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Abstract: A direct model, using the explicit geometry of stacked products in boxes, was developed and used to study the local and average airflow through stacks of horticultural products. The discrete element method was employed to generate a random stacking of spherical products in the box. A computational fluid dynamics model was then applied to study explicitly the airflow through the air gaps in the box and in the voids between the stacks of different random fillings. The flow resistance was affected by the confinement ratio, product size, porosity, box vent hole ratio, and much less by the random filling. The predicted pressure drop over stacks agreed with experimental correlations for porous media. Air velocity profiles inside the boxes compared well to measurements. The methodology was used to obtain more accurate pressure drop correlation for stacks of vented boxes that can now be used in large scale simulations of cool rooms. [Copyright &y& Elsevier]

Abstract: Thermographic IR-imaging was used as a non-destructive tool to evaluate the surface quality of apples. Experiments were carried out on apple fruit of two different cultivars (Jonagored and Elshof) picked at two different picking dates (early and late). First, the emissivity of the apple skin was determined as 0.96 for both cultivars. Next, recordings were made of individual fruit of both cultivars cooled from 20°C to 12°C. In this experiment Elshof apples had a faster cooling rate and lower temperature than Jonagored apples. Finally, a storage experiment was carried out under standardised conditions with quality assessment after 4 and 8 months of CA storage and at each storage period after 0, 1, and 2 weeks of shelf life. Next to the determination of general quality parameters (weight, diameter), thermographic images of the surface of each apple were obtained. Temperature profiles were recorded for batches of four fruits and of all individual fruit within this batch while they were cooled from 12°C to 1°C. The surface cooling rate and final fruit surface temperature were estimated. All data were calibrated for background temperature and corrected for apple dimensions and convection coefficients. ANOVA analysis showed significant differences between both cultivars, picking dates and storage conditions for the cooling rate. The final surface temperature differed significantly between different storage and shelf life periods. Only the difference in cooling rate with a faster cooling for Elshof than for Jonagored was explained in terms of wax structural characteristics and transpiration rates. The results also show the importance of data correction. [Copyright &y& Elsevier]

Abstract: As an application of the CA cool storage simulation model developed and validated earlier, the implications of different product loading strategies (batch-wise and step-wise) on the product quality, mechanical plants performance and design aspects were investigated by considering a hypothetical CA cool storage facility. The batch-wise product loading was found to be advantageous with regards to firmness loss of the produce but was marginally energy intensive over the step-wise product loading strategy. Moreover, the step-wise loading scheme required low capacity individual evaporators and higher plant capacity of the gas-handling unit (N2 generator and CO2 scrubber), as compared to the batch-wise product loading. It was demonstrated that using the model, appraisal of the implication of practical industrial operational procedures such as product loading strategy, on product quality and plant performance/design was possible, owing to the discrete continuous modeling approach. [Copyright &y& Elsevier]

Abstract: In this paper, a controlled atmosphere storage model, developed earlier, is validated using an industrial CA cool storage facility with stepwise product loading strategy. The proposed combined continuous and discrete CA cool storage simulation model was able to represent the step response transients and continuous events, with accuracy less than the observed variability or at best with accuracy level as set by the measurement instrument. Moreover, the handling of discrete/continuous events enabled the implementation of practical operational procedures and to investigate their implication on plant performance/design and directly on the product quality. The model is a valid working model for design and optimization of CA cool storage facilities both with respect to plant performance and final quality of the stored product. [Copyright &y& Elsevier]

Abstract: A transient three-dimensional CFD model was developed to calculate the velocity, temperature and moisture distribution in an existing empty and loaded cool store. The dynamic behaviour of the fan and cooler was modelled. The model accounted for turbulence by means of the standard k-ε model with standard wall profiles. The model was validated by means of velocity, air and product temperature. An average accuracy of 22% on the velocity magnitudes inside the empty cold store was achieved and the predicted temperature distribution was more uniform than predicted. In the loaded cold store, an average accuracy of 20% on the velocity magnitudes was observed. The model was capable of predicting both the air and product temperature with reasonable accuracy. [Copyright &y& Elsevier]

Simulation of dynamic processes in controlled atmosphere (CA) cool room storage systems has been developed. The model consists of three interacting sub-models for the prediction of the transient behavior of the processes in the three units, namely, the cool room, the refrigeration system and the gas-handling unit. Several modules representing each of the components in these units were developed based on energy and mass balances. The modules were then arranged to form the sub-models, which were interconnected, in turn, into the global CA cool storage system model. The modules were implemented in an object-oriented computational environment, (EcosimPro) which can handle both continuous and discrete events. The model was validated using experimental data from a pilot plant CA cool storage facility. Model predictions of the most important discrete and continuous processes were found to agree to the experimental data with a maximum difference less than the observed spatial variability or at best with the accuracy level as set by the measurement instruments. As product respiration and quality models are incorporated, it is possible to use the model for optimization of plant performance with respect to the final quality of the stored product. Moreover, the handling of discrete/continuous events enables the implementation of practical operational procedures and to investigate their implication directly on the product quality and plant performance/design. [Copyright &y& Elsevier]

Effects of deviations in airflow properties and product properties on cooling of chicory roots were studied based on numerical simulations with a validated transient model of coupled heat and mass transfer in bulks of chicory roots. The model was solved for a one-dimension 1-m deep bulk of chicory roots cooled at various levels of air velocity, temperature and relative humidity. Variations in bulk porosity, heat of respiration and product heat capacity were studied as well. The results led to an improved understanding of the cooling process with respect to control strategies and cold store practice. The smallest sensitivity of product temperature with respect to process conditions was found at low velocity (0.1 m s−1), low temperature (1 °C) and high RH (95%). Small deviations of these conditions could, however, still lead to increased weight losses by as much as 4% after 3 months of storage. Variations of bulk porosity and of respiration rates significantly affected weight loss variations. [Copyright &y& Elsevier]