Evaporator design for an isokinetic total water content probe in a naturally aspirating configuration

Abstract

A number of recent aircraft turbofan power failure events have been linked to ice accretion in the initial compressor stages while the aircraft is traversing the anvil region of storm clouds. The water content in such cloud regions is not well known and the accuracy of most existing water content probes is likely to be poor under such conditions. A new cloud water content probe is being developed for airborne characterisation of such clouds and a critical feature of the probe is the evaporator. In this work we develop some analytical expressions to assist in the design and characterisation of the evaporator. In particular, we consider the issue of convective heat transfer to the ice and water particles moving with the air flow through the evaporator. For the particular evaporator design we are considering, it is shown that ice particles larger than 100 μm are unlikely to have sufficient residence time to evaporate if they remain suspended in the heated air. Although these larger ice particles are likely to impact on the evaporator walls so there is also an opportunity for direct conduction heating, the present analysis indicates that particles larger than 100 μm may not adhere to the walls. However, there are many uncertainties in the present analysis and experiments are needed to determine the actual performance of the evaporator.