Effect of greenhouse on crop drying under natural and forced convection I: Evaluation of convective mass transfer coefficient

In this paper, a study of convective mass transfer coefficient and rate of moisture removal from cabbage and peas for open sun drying and inside greenhouse drying has been performed as a function of climatic parameters. The hourly data for the rate of moisture removal, crop temperature, relative humidity inside and outside the greenhouse and ambient air temperature for complete drying have been recorded. The experiments were conducted after the crop harvesting season from September to December 2001. These data were used for determination of the coefficient of convective mass transfer and then for development of the empirical relation of convective mass transfer coefficient with drying time under natural and forced modes. The empirical relations with convective mass transfer for open and greenhouse drying have been compared. The convective mass transfer coefficient was lower for drying inside the greenhouse with natural mode as compared to open sun drying. Its value was doubled under the forced mode inside the greenhouse drying compared to natural convection in the initial stage of drying.

[1]  Miguel Ángel Condorí,et al.  The performance of forced convection greenhouse driers , 1998 .

[2]  S. Sokhansanj,et al.  Moisture transport caused by natural convection in grain stores , 1990 .

[3]  R. D. Gibson.  Theory and problems of heat transfer, (schaum's outline series): McGraw-Hill, New York (1978) , 1979 .

[4]  Steven C. Chapra,et al.  Numerical Methods for Engineers , 1986 .

[5]  P. J. Lunde.  Solar thermal engineering: Space heating and hot water systems , 1980 .

[6]  C. Z. Karakostas,et al.  Instrumentation, Measurements and Numerical Analysis of Bridges: An Example of the Cable-Stayed Bridge on Evripos Channel, Greece , 2001 .

[7]  G. N. Tiwari,et al.  Convective heat transfer coefficient of crops in forced convection drying – an experimental study , 2001 .

[8]  G. Crapiste,et al.  DETERMINATION of HEAT TRANSFER COEFFICIENTS DURING DRYING of FOODSTUFFS , 1995 .

[9]  I. Dincer,et al.  Determination of moisture diffusivities and moisture transfer coefficients for wooden slabs subject to drying , 1996, Wood Science and Technology.

[10]  C. Ertekin,et al.  Mathematical modeling of thin layer solar drying of sultana grapes , 2001 .

[11]  Miguel Ángel Condorí,et al.  Solar drying of sweet pepper and garlic using the tunnel greenhouse drier , 2001 .

[12]  J. Watmuff,et al.  Solar and wind induced external coefficients - Solar collectors , 1977 .

[13]  I. Dincer,et al.  A modelling study for moisture diffusivities and moisture transfer coefficients in drying of solid objects , 1996 .

[14]  G. N. Tiwari,et al.  Evaluation of convective heat transfer coefficient in crop drying under open sun drying conditions , 2001 .

[15]  Ibrahim Dincer,et al.  Moisture Loss from Wood Products During Drying—Part I: Moisture Diffusivities and Moisture Transfer Coefficients , 1998 .