高大平房仓强制循环双层屋面隔热性能的模拟实验与数值分析

Experiment and Numerical Analysis on Mechanically Ventilated Double-Skin Roof in Granary

本研究基于粮食平房仓模拟实验台,对通风隔热屋面进行对比实验,确定不同几何参数和运行工况对仓房屋面隔热性能的影响,为现役粮食仓房隔热改造提供设计参考。通过在模拟辐射工况下采用不同架空层入口风速和层间净空高度对仓内温、湿度进行监测,结果表明:自然风速工况下,0.05~0.10 m的层间厚度能够有效隔绝来自仓房屋面的热量,粮堆表面温度升幅在1.69~4.22℃之间,相对湿度变化范围为-1.25%~2.72%,最高温度控制在常温储粮范围以内(≤25℃)。基于ANSYS软件平台对架空层性能参数进行优化,模拟与实验结果的误差在2.07%~7.35%。数值模拟表明,双层屋面平房仓在采用强制循环时,通过调整入口风速、空气夹层厚度,可使空气层换热产生明显的入口段效应,消除常规屋面结构条件下仓内上方的热积聚,使粮堆表面平均温度维持在21.88℃。

To improve the insulation performance of granary roof,an experiment system was set up with fans fixed on its overhead ceiling.The experiment granary was designed in a laboratory scale and its roof was geometrically similar to the actual.The double-skin roof was open-ended to enable air flow and the airgap between the overhead ceiling and the roof varied from 0.05 m to 0.10 m.According to different working conditions,a set of air flow rates were adopted in a range of 60~114.6 m3/h.Measuring probes were set at three layers along the depth of the grain bulk.Temperature and humidity data were collected through a data logger connected to the lab computer.The experiment results indicated that a bulk temperature lower than 25℃could be obtained under a hot ambient by using the ventilated double-skin roof.The temperature rise at the bulk surface was only 1.69~4.22℃,which was significantly cut down compared to the normal roof condition.Furthermore,a computational fluid dynamics(CFD)model had been proposed based on the experimental prototype to characterize the air flow and heat transfer in the ventilated double-skin roof.It was validated by experimental results with an error less than 7.35%.Numerical analyses were carried out using the CFD model to show the matching between the size(such as the air-gap thickness)and the flow rate through the roof.Given an airgap of 0.05 m,the optimal air velocity at the open end was 0.05~0.06 m/s.The entrance region of convection was expanded by changing the airgap thickness or the air velocity,which resulted in a 4~5℃temperature drop in the double-skin roof.With an airgap thickness of 0.06 m and an air velocity of 0.05 m/s,the roof temperature remains at about 24℃through more efficient heat removing generated from the entrance effectiveness.