Mahesh Kumar. Department of Mechanical Engineering, Guru Jambheshwar University of Science & Technology, Hisar, India

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IBIMA Publishing Intrnational Journal of Rnwabl Enrgy & Biofuls http://www.ibimapublishing.com/journals/ijreb/ijrb.html Vol. 014 (014), Articl ID 961114, 11 pags DOI: 10.5171/014.

1 IBIMA Publishing Intrnational Journal of Rnwabl Enrgy & Biofuls Vol. 014 (014), Articl ID , 11 pags DOI: / Rsarch Articl Effct of Siz on th Convctiv Hat and Mass Transfr Cofficints during Natural Convction Grnhous Drying of Khoa-A Hat Dsiccatd Milk Product Mahsh Kumar Dpartmnt of Mchanical Enginring, Guru Jambhshwar Univrsity of Scinc & Tchnology, Hisar, India Corrspondnc should b addrssd to: Mahsh Kumar; mkshandilya1@gmail.com Rcivd 0 Sptmbr 013; Accptd 4 Octobr 013; Publishd 31 Dcmbr 013 Acadmic Editor: Mohammad Nurul Alam Hawladr Copyright 014 Mahsh Kumar. Distributd undr Crativ Commons CC-BY 3.0 Abstract In this rsarch papr, th convctiv hat and mass transfr cofficints ar valuatd for khoa drying undr natural convction grnhous mod for diffrnt sizs of khoa sampls for a givn mass. Th khoa pics of dimnsions m 3, m 3, and m 3 with total quantity of 100 g ar drid in th roof typ vn span grnhous with a floor ara of m. Th khoa has bn drid at atmosphric prssur till thr is almost no variation in its mass is rcordd. Th xprimntal data ar usd to dtrmin th valus of th constants in th Nusslt numbr xprssion by simpl linar rgrssion analysis and, consquntly th convctiv hat transfr cofficints ar valuatd. Th mass transfr cofficints hav also bn valuatd. Th convctiv hat and mass transfr cofficints ar obsrvd to dcras with th incras in siz of th khoa sampl and ar found mor for th khoa pics having dimnsion m 3. Th xprimntal rror in trms of prcnt uncrtainty has also bn valuatd. Kywords: Khoa; Khoa drying; Convctiv hat transfr cofficint; mass transfr cofficint; Grnhous drying; Natural convction. Introduction Solar nrgy is abundant, non-pollutant, and rnwabl form of nrgy. It can b ffctivly usd for product drying, if harvstd proprly. Th traditional tchniqu for product dhydration is th opn sun drying mthod which has many disadvantags lik product pollution and contamination. An advancd and altrnativ mthod to th traditional tchniqus is grnhous drying. In grnhous drying th product is placd in trays which rciv solar radiation through th plastic covr and moistur is rmovd ithr by natural convction or forcd air flow. Th us of appropriat grnhous dryr improvs th quality of th product and lad to rduction of drying tim intrval (Condori t al., 001). Khoa is a hat dsiccatd, partially dhydratd milk product. It forms an important bas for prparation of milk Cit this Articl as: Mahsh Kumar (014), "Effct of Siz on th Convctiv Hat and Mass Transfr Cofficints during Natural Convction Grnhous Drying of Khoa-A Hat Dsiccatd Milk Product," Intrnational Journal of Rnwabl Enrgy & Biofuls, Vol. 014 (014), Articl ID , DOI: /

2 Intrnational Journal of Rnwabl Enrgy & Biofuls swts which ar an intgral part of th Indian food hritag. About six lakh tonns of khoa is bing manufacturd annually, mostly in privat and unorganizd sctors of India by utilizing about 7% of th total milk producd (Kumar t al., 010; Kumar 013). It contains sufficint amount of moistur which hlps in th growth of microorganisms. Th shlf-lif of khoa is chifly influncd by th moistur contnts among othr factors lik storag tmpratur, raw matrial quality, sanitation conditions, and packaging. Th prsnc of moulds in khoa causs its fast dtrioration by producing discoloration dfcts as wll as disagrabl flavors. Solar radiation significantly rducs th counts of ths microorganisms (Kumar t al., 1996; Chavan, and Kulkarni, 006; Rajarajan t al., 007). Khoa drying is a continuous hat and mass transfr phnomnon. Th hat nrgy supplid to th khoa surfac is utilizd in two ways, i.., to rmov th moistur prsnt in th product through th provision of latnt hat of vaporization and to incras th product surfac tmpratur in th form of snsibl hat which causs vaporation of th moistur to th surrounding air. Rmoval of moistur occurs from th intrior of th khoa du to inducd vapor prssur diffrnc btwn th khoa and th surrounding mdium. Th convctiv hat transfr cofficint is an important paramtr in drying rat simulation, sinc th tmpratur diffrnc btwn th air and th product varis with this cofficint. Th convctiv mass transfr cofficints for various shaps and sizs of jaggry pics in a controlld nvironmnt wr valuatd by Tiwari t al., (004). It was obsrvd that th convctiv mass transfr cofficint in forcd convction is highr than th natural convction mod. Th ffct of shap and siz of jaggry for a givn mass on convctiv mass transfr cofficint for natural as wll as forcd convction grnhous drying was studid Kumar and Tiwari (006). Th convctiv hat transfr cofficints of khoa wr invstigatd by Kumar t al. (011a) in an opn sun drying and grnhous drying for natural as wll as for forcd convction mods for drying a khoa pic of siz m 3 for thr conscutiv days. Th convctiv hat transfr cofficints undr forcd convction wr rportd highr than th natural convction mod. Th convctiv hat transfr cofficints wr obsrvd to dcras with th drying day progrssion from th first day to th third day and wr found to vary in a rang of 0.54 to 1.09 W/m o C. In th prsnt study th ffct of siz on th convctiv hat and mass transfr cofficints of khoa for a givn mass with grnhous drying undr natural convction mod has bn valuatd. This rsarch work would b hlpful in th dsign of an fficint grnhous for drying khoa to its optimum storag moistur lvl. Matrials and Mthods Exprimntal St-Up and Instrumntation Dtails A roof typ vn span grnhous of m ffctiv floor ara was fabricatd of PVC pip and a UV film covring of 00 microns. Th cntral hight and th walls wr maintaind as 0.6 m and 0.4 m rspctivly. An air vnt with an ffctiv opning of m was providd at th roof for natural convction. A photograph of th xprimntal stup for grnhous drying and khoa sampl is shown in Fig.1.

3 3 Intrnational Journal of Rnwabl Enrgy & Biofuls Fig. 1: A Photographs of Exprimntal Unit Exprimntal unit was locatd on th opn floor of a thr-floor building to hav a good xposur to th solar radiation. Du to mor availability of sunlight th orintation of th grnhous was kpt ast-wst. Th xprimnts wr carrid out with total quantity of khoa as 100 g for ach dimnsion of th khoa pics, i.., m 3, m 3, and m 3. For ach xprimnt, khoa pics of 1.5 cm thicknss for singl layr drying wr kpt in a wir msh tray of 0.09 m 0.06 m siz dirctly ovr th digital wighing balanc of 6 kg capacity (TJ-6000, Scaltch, mad in India) with a last count of 0.1 g. Th khoa and air tmpraturs at diffrnt locations wr masurd by calibratd coppr-constantan thrmocoupls connctd to a tn channl digital tmpratur indicator with a last count of 0.1 o C. For masuring khoa surfac tmpratur four thrmocoupls wr placd at th sampl surfacs and thn thir avrag valu was considrd. To obtain accurat radings of th tmpraturs th thrmocoupls hav bn calibratd with rspct to th ZEAL thrmomtr (mad in England). Th rlativ humidity (γ or RH) and th tmpratur just abov th khoa surfac was masurd by a digital humidity/tmpratur mtr (Lutron-HT 3006, mad in Taiwan) with last counts of 0.1% RH and 0.1 o C. Th various dimnsions and th locations of masurd paramtrs ar shown in a schmatic of th xprimntal unit in Fig..

4 Intrnational Journal of Rnwabl Enrgy & Biofuls 4 Fig. : A Schmatic Viw of Exprimntal Unit Sampl Prparation and Exprimntal Obsrvations Th khoa sampl was prpard by following th traditional khoa making procss. Th frsh milk was hatd ovr an lctric hot plat in an aluminum opn pan. Th hating was stoppd and th product was allowd to cool to room tmpratur whn th dsird consistncy was obtaind. Thn cuboids shapd pics of khoa sampl of siz m3, m3, and m3 of total quantity of khoa as 100 g wr prpard with th hlp of woodn molds. For ach xprimnt prformd frsh sampl of khoa of th sam shap and mass was prpard by following th abov procdur. Th obsrvation tim intrval for khoa drying was takn an hour. Exprimnts wr prformd during th month of Octobr 01 at Guru Jambhshwar Univrsity of Scinc and Tchnology Hisar (9o5 5 N 75o45 55 E). Procdur For ach xprimnt th initial mass of khoa sampls was kpt constant as 100 g. Th khoa sampl was kpt in th wir msh tray dirctly ovr th digital wighing balanc. Th moistur vaporatd was calculatd by taking th diffrnc of mass of khoa btwn two conscutiv radings. Th hourly data for rat of moistur rmoval, khoa surfac tmpratur, rlativ humidity insid th grnhous, tmpratur just abov th khoa surfac, and ambint tmpratur hav bn rcordd. Th khoa sampls wr drid till no variation in its mass was rcordd. Thortical Considrations Thrmal Modling Tchniqu and Computation Th convctiv hat transfr cofficint for vaporation undr natural convction can b dtrmind by using th following rlations (Kumar t al., 01a): hc X n = C (Gr Pr ) Kv K n hc = v C (Gr Pr ) X Nu = (1) Th rat of hat utilizd to vaporat moistur is givn as (Kumar t al., 01a)

5 5 Intrnational Journal of Rnwabl Enrgy & Biofuls. Q = h c [ P( T ) γ P( T )] k () On substituting hc from Equation (1), Equation () bcoms K X. v = C GrPr Q n ( ) [ P( T ) γ P( T )] k (3) Th moistur vaporatd is dtrmind by dividing Equation (3) by th latnt hat of vaporization (λ) and multiplying th ara of khoa drying tray (A t) and tim intrval (t). C and xponnt n wr obtaind from th abov quations for natural convction grnhous drying mod. Th xprimntal constants (C & n) wr considrd furthr for valuating th valus of convctiv hat transfr cofficints from Equation (1). Th physical proprtis of humid air wr dtrmind by th xprssions givn in Appndix-A. Th mass transfr cofficint (h m ) wr calculatd from Equation (9) as givn blow (Kumar t al., 01b): h m = ( ) γ P( T ) P Tk T hc (9) k T (4) K Xλ v Lt [ P( T ) γ P( T )] A t = Z v k ( Gr Pr) n [ m / Z] = C (5) Taking th logarithm of both sids of Equation (5), ln[ m v / Z] lnc + nln t ( Gr Pr) = (6) This is th form of a linar quation, y = mx + c (7) Whr y =In[ mv /z], m = n, = In(Gr Pr) and c = In C, thus, C = c Valus of m and c in Equation (7) ar obtaind by using th simpl linar rgrssion mthod by using th following formula: N xy x y N x ( x) x y x N x ( x) m & = = xy c (8) Th xprimntal data givn in Tabls 1-3 for Tk, T, γ, and mv wr usd to dtrmin th valus of y and for diffrnt tim intrvals. Thn th constant Exprimntal Error Th xprimntal rror was valuatd in trms of prcnt uncrtainty (intrnal + xtrnal) for th mass of moistur vaporatd. Th following quation was usd for intrnal uncrtainty (Kumar 013): I 1 + σ + Kσ N U = ( σ ) N (10) Th prcnt intrnal uncrtainty was dtrmind by using th following xprssion: % intrnal uncrtainty = (U I/man of th total obsrvations) 100 (11) For xtrnal uncrtainty, th last counts of all th instrumnts usd in masuring th obsrvation data wr considrd. Rsults and Discussion Th xprimntal data rcordd for khoa drying undr natural convction grnhous mod for khoa pics with dimnsions m 3, m 3, and ar prsntd rspctivly in Tabls 1,, and 3 givn in Appndix-II. Th data givn in Tabls 1-3 (Appndix-II) wr usd to dtrmin th valus of th constant C and xponnt n in th Nusslt xprssion by simpl linar rgrssion o

6 Intrnational Journal of Rnwabl Enrgy & Biofuls 6 analysis. Thn th valus of ths constants wr considrd furthr for dtrmining th valus of th convctiv hat transfr cofficint by Equation (1). Aftr dtrmining th convctiv hat transfr cofficints, th mass transfr cofficints wr valuatd from Equation (9). Th valuatd valus of xprimntal constants (C & n), th convctiv hat transfr cofficints (h c ), and th mass transfr cofficints (h m ) during drying all th khoa sampls insid th grnhous undr natural convction mod ar summarizd in Tabl 4. Th rang of Grashof numbr and Prandtl numbr has also bn givn. Th product of Grashof and Prandtl numbrs has bn obsrvd as Gr Pr 10 7, which indicats that th ntir khoa drying falls within a laminar flow (Kumar t al., 011b). Tabl 4: Rsults of Evaluatd Paramtrs and th Convctiv Hat and Mass Transfr Cofficints for Khoa Pics C n Gr 10 5 Pr h c (W/m o C) h m (W/m o C) 1 st Sampl ( m 3 ) Drying, Octobr 10, nd Sampl ( m 3 ) Drying, Octobr 11, rd Sampl ( m 3 ) Drying, Octobr 1, It has bn obsrvd from Tabl 4 that th valus of convctiv hat and mass transfr cofficints ar mor for th khoa pic of dimnsion m 3. Th convctiv hat and mass transfr cofficints dcras with th incras in siz of th khoa pics which is du to dcras in rmoval of moistur contnts. Th hourly variations in th convctiv hat and mass transfr cofficints for ach sampl of th givn dimnsions ar illustratd in Figurs 3 and 4 rspctivly. Fig. 3: Variations in Convctiv Hat Transfr Cofficints vrsus Tim Fig. 4: Variations in Mass Transfr Cofficints vrsus Tim

7 7 Intrnational Journal of Rnwabl Enrgy & Biofuls From Figurs 3 & 4 it can b sn that th convctiv hat and mass transfr cofficints dcras with th progrssion of drying tim intrval for ach sampl of khoa. This is bcaus of dcras in moistur rmoval with th incras in drying tim intrval for a particular day. In ordr to mak a comparison, th avrag valus of convctiv hat and mass transfr cofficints hav also bn calculatd for ach dimnsions of th khoa sampl. Th avrag valus of convctiv hat transfr cofficints ar found.53 W/m o C, 1.95 W/m o C, and 1.59 W/m o C for th khoa pics of siz m 3, m 3, and m 3 rspctivly. Th avrag valu of convctiv hat transfr cofficints is obsrvd to incras by 59.1% by dcrasing th khoa sampl siz from m 3 to m 3. This could b du to incras in xposur of khoa surfac ara to solar radiations which causs incrasd moistur rmoval rat. Th avrag valu of th convctiv hat transfr cofficints has bn plottd in Figur 5. Fig. 5: Avrag Valu of th Convctiv Hat Transfr Cofficints for Each Sampl Th avrag valus of mass transfr cofficints ar found 60.6 W/m o C, 50.5 W/m o C, and W/m o C for th khoa pics of siz m 3, m 3, and m 3 rspctivly. Th avrag valu of mass transfr cofficints is obsrvd to incras by 51.69% by dcrasing th khoa sampl siz from m 3 to m 3. This could b du to incrasd moistur rmoval rat and thus th convctiv hat transfr cofficints valus with th dcras in siz of th givn khoa sampls. Th avrag valu of th mass transfr cofficints for all th khoa sampls is illustratd in Figur 6. Fig. 6: Avrag Valu of th Mass Transfr Cofficints for Each Sampl Th avrag valu of prcnt uncrtainty (intrnal + xtrnal) is valuatd as 33.54%. Thus th diffrnt valus of th convctiv hat and mass transfr cofficints wr found to b within th givn rang. To show th variability of convctiv hat and mass transfr cofficints valus from its tru valu SPSS softwar (vrsion 16.0) has bn usd which providd rror bars with 95% confidnc intrval. Error bars for th convctiv hat and mass transfr cofficints ar illustratd in Figur 7(a) and (b) rspctivly.

8 Intrnational Journal of Rnwabl Enrgy & Biofuls 8 Fig. 7: Error Bars for th Convctiv Hat and Mass Transfr Cofficints Conclusions Th ffct of th siz on th convctiv hat and mass transfr cofficints for khoa drying undr natural convction grnhous mod for a givn mass has bn dtrmind. Th convctiv hat and mass transfr cofficints ar mor for th pics of dimnsion m 3. Th convctiv hat and mass transfr cofficints dcras with th incras in siz of th khoa pics which could b du to dcras in rmoval of moistur contnts. Th avrag valus of convctiv hat and mass transfr cofficints ar found to incras from 1.59 W/m o C to.53 W/m o C and W/m o C to 60.6 W/m o C rspctivly for dcrasing th siz of khoa pics from m 3 to m 3. Th convctiv hat and mass transfr cofficints ar also obsrvd to dcras with th progrssion of drying tim intrval during ach day of drying. This is bcaus of dcras in moistur rmoval with th incras in drying tim intrval. Thus from th prsnt rsarch work it is infrrd that th siz of khoa pics plays a significant rol in its drying. This rsarch work would b highly usful in th dsign of an fficint grnhous dryr for khoa drying to its optimum storag moistur lvl. Nomnclatur A t Ara of wir msh tray, m C Exprimntal constant C v Spcific hat of humid air, J/kg o C g Acclration du to gravity, m/s Gr Grashof numbr = β g X 3 ρ v T / µ v h c Convctiv hat transfr cofficint, W/m o C h c, av Avrag convctiv hat transfr cofficint, W/m o C h m Mass transfr cofficint, W/m o C h m, av Avrag mass transfr cofficint, W/m o C K v Thrmal conductivity of humid air, W/m o C m v Mass vaporatd, kg n Exprimntal constant

9 9 Intrnational Journal of Rnwabl Enrgy & Biofuls N Numbr of obsrvations in ach st of tabls N o Numbr of sts N u Nusslt numbr = h c X / K v Pr Prandtl numbr = µ v C v / K v P(T ) Partial vapor prssur at tmpratur T, N/m. Q Rat of hat utilizd to vaporat moistur, J/m s T k Tmpratur of khoa surfac, o C T Tmpratur just abov th khoa surfac, o C t Tim, s T Effctiv tmpratur diffrnc, o C X Charactristic dimnsion, m Grk Symbols β Cofficint of volumtric xpansion (K -1 ) γ Rlativ humidity (%) λ Latnt hat of vaporization, J/kg µ v Dynamic viscosity of humid air, N s/m ρ v Dnsity of humid air, kg/m 3 σ Standard dviation Rfrncs Chavan, K. D. & Kulkarni, M. B. (006). "Solar Radiation- An Effctiv Approach for Khoa Prsrvation," Journal of Dairying, Foods and Hom Scincs, 5(3/4), Pp Condori, M., Echazu, R. & Saravia, L. (001). "Solar Drying of Swt Pppr and Garlic Using th Tunnl Grnhous Drir," Rnwabl Enrgy, (4), Pp Kumar, A. & Tiwari, G. N. (006). "Effct of Shap and Siz on Convctiv Mass Transfr Cofficint During Grnhous Drying of Jaggry," Journal of Food Enginring, 73, Pp Kumar, C. N., Kumarsan, G. & Saravanan, K. (1996). 'Incidnc of Moulds in Khoa,' Indian Journal of Dairy Scinc, 49, Pp Kumar, M. (013a). "Up-Gradation of Khoa Production and Prsrvation Tchnologis," S-JPSET, 3(1), Pp Kumar, M. (013b). "Forcd Convction Grnhous Papad Drying: An Exprimntal Study," Journal of Enginring Scinc and Tchnology, 8 (), Pp Kumar, M., Kasana, K. S., Kumar, S. & Prakash, O. (011a). 'Exprimntal Invstigation on Convctiv Hat Transfr Cofficint for Khoa Drying,' Intrnational Journal of Currnt Rsarch, 3(8), Pp Kumar, M., Khatak, P., Sahdv, R. K. & Prakash, O. (011b). "Th Effct of Opn Sun and Indoor Forcd Convction on Hat Transfr Cofficints for th Drying of Papad," Journal of Enrgy in Southrn Africa, (), Pp Kumar, M., Kumar, S., Prakash, O. & Kasana, K. S. (01b). "Evaporativ Hat Transfr Cofficints during Snsibl Hating of Milk," S-JPSET, 3(1), Pp Kumar, M., Prakash, O. & Kasana, K. S. (01a). "Exprimntal Invstigation on Natural Convctiv Hating of Milk," Journal of Food Procss Enginring, 35(5), Pp

10 Intrnational Journal of Rnwabl Enrgy & Biofuls 10 Kumar, M., Prakash, O., Kasana, K. S. & Dabur, R. S. (010). 'Tchnological Advancmnt in Khoa Making,' Indian Dairyman, 6(1), Pp Rajarajan, G., Kumar, C. N. & Elango, A., (007). "Distribution Pattrn of Moulds in Air and Khoa Sampls Collctd from Diffrnt Sctions of Khoa Plants," Indian Journal of Dairy Scinc, 60(), Pp Tiwari, G. N., Kumar, S. & Prakash, O. (004). "Evaluation of Convctiv Mass Transfr Cofficint during Drying of Jaggry," Journal of Food Enginring, 63, Pp Appndix-I Th following xprssions wr usd for dtrmining th valus of th physical proprtis of humid air (Kumar t al., 01a; Kumar 013): Cv = (1) T i Ti Ti 4 K v = T i (13) ρ = (14) v ( T ) i µ = (15) 8 v T i P ( T ) = xp ( ) (16) T i Whr T = ( T + T ) i k

11 11 Intrnational Journal of Rnwabl Enrgy & Biofuls Appndix-II Tabl 1: Khoa Drying Obsrvations for 1 st Sampl with Dimnsion m 3 on Octobr 10, 01 Sampl Tim T k T m v 10 3 (kg) γ (%) First am pm pm Tabl : Khoa Drying Obsrvations for nd Sampl with Dimnsion m 3 on Octobr 11, 01 Sampl Tim T k T m v 10 3 (kg) γ (%) Scond am pm pm Tabl 3: Khoa Drying Obsrvations for 3 rd Sampl with Dimnsion m 3 on Octobr 1, 01 Sampl Tim T k T m v 10 3 (kg) γ (%) Third am pm pm

FORCED CONVECTION GREENHOUSE PAPAD DRYING: AN EXPERIMENTAL STUDY

Journal of Enginring Scinc and Tchnology Vol. 8, No. 2 (2013) 177-189 School of Enginring, Taylor s Unirsity FORCED CONVECTION GREENHOUSE PAPAD DRYING: AN EXPERIMENTAL STUDY MAHESH KUMAR Mchanical Enginring