Govinda Rao Yenni

Bio: Govinda Rao Yenni is an academic researcher from Indian Space Research Organisation. The author has contributed to research in topics: Thermal contact conductance & Thermal emittance. The author has an hindex of 2, co-authored 5 publications receiving 34 citations.

Emissivity estimation of spacecraft thermal control surfaces at cryogenic temperatures – a novel experimental approach

Abstract: Painted surfaces are useful for thermal control in spacecrafts. Knowledge of emissivity of such painted surfaces over the range of working temperatures is critical in eventually deciding the adequacy of any thermal control strategy. In view of the very low temperatures involved and also because of the variation of temperature in the spacecraft, the emissivity is invariably a function of temperature, which makes its determination formidable and challenging. A “straight forward” technique to measure or estimate emissivity at cryogenic temperatures is to use a steady state calorimetric technique coupled with energy balance. This involves heat transfer by radiation under steady state conditions between an evacuated cryogenic shroud and a heated test sample, centrally suspended inside the shroud. Apart from the heat supplied, knowledge of temperatures, the internal surface area and emissivity of the shroud is required to estimate the emissivity of the unknown test sample. The view factor can be taken care of, if the test sample is much smaller compared to the shroud, resulting in a view factor of 1 between the sample and the shroud. The key difficulty associated with the seemingly simple procedure is the shroud emissivity, which is often unknown at very low cryogenic temperatures. This paper presents a novel experimental approach for the in-situ estimation of cryogenic shroud (coated with ECP2200 paint) emissivity using measured data from experiments on a plane surface substrate and a cavity surface substrate (a surface with an array of hexagonal cavities) coated with an unknown test sample (Aeroglaze Z307 paint). For an average cryogenic shroud temperature of 32.53 K, the shroud emissivity has been estimated to be 0.355. Following this, the emissivities of the plane surface substrate and the cavity surface substrate coated with Aeroglaze Z307 are estimated. The associated measurement uncertainties are systematically quantified and presented.

Measurement of Total Hemispherical Emittance of Spacecraft Thermal Control Coatings at Low Temperatures

Abstract: Spacecraft payloads that operate at cryogenic temperatures often use passive thermal control systems that incorporate a variety of thermal control coatings to reject heat to space. The thermal performance of these systems depends significantly on the emittance of their thermal control coatings. This paper presents total hemispherical emittance measurements carried out at the ISRO Satellite Centre (ISAC) for thermal control coatings: Aeroglaze Z307 absorptive conductive polyurethane black coating (from 8 0K to 150 K) and PUC conductive black polyurethane coating (from 70 K to 200 K). The experiments were conducted in vacuum using a steady-state calorimetric method. This paper highlights the importance of obtaining a steady state for accurately estimating the emittance at cryogenic temperatures and the criterion for achieving this. The results indicate that the emittance in the cryogenic temperature range increases with temperature for the coatings considered in this paper. Determination of the uncertainty ...

Measurement of Total Hemispherical Emittance of Spacecraft Thermal Control Coatings at Low Temperatures

Abstract: Spacecraft payloads that operate at cryogenic temperatures often use passive thermal control systems that incorporate a variety of thermal control coatings to reject heat to space. The thermal performance of these systems depends significantly on the emittance of their thermal control coatings. This paper presents total hemispherical emittance measurements carried out at the ISRO Satellite Centre (ISAC) for thermal control coatings: Aeroglaze Z307 absorptive conductive polyurethane black coating (from 8 0K to 150 K) and PUC conductive black polyurethane coating (from 70 K to 200 K). The experiments were conducted in vacuum using a steady-state calorimetric method. This paper highlights the importance of obtaining a steady state for accurately estimating the emittance at cryogenic temperatures and the criterion for achieving this. The results indicate that the emittance in the cryogenic temperature range increases with temperature for the coatings considered in this paper. Determination of the uncertainty ...