A computational analysis of heat transfer and fluid flow in high-speed scanning of laser micro-welding

Abstract There are two general classes of mathematical problems encountered in science and engineering for which high-speed mechanical computation is required. One of these embraces those problems of such complexity that it is impractical to obtain even a few solutions by conventional analysis. In the other class are problems which may be of only moderate complexity, but in which it is necessary to obtain a large number of solutions before the results become of practical value. It is the intent of this paper to discuss some of the applications that have been made of the California Institute of Technology “electric-analog computer” to heat-transfer and fluid-flow problems of both of the classes mentioned.

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Time-Dependent Solution of Unsteady Fluid Flow Equations for High Speed Oscillating Compressible Flows and Blast Wave Propagations

Volume 1: Beyond Design Basis; Codes and Standards; Computational Fluid Dynamics (CFD); Decontamination and Decommissioning; Nuclear Fuel and Engineering; Nuclear Plant Engineering ◽

10.1115/icone2020-16419 ◽

2020 ◽

Author(s):

Ramlala P. Sinha

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Blast Wave ◽

High Speed ◽

Fluid Dynamic ◽

Time Dependent ◽

Arbitrary Boundary ◽

One Dimensional ◽

Unsteady Fluid ◽

Energy Equations

Abstract A solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube has been obtained numerically, assuming one dimensional, viscous, and heat conducting flow, by solving the appropriate fluid dynamic and energy equations. The tube is approximated by a right circular cylinder closed at one end with a piston oscillating at very high resonant frequency at the other end. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. The solution would also be valid for tapered tubes if the variations in the cross-sectional area are small. In successfully predicting the time dependent results, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and nuclear explosion blast wave propagations in one dimensional and/or radial spherical coordinates with or without including energy generation / addition terms.

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Vascular design for thermal management of heated structures

The Aeronautical Journal ◽

10.1017/s0001924000003067 ◽

2009 ◽

Vol 113 (1144) ◽

pp. 397-407 ◽

Cited By ~ 11

Author(s):

J. Lee ◽

S. Lorente ◽

A. Bejan

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Thermal Resistance ◽

High Speed ◽

The Body ◽

Three Dimensions ◽

Local Pressure ◽

Pressure Losses ◽

Flow And Heat Transfer ◽

Four Levels

Abstract Vascular structures are contemplated for cooling the skins and leading surfaces of future high speed aircraft. This paper evaluates the proposal to cool with a flow architecture shaped as trees (dendritic) a parallelepipedic body that is heated uniformly. The coolant enters the body through one face and exits through the opposite face. The vasculature connects the two faces, and consists of trees that alternate with upside down trees. The fields for fluid flow and heat transfer are determined numerically in three dimensions. The effect of local pressure losses at bends, junctions and entrances is documented. Designs with tree-shaped architectures having up to four levels of bifurcation are evaluated for fluid flow and heat transfer performance, and are compared with the performance of a design with a single sheet of fluid sweeping the upper surface of the body. The fluid flow conductance of the tree designs increases when the number of bifurcation levels increases. The thermal performance of tree designs can be improved by endowing the tree design with more freedom such that the bifurcations generate asymmetric daughter channels. The tree designs outperform the fluid sheet design dramatically: the global thermal resistance of the tree designs is roughly one tenth of the global thermal resistance of the fluid sheet design.

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High-Speed Visual Analysis of Fluid Flow and Heat Transfer in Oscillating Heat Pipes with Different Diameters

10.20944/preprints201610.0110.v1 ◽

2016 ◽

Author(s):

Xiangdong Liu ◽

Qing Sun ◽

Chengbin Zhang ◽

Liangyu Wu

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Thermal Performance ◽

Slug Flow ◽

High Speed ◽

Bubbly Flow ◽

Heat Pipes ◽

Working Fluid ◽

Flow And Heat Transfer ◽

Inner Diameter

The oscillating heat pipe (OHP) is a new member in the family of heat pipes, and it has great potential applications in energy conservation. However, the fluid flow and heat transfer in the OHP as well as the fundamental effects of inner diameter on them have not been fully understood, which are essential to the design and optimization of the OHP in real applications. Therefore, by combining the high-speed visualization method and infrared thermal imaging technique, the fluid flow and thermal performance in the OHPs with inner diameters of 1, 2 and 3 mm are presented and analyzed. The results indicate that three fluid flow motions, including small oscillation, bulk oscillation and circulation, coexist or, respectively, exist alone with the increasing heating load under different inner diameters, with three flow patterns occurring in the OHPs, viz. bubbly flow, slug flow and annular flow. These fluid flow motions are closely correlated with the heat and mass transfer performance in the OHPs, which can be reflected by the characteristics of infrared thermal images of condensers. The decrease in the inner diameter increases the frictional flow resistance and capillary instability while restricting the nucleate boiling in OHPs, which leads to a smaller proportion of bubbly flow, a larger proportion of short slug flow, a poorer thermal performance, and easier dry-out of working fluid. In addition, when compared with the 2 mm OHP, the increasing role of gravity induces the thermosyphon effect and weakens the 'bubble pumping' action, which results in a little smaller and bigger thermal resistances of 3 mm OHP under small and bulk oscillation of working fluid, respectively.

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