热阻力概念的修正及计算方法

以隧道火灾为背景,对一维加热管流中的热阻力进行了研究。通过压力场数值模拟与理论分析,直接证实了热阻力的存在,并表明传统概念上的热阻力明显大于实际的能量损失。根据能量方程提出水平无粘管流的热阻力应等于气流经过加热区的全压力降,而非静压力降;等截面管流的热阻力大小应为传统热阻力值的1/2。这一修正使热阻力概念具有了严格的流体力学意义。在定义新的热阻力系数基础上,建立了2个热阻力系数表达式及低马赫数条件下热阻力的近似表达式。将该近似表达式与热损失方程进行对比,表明两者在低马赫数条件下具有一致性。研究成果进一步发展了热阻力理论体系,对隧道火灾及其它相关工程热物理问题的研究与应用都具有重要价值。

Revised Concept and Calculation Methods of Thermal Drag

Thermal drag in duct flow under heating is studied on the background of tunnel fire. Numerical simulation of pressure field directly proves the existence of thermal drag and indicates that the value of traditional thermal drag is much larger than the real loss of energy. Based on energy equation, it is proposed that thermal drag in non-viscous horizontal duct should be equal to total pressure loss of air flow passing through heating zone, and not equal to static pressure loss. The value of revised thermal drag is half of the traditional value in uniform cross section duct. The revised concept of thermal drag is endowed with strict meaning of fluid mechanics. By introducing a new thermal drag coefficient, formulas for two thermal drag coefficients are deduced and an approximate formula for thermal drag under small Mach number is estabilished. Consistency between the formula and equation of stagnation pressure loss is showed by comparison, and the formula is proved a accurate and practical method under low maeh. The results develop the theory of thermal drag in duct flow and it is of practical value to be applied to engineering thermophysies.