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ix, 174 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1972

This work considers the conjugate convective heat transfer between a sphere containing heat sources and a concentric envelope maintained at a specified constant temperature. The space between the two is filled with an essentially incompressible fluid. Steady, laminar and rotationally symmetrical free convection is assumed to take place over the gap width and conduction is the sole transport mechanism considered inside the core. Two limiting cases, of an inner sphere of infinitely large relative heat conductivity, leading to an isothermal core to fluid interface; and of the converse case of small conductivity leading to a constant flux interface are considered separately. The analysis of heat transport leads to the solution of the governing equations through regular perturbation expansions with the Grashof number as main parameter. The ratio of conductivities, radius ratio and Prandtl number appear as secondary parameters. Streamlines, isovorticity curves and isotherms are obtained for various combinations of the parameters. The velocity distribution is determined and both local and overall values of the Nusselt number are obtained. A flow visualization test was undertaken and the core surface temperature distribution was determined experimentally. Reasonable qualitative agreement with the analysis is found. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

This thesis presents experimental results of combined free aid forced convection laminar heat transfer for water flowing through a circular horizontal tube with uniform wall heat flux. The Reynolds number ranged from 100 to 2000, and changes in heat transfer rate allowed a variation, of Grashof number from 300 to 30,000. The Prandtl number ranged from 4 to 9. The effect of secondary flow created by free convection occurring at higher Grashof number indicates an increase in Nusselt number up to 200 per cent. For the fully-developed region two tentative correlations are given. The expression Nu = 48/11 + 0.047 Pr¹′³(Re Ra)¹′⁵correlates 53 per cent of the data to within ± 10 per cent. Another slightly more accurate expression which correlates 68 per cent of the data to within ± 10 per cent, but does not satisfy the pure forced convection, is Nu = 2.41 + 0.082 Pr¹′³ (Re Ra)¹′⁵. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A theoretical analysis and experimental results are presented for .free convection and combined free and forced convection from a heated horizontal surface. The principal objective was to investigate a laminar boundary layer flow which had been shown, theoretically only, to form above a heated surface. This boundary layer flow is fundamentally different from flows above inclined or vertical surfaces since the driving force or buoyancy force acts perpendicular to the primary boundary layer motion. The flows analyzed are those for which the system of partial differential equations describing the flow can be reduced to simultaneous total differential equations. The method involves the introduction of similarity parameters and then the numerical integration of the resulting simplified system of total differential equations. These solutions are restricted, for 2-dimensional flow, to a semi-infinite surface, and for axially-symmetrical flow, to an infinite disc. In conjunction with the former only free convection is considered while for the latter combined convection is considered as well. The flow was examined experimentally with a semi-focusing colour schlieren system. From the photographs it may be concluded that the semi-infinite surface analysis would correctly portray a physical flow. The flow, though, remains laminar for a short distance only and then breaks down into an unstable cellular pattern. The axially-symmetrical analysis, although it yielded analytically a valid boundary layer solution, appears to have no physical parallel above a disc of finite radius. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The problem of laminar combined free and forced convection through vertical noncircular ducts and passages in the fully developed region has been treated. The fluid properties are considered to be constant, except the variation of the density in the buoyancy term of the momentum equation. Pressure work and viscous dissipation terms of the energy equation have been neglected. Heat flux has been considered to be constant in the flow direction. A general solution to the problem has been obtained in "the form of infinite series containing modified Bessel functions. Two possible thermal boundary conditions on the circumference of the heated wall have been analyzed, Case 1 - uniform circumferential wall temperature, and Case 2 - uniform circumferential wall heat flux. Information of engineering interest like Nusselt number, heat flux, ratio, shear stress ratio, temperature distribution on the' wall, velocity and temperature distributions in the flow field have been obtained for two sets of geometries, namely, (i) flow through regular polygonal ducts, and (ii) flow between cylinders arranged in regular arrays. For flow through regular polygonal ducts, the case of uniform circumferential wall temperature results in higher values of Nusselt numbers as compared to the case of uniform circumferential wall heat flux. This difference in Nusselt number values decreases as the number of sides of the regular polygon is increased, until for a circle it completely disappears. For both the cases, at higher values of Rayleigh number, the Nusselt number is less sensitive to the number of sides of the polygon. Also, at higher values of Rayleigh number, both the cases tend to produce the same results. For low sided polygons, an increase in Rayleigh number tends to shift the maximum value of shear stress from the centre of the duct wall towards the apex of the duct. For flow between cylinders arranged in regular arrays, Case 1 results in higher values of Nusselt number compared to Case 2, for low spacing ratios. However, as the spacing ratio is increased, the two cases tend to produce the same results. Cylinders arranged in equilateral triangular arrays produce higher values of Nusselt number compared to those in square arrays. This difference in Nusselt number values decreases when the spacing ratio is high. For higher values of Rayleigh number, however, the results are less sensitive to the type of arrays. Also, at higher values of Rayleigh number, both the cases tend to produce the same results. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Analysis of combined free and forced convection through vertical non-circular ducts has been carried out using variational technique. Fully developed flow with uniform axial heat input is assumed. All fluid properties are considered invariant with temperature except the variation of density in the buoyancy term of the equation of motion. A general study of the problem has been made in three stages: (i) Forced convection without circumferential wall conduction. For this case, a known velocity expression is used and a particularly simple variational expression has been presented. Nusselt numbers are calculated for rectangular, rhombic, isosceles triangular, and right-angled triangular ducts. Results compared with the available solutions have shown excellent agreement. (ii) Combined free and forced convection without circumferential wall conduction. Nusselt numbers have been computed for rectangular and rhombic ducts. A finite-difference procedure has also been carried out and the results are presented for rhombic duct only. In both of the above cases (i) and (ii), the condition of uniform peripheral heat flux has been directly utilized in deriving the variational expression, thus releasing the thermal boundary condition from satisfying exactly the condition at the wall. The condition of uniform circumferential heat flux results in lower values of Nusselt numbers as compared to that of uniform circumferential wall temperature. This difference in Nusselt number values decreases with the increase in Rayleigh number. At higher values of Rayleigh number, both the conditions tend to produce about the same results. (iii) Conjugate problem of combined free and forced convection when peripheral wall conduction is included. The equations coupling heat conduction in the walls with the convection inside the fluid are solved to establish the influence of peripheral wall conduction. The problem has been solved in a generalized way and the results have been presented for rectangular ducts. It is found that large values of the free convection effects and/or of the conduction parameter tend to minimize the asymmetries in circumferential wall temperature. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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Call number: LD2668 .T4 1963 C85 / Master of Science