隔热结构对塞块式量热计热流测量的影响

塞块式量热计是热结构试验中常用的热流传感器,其侧向传热是测量误差的重要来源。在对塞块式量热计传热分析的基础上,设计了一种改进型隔热结构,并提出了一种基于半无限大体假定的热损失修正方法。通过建立塞块式量热计的有限元数值模型,分析了量热塞与隔热材料的接触热阻对数据处理结果的影响,在接触热阻较大时(R=1×10-3 m2·K/W),未修正时最大测量误差不超过-9%,而修正后最大误差超过了20%;在接触热阻较小时(R=1×10-4 m2·K/W),未修正时的最大测量误差约-20%,修正后则不大于1.5%。可见该修正方法只适用于接触热阻较小的情况。。数值模拟结果还表明,在隔热层表面附近增加金属尖楔的改进型结构,隔热材料最高温度从超过2000℃降低到300℃以下,有利于保护隔热材料不被烧损,间楔与传感器之间的换热面积只有总侧向面积的约2.9%,两者之间的换热几乎不影响数据处理方法的选择。

Effects of adiabatic structure on heat flux measurement using a slug calorimeter

Slug calorimeter is widely used in thermal protection tests,and lateral heat conduc-tion is one of the most important sources of heat flux measurement error using a slug calorime-ter.An improved adiabatic structure is designed based on slug calorimeter heat transfer analysis, and a heat loss correction method is proposed based on semi-infinite body assumption.FEA(Fi-nite Element Analysis)model is developed to study effects of thermal contact resistance (TCR) between the slug and the adiabatic structure on data reduction results.If TCR is large (R= 1 × 10-3 m2 ·K/W),the max measurement error is less than-9% without correction and more than 20% with correction.On the other hand,when TCR is small (R= 1 ×10-4 m2 ·K/W),the error is about-20% without correction and less than 1 .5% with correction.It is concluded that the correction method can only used in the situation when TCR can be neglected.Numerical simula-tion results also show that using the improved structure with a metal sharp wedge structure add-ed near the surface of adiabatic layer,the max temperature of adiabatic material decreases from o-ver 2000℃ to less than 300℃,which means that with the improved structure,the adiabatic ma-terial is protected efficientlly from ablation.The heat transfer area between the metal wedge and the slug is only about 2 .9% of the total lateral area,which hardly effects selection of data reduc-tion methods.