Heat Transfer During the Freezing of Liver in a Plate Freezer

The overall heat transfer coefficient was determined for a vertical plate freezer by the transient temperature method and used in a modification of Plank's equation by Cleland and Earle to predict the freezing time of blocks of pig liver. A comparison of predicted and previously published experimental freezing times showed an average absolute error of 6.5%. Overall heat transfer coefficients for the main types of fibreboard packaging were also determined together with their effect on predicted freezing time. This work has highlighted many of the advantages of plate freezing which has yet to gain wide acceptance in the U.K. meat industry.     

Measurement of Convective Heat Transfer Coefficients During Food Freezing Processes

Any prediction of freezing time for a food product depends on accurate heat transfer coefficients. The purpose of this investigation was to examine experimental procedures for accurate determination of convective transfer coefficients during freezing of food products. Measurements of heat transfer coefficients during cooling of any acrylic transducer and ground beef with similar size and shape were conducted at air temperatures below initial freezing point of the product. The results indicate that accurate measurements of the coefficients can be achieved through nonlinear regression analysis of temperature histories within an acrylic transducer.     

Modeling Flow and Heat Transfer During Freezing of Foods in Forced Airstreams

ABSTRACT: Mathematical modeling of food freezing has been limited to the modeling of the internal heat transfer where the external convective heat-transfer coefficients are assumed or empirically estimated. Previous procedures followed to solve the external boundary layer in tandem with the internal heat transfer were constrained by numerical complexities due to the transient nature of the heat transfer, requiring unsteady formulation for the flow. In this article, attempts have been made to decouple the flow and heat transfer equations for the external boundary layer flow over a food product being frozen. The flow equations have been solved as a steady-state problem using Falker-Skan transformations of the boundary layer equation. The heat-transfer equation for fluid flow is solved as an unsteady-state problem in conjunction with the internal heat transfer and phase change inside the product undergoing freezing. The model is validated for a case of air-impingement freezing.     

鲢鱼肉冷冻过程中传热预测模型的建立与验证

准确模拟冷冻过程、预测冻结时间对速冻设备的设计与控制以及保证产品质量均有重要意义。本文在鲢鱼肉热物性参数预测模型和焓模式数学模型的基础之上,采用有限差分法对平板状鲢鱼肉建立物理模型,分别预测了鲢鱼肉热中心及边界层的冷冻过程和冻结时间。实验验证表明,厚度为44 mm的鲢鱼肉的热中心和边界层的模拟温度与实验温度的平均差方和分别为1.85和1.30,冻结时间的预测相对误差为-1.64%。在此基础上,对厚度分别为24 mm和34 mm的鲢鱼肉热中心的降温过程进行了模拟,其热中心的模拟温度与实验温度的平均差方和分别为1.73和1.58。说明将热物性参数预测模型和数值模拟相结合的方法,建立的模型具有很高的拟合精度,并能实现对不同厚度鲢鱼肉的冷冻过程进行模拟,为淡水鱼冷冻加工、品质控制及设备开发提供了模拟方法。     

Heat Transfer During Brining of Cuartirolo Argentino Cheese

The heat transfer which occurs during the brining of Cuartirolo Argentino cheese is mathematically modelled as a conduction process. The thermal diffusivity of the cheese was determined experimentally and shown to agree with the value calculated from thermal conductivity, density and heat capacity measurements. The theoretical and experimental temperature profiles in the time and spatial domains showed good agreement, thus demonstrating the applicability of the proposed model.     

Modeling Heat Transfer During Oven Roasting of Unstuffed Turkeys

A finite element method was used to solve the unsteady state heat transfer equations for heating of turkeys in a conventional electric oven. Breast, and thigh and wing joint temperature in 5.9, 6.8, 8.6, 9.5, and 10.4 kg turkeys were simulated. A surface heat transfer coefficient of 19.252 W/m2K determined by transient temperature measurements in the same oven, was used. Thermal conductivity measured using a line heat source probe from 0 to 80°C was 0.464 W/mK. Simulated temperatures were within 1.33, 1.47, and 1.22°C of experimental values of temperature in the breast, thigh, and wing joint, respectively. Initial temperature 1,2, and 3°C lower than 4°C required additional baking time of 16,22, and 27 min., respectively for the thigh joint to reach the target endpoint temperature.     

Heat Transfer Model Performance in Simulation of Process Deviations

Performance of thermal process simulation software was tested for predicting internal product temperature and lethality. Responses were tested for process deviations on canned products with a wide range of heating characteristics for computer-based on-line control of retorts. Static and agitated processes were tested with products exhibiting heating rate factors (fh) ranging from 2 to 70 min. Cans were fitted with thermocouples and subjected to deviations of various types. Center temperature profiles and lethalities predicted by the model in response to dynamic retort temperatures were compared with those measured by thermocouples. Profiles agreed, and process lethalities calculated from predicted and measured profiles agreed ±10% with the model slightly underpredicting measured lethality.     

Heat Transfer During the Washing of Small Curd Cottage Cheese

The heat transfer which occurs during the cooling of small curd cottage cheese during washing is mathematically modeled as a conduction process. The thermal diffusivity for curd was determined experimentally and shown to agree with predictions of correlations in the Literature. Heat transfer occurs rapidly in curd, and is a relatively less significant design basis for washing systems than mass transfer.     

鲜食玉米冷冻加工过程的传热分析

鲜食玉米由于其良好的保健功效,受到越来越多的人的喜爱,拥有广阔的市场前景。作为鲜食玉米处理工艺中的冻结过程,对鲜食玉米的保鲜质量与生产能耗有着重要的意义。目前对鲜食玉米冻结过程进行传热分析的研究很少,本文采用数值方法,将鲜食玉米模拟为具有同轴的双层圆柱,建立模型并研究其传热过程,为鲜食玉米的冻结生产提供理论指导。     

Finite Element Modeling of Heat Transfer in Meat Patties During Single-sided Pan-frying

Our objectives were to mathematically model heat transfer in meat patties during single-sided pan-frying without and with turn-over, using the finite element method. Moisture loss rate was determined and included in the model to account for evaporation loss. The model was validated by comparing predicted and experimental temperature profiles monitored at three axial positions during pan-frying (one side and turn-over) at 140 and 180°C. Moisture loss rate, cooking time, and crust formation were functions of pan temperature and/or turn-over frequency and time. The least cooked point, predicted at the periphery of the top surface (no turnover) and midplane (one turn-over), required 20 and 10 min, respectively, to be cooked well-done at 160°C. Turning-over more than once slightly decreased frying time, but may not produce crusted surface.     

Two Dimensional Heat Conduction in Food Undergoing Freezing: Development of Computerized Model

A model was developed to simulate two dimensional heat conduction in anisotropic food which was undergoing a freezing process. This model utilized a well verified transient state heat conduction equation. We assumed convective and radiative heat exchanges as well as moisture loss on the boundary surface of food to develop our model. Empirical formulae, whose applicability was verified, were used to estimate the temperature dependent thermophysical property values of food in the model. Since the model is nonlinear, a computer program package was prepared to solve it numerically by applying a finite element method. Sample application of computerized procedure was presented for simulating rectangular or finitely cylindrical food.     

烟叶在叶片复烤机干燥过程中的传热传质研究

烟叶在叶片复烤机内的干燥包含传热和传质两个过程.通过对传热传质过程的分析,建立干燥过程的数学模型,分别总结出烟叶在恒速干燥阶段和降速干燥阶段的能量平衡方程,推导出烟叶温度、水分随热空气的温度以及干燥时间的变化关系,对于优化控制设备的工艺参数、指导烟叶复烤生产、节约能耗有着重要的作用.     

Immersion Chilling and Freezing: Phase Change and Mass Transfer in Model Food

The influence of immersion chilling and freezing process variables (temperature, concentration, agitation) on phase change and salt gain, was studied on a gelatin gel dipped into a NaCl solution, with particular emphasis on unsteady state (first hour). Under freezing conditions, water loss was <2 g/100g initial gel and salt gain remained low (<1 g/100g initial gel). Salt penetration was hindered by formation of an ice barrier, which was favored by high concentration and low temperature. Under chilling conditions, salt gain was higher (up to 2 g/100g initial gel), and was enhanced when temperature or concentration increased.     

Estimation of Heat and Mass Transfer Coefficients During Air-Freezing of Cucumber

Freezing of foods involves coupled heat and mass transfer. It is essential to optimally design the freezing equipment and maximise the efficiency of the freezing process. Therefore, it is necessary to estimate the heat and mass transfer coefficients. In this study, the surface heat and mass transfer coefficients were estimated employing the Hilbert equation as well as the corresponding thermal and diffusive boundary layers during freezing of unpeeled cucumber at low air temperatures (?10 to??18 and??25°C). The estimated mean heat transfer coefficients ranged from 10.99 W m^?2 K^?1 for 0.5 m s^?1 up to 40.07 W m^?2 K^?1 for 5.0 m s^?1. The respective mass transfer coefficients ranged from 8.98 up to 32.40 m s^?1. The estimated heat transfer coefficients were compared with the respective ones calculated from Dincer and Dincer and Cengeli during air-cooling (22 to 2°C) of unpeeled cucumbers of similar size as well as other agricultural cylindrical products.     

Heat and Mass Transfer During the Warm Water Blanching of Potatoes

A model of heat and mass transfer with simultaneous chemical reaction is proposed for analyzing the influence of operating variables on the reducing sugar content at the surface of blanched potatoes. This content is partially responsible for the color of the finished product. The involved parameters (potato thermal conductivity, heat transfer coefficient of the system and kinetic constants for overall reaction of reducing sugar generation) were evaluated in separate experiments. The apparent diffusion coefficient of reducing sugars in potatoes was the only parameter obtained from blanching experiments. Temperature and concentration profiles and effect of blanching temperature on surface reducing sugar content are analyzed using the developed model. The possible underestimation of the diffusion coefficient when simultaneous starch hydrolysis is not taken into account is also considered.     

微波加热鸡肉和土豆的传热仿真分析研究

为了更好地了解与研究家用微波炉微波加热过程中即食食品的传热特性,本文建立了电磁与传热耦合的仿真模型,研究鸡肉和土豆的空间温度和瞬态温度变化规律,并通过实验研究在-5~95℃范围内,鸡肉在频率为2450 MHz时的介电特性和热物理特性。基于温度对鸡肉介电和热物理特性的分析,将温度可分成两个范围:-5~0℃和0~95℃,各温度范围内的鸡肉特性变化趋势不同。仿真模型包括加热腔、波导以及可旋转的转盘和物料。通过比较不同转速对仿真结果的影响,综合考虑仿真所用时间以及物料的均匀性,选用7.5 r/min作为转盘转速。当微波功率为700 W时,组合样品的仿真结果显示,经过90 s的微波加热,空间温度场分布和瞬态温度曲线与实验结果保持一致,微波仿真组合样品的模型是可行的,研究结果为优化微波加热冷藏快餐的均匀性研究提供一定依据。     

Heat and Moisture Transfer and Hygrophysical Changes in Elastoplastic Hollow Cylinder-food During Drying

There are many dried foods of hollow cylinder-shapes in the market. Hygrostress cracks form in these foods during drying without a careful process control. The objective of the present work was to develop a simulation method for heat and moisture transfer in hollow cylinder-food coupled with hygrophysical changes. A modified Luikov's model was used for the development together with a virtual work minimization principle, critical tensile stress criterion for crack formation, and critical crack-tip-opening angle criterion for crack propagation. The developed, computerized simulation model was validated through drying experiments of samples made from a starch hydrate.     

Robustness of a Cross Contamination Model Describing Transfer of Pathogens During Grinding of Meat

This study aimed to evaluate a cross contamination model¹ for its capability of describing transfer of Salmonella spp. and L. monocytogenes during grinding of varying sizes and numbers of pieces of meats in two grinder systems. Data from 19 trials were collected. Three evaluation approaches were applied: i) Acceptable Simulation Zone method compared observed with simulated transfer, ii) each trial was fitted and parameters were integrated in a Quantitative Microbiological Risk Assessment model, iii) the Total Transfer Potential was calculated from fitted parameters. Risk estimates revealed that grinding was influenced by sharpness of grinder knife, specific grinder and grinding temperature.     

Modeling Simultaneous Shrinkage and Heat and Mass Transfer of a Thin, Nonporous Film During Drying

Thin films of food products have long been dried commercially but the thin film drying process is not well understood. Modeling of a drying system is essential for understanding and improving it. A theoretical model for predicting the drying rate of thin films of nonporous foods was proposed, developed and evaluated. The model simultaneously considered shrinkage and heat and mass transfer within thin films dried on a surface with given boundary conditions. A finite element formulation of the model was used to develop numerical solutions of two governing equations. Starch was selected as a representative material for drying tests. Experimentally determined drying curves of modified corn, potato and rice starch films were compared to model predictions. The technique was useful in explaining the complex relationships of temperature, moisture and thickness profiles of drying films.