Mulugeta Admasu Delele

Design of Packaging Vents for Cooling Fresh Horticultural Produce

This review focuses on the design of vents in packages used for handling horticulture produce. The studies on vent designs that are conducted to obtain fundamental understanding of the mechanisms by which different parameters affect the rate and homogeneity of the airflow and the cooling process are presented. Ventilated packages should be designed in such a way that they can provide a uniform airflow distribution and consequently uniform produce cooling. Total opening area and opening size and position show a significant effect on pressure drop, air distribution uniformity and cooling efficiency. Recent advances in measurement and mathematical modelling techniques have provided powerful tools to develop detailed investigations of local airflow rate and heat and mass transfer processes within complex packaging structures. The complexity of the physical structure of the packed systems and the biological variability of the produce make both experimental and model-based studies of transport processes challenging. In many of the available mathematical models, the packed structure is assumed as a porous medium; the limitations of the porous media approach are evident during vented package design studies principally when the container-to-produce dimension ratio is below a certain value. The complex and chaotic structure within horticultural produce ventilated packages during a forced-air precooling process complicates the numerical study of energy and mass transfer considering each individual produce. Future research efforts should be directed to detailed models of the vented package, the complex produce stacking within the package, as well as their interaction with adjacent produce, stacks and surrounding environment. For the validation of the numerical models, the development of better experimental techniques taking into account the complex packaging system is also very important.

Investigating the Effects of Table Grape Package Components and Stacking on Airflow, Heat and Mass Transfer Using 3-D CFD Modelling

The flow phenomenon during cooling and handling of packed table grapes was studied using a computational fluid dynamic (CFD) model and validated using experimental results. The effects of the packaging components (bunch carry bag and plastic liners) and box stacking on airflow, heat and mass transfer were analysed. The carton box was explicitly modelled, grape bunch with the carry bag was treated as a porous medium and perforated plastic liners were taken as a porous jump. Pressure loss coefficients of grape bunch with the carry bag and perforated plastic liners were determined using wind tunnel experiments. Compared with the cooling of bulk grape bunch, the presence of the carry bag increased the half and seven eighth cooling time by 61.09 and 97.34xa0%, respectively. The addition of plastic liners over the bunch carry bag increased the half and seven eighth cooling time by up to 168.90 and 185.22xa0%, respectively. Non-perforated liners were most effective in preventing moisture loss but also generated the highest condensation of water vapour inside the package. For perforated plastic liners, cooling with a high relative humidity (RH) air minimised fruit moisture loss. Partial cooling of the grape bunch inside the carry bag before covering it with a non-perforated plastic liner maintained the required high RH inside the package without condensation. The stacking of packages over the pallet affected the airflow pattern, the cooling rate and moisture transfer. There was a good agreement between measured and predicted results. The result demonstrated clearly the applicability of CFD models to determine optimum table grape packaging and cooling procedures.

CFD Modelling of the 3D Spatial and Temporal Distribution of 1-methylcyclopropene in a Fruit Storage Container

In this paper, a direct model based on explicit geometry of stacked products in boxes was developed and used to study the diffusion, convection and adsorption of 1-methylcyclopropene (1-MCP) gas in cool stores for apple fruit. The discrete element method was employed to generate random stacking of spherical products in a box. A three-dimensional finite volume-based computational fluid dynamics model was developed, verified and used to study the distribution and partitioning of the 1-MCP gas inside loaded container. The study addressed the gas distribution in a 500xa0L container with or without air circulation. For each case, 80xa0kg Jonagold apples at 1xa0°C and a 1-MCP dose of 1xa0μLxa0L−1 was used to collect validation data. In the presence of air circulation, diffusion–convection in air and diffusion adsorption in the product was applied. Simulations were performed with an unstructured tetrahedral mesh using the software ANSYS-CFX, a Reynolds-averaged Navier–Stokes solver. The case without air circulation was modelled as a diffusion problem in air and diffusion coupled with adsorption inside the product. Convection–diffusion–adsorption model parameters that were previously developed and validated were applied. The estimated equilibrium distribution of the 1-MCP gas equals 11, 34 and 55xa0% as unbounded in fruit, bonded in fruit and remaining in container, respectively. Profiles of free (unbounded) and adsorbed (bounded) 1-MCP concentrations inside fruit were estimated for reduced dosages: 0.5, 0.3, 0.1 and 0.02xa0μLxa0L−1.

Investigation of dry powder aerosolization mechanisms in different channel designs

Aerosolization efficiency is the key characteristic of dry powder inhaler (DPI). However, lack of knowledge about powder dispersion and deposition is still a major obstacle to further improve inhaler. In the current work, both the in vitro deposition experiments and numerical simulations were employed to investigate the performance of three different DPI channel designs. The powder model was commercially available Seretide Accuhaler, which contains carrier lactose and drug mixture of fluticasone propionate (FP) and salmeterol xinafoate (SX). The in vitro results, such as the mass mediate aerodynamic diameter (MMAD), fine particle fraction (FPF) and fine particle dose (FPD), were obtained by the Next Generation Impactor (NGI). The values of MMAD were significantly (p<0.05) affected by channel design. However, based on the FPF result, the three channel designs had similar capabilities of aerosolization. It was demonstrated that particle-wall collision was the dominant mechanism for the detachment and de-agglomeration at these conditions. Furthermore, good linear correlations were found between the FPD values on the first 4 stages of NGI and the outlet velocities of their corresponding particles, which would be used for a potential on-line approach to the evaluation of DPI efficiency.

Multiscale Modeling of Food Processes

Food unit operations involve complex transport phenomena. As experimental characterization of transport processes is not usually straightforward, mathematical models are often used to improve our understanding of them, and, more importantly, to design and optimize food processes. Contrary to typical engineering materials such as steel or brick, food tissues are intrinsically multiscale assemblies with different characteristics at each spatial scale. As a consequence, multiscale modeling is required. This article gives a systematic introduction to multiscale modeling in food processes, including imaging techniques for food microstructure, model formulation, and numerical solution techniques. Several applications in food process engineering will be presented. The article concludes with a discussion on future prospects for the use of multiscale modeling.