PERFORMANCE EVALUATION OF RACK TYPE SOLAR DRYER

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 7, Issue 6, November December 216, pp , Article ID: IJMET_7_6_17 Available online at Journal Impact Factor (216): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication PERFORMANCE EVALUATION OF RACK TYPE SOLAR DRYER Dinesh Acharya Department of Physics, Tri-Chandra Campus, Tribhuvan University Kathmandu, Nepal Prof. Dr. Tri Ratna Bajracharya Center for Energy Studies (CES), Institute of Engineering, Pulchowk, Lalitpur, Nepal ABSTRACT The use of solar dryer is slowly finding its way for food drying in Nepal. The use of direct type dryer is being common for household purpose but the indirect type dryer still has limited application. This work is an attempt to evaluate the performance of the existing design of indirect type solar dryer. In this study solar rack dryer with drying capacity of 1 kg cauliflower per batch is used, however only 6kg of fresh cauliflower is used. Some known quantity of cauliflower is kept into the electric oven until it will bone dry. The difference between the initial and final weight of the cauliflower is the total amount of water contain. It can easily be built with commonly available Materials. The dryer uses corrugated aluminum plate as an absorber surface. The insulating material used is Styrofoam. The drying chamber has 6 trays with 1 door for material loading and unloading. The maximum efficiency of the dryer was found to be 3.14% after performance evaluation. Key words: Solar dryer, solar isolation, absorber plate, efficiency and cost. Cite this Article: Dinesh Acharya and Prof. Dr. Tri Ratna Bajracharya, Performance Evaluation of Rack Type Solar Dryer. International Journal of Mechanical Engineering and Technology, 7(6), 216, pp INTRODUCTION Renewable energy technology bridges the gap between mounting global energy demand and dwindling supply of finite conventional energy sources. The two factors that must be constantly looked into are the efficiency and economics of installing such an application. Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of photovoltaic panels, solar thermal collectors, with electrical or mechanical equipment, to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air. Utilization of solar energy is of great importance to all over the world. In various forms of technology, solar thermal applications have been in energy conversion devices, central heating, and cooking, drying and even refrigeration. Drying is a vital operation in any industrial process and daily needs, requiring substantial conventional energy. Drying of clothes is a daily 158

2 Performance Evaluation of Rack Type Solar Dryer operation (Alam S., 29). Solar drying is a continuous process where the moisture content and temperature of the substance as well as the air change simultaneously along with the two basic inputs to the system (namely, the solar isolation and the ambient air temperature). Drying is essentially simultaneous process of heat and mass transfer. Absorption of heat by material supplies the energy necessary for vaporization of water from it. The purpose of solar drying is to supply more heat to the product than is available under normal ambient conditions. This will step down the equilibrium moisture content and speed up the removal of the moisture from the product. Heat is supplied to product directly or by solar heated air and moisture within the products moves from the interior to the surface by diffusion. Then it is carried by the heated air supplied by natural convection or forced convection. This process continues till the equilibrium moisture content is reached. When the moisture content of the product is in equilibrium with the relative humidity of the environment, the moisture content is termed as EMC (equilibrium moisture content). Equilibrium moisture content is usually expressed as a function of drying air temperature and relative humidity. With ambient conditions, the drying is very slow and in the case of high relative humidity, the equilibrium moisture content is high and solar dried products are not suitable for safe storage (Tuladhar M.R., et. al., 28). Research and Development works on different types of solar dryers have been done since197's in the country. Among various types of solar dryers available in the world, mostly three types are used in Nepal, namely, cabinet, rack and tunnel solar dryer. These solar dryers operate on direct, indirect or mixed mode of heating (Joshi C.B., 24). Various Organizations are also promoting these technologies. Cabinet type solar dryer is most commonly used for domestic purpose and small scale drying. Tunnel type dryer is used for large scale commercial purpose. Rack type solar dryer is being used for medium scale purposes. Planned development of solar dryer has been introduced in Nepal since the Eighth Five Year Plan ( ).Emphasis upon its development has however been given only during the ninth five year plan ( ).On this basis, the government introduced the policy of subsidizing the dryer's cost by up to 75% and providing bank loans to women's group at low interest rate (Joshi, C.B. and Gewali, M.B. 22). In order to promote all forms of alternative energy technologies, including solar dryers, Government of Nepal established 'Alternative Energy Promotion Center (AEPC)' under the then Ministry of Science and Technology in Since then, the policy for subsidizing the solar dryer through AEPC was implemented. Exactly, 5% subsidy is provided for family sized solar dryers, up to NRs 2, and 7% subsidy is provided for commercial use of solar dryers in rural areas. ( 2. EXPERIMENT DETAILS For this experiment we have designed a solar dryer which was fabricated at Sun works Kathmandu. The capacity of dryer is 1 kg per batch but we performed an experiment with 6 kg of cauliflower per batch. The experiment was done in Renewable Energy Test Station (RETS) under Nepal Academy of Science and Technology (NAST). There are six drawers to access trays; this is for no loss of heat while working with tray. To determine the amount of moisture content in the experiment cauliflower, electric oven was used. Some known quantity of cauliflower was kept into the electric oven until it was bone dry. The first experiment was conducted for four day from 7 th May to 1 th May 213. Experiment was carried out for three hour in first day, four hour for second day, three hours for third day and one hour only for fourth day because of presence of favorable climate which is sufficient to evaporate all water from the fresh cauliflower. In each day after performing experiment specimen was packed to preserve its condition and then experiment was continued in next day. The second experiment was conducted for three day from 2 nd June to 4 th June 213. Experiment was carried out for four hour in first day, four hour for second day and five hours for third day. Second experiment was also for the design material i.e. cauliflower. During the experiment the weather condition was not so favorable. The wind was too erratic. It was very difficult to take the wind velocity readings, unusual windy day have affected the experiment time as well. Therefore, time required to dry same amount of cauliflower was 13 hours. Details of experiment are presented in Table

3 Dinesh Acharya and Prof. Dr. Tri Ratna Bajracharya Figure 1 Detailed Drawing of Solar Dryer 16

4 Performance Evaluation of Rack Type Solar Dryer Table 1 Comparison of observed experimental data S.N Particular First Experiment Second Experiment 1 Date of experiment to to Material Cauliflower Cauliflower 3 Initial Weight(gram) Final Weight(gram) Drying time(hrs) 11( ) 13(4+4+5) 6 Average ambient temp(t C) Average Solar Radiation(W/m 2 ) Average Relative Humidity (%) Average inlet velocity(m/s) Average inlet velocity(m/s) Average Plate temp(t C) Average Chamber temp(t C) Average outlet temp(t C) RESULTS AND DISCUSSION 3.1. Theoretical Efficiency The amount of water to be evaporated (Mw) from the product during drying process can be calculated by using the value of its initial moisture content (Mi) and desired final moisture content (Mf) as given below. = ( ) (1 ) (1) Theoretical mass of air required is = (2 1) (2) The overall thermal theoretical efficiency of the dryer can be simply calculated by the ratio of heat utilization by the dryer to the input energy from the sun. The energy input to the dryer is proportional to the exposed absorber area. This input energy is utilized by the dryer to increase the temperature of the air, overall material (material and water content) and for evaporation of the moisture from the material ( ) = ( ) )+" (#+#$) % 36 (3) Therefore net efficiency of dryer is 161

5 Dinesh Acharya and Prof. Dr. Tri Ratna Bajracharya ( ) = " (#) % 36 (4) The theoretical efficiency for the solar dryer will be 27.5% Experimental Efficiency In first experiment the total drying time required was 11 hours and the average solar insolation was W/m 2 and average plate temperature was C, the variation on solar isolation and temperature is shown in fig3.the initial weight of fresh cauliflower was 6 grams and the final dried weight attained was 186 grams (fig2). From equation (4) ( ))* = (5) ( ))*=3.14% (6) Thus the efficiency was calculated as 3.14%.The average relative humidity throughout the experiment was found to be 54.56%. Similarly, in second experiment the total drying time required was 13 hours and the average solar insolation was W/m 2 and average plate temperature was C, the variation on solar isolation and temperature is shown in (fig5).the initial weight of fresh cauliflower was 6 grams and the final dried weight attained was 1736 grams (fig4). Also From equation (4) ( ))* = (7) ( ))*=27.2% (8) Thus the efficiency was calculated as 27.2%.The average relative humidity throughout the experiment was found to be 5.41%. The plot is between weight, solar Insolation, plate temperature and time is shown. It is find that when insolation is increase the plate temperature is also high which is directly proportional to drying of cauliflower, so drying process is high if there is high amount of insolation. Nevertheless, the efficiency calculated after the experiment was obtained up to 3.14%. The attained efficiency was greater than the theoretical efficiency calculated before the fabrication. This is because of the fact that the theoretical design was done assuming the collector efficiency to be 65%. However, the use of fan for Forced Type convection must have increased the collector efficiency and thereby the efficiency of the dryer. On top of it, the insulation material used was polystyrene (Styrofoam) which is better. This also might have contributed in higher efficiency. The results of the experiment are as follows: 162

6 Performance Evaluation of Rack Type Solar Dryer Weight(Gram) Weight 1st Experiment Day1 Day2 Day3 Day4 Time(Hour) Figure 2 The graph of Weight vs. time in first experiment Solar InsolationW/m 2 Solar Tempera Day1 Day2 Day3 Day Plate TemperatureT C Time(Hour) Figure 3 The graph of Solar Insolation and plate temperature vs. time in first experiment Weight of 2nd Experiment Weight(Gram) Weight of 2nd Experiment Day1 Day2 Day3 Time(Hour) Figure 4 The graph of Weight vs. time in Second experiment 163

7 Dinesh Acharya and Prof. Dr. Tri Ratna Bajracharya 9 9 Solar Insolation (W/m 2 ) Day1 Day2 Day3 Solar Insolation Temperature Plate Temperature ( C) Time (Hours) Figure 5 The graph of Solar Insolation and plate temperature vs. time in Second experiment 4. CONCLUSION We performed two sets of experiments for design material cauliflower. First set of experiment done for four days and second set of experiment done for three days. The finding is that when solar insolation is high, plate temperature is also high so for higher solar insolation the capacity of draying is effective. The maximum efficiency obtained was 3.14% in first set experiment of cauliflower where as in second experiment efficiency was 27.2%, this is due to low solar insolation and low temperature of the plate. 5. ACKNOWLEDGEMENT I would like to express my gratitude to dean of institute of engineering Prof. Dr. Tri Ratna Bajracharya. My profound gratitude goes to Institute of Engineering Pulchowk, Renewable Energy Test Station (RETS), Nepal Academy of Science And Technology (NAST).I am particularly grateful to Er. Niraj Shrestha, Sun Works Nepal Kirtipur, Er. Bhim Dahal, Department of Metrology, Tri Chandra Multiple Campus and the Golden Gate International College. REFERENCE [1] Joshi, C.B., Gewali, M.B., Bhandari, R.C., Performance of Solar Drying System: A Case Study of Nepal, International Energy Journal, Vol.85, pp53-57 (24). [2] Bala, B.K., Solar Drying System: Simulation and optimization, (1991). [3] Duffie, john A. and Beckmann, W.A., Solar Energy of Thermal Processes, A Wiley Interscience Publication, New York, 198, pp [4] Goswami, Y., Kreith, F. and Kreider, J. F., Principles of Solar Engineering, Second Edition, Taylor and Francis Company (2) [5] Rai, G.D., Solar Energy Utilization, 4thEdition, Khanna Publishers (25). [6] Rajput R.k., Heat and Mass transfer, Second Edition, S Chand and Company (22). [7] Fuller R.J., Lhendup T.and Lu Aye, Technical and Financial Evaluation of a Solar Dryer in Bhutan, ANZSES Conference, Dunedin (25). [8] Han F.X., Nan Y.J., WEI, Y.K., Wan,L., GENERI: International Solar Energy Application Training Workshop, Natural Energy Research Institute, Gansu Academy of Sciences (1994). [9] RECAST, Renewable Energy Technologies in Asia: Development of Solar Dryer in Nepal, RECAST (21)

8 Performance Evaluation of Rack Type Solar Dryer [1] Kumar S., Bhattacharya S.C., Regional Research and Dissemination Project on Renewable Energy Technologies in Asia (25). [11] Fleming P.D. Ekechukeu, O.V., Norton,B. and Robert, S.D., Design Installation, and Preliminary Testing of a Natural-Circulation Solar-Energy Tropical-Crop Dryer (24). [12] Alam, S.Z., Design and Development of a Solar Cloth Dryer, Department of Mechanical Engineering, National Institute of Technology, Rourkela, 29. [13] Byanjankar, M.R. and Bhandari, R.C., Design, Fabrication and Performance Evaluation of an Innovative Solar Dryer, B.E Project report, Department of Mechanical Engineering, Tribhuvan University, Lalitpur (22). [14] Tuladhar M. R.,Shakya N., Pyakurel P. and Baral P., Design Improvement Fabrication and Performance Evaluation of an Indirect Rack Type Solar Dryer, B.E Project report, Department of Mechanical Engineering, Tribhuvan University, Lalitpur (28). [15] Ajeet Kumar Rai, Shahbaz Ahmad and Sarfaraj Ahamad Idrisi, Design, Fabrication and Heat Transfer Study of Green House Dryer. International Journal of Mechanical Engineering and Technology (IJMET), 4(4), 213, pp [16] Ghanim Kadhim Abdul Sada, Dhamyaa Saad Khudhour and Moumin Mahdi Issa, Utilization of Solar Energy for Enhancement E fficiency of Steam Power Plant. International Journal of Mechanical Engineering and Technology (IJMET), 7(5), 216, pp