不同冷却方式对冷鲜鸡肉品质的影响

目的 探究不同冷却方式对鸡肉水分分布、蛋白质变性等理化性质的影响.方法 分析风冷、真空冷却和浸没式真空冷却对鸡肉的冷却速率、pH、色差、质构等指标的影响,通过低场核磁共振和差式扫描量热技术分析冷却后鸡肉中水分分布和肌蛋白的变化.结果 风冷的冷却速率最慢,肉色暗沉,且质量损失率高,硬度和剪切力也较大;真空冷却的冷却速率最快,肉色较为鲜艳,其质量损失率、硬度和剪切力也最大;浸没式真空冷却能有效减小鸡肉的质量损失率(P<0.05),肉色最鲜艳,弹性和回复性也最好.通过差式扫描量热法分析可知,3种冷却方式下肌蛋白的变性焓均减小,风冷组的肌球蛋白、肌浆蛋白和肌动蛋白降解最多,真空冷却组的蛋白降解较风冷组更好,浸没式真空冷却组的蛋白降解最小,与对照组无显著差异;由低场核磁共振分析可知,风冷组不易流动水组分显著降低(P<0.05),自由水显著增加(P<0.05),真空冷却自由水组分显著降低(P<0.05),浸没式真空冷却后鸡肉中水分分布与对照组无显著差异.结论 浸没式真空冷却弥补了真空冷却不足,在一定程度上提高了鸡肉品质.     

On reducing the size of liquid separators for injector circulation plate freezers

Liquid separators for injector plate freezers are large because the liquid level rises towards the end of the freezing process. To calculate the volume of liquid being collected in the separator during freezing the freezing time and the heat removed must be evaluated. A simple method of freezing time estimation based on the progression of a phase change front is proposed. The size of separators can be reduced considerably by letting part of the liquid feed by-pass the injector during initial freezing. With this arrangement the injector dimensions are based upon a refrigerating capacity lower than the maximum.     

Comparison between fixed and fluidized bed continuous pea freezers

Analytical equations for predicting production rates of continuous fixed bed pea freezers are derived on the basis of a simplified model for freezing individual particles. Comparisons with models of continuous fluidized bed freezers of the same dimensions show production rates 20–30% higher for fluidized beds. The bed height proves to be an important operating variable for obtaining the maximum production rate in these types of freezers. From the standpoint of power consumption in blowers the fixed bed requires 1.7–2.1 times more power for attaining equal production rates.     

Comparison between fixed and fluidized bed continuous pea freezersComparaison des congélateurs continus pour petits pois à lit fixe et à lit fluidisé

Analytical equations for predicting production rates of continuous fixed bed pea freezers are derived on the basis of a simplified model for freezing individual particles. Comparisons with models of continuous fluidized bed freezers of the same dimensions show production rates 20–30% higher for fluidized beds. The bed height proves to be an important operating variable for obtaining the maximum production rate in these types of freezers. From the standpoint of power consumption in blowers the fixed bed requires 1.7–2.1 times more power for attaining equal production rates.     

风道结构对自提冷冻冷藏柜空气流场和温度场的影响

风道结构的改变可有效改善自提冷冻柜内部气流组织和优化热环境性能。本文在自提冷冻冷藏柜有负载状态下,针对上送上回的送回风方式,改变风道结构,即轴流挡板角度(30°、45°、60°、90°)、背部送风孔板开孔方式(上疏下密的非均匀式开孔、下部集中式开孔、等间距式开孔)以及送风板开孔率(6%、8%、10%),建立10种模型并对比分析,选取最优结构模型。并将原始结构(挡板角度45°、集中开孔方式、开孔率6%)模拟与实测结果进行对比,验证了模型的正确性。数值模拟和实验验证结果显示,回风板角度60°时相比于原对照组45°的均匀性提高了23. 0%,非均匀开孔方式相比于集中式开孔速度均匀性提高了4. 8%,且开孔率为8%时比原6%的整体均匀性提高了5. 1%,因此在回风板角度α=60°,送风板非均匀式开孔、开孔率φ=8%时冷冻柜气流组织合理,热环境性能较为理想。     

碳氢制冷剂在小型商用冷柜上应用分析

碳氢制冷剂作为天然制冷剂的一种,因其热物理性质与环保性能(ODP为0,GWP极低)俱佳而受到国内外学者的广泛关注。本文从碳氢制冷剂的循环热力学性能出发,对碳氢制冷剂应用于小型商用冷柜的理论和实验进展进行论述,并介绍了压缩机、润滑油以及其他相关方面的研究进展。研究表明,相比于小型商用冷柜中使用的传统制冷剂,碳氢制冷剂的单位制冷量和性能系数较高,排气温度较低,实际运行时冷却速度和噪声水平都有较大改善。然而,碳氢类物质具有可燃性。虽然小型商用冷柜中碳氢制冷剂充注量较小,但要使得碳氢制冷剂在小型商用冷柜中大规模应用,需要做相应的泄漏燃爆实验。