Drying operations can help in reducing the moisture content of food materials for avoidance of microbial growth and deterioration, for shelf life elongation, to minimize packaging and improving storage for easy transportation. Thin-layer drying of materials is necessary to understand the fundamental transport mechanism and a prerequisite to successfully simulate or scale up the whole process for optimization or control of the operating conditions. Researchers have shown that to rely solely on experimental drying practices without mathematical considerations for the drying kinetics, can significantly affect the efficiency of dryers, increase the cost of production, and reduce the quality of the dried product. An effective model is necessary for the process design, optimization, energy integration and control; hence, the use of mathematical models in finding the drying kinetics of agricultural products is very important. The statistical criteria in use for the evaluation of the best model(s) has it that coefficient of determination (R 2 ) has to be close to unity while the rest statistical measures will have values tending to zero. In this work, the essence of drying using thin-layer, general approaches to modeling for food drying mechanisms thin layer drying models and optimization of the drying processes have been discussed.

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Shell and tube heat exchangers in their various construction modifications are probably the most widespread and commonly used basic heat exchanger configuration in the process industries. There are many modifications of the basic configuration which can be used to solve special problems. Baffles serve two functions: Most importantly, they support the tubes in the proper position during assembly and operation and prevent vibration of the tubes caused by flow-induced eddies, and secondly, they guide the shell-side flow back and forth across the tube field, increasing the velocity and the heat transfer coefficient. The objective of this paper is to find the baffle spacing at fixed baffle cut that will give us the optimal values for the overall heat transfer coefficient. To do this Microsoft Excel 2003 package was employed. The results obtained from previous studies showed that to obtain optimal values for the overall heat transfer coefficient for the shell and tube heat exchangers a baffle cut of 20 to 25 percent of the diameter is common and the maximum spacing depends on how much support the tubes need. This was used to validate the results obtained from this study.

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In an attempt to easily determine the desired moisture content at any time (t), of selected freshly harvested roots and tubers (yellow cassava, carrot, cocoyam and yam) of economic importance subjected to drying under unsteady temperature conditions such as sun drying, especially in the rural areas where there is no electricity or funds availability to acquire suitable drying equipment by local farmers; the drying constants based on established model that is anchored on mass of the material at any time t was carried out. In this study, three mass classifications, namely: small, medium and large were prepared for each material and subjected to oven drying at a given temperature till bone dry mass. The experimental values obtained were computed and graphs plotted to obtain the slopes as drying constants of values 0.3114, 0.1092, 0.3736 and 0.3790 for bulk samples of yellow cassava, carrot, cocoyam and yam respectively.

Polycyclic aromatic hydrocarbons occur naturally in petroleum oil and coal and the burning of fuel and the activities of paper mills also release these compounds to the environment. Batch experimental adsorption study for both soil fractions was conducted in a soil slurry system at ambient temperature, using <0.02mm particle sizes. Comparison was made of the linear least-squares method and a trial-and-error nonlinear method of some widely used isotherm models for the adsorption of naphthalene on clay and silt fractions. The experimental results were fitted to the Langmuir, Freundlich, Radke-Prausnitz, Sips, Temkin and Redlich-Peterson isotherms to obtain their characteristic parameters of each model. The coefficient of determination obtained from the different models using the linear method showed that Freundlich isotherm had the highest values for both clay and silt soil fractions with values of 0.843 and 0.897 respectively. The equilibrium data did not fit the Langmuir isotherm with values of 0.287 and 0.021 for clay and silt soil respectively. Using the nonlinear method the equilibrium data gave good fit for Radke-Prausnitz, Sips, Temkin and Redlich-Peterson isotherms. Sips isotherm gave the best fit for silt soil with the r2value of 0.9779 and this was followed by Temkin isotherm for clay soil with the value of 0.9673.