Showing papers by "Ephraim M Sparrow published in 2018"

Fluid flow and heat transfer for a particle-laden gas modeled as a two-phase turbulent flow

Abstract: Purpose The purpose of this study is to examine the physical processes experienced by a particle-laden gas due to various types of collisions, different heat transfer modalities and jet axis switching Here, attention is focused on a particle-laden gas subjected to jet axis switching while experiencing fluid flow and heat transfer Design/methodology/approach The methodology used to model and solve these complex problems is numerical simulation treated here as a two-phase turbulent flow in which the gas and the particles keep their separate identities For the turbulent flow model, validation was achieved by comparisons with appropriate experimental data The considered interactions between the fluid and the particles include one-way fluid–particle interactions, two-way fluid–particle interactions and particle–particle interactions Findings For the fluid flow portion of the work, emphasis was placed on the particle collection efficiency and on independent variables that affect this quantity and the trajectories of the fluid and of the particles as they traverse the space between the jet orifice and the impingement plate The extent of the effect depended on four factors: particle size, particle density, number of particles and the velocity of the fluid flow The major effect on the heat transferred to the impingement plate occurred when direct heat transfer between the impinging particles and the plate was taken into account Originality/value This paper deals with issues never before dealt with in the published literature: the effect of jet axis switching on the fluid mechanics of gas-particle flows without heat transfer and the effect of jet axis switching and the presence of particles on jet impingement heat transfer The overall focus of the work is on the impact of jet axis switching on particle-laden fluid flow and heat transfer

Enhancement of Jet Impingement Heat Transfer by Means of Jet Axis Switching

Abstract: The method of numerical simulation has been used here to establish the heat transfer characteristics of a fluid jet impinging on a target surface. In particular, it was demonstrated that a fluid mechanic phenomenon designated as jet axis switching has a tremendous effect on both the magnitude and surface distribution of the impingement heat transfer coefficient. The neglect of this phenomenon, which has been common in the literature on jet impingement heat transfer, gives rise to significant inaccuracies in the predicted values of the heat transfer coefficient. As an essential prelude to the heat transfer analysis, the fluid mechanics of jet impingement were set forth in detail in order to document the jet-axis switching phenomenon. For this purpose, color contour and velocity vector diagrams are displayed to show the change of shape experienced by the jet as it passes through an unconfined space. The local heat transfer coefficient at all points of the impingement plate was determined. The highest values of the Nusselt number do not occur when the plate is nearest to the origin of the jet. Off-axis peaks of the local Nusselt number were found to exist at locations between z/b = 0 and 3 for respective impingement plate positions X max /b = 30 and 10. The numerical predictions compared favorably with experimental results from the literature.

Fluid-mechanic interactions between a pipe flow having circumferential pressure variations and a piezometer ring

Abstract: Purpose This paper aims to investigate and understand the fluid mechanics of piezometer rings, a device frequently encountered in engineering practice. Design/methodology/approach The investigation, implemented by numerical simulation, is based on turbulent flow in a pipe with a 90-degree bend. The pipe Reynolds numbers ranged from approximately 50,000 to 200,000. Two rings, with different dimensions, were investigated. Each ring consisted of four radially deployed straight segments of tubing which connect the pipe to a surrounding circular ring. The interconnections between the pipe and the ring were situated at 90-degree intervals around the circumference of the pipe. Findings The focus was directed to optimal circumferential locations of the radial connections, the optimal circumferential locations for accurate pressure measurements and the pressure drop penalty incurred by the use of a piezometer ring. For both of the investigated piezometer ring configurations, it was found that measurement locations situated just beyond the points of intermediate circumferential pressure variations were suitable for determining accurate values. The pressure drop was seen to increase because of the presence of the ring. For the smaller ring configuration, the increase in relative pressure drop was on the order 15 per cent, whereas the larger ring configuration lead to a 10 per cent increase. Originality/value This is the first attempt known to the authors to investigate and understand the fluid mechanics of piezometer rings.

In-bend pressure drop and post-bend heat transfer for a bend with a partial blockage at its inlet

Abstract: This paper describes a three-part numerical investigation of fluid flow and heat transfer in a never-previously-studied pipe bend situation. The investigation deals with downstream fluid-flow and heat transfer processes which are affected by upstream flow disturbances. The studied physical situation is a 90° pipe bend fitted with a wall-adjacent obstruction that partially blocks the inlet cross section. The first phase of the work consisted of validating numerical simulation results with experimental data. In the second phase, the impact of the inlet flow distribution on the pressure drop is determined. Heat transfer downstream of the bend exit comprises the third section of the paper. The heat transfer results are reported in terms of the circumferentially averaged Nusselt numbers which are displayed as a function of axial position for Reynolds numbers between 100 and 10,000. It was found that the disturbances caused by the blockage significantly enhance the Nusselt number values.