DETERMINATION OF THE MASS TRANSFER COEFFICIENT DURING DRYING OF AGRICULTURAL CROPS

M. Markowski, I. Bialobrzewski
Drying, freezing, de-frosting and packing as well as storage are in the group of technological processes of vegetable processing during which the raw material exchanges heat and mass with the environment. Since the energy outlays needed to carry out these processes are usually high (e.g. convective drying, cooling, storing) it is important of optimise them in order to reduce the costs of obtaining a high-quality product (Karel et al., 1985). The optimal conditions during the process may be determined effectively and cheaply using the standard methods of the process optimisation (Banga and Singh, 1994). Those methods make us use mathematical models describing the processes under investigation (Pabis, 1985). Among the many available types of mathematical models of food processing, models formed from differential equations may be distinguished (Alagusundaram et al., 1990). According to the character of changes of analysed values, we may distinguish models with lumped parameters (Markowski and Bialobrzewski, 1997) as well as the models with distributed parameters (Tsukada et al., 1991). The models with distributed parameters are made up of partial differential equations and make it possible to determine changes in values depending both on time and location (e.g. change of concentration of phenolic compounds in apple slices according to the time of treatment and location within the slice). Such models are usually created using the equations of mass, momentum and energy balances applied to a single particle or the entire bed of particles of the raw material being processed. The models used in the process of food engineering are usually highly non-linear and the simulation results are usually obtained on the basis of the finite elements method (Tsukada et al., 1991), and less frequently on the basis of the finite differences method.

Among many problems connected with the development and study of models with distributed parameters as applied to food processing the problem of identification of parameters of the model is worth stressing. It appears that the models of food processing (including food storage) are very often susceptible to changes of parameters. This equally applies to balance equations as well as initial and boundary conditions. The purpose of this paper is to present the method of determination of the surface mass transfer coefficient during food processing in which the mass transport is of great importance. Cases of carrot, celery and barley drying will be analysed.

Markowski, M. and Bialobrzewski, I. (1998). DETERMINATION OF THE MASS TRANSFER COEFFICIENT DURING DRYING OF AGRICULTURAL CROPS. Acta Hortic. 476, 329-336
DOI: 10.17660/ActaHortic.1998.476.38
https://doi.org/10.17660/ActaHortic.1998.476.38
Mass transfer coefficient, drying, vegetables

Acta Horticulturae