 3,672 pieces equivalent to 4.06kg of groundnut at minimum capacity of 0.8475m 2 , was carried out. The solar food dryer with air vents gap diameter of 10cm was tested at Sokoto Energy Research Centre from 29 th September 2012 to 1 st October 2012. It was used to dry 6kg of groundnut per day for three consecutive days. After drying for about 8 hours each day, it was found that the mass of the groundnut reduced to 4.5kg in the first day, 4.0kg in the second day and 3.5kg in the third day. At the end of the study, the collector's efficiency was 28.3% , dryer's efficiency was 23.0% and the system efficiency was 81.3%, while the drying rate of groundnut was 0.25kg/hr

Analysis and Testing of a Natural Convection Solar Dryer for the Tropics

Solar dryers are imperative for the tropical and sub-Saharan African countries, which are faced with the duo challenges of inadequate electrical energy supply, which has severely limited the application of conventional refrigeration as a means of preservation of agricultural produce, and the need to make produce competitive in the international market. In this study, a cost-effective natural convection solar dryer was developed; the thermal and drying analyses were done and tested to obtain some performance evaluation parameters for the system in order to examine its efficiency and effectiveness by drying some plantain fillets. The collector and system efficiencies are found to be 46.4% and 78.73%, respectively, while a percentage moisture removal of 77.5% was achieved at the 20th hour in order to give final moisture contents of 15.75% in the product, which still maintained its integrity. With a cost of about $195.00, it has been affordable for the small- and medium-scale enterprises as well as for private use in domestic applications.

Construction and Performance Analysis of an Indirect Solar Dryer Integrated with Solar Air Heater

The use of conventional sources of energy for drying agricultural product is an expensive process in developing countries. Therefore, an appropriate technology for drying of agricultural produce has been developed and its performance for the drying of tomatoes was evaluated. An indirect type natural convection solar dryer was developed. The aim of this study is to evaluate dryer performance under natural and forced convection modes of drying. In natural and forced convection, air mass flow rates of 0.00653kg/s and 0.019kg/s respectively were obtained. Hot air reached an average drying temperature of 45°C in natural convection and 40°C in forced convection. The results obtained from natural and forced convection modes of drying were also compared with open sun drying. The colour, flavour and time required for drying is favorable in solar drying as compared to sun drying.

Diffuse Solar System Design and Utilization in Agriculture and Domestic Applications

Diffuse solar radiation is a component of total solar radiation that is good for low temperature grade heating. Since the portion of the scattered radiation from the sun, which consists of short and long waves, that reaches the earth is diffused, its utilization in Agriculture as this paper suggested, has multiple phase change material, which as well could serve as heat exchange for domestic (residential) applications. The Diffuse Solar System designed, consists of three functional units: the solar collector, thermal storage (heat sink) and a dryer cabinet. The thermal storage ranges from 140 – 1500F (60 – 500C) for heating system and 60 – 700F (15 – 200C) for residential cooling. Likewise, a natural convection solar dryer with collector efficiency of about 42% and drying efficiency of about 53% would dry tomatoes with initial moisture contents of 94% wet basis, to safe moisture content of about 4% wet basis and 35.2 – 86.8% ascorbic acid (vitamin C) retention with acceptable colour and texture. Keywords: Solar radiation, Heat sink, Ascorbic acid, Collectors, Reflectors, Yeast/mould count and Efficiency.

COMPARATIVE PERFORMANCE OF SOLAR TUNNEL GREENHOUSE AND OPEN SUN DRIING SYSTEMS DURING SEEDLESS GRAPE DRYING

Drying is simply the process of moisture removal from an agricultural product, and can be performed by different methods. The main purpose of this research work was to study the thermal performance of two different solar driers (active and passive dryers) based on the energy balance equations for the drying air and the drying product during dehydration process of seedless grapes in August 2009 under the climatic conditions of El-Mansoura city (31.05oN and 31.37 oE), Egypt. Three identical solar tunnel greenhouse driers (STGD) were functioned as an active solar drier, and an open sun drier (OSD) under direct solar radiation without cover (as a passive solar drier) to dry seedless grapes. The three active solar driers were operated under three different mass flow rates of 0.122, 0.183, and 0.259 kg/s. Three different shapes of grapes (clusters, parts, and grains) with total quantity of 33 kg, were spread on wire mesh tray with floor surface area of 2.0 m2. The results of greenhouse solar driers were compared individually with open sun drying. During the drying process, it was observed that, the hourly average air drying temperatures inside the three active solar dryers were increased to 49.9, 45.5, and 40.1oC, respectively, whereas the hourly average ambient air temperature was 31.6oC. The seedless grapes could be dried from initial moisture content of 79.1%wb to 17.1, 18.5, and 20.8%wb within drying time of 61, 61, and 71 hrs, using the three active solar dryers, respectively, while it was taken 96 hrs under open sun drying method to reach the final moisture content of 21.2%wb. The daily average thermal efficiencies for the four different solar drying modes, respectively, were 22.37%, 21.57%, 19.12%, 1and 10.81%. The quality of raisin (dried grapes) in terms of physicochemical parameters such as colour retention and water activity were evaluated. The overall study concluded that good quality dehydrated raisin could be produced by using active solar dryers as compared with passive sun drying method. The produced raisin of grapes under different drying methods had various colours. They, respectively, were light brown and dark brown when the grapes dried under active solar dryers and passive sun drying method. The experimental work showed that, the solar tunnel greenhouse drying (active solar dryer) was satisfactory and competitive to a natural convection solar drying process (passive dryer).