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 南方水产科学   2018, Vol. 14 Issue (5): 95-102.  DOI: 10.3969/j.issn.2095-0780.2018.05.012 0

### 引用本文 [复制中英文]

[复制中文]
HU Xiaoliang, WANG Xichang, LI Yulin, WANG Yifen, SHEN Jian. Numerical simulation of temperature distribution during radio frequency tempering of pollack surimi based on dielectric properties[J]. South China Fisheries Science, 2018, 14(5): 95-102. DOI: 10.3969/j.issn.2095-0780.2018.05.012.
[复制英文]

### 文章历史

1. 上海海洋大学食品学院，上海 201306;
2. 中国水产科学研究院渔业机械仪器研究所，上海 200092;
3. 农业农村部远洋渔船与装备重点实验室，上海 200092

Numerical simulation of temperature distribution during radio frequency tempering of pollack surimi based on dielectric properties
HU Xiaoliang1,2,3, WANG Xichang1, LI Yulin1, WANG Yifen1, SHEN Jian2,3
1. College of Food Sciences & Technology, Shanghai Ocean University, Shanghai 201306, China;
2. Fishery Machinery and Instrument Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200092, China;
3. Key Laboratory of Ocean Fishing Vessel and Engineering, Ministry of Agriculture and Rural Affairs, Shanghai 200092, China
Abstract: Radio frequency tempering has properties of selective heating. As the increase of temperature, the hotter part of the thawed material absorbs more energy; heat increases rapidly with the change of dielectric properties, while the corresponding cooler part absorbs less energy, which leads to the difference of temperature distribution and will reduce the quality of thawed materials. Increasing uniformity of temperature distribution is most concerned during radio frequency. In this paper, the dielectric properties of pollock (Theragra chalcogramma) surimi were determined by open ended coaxial-line probe method. The regression equations of the dielectric constant and dielectric loss were obtained. Based on the dielectric property, a numerical simulation of the temperature distribution during radio frequency tempering of pollack surimi was carried out by COMSOL Multiphysics software. In order to obtain the physical process of radio frequency tempering for dynamic numerical simulation, the finite element method was used to solve the electromagnetic wave dissipation and heat transfer coupling equation, and was experimentally verified by conducting radio frequency tempering on pollack surimi. The results show that the simulation of coupling equation based on dielcetric property can predict the temperature distribution of the samples accurately during radio frequency tempering.
Key words: pollock surimi    dielectric properties    radio frequency    tempering    numerical simulation

1 材料与方法 1.1 无线电波加热理论基础

 $\quad\quad\quad\quad\quad\; \varepsilon = {\varepsilon _0}{\varepsilon _r} = {\varepsilon _0}\left( {{\varepsilon _r}' - j{\varepsilon _r}''} \right) = \varepsilon ' - j\varepsilon ''$ (1)

 $\quad\quad\quad\quad\quad\quad\quad \tan \delta = \varepsilon ''/\varepsilon ' = {\varepsilon _r}''/{\varepsilon _r}'$ (2)

 $\quad\quad\quad \quad P = 2{\text {π}} f{\varepsilon _0}{\varepsilon _r}''{E^2} = 5.56 \times {10^{ - 11}}f{\varepsilon _r}''{E^2}$ (3)

 $\quad\quad\quad\quad\quad\quad\quad \rho {C_{\rm p}}\frac{{\partial T}}{{\partial t}} = \nabla \left( {k\nabla T} \right) + P$ (4)

 $\quad\quad\quad\quad\quad\quad\quad - k\nabla T = h\left( {T - {T_{\rm air}}} \right)$ (5)

1.2 实验材料

1.3 狭鳕鱼糜介电特性测定

1.4 模型建立

1.5 模型验证

 图 1 鱼糜温度测定点示意图 Fig.1 Diagram of temperature measurement point of surimi
1.6 数据分析

2 结果与分析 2.1 介电常数

 图 2 频率对狭鳕鱼糜介电常数的影响 Fig.2 Effect of frequency on dielectric constant of pollack surimi

27.1 MHz和915 MHz为食品加工业中常用的频率。图3为27.1 MHz和915 MHz频率下狭鳕鱼糜的介电常数随温度的变化关系。在27.1 MHz和915 MHz频率下狭鳕鱼糜的介电常数随温度的变化趋势一致。温度为–18~ – 6 ℃时，狭鳕鱼糜的介电常数随着温度的升高平缓增大；温度为–6~0 ℃时，狭鳕鱼糜的介电常数随着温度的升高急剧增大；温度高于0 ℃时，狭鳕鱼糜的介电常数随着温度的升高而逐渐降低。通常情况下介电常数与物料的湿度成正相关[19]。狭鳕鱼糜的水分质量分数为74%，温度为–18~ – 6 ℃时，鱼糜处于冻结状态，狭鳕鱼糜的水分绝大部分以冰晶形式存在；温度继续升高，冰晶开始融化成自由水，所以温度为– 6~0 ℃时，狭鳕鱼糜的介电常数出现了急剧增大；温度进一步升高后，鱼糜介电常数逐渐减小，这可能是由于温度升高导致分子运动加剧，使水分子有序排列被打乱，从而使其储存电磁能的能力下降。贾敏等[20]研究了鲍的介电常数随温度的变化情况，结果表明鲍样品的介电常数随温度升高，出现先上升后下降的现象，这与鲍样品在加热过程中水分的状态与含量的变化有关。Piyasena等[6]研究了介电常数随温度的变化规律，也得出了类似结论。

 图 3 温度对狭鳕鱼糜介电常数的影响 Fig.3 Effect of temperature on dielectric constant of pollack surimi
2.2 介电损失

 图 4 频率对狭鳕鱼糜介电损失的影响 Fig.4 Effect of frequency on loss factor of pollack surimi

 图 5 温度对狭鳕鱼糜介电损失的影响 Fig.5 Effect of temperature on loss factor of pollack surimi
2.3 介电特性的拟合方程

2.4 数值模拟

 图 6 加热腔体内部电场强度分布 Fig.6 Distribution of electric field intensity in heating chamber

 图 7 无线电波加热后鱼糜温度分布的比较 Fig.7 Comparison of temperature distribution in surimi tempered by radio frequency

2.5 模型验证

 图 8 无线电波加热过程中温度模拟值与实测值的比较 Fig.8 Comparison of simulated and measured temperature during radio frequency tempering
3 结论

1)狭鳕鱼糜的介电常数随着温度的升高先增大后减小；在27.1 MHz和915 MHz频率下狭鳕鱼糜的介电常数随温度的变化趋势一致。狭鳕鱼糜的介电损失随着温度的升高而增大，频率为27.1 MHz时狭鳕鱼糜的介电损失值大于915 MHz。

2)通过模拟值与实测值的比较，表明应用COMSOL Multiphysics软件获得的电磁波耗散及热传递耦合方程可准确地模拟无线电波加热过程的温度变化，从而用于预测物料的温度分布。

3)无线电波具有整体加热的特性，物料温度分布均匀性较好，但随着加热时间的延长，物料边角部位会发生“热逃逸”现象。