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Solar Energy 99 (2014) 47–54

Performance analysis of solar drying system for red chili

Ahmad Fudholi a,⇑, Kamaruzzaman Sopian a, Mohammad H. Yazdi a,Mohd Hafidz Ruslan a, Mohamed Gabbasa a, Hussein A. Kazem b

a Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor, Malaysiab Faculty of Engineering-Sohar University, PO Box 44, Sohar PCI 311, Oman

Received 24 July 2013; received in revised form 30 September 2013; accepted 17 October 2013Available online 26 November 2013

Communicated by: Associate Editor I. Farkas

Abstract

This study is concerned with performance analysis of solar drying system for red chili. Red chili was dried to final moisture content of10% w.b from 80% w.b in 33 h using this system. In this study, energy and exergy analyses of the solar drying process were performed forred chili. Using the first law of thermodynamics, energy analysis was carried out to estimate the useful energy gained from the collectors.However, exergy analysis during solar drying process was estimated by applying the second law of thermodynamics. The specific energyconsumption (SEC) was 5.26 kW h/kg. The values of evaporative capacity and improvement potential were from 0.13 kg/s to 2.36 kg/sand 0 W to 135 W, respectively. The efficiencies of the solar collector, drying system, pick-up, and exergy were 28%, 13%, 45%, and 57%respectively, at an average solar radiation of 420 W/m2 and a mass flow rate of 0.07 kg/s.� 2013 Elsevier Ltd. All rights reserved.

Keywords: Energy analysis; Exergy analysis; Improvement potential; Specific energy consumption; Solar drying; Red chili

1. Introduction

Red chili is traditionally dried directly under the opensun. Open sun drying requires a large open space and longdrying times. Although this traditional method requiresonly a small investment, open sun drying is highly depen-dent on the availability of sunshine and is susceptible tocontamination from foreign materials (dust and sand) aswell as insect and fungal infestations, which thrive in moistconditions. Such contaminations render the products unus-able. Most agricultural and marine products require dryingto preserve the quality of the final product, but open sundrying results in low-quality products. Therefore, solardrying has become one of the most attractive and promis-ing applications of solar energy systems as an alternative toopen sun drying.

0038-092X/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.solener.2013.10.019

⇑ Corresponding author. Tel.: +60 132924765.E-mail address: a.fudholi@gmail.com (A. Fudholi).

Several studies reported on the solar drying systems foragricultural and marine products (Bala and Janjai, 2012,2005; Belessiotis and Delyannis, 2011; Fudholi et al.,2010; Bala et al., 2005; Bala and Mondal, 2001). Severalstudies specifically investigated solar drying systems forred chili. Janjai et al. (2011) reported the use of a solargreenhouse dryer for the commercial drying of 1000 kg offruits or vegetables in Champasak, Lao People’s Demo-cratic Republic. The researchers also reported the installa-tion of six units of greenhouse dryers at agro-industrialsites in Thailand between 2008 and 2009. Lhendup (2005)conducted a technical and economic performance analysisof solar drying red chili in Bhutan. Hossain and Bala(2007) studied a mixed-mode forced convection solar tun-nel dryer for drying red chili in Bangladesh. Hossainet al. (2005) then used a simulation model to evaluate thetechnical and economical performance of the solar tunneldryer.

Nomenclature

Ac collector area (m2)C specific heat of air (J kg�1 �C�1)E evaporative capacity (kg/h)Ex exergy (W)G solar radiation (W/m2)H relative humidity (%)h0 absolute humidity of air leaving the drying

chamber (%)hi absolute humidity of air entering the drying

chamber (%)has absolute humidity of the air entering the dryer

at the point of adiabatic saturation (%)IP improvement potential (W)L latent heat of vaporisation of water at exit air

temperature (J/kg)M moisture content (%)Mf final moisture content fraction on wet basis (%)Mi initial moisture content fraction on wet basis

(%)mo initial weight of product (kg)_m air mass flow rate (kg/s)P power (W)S saving in drying time (%)SEC specific energy consumption (kW h/kg)SMER specific moisture extraction rate (kg/kW h)

T temperature (�C)t drying time (h)tOS time taken for drying the product in open sun

(h)tSD time taken for drying in solar drying (h)v volumetric airflow (m3/s)W mass of water evaporated from the product (kg)Xa ambient absolute humidity (%)Xd dryer outlet absolute humidity (%)XR uncertainty in resultsx1,x2,xn uncertainty in the independent variablesq density of air (kg/m3)g efficiency (%)

Subscripts

a ambientc chamberdci inflow of drying chamberdco outflow of drying chamberf fanh heateri inleto outlett total

48 A. Fudholi et al. / Solar Energy 99 (2014) 47–54

Exergy is defined as the maximum amount of work thatcan be produced by a system or a flow of matter or energyto reach equilibrium with a reference environment. Energyand exergy analyses of the drying process should beperformed to determine the energy interactions and ther-modynamic behavior of drying air throughout a dryingchamber. Exergy analysis allows for a more efficient energyresource use because the analysis enables the determinationof the locations, types, and true magnitudes of the losses.Therefore, exergy analyses can reveal where and by howmuch designing more efficient thermal systems is possibleby reducing the sources of existing inefficiencies. Increasedefficiency can often contribute in an making these pro-cesses environmentally friendly by directly reducing theirreversibilities (where exergy is destroyed) that mightotherwise occur. Therefore, exergy is one of the mostpowerful tools in providing optimum drying conditions.In the past few decades, thermodynamic analysis, particu-larly exergy analysis, has become an essential tool in thesystem design, analysis, and optimization of a thermalsystem (Chowdhury et al., 2011). The energy analysismethod is widely used in evaluating the performance ofthe food drying system, but studies on exergy analysisremain relatively limited.

Several studies were conducted on the exergy analyses offood drying. Midili and Kucuk (2003) performed energy

and exergy analyses of the drying process of shelled andunshelled pistachios by using a solar drying cabinet.Akpinar (2004) performed energy and exergy analyses indrying red pepper slices by using a convective type dryer.Dincer and Sahin (2004) developed a new model for thethermodynamic analysis of the drying process. Akpinaret al. (2006) conducted first and second law analyses ofthe thermodynamics of the pumpkin drying process. Colakand Hepbasli (2007) performed exergy analysis on the thinlayer of a green olive in a tray dryer. Corzo et al. (2008)performed energy and exergy analyses of the thin layerdrying of coroba slices at three different air temperatures.Ozgener and Ozgener (2009) examined the exergy variationduring the drying process in a passively heated solargreenhouse. Akpinar (2010) performed energy and exergyanalyses of the solar drying process of mint leaves. Exergyefficiencies were derived as a function of the drying timeand temperature of the drying air. Akpinar (2011) reportedon the energy and exergy analyses of the solar drying ofparsley leaves and the variations of the exergy inflow,outflow, and loss with the drying time. Chowdhury et al.(2011) also reported that exergy inflow, outflow, andexergy loss follow similar pattern. The variations in theexergy inflow, outflow, and loss in solar drying are causedby variations in daily solar radiation. However, no studyhas reported on the exergy analysis of the solar drying

A. Fudholi et al. / Solar Energy 99 (2014) 47–54 49

system for red chili. Therefore, the main objective of thisstudy is to perform energy and exergy analyses of the solardrying system for red chili.

2. Material and methods

Samples of chili (C. annuum L.) were obtained from thefarm of Universiti Kebangsaan Malaysia, Selangor,Malaysia. A total of 0.4 kg of fresh red chili was used ineach experiment. About 0.4 kg of red chili were takenand dried in an oven at a temperature of 120 ± 1 �C untila constant weight was reached. The initial and final massesof the red chili were recorded using an electronic balance.The procedure was repeated at 1 h intervals until the endof the drying process. The average moisture content was80.2% (w.b).

The solar drying system was installed in the SolarEnergy Research Park, Solar Energy Research Institute,Universiti Kebangsaan Malaysia. The solar drying systemconsists of a finned double-pass solar collector, a blower,and a flat bed drying chamber. The drying system isclassified as a forced convection indirect type. A schematicdiagram of the solar dryer is shown in Fig. 1. The widthand length of the collector are 1.2 and 2.4 m, respectively.The solar collector array consists of four solar collectors.The total area of the collector is 11.52 m2. The collectorhas a glass cover, and the sides are insulated and paintedblack on an aluminum absorber plate. The upper channeldepth is 3.5 cm, and the lower depth is 7 cm. The bottomand sides of the collector are insulated with 2.5 cm thickfiberglass wool to minimize heat losses. Air initially entersthe collector through the first channel formed by the glassthat covers the absorber plate and then through the secondchannel formed by the back plate and the finned absorberplate. The drying chamber is 2.4 m in length, 1.0 m inwidth, and 0.6 m in height.

The drying process was conducted from 9:00 AM to5:00 PM. The solar dryer was shut down at night. Thedrying process was continued until the next day, and theprocess was repeated until the required equilibrium mois-ture content was reached. For the experiments, the solardryer was loaded to its full capacity of 40 kg of red chili,which was divided and equally distributed on eight trays.

Air inlet

Double-pass solar collector with finned absorber

Drying chamber

Blower

Auxiliary heater

15o

Fig. 1. The schematic of solar drying system.

The red chili was also placed in a small tray positioned atthe center of the dryer to determine the moisture loss byusing a Camry R9364 digital electronic balance thatwas placed on the top center of the drying chamber. Thebalance has an accuracy of 0.01 g. The air temperature(ambient, collector inlet, and collector outlet tempera-tures), radiation intensity, and air velocity were measured.The air temperatures before entering, inside, and outsidethe dryer chamber were also measured. Relative humiditysensors were installed in the inlet, middle, and outletsections of the drying chamber. An air flow DTA 4000anemometer was used to determine the air flow velocityin the solar collector. T-type thermocouples and a Li-200pyranometer with accuracies of 0.018 �C and 1%, respec-tively, were used. During the drying process, the tempera-ture and relative humidity in the solar dryer wererecorded at 1 min intervals by using the ADAM DataAcquisition System, which is connected to a computer.An experimental uncertainty analysis was also performed(Fudholi et al., 2013a). The uncertainty estimation wascalculated using (El-Sebaii et al., 2011; Akpinar, 2010):

X R ¼ ½ðx1Þ2 þ ðx2Þ2 þ . . . ðxnÞ2�1=2 ð1Þ

The schematic illustration of the drying system with theinput and output terms is shown in Fig. 2. The figure showsthe four major points to consider, namely, (1) input of dry-ing air to the drying chamber to dry the products, (2) inputof moist products to be dried in the chamber, (3) output ofthe moist air after removing the evaporated moisture fromthe products, and (4) output of the dried products. Themoisture contents are reduced to the level required for eachcommodity of the product. In the analysis, the thermody-namic balance equations for the mass, energy, entropy,and exergy of the drying system as a control volume arefirst written for the product, air, and moisture content inthe air (Fig. 2). Comprehensive details of such an analysiswere provided by Dincer (2011). Using exergy calculationsof drying process, Exergy Band Diagram is shown inFig. 3.

3. Performances analyses

The performances of solar drying systems for red chilihave been reported by Fudholi et al. (2013a), such as

Fig. 2. The schematic illustration of the drying system (Dincer, 2011).

Drying chamber

Exdci

[12.7-505.7 W]

Exdco

[11.7-489.7 W] Exloss

[1-238.4 W]

Fig. 3. Band diagram of exergy balance.

50 A. Fudholi et al. / Solar Energy 99 (2014) 47–54

saving in drying time (S), specific moisture extraction rate(SMER), and evaporative capacity (E). Fudholi et al.(2013a) evaluated the time savings when drying chili bycomparing solar and open sun drying. The performanceof solar drying compared with that of open sun dryingwas calculated using the following equation:

S ¼ tOS � tSD

tOS� 100 ð2Þ

The specific moisture extraction rate (SMER), which isthe energy required to remove 1 kg of water, was calculatedusing Eq. (3), as reported by Fudholi et al. (2013a):

SMER ¼ WP t

ð3Þ

In this study, the specific energy consumption (SEC) ofthe solar drying system was obtained using Eq. (4), asreported by Fudholi et al. (2012):

SEC ¼ P t

Wð4Þ

Evaporative capacity was used as a performance mea-sure for solar dryers. The weight of the water that can beextracted by air flow from the products to be dried wasdefined by Jannot and Coulibaly (1998) as:

E ¼ _mðX d � X aÞ ð5Þ

3.1. Energy analysis

The useful energy gained from the collector was calcu-lated using the magnitude of solar radiation. The thermalefficiency of a solar collector is the ratio of useful heatgained to the solar radiation incident on the plane of thecollector. This thermal efficiency is expressed as (Fudholiet al., 2013a,b,c):

gc ¼Q

AcG¼ _mCðT o � T iÞ

AcG� 100% ð6Þ

System drying efficiency is defined as the ratio of theenergy required to evaporate moisture to the heat suppliedto the dryer. The heat supplied to the dryer for the solarcollector is the solar radiation incident on the solar

collector. System drying efficiency is a measure of the over-all effectiveness of a drying system. The system drying effi-ciency can be obtained using the following equation:

gd ¼WL

AcGþ P f þ P hð7Þ

Pick-up efficiency is useful for evaluating the actualevaporation of moisture from the product inside the drier.It is a direct measure of how efficiently the capacity of airto absorb moisture is used. The pick-up efficiency is definedas the ratio of the moisture picked up by the air in the dry-ing chamber to the theoretical capacity of the air to absorbmoisture. Mathematically it can be expressed by the fol-lowing equation (Banout et al., 2011):

gp ¼h0 � hi

has � hi¼ W

vqtðhas � hiÞð8Þ

Which the mass of water removed (W) from a wet prod-uct can be calculated:

W ¼ moðMi �Mf Þ100�Mf

ð9Þ

3.2. Exergy analysis

The exergy values were calculated using the characteris-tics of the working medium from the first-law energy bal-ance. For this purpose, the general form of the exergyequation applicable for a steady flow system can beexpressed as (Akbulut and Durmus, 2010):

Ex ¼ _mC ðT � T aÞ � T a lnTT a

� �ð10Þ

For exergy inflow of drying chamber:

Exdci ¼ _mC ðT dci � T aÞ � T a lnT dci

T a

� �ð11Þ

For exergy outflow of drying chamber:

Exdco ¼ _mC ðT dco � T aÞ � T a lnT dco

T a

� �ð12Þ

However, during the solar drying process, the exergylosses are determined using the following equation:

Exloss ¼ Exdci � Exdco ð13Þ

The exergy efficiency can be defined as the ratio ofenergy use (investment) in the drying of the product toexergy of the drying air supplied to the system. However,it is explained as ratio of exergy outflow to exergy inflowfor drying chamber. Considering this definition, the exergyefficiencies of drying chamber can be determined. Thus, thegeneral form of exergy efficiency is written as (Akpinar,2010; Akbulut and Durmus, 2010):

gEx ¼Exdco

Exdci¼ 1� Exloss

Exdcið14Þ

A. Fudholi et al. / Solar Energy 99 (2014) 47–54 51

The maximum improvement in the exergy efficiency fora system or process is obviously achieved when the exergyloss (Exloss) is minimized. The concept of an exergetic“improvement potential” (IP) can be considered as a usefultool in analyzing systems or processes more effectively. TheIP of a system or process is given by (Fudholi et al., 2013b;Akpinar, 2010):

IP ¼ ð1� gExÞExloss ð15Þ

4. Results and discussion

During the 5 d (33 h) experimentation period, the dailymean values of the drying chamber air temperature, dryingchamber relative humidity, and solar radiation rangedfrom 28 �C to 55 �C, 18–74%, and 104 W/m2 to 820 W/m2,respectively, with corresponding average values of 45 �C,30%, and 420 W/m2, as shown in Fig. 4. The dryingtemperature and relative humidity under solar drying con-tinuously varied with increasing drying time. The resultsrevealed that the drying temperature in solar drying wasgreater than the ambient temperature, whereas the relativehumidity in this system was lower than the ambient relativehumidity. The drying temperature and relative humidityvalues also significantly differed at 15 �C and 30%, respec-tively, during the 33 h drying period.

The efficiency of the collector ranged from 11% to 74%with an average value of 28% at a drying air flow rate of0.07 kg/s. The thermal efficiency rates during the 5 d ofdrying are shown in Fig. 5, which illustrates the increasein the thermal efficiency of the collector at a low solar radi-ation. During the solar drying process, the useful energygained from the collector ranged from 399 W to 1978 W,as shown in Fig. 5.

The results of the drying curve of the red chili via opensun and solar drying are shown in Fig. 6. The drying curverevealed the profile change in the moisture content (M)

0

200

400

600

800

1000

9:30

11:30

13:30

15:30 9:3

011

:3013

:3015

:30 9:30

11

Time of the

Sola

r rad

iatio

n (W

/m2 )

Solar radiationAmbient temperatureAmbient relative humidity

Fig. 4. Temperatures (ambient and chamber), relative humidity of chamber, am20, 2012.

versus drying time (t). The final drying levels of the red chiliwere obtained after 33 h in the solar drying system but tookabout 65 h in the open sun drying system. A 49% saving indrying time was obtained for solar drying compared withopen sun drying. Fig. 6 clearly indicates that the dryingrate in the solar drying system under forced convectioncan be much higher than that of the open sun drying, asreported by Akpinar (2010).

The drying time obtained in the present study wascompared with the results obtained in previous studies.Fudholi et al. (2010) reported that the moisture contentof fresh chili decreased from 80% (w.b) to 5% (w.b) in48 h of solar drying. Banout et al. (2011) compared theuse of a double-pass solar dryer with a cabinet dryervia open sun drying of red chili in Central Vietnam.Drying 40 kg of red chili by using a double-pass solardryer reduced the moisture content from 90% (w.b) to10% (w.b) in 32 h (including nights). Mohanraj andChandrasekar (2009) reported that 40 kg of chili by usinga forced convection solar drier integrated with gravel asheat storage material reduced the moisture content from73% (w.b) to 9% (w.b) in 24 h with drying efficiency of21%. Janjai et al. (2011) reported the use of a solar green-house dryer to dry 300 kg of red chili. In this dryer, themoisture content was reduced from 75% to 15% in 3 d.Kaewkiew et al. (2012) investigated the performance ofa large-scale greenhouse dryer to dry red chili in Thai-land. Drying 500 kg of red chili by using this dryerreduced the moisture content from 74% to 9% in 3 d.Kaleemullah and Kailappan (2005) studied the dryingkinetics of red chili in a rotary dryer. They conducted dry-ing experiments at a temperature range of 50 �C to 65 �Cfor 19 h to 33 h and observed that the quality of dried redchili and drying time increased at a low drying tempera-ture. By contrast, the quality of dried red chili and dryingtime decreased with increasing drying temperature. How-ever, Kaleemullah and Kailappan (2005) concluded that

:3013

:3015

:30 9:30

11:30

13:30

10:30

12:30

day

0

20

40

60

80

100

Tem

pera

ture

, Hum

idity

(o C

, %)

Chamber temperatureChaber humidity

bient relative humidity, and solar radiation from March 16, 2012 to March

0200400600800

100012001400160018002000

9:30

11:30

13:30

15:30 9:3

011

:3013

:3015

:30 9:30

11:30

13:30

15:30 9:3

011

:3013

:3010

:3012

:30

Time of the day

Ener

gy g

aine

d fr

om th

e co

llect

or,

Sola

r rad

iatio

n (W

, W/m

2 )

0

20

40

60

80

100

Ther

mal

effi

cien

cy (%

)

Solar radiation Energy gained from the collector Thermal efficiency

Fig. 5. Energy gained from the collector, thermal efficiency and solar radiation with drying time from March 16, 2012 to March 20, 2012.

0

10

20

30

40

50

60

70

80

90

0 8 16 24 32 40 48 56 64 72

Drying time (h)

Moi

stur

e co

nten

t, w

b (%

)

Solar dryingOpen sun drying

Fig. 6. Moisture content (wet basis) variation with drying time.

52 A. Fudholi et al. / Solar Energy 99 (2014) 47–54

the performance of red chili dried at 55 �C was the best interms of drying time and quality of dried red chili.

The experimental results showed that solar drying 40 kgof dry red chili without auxiliary heating to reduce themoisture content of 80–10% within 33 h (5 d of drying).Adding L = 2407 kJ/kg (668 W h/kg), t = 33 h, and

0

100

200

300

400

500

600

9:30

11:30

13:30

15:30 9:3

011

:3013

:3015

:30 9:30

1Time of t

Impr

ovem

ent p

oten

tial,

Exer

gy (W

, W))

Exergy inflow ExImprovement potential Ex

Fig. 7. Improvement potential, exergy efficiency, and exergie

S = 420 W/m2 to Eq. (7) yielded a drying efficiency of12.7%. Eq. (8) and a psychometric chart determined thepick-up efficiency to be 44.9%. The specific energy con-sumption (SEC) of 5.26 kW h/kg was calculated accordingto Eq. (4). The evaporative capacity, which ranged from0.13 kg/h to 2.36 kg/h with an average of 0.97 kg/h, was

1:30

13:30

15:30 9:3

011

:3013

:3010

:3012

:30

he day

0

20

40

60

80

100

Exer

gy e

ffici

ency

(%)

ergy outflow Exergy lossergy efficiency

s (inflow, outflow, and loss) variation with drying time.

Table 1Performance evaluation of the solar drying system.

Parameters Unit Value

Initial weight of product (total) kg 40Final weight of product (total) kg 8Initial moisture content (wet basis) % 80Final moisture content (wet basis) % 10Air mass flow rate kg/s 0.07Average solar radiation W/m2 420Average ambient temperature �C 30Average drying chamber temperature �C 44Average ambient relative humidity % 62Average drying chamber humidity % 33Drying time h 33Blower energy kW h 4.13Solar energy kW h 160.43Evaporative capacity kg/h 0.97Specific energy consumption kW h/kg 5.26Overall heat collection (thermal) efficiency % 28Overall drying efficiency, up to 10% wb % 13Pick-up efficiency, up to 10% wb % 45Overall exergy efficiency, up to 10% wb % 57Overall improvement potential, up to 10% wb W 47.29

A. Fudholi et al. / Solar Energy 99 (2014) 47–54 53

calculated using Eq. (5). Evaporative capacity increasedwith increasing solar radiation.

Using exergy analysis of drying process, Exergy BandDiagram was obtained as shown in Fig. 3. Minimum andmaximum the exergy inflow, outflow, and loss of 12.7 Wand 505.7 W, 11.7 W and 489.7 W, and 1 W and238.4 W, respectively, was observed. The exergy inflow,outflow, and loss variation with respect to time are givenin Fig. 7. Exergy inflow, outflow, and loss follow similarpatterns as similarly reported by Chowdhury et al. (2011)and Akpinar (2011). The variations in the exergy inflow,outflow, and loss of the solar drying process were causedby variations in the daily solar radiation. Midilli andKucuk (2003) reported similar findings, where exergy effi-ciency decreased with increasing drying air temperature.

During the solar drying process, the exergy efficiencywas calculated using Eq. (14), which revealed a range of43–97% as shown in Fig. 7. The exergy efficiency valuesvaried between 43% and 97% with an average of 57%.The values of the improvement potential ranged from0 W to 135 W with an average of 47 W, as shown inFig. 7. The summary of the experimental results and obser-vations are given in Table 1. The collector, drying system,and pick-up efficiencies were 28%, 13%, and 45%, respec-tively, at an average solar radiation of 420 W/m2 and anair flow rate of 0.07 kg/s.

5. Conclusion

The energy and exergy analyses of the solar drying sys-tem for red chili were performed in this study. Given theresults from these analyses, the following remarks may beconcluded:

� Drying red chili via solar drying reduced the moisturecontent from 80% (w.b) to 10% (w.b) in 33 h.

� The solar drying system was compared with open sundrying. A 49% saving in drying time was obtained forthe solar drying system compared with that of the opensun drying.� An SEC of 5.26 kg/kW h was obtained. The evaporative

capacity of the solar drying system ranged from 0.13 kg/hto 2.36 kg/h with an average of 0.97 kg/h.� The solar collector, drying system, and pick-up effi-

ciency rates were 28%, 13%, and 45%, respectively, atan average solar radiation of 420 W/m2 and an air flowrate of 0.07 kg/s. Maximum and minimum collector effi-ciencies of 52% and 11%, respectively, were observed.The drying temperature varied between 28 �C and55 �C with an average of 44 �C.� The values for improvement potential ranged from 0 W

and 135 W with an average of 47 W. The values for exer-gy efficiency varied between 43% and 97% with an aver-age of 57%.� The variations of exergy with drying time were showed

to determine when and where the minimum and maxi-mum values of the exergy losses took place during thedrying process.� Exergy analysis is a useful method in establishing strat-

egies for the design and operation of solar drying sys-tems, where the optimal use of energy is important.Therefore, exergy analysis should be used to conductperformance evaluations of solar drying systems withthe highest possible thermodynamic efficiencies.

Acknowledgements

The authors would like to thank the Yayasan Felda forfunding this research grant (RMK9 RS-DL-001-2007), andthe Solar Energy Research Institute (SERI), Universiti Ke-bangsaan Malaysia for support.

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