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.     

Heat and Mass Transfer Coefficients in Drying of Starch Based Food Systems

Experiments were conducted to measure the temperature and moisture content of starch and starch-fructose samples during drying. A two-dimensional finite element model was developed. An exhaustive parameter estimation technique was applied in conjunction with the model and drying data to estimate the moisture filtration coefficient k_p and the surface heat and mass transfer coefficients, h_q and h_m. Minimization of the deviation between experimental and simulation data resulted in a k_p value of 0.51*10^?7 kg.m/N.h and 0.52*10^?7 kg.m/N.h for the starch and starch-fructose samples. Corresponding values of h_q were 15.8 W/m²K and 21.2 W/m²K and that of h_m were 1.12*10^?6 m/s and 0.94*10^?6 m/s respectively.     

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.     

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.     

Cooling of Shell Eggs with Cryogenic Carbon Dioxide: a Finite Element Analysis of Heat Transfer

Cryogenic carbon dioxide cooling of shell eggs was simulated using an axisymmetric unsteady state finite element heat transfer model. The egg was assumed to be a composite system of elliptical shape, consisting of yolk, albumen, air cell, and shell, each isotropic. An enthalpy formulation of the heat transfer problem was used to account for ice formation and growth in the region between the albumen and the shell during cooling. Simulated temperature profiles were compared with analytical and observed data and showed good agreement. The numerical simulation was used to gain an understanding of the two processes encompassed by cryogenic cooling, rapid cooling and equilibration.     

烟叶在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2个过程。通过对传热传质过程的分析,建立了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。     

Heat and Mass Transport during Microwave Heating of Mashed Potato in Domestic Oven—Model Development,Validation, and Sensitivity Analysis

A 3‐dimensional finite‐element model coupling electromagnetics and heat and mass transfer was developed to understand the interactions between the microwaves and fresh mashed potato in a 500 mL tray. The model was validated by performing heating of mashed potato from 25 °C on a rotating turntable in a microwave oven, rated at 1200 W, for 3 min. The simulated spatial temperature profiles on the top and bottom layer of the mashed potato showed similar hot and cold spots when compared to the thermal images acquired by an infrared camera. Transient temperature profiles at 6 locations collected by fiber‐optic sensors showed good agreement with predicted results, with the root mean square error ranging from 1.6 to 11.7 °C. The predicted total moisture loss matched well with the observed result. Several input parameters, such as the evaporation rate constant, the intrinsic permeability of water and gas, and the diffusion coefficient of water and gas, are not readily available for mashed potato, and they cannot be easily measured experimentally. Reported values for raw potato were used as baseline values. A sensitivity analysis of these input parameters on the temperature profiles and the total moisture loss was evaluated by changing the baseline values to their 10% and 1000%. The sensitivity analysis showed that the gas diffusion coefficient, intrinsic water permeability, and the evaporation rate constant greatly influenced the predicted temperature and total moisture loss, while the intrinsic gas permeability and the water diffusion coefficient had little influence.     

基于介电特性的白蘑菇微波冻干传热传质模拟

真空冷冻干燥技术常用来生产高品质的冻干白蘑菇,但其能耗大、干燥时间长的缺点限制了其推广应用。与传统冷冻干燥技术相比,微波冷冻干燥可节约干燥时间和能耗,同时可保持其冻干产品的特点。微波冷冻干燥过程的质热传递现象极为复杂,其过程的预测对干燥过程的控制至关重要。此外,目前国内外对于微波冻干过程的传热传质模拟都未考虑物料介电损耗因子变化会导致其微波吸收特性的改变,故模拟结果都不甚理想。本文通过矢量网络分析仪对白蘑菇介电特性进行精确测定,得出白蘑菇介电损损耗因子相对其温度和水分含量的回归方程;在此基础上利用较为通用的升华-冷凝模型对微波冻干过程质热传递进行了数值模拟研究,通过白蘑菇微波冻干试验验证,表明考虑了介电特性的微波冻干质热传递模型可对物料温度分布进行较准确的预测。     

油菜籽热风干燥传热传质与优化的研究进展

油菜是经济价值高、发展潜力大的油料作物,也是蛋白质、饲料、蜜源和能源作物,油菜籽的干燥和储存联系油菜高产栽培和油脂深加工综合利用。本文在分析油菜籽干燥特点和主要干燥技术的基础上,综述了油菜籽热风干燥传热传质与优化的研究进展,以期为油菜籽热风干燥装置设计、干燥工艺、参数和过程优化等的研究提供依据。目前,有关油菜籽热风干燥传热传质与优化的研究多限于实验层面,不具有广泛适用性。传统干燥理论和模型大多以Luikov理论和Whitaker理论为基础,对其适当简化或修正,由于假设多孔介质为均匀分布连续介质,无法揭示局部和整体之间的本质联系。将分形理论与孔道网络模型相结合是多孔介质干燥尺度综合的有效方法。数值研究有宏观、多尺度和微观三个层面,借助CFD技术可以有效获悉干燥速率、能量消耗和湿分分布等信息,以优化干燥装置和过程控制。油菜籽热风干燥实验研究主要集中在干燥特性、干燥品质及其测量技术等方面,为获得良好的干燥品质,应注意干燥工艺、参数和过程优化。     

稻谷的微波干燥特性及质热模型

微波干燥时谷物的失水、温度变化过程均可分二个阶段。干燥功率０．２Ｗ／ｇ或０．２Ｗ／ｇ以下，发芽率高，爆腰率低。干燥贮藏后脂肪酸含量比热风的低。建立了谷物微波干燥的水分和热量传递模型，确定了水分扩散系数。     

Explicit Finite Difference Methods for Heat Transfer Simulation and Thermal Process Design

A considerable difference between two explicit finite difference heat transfer simulation approaches was described. Time step restrictions, which are often the basis for criticism of explicit methods, were shown to be less severe when the surface was not considered to have thermal mass. Thermal process design combines heat transfer and reaction kinetics considerations. Accuracy of lethality estimates depends on time step size. Guidelines were developed for applying discrete time-temperature data to thermal process calculations. For time steps small enough to permit a linear temperature change approximation, it was shown that for increasing (decreasing) temperatures, a value within 50 to 60% (40 to 50%) of total temperature change should be used.     

类长圆形葡萄强制通风预泠过程的有限元法研究

建立了纵剖面为类长圆形的葡萄强制通风预冷过程的传热数学模型，并用有限单元法对所建模型进行了求解，得出了预冷过程任意时刻葡萄内部的温度场及关键性参数如半冷却时间、7／8冷却时间等，并用试验结果进行了验证。结果发现，有限单元法对模型的求解能精确地对预冷过程进行预测。     

农产品热风干燥传热传质数值模拟研究进展

干燥是农产品安全贮藏的重要手段。热风干燥具有成本低、效率高、可持续大量干燥等优点,在农产品干燥中应用十分广泛。农产品热风干燥过程包含复杂的传热传质过程,对该过程进行准确预测可为绿色节能提质增效的干燥工艺开发、设备研制等提供重要理论依据。本文综述了农产品热风干燥传热传质过程的三种常用的数值模拟方法,即干燥动力学模型方法、连续介质假设模型方法和孔道网络模型方法。简要回顾这三种方法的发展历程,重点介绍其基本理论及数学模型,阐述其在农产品热风干燥研究中的应用,总结其优缺点,并对其未来发展进行展望。     

纸页干燥过程计算模型

基于多孔介质传热传质理论，建立了计算纸页抄造过程干燥参数变化规律的模型，以此模型计算了纸板在烘缸表面和自由行走阶段的温度、水分的变化。计算结果表明，自由行走阶段水分的蒸发率大于纸在烘缸表面的蒸发率；在干燥部的中前段，相对水分蒸发率随烘缸数增加呈线性增加。与实测值的比较证明了模型计算结果的准确性，该模型还可用于烘缸数的选择与设计。     

电热变模温高光模具加热棒传热过程数值模拟研究

电热变模温高光模具可以有效消除传统注塑成型过程中制件的熔接线、浮纤、银纹等缺陷.电加热棒的性质对塑件的质量有着重要影响.文章对电热变模温高光模具的加热棒在加热过程中传热过程进行模拟,分析加热棒热传递情况以及加热棒损坏的影响因子,为电热变模温高光模具结构设计和加热棒的选用提供依据.     

Heat Transfer and Microbial Kinetics Modeling to Determine the Location of Microorganisms within Cucumber Fruit

ABSTRACT: Microbiological and modeling (combined heat transfer and microbial kinetic equations [HTMK] model) approaches were used to determine the location of microorganisms within cucumber. The total number of aerobes found within/on cucumbers varied from 10⁵ to 10⁷ colony-forming units (CFU) /g. The highest and the least amount of microbiota were respectively found at the blossom end and middle part of the cucumbers and were within the 1st 6 mm of the cucumber surface. A comparison of the calculated thermal death time from the HTMK model with the values obtained from experimental data showed that total aerobic microorganisms were located within 0.65 mm of the fruit surface.     

热泵式长豇豆干燥工艺优化

为保证热泵干燥后长豇豆产品的复水性和色泽等品质参数良好,同时降低豇豆干燥过程中的能量消耗,提高豇豆干燥生产的效率,采用Box-Behnken试验设计,分析干燥温度、漂烫时间和铺料密度3 个因素对豇豆产品的复水率、色差、单位耗能量和耗时4 个参数的影响,建立多元回归模型,并对干燥工艺参数进行优化,得到热泵式长豇豆干燥工艺的最佳条件为漂烫时间3 min、铺料密度2 kg/m2、干燥温度50 ℃。在该工艺条件下,实际测得长豇豆复水率1.15,色差值22.39,单位耗能量14.31（kW·h）/kg,耗时7 h,与预测值误差极小,为豇豆在实际热泵式干燥设备生产加工中的应用提供一定的理论依据。     

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.     

Finite Element Modeling of Fluid Flow, Heat Transfer, and Melting of Biomaterials in a Single-screw Extruder

ABSTRACT: A mathematical model was developed to simulate non-isothermal plug flow of granular starch in feed zone, melting in transition zone, and non-Newtonian melt flow in metering zone and die channel during single-screw extrusion processing. The maximum deviations between the predicted and experimental pressure at the die entrance, product temperature at the die entrance, and minimum residence time were about 20%, 2.5%, and 8%, respectively, of the measured values when the barrel temperatures were 50°C in the feed zone and 120°C in the rest zones. The deviations were within 40%, 4%, and 15%, respectively, of the measured values when the barrel temperatures were 50°C in the feed zone and 140°C in the rest zones. Simulations were carried out to investigate the operating characteristics of an extruder, the melting degree, and profiles of pressure and bulk temperature during extrusion.     

热疗纺织品热性能测试评价及传热机制研究进展

针对目前热疗纺织品的实际应用、疗效评价、使用安全性及热舒适性等问题,总结了具有热敷、热疗及其他保健作用的可穿戴产品的研究、应用及发展现状。首先,将热疗产品分为电加热、红外线发热两类,分析现阶段热疗纺织品的热性能测试及治疗疗效评估方法,分别从人体热生理实验、动物实验优缺点来阐述不同实验方法对热性能预测的影响。然后,通过可穿戴式热疗产品传热机制的研究,阐述了皮肤传热模型与纺织品传热模型的研究现状,总结了有限元模拟在人体皮肤组织及纺织品热传递研究中的应用。最后,指出在未来的研究中,应全面准确地模拟人体生物组织与纺织品的热传递系统,建立可穿戴热疗纺织品的热舒适性及治疗安全性测评标准。