INVESTIGATION OF INDIRECT SOLAR DRYING OF GINGER RHIZOMES (ZINGIBER OFFICINALE): A COMPARATIVE STUDY

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1 Journal of Engineering Siene and ehnology Vol. 12, No. 7 (2017) Shool of Engineering, aylor s University INVESIGAION OF INDIREC SOLAR DRYING OF GINGER RHIZOMES (ZINGIBER OFFICINALE): A COMPARAIVE SUDY SUNIL K. SANSANIWAL 1, *, M. KUMAR 2, RAJNEESH 3, V. KUMAR 2 1 Centre for Energy and Environment, Malaviya National Institute of ehnology (NI), Jaipur , India 2 Mehanial Engineering Department, Guru Jambheshwar University of Siene & ehnology, Hisar , India 3 Mehanial Engineering Department, National Institute of ehnology (NI), Kurukshetra , India *Corresponding author: sansaniwal@gmail.om Abstrat In this ommuniation, an attempt has been made to investigate the drying kinetis of ginger rhizomes under natural and fored onvetion indiret solar drying modes. Various experiments were onduted during the months of Marh and April 2014 in the limate onditions of Hisar (29 o 5 5 N, 75 o E), India. he data thus obtained for natural and fored onvetion drying modes was used to determine the onstants C and n in the Nusselt number expression through linear regression analysis. Based on the values of these onstants, the onvetive heat transfer oeffiients for natural and fored onvetion drying modes were evaluated and reported to vary from 0.59 to 5.42 W/m 2 C and 2.52 to 6.33 W/m 2 C, respetively. As ompared to the natural onvetion drying mode, the average olletor effiieny and moisture removing rates were obtained to be higher under fored onvetion drying mode. Further, the experimental errors in terms of perent unertainty were also determined. Keywords: Solar drying, Indiret solar dryer, Ginger drying, Natural and fored onvetion heat transfer, Convetive heat transfer oeffiient, Moisture removing rate. 1. Introdution Ginger (Zingiber offiinale) is an important edible spie extensively grown worldwide. It is believed to be a native eonomi rop of South East Asia. India is the largest ginger produing ountry in the world. he ginger has many mediinal properties and thus widely used in Ayurveda and ooking appliations. he ginger mainly onsists of fibrous ontent, volatile oil and non-volatile ether extrat. It is onsumed as green ginger, dried ginger and in powder form. he drying of ginger is an important pratie for self-life enhanement and preservation and thus it is 1956

2 Investigation of Indiret Solar Drying of Ginger Rhizomes Nomenlatures A o, Area of olletor outlet, m 2 A t Area of the tray, m 2 C Constant v Speifi heat, J/kg C Gr Grashof number h Convetive heat transfer oeffiient, W/m 2 C h,avg Average onvetive heat transfer oeffiient, W/m 2 C I Solar irradiation, W/m 2 K v hermal ondutivity, W/m C M exp,i Experimental moisture ratio M initial Initial moisture removing rate, % dry basis M pre,i Predited moisture ratio n Number of drying model onstants, onstant N Number of observations N o Number of sets Nu Nusselt number P() Partial vapour pressure at temperature, N/m 2 Pr Prandtl number Q e Rate of heat utilized to evaporate moisture, J/m 2 s Q i Heat input, J/s Q o Heat output, J/s Re Reynolds number RH Relative humidity RD Resistane temperature detetor t ime interval, s Produt temperature, C e Produt surrounding temperature, C i, emperature at olletor inlet, C i, emperature at dryer inlet, C o, emperature at olletor outlet, C o,d emperature at dryer outlet, C s Average surfae temperature of absorber plate, C V i Average air veloity at olletor inlet, m/s V o Average air veloity at olletor outlet, m/s W d Weight of dry ginger, g W w Weight of wet ginger, g X Charateristis length, m Greek Symbols δ Standard deviation η Colletor effiieny, % λ Latent heat of vaporization, kj μ Dynami visosity, kg/m.s ρ v Density of humid air, kg/m 3 frequently dried through the traditional methods like open sun drying. Open sun drying is a heap and easy method of drying, however, this tehnique is suffering from various bottleneks suh as poor drying quality, larger drying time and the drying produt is vulnerable to the environmental debris, rain, animals, et. [1-3].

3 1958 S. K. Sansaniwal et al. Various eminent researhers have developed various drying methods worldwide to explore the most effetive method of drying. he fored onvetion solar drying is an emerging and widely used tehnique of produt drying. It involves the appliation of a fan to fore the air aross the drying unit to enhane the speifi moisture removing rate for effiient produt drying [4]. he produt quality obtained under fored onvetion indiret solar drying an meet the international market standards. Many researhers have studied the drying harateristis of ginger rhizomes using various types of solar drying systems. Some of them are: Mani et al. [5] evaluated the onvetive heat transfer oeffiient of ginger in open sun drying onditions under natural onvetion mode. he onvetive heat transfer oeffiient of ginger was reported to be 26.3 W/m 2 C. Similar study Akpinar and oraman [6] evaluated the onvetive heat transfer oeffiient of ginger to be ranging from 0.3 to 2.1 W/m 2 C in a ylone type onvetive dryer for air drying temperature of C and air veloity of m/s). he average moisture diffusivity and ativation energy were also examined and obtained to be varied from to m 2 /s and 13.3 to 22.7 kj/mol respetively. Prasad et al. [2] experimentally studied the ginger drying and ompared the results with solar hybrid dryer and open sun drying. he drying rate of hybrid dryer was reported to be higher than open sun drying. he overall drying effiieny of dryer was obtained to be 18% and 13% under summer and winter limati onditions respetively. Phounghandang et al. [7] developed the tray dryer, heat pump dehumidified dryer and mixed mode solar dryer for ginger drying. he best quality of ginger was obtained in heat pump dehumidified dryer and mixed mode solar dryer at 40 C and 62.8 C respetively without any pre-treatment of produt. he modified page model was reported best suitable for desribing the drying behaviour of ginger. Phounghandang and Saentaweesuk [8] studied the drying harateristis of ginger under tray and heat pump assisted dehumidifier inorporated with single and two stages drying. he two-stage heat pump dehumidifier redued the drying time by 59.3% at 40 C. Rajagopal et al. [9] experimentally studied the solar drying of opra (Coos nuifera) under fored onvetion drying mode and ompared the results with natural onvetion solar drying. he moisture ontent was observed to be redued from 52.3 to 8% for drying hamber temperature of C under natural and fored onvetion drying modes. Deshmukh et al. [10] investigated the drying harateristis of ginger in a mixed mode solar abinet dryer and redued its moisture from to 12.2% (db). As ompared to open sun drying, the solar abinet dryer was observed better in several aspets of produt quality, drying time and power requirement. he page model was reported to be most suitable to desribe the drying kinetis of ginger. haya et al. [11] designed a fored onvetion indiret solar dryer for three different airflow modes namely, liking mode, rossing mode and mixed mode. As ompared to liking mode, the drying temperature in rossing mode was observed higher by 8 C. For eah mode of airflow, the drying temperature obtained in drying hamber was reported to vary from 40 to 69 C on eah tray. Amedorme et al. [12] designed a fored onvetion indiret solar dryer for drying Moringa leaves (Moringa olivera) and redued its moisture from 80 to 10% (wb) with a drying effiieny of 25%. Deshmukh et al. [13] investigated the drying kinetis of untreated ginger for different air temperatures (45-65 C) and at a onstant air veloity of 1.8 m/s. he

4 Investigation of Indiret Solar Drying of Ginger Rhizomes page model was found suitable best for desribing the drying kinetis of ginger among various statistially evaluated models. Mehta et al. [14] presented the drying performane of ginger inside a fored onvetion indiret solar dryer omprising a thermal storage for late evening drying. he moisture ontent of ginger was observed to be redued from 84 to 9.63% in 36 hours with a dryer effiieny of 30%. Aggarwal [15] developed an indiret solar dryer inorporated with a solar ell for running fan and bulbs in olletor unit for air heating during loudy or night time drying of hill produts. he drying potential and quality were found to be improved. Azimi et al. [16] studied the drying behaviour of eggplant (Solanum melongena) by using an indiret solar dryer. For both indiret and open sun drying, the midilli and kuuk model was reported better to study the drying kinetis of eggplant. Loha et al. [17] developed a fored onvetion abinet dryer for single layer ginger drying at different air-drying temperatures (45 to 60 C) and at a onstant air veloity of 1.3 m/s. he moisture ontent of ginger was observed to be redued from 87 to 6% (wb). Besides, the drying auray of different models was also determined by using non-linear regression method. Singh [18] studied a fored onvetion indiret solar dryer for drying silk ooon. he moisture ontent was redued from 60 to 12% (wb) at drying temperature of air varying from 50 to 75 C. In ontrast of eletrial oven drying, an eletrial energy of 0.75 kwh/kg was saved. Further, the Wang and Singh model was validated in good agreement with the experimental data. Mohanraj and Chandrasekar [4] evaluated the drying performane of hili (Capsium annuum) inside a fored onvetion indiret solar dryer integrated with different sensible heat storage material. he moisture ontent of hilli was observed to be redued from 72.8 to 9.1% (wb) in 24 hours with dryer effiieny of 21% and speifi moisture extration rate of 0.87 kg/kwh. Jain et al. [19] ompared the drying performane of fored onvetion solar dryer with an eletrially operated mehanial dryer for drying groundnut (Arahis hypogaea), ginger (Zingiber offiinale) and garli (Allium sativum). he ost-benefit ratios obtained for solar and mehanial dryers were reported to be 1.56 and 1.18 respetively. Kumar [20] evaluated the performane of a fored onvetion indiret solar dryer for ginger drying and obtained the onvetive heat transfer (3.95 W/m 2 C) and evaporative heat transfer oeffiient (160.5 W/m 2 C). he average olletor effiieny of the dryer was reported to be 14.5%. However, the experimental error in terms of perentage unertainty was alulated to be 20.87%. Anum et al. [21] arried out the drying performane of onion (Allium epa), ginger (Zingiber offiinale) and abbage (Brassia oleraea) inside a hybrid solar dryer (olletor area 34% + drying area 64%). he moisture ontents of onion (88.5 to 10.3%), ginger (55.8 to 15.7%) and abbage (72.5 to 15.0%) were redued in the drying time varying from 10 to 16 hours. Solar energy was observed to be apable of removing more than 70% moisture of the produts. he overall effiieny of the dryer was obtained to be 42.8%. Sansaniwal and Kumar [22] investigated the drying harateristis of ginger in terms of onvetive heat transfer oeffiients and moisture removing rates, inside a natural onvetion indiret solar abinet dryer. he average onvetive heat transfer oeffiients were obtained to be varied from 0.59 to 5.42 W/m 2 C and reported to derease with inrease in mass of ginger samples and progression of drying days. However, the moisture removing rate was observed to inrease with inrease in

5 1960 S. K. Sansaniwal et al. mass of ginger samples while it was dereased with the progression of drying days. he average olletor effiieny of dryer was alulated to be varied from 15.0 to 16.1%. he modified page model was reported suitable for desribing the drying kinetis of ginger. Pandey et al. [23] developed a abinet solar dryer operated under natural and fored onvetion modes for drying ginger at different air-drying temperatures (28 to 58 C) and flow rates ( to m 3 /s). As ompared to natural onvetion, the faster drying rates were observed in solar (using blower) and mixed drying (using blower and heater) modes. he olletor effiieny was alulated to be varied from 10 to 23%. Further, the same dryer was also used for hili (Capsium annuum) drying. Borah et al. [24] ompared the effet of drying on texture and olour harateristis of ginger (Zingiber offiinale) and turmeri (Curuma longa) in four different drying methods namely, integrated drying system (IDS), fluidized bed dryer (FBD), eletrial oven (EO) and open sun drying (OSD). he minimum rushing strength of ginger ( g) was observed in IDS whereas the maximum value was obtained in OSD ( g). he olour loss values for ginger in IDS (34.8), FBD (38.1), EO (37.5) and OSD (32.2) were also obtained. On the other hand, the turmeri dried in IDS laimed maximum rushing strength ( g) while the minimum value was alulated for EO ( g). Similarly, the olour loss values for turmeri in IDS (52.7), FBD (61.0), EO (67.3) and OSD (58.2) were obtained. Among various drying methods, IDS was found best for produt drying with quality texture and olour of different spies. In the present study, an indiret solar dryer has been fabriated to study the drying harateristis of ginger under natural and fored onvetion drying modes in the meteorologial onditions of Hisar (29 o 09 N, 75 o 42 E), India. he performane evaluation of solar drying system was arried out in terms of olletor effiieny, moisture removing rates and onvetive heat transfer oeffiients for different drying modes and drying time intervals. 2. Material and methods 2.1. Experimental setup and instrumentation he shemati and pitorial view of fored onvetion indiret solar dryer fabriated in the meteorologial onditions of Hisar (29 o 09 N, 75 o 42 E), India is shown in Fig. 1. It was omprised of mainly two omponents namely, the flat plate olletor and drying hamber. he olletor unit having blak oated absorber plate made of galvanized iron was used for air heating. A transparent glass sheet of thikness 8 mm was loated over the olletor to ahieve the desired glazing effets attributed towards minimizing the thermal losses. Solar olletor unit (1.3 m 1 m) and drying hamber (0.41 m 0.45 m 0.53 m) were made thermally insulated with glass wool to minimize the energy losses. For fored onvetion drying mode, an indued fan (12 VDC) driven by the solar panel (1.195 m m m) was installed inside the dryer himney (0.11 m 0.11 m 0.26 m) mounted at the top of the drying hamber. he fresh air was suked in and got heated up inside the olletor unit and then allowed to flow into the drying hamber through PVC pipe as shown in Fig. 1. he aurately weighed ginger samples of initial moisture ontent 78% (db) were evenly distributed on the retangular shaped wire mesh tray (0.11 m 0.20

6 Investigation of Indiret Solar Drying of Ginger Rhizomes m). he heated drying air evaporated the moisture of given mass of ginger samples (i.e. 285 g). After predetermined time interval of 1 hour, the weight redution of the produt was reorded by using an eletroni weighing balane (model J 6000, apaity 6 kg, least ount of 0.1 g). A digital hygrometer (model H-315) was loated just above the produt surfae to monitor the relative humidity and produt surrounding temperature. he temperature of drying air was measured by using resistane temperature detetors (P-100 with auray ± 0.1 C) installed at different loations of olletor unit and drying hamber as shown in Fig. 1. he veloity of fresh air at the inlet of olletor unit was measured by using a digital anemometer (model AM-4201, least ount 0.1 m/s). A digital solar power meter (model WACO-206, least readability ± 10 W/m 2 ) was used to measure the intensity of solar radiation during the drying days. (a) Shemati view of indiret solar dryer. (b) Pitorial view of indiret solar dryer. Fig. 1. Shemati and pitorial view of indiret solar dryer [22].

7 1962 S. K. Sansaniwal et al Sample preparation he fresh ginger was purhased from the loal market of Hisar, India and washed thoroughly to remove the surfae dust. he lean ginger was hand peeled by knife and shaped ylindrially with diameter 1.7 m and length 3 m. he samples were aommodated in a retangular shaped wire mesh tray plaed on the weighing balane. he initial moisture ontent of fresh ginger was determined by using hot air oven drying method [25] Experimental proedure he experimental observations were reorded between 9:00 am to 6:00 pm in the month of Marh and April 2014 at Guru Jambheshwar University of Siene and ehnology, Hisar (29 o 09 N, 75 o 42 E), India. A fixed size retangular shaped wire mesh tray was used to aommodate the given mass of ginger samples (i.e. 285 g). he tray was kept on the digital eletroni balane mahine to determine the moisture removing rate (MRR) for eah drying hour. A digital hygrometer was kept just above the surfae of ginger samples faing its probe towards the sample surfae. Every time, it was started one minute before reording the observations. he temperature was measured by using the alibrated RD s installed at different loations in the drying system i.e. absorbing plate, dryer inlet, produt surfae and himney inlet and outlet temperature. A digital anemometer was used to measure the volume flow rate of air at the olletor and dryer inlet passage. he solar radiation data was olleted by using the digital solar power meter. he experimental observations were reorded at every 1 hour time interval and the measurement was disontinued when the onstant weight of ginger samples was ahieved. he differene in weight of fresh (or wet) sample and dried sample diretly gave the quantity of water evaporated during any drying time interval. he fresh and dried ginger samples are shown in Fig. 2. Fig. 2. Fresh and dried ginger samples. he data thus obtained from the measurements of ginger weight was used to study the drying kinetis of ginger in terms of moisture removing rate and onvetive heat transfer oeffiient. he moisture removing rate was expressed on dry basis. herefore, the initial moisture removing rate on % dry basis an be alulated by using Eq. (1) [22]: M initial WwWd 100 (1) W d

8 Investigation of Indiret Solar Drying of Ginger Rhizomes heoretial onsiderations 3.1. hermal modelling he onvetive heat transfer oeffiients for evaporation were determined by using the following expression [26, 27]: hx Nu C Gr Pr n (2) K v he rate of heat utilized to evaporate the moisture is given in the following forms [26, 27]: Q 0.016h P P e e On substituting h from Eq. (2), Eq. (3) may be re-written as follows [26, 27]: Kv Q C Gr Pr n P P X e e he moisture evaporated during drying an be determined by dividing Eq. (4) with the latent heat of vaporization () and multiplying it with the area of tray (A t ) and drying time interval (t) given as follows [26, 27]: Qe K mev At t C Gr P P e At t X Let, v n Pr K v P P e A t t Z X Substitute the value of Z in Eq. (5) will give the following expression [26, 27]: m ev C Gr Pr n Z (6) aking logarithm on both sides of Eq. (6), m ev ln ln C nln Gr Pr Z his is in the form of a linear equation and may be analogous as [26, 27]: y mx C (8) where mev y ln, Z m = n and = ln C For natural onvetion analysis [26, 27]: x ln Gr Pr and for fored onvetion analysis [26, 27]: x ln Re Pr (3) (4) (5) (7)

9 1964 S. K. Sansaniwal et al. he values of onstant n and C in Eq. (8) were obtained by using the simple linear regression method given as follows [26, 27]: N X Y X Y m 2 N X X and 2 2 NX 0 X 0 X Y X X Y (9) (10) 3.2. hermal properties of air he physial properties of humid air were evaluated by using the following expressions [27]: C (11) K K v i i i 4 v (12) i v i (13) 5 8 v (14) i 5144 P ( ) exp i where 2 i e he physial properties of humid air were used to determine the values of Grashof number (Gr) and Prandtl number (Pr). Whereas the values of onstants C and n used in Nusselt number expression were alulated by using the linear regression analysis. Based on the values of these onstants, the values of onvetive heat transfer oeffiient were evaluated from Eq. (2) at the inrement of one hour of observation. (15) 3.3. Solar flat plate olletor effiieny he heat gained by drying air or the total heat at the olletor outlet is given by the following expression [28]: o o o, v o, i, v Q V A C (16) whereas the total amount of heat reeived by solar olletor is given as follows [28]: Q I A (17) i herefore, the effiieny of solar flat plate olletor an be determined by dividing Eqs. (16) and (17), i.e., Q o (18) Qi

10 Investigation of Indiret Solar Drying of Ginger Rhizomes Experimental error he experimental errors were also determined in terms of perent unertainty for the mass evaporated during the drying proess. So, the internal unertainty was alulated by using the following expressions [29]: % unertainity = U mean of the total observations 100 (19) where N U (20) N 4. Result and disussion o he given mass of ginger samples having the ylindrial shape (diameter 1.7 m, length 3 m) was dried under natural and fored onvetion drying mode. he drying tests of given mass of ginger samples were run by using a fixed size wire mesh tray of retangular shape. he olletor effiieny, moisture removing rate (%, db) and onvetive heat transfer oeffiients were evaluated for the given mass of ginger samples under natural and fored onvetion drying modes as given in able 1 to 5. ime able 1. Observations for natural onvetion indiret solar drying of given mass of ginger samples on first day of drying. s i, o, I e Mass M evp h (W/m 2 C) 09: : : : : : : : : : ime able 2. Observations for natural onvetion indiret solar drying of given mass of ginger samples on seond day of drying. s i, o, I e Mass M evp h (W/m 2 C) 09: : : : : : : : : :

11 1966 S. K. Sansaniwal et al. ime able 3. Observations for natural onvetion indiret solar drying of given mass of ginger samples on third day of drying. s i, o, I e Mass M evp h (W/m 2 C) 09: : : : : : : : : : ime able 4. Observations for fored onvetion indiret solar drying of given mass of ginger samples on first day of drying. s i, o, I e Mass M evp h (W/m 2 C) 09: : : : : : : : : : able 5. Observations for fored onvetion indiret solar drying of given mass of ginger samples on seond day of drying. ime s i, o, I e Mass M evp h (W/m 2 C) 09: : : : : : : : : : he data given in able 1 to 5 was used to determine the olletor effiieny, moisture removing rate and onvetive heat transfer oeffiients for the given

12 Investigation of Indiret Solar Drying of Ginger Rhizomes mass of ginger samples under natural and fored onvetion drying modes for the drying time interval of 1 hour on different days of drying as shown in Figs. 3 to 5. he effiieny of solar flat plate olletor is a measure of air heating apability during the drying time. It highly depends on the veloity of air passing through the olletor unit. When the ambient air make ontat with hot absorber plate, it gets heated up and losses its density. hus, the air flow in natural onvetion drying mode takes plae due to the buoyany effets. On the other hand, in fored onvetion drying mode, an external aid is required to push the air inside the olletor unit for faster heating of air. his an be ahieved by using either a blower at the olletor inlet passage or an indued fan at the olletor outlet. In the present study, an indued fan was installed inside the dryer himney mounted at the top of the drying hamber. As ompared to natural onvetion drying mode, the effiieny of air heating in fored onvetion drying mode is observed more due to the laminar flow of air at onstant speed. From Fig. 3, the olletor effiieny obtained under fored onvetion drying mode is high and reported to lie in between to 33.92% whereas it is observed less under natural onvetion drying mode and obtained to be ranging from to 16.14%. Fig. 3. Variations in the olletor effiieny with respet to time under natural and fored onvetion indiret solar drying modes of given mass of ginger samples. he moisture removing rate is the rate by whih any produt losses its water ontent during the drying time. It highly depends on the moisture present in the given mass of produt along with the ondition of drying air suh as temperature, humidity, flow rate et. In general, the moisture present in given mass of ginger samples exists in two forms namely, free moisture and bound moisture. he free moisture is present in the outer resins of ginger whih an be easily evaporated by optimum heated air. Whereas the bound moisture takes plae in the internal ells of ginger mass under apillary ation whih takes time for evaporation and leads to the higher drying time. For faster drying of given ginger mass, a high volume of heated air is required to evaporate the bound moisture [30, 31]. herefore, the fored onvetion drying mode an fulfil suh requirements of drying air and substantially redues the produt drying time. From Fig. 4, it an be observed that the fored onvetion drying of given mass of ginger samples ompletes in two days while the same proess requires one additional day for its

13 1968 S. K. Sansaniwal et al. ompletion under natural onvetion drying mode. Further, it may also be onluded that the moisture removing rates during the initial drying days are more and dereases signifiantly with the progression of drying days (i.e. from first day of drying to next day of drying). his fat may be explained due to the attainment of equilibrium (or onstant) weight by given mass of ginger samples at the ompletion of drying proess. Fig. 4. Variations in moisture removing rate (%, db) with respet to time under natural and fored onvetion indiret solar drying modes of given mass of ginger samples. From Fig. 5, it has been observed that the value of onvetive heat transfer oeffiients dereases with the progression of drying days. his derease is due to ontinuous redution in the moisture removal rate from first day to next day of drying as disussed earlier in the previous setion. Due to faster heating proess, the values of onvetive heat transfer oeffiients are reported higher under fored onvetion drying mode and observed to vary from 2.52 to 6.33 W/m 2 C against the variation of 0.59 to 5.42 W/m 2 C for natural onvetion drying mode. Further, the values of onvetive heat transfer oeffiient are also observed to be depending on the mass of fresh ginger samples and presumed that the drying kinetis is highly dependent on the given mass of ginger samples. Fig. 5. Variations in onvetive heat transfer oeffiients with respet to time under natural and fored onvetion indiret solar drying modes of given mass of ginger samples.

14 Investigation of Indiret Solar Drying of Ginger Rhizomes Conlusion In the present study, an indiret solar dryer has been designed and developed to investigate the drying kinetis of ginger in terms of onvetive heat transfer oeffiients, moisture removing rates and olletor effiieny under natural and fored onvetion drying modes. he data obtained through the experimental observations was used to determine the onstants C and n in Nusselt number expression using the simple linear regression analysis. Based on these onstants, the onvetive heat transfer oeffiients were evaluated and reported to be higher under fored onvetion drying mode. he onvetive heat transfer oeffiients obtained under natural and fored onvetion drying modes were reported to vary from 0.59 to 5.42 W/m 2 C and 2.52 to 6.33 W/m 2 C respetively. Besides, the moisture removing rates were also obtained to be higher under fored onvetion drying mode whih ultimately redued the produt drying time. Further, the average olletor effiieny under natural onvetion drying mode was alulated to be varied from to 16.14%. However, it was obtained to be higher in fored onvetion drying mode and found to lie in between to 33.92%, respetively. herefore, the fored onvetion drying method was reommended for the drying of produts having high moisture ontents and requires either immediate onsumption or quik preservation. Moreover, the experimental errors evaluated for the present study were found to be %. his researh work would be useful in the optimum designing of solar dryers for drying of various produts suh as vegetables, fruits, rops, herbals et. Aknowledgment One of the authors (S. K. Sansaniwal) would like to onvey his sinere thanks to Guru Jambheshwar University of Siene and ehnology, Hisar for providing all the laboratory failities and tehnial assistane to arry out this investigation suessfully. he fruitful suggestions and omments raised by the referees of the paper enabling us to modify it in the present form are also duly aknowledged. Referenes 1. Jayashree, E.; Visvanathan, R.; and Zahariah,.J. (2014). Quality of dry ginger (Zingiber Offiinale) by different drying methods. Journal of Food Siene and ehnology, 51(11), Prasad, J.; Prasad, A.; and Vijay, V.K. (2006). Studies on the drying harateristis of zingiber offiinale under open sun and solar biomass (Hybrid drying). International Journal of Green Energy, 3(1), Kumar, M.; Sansaniwal, S.K.; and Khatak, P. (2016). Progress in solar dryers for drying various ommodities. Renewable and Sustainable Energy Reviews, 55, Mohanraj, M.; and Chandrasekar, P. (2009). Performane of a fored onvetion solar drier integrated with gravel as heat storage material for hilli drying. Journal of Engineering Siene and ehnology (JESEC), 4(3), Mani, M.; Kaew-on, J.; and Boonma, P. (2008). Determination of onvetive heat transfer oeffiient of ginger drying under natural onvetion. Retrieved

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