Search results for "Heat transfer coefficient"
showing 10 items of 42 documents
On the effectiveness of Finite Element simulation of orthogonal cutting with particular reference to temperature prediction
2007
Abstract Finite Element simulation of orthogonal cutting is nowadays assuming a large relevance; in fact a very large number of papers may be found out in technical literature on this topic. In recent years, numerical simulation was performed to investigate various phenomena such as chip segmentation, force prediction and tool wear. On the other hand, some drawbacks have to be highlighted; due to the geometrical and computational complexity of the updated-Lagrangian formulation mostly used in FE codes, a cutting time of only a few milliseconds can be effectively simulated. Therefore, steady-state thermal conditions are not reached and the simulation of the thermal phenomenon may be ineffect…
A simple inverse procedure to determine heat flux on the tool in orthogonal cutting
2006
The applications of numerical simulation to machining processes have been more and more increasing in the last decade: today, a quite effective predictive capability has been reached, at least as far as global cutting variables (for instance cutting forces) are concerned. On the other hand, the capability to predict local cutting variables (i.e. stresses acting on the tool, temperature distribution, residual stresses in the machined surface) has to be furtherly improved, as well as effective experimental procedures to validate numerical results have to be developed. The aim of this paper is the proposition of an innovative approach, based on an simple inverse procedure, in order to identify…
Effect of a finite external heat transfer coefficient on the Darcy-Bénard instability in a vertical porous cylinder
2013
Publised version of an article from the journal: Physics of Fluids. Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Article appears in Volume 25 issue 4 of the journal: http://dx.doi.org/10.1063/1.4799253 The onset of thermal convection in a vertical porous cylinder is studied by considering the heating from below and the cooling from above as caused by external forced convection processes. These processes are parametrised through a finite Biot number, and hence through third-kind, or Robin, temperature conditions imposed on the lower and upper b…
Investigation of Flow and Heat Transfer in Corrugated-Undulated Plate Heat Exchangers
2000
An experimental and numerical investigation of heat transfer and fluid flow was conducted for corrugated-undulated plate heat exchanger configurations under transitional and weakly turbulent conditions. For a given geometry of the corrugated plates the geometrical characteristics of the undulated plates, the angle formed by the latter with the main flow direction, and the Reynolds number were made to vary. Distributions of the local heat transfer coefficient were obtained by using liquid-crystal thermography, and surface-averaged values were computed; friction coefficients were measured by wall pressure tappings. Overall heat transfer and pressure drop correlations were derived. Three-dimen…
Heat transfer and flow resistance for stacked wire gauzes: Experiments and modelling
2012
Abstract The study deals with the flow resistance and heat transport properties of woven and knitted wire gauzes stacked in a tubular apparatus. The experimental programme included flow resistance and heat transfer experiments performed for air flow ( Re = 2–300) using three woven gauzes and one knitted gauze. During the heat transfer experiments, the gauzes were heated by electric current flowing directly through them. The models describing the flow resistance and the heat transfer were put forward. Both the models base on the concept of the laminar flow developing in a short capillary channel (i.e. the gauze mesh). The model describing the flow resistance does not contain the experimenta…
Investigation of the Cooling of Hot Walls by Liquid Water Sprays
1999
An experimental study was conducted for the heat transfer from hot walls to liquid water sprays. Four full cone, swirl spray nozzles were used at different upstream pressures, giving mass fluxes impinging on the wall, G, from 8 to 80 kg m(-2) s(-1), mean droplet velocities, U, from 13 to 28 m s(-1) and mean droplet diameters, D, from 0.4 to 2.2 mm. A target consisting of two slabs of beryllium-copper alloy, each 4 x 5 cm in size and 1.1 mm thick, was electrically heated to about 300 degrees C and then rapidly and symmetrically cooled by water sprays issuing from two identical nozzles. The midplane temperature was measured by a fast response, thin-foil thermocouple and the experimental data …
Local Effects of Longitudinal Heat Conduction in Plate Heat Exchangers
2007
Abstract In a plate heat exchanger, heat transfer from the hot to the cold fluid is a multi-dimensional conjugate problem, in which longitudinal heat conduction (LHC) along the dividing walls often plays some role and can not be neglected. Large-scale , or end-to-end, LHC is always detrimental to the exchanger’s effectiveness. On the contrary, if significant non-uniformities exist in the distribution of either convective heat transfer coefficient, small-scale , or local, LHC may actually enhance the exchanger’s performance by improving the thermal coupling between high heat transfer spots located on the opposite sides of the dividing wall.
The Nukiyama Curve in Water Spray Cooling: its Derivation from Temperature-Time Histories and its Dependence on the Quantities that Characterize Drop…
2007
Abstract Heat transfer from hot aluminium walls to cold water sprays was investigated. The method used was the transient two-side symmetric cooling of a planar aluminium target, previously heated to temperatures of up to 750 K, by twin sprays issuing from full-cone swirl spray nozzles of various gauge. The target’s mid-plane temperature was recorded during the cooling transient by thin-foil K thermocouples and a high-frequency data acquisition system. In order to determine the wall temperature Tw, the wall heat flux q w ″ and the q w ″ - T w heat transfer (Nukiyama) curve, two different approaches were used: the first was based on the solution of an inverse heat conduction problem, the seco…
A study of turbulent heat transfer in curved pipes by numerical simulation
2013
Abstract Turbulent heat transfer in curved pipes was studied by numerical simulation. Two curvatures δ (pipe radius a/curvature radius c) were considered, 0.1 and 0.3; results were also obtained for a straight pipe (δ = 0) for comparison purposes. A tract of pipe 5 diameters in length was chosen as the computational domain and was discretized by finite volume multiblock-structured grids of ∼5.3 × 106 hexahedral cells. Fully developed conditions were assumed; the friction velocity Reynolds number was 500, corresponding to bulk Reynolds numbers between 12 630 and ∼17 350 according to the curvature, while the Prandtl number was 0.86 (representative of saturated liquid water at 58 bar). Simulat…
Investigation of flow and heat transfer in corrugated passages—I. Experimental results
1996
Abstract An experimental and numerical study of flow and heat transfer was conducted for a crossed-corrugated geometry, representative of compact heat exchangers including air preheaters for fossil-fuelled power plant. In this paper, we describe the method of applying thermochromic liquid crystals and true-colour image processing to give local Nusselt number distribution over the surface, and average Nu, both of quantitative reliability; a careful uncertainty analysis is also presented. Typical experimental results for heat transfer and pressure drop are presented and discussed for various geometries and Reynolds numbers, and are compared with literature data. Numerical predictions are disc…