A theoretical study on the maximum evaporation rate obtainable in a small-scale indirect solar dryer is presented, considering evaporation of free water. A mathematical model of the evolution of the temperature and the specific humidity of the airflow along the drying chamber is presented. Based on the results, some simplifications are proposed and justified in order to calculate the maximum evaporation rate as a function of a reduced number of parameters, to study their effect. The results show that the effect of the air mass flow rate on the maximum evaporation rate depends on the aspect ratio of the drying chamber, defined as the ratio of the total drying area to the cross section in the drying chamber. Design and operation criteria can be extracted from the results. As a global result, for the typical range of dimensions and air mass flow rates employed in solar dryers, the drying chamber aspect ratio should be between 200 and 300 to obtain a proper evaporation rate. Within that range, doubling the air mass flow rate the maximum evaporation rate obtainable increases around 20%.

Issue Section:
Technical Brief
Keywords:
Collector, Drying, Heat transfer, Mass Transfer, Renewable, Solar
Topics:
Dryers, Drying, Evaporation, Solar energy, Flow (Dynamics), Temperature, Water

References

1.
Mustayen
,
A. G. M. B.
,
Mekhilef
,
S.
, and
Saidur
,
R.
,
2014
, “
Performance Study on Different Solar Dryers: A Review
,”
Renewable Sustainable Energy Rev.
,
34
, pp.
463
–
470
.
Google Scholar
Crossref
Search ADS
 
2.
Ekechukwu
,
O. V.
, and
Norton
,
B.
,
1999
, “
Review of Solar Energy Drying Systems II: An Overview on Solar Drying Technology
,”
Energy Convers. Manage.
,
40
(
6
), pp.
615
–
655
.
Google Scholar
Crossref
Search ADS
 
3.
Blanco-Cano
,
L.
,
Soria-Verdugo
,
A.
,
Garcia-Gutierrez
,
L. M.
, and
Ruiz-Rivas
,
U.
,
2013
, “
Modelling and Design of Indirect Solar Dryers for Batch Drying
,” International Conference on Renewable Energies and Power Quality (
ICREPQ'13
), Bilbao, Spain, Mar. 20–22. Paper No. 542.
4.
Leon
,
A. M.
,
Kumar
,
S.
, and
Bhattacharya
,
S. C.
,
2002
, “
A Comprehensive Procedure for Performance Evaluation of Solar Food Dryers
,”
Renewable Sustainable Energy Rev.
,
6
(
4
), pp.
367
–
393
.
Google Scholar
Crossref
Search ADS
 
5.
Altobelli
,
F.
,
Condorí
,
M.
,
Duran
,
G.
, and
Martinez
,
C.
,
2014
, “
Solar Dryer Efficiency Considering the Total Drying Potential. Application of This Potential as a Resource Indicator in North-Western Argentina
,”
Sol. Energy
,
105
, pp.
742
–
759
.
Google Scholar
Crossref
Search ADS
 
6.
Passamai
,
V.
, and
Saravia
,
L.
,
1997
, “
Relationship Between a Solar Drying Model of Red Pepper and the Kinetics of Pure Water Evaporation
,”
Drying Technol.
,
15
(
5
), pp.
1419
–
1432
.
Google Scholar
Crossref
Search ADS
 
7.
Duffie
,
J. A.
, and
Beckman
,
W. A.
,
2006
,
Solar Engineering of Thermal Processes
, 3rd ed.,
Wiley
, Hoboken,
NJ
, Chap. 6.
8.
Oztop
,
H. F.
,
Bayrak
,
F.
, and
Hepbasli
,
A.
,
2013
, “
Energetic and Exergetic Aspects of Solar Air Heating (Solar Collector) Systems
,”
Renewable Sustainable Energy Rev.
,
21
, pp.
59
–
83
.
Google Scholar
Crossref
Search ADS
 
9.
Ito
,
S.
,
Kashima
,
M.
, and
Miura
,
N.
,
2006
, “
Flow Control and Unsteady-State Analysis on Thermal Performance of Solar Air Collectors
,”
ASME J. Sol. Energy Eng.
,
128
(3), pp.
354
–
359
.
Google Scholar
Crossref
Search ADS
 
10.
Karim
,
M. A.
, and
Hawlader
,
M. N. A.
,
2004
, “
Development of Solar Air Collectors for Drying Applications
,”
Energy Convers. Manage.
,
45
(
3
), pp.
329
–
344
.
Google Scholar
Crossref
Search ADS
 
11.
Kutscher
,
C. F.
,
Christense
,
C.
, and
Barker
,
G.
,
1993
, “
Unglazed Transpired Solar Collectors: Heat Loss Theory
,”
ASME J. Sol. Energy Eng.
,
115
(
3
), pp.
182
–
188
.
Google Scholar
Crossref
Search ADS
 
12.
Treybal
,
R. E.
,
1987
,
Mass-Transfer Operations
, 3rd ed.,
McGraw-Hill
,
New York
, Chap. 12.
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