Postharvest Biology and Technology 86 (2013) 536–545 Contents lists available at ScienceDirect Postharvest Biology and Technology journal h om epa ge : www.elsevier.com/locate/postharvbio Studying airflow and heat transfer characteristics of a horticultural produce packaging system using a 3-D CFD model. Part I: Model development and validation M.A. Delele a,d , M.E.K. Ngcobo b , S.T. Getahun a , L. Chen c , J. Mellmann d , Umezuruike Linus Opara a,∗ a Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa b Perishable Products Export Control Board, 45 Silwerboom Avenue, Plattekloof, Parow 7500, South Africa c School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China d Department of Postharvest Technology, Leibniz Institute of Agricultural Engineering (ATB) Potsdam-Bornim, Max-Eyth-Allee 100, Potsdam 14469, Germany a r t i c l e i n f o Article history: Received 10 June 2013 Accepted 17 August 2013 Keywords: CFD Horticulture Packaging Airflow Heat transfer Precooling a b s t r a c t A 3-D computational fluid dynamics (CFD) model of airflow and heat transfer processes within packed horticultural produce was developed. The model included explicit geometries of the product and package. Model results showed that airflow and temperature inside produce bulk were heterogeneous. The regions near the package vents showed relatively higher cooling air velocity and turbulence intensity. The coldest region was located behind the entrance vents. Pressure drops through entrance and exit vents were 51.1% and 45.2%, respectively. As the cooling air passed through the package vents and produce bulk, there was an increase in turbulence intensity. Validation of the model was conducted using experimental results. There was a good agreement between the predicted and measured results, average relative errors of predicted pressure drop and produce temperature were 13.80% and 16.27%, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Horticultural produce is highly perishable and maintaining the required produce quality during postharvest handling period is challenging. The rate of produce deterioration can be mini- mized by applying proper packaging and refrigeration technologies (Opara and Zou, 2006; Ladaniya, 2008). Supplying a specific pro- duce volume in an attractive way, keeping produce clean and hygienic, providing protection against mechanical injuries, mini- mizing produce moisture loss and retarding microbial decay are the main objectives of a produce packaging system. Low temper- ature handling of produce decreases respiratory and enzymatic activities, retards microbial growth, minimizes moisture loss and reduces ethylene production (Ladaniya, 2008). The efficiency of horticultural produce cooling depends on the cooling method, cool- ing medium property, produce thermo-physical and physiological behaviour, initial produce temperature, required storage tempera- ture, package design and stacking pattern (Vigneault and de Castro, ∗ Corresponding author. Tel.: +27 21 808 4064; fax: +27 21 808 3743. E-mail addresses: opara@sun.ac.za, umunam@yahoo.co.uk (U.L. Opara). 2005; Pathare et al., 2012). Forced-air cooling is the most widely used produce cooling method (Castro et al., 2004). In this method, cooling is performed by forcing cold air through stacked packages and around each individual piece of produce. The most important drawback of packaging systems is their influence on produce cooling rates. Packaging material increases cooling airflow resistance and blocks direct contact of cooling air and produce. In order to minimize such negative effects, packages are usually designed with vents. A number of researchers have studied airflow as well as the heat and mass transfer character- istics of ventilated packing systems using experimental methods (Castro et al., 2004, 2005; Vigneault and de Castro, 2005; Ladaniya, 2008; Ngcobo et al., 2012). However, experimental studies are usu- ally expensive, time consuming and in the case of studies that deal with biological materials the natural variability of produce makes generalization very difficult. Validated mathematical models that take into account the physical, chemical and biological processes of produce are becom- ing a viable alternative. Validated mathematical models can answer ‘what if’ questions by a relatively cheaper method. The computational fluid dynamics (CFD) modelling technique is the pri- mary method of choice for modelling transport processes during 0925-5214/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.postharvbio.2013.08.014