Heat transfer coefficients across bonds and contacts

The purpose of this investigation was to experimentally determine heat transfer coefficients across interfaces, including the effects of the thermal conductivity of the adherends, the hardness of the adherends, the bond thickness, and the type of adhesive. Aluminum alloy, steel, copper, and extruded nylon rods were used as adherends; all 1.875 inches diameter and 8 inches long. Each was cut radially at its midpoint and faced off to the desired surface finish. Bare interface tests were conducted before the adherends were bonded together. The adhesives used were high grade silica refractory cement, two-part epoxy resin adhesive, and thermosetting synthetic rubber-phenolic base adhesive. An electrical resistance heater was placed on top of the test cylinder to furnish heat and a constant temperature water bath was used to conduct the heat away from the bottom of the test cylinder. An aluminum alloy tube was placed around the test cylinder as a radiation shield and to reduce convective currents. A transite pressure pipe was placed around this to further minimize losses and provide firm perimeter protection. Temperature gradients through the test cylinders were determined by the use of twelve iron-constantan thermocouples located at pre-designated spacings. Heat flows were then calculated by using Fourier\u27s Law, the measured temperature gradients, and the thermal conductivities of the adherends. The thermal resistance was determined for bare and bonded interfaces. The heat losses across the interface were less than 5 per cent for all tests. The following conclusions were made as a result of this investigation. The thermal resistance of the bonded interface increased as the bond thickness was increased. The thermal resistance decreased as the thermal conductivity of the adherend increased and the hardness decreased. An interface bonded with silica cement showed the least thermal resistance. The thermal resistance of an epoxy resin bond was consistently less than that of a bare interface for all materials bonded --Abstract, pages ii-iii