Part I: Heat transfer coefficients and corrections for thermocouples in the boundary layer of a sphere. Part II: Local convective heat transfer from a sphere. Part III: Thermal transfer in turbulent gas streams. Effect of turbulence on local transport from spheres

Abstract

Part I: The deviation of thermocouple temperatures from the temperature of the fluid surrounding the junction as a result of conduction along the leads was studied. Measurements were made around a 1/2-inch heated sphere in the plane of the equator normal to a stream whose velocity was 16 feet per second. Point air temperatures in the boundary layer of the sphere were predicted from the indications of a 0.001-inch diameter thermocouple with wires of platinum and platinum alloyed with 10% rhodium. The method employed also determined the heat transfer coefficients for the thermocouple wire in the boundary layer. These local heat transfer coefficients are lower than those observed in a uniform stream whose velocity is equal to the local velocity in the boundary layer. Part II: The local convective heat transfer from a heated sphere 0.5 inch in diameter was determined by means of temperature gradients measured in the boundary layer. Point temperatures were obtained in the boundary layer with a 0.001-inch diameter thermocouple mounted on a probe. The sphere was suspended in air streams at velocities of 4, 8, 16, and 32 feet per second and at a turbulence level of 0.013. Local Nusselt numbers were computed for seven positions around the sphere at Reynolds numbers between 800 and 7000. Part III: The present investigation was undertaken because of the absence of data concerning the effect of level of turbulence upon local thermal transport from spheres. A series of measurements was made of the local thermal transport in the forward hemisphere and a part of the after hemisphere of a silver sphere 0.5 inch in diameter. The measurements were made in an air stream the longitudinal turbulence level of which was varied between 0.013 and 0.146 for Reynolds numbers up to 3600. At a turbulence level of 0.013 and a Reynolds number of 3600, the local heat transfer varied by a factor of seven around the sphere. Increasing the level of turbulence to 0.15 increased the over-all heat transfer 20 per cent. The local heat transfer varied by a factor of three at this high level of turbulence.