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Heat transfer and airflow in an insulated box with phase change material for food transport : experimental and modelling approaches.

Author(s) : LEUNGTONGKUM T.

Type of monograph: Doctoral thesis

Summary

Insulated boxes equipped with a Phase Change Material (PCM) play an important role in food transport due to low cost and flexibility. However, temperature control during the transport is complex due to the variation of operating conditions, which may lead to product degradation. An empirical approach is mainly used in practice to choose the box and PCM for some specific conditions. Thus, physical-based models allowing the prediction of food temperature evolution under wide ranges of transport conditions are necessary. The development of such models requires the understanding of heat transfer and airflow.Regarding literature study, several works considered only heat conduction in the air inside the box, some recent works took natural convection into account. According to our knowledge, no study included radiation between product and wall/PCM surface. Many fundamental studies concern all heat transfer modes in empty cavities. They often imposed two different wall temperatures while the other walls were adiabatic. Some works included a small solid object or porous media. These works could not be applied to food transport in an insulated box with PCM.This Ph.D. thesis aimed to develop an experimental and numerical methodologies to study heat transfer and airflow in this equipment.First, two types of measurements were undertaken: temperature by thermocouples and air velocity by Particle Image Velocimetry. In these studies, the 45-L insulated boxes had a heat transmission coefficient of 0.9 W‧m-2‧K-1, PCM was ice (melting point ~ 0°C, 3.5 kg) and the test product was Tylose (16 kg) whose thermo-physical properties are close to ones of meat. The influence of several parameters was studied: i) loading conditions (empty, loaded with extruded polystyrene and loaded with test product), ii) PCM position (on a side wall and at the top), iii) aspect ratio of box (height/length ≈ 1 and 1.7), iv) ambient temperature (10°C to 30°C), v) initial test product temperature (4°C and 10°C) and vi) spacing beneath the test product (no space and 20 mm). The results showed the importance of natural convection in the box. PCM should be placed at the top of a box of low aspect ratio. Loading the product with high temperature should be avoided. The required amount of PCM can be estimated in function of ambient temperature.Second, three numerical models were developed: a) lumped model predicts average product temperature but cannot identify the warmest/coldest positions, b) zonal model takes heat transfer and airflow into account, it differentiates the warmer and colder regions and c) CFD model describes in-depth temperature and air velocity fields, but high computing resources are inevitable. These models were validated by comparison with the experimental results and showed good agreement. Finally, this thesis demonstrates how to use these models to answer several practical questions such as the effect of box design and operating conditions.

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Pages: 300 p.

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  • Original title: Heat transfer and airflow in an insulated box with phase change material for food transport : experimental and modelling approaches.
  • Record ID : 30032290
  • Languages: English
  • Subject: Technology
  • Publication: Université Paris Saclay - Antony - France
  • Publication date: 2023/10/24

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