Kostadin Fikiin

Predictive equations for thermophysical properties and enthalpy during cooling and freezing of food materials

Abstract Good knowledge of thermophysical characteristics of a wide range of foodstuffs has a major importance for the accurate prediction of their unsteady-state temperature distribution, the process duration and energy consumption in cooling and freezing (heating and thawing). Such information is necessary to predict the microbiology and biochemistry of spoilage and to control the product safety and quality, as well as for the design, optimisation and efficient operation of refrigerating and thermal systems in the food and biotechnological industries. The purpose of this paper is to present reliable unified equations for determination of the specific heat capacity, enthalpy, thermal conductivity, Kirchhoff function, etc. on the basis of generalised parameters (moisture content, actual and initial freezing temperatures). The relationship between the volumetric specific enthalpy and the Kirchhoff function is also derived. The proposed formulae have large areas of application. They cover practically all industrially processed food materials except those consisting mainly of fats. The equations may easily be used for both simple and rapid engineering calculations and for implementation in more sophisticated mathematical models and computer software, including the cases in which advanced enthalpy methods for numerical heat transfer simulations are involved.

Generalized numerical modelling of unsteady heat transfer during cooling and freezing using an improved enthalpy method and quasi-one-dimensional formulation

Abstract A numerical solution of a generalized Stefan problem is presented. It covers a great variety of unsteady heat conduction cases accompanied by phase transformations. A mathematical model is developed for determination of the unsteady-state temperature and enthalpy fields (as well as the space-time evolution of the phase content) and of the cooling and freezing (heating and thawing) times of food materials and other bodies of various configuration (representing multicomponent two-phase systems having one freezable component). An improved enthalpy method is proposed by which all non-linearities, caused by the temperature dependence of the thermophysical coefficients, are introduced in a functional relationship between the volumetric specific enthalpy and the Kirchhoff function. Thus the non-linearities are eliminated as a factor making the solution difficult. The applied approach possesses great adaptivity and flexibility in solving complicated moving boundary problems: it is suitable for both isothermal and non-isothermal phase change, reaches a high degree of correspondence between the real physical phenomenon and its mathematical formalization, uses uniform and easy fixed-grid computational techniques, makes it possible to avoid complications and to eliminate possible errors caused by ‘jumping’ of the equivalent specific heat capacity peak at the maximum of the latent heat effect, etc. Efficient procedures and algorithms for computer simulation of complex refrigerating technological processes are created. Experimental verification demonstrating the applicability and accuracy of the model is carried out.

Ice content prediction methods during food freezing: a survey of the Eastern European literature

Abstract The paper presents a critical synopsis of several methods for determination of the ice content in foods during freezing or thawing as a function of the temperature. Relationships established in Eastern Europe are mainly considered, including the methods of Bartlett-Tchigeov, Rutov, Latyshev and Jadan. The ability and the limits of applicability of every method are discussed and critically evaluated. On the basis of a comparative analysis recommendations are made for implementation of some of these methods in software for computer simulation of the thermophysical properties and thermal behaviour of foods during refrigerated processing, storage, transport and distribution.

Equivalent thermophysical properties and surface heat transfer coefficient of fruit layers in trays during cooling

Abstract Experimental engineering data and predictive equations are established for the equivalent thermophysical properties (thermal conductivity, thermal diffusivity, specific heat capacity and density) and surface heat transfer coefficient of bulk layers of fruits (strawberries, raspberries, apricots, peaches, grapes and apples) in trays. Both packed layers and uncovered trays are considered as a system of fruits and air. In the first case the influence of air inclusions and free convection in closed space is taken into account, while in the second – special attention is devoted to the effect of air infiltration between the fruits placed in trays and pallets. The regression equations derived give the relationship between the considered equivalent values and the velocity of longitudinal air flow between the trays. The results are appropriate to be used for mathematical modelling and engineering calculations in real industrial heat transfer scenarios.

Another Well-Deserved Honourable Distinction for Professor Da-Wen Sun, a World-Renowned Food Scientist

Professor Da-Wen Sun, UCD School of Biosystems and Food Engineering, has been elected Full Member—Academician of the International Academy of Refrigeration at its recent general assembly held on 26 April 2018 in St. Petersburg, Russia. This is the sixth academician title that Professor Sun has been awarded since his first election to the Royal Irish Academy in 2010 and subsequently to Academia Europaea (The Academy of Europe), Polish Academy of Sciences, International Academy of Food Science and Technology, and International Academy of Agricultural and Biosystems Engineering. The International Academy of Refrigeration (IAR, www. maxiar.spb.ru) is a non-governmental and non-profit organisation, which is comprised of leading scientists, academics, professionals, engineers and businessmen. Its activities focus on solving complex fundamental and applied problems in refrigeration and cryogenic engineering, low-temperature energy, air conditioning, food processing and storage, ecology, economics, cryobiology, cryomedicine, еtc. IAR is headquartered in St. Petersburg, Russia, where it was legally established in 1995, being the successor of the Academy of Refrigeration registered in 1993. Famous academicians of IAR include Nobel laureates and deputies of the State Duma (Parliament) of Russia (e.g. Zhores Ivanovich Alferov, the winner of 2000 Nobel Prize in Physics) and past and present Directors General of the International Institute of Refrigeration based in Paris, France. Alongside the traditionally strong position of IAR in the post-Soviet areas where national and regional branches are established, the academy enrolls full members—academicians, corresponding members and academic advisers from all around the world. The full membership (academician) of IAR represents the highest honour in the concerned field. Professor Sun has contributed enormously to the advancement of food refrigeration engineering on a global scale. He began working on novel refrigeration processes and systems as early as in 1994, and since joining UCD, he has focused on food chilling and freezing technologies, thereby obtaining valuable cutting-edge research results. Professor Sun has published over 100 journal articles in food chilling and freezing technologies. In July 2013, Professor Sun has been presented with the Frozen Food Foundation Freezing Research Award by the International Association for Food Protection (IAFP) for his significant contributions to enhancing the field of food freezing technologies. This is the first time this prestigious award has been presented to a scientist outside the USA. Professor Sun is among the world’s top professionals in food engineering research and education. He has published over 500 peer-reviewed journal papers (Web of Science hindex = 89, SCOPUS h-index = 94) with 50 papers being designated by ESI as Highly Cited/Hot Papers in Field. Many of his scholarly works have become standard reference materials, specifically in vacuum cooling, ultrasound-assisted freezing, computer vision of foods, food engineering models involving computational fluid dynamics, etc. Professor Sun has been honoured as one of the Highly Cited Researchers in the last three consecutive years (2015–2017) by Clarivate Analytics (formerly Thomson Reuters). I have had the chance to meet Professor Da-Wen Sun for the first time at the early stage of his career, when he attended the international conference on Advances in the Refrigeration Systems, Food Technologies and Cold Chain, which took place in Sofia, Bulgaria, in 1998 and was co-organised by myself under the aegis of the International Institute of Refrigeration. I still remember quite well the professional dynamism, spirit and purposefulness of his participation, which made an obvious impact on the audience. Since then, I have had many further occasions to cooperate and interact with Professor Sun on different joint initiatives and projects, where I have enjoyed the efficiency and accuracy of his contribution. * Kostadin Fikiin k.fikiin@tu-sofia.bg