DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF AN INDIRECT SOLAR DRYER FOR DRYING AGRICULTURAL PRODUCTS

Transcription

1 DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF AN INDIRECT SOLAR DRYER FOR DRYING AGRICULTURAL PRODUCTS Kaustav Bharadwaz 1, Debashish Barman 2, Debottam Bhowmik 3, Zunaid Ahmed Students, Dept. of Mechanical Enineerin, RSET, Guwahati, Assam, India 4 Assistant Professor and Head, Dept. of Mechanical Enineerin, RSET, Guwahati, Assam, India *** Abstract- In a developin country like India, havin the second larest population and ariculture as the source of income to nearly 60 % of the total population, post - harvest and storae loss of aricultural commodities is a major quandary, which needs to be addressed in due dilience. Many food preservation techniques like cold storae, dryin, etc. have been evolved out over the years to tackle the above losses. The major constraint is that almost all the technoloies are utilizin fossil fuel resources, which are depletin very fast and wise use of these precious resources are preferred for lon-term enery sustainability. Therefore, sustainable methods for food preservation are the need of the hour. Solar dryin is one of the best choices in this context. This paper presents the desin, fabrication and performance evaluation of an indirect forced convection solar dryer consistin of a solar air collector, dryin cabinet and a centrifual blower. The dryer has been desined indienously usin locally available materials for construction and it is cost effective. In the dryer, the heated air from a separate solar collector is allowed to pass throuh the products placed inside the dryin chamber. The solar enery which is et absorbed inside the collector is allowed to pass throuh some well created baffles. The baffles are placed inside the collector so that flow of hot air inside the collector become non linear, thus, takin more time to pass from the collector to the dryin chamber and the air et heated. A centrifual blower has also been employed in order to speed up the rate of dryin process. The dryer can be used effectively for dryin aricultural products and as a model reen apple slices were used to evaluate the performance. Key words: Indirect solar dryer, forced convection, dryin, aricultural products, reen apple 1. INTRODUCTION is one of the methods used to preserve food products for loner periods. The heat from the sun coupled with the wind has been used to dry food for preservation for several years. is the oldest preservation technique of aricultural products and it is an enery intensive process. Hih prices and shortaes of fossil fuels have increased the emphasis on usin alternative renewable enery resources. of aricultural products like fruits and veetables usin renewable enery such as solar enery is environmental friendly and has less environmental impact. Solar thermal technoloy is a technoloy that is rapidly ainin acceptance as an enery savin measure in ariculture application. It is preferred to other alternative sources of enery such as wind and shale, because it is abundant, inexhaustible, and non-pollutin. Different types of solar dryers have been desined, developed and tested in the different reions of the tropics and subtropics [1, 2]. The two major cateories of the dryers are natural convection solar dryers and forced convection solar dryers [3]. In the natural convection solar dryers the airflow is established by buoyancy induced airflow while in forced convection solar dryers the airflow is provided by usin fan operated either by electricity/solar module or fossil fuel. Solar air dryers are simple devices to heat air by utilizin solar enery and it is employed in many applications requirin low to moderate temperature below 80 C, such as crop dryin and space heatin. of aricultural products under direct sunliht also has several disadvantaes like poor quality and contamination [3]. In comparison to natural sun dryin, solar dryers enerate hiher temperatures, lower relative humidity, lower product moisture content and reduced spoilae durin the dryin process. In addition, it takes up less space, takes less time and relatively inexpensive compared to artificial mechanical dryin method. Thus, solar dryin is a better alternative solution to all the drawbacks of natural dryin and artificial mechanical dryin. Solar dryers are a very useful device for aricultural crop dryin, food processin industries for dehydration of fruits and veetables, fish and meat dryin, dairy industries for production of milk powder, seasonin of wood and timber, textile industries for dryin of textile materials, etc. Thus, solar dryer is one of the many ways of makin use of solar enery efficiently in meetin man s demand for enery and food supply, total system cost is a most important consideration in desinin a solar dryer for aricultural uses. No matter how well a solar system operates, it will not ain widespread use unless it presents an economically feasible alternative to other available enery sources 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1684

2 The application of solar dryers in developin countries can reduce post-harvest losses and sinificantly contribute to the availability of food in these countries. Estimated post-harvest losses are enerally cited to be of the order of 40% but they can, under very adverse conditions, be nearly as hih as 80%. A sinificant percentae of these losses are related to improper and/or untimely dryin of foodstuffs such as cereal rains, pulses, tubers, meat, fish, etc. [4, 5]. Use of indirect type natural convection solar dryer for dryin rapes, fis, onions, apples, tomatoes and reen peas has been reported [3]. Solar dryin is a potential decentralized thermal application of solar enery particularly in developin countries [6]. However, so far, there has been very little field penetration of solar dryin technoloy. In the initial phase of dissemination, identification of suitable areas for usin solar dryers would be extremely helpful towards their market penetration. Thus, the solar dryer is one of the many ways of makin use of solar enery efficiently in meetin man s demand for enery and food supply. No matter how well a solar system operates, it will not ain widespread use unless it presents an economically feasible alternative to other available enery sources. 2. DESIGN APPROACH AND METHODOLOGY In this project we have desined, fabricated and evaluated the performance of an indirect type solar dryer also called forced convection (active) type for dryin aricultural products. The workin model of indirect type solar dryer is based upon the concept of solar radiation absorption. The solar enery (sun enery) is trapped inside by usin solar collector. The collector was made of wood and the absorber plate was painted with black colour so that it absorbs the maximum amount of sun radiation fallin on it. A special care was taken by alinin it in an acute anle (30-40 derees) so that the collector receives maximum amount of radiation. The solar enery, which ets absorbed inside the collector was allowed to pass throuh four well created baffles. The baffles were placed inside the collector so that flow of hot air inside the collector is not linear and when it is not linear, it will take more time to travel and thereby it will raise the temperature of the air trapped inside. This hih temperature air ets exhausted from the collector throuh the passae provided at the exit of the collector. The temperature at the entry and exit of solar collector was measured usin diital thermometer. The hot air was then sucked by usin a centrifual air blower so that this hot air ets forced inside the dryin chamber. The products (reen apple slices) were placed on the dryin trays in the horizontal manner. The hot air was forced from the solar collector onto the dryin chamber with the help of a centrifual blower and the heated air inside the dryin chamber moves out throuh the exhaust vent. The orthoonal view of the indirect solar dryer is shown in Fi- 1. Fi- 1: Orthoonal view of the Indirect Solar Dryer (dimensions in cm) 2.1 Appliances used The appliances used in solar dryer consist of solar collector (air heater), cover plate, absorber plate, dryin cabinet and air blower,which are mentioned below alon with the specifications: Solar Collector: The inner box of the solar air collector was constructed usin 1 mm thick alvanized plate and the surface facin sunliht was painted with black paint.the solar collector was insulated with wood of about 3cm thickness and thermal conductivity of 0.04 Wm-1 K-1 on all sides. The solar collector assembly consists of air flow channel enclosed by transparent cover (fibre lass). The fibre lass is a sinle layer of 4 mm thick transparent lass sheet. It has a surface area of 0.82 by 1.20 cm, thermal conductivity Wm-1 K-1 and of transmittance above Cover plate: This is a transparent sheet used to cover the absorber, thereby preventin dust and rain from comin in contact with the absorber. The material used in the cover plate is fibre lass of havin lenth of 170 cm, breadth 100 cm and thickness 4 mm. Absorber plate: This is a metal sheet painted black and placed below the cover to absorb, the incident solar radiation transmitted by cover thereby heatin the air between it and the cover. Here GI sheet is chosen because its quick response in absorption of solar radiation and also aluminium sheet is placed 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1685

3 below the GI sheet because of its ood ability to keep the absorbed solar radiation. Insulation: This is used to minimize heat loss from the system. Insulations were provided on the surface of the pipes connectin the collector with the dryer. The insulatin material used is foam rubber. Construction of the solar collector is shown in Fi.2 Fi-4: Air Blower Fi-2: Construction of solar collector Cabinet: The dryin cabinet toether with the structural frame of the dryer was built from wellseasoned woods, which could withstand termite and atmospheric attacks. An outlet vent was provided toward the upper end at the back of the cabinet to facilitate and control the convection flow of air throuh the dryer (Fi-3). Access door to the dryin chamber was also provided at the side of the cabinet. ber dimensions are: Lenth=146 cm, Breadth=100 cm, Heiht=60 cm, Thickness=0.45 cm. Electronic devices: The electronic devices that were employed for calculatin the readins include Hyrometer ( Rane: C to 50 0 C, dimension (l b h): 30cm 9cm 2.5cm), Diital LCD Thermometer ( Rane: C to C and accuracy: +1 0 C, Operatin Voltae: 2 1.5V ), Diital Thermometer Temperature Test Pen (Temperature rane: C to C ). 2.2 Experimental setup The solar dryer was placed on the round level of a buildin based on the desin. A centrifual pump was employed in order to speed up the rate of dryin process and baffles were employed as a new introduction. The baffles were placed inside the collector so that flow of hot air inside the collector becomes non-linear, thus it will take more time to travel and thereby it will raise the temperature of the air trapped inside. The experimental setup of the solar dryer is shown in Fi-5. Fi-3: Construction of Cabinet Air Blower: The air blower that is used is the centrifual air blower that has a Horse Power of 0.28; Power of 210 Watts; Speed is 2800 rpm(fi-4). Fi-5: The experimental Setup of the Solar Dryer 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1686

4 2.3 Thermal Analysis In the desin, a flat plate collector with an area of 1.7 x 1 m 2 is considered. The performance of the collector is described by an enery balance that indicates the conversion of solar radiation into useful enery ain and losses. The thermal analysis was done to calculate the heat ain and the losses for flow of air between lass cover and absorber plate. Several formulations were employed and calculations were done to find out the overall efficiency of the dryer and the collector. The concept of heat transfer has been used throuhout the whole project. The transmittance ( ) of a lass cover for solar radiation depends on the anle of incidence. Typical values for clear lass are iven in Table 1. Table-1: Transmittance of a lass cover Transmittance of a Glass Cover : ( ): The absorptance ( ) of the black plate for solar radiation also depends on the anle of incidence. Table 2 shows typical values for ( ) and the product ( ). ( ). Table- 2 : Absorptance of black plate Absorptance of a Black Plate. I I cos I (1) in b d Where I b is the beam solar irradiance, is the anle of incidence, and I d is the diffuse irradiance. If there is one lass cover the solar irradiance on the black plate is ( ). I cos I b m d...(2) Where m is the mean value of ( ). The solar radiation flux q abs absorbed by the black plate is iven by q ( ). ( ) I cos (. ) I abs b m d... (3) Where (. ) m is the mean value of ( ). ( ). The mean value of ( ). ( ) can be found by means of interals over the hemispherical sky as follows: /2 /2 (. ) m [ ( ). ( ).sin.cos. d( )]/[ sin.cos. d( )] 0 0 For one lass cover the result is approximately (. ) m = Heat Losses The lass cover behaves nearly as a black body for lon-wave radiation. We can assume that the emittance c of the lass cover is The emittance b of the black plate for lon-wave radiation depends on whether the surface is nonselective or selective. Typically we have : ( ): ( ). ( ): The solar irradiance I in incident on the cover lass is iven by b = 0.92 for a non-selective surface, b = 0.10 for a selective surface. We shall consider a collector with one lass cover. Let T a = ambient temperature, T b = black plate temperature, T c = lass cover temperature, where absolute temperatures must be used for radiation calculations. 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1687

5 Heat is lost by conduction throuh the back insulation. It can be reduced to a low rate by inexpensive insulation materials. Typically the back loss miht be iven by the formula h ( T T ) ba b a..(4) where the heat transfer coefficient is h ba = 0.3W/m 2 K. Heat is lost from the black plate to the lass cover by convection and radiation. Experience has shown that, for free convection the Nusselt number Nu in air spaces between parallel plates with Grashoff numbers (Gr)in the rane 10 4 to 10 7, we have N u = Gr for horizontal plates, N = Gr for plates tilted at an anle u 45. Here G r =. (T b T c)l 3 / 2,.(5) where we assume as a typical example for air: = acceleration of ravity == 9.8m/s 2, = coefficient of thermal expansion = 1/T, T = 69 C = 342K, = T T = 89 C 40 C = 49K, b c L = spacin = 50mm = 0.075m, = kinematic viscosity = m 2 /s. G r (0.194*10 5 )^2 =9.8* *49*0.075^3/ This ives G r = , which is within the rane 10 4 to 10 7 mentioned above. Assume a tilt anle 45. Then we estimate, by interpolation, N u = Gr = Also since N u = hl/k, h=8.386* /0.075 h = 3.07W/m 2 K where h = heat transfer coefficient, L = 0.075m, k = thermal conductivity of air = W/mK, we have h = 3.07W/m 2 K =0.875 ( )=0.95 I =( ) 2 W / m T mass of air =0.0214k/sec =0.94 ; r= 0.94 The Overall Heat transfer coefficient (U) 1 1 K* A 1..(6) U h* A L h* A h K A = m =3.07 W / m = W / mk 2 U =2.5 W / m K 2 The enery balance on the absorber is obtained by equatin the total heat ained to the total heat loosed by the heat absorber of the solar collector. Therefore, IAc Qu Qcond Qconv QR Q (7) 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1688

6 If is the transmittance of the top lazin and IT is the total solar radiation incident on the top surface, where total solar radiation value is ( ) W/m2. Therefore, IA I A c T c.(8) = =1120 W Q U A ( T T ).. (9) L L c c a = ( ) = W where: = U overall heat transfer coefficient of the absorber (Wm 2K 1); L For an absorber (1 ) and hence, Q ( ) I A Q (10) u T c L = ( ) = W The collector heat removal factor, F R is the quantity that relates the actual useful enery ained of a collector. Therefore,. ma C pa ( T c - T a F ) R A c [ I T - U L ( T c - T...(11) a )] =( ( )/ (1.75[ ( )] = W If Q the heated air leavin the collector is at collector temperature, the heat ained by the air is: Q A F [( ) I U A ( T T )].... (12) c R T L c c a = [ ( )] = W The thermal efficiency of the collector is iven by: n c Q c AI T..... (13) = / ( ) = % The thermal efficiency of the dryer is iven by: n d ML I At c ( )...(14) =( ^6)/ = % 2.4 Experimental Procedure The experiments were conducted in the months of March and April, from daily 9 am to 4:30 pm. The readins of the temperatures at the entry, middle and exit of the lass cover, absorber plate and bottom insulation were calculated usin various electronic instruments as mentioned above. The temperature of the air in the dryin chamber and the atmosphere were measured usin hyrometer. Good quality reen apples were washed and cut into small slices ( 5mm ). The sample was measured usin a diital weihin pan and 800 rams of the slices divided equally in two parts were used for dryin. One part of the sample was placed inside the dryin chamber and the other part was placed under direct sunliht. Temperature and humidity readins were taken at equal intervals from 9 am to 4 pm. Chemical analysis of the solar dried and sun dried samples was carried out in order to find out its quality. Chemical analysis was carried out usin standard methods [7] to find out the oranic matter (OM),crude protein(cp),ether extract(ee),ash content and dry matter(dm) of samples. 3. RESULTS AND DISCUSSIONS The results of the hourly variations of the temperatures in the dryin chamber and solar collector compared to the ambient temperature are shown in Table- 3 and Chart-1. The temperature inside the dryin chamber and the solar collector was much hiher than the ambient temperature durin most hours of the dayliht. The temperature inside the dryin chamber was found to be the hihest (51 0 C) at 1 pm. The relative humidity percentae of the dryin chamber and the ambient 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1689

7 air humidity was observed and the results are iven in the Table -4 and Chart- 2. The relative humidity percentae in dryin chamber was almost equal to the ambient humidity percentae at 9 am, but the humidity percentae declines sharply up to 3pm in the dryin chamber compared to the ambient humidity. The lowest humidity inside the dryin chamber was also recorded at 1 pm. The hiher temperature and lower humidity favours better dryin without much chane in colour (Fis-6,7,8). Other workers have also reported that aricultural products specially fruit and veetables require hiher temperature for safe dryin and dryin under controlled condition at specific humidity ives superior quality products [8]. Use of forced convection solar dryer for dryin fruits and veetables has been reported by several workers and it is considered as more efficient than natural convection dryers [9,10]. In the present study the thermal efficiency of the collector and the dryer was found to be % and 13.8 % respectively. Table -3: A typical day results of the diurnal variation of temperatures in the solar dryer Time (hr) Ambient Temp.(C) ber Temp.(C) Collector Temperat ure(c) 9.00 am am am pm pm pm pm pm Chart-1: Variation of temperatures in solar collector, dryin chamber and ambient temperature Table - 4: A typical day results of the diurnal variation of relative humidity in the dryer Time (hr) Ambi ent Temp.(C) DBT Ambi ent Temp.(C) WBT Ambie nt Air Humidi ty (%) b er Temp. (C) DBT ber Temp.(C) WBT ber Humi dity (%) 9 am am am am pm pm pm pm Chart- 2 : Variation of the relative humidity of the ambient air and dryin chamber 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1690

8 The results of hourly moisture loss and mass of the reen apple slices in the dryin chamber and under sun dryin are shown in the Table- 5 and Chart-3. The percentae of moisture loss of the sample in the dryin chamber was found to be hiher as compared to the sun dryin in all the hours from 10 am to 4 pm. The mass of water removed in the dryin chamber was also found to be hiher (164.2 ) as compared to the sun dryin (155.4 ). Table -5 : Hourly moisture loss and mass of the reen apple sample Time (hr) Mass of reen apple () (Dryi n ber) Moist -ure Loss () (Dryi n ber) % Moist ure Loss (Dryi n ber) Mass of reen apple () (Sun ) Moist ure Loss () (Sun % Moist ure Loss (Sun 9.00 am a m 11.00a m 12.00p m 1.00pm pm pm pm content of the solar dried samples was found to be hiher compared to the sun dried samples, which indicates the loss of crude protein durin sun dryin. Lower oranic matter and hiher dry matter in the solar dried samples compared to the sun dried samples also suests that solar dryin is advantaeous for better preservation. Table -6: Chemical analysis of the sun dried and solar dried reen apple slices Samples Sun dried reen apple slices Solar dried reen apple slices OM % ± ± 0.13 CP % EE % Ash % DM 2.78 ± ± ± ± ± ± ± ± 0.20 Fi-6: Fresh Sample of Green Apple Slices Chart- 3: Hourly moisture loss of reen apple sample at different time period The results of the chemical analysis in respect to the oranic matter(om),crude protein(cp),ether extract(ee), ash and dry matter (DM) content of the reen apple slices dried under the open sun and the solar dryer are shown in the Table -6. Crude protein Fi-7: Green Apple slices dried inside the dryin chamber Fi-8: Green Apple slices dried under open sunliht 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1691

9 4. CONCLUSIONS An indirect forced convection solar dryer was desined, fabricated and its performance was evaluated usin reen apple slices. The dryer has been desined indienously usin locally available materials for construction and it is cost effective. In the dryer, the heated air from a separate solar collector is allowed to pass throuh the products placed inside the dryin chamber. The solar enery which is et absorbed inside the collector is allowed to pass throuh some well created baffles. The temperature inside the dryin chamber and the solar collector was much hiher than the ambient temperature durin most hours of the dayliht, which was useful for better dryin. The relative humidity inside the dryin chamber was also less durin different time. The percentae of moisture loss and mass of water removed in the dryin chamber was hiher compared to open sun dryin. Hiher crude protein and dry matter contents in the solar dried reen apple slices also indicate that the solar dryin is better than the sun dryin. The constructed solar dryer will be useful for dryin aricultural products in rural areas as it is cost effective. ACKNOWLEDGEMENT We are thankful to Prof. P Muthukumar, Department of Mechanical Enineerin, IIT Guwahati and Dr. Dilip Kumar Sarma, Director, ICAR-NRC on Pi, Guwahati for their advice and help both theoretically and practically. We would like to take the opportunity to thank the Principal, Royal School of Enineerin and Technoloy, Guwahati and entire faculty members of Department of Mechanical Enineerin, Royal School of Enineerin & Technoloy, Guwahati for their valuable help and support. [3] A.A. El-Sebaii and S.M. Shalaby Solar dryin of aricultural products: A review, Renewable and Sustainable Enery Reviews, [4] M.W.Bassey, Development and use of solar dryin technoloies, Nierian Journal of Solar Enery, [5] I.T. Torul, I.T. and D. Pehlivan, Modellin of thin layer dryin kinetics of some fruits under open-air sun dryin process, Journal of Food Enineerin, [6] A. Sharma, et. al, Solar- enery dryin systems: A review. Renewable and Sustainable Enery Reviews, [7] AOAC Official methods of analysis 15 th Edn. Association of Official Analytical Chemicals Arlinton,Virinia, [8] Gutti Babaana et.al, Desin and construction of forced /natural convection solar veetable dryer with heat storae, ARPN Journal of Enineerin and Applied Sciences, [9] Vinay Narayan Hede et.al, Desin,fabrication and performance evaluation of solar dryer for banana, Enery,Sustainability and Society, [10] M Isiaka et.al, Effect of selected factors on dryin process of tomato in forced convection solar enery dryer, Research Journal of Applied Science in Enineerin and Technoloy, BIOGRAPHIES Kaustav Bharadwaz, Student, Mechanical Enineerin, RSET, Guwahati, Assam, India REFERENCES [1] Y. Baradey et.al, Solar dryin of fruits and veetables,international Journal of Recent Developments in Enineerin and Technoloy, [2] Sushrut S. Halewadimath et. al, Experimental analysis of solar air dryer for aricultural products,international Research Journal of Enineerin and Technoloy(IRJET), , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Pae 1692