利用計算流體力學模式探討罐頭食品中旋轉對抑制細菌之研究

Influence of Rotation Speed on the Sterilization of a Steamed Liquid Food Can Using Numerical Simulation.

莊依潔(I-Chieh chuang)

指導教授 ： 鄧志浩

中原大學/工學院/土木工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200952

摘要

以數值計算流體動力學軟體( ANSYS FLUENT )研究罐頭在殺菌過程中當加入旋轉動力後罐頭內溶液( 羧甲基纖維素，CMC )溫度及濃度的變化。我們設定在此作用下罐頭的外壁溫度皆為121°C，當罐頭受到外力旋轉力時，會產生自然對流。罐頭內溶液的特性除了密度和黏滯力，其他皆為定值。利用統域方程式中的能量、動量以及質量方程式來進行模擬，模擬中我們將罐頭加入五種不同的轉速( 5、10、15、20、25rpm )和三段時間( 1、19、43分鐘 )研究其濃度、最慢加熱區域( SHZ )及速度的變化量。在我們研究中，我們先探討under-relaxation factors(λ)在三種不同的值(0.25、0.5、0.8)下所呈現之結果選出最佳的因子，進而，針對我們所選出來的因子進行模擬。
最後的結果我們發現under-relaxation factors(λ)在0.5時為最佳狀態；當我們將溫度設定為100℃，發現當罐頭從靜止狀態到罐頭外部的轉速達到25rpm時，加熱的時間省了10%；而當罐頭外部的轉速越大時，罐頭內部溶液的濃度值差距為1-0.1%，因此轉速對於罐頭的殺菌作用而言沒有產生很大的效益。

關鍵字

殺菌作用 ； 溫度分布 ； 最慢加熱區 ； 計算流體動力學 ； 自然對流

並列摘要

This paper presents an efficient way for the sterilization of a liquid food (aqueous solution of sodium carboxy-methyl cellulose, CMC ) can lying vertically and rotated axially by using a commercial computational fluid dynamics package ( ANSYS FLUENT ). Aside from the forced convection applied by rotating the can, the simulation involved effect of the natural convection with steam heating to 121 ℃ around all of the can sides. The liquid food in the can was assumed to have constant properties, except for the density (Boussinesq assumption) and viscosity (temperature dependent). By solving the governing equations of mass, momentum and energy, we compared the species and the temperature profile in the thermal sterilization which emphasizes the slowest heating zone (SHZ) of viscous rotation speeds compared to that of a stationary can. The simulation results of temperature profiles with different rotation speeds ( 5, 10, 15, 20, and 25 rpm ) for different periods (1, 19, and 43 minutes).
In our study, first we choose the optimal factor in the under-relaxation factors ( λ ) with different value ( 0.25, 0.5, 0.8 ) used in our simulation. Finally, we found the under-relaxation factors at 0.5 is the best condition. With the higher rotational speed (25rpm), the heating process time is further reduced when reaching the same lowest temperature (100℃) at the SHZ of the liquid food can. When the rotation speed increased, the species concentration value decreased 1-0.1% in the liquid food can. Therefore, the rotation speed did not produce great benefits for the sterilization of can.

並列關鍵字

CMC ； Natural and forced convections ； computation fluid dynamics ； temperature distribution ； sterilization ； SHZ (slowest heating zone).

參考文獻

Christiansen, E. B. and Craig, S. E. (1962). Heat transfer to pseudoplastic

Agricultural Engineers. St. Joseph, MI: American Society of Agricultural

temperature and velocity profiles during natural convection heating of canned

Mass Transfer, 20, 301-309.

coldest point during sterilization of canned food. In The 26th Australian