Modeling and Experimental Investigation a Solar Tray Dryer with Indirect Forced

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1 Author name / JHMR 00 (01) Journal of Solar Energy Research 1 (017) 4-47 Journal Journal of Solar of Solar Energy Energy Research (JSER) (JSER) Journal homeage: jser.ir.jser.ut.ac.ir Modeling and Exerimental Investigation a Solar ray Dryer ith Indirect Forced Click here tye the title Convection of your using aer Phase Caitalize Change first Materials letter of each ords Mojarrad First Author a *M. a Rahimi Second Author a A. Abdollahour b* b M. akzadeh a A. a Chemical Engineering Deartment University of Isfahan Hezar Jerib Ave. Isfahan Iran. a First affiliation Address City and Postcode Country b University of Mohagheghe Ardabili Ardabil Iran. Second affiliation Address City and Postcode Country * Mojtaba.mojarad@gmail.com ARICLE INFO ARICLE INFO Received: 19 October 016 Received in in revised form: form: Acceted: 9 January 017 Available Acceted: online: 0 January 017 Keyords: ye Solar -6 energy; keyords Solar tray here dryer; Collector; Energy searated storage by semicolons ; A B S R A C A B S R A C Solar energy is raidly gaining attention in different industries esecially agricultural industries. Alication of this clean energy in drying industry resulted in many investigations in academia. Dryers ith energy storage Click can reduce here thermal and insert fluctuations your abstract of solar text. irradiations Click here and also insert enhance your abstract drying efficiency text. Click of here agricultural and roducts. insert In this your study abstract araffin text. hase Click change here material and insert has your been abstract used as energy text. Click storage here and and the insert erformance your of a solar abstract tray dryer text. ith Click indirect here forced and insert convection your has abstract been text. investigated. Click here he and mathematical insert your model abstract of the text. energy balance Click for the here rocess and has insert been your derived. abstract he text. effect Click of here arameters and insert namely your inlet abstract air velocity text. Click and here collector and surface area insert on the your final moisture abstract text. content Click of samles here and and insert air outlet your temerature abstract text. have Click been here studied. and Air insert inlet your temerature has abstract been tested text. at Click to levels here of and 1 insert and m/s your using abstract a collector text. Click surface here area and of insert m ith your and abstract ithout text. energy storage. Click he integration here and insert of energy your storage abstract enhances text. Click the here efficiency and insert by your 7% abstract and reduces text. the Click outlet here moisture and content. insert Loer your inlet air abstract velocity text. and Click larger here collector and insert surface your area abstract results in text. loer Click final here moisture and insert content your of samles. On abstract the other text. hand Click for here higher and ambient insert your temerature abstract text. even Click higher here inlet and insert air velocity your abstract can result text Click in loer moisture here content and of insert roducts. your Comarison abstract text of Click exerimental here and data insert ith your simulation abstract text results Click shos here correlation and insert coefficient of your abstract text Click here and insert your abstract text Click here and insert your abstract text Click here and insert your abst 017 Published by University of ehran Press. All rights reserved. 01Published by University of ehran Press. All rights reserved. 1. Introduction Raid utilization of non-reneable energy resources as ell as their ollution consequences resulted in groing environmental destruction. Noadays the fundamental challenge for researchers is to exloit and otimize clean energy sources. Solar energy is the cheaest available energy source for several alications esecially agricultural and dryer industries [1]. Due to the intermittency of solar energy in a 4 hour eriod storage of excessive available diurnal energy for exloitation during night-time not only shortens the drying eriod and consequently increases dryer s annual caacity but also dramatically decreases its oerational costs[]. hermal energy storage is knon to be a key technology to tackle energy suly and demand mismatch. hermal energy can be stored sensibly latently and chemically (using a reversible chemical reaction). Hoever latent thermal energy storage using hase change materials (PCMs) is the most effective one. he reason is due to the high energy storage caacity as ell as almost constant temerature in the long eriod of energy storage []. Among available PCMs olyethylene glycol received considerable attention. 4 Suitable thermohysical roerties such as desirable hase change temerature high latent heat caacity congruent melting non-toxicity lack of suercooling lo vaour ressure lo volume change during solid-liquid hase change rocess and also high thermal and chemical stability resulted in the high interest [4]. In 010 KenisarinandMurat comrehensively investigated materials hich could be otentially used as PCMs for a temerature range of 10 to 1000 C. It is obvious that no material can simultaneously satisfy all the desirable requirements of a suitable PCM; therefore selection of a PCM for a certain alication requires careful consideration of the roerties of several materials. Design and determination of oerational details for a latent thermal energy storage system deends uon the hysicochemical roerties of the PCM such as energy storage density to volume ratio [5]. Devahastin and Saovakhon(006) investigated the ossibility of thermal energy storage in solid araffin as a PCM. Paraffin as used to store solar energy during drying and released energy hen solar energy as not sufficient or not available here the effect of PCM integration on the drying kinetics of seet otato as investigated. Heat transfer characteristics

2 temerature rofiles as ell as the effect of inlet air temerature and velocity on charging and discharging eriods ere studied [6]. Solar dryer are among those solar systems ith great otential of PCM integration. In solar dryers PCM integration is due to solar energy storage and continuous solar drying in the hours ith no sun availability. Numerous studies have been conducted using these systems for various drying materials [7-10]. Chen et al. develoed a theoretical transient model to investigate the novel concet of solar dryer ith absorbing flat reverse collector ith thermal storage and natural air convection. he efficiency of the acked bed system as investigated for onion drying of its trays. It as shon that samle temerature deends uon air flo channel ih and acked bed height. hermal energy storage is effective during non-irradiation hours by greatly decreasing drying temerature fluctuation [11 1]. he develoed mathematical model is suitable for evaluating the erformance of absorbing reverse collector ith thermal storage in solar convective drying. he model is also suitable for redicting samle temerature moisture content and samle drying rate. he drying rocess in solar systems is greatly comlicated due to the simultaneous heat and mass transfer. he samle roerties and PCM behaviour is greatly effective on the analysis. Moreover PCM integration in solar drying systems significantly enhances energetic and exegetic efficiencies of the system [1 14]. In this study a mathematical model is develoed to investigate the erformance of a PCM in a solar dryer. Exerimental and theoretical investigation of efficiency as ell as the erformance of a solar tray dryer ith solar energy storage in a PCM is conducted. Furthermore the effect of thermal energy storage on effective arameters such as outlet air moisture content and temerature is also studied.. Materials and Methods he selected drying material in this study as banana. o reare samles first bananas ere eeled and from each samle 6 ieces ere selected ith identical dimensions. In each exeriment 50 grams of samles ere eighed and then ut in the baskets. hereafter the baskets containing samles ere transferred inside the drying chamber through the mounted hatches on the dryer s door. o determine roduct eight a digital scale (model APX-15 manufactured by Denver Instrument Co. Colorado United States) ith gram accuracy as used. Ambient air temerature as measured by means of a digital thermometer (model P00 tem manufactured by Dostmann Germany) ith 0.1 C accuracy as used. In order to measure air velocity an anemometer (model esto 45 manufactured by esto Co. England) as used ith an accuracy of 0.01 m/s. An air temerature measurement device ith a data acquisition system linked ith temerature sensors as used to measure temerature at different oints of the system including inside chamber collector and ambient. Data acquisition time interval as first set at 0 minutes hich as then gradually increased by decreasing drying rate. After conducting exeriments exerimental data ere lotted as drying kinetic curves. he thermohysicalroerties of the PCM are shon in able 1. able 1. hermohysical roerties of araffin Proerty Unit Value Melting oint C 60 Solid density kg/m 910 Liquid density kg/m 80 Solid conductivity W/m.K 0.4 Liquid conductivity W/m.K 0. Solid secific thermal caacity J/kg.K 000 Liquid secific thermal caacity J/kg.K 150 Latent heat J/kg Solar dryer Figure 1 shos a icture of the exerimental setu. he system consisted of a drying chamber to flat tye solar collectors and the thermocoules. Inside the dryer to trays ere used simultaneously and air as circulated by means of a bloer. he bloer as mounted at the entrance of the first collector. hree small baskets ere considered to ut samles on each tray. he four legs of the dryer are equied ith heels in order to enable orientation change of collectors toards a roer solar angle to absorb maximum solar irradiation. Drying exeriments ere conducted for either ith or ithout the PCM. In the exeriments ith the PCM 65.6kg of araffin as used as thermal storage. An exhaust fan as mounted at the bottom of the dryer to transfer the heated air inside the collector (by greenhouse effect) to the chamber. Each drying samle as ut on a container to facilitate the eighing rocess. Galvanized containers ith 0.9mm thickness as used for PCM hose dimensions ere 100cm (L) 0cm (W) 4cm (H). en containers ere manufactured and mounted at the bottom of Collector 1. he distance beteen the to of the containers and the glass (Collector 1) as 16cm through hich the air as blon. Figure 1 shos the arrangement of the containers. Figure 1. he resentation of the solar dryer and thermal energy storage containers.. Modelling Assumtions he simlifying assumtions for the model include: Air moisture content distribution only exists along air flo direction and is constant beteen to trays 44

3 Air is considered as an ideal gas Pressure loss inside the drying chamber is negligible emerature distribution inside the drying samle is negligible Conduction along air flo direction is negligible as comared to the fluid bulk convection Works by external forces (such as gravitational force) and molecular mechanism (such as viscous forces) are negligible.. Exerimental Procedure Exeriments ere conducted in summer 014. One of the objectives of this study as to investigate the effect of inlet air velocity on drying erformance in a three-day eriod. able shos the selected values for the modeling arameters. During the exeriments the absolute moisture content of the drying air as measured and recorded using a m collector area. Acc Inut Outut (1) d V C m g in o G H G H sch k ch 1 sch k ch na h c ch i H able. Constants used in the chamber modeling Constant Value n 9 m M ( kg kmol ) A m ( ) P V m V m k k A m A m 1.08 c a J kg K 1005 ca ( J kg K) 1851 c J kg K 810 c J kg K 4187 h fg 0 J kg ms ( kg ) Results and Discussion In this section first the mathematical model is resented and then the exerimental results are analyzed. It should be noted that to revent systematic bias the exeriments ere conducted randomly. Moreover each exeriment as () 45 relicated three times and the averages of the relication results are reorted..1. Energy and Mass Balance Equations In this sectionenergy and mass balance equations are develoed for air and the drying samle Energy Balance for Air in the Drying Chamber Each tray is considered as a fully mixed system here heat and mass transfer occur. herefore energy conservation equation for air flo over each tray is: Enthaly of air er unit dry air mass is calculated as H C h H () ch in m g in 0 fg in Hch out Cm 0 hf g H ou t (4) Substituting Equations () and (4) in Equation () gives: d VC Gs C ch k m g in (5) na h d c ch i mv K nv chc Gs C ch k m g in na hc ch i.1.. Mass Balance for Air Moisture Content inside the Chamber he moisture content of the air varies due to the evaoration from drying samles. Based on mass conservation equation for the moisture content over each tray: mv K nv Hch 1H t (7) G H G H na N M sch k 1 sch k.1.. Energy Balance for Drying Samle he energy of the samles on each tray are affected by convection from hot air as ell as its consequent ater evaoration. herefore energy conservation equation yields: (8) du i hc ch i ch i na nan im hfg (6) he internal energy of the samle er unit dry mass is: U C C X (9) 0 Substitution of Equation (9) in Equation (8) gives: (10) di ms C CX i A hc ch i ch i N im h fg Wherem sis the mass of the dried solid in each drying samle Mass Balance for Moisture Content in Drying Samle For the drying samle mass balance gives:

4 dx i ms N im A (11) Molar moisture content flux is given by: ms dx N A M (1) Convective heat transfer coefficient beteen air and samle is: 0.5 hc ch 17.5mch k (1) Latent heat of evaoration as calculated by: h (14) fg Moreover air flo density inside the chamber is: (15) ch f he kinetic equation used in the model as obtained by means of curve fitting over exerimental data: dx a a a 1 ch X (16) Where is temerature in C X is moisture content on dry basis and a i are kinetic constants. Equation (16) as used to redict evaoration flux in Equation (10). Based on the fitting results for different velocities kinetic model constants ere calculated hich are tabulate in able. able. Kinetic model constants CONSAN VALUE a a.91 a.77 Figure. Moisture content variation ithout PCM for air inlet velocities of 1 and m/s When air velocity as lo air temerature raised higher in Collector 1; therefore the drying chamber as hotter and consequently the drying rate as higher resulting in loer samle moisture content. In other ords air velocity raise did not affect the drying rate since it reduced external mass transfer resistance hile the drying rocess of banana is controlled by molecular diffusion inside the samle. On the other hand increasing air temerature increased the drying samle temerature hich in turn increased molecular diffusion coefficient of samle resulting in higher drying rate. Figure shos the variations of ambient temerature and collector outlet temerature during the drying rocess. Based on the figure maximum collector outlet temerature as 5 C. he obtained model as evaluated using analysis of variance (ANOVA) based on correlation coefficient (R ) hich as calculated to be 96.7%... Effect of Air Velocity using One Collector ithout PCM In this mode solar irradiation as revented on the dryer by means of covering the dryer glass. In other ords drying air as heated only in Collector 1. Figure shos the effect of air inlet velocity on moisture content variations versus time. As it is shon loer air velocities resulted in loer instantaneous and final moisture content. Figure. Comarison of collector outlet temerature and ambient temerature ithout PCM ith modeling results for air velocity of 1m/s 46.. Effect of Air Velocity using One Collector ith PCM Figure 4 shos the effect of air inlet velocity on moisture content variation versus time ith PCM integration. According to the figure loer air velocity resulted in faster samle moisture content reduction. he exeriments ithout PCM (see Figure ) ere conducted in the hottest months of the year (July and August) hile those ith PCM ere carried out in fall. Comaring Figure ith Figure 4 it is clear that the amounts of moisture content reduction in Figure 4 (ith PCM) ere 0.58 and 0.61 on dry basis hile the same amounts for Figure (ithout PCM) ere 0.9

5 and 0.9 on dry basis resectively. his confirms the benefit of thermal energy storage. It is orth ointing out that the exeriments ith PCM ere conducted in colder ambient temerature (about 14 C colder); nevertheless the drying rate is almost the same as that of those exeriments ithout PCM in hot ambient temeratures (in July and August). his comarison enlightens the evaluation of thermal energy storage. ere air inlet velocity resence/lack of PCM and collector surface area. Mathematical modelling of the rocess as derived by energy conservation equations together ith kinetic equations from exerimental analysis ith correlation coefficient of 96.7%. Air inlet velocity as investigated for to levels of 1 and m/s. According to the results loer air velocity resulted in loer samle moisture content. Furthermore the results indicated that PCM integration resulted in loer moisture content than the case ithout PCM. Comaring air outlet moisture content integration of PCM reduced the outlet moisture content efficiency by 7% hich can greatly shorten the required drying eriod and rovide economic advantages. Figure 4. Moisture content variation ith PCM for air inlet velocities of 1 and m/s Figure 5 shos that maximum and minimum ambient temeratures ere 9 and 16.4 C resectively and collector outlet temerature as 46 C. On the other hand in Figure 6 maximum and minimum ambient temeratures ere 7.6 and 17.8 C resectively and collector outlet temerature as 6 C. herefore higher air velocity reduced collector outlet temerature in Figure 6. It is obvious that loer air velocity gave higher collector outlet temerature and moisture content reduction as faster. Figure 6. Collector outlet temerature and ambient temerature variation ith PCM for air velocity of m/s 4. Conclusions Solar dryers are considered as suitable otions to exloit the chea solar energy source. Several scenarios are develoed to otimize utilization of this technology. Integration of thermal energy storage revents the effect of temerature fluctuations by solar irradiation and increases drying efficiency during energy release eriod. In this study the drying rocess of banana samles as investigated using indirect forced convection solar dryer using araffin as PCM. he effects of three arameters ere studied hich 47 References [1] Lahsasni S. et al hin layer convective solar drying and mathematical modeling of rickly ear eel (Ountia ficus indica). Energy 9() [] Mohajer A. et al. 01. Exerimental investigation of a hybrid solar drier and ater heater system. Energy Conversion and Management [] Bal L. M. et al Solar dryer ith thermal energy storage systems for drying agricultural food roducts: a revie. Reneable and Sustainable Energy Revies 14(8) [4] Alkilani M. M. et al Revie of solar air collectors ith thermal storage units. Reneable and Sustainable Energy Revies 15() [5] Kenisarin M. M High-temerature hase change materials for thermal energy storage. Reneable and Sustainable Energy Revies 14() [6] Devahastin S. & Pitaksuriyarat S Use of latent heat storage to conserve energy during drying and its effect on drying kinetics of a food roduct. Alied thermal engineering 6(14) [7] Hossain M. A. & Bala B. K Drying of hot chilli using solar tunnel drier. Solar Energy 81(1) [8] Hui Y. H Handbook of food science technology and engineering (Vol. 149). CRC ress. [9] Condorı M. Echazu R. & Saravia L Solar drying of seet eer and garlic using the tunnel greenhouse drier. Reneable Energy (4) [10] Gallali Y. M. et al Preservation of fruits and vegetables using solar drier: a comarative study of natural and solar drying III; chemical analysis and sensory evaluation data of the dried samles (graes figs tomatoes and onions). Reneable Energy 19(1) 0-1. [11] Gallali Y. M. et al Preservation of fruits and vegetables using solar drier: a comarative study of natural and solar drying III; chemical analysis and sensory evaluation data of the dried samles (graes figs tomatoes and onions). Reneable Energy 19(1) 0-1. [1] Pangavhane D. R. & Sahney R. L. 00. Revie of research and develoment ork on solar dryers for grae drying. Energy conversion and management 4(1) [1] Midilli A. & Kucuk H. 00. Mathematical modeling of thin layer drying of istachio by using solar energy. Energy conver [14] Amer B. M. A. et al Design and erformance evaluation of a ne hybrid solar dryer for banana. Energy Conversion and Management 51(4)