Computational fluid dynamics (CFD) is a powerful numerical tool that is becoming widely used to simulate many processes in the food industry. Recent progression in computing efficacy coupled with reduced costs of CFD software packages has advanced CFD as a viable technique to provide effective and efficient design solutions. This paper discusses the fundamentals involved in developing a CFD solution. It also provides a state-of-the-art review on various CFD applications in the food industry such as ventilation, drying, sterilisation, refrigeration, cold display and storage, and mixing and elucidates the physical models most commonly used in these applications. The challenges faced by modellers using CFD in the food industry are also discussed.

Computational fluid dynamics (CFD) ¿ an effective and efficient design and analysis tool for the food industry: A review

Temperature homogeneity in most food refrigeration systems is directly governed by the airflow patterns in the system. Numerical modelling of airflow provides an opportunity to develop improved understanding of the underlying phenomena influencing system performance, which can lead to reduced temperature heterogeneity and increased effectiveness and efficiency of refrigeration systems. With the rapid advances in computational power of recent years, the use of Computational Fluid Dynamics (CFD) techniques in this application has become popular. This paper reviews the application of CFD and other numerical modelling techniques to the prediction of airflow in refrigerated food applications including cool stores, transport equipments and retail display cabinets.

A review of numerical models of airflow in refrigerated food applications

Several studies have shown a significant level of temperature and humidity heterogeneity, with non-uniform airflow in the refrigeration equipment, which lead to a deterioration in food quality and safety. As the product is present in several different types of equipment along the supply chain, it is difficult to control and maintain the temperature throughout the cold chain. Basic to advanced approaches, from field studies to combined deterministic and stochastic modelling, are presented in this review article. Deterministic modelling (heat/mass transfer, airflow, quality and microbiology) in cold chain equipment, and combined deterministic and stochastic modelling in food processing and the cold chain are presented. This approach makes it possible to take into account the variability of the input parameters of the model such as the initial product characteristic (moisture content, temperature, contamination, etc.) and the operating conditions (ambient temperature, residence time in the equipment etc.). This review provides an insight into the background, problematic and transfer mechanism of food refrigeration.

Experimental investigation and modelling in the food cold chain: Thermal and quality evolution

Experimental and computational methods are used to address those parameters that have significant effects on the amount of entrained (warm) air in an open refrigerated display case. These parameters are identified, quantified, and the rate of entrainment is expressed as a function of these parameters. It is found that the turbulence intensity, the shape of the mean velocity profile at the discharge air grill, and the Reynolds number are mainly responsible for the amount of entrained air in a display case. It is also concluded that lower Reynolds numbers will reduce the amount of the entrained air in the display case, however, the trade off will be higher temperature of the food products on shelves. Digital particle image velocimetry (DPIV) was used to map the entire mean velocity flowfield and the turbulence intensity. The laser doppler velocimetry technique was also used to verify the mean velocity and turbulence intensity measurements made by DPIV. The results indicated an excellent agreement between both methods. Parametric studies for the rate of entrainment of the outside air into the display case were performed using a computational fluid dynamics tool. The results indicate that lowering the Reynolds number of the air curtain reduces the entrainment rate. However, sufficiently high momentum should still exist to enforce the integrity of the air curtain structure.

Jet entrainment rate in air curtain of open refrigerated display cases

Over the past 5 years, two-dimensional particle image velocimetry (PIV) techniques [E. Thomas, Jr., Phys. Plasmas 6, 2672 (1999)] have been used to obtain detailed measurements of microparticle transport in dusty plasmas. This Letter reports on an extension of these techniques to a three-dimensional velocity vector measurement approach using stereoscopic PIV. Initial measurements using the stereoscopic PIV diagnostic are presented.

Application of stereoscopic particle image velocimetry to studies of transport in a dusty (complex) plasma

Computational Fluid Dynamics (CFD) modeling is effectively coupled with the experimental
technique of Digital Particle Image Velocimetry (DPIV), to study the flowfield
characteristics and performance of the air curtain of a medium-temperature open vertical
refrigerated display case used in supermarkets. A global comparison of the flowfield and
quantification of the entrained air into the case indicate that there is a considerable
amount of cold air spillage from a typical display case that is replaced by the ambient
warm entrained air across the air curtain, lowering the energy efficiency of the case. The
computational model that is developed from the marriage of CFD and DPIV techniques
provides a reliable simulation tool that can be used for the design optimization of air
curtains. A correct estimate of the infiltration rate by changing different parameters in a
validated computational simulation model will provide a feasible tool for minimizing the
spillage of the cold air, and thereby designing more energy efficient open display cases.

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The Application of Advanced Methods in Analyzing the Performance of the Air Curtain in a Refrigerated Display Case

Purpose – To address the effects of velocity profile at the discharge air grille (DAG) on the amount of entrained air into an open refrigerated display case (ORDC).Design/methodology/approach – The performance of an ORDC was studied by CFD, DPIV and LDV. The actual measured velocity profile at the DAG and total flow rate of the display case at its nominal operating conditions are used as guidelines throughout the CFD modeling.Findings – It was found that a skewed parabolic profile with the peak shifted towards the inner section of the case generates the minimum entrainment and demonstrates that with simple changes to the geometry of the DAG, a significant reduction in the entrainment rate could be achieved.Research limitations/implications – This study finds the optimum infiltration rate of a manufactured ORDC. A fundamental study is currently being done to address all the effective parameters that can affect the infiltration rate of any ORDCs.Originality/value – This paper presents this fact that the vel...

Ramin Faramarzi

Papers

Jet entrainment rate in air curtain of open refrigerated display cases

The Application of Advanced Methods in Analyzing the Performance of the Air Curtain in a Refrigerated Display Case

Jet entrainment minimization in an air curtain of open refrigerated display case

CFD Design of Air Curtain for Open Refrigerated Display Cases

Air curtain performance studies in open vertical refrigerated display cases