Hsu, Nan-Teh (1956) Part I. Local convective thermal transfer from spherical surface. Part II. Temperature gradients in turbulent gas streams measurement of temperature, energy and pressure gradients. Part III. Temperature gradients in turbulent gas streams behavior near boundary in two-dimensional flow. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-03242004-110420
The local convective thermal transfer from a spherical surface in an air stream was experimentally investigated by measuring the temperature distribution in the air stream surrounding the sphere. The investigation was carried out in an air stream of known turbulence level at bulk velocities of 8 and 16 feet per second using two different half-inch spheres. The local thermal flux over the spherical surface was calculated from the detailed measurements of temperature distribution in the air close to the surface. These results are compared with available experimental results obtained at higher velocities with larger spheres.
In the forward region of the sphere from the stagnation point up to an angle of about 80[degrees], the experimental radial temperature distributions are correlated empirically in terms of the displacement thickness of the thermal boundary layer. Over this region the experimental and correlated results are compared in terms of the Nusselt and Reynolds numbers with the results of theoretical analyses based on the laminar boundary layer theory. There is satisfactory agreement with the theoretical results obtained by the method of Drake and the application of the solutions of Eckert.
The integrated values of thermal transfer are in agreement with the gross values obtained from simultaneous over-all measurements. There is also fair agreement between the integrated results and available published information on the gross thermal transfer from a sphere.
A detailed knowledge of the distribution of temperature, thermal flux, and the pressure gradients associated with the turbulent flow of fluids is of importance in creating a background of experimental facts from which it is possible to predict the transfer characteristics for a particular physical situation.
Special methods and equipment employed in the measurement and control of temperature and thermal flux in an investigation of thermal transfer in turbulent gas streams are described. Measurements of the thermal flux and the pressure gradient are presented as a function of the imposed temperature distribution and macroscopic flow rate. They extend from gross velocities of 10 to 90 feet per second and to average temperature gradients as high as 1000[degrees] F. per foot.
The results represent a contribution to the knowledge of the shear and the thermal flux associated with the nonisothermal flow of air between parallel plates. As expected, the thermal transfer coefficients for nonuniform transfer are larger than those obtained in this work under conditions of uniform transfer.
The region near the boundary of a turbulently flowing fluid accounts for the greater part of the resistance to thermal transfer to or from the stream. An understanding of the influence of conditions of flow upon the temperature distribution near the boundary of turbulently flowing streams is required in order to permit the recent advances in fluid mechanics to be applied to the prediction of thermal transfer in steady flow.
The detailed temperature distribution near the boundary of a turbulent air stream flowing between parallel plates was measured at gross velocities from 10 to 90 feet per second and for average temperature gradients as high as 1000[degrees] F. per foot. The corresponding value of thermal flux was determined directly, and from these primary measurements the temperature gradient and eddy conductivity were established as a function of flow conditions.
The eddy conductivity was correlated with the position in the stream and the gross conditions of flow. The measurements permit estimation of the thermal transfer to a turbulently flowing air stream in conduits of large radius to be made with accuracy adequate for some engineering purposes for a variety of uniform and nonuniform conditions of thermal transfer.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Major Option:||Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||1 January 1956|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||25 Mar 2004|
|Last Modified:||26 Dec 2012 02:35|
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