ShareICR 2019: an overview of current refrigeration research (part II)
PARTIE II - See part I
Optimal design and operation of food refrigeration processes, along with the importance of a reliable, efficient food cold chain were addressed in 2 keynotes:
Don Cleland [5] stresses that optimal design and operation of food refrigeration processes requires knowledge of thermal properties including density, specific heat capacity (and hence enthalpy), thermal conductivity and initial freezing point of foodstuffs. Measurement of such properties is time-consuming and expensive given the wide range of foods and variations in composition and structure. Therefore there is an ongoing need for prediction of thermal properties of complete food products from the food composition (which is usually known or is simple and low-cost to measure). The author recommends accurate yet easy to implement methods to predict effective product thermal properties from composition data in the temperatures range most relevant to refrigerated foods, taking into account change in ice fraction below the freezing point, the presence of air voids and, for packaged food items, the effect of packaging. The methods use mechanistic rather than empirical models whenever possible so that they are more likely to be generally applicable.
Gérald Cavalier [6] points out for its part that the certification of the cold chain is a way to guarantee its safety and performance. Since the beginning, alongside with cold chain development, certification schemes were developed, through tests in a first time, then with product certification and then companies and staff certification. Nowadays certification schemes are available for nearly all cold chain equipment, whether mandatory or voluntary. They have proved their interest and their capacity to increase the performance of cold chain. However, they are not implemented all over the world, for example for refrigerated transport equipment. The fast development of big data, the internet of things, the capacities of data exchanges offer new possibilities to develop a connected cold chain. These technologies will help assess the global performance of the cold chain for each fresh and frozen product transported from farm to fork and laboratory to lavatory. They will not replace the certification of equipment and people but will usefully complete it. The certification of the full cold chain is then our challenge for the next twenty years.
Caloric cooling technologies, which are considered as potential alternatives to traditional vapour compression technology, are the subject of intense R&D work as illustrated by two keynotes regarding respectively magnetic and elastocaloric cooling.
According to Andrej Kitanovski, Katja Klinar and Urban Tomc [7], in the past two decades we have witnessed a substantial increase in basic and applied research efforts to bring magnetocaloric refrigeration technology to the market. Despite the significant research progress that has been made, there are several critical issues that need to be solved in the near future. These concern magnetocaloric materials, regenerators and heat transfer, magnetic field sources, as well as hydraulics.
The authors stress that the most recent developments in finding rare-earth-free static hybrid magnetic field sources will not only enable a very high frequency of the operation, but will also lead to a substantial cost reduction and an improvement of the technology’s environmental footprint. The long-term future of magnetocaloric devices, especially with the development of nano-engineering, could lead to fully embodied systems with integrated magnetic field sources.
David Catalini and Yunho Hwang [8] report that significant progress was made in elastocaloric cooling field. New shape-memory alloy (SMA) materials have been developed with a longer fatigue life and a tuned composition along its length. This can be important for the fabrication of regenerators in which the transformation temperature is as close as possible to the temperature of the material in operating conditions right before the transformation. This will keep the stress required to a minimum. Analytical tools were developed to estimate material properties with simplified experimental set-ups, and experimental rigs were developed to increase the accuracy of the material properties measurements. The temperature lift performance of the systems in operation is setting new records. While research on elastocaloric cooling in still in an early stage of development, many research outcomes have revealed its potential for future development.
Summaries of other keynotes will be featured in the October 2019 issue of the IIR Newsletter.
All of these keynotes are already available in the Fridoc database (see below). All the other communications of the Montreal congress are being put online.
IIR members benefit from a quota of free downloads.
[5] Don Cleland, Prediction of food thermal properties to enable accurate, design of food refrigeration processes, https://bit.ly/2mdlfDy[6] Gérald Cavalier, Cold chain certification, https://bit.ly/2nFJeM1
[7] Andrej Kitanovski, Katja Klinar, Urban Tomc, Magnetocaloric refrigeration and heat pumping: the present, tomorrow, and the future, https://bit.ly/2n68fQm
[8] David Catalini, Yunho Hwang, Recent advances in elastocaloric cooling technologies: Where they stand and what prospects are, https://bit.ly/2lxQqcr