Telemetric Measurement of Heat Transfer Coefficients in Gaseous Flow: First Test of a Recent Sensor Concept in a Rotating Application

Abstract

Heat transfer coefficients are very important for the design of the various flow paths found in turbomachinery. An accurate measurement of heat transfer is difficult for circumstances of gaseous flow in combination with good thermal conductivity of the boundaries along the flow path. The majority of the measurement methods applied frequently have at least one of the following problems: (1) the measurement system as for instance a heat flux sensor is a thermal barrier in the object of interest, and (2) the sensor introduces for measurement reasons a lot of heat into the object of interest. In both cases the main error results from the modification of the system, which is critical for the investigation of any kind of flow influenced by buoyancy. Furthermore, insufficient fluid reference temperature and/or heat flux with changing sign corrupts any attempt to calculate reliable heat transfer coefficients. The measurement of heat transfer coefficients becomes even more complicated if the flow path of interest rotates at some thousand rpm as for instance in gas turbines or any other fast rotating machine with fluid flow. This contribution presents a new test rig and an experimental investigation of a setup for the direct telemetric measurement of local heat transfer coefficients in gaseous flow with metallic boundaries. The test rig has a complex instrumentation and the measurements are transferred from the rotating to the stationary frame via newly in house developed telemetry system. The measurements presented are based on a recent measurement/sensor concept tested for the first time in the rotating frame. The measurement setup features miniaturized sensor dimensions and low energy consumption. Therefore, the sensor concept is very well suited for use with telemetry system as necessary for many turbomachinery research applications. Furthermore, measurements of the radial distribution of the heat transfer coefficient of a rotating free disc are presented. Additionally a comparison with correlations found in literature as well as a discussion of the results is included.