AN EVAPORATING FILM CALORIMETRIC ENTHALPY PROBE

A calorimetric enthalpy probe of small size, cap able of continuous operation in a high temperature, high heat flux environment, such as an arc, is described. The instrument operates by re moving a sample from a hot gas stream and cooling it by evaporative film cooling until the temperature of the gas sample is low enough for measurement by conventional means. The composition of the cooled gas sample is measured and the total enthalpy of the hot gas entering the instrument is determined by an energy balance technique. The structure of the instrument may be maintined at a tolerable temperature level by forced con vective cooling or by evaporative film cooling. The instrument has been compared for accuracy with gas temperature measurements made by conventional techniques at temperatures between 2100 and 4300 R. These tests, using nitrogen as the test gas and water as the evaporative coolant, have shown an average deviation of 2.3% between the methods of measurement. An instrument with an outside diameter of 0.1 in. has been fabricated and tested. This instrument is de signed to measure an enthalpy of 15,000 Btu/#. To complement the enthalpy determination instrument, an instrument for continuous measurement of the gas- sample composition has been developed.