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ABSTRACT
The prototyping of dryer design and performance by application of the trial-and-error technique in one-factor-at-a-time testing is completely arbitrary, expensive and time consuming. Reducing product development lead-time and cost while concurrently improving customer satisfaction for a good manufacturer enhance rapid response to market demand which is a highly effective way of improving returns on investment. In this study a numerical model for the digital prototyping of the rectangular passive greenhouse dryer design and the optimization of the batch process in the solar dryer was developed using computer-aided engineering analysis approach to product development. System dynamics methodology was employed in the mathematical modelling of the batch process in the rectangular passive dryer and prediction of the global solar radiation in KainjiNew Bussa, the experimental location. The transient convection-diffusion model was discretized by the finite volume method. Relevant technological/practical constraints were determined. An interactive, user-friendly computer package ANSYS 14.0 was then used to develop an empirical model. The package was used for the computational fluid dynamics simulation and response surface methodology optimization to specify the dryer parameters that maximize the dryer mean temperature. The numerical solution was applied to the optimization of a practical rectangular passive greenhouse dryer which was tested and results compared. Results obtained showed that the numerical procedure is able to specify the optimum dryer parameters that maximize the mean temperature of the drying air within the cavity. The results of the simulations of temperature within the rectangular passive greenhouse dryer’s cavity were within 25' ≤ I ≤ 49.18' and those of experimental studies yielded the range 25' ≤ I ≤ 49.42'. These results represent accuracy of 85.77%. Hence, the numerical simulations predict with degree of accuracy the transient temperature distribution in the passive greenhouse dryer. The factorial experiments in a central composite design revealed that only the inlet vent dimensions influence the mean temperature within the greenhouse dryer. The parametric analysis for robust design yielded the inlet vent height of 0.27m and inlet vent width of 0.45m as the optimum design variables that maximize the mean temperature of the drying air as 320.48K (47.30 °C). When these values are applied to the design and fabrication of a practical rectangular passive greenhouse dryer, the psychrometric studies of the dryer showed that the maximum xxxiv cavity and ambient air dry bulb temperature and relative humidity are 49.42°C, 6.167% and 42.71°C, 11.33% respectively (and the corresponding drying potency as 10.429kPa and 6.161kPa, respectively). The results of the comparative analysis of the optimization and empirical study revealed the mean temperature of the numerical procedure and that of the experimental procedure as 47.30°C and 41.35°C, respectively, representing 87.42% accuracy. The mechanistic model developed, its technological/practical constraints in studying the dryer and the numerical approach established facilitated the prototyping and optimization of the batch process in the passive greenhouse dryer. Consequently, it enabled effective greenhouse-drying of additional commercially important freshwater fish species to moisture content indicated [Bagrus bayad (23.41%), Lates niloticus (12.60%), Clarias gariepinius (16.80%) and Clarias anguillaries (17.76%)]. This prevented autolysis process, bacterial spoilage as well as the oxidation processes.
