Kunikazu Torikoshi

Heat transfer and thermoelectric voltage at metallic point contacts

Metallic point contacts have been extensively studied from the viewpoint of their interesting, and often nonlinear, electrical properties. Their thermal characteristics, however, have largely been ignored, even though they show great potential as microscale temperature sensors. It has been previously demonstrated that when a temperature drop exists across a point contact consisting of two identical metals, a thermoelectric voltage can be generated, provided the mean contact radius is comparable in size to the electron mean free path. In the present experimental study, a point contact is formed by pressing a sharply etched Ag whisker against either an Ag or a Cu flat plate

Thermoelectric voltage at metallic point contacts from nonequilibrium effects

This paper presents results for thermoelectric voltage experiments carried out with metallic point contacts. The motivation for this work is the fundamental understanding of the nonequilibrium state between electrons and phonons, and for applying this phenomenon to a point temperature measurement of small heating elements like an LSI (Large-Scale integration electronic chip. The experiments were carried out by using gold, silver, copper, and tungsten point contacts under cryogenic conditions, and a heat flux through the point contact was applied via a temperature difference across the contact. In this condition, thermoelectric voltages appeared even when the entire open circuit consisted of only one material. This phenomenon was explained theoretically by considering the nonequilibrium effect between the phonon and electron temperatures, and the geometric effect at the point contact. Good agreement was found between the theory and the experiment.

Heat transfer from a tube immersed in a fluidized bed with frosting.

Heat-transfer and flow-visualization experiments were performed for a single cooled tube immersed horizontally in a fluidized bed under frosting conditions. Measurements were made from local and average heat-transfer coefficients around the cooled tube surface. Glass beads having nominal diameters of 0.43 mm, 0.89 mm, and 1.6 mm were employed as the bed material. The 30 mm diameter tube was located 100 mm above the distributor. All the results obtained under frosting conditions were for an air temperature of about 5{degrees}C and an air relative humidity of about 80 percent. The heat-transfer coefficient with frosting evaluated in this investigation includes the heat-transfer coefficient from the frost surface to the bed and the thermal resistance of the frost layer. Comparisons are made to heat-transfer data without frosting. The heat transfer is found to be larger with frosting than without frosting under the fluidization state.