U型方管中爆燃向爆震转变特性实验研究

以脉冲爆震发动机(PDE)用曲管爆震燃烧室为应用背景,对气相(乙烯/空气)燃烧波在U型方管实验器中的传播过程进行了实验研究。通过改变实验器中弯曲段进口气流入射激波强度,基于弯曲段内压力、波速的测量及高速摄影实验得到了U型方管实验器中半圆型弯段内的爆燃向爆震转变(DDT)特性。结果表明,弯曲段中DDT特性受到入射激波速度的影响:当入射激波速度小于794m/s(43.6%VCJ,VCJ为理论Chapman-Jouguet爆震波速),在弯曲段内不能形成爆震;当入射激波速度介于870~908m/s(47.8%VCJ^50.0%VCJ)之间,弯曲段内首先会产生局部爆炸,并最终形成爆震;当入射激波速度大于934m/s(51.3%VCJ),爆燃波可以直接在弯曲段入口转化为爆震波。

A Numerical Model of a U-Tube Vertical Ground Heat Exchanger Used as an Evaporator

The paper presents a general distributed model of a vertical U-tube direct expansion heat exchanger coupled with the ground. This model is developed for studying the dynamic thermal behavior of a buried heat exchanger which is an integral part of a so-called direct expansion heat pump. The transient conservative equations of mass, momentum and energy considering single and two-phase flow of refrigerant are derived and presented. The diffusive heat exchange with the ground is treated using an analytical approach to treat short-time scale response of vertical boreholes based on an imposed temperature. The thermal interference between the two pipes of the heat exchanger is also considered. The mathematical equations of the model are numerically presented using a control volume formulation and the solution of the system of equations is obtained by successive iterations. The dynamic behavior of the evaporator is simulated and the numerical results are analyzed regarding spatial parameters distribution and thermal interference influence.