Experimental Investigation of Phase Change Material Based Thermal Storage System for Solar Dryer Applications

Transcription

1 Volume 117 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Experimental Investigation of Phase Change Material Based Thermal Storage System for Solar Dryer Applications 1 Abishek Ganesh and 2 P. Sudhakar 1 Department of Mechanical Engineering, SRM University, Kattankulathur, Chennai, India. gabishek29@gmail.com 2 Department of Mechanical Engineering, SRM University, Kattankulathur, Chennai, India. Abstract Solar drying is an advanced technology which utilizes the radiation from sun to dry food crops. Food grains and vegetable/fruits have a lower shelf life due to its moisture content. The dried products have longer shelf life. Food substances require controlled drying environment, in order to retain the natural parameters like physical and chemical properties. The proposed work involves the design and construction of solar cabinet dryers using Phase Change Material to store the thermal energy. Tests were taken with and without drying products, forced convection in normal arrangement and honeycomb arrangement. The honeycomb structure provided more efficiency in both natural and forced convection, 54.9 and 69.9 % respectively. Also, the weight of the drying product (potato) was reduced from 1Kg to 452 gm and 1kg to 512gm in natural and forced honeycomb structure respectively. Keywords:Solar dryers, natural convection, forced convection, honeycomb structure, phase change material. 331

2 1. Introduction The wide spread use of solar dryers in agriculture industry has led to the development of creating various design approaches to the same. These designs and factors that affects the thermal performance of solar dryers were mentioned in [1,2]. The different methods using double pass solar collectors to improve the performance of solar dryers is mentioned in [3]. The performance of the v- groove absorber plate, fins and material that is used to store thermal storage are referred from [4-12]. The technique that is essential in terms to overcome the irregular nature if solar energy in drying system is to use the thermal energy storage materials. The materials store abundant energy during the sunshine hours and used the stored energy in non- sunshine hours. The solid and liquid material that is used in review of sensible heat storage media for drying plants is tabulated [13]. El-sebaii et al investigated with the help of indirect solar dryer, using sand as a storage material [14]. Mohjer et al [15] determined that the drying time of grapes is reduced to approximately 16% with the help of sensible heat storage material, by using water as storage material. The PCM ability of the sensible heat storage material is to store large amount of energy during the melting process and benefits its later the constant temperature [15]. The benefits and the process of designing and fabricating PCM in bed grain dryer is experimented numerically and analyzed the effect of using paraffin wax as the storage medium of food products by Devahastin et al and Pitaksuriyarat [16,17] with the help of above analyzing process they could conclude with a results. It states that the energy that is used to dry the sweet potatoes is reduced approximately to one-third with air velocity is 1-2 m/s. it also states that it can be used to dry agricultural products at the temperature of C [18]. A seeded grapes was experimented in solar dryer by Cakmak and Yilvis [19]. They used calcium chloride hexahydrate as a important medium in one of the lower section of two collectors of the system. This process indicates the reciprocal relationship between the air velocity and drying time period [20]. The storage system analyzed was 50% more efficient when the taken mass flow rate was kg/s [21,22]. The two important method used in PCM indirect solar dryer is the usage of solar air heater with built in PCM is mentioned in [19]. The high upper losses is the main drawback of this method secondly, the heat storage unit is connected in series to the heater is presented in [17,20]. In which the high upper loss problem is solved but still have high overall heat losses. The PCM is placed at the bottom of drying compartment, thus overcoming demerits of all previous designs. Its drying temperature is mentioned as 40± 2.5 and 50± 2.5 respectively. In which the solar energy storage is implemented and the thermal energy storage unit is also implemented with phase change material is implemented to determine the material[23].here the system is enhanced with the heat recovery system to intake the solar energy to the dryer based on the approach the exegetic efficiency of the system reaches the maximum rate[24].the next process is based on drying the carpet using solar dryers were the system is fabricated with 332

3 flat plate solar air heater which is designed in such a way that it can dry the carpet in 7.5hours[25,26]. 2. Experimental Setup The experimental setup consists of two major components- solar dryer and solar air heater. The former is composed of components like insulation material, absorber plate, glass and coating material. The absorber plate is made up of aluminum with thickness of 1mm and the area of 1m 2 *1m 2 which is used for absorbing solar energy the alternative material that can be used for absorber plate is copper which as the high heat capacity than aluminum in absorbing solar energy which can be used in real time system. The insulating material that is used in the proposed model is foam with the thickness of 40mm which is used to reduce the heat losses. The important material that used in the experiment is glass with thickness of 5mm. the solar air heater consist of inlet 25mm diameter and 10 outlet of 25mm diameter. The coating material used in the absorber plate is black paint to absorb solar energy more efficiently. The latter is designed by taking width of 540mm and height of 700mm in one side and 800mm in other side which consist of 3 drying trays which is made up of stainless steel material which is placed 100mm difference to each other. And PCM tray is being used of which has the gap of 200mm and the materials like aluminum and foam of 1mm and 20mm thickness used inside the drying chamber. Additionally the cooling fan is also fixed at the top of the chamber to drive the air. Two sets of tests were conducted, with and without drying products. The no load test was a preliminary test with no PCM incorporated in it. Full load test is taken such that PCM was arranged in two ways- normal arrangement and honeycomb arrangements. Figure 1: Normal Arrangement of PCM 333

4 Figure 2: Honeycomb Arrangement of PCM 3. Experimental Preparations The sealed packets of PCM were arranged in both normal and honeycomb structure. The melting point of paraffin wax is 56 C. 4Kg of paraffin wax was taken such it was divided into 9 such packets, each with a capacity of gm. 1 kg of potato was taken and divided into three trays, each containing gm in the drying chamber. Totally 10 thermocouples were placed, four in outlet duct, tray, 7 in drying chamber. In solar air heater, 7 thermocouples placed, four in absorber plate, one on glass, one on plate and one in the inlet of air heater. The radiation was measured using radiation meter and wind velocity and ambient temperature using anemometer. The readings were noted for every 30 minutes. During non shine hours, the aluminum covers containing the PCM were placed in drying chamber and the potatoes were dried using the absorbed heat from the PCM. The temperatures of the same were measured by using thermocouples placed at 8 locations, one in tray containing potatoes, one in PCM tray, and four around the drying chamber. The readings were noted during the off sunshine hours of 4 pm to 7 pm at an interval of 30 minutes each. 4. Drying Parameters Calculations of natural convection: Drying characteristics of solar dryer in natural convection using normal and honey comb arrangement. 1) Amount of water content in product, Mtw Mtw= Wg*(Mi)/

5 Where Wg= material weight Mi= moisture content present in product initially. 2) completely dried weight of material, Wcdw Wcdw= Wg*(1-(Mi/100)) Where, Wcdw= complete dried weight (kg) 3) Water removed while drying, Mw kg Mw= [(mi-mf/100-mf)]*w Where mf = moisture content after drying,% mi= moisture content before drying, % W= product s mass, Kg 4) Amount of water removed per hour mw, Kg/h mw= Mw/Td Where, mw=mass of water to be removed during drying, Kg Td= assumed drying time, hr 5) Total energy required, Q(kJ) Q=(CDW*Cp(Tf-Ta))+(Mtw*Cw(Tf-Ta))+(Mw* ) Where, CDW = complete dried weight of moisture, Kg Cp= specific heat of wet product, kj/kg C Tf= final temperature, C Ta= ambient temperature, C Mw= mass of water to be removed by drying, Kg Cw= specific heat of water, kj/kg C Mtw= total quantity of water in product, kg = Latent heat of vaporization, kj/kg 6) the energy required per hour, Qt, kj/hr Qt=Q/Td Where, Q= total energy required, kj Td= assumed drying time, hr 7) Area of collector, Ac Ac= Qt*100/(I* ) I= solar irradiance = efficiency of collector Calculation of forced convection: Velocity of air coming out of blower is found out by anemometer. Velocity, c= 4.1 m/s (0.047kg/s) Atmospheric pressure of air,p=1.013*10 5 Pa 8) The mass flow rate of air entering the blower is given by M= *Ac Where, = density kg/m 3 A=diameter of blower, cm 2 9) Density, =P/R*T 335

6 R= gas constant T=ambient temperature 10) heat transfer, Q=m*Cp* T 11) efficiency, =Q/I*A A= Area of collector 5. Results and Discussions The test was carried out without any load (drying product). It was observed that the relative humidity of the outlet temperature is comparatively lower than the that of inlet temperature due to the fact that the pressure of sensible heat of air along the length of dryer was considerably low. Figure 3: Characteristic Curve of Natural Convection without Drying Material Figure 4: Characteristic Curve of Forced Convection without Drying Material 336

7 Figure 5: Characteristic Curve of Natural Convection with Drying Material Under Normal Arrangement Figure 6: Characteristic Curve of Forced Convection with Drying Material Under Normal Arrangement 337

8 Figure 7: Characteristic Curve of Natural Convection with Drying Material Under Honeycomb Arrangement Figure 8: Characteristic Curve of Forced Convection with Drying Material Under Honeycomb Arrangement 338

9 Figure 9: Efficiency Vs. Time Curve for Natural and Forced Convection of Natural and Honeycomb Arrangement The test was carried out without any load (drying product) under forced convection. It was observed that the relative humidity of the outlet temperature is comparatively lower than the that of inlet temperature due to the fact that the pressure of sensible heat of air along the length of dryer was considerably low. Fig 3 and 4 explains the test taken without drying material under natural convection.. The experiment was carried out from time interval of am to 4.30 pm. Fig 5 and 6 demonstrates that the results of test taken with drying material to know the trend of various operating parameters with respect to time. When the materials were placed in drying chamber, the PCM was arranged both normally as well as honey comb structure. This resulted in drying outlet temperature. Characteristic curve of natural convection with drying material under honeycomb arrangement. Fig 9. Efficiency Vs. time curve for natural and forced convection of natural and honeycomb arrangement. 6. Conclusion Natural and forced convection was taken on drying chamber by arranging the paraffin wax packed in aluminum sheets on both normal and honeycomb type arrangement. It was observed that in normal arrangement of natural convection, 384gm of potato was left out of taken 1kg while in forced convection, 458g was available. In the honey comb structure, natural convection yielded 428gm while 339

10 honeycomb structure yielded 512gm. Also the efficiency of forced convection by arranging the packets in honeycomb type is much higher, about 69.9%, compared to the conventional arrangement. The normal arrangement of forced convection yielded 48.7%. Honeycomb arrangement of natural convection gave 53.25% while normal arrangement of natural convection yielded 37.52% References [1] Erteken C., Yaldiz O., Drying of eggplant and selection of a suitable thin layer drying model, Journal of Food Engineering 63 (2004), [2] Muhlbauer W., Present status of solar crop drying, Energy Agric., 5 (2) (1986) [3] Rawat D.S., Jaurker A.R., Performance Evaluations of two pass solar air Heater using 600 Inclined V-shaped Ribs on absorber plate, International Journal of Engineering Science Invention 3 (8) (2014), [4] Karim M., Hawlader M., Performance investigation of flat plate, v- corrugated and finned air collectors, Energy Convers Manage 31 (2006), [5] El-Sebaii A.A., Aboul-Enein S., Ramadan M.R.I., Shalaby S.M., Moharram B.M., Investigation of thermal performance of -double pass-flat and v-corrugated plate solar air heater, Energy 36 (2011), [6] Gao W., Lin W., Liu T., Xia C., Analytical and experimental studies on the thermal performances of cross-corrugated and flat-plate solar air collectors, Appl Energy (2007), [7] Karsli, S., Performance analysis of new-design solar air collectors for drying applications, Renew Energy 32 (2007), [8] Datta G., Garg H.P., Ray R.A., Prakash J., Performance Prediction of cabinet type solar drier, Sol. Wind tech., 5 (3), (1988). [9] Tiwari G.N., Bhatia P.S., Singh A.K., Sutar R.F., Design parameters of a shallow bed solar crop dryer with reflector, Energy Convers Manage 35 (6) (1994) [10] Chauhan P.M., Choudhury C., Garg H.P., Comparative performance of coriander dryer coupled to solar air heater and solar air-heater-cum-rock bed storage, Apply Thermal Eng., 16 (6) (1996) [11] Jain D., Jain R.K., Performance evaluation of an inclined multipass solar air heater within built thermal storage on deep-bed 340

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