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Technical Brief

Evaluation of the Maximum Evaporation Rate in Small-Scale Indirect Solar Dryers

[+] Author and Article Information
Lucía Blanco-Cano

Appropriate Technologies for Sustainable
Development Group (GTA),
Department of Thermal and Fluids Engineering,
Universidad Carlos III de Madrid,
Avenida Universidad 30,
Leganés 28911, Spain
e-mail: lbcano@ing.uc3m.es

Antonio Soria-Verdugo

Appropriate Technologies for Sustainable
Development Group (GTA),
Energy System Engineering (ISE),
Department of Thermal and Fluids Engineering,
Universidad Carlos III de Madrid,
Avenida Universidad 30,
Leganés 28911, Spain
e-mail: asoria@ing.uc3m.es

Luis Miguel Garcia-Gutierrez

Energy System Engineering (ISE),
Department of Thermal and Fluids Engineering,
Universidad Carlos III de Madrid,
Avenida Universidad 30,
Leganés 28911, Spain
e-mail: lmgarcia@ing.uc3m.es

Ulpiano Ruiz-Rivas

Appropriate Technologies for Sustainable
Development Group (GTA),
Energy System Engineering (ISE),
Department of Thermal and Fluids Engineering,
Universidad Carlos III de Madrid,
Avenida Universidad 30,
Leganés 28911 Spain
e-mail: ulpiano@ing.uc3m.es

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received July 14, 2015; final manuscript received December 16, 2015; published online January 13, 2016. Assoc. Editor: Prof. Nesrin Ozalp.

J. Sol. Energy Eng 138(2), 024502 (Jan 13, 2016) (4 pages) Paper No: SOL-15-1218; doi: 10.1115/1.4032351 History: Received July 14, 2015; Revised December 16, 2015

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%.

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Figures

Grahic Jump Location
Fig. 1

(a) Scheme of an indirect solar dryer with the configuration considered in this study and (b) control volume in the drying chamber

Grahic Jump Location
Fig. 2

Evolution of (a) temperature and (b) specific humidity of the air and the liquid surface along the drying chamber

Grahic Jump Location
Fig. 3

Maximum evaporation rate as a function of (a) the air mass flow rate and (b) the aspect ratio

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