一种新的湿蒸汽湿度测量的微波加热法

A New Approach to Measure Wetness of Wet Steam by Microwave Heating

测量流动湿蒸汽的湿度意义重大但也很困难。本文提出了一种测量湿蒸汽湿度的微波加热法。微波加热应用于湿度测量有四个显著的优点:一是微波加热中热量从水滴、水膜与蒸汽分子内部产生,不依赖于传导和对流等传热过程,且加热速度快;二是微波加热具有选择性,由于液态水的介电常数约为水蒸汽的介电常数的80倍,加热过程中水滴和水膜吸收更多的微波能量而气化,符合热力法湿度测量的要求;三是微波加热基本没有热惯性,一旦微波源切断加热即停止;四是加热过程中散失到外界的热量小。上述特性使微波加热法湿度探针具有加热段短、测量精度高的特点。给出了微波加热法测量湿度的原理、误差分析、初步设计的探针结构以及实验验证的结果。

Measuring the wetness of flowing wet steam is of great importance but difficult.In this paper,a new approach is proposed to measure the wetness of flowing wet steam by microwave heating,which shows four significant advantages in principle.1） By microwave heating,heat is generated from inside the molecules of water droplets,water film and water vapor,rather than transferred from the outside by conduction and convection,thus wet steam is rapidly heated.2） The water droplets and film absorb more microwave energy and evaporate due to the fact that their dielectric constants are about 80 times the water vapor＇s.Rapid evaporation of liquid water in wet steam especially meets the requirement of wetness measurement by using a heating method.3） There is no thermal inertia by microwave heating.Once the microwave input is cut off,the heating is stopped.4） The heat loss to the outside is small.These characteristics allow to develop a wetness probe with short heating segment and high accuracy.The measuring principle is introduced and the error analysis is carried out.The preliminary probe structure and test results for validation purpose are also shown.