Simulation of high pressure freezing processes by enthalpy method

Proceeding of International Conference on Fluid and Thermal Energy Conversion , 1994

A mathematical model was developed and used to predict the time needed ta freezn agriculural products in the fast-cryogenic freezrngprocess. The comparison with the experimental rezult was shown. The model could also predict the variation of product, trays and gas temperatur inside the freezing cabin during the process.

Biotechnology Progress, 2004

Different ice modifications were obtained during freezing processes at several pressure levels from atmospheric pressure up to 300 MPa. In the pressure range between 210 and 240 MPa, a metastable ice I modification area was observed, as the nucleation of ice I crystals in the thermodynamically stable region of ice III was reached. A significant degree of supercooling was obtained before freezing the tissue water to ice III, which has to be considered when designing pressure-supported freezing processes. The effect of supercooling phenomenon on the phase transition time is discussed using a mathematical model based on the solution of the heat transfer governing differential equations. Phase transition and freezing times for the different freezing paths experimented are compared for the processes: freezing at atmospheric pressure, pressure-assisted freezing, and pressure-shift freezing. Different metastable states of liquid water are defined according to their process-dependent stability.

Journal of Food Science, 1982

A model is proposed for freezing time calculations which combines Plank's equation with the unsteady heat transfer solutions for the cooling of a slab of constant properties through the addition of precooling, change of phase and tempering periods. The change of thermal properties with the ice content is taken into account by proposing average values for the different periods. No adjustable parameters are used in developing the model. Results are compared for the case of beef freezing with those obtained numerically by using a heat transfer model with simultaneous change of phase and with experimental measurements showing good agreement.

Journal of Food Process Engineering, 2019

The aim of this research was to model the heat transfer during the freezing process of cubed yellow potatoes (Solanum tuberosum L.) and ullucus (Ullucus tuberosus Caldas). A mathematical model was developed using the three-dimensional (3D) finite difference scheme to simulate the freezing process of suspended and in-contact-with-a-surface cubic particles. The thermophysical properties were predicted using the proximal composition and the convective heat transfer coefficient (h) was obtained by optimizing the root mean square error (RMSE) value. A pseudo h was included to simulate the heat transfer of cubic particles in-contact-with-a-surface. Low values of h were found for suspended frozen cubes (17-27 W/m2 C) and high values of pseudo h (295-371 W/m 2 C) were determined for frozen cubes in-contact-with-a-surface. An excellent agreement was observed between experimental and predicted temperatures histories (RMSE: 0.6-1.7 C) at different thermocouples positions. In conclusion, the developed model simulated correctly the freezing profile of potato and ullucu in cubic shape. With this model, the possible effects of h and external temperature on freezing times of these vegetables under different positions were evaluated and were represented by polynomial equations that could be used in the industry. Practical Applications In this research, a simple and easy-to-implement mathematical model was developed to simulate the heat transfer during freezing process of yellow potatoes and ullucus in cubes. The 3D finite difference scheme developed can be used to simulate the freezing of suspended cubed food, as is the case of fluidized bed freezers, or that are in contact with a metal surface, as in plate freezers. In addition, this study presented polynomial equations that allow the quick and precise calculation of the freezing times of cubed yellow potatoes and ullucus. 1 | INTRODUCTION The freezing process is the reducing of the temperature of food below its freezing point (James, Purnell, & James, 2015). Freezing is used for preserving food because it decreases the speed of physical, chemical, and sensory reactions (Wu, Zhang, Adhikari, & Sun, 2017; Xu, Zhang, Mujumdar, & Adhikari, 2017). Peru is a large exporter of fruits and vegetables, being the United States one of its most important markets (Meade, Baldwin, & Calvin, 2010). Peruvian frozen vegetables are highly valued in market due to their nutritional and functional

Journal of Food Science, 1977

The problem of onedimensional heat transfer in finite slabs of freezing food materials cooled from both sides is considered. The authors' modification to Plank's equation is compared with a numerical scheme. The paper shows that in the important slab freezing problem a simple formula, based on an approximate analytical solution, is at least as accurate as a complex finite difference formulation, and has some substantial practical advantages.

Journal of Food Engineering, 2001

Cryomechanical freezing consists of a two-step process. During the ®rst step, the foodstu gets into contact with a cryogenic refrigerant for a very short period of time, during which a thin frozen crust is formed. Immediately afterwards, freezing is completed in a conventional cold air-blast freezer. In this work, the heat transfer process during cryomechanical freezing was modelled using the enthalpy formulation with a ®nite volume scheme. The results of the model were successfully compared with experimental data obtained in the literature for a model food (cylinders of gelatin) and for real foodstus (hamburgers, meatballs and strawberries) in a pilot prototype.

Journal of Food Engineering, 2000

Cylindrical gelatin gels were frozen at atmospheric pressure with dierent operating conditions (air-blast freezing at dierent air temperatures and brine freezing). A method to calculate a local freezing rate was proposed to take into account the variation of freezing rate as a function of the radius. A linear evolution of the local freezing rate according to the radius was observed whatever the freezing process was. Frozen gels were freeze-dried and sliced perpendicularly to the heat¯ux. The ice crystal marks were measured according to the radial position with image analysis software. Each radial distribution of ice crystal size was characterised by the mean representative diameter. A linear regression permitted to link the ice crystal mean representative diameter to the radial position. On addition, the variation in the mean diameter with the local freezing rate was ®tted by a power law.

Mushrooms are widely commercialized products which are very susceptible to enzymatic browning. Therefore their short shelf-life makes their preservation a crucial task. Freezing of previously blanched mushrooms, either whole or sliced, is a common process to obtain longer durability. A numerical model using the finite element technique was applied to predict freezing times of mushrooms considering the actual shape of the product. The original heat transfer equation was reformulated using a combined enthalpy and Kirchhoff formulation in order to obtain accurate numerical results and enhance the computational speed of the program. A three dimensional geometry was used to describe the sliced mushroom shape. Digital image reconstruction was used to obtain the irregular contour of the food product. The numerical predictions agreed with the experimental time-temperature curves during freezing of mushrooms in a tunnel (maximum absolute error < 3.2ºC). The codes were applied to determine...

Frozen Food Science and Technology, 2008

Journal of Food Engineering, 2007

The SAFE ICE project, supported by the European Commission, addresses and overcomes specific scientific and technological hurdles to make an informed judgment on the relevance of food related effects of High-Pressure in the Low-Temperature (HPLT) domain as well as to realize and to deliver their full benefits to the end users. Such hurdles include the lack of systematic data, and a limited understanding related to the mechanisms involved in phase transitions under pressure at subzero temperatures. The project involves seven partners, bringing together academic and research centres with food industry and equipment manufacturing parties. The main findings of the research carried out in the frame of the project are: the systematic compilation of thermophysical properties of water, aqueous model solutions and model foods to be applied in mathematical models able to reproduce and predict freezing and thawing time profiles at high pressure; the comprehension of the kinetics of phase transition phenomena at HP, including the definition of metastable phases; a key to define critical processing parameters to obtain optimized freezing and thawing paths; the study of the effect of HPLT on key food spoilage enzymes and on microorganisms; the study of consumer acceptance of the technology; the evaluation of the impact of SAFE ICE processes on food quality related parameters and the development of prototypes (HPLT microscopic cell and HPLT differential thermal analysis cell) and process and products concepts for industrial development of SAFE ICE processes.

Food and Environment II, 2013

Modelling of heat transfer-controlled cooling and freezing time predictions are very important for a good preservation of foodstuffs. In that regard, we used a computer code based on the finite-element method that allowed us to analyse the phase-change of various foodstuffs during their freezing. The model was exercised to predict process times. The results can be used to design high efficiency plants. In this work, the results predicted by the FEM program are compared with the experimental values given in technical literature.

Applied Thermal Engineering, 2011

In this article a convective freezing procedure, based on five different air velocities, applied to green beans is presented. Equations to predict the initial freezing temperature, thermal conductivity and specific heat of a food product as a function of its composition and temperature are reported. These equations were coupled to the Tchigeov method, which predicts the ice fraction formed at temperatures below the freezing point for green beans. This procedure enabled the prediction of the thermal properties and the values obtained were in good agreement with data reported in the literature. Furthermore, a computational code in finite differences was developed to solve the transient heat conduction equation, transformed by the introduction of the enthalpy and Kirchhoff functions. This numerical model was used to fit experimental time-temperature data for freezing green beans. The procedure represents a useful method to predict the thermal properties and temperature evolution within a food product subjected to a freezing process.

Journal of Food Engineering - J FOOD ENG, 2005

Cylindrical specimens (7.8 mm diameter, 35 mm length) of gelatin gel (2% gelatin, w/w) were frozen by pressure shift freezing (PSF) at 100 MPa (−8.4 °C), 150 MPa (−14 °C) and 200 MPa (−20 °C) as well as conventional air freezing (CAF) and liquid immersion freezing (LIF) at −20 °C. Pressure and temperature profiles of gel samples were gathered during the freezing process. The ovoid microstructure of ice crystals in frozen gelatin gels after freeze-drying was evaluated for area, equivalent diameter, roundness and elongation. Equivalent diameter (mean ± s.d.) of the ice crystals was 145 ± 66, 84 ± 26, 91 ± 30, 73 ± 29, and 44 ± 16 μm for test samples subjected to CAF, LIF and PSF at 100, 150 and 200 MPa, respectively. Roundness and elongation were somewhat variable and did not show a clear trend with the different freezing techniques. Results from this study with a model food (gelatin gel) confirm that the PSF process promotes the production of larger number of smaller ice crystal in the frozen sample that help to retain a better texture in the product.

International Journal of Energy Research, 2003

This article presents a numerical simulation that estimates the freezing time for different products. In this regard, the freezing process is mathematically modelled by transient heat conduction equations that incorporate the physical properties of the three distinct regions that exist during a freezing process. These regions are namely, the solid phase region, the liquid phase region and the interface region. This model is experimentally validated and used to estimate the freezing time for three different food products, which are namely, fish balls, cherry juice and peas balls. The freezing times estimated numerically through the present model agree well with those reported in the literature and are in excellent agreement with the experimental data.