Effect of interstitial compounds in controlling thermal contact conductance across pressed joints at cryogenic temperature and low contact pressure

Abstract

• Study of thermal contact conductance across joints at low temperature and contact pressure. • Effect of interstitials across joints formed with combinations of AA2219, Ti6Al4V and AISI 321. • Silicon compound enhances thermal contact conductance up to 25 times while acrylate sealant enhances by 8 times. • Epoxy adhesive coating reduces thermal contact conductance by about 50%. • Design monograms are generated to aid selection of joints and interstitials. Heat transfer across pressed joint is significantly governed by thermal contact conductance which in turn depends on thermophysical properties of materials in contact, surface properties, contact pressure, working temperature and interstitials present at the interface. Application of interstitials is an effective technique to control thermal contact conductance at ambient temperature. In the present study, thermal contact conductance across joints at cryogenic temperature in presence of interstitials like silicon based conductive compound, epoxy based adhesive layer and acrylate based anaerobic sealant are explored. These interstitials have different thermophysical characteristics and retain their properties at cryogenic temperature. The joints are investigated for low contact pressure applications, for which thermal contact conductance control is difficult. Specimens are made from cryogenic compatible alloys namely Aluminium alloy AA2219, Stainless steel AISI 321 and Titanium alloy Ti6Al4V with a surface roughness of 0.9 µm. Each interstitial is applied across all six similar and dissimilar pressed joints formed between the materials and thermal characteristics are evaluated experimentally. Investigation is carried out over a temperature range of 150 K to 300 K, with a contact pressure of 140 kPa. The silicon compound enhances thermal contact conductance up to 25 times that of a bare joint while acrylate sealant enhances up to 8 times. The epoxy adhesive coating reduces thermal contact conductance by about 50%. Based on results, monograms are generated for joints based on thermal contact conductance and enhancement factor observed .