A model to design high-pressure processes towards an uniform temperature distribution
ABSTRACT A mathematical model has been developed to describe the phenomena of heat and mass transfer taking place during the high-pressure treatment of foods. It has proved that convection currents in the pressure medium play an important role in the thermal evolution of the processed samples especially when the filling ratio in the pressure vessel is low. This model shows to be an extremely useful toot to design high-pressure processes seeking a uniform temperature distribution. (c) 2006 Elsevier Ltd. All rights reserved.
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ABSTRACT: The present work is development of a simple method to evaluate the skin temperature and thermal diffusivity variations of regular shaped food products subjected to natural convection cooling at constant pressure. Experimental investigations were carried on the sample chosen (potato), which is approximately of spherical geometry. The variation of temperature within the food product is measured at several locations from center to skin, under natural convection environment using a deep freezer, maintained at -10°C. Skin temperature is obtained based extrapolation of temperature profile from center towards skin. Thermal diffusivity variation iscalculated using one-dimensional Fourier’s equation and is plotted against skin temperature of the product.
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ABSTRACT: Nowadays, consumers look for minimally processed, additive-free food products that maintain their organoleptic properties. This has promoted the develop-ment of new technologies for food processing. One emerging technology is high hydrostatic pressure, as it proves to be very effective in prolonging the shelf life of foods without losing its properties. Recent works have been done on the modelling and simulation of the effect of the combination of thermal and high pressure processes. These focus mainly on the inactivation that occurs during the process of certain enzymes and microorganisms that are harmful to food. Various mathematical models that study the behavior of these enzymes and microorganisms during and after the process have been proposed. Such models need as an input the temperature and pressure profiles of the whole process. In this work we present some of the existent two dimensional models to calculate the temperature profile for solid type foods and we propose a simplification to a one dimensional model. The temperature profile of the one dimensional model is calculated both numerically and analytically, and these solutions are compared to the resulting temperature profile of the two dimensional model. This dimensional reduction is reasonable to do in some cases, which are specified in this work.
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ABSTRACT: Cooling is an important task in the food industry. Harvested agricultural produce is subjected to precooling before packaging, processing and transportation. Heat moves to surface of product in a mixed-mode of conduction and convection, and from surface to environment by convection. Therefore, estimation of thermal properties (like thermal diffusivity) is important to analyze heat transfer phenomena and design of refrigeration and processing equipments. This work presents a simple method to estimate thermal diffusivity variations of selected regular shaped food products subjected to natural convection cooling. Experimental investigations were carried out on fruits and vegetables. Samples chosen were melon, orange and potato (spherical) and bottle gourd (cylindrical). The experimental setup consists of a deep-freezer maintained at -10˚C and 1 atm. The variation of temperature within a product is measured along the radial direction using copper-constantan thermocouples. The output of thermocouples is read on a digital microvolt meter. The temperature of thermocouples was recorded at regular intervals of 5 minutes. Variation of surface temperature is obtained based on radial temperature profiles. Thermal diffusivity (α) variation is calculated for each time interval using one-dimensional Fourier's equation. Correlation for thermal diffusivity as a function of surface temperature is developed for each of the sample.The 3rd International Symposium on Processing of Foods, Vegetables and Fruits, The University of Nottingham Teaching Centre Level 2, Chulan Tower No 3 Jalan Conlay 50450 Kuala Lumpur, Malaysia; 08/2014