利用CFD对不同尺寸上下冲击式速冻机静压腔流场的研究

Study on the Flow Field of Hydrostatic Cavity of Impinging Freezer with Different Sizes by CFD

为进一步优化上下冲击式速冻机的冻结效果,本文以静压腔尺寸为4 m×1.5 m×2 m的实体速冻机为基础,保证入口压力为190 Pa、入口体积流量为2.64 m^3/s不变,提出了4 m×1.5 m×1.5 m、4 m×2 m×1.5 m、4 m×2 m×2 m、4 m×2.5 m×1.5 m、4 m×2.5 m×2 m等5种不同的静压腔尺寸,通过CFD来模拟静压腔尺寸变化对于速冻机内部流场的改变,从速冻机喷嘴出口风速、钢带表面气流的矢量分布、钢带表面换热强度及换热均匀性等方面来综合分析静压腔内部换热特性。结果表明:在静压腔入口流量相同、压力不变的情况下,唯有4 m×1.5 m×1.5 m的出口风速与原有尺寸的出口风速相差较小,其余尺寸的出口风速略小但变化幅度不明显。而该尺寸的换热强度以及换热均匀性却远不如4 m×2.5 m×1.5 m、4 m×2.5 m×2 m。此外,静压腔尺寸为4 m×2 m×2 m的换热强度虽然比4 m×1.5 m×2 m的换热强度高约4.85%,但均匀性较差,不足以成为优选设计。4 m×2.5 m×1.5 m与4 m×2.5 m×2 m的换热强度达到177.76和177.39,比原有尺寸下钢带表面换热强度高约6.81%和6.59%,且均匀性也为最佳。结合上述因素,4 m×2.5 m×1.5 m和4 m×2.5 m×2 m在出口风速、换热强度及均匀性方面均为5种尺寸中最优的设计。

Since traditional impact freezers have low freezing efficiency and high food weight loss,upper and lower impact freezers have gradually been recognized as new types with high efficiency by the food quick-freezing industry.In order to further optimize the freezing effect of the upper and lower impact freezers,a solid impact freezer with a hydrostatic cavity size of 4 m×1.5 m×2 m was taken as the baseline.The internal flow fields of five different dimensions of hydrostatic cavities including 4 m×1.5 m×1.5 m,4 m×2 m×1.5 m,4 m×2 m×2 m,4 m×2.5 m×1.5 m,and 4 m×2 m×2 m were simulated by computational fluid dynamics(CFD)with the inlet pressure of 190 Pa and inlet flow rate of 4.4 m^3/s.The internal heat transfer characteristics of the hydrostatic cavity were also analyzed comprehensively in terms of the nozzle outlet wind velocity of the impact freezer,vector distribution of the air flow on the surface of the steel belt,surface heat transfer intensity and heat transfer uniformity of the steel belt.The results showed that under the condition of the same inlet flow and constant pressure,only the outlet wind velocity of the cavity of dimensions 4 m×1.5 m×1.5 m differed slightly from that of the original size,and the wind velocities of the other sizes were slightly lower,but the range of change was not apparent.However,the heat transfer intensity and uniformity of this size were far less than those for the cavities with dimensions of 4 m×2.5 m×1.5 m and 4 m×2.5 m×2 m.In addition,although the heat transfer intensity of the hydrostatic cavity of dimensions 4 m×2 m×2 m was approximately 4.85%higher than that of the cavity of dimensions 4 m×1.5 m×2 m,its uniformity was poor and insufficient for it to be the optimal design.The heat transfer intensity of the cavities of dimensions 4 m×2.5 m×1.5 m and 4 m×2.5 m×2 m reached 177.76 and 177.39,which were approximately 6.81%and 6.59%higher than the surface heat transfer intensity of the steel belt under the original size.Additionally,the uniformity was the best.Combined with the above factors,the cavities of dimensions 4 m×2.5 m×1.5 m and 4 m×2.5 m×2 m were the optimal designs among the five sizes in terms of the outlet wind velocity,heat transfer intensity,and uniformity.