Numerical Simulations and Experimental Characterization of Heat Transfer From a Periodic Impingement of Droplets

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Mario F. Trujillo ◽  
Jorge Alvarado ◽  
Eelco Gehring ◽  
Guillermo S. Soriano
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Numerical Simulations ◽  
Droplet Impact ◽  
Numerical Comparison ◽  
Temperature Profiles ◽  
Conductive Heat ◽  
Radial Temperature ◽  
The Impact

In this combined experimental and simulation investigation, a stream of HFE-7100 droplets striking a prewetted surface under constant heat flux was studied. An implicit free surface capturing technique based on the Volume-of-Fluid (VOF) approach was employed to simulate this process numerically. Experimentally, an infrared thermography technique was used to measure the temperature distribution of the surface consisting of a 100 nm ITO layer on a ZnSe substrate. The heat flux was varied to investigate the heat transfer behavior of periodic droplet impingement at the solid–liquid interface. In both experiments and simulations, the morphology of the impact zone was characterized by a quasi-stationary liquid impact crater. Comparison of the radial temperature profiles on the impinging surface between the experiments and numerical simulations yielded reasonable agreement. Due to the strong radial flow emanating from successive droplet impacts, the temperature distribution inside the crater region was found to be significantly reduced from its saturated value. In effect, the heat transfer mode in this region was governed by single phase convective and conductive heat transfer, and was mostly affected by the HFE-7100 mass flow rates or the number of droplets. At higher heat fluxes, the minimum temperature, and its gradient with respect to the radial coordinate, increased considerably. Numerical comparison between average and instantaneous temperature profiles within the droplet impact region showed the effect of thermal mixing produced by the liquid crowns formed during successive droplet impact events.

A Study of the Heating Section of a Gas Heated Steam Reformer

2007 ◽  
Vol 5 (1) ◽  
Author(s):  
Margrete H. Wesenberg ◽  
Jochen Ströhle ◽  
Hallvard F Svendsen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fixed Bed ◽  
Two Dimensions ◽  
Fixed Bed Reactor ◽  
Discrete Ordinates ◽  
Temperature Profiles ◽  
Radial Temperature ◽  
Steam Reformer ◽  
Heating Section

A gas heated steam reformer (GHR) which converts natural gas to synthesis gas for methanol or Fischer-Tropsch purposes has been modelled for steady state conditions. The model is in two dimensions and is made up of a fixed bed reactor model, representing one of the reactor tubes in the GHR, and an annulus model, representing the annular space on the shell side of the GHR where hot, fully converted syngas emits heat to the reactor tube. The annulus model is described and evaluated in this article. This is a plug flow model which involves heat transfer in radial direction caused by radiation and by turbulence. The gas radiation is modelled by the use of the discrete ordinates method and the effect on heat transfer from turbulence is modelled as an effective radial thermal conductivity. Both heat transfer mechanisms vary with the radial position. An additional annulus model, made in the commercial CFD code FLUENT and based on the k-? turbulence model and the discrete ordinates radiation model, is used to estimate effective radial thermal conductivities. These were implemented in the annulus model of the GHR model. The reactor and the annulus models were combined and linked by the wall temperature profile and the heat flux profile on the outer reactor tube wall. The simulation results were used to study the heat flux and temperature profiles along the reactor length and the radial temperature profiles in the annulus.

Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling: Part 1 — Effect of Density Ratio

2020 ◽  
Author(s):  
Shuo Mao ◽  
Ridge A. Sibold ◽  
Stephen Lash ◽  
Wing F. Ng ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Guide Vane ◽  
Density Ratio ◽  
Momentum Ratio ◽  
Blowing Ratio ◽  
Nozzle Guide Vane ◽  
Nozzle Guide ◽  
The Impact

Abstract Nozzle guide vane platforms often employ complex cooling schemes to mitigate ever-increasing thermal loads on endwall. Understanding the impact of advanced cooling schemes amid the highly complex three-dimensional secondary flow is vital to engine efficiency and durability. This study analyzes and describes the effect of coolant to mainstream blowing ratio, momentum ratio and density ratio for a typical axisymmetric converging nozzle guide vane platform with an upstream doublet staggered, steep-injection, cylindrical hole jet purge cooling scheme. Nominal flow conditions were engine representative and as follows: Maexit = 0.85, Reexit/Cax = 1.5 × 106 and an inlet large-scale freestream turbulence intensity of 16%. Two blowing ratios were investigated, each corresponding to upper and lower engine extrema at M = 3.5 and 2.5, respectively. For each blowing ratio, the coolant to mainstream density ratio was varied between DR = 1.2, representing typical experimental neglect of coolant density, and DR = 1.95, representative of typical engine conditions. An optimal coolant momentum ratio between = 6.3 and 10.2 is identified for in-passage film effectiveness and net heat flux reduction, at which the coolant suppresses and overcomes secondary flows but imparts minimal turbulence and remains attached to endwall. Progression beyond this point leads to cooling effectiveness degradation and increased endwall heat flux. Endwall heat transfer does not scale well with one single parameter; increasing with increasing mass flux for the low density case but decreasing with increasing mass flux of high density coolant. From the results gathered, both coolant to mainstream density ratio and blowing ratio should be considered for accurate testing, analysis and prediction of purge jet cooling scheme performance.

Nanoparticle aggregation kinematics on the quadratic convective magnetohydrodynamic flow of nanomaterial past an inclined flat plate with sensitivity analysis

2021 ◽  
pp. 095440892110562
Author(s):  
AS Sabu ◽  
Joby Mackolil ◽  
B Mahanthesh ◽  
Alphonsa Mathew
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Sensitivity Analysis ◽  
Heat Transfer Coefficient ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Inclined Plate ◽  
The Impact ◽  
The Heat Transfer Coefficient

The study focuses on the aggregation kinematics in the quadratic convective magneto-hydrodynamics of ethylene glycol-titania ([Formula: see text]) nanofluid flowing through an inclined flat plate. The modified Krieger-Dougherty and Maxwell-Bruggeman models are used for the effective viscosity and thermal conductivity to account for the aggregation aspect. The effects of an exponential space-dependent heat source and thermal radiation are incorporated. The impact of pertinent parameters on the heat transfer coefficient is explored by using the Response Surface Methodology and Sensitivity Analysis. The effects of several parameters on the skin friction and heat transfer coefficient at the plate are displayed via surface graphs. The velocity and thermal profiles are compared for two physical scenarios: flow over a vertical plate and flow over an inclined plate. The nonlinear problem is solved using the Runge–Kutta-based shooting technique. It was found that the velocity profile significantly decreased as the inclination of the plate increased on the other hand the temperature profile improved. The heat transfer coefficient decreased due to the increase in the Hartmann number. The exponential heat source has a decreasing effect on the heat flux and the angle of inclination is more sensitive to the heat transfer coefficient than other variables. Further, when radiation is incremented, the sensitivity of the heat flux toward the inclination angle augments at the rate 0.5094% and the sensitivity toward the exponential heat source augments at the rate 0.0925%. In addition, 41.1388% decrement in wall shear stress is observed when the plate inclination is incremented from [Formula: see text] to [Formula: see text].

Using ProCAST to Study the Effects of SEED Process Parameters on the Radial Temperature Distribution in Semi-Solid Slugs

2020 ◽  
Vol 993 ◽  
pp. 1004-1010
Author(s):  
Min Luo ◽  
Da Quan Li ◽  
Wen Ying Qu ◽  
Stephen P. Midson ◽  
Qiang Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Transfer Coefficient ◽  
Solid Fraction ◽  
Process Parameters ◽  
Radial Temperature ◽  
Fraction Distribution ◽  
Semi Solid ◽  
The Heat Transfer Coefficient

The SEED (Swirled Enthalpy Equilibrium Device) process was used to produce semi-solid slurries. One of the factors that controls whether or not a slug can be used to produce high quality castings is the solid fraction distribution within the slug, and the solid fraction distribution is strongly dependent upon the temperature distribution. In this study, a model has been developed using ProCAST to investigate the relationship between process parameters and the temperature distribution within slugs. The parameters examined included the heat transfer coefficient between the crucible and slug, the heat transfer coefficient between the crucible and air, the slug diameter, and the initial melt temperature (pouring temperature). It was found that the most important parameters controlling the temperature distribution within slugs were the crucible size and the heat transfer coefficient between crucible and air. Adjustment of other parameters had little influence on the temperature distribution. Processing parameters will be discussed in order to allow the SEED process to be used for the production of large diameter slugs (>100 mm), and for narrow freezing range (0.3<fs<0.5, fs is fraction solid) alloys such as 6063.

Analysis to Reduce Thermal Stress in Oxide Single Crystal During Czochralski Growth

2004 ◽  
Author(s):  
Shigeki Hirasawa ◽  
Hiroyuki Ishibashi ◽  
Kazuhisa Kurashige ◽  
Akihiro Gunji
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Temperature Distribution ◽  
Thermal Radiation ◽  
Single Crystal ◽  
Radiation Heat Transfer ◽  
Heat Transfer Analysis ◽  
Czochralski Growth ◽  
Radiation Heat ◽  
Radial Temperature

Temperature distributions and thermal stress distributions in a semi-transparent GSO crystal during Czochralski (CZ) single crystal growth were numerically investigated by thermal radiation heat transfer analysis and anisotropy stress analysis. As GSO has special optical properties, such as semi-transparency at a wavelength shorter than 4.5 μm, thermal radiation heat transfer was calculated by the Monte Carlo method. These calculations showed that thermal stress is caused by the radial temperature distribution on the outside of the upper part of the crystal. To reduce this temperature distribution, the following three manufacturing conditions were found to be effective: use a sharp taper angle of the crystal, install a lid to the top of the insulator, and install a ring around the tapered part of the crystal.

Evaluation of response characteristics of thin film gauge for conductive heat transfer mode

2020 ◽  
pp. 014233122096066
Author(s):  
Tanweer Alam ◽  
Rakesh Kumar
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Short Duration ◽  
Temperature Data ◽  
Heat Transfer Analysis ◽  
Transient Temperature ◽  
Conductive Heat ◽  
Sensing Element ◽  
Element Analysis

Heat transfer analysis is the one of the most important designing aspects for many engineering systems. The design prospect in the preview of heat transfer focuses on the prediction of heat flux with the help of measured transient temperature data. Thin film gauges are one of the most predominant method for the heat flux prediction especially for short duration transient temperature measurement. Thin film gauges are usually exposed to the heated environment for the measurement purpose. However, there are some prominent research areas like ablation phenomenon met to spacecraft thermal shields during re-entry to the atmosphere, for which direct exposure of the thin film gauge to the heated environment causes the functional and working difficulties associated with the gauge. In the present study, it is aimed to investigate the suitability of thin film gauge for the conduction-based short duration measurement. An experimental set up is fabricated, which is used to supply the heat load to the hand-made thin film gauge using platinum as sensing element and quartz as a substrate. The transient temperature data is recorded during experiment is further compared with the simulated temperature histories obtained through finite element analysis. The heat flux estimation for both the analysis is made using measured transient temperature data by convolute integral of one- dimensional heat conduction equation. The estimated heat flux value for the experimental and numerical result is found to be in excellent agreement.

scholarly journals The Influence of Different Facings of Polyisocyanurate Boards on Heat Transfer through the Wall Corners of Insulated Buildings

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1991 ◽  
Author(s):  
Tomas Makaveckas ◽  
Raimondas Bliūdžius ◽  
Arūnas Burlingis
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Insulation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermal Bridge ◽  
Thermal Bridges ◽  
The Impact ◽  
Heat Flow Meter

Polyisocyanurate (PIR) thermal insulation boards faced with carboard, plastic, aluminum, or multilayer facings are used for thermal insulation of buildings. Facing materials are selected according to the conditions of use of PIR products. At the corners of the building where these products are joined, facings can be in the direction of the heat flux movement and significantly increase heat transfer through the linear thermal bridge formed in the connection of PIR boards with facing of both walls. Analyzing the installation of PIR thermal insulation products on the walls of a building, the structural schemes of linear thermal bridges were created, numerical calculations of the heat transfer coefficients of the linear thermal bridges were performed, and the influence of various facings on the heat transfer through the thermal bridge was evaluated. Furthermore, an experimental measurement using a heat flow meter apparatus was performed in order to confirm the results obtained by numerical calculation. This study provides more understanding concerning the necessity to evaluate the impact of different thermal conductivity facings on the heat transfer through corners of buildings insulated with PIR boards.

Thermal effect on large-aspect-ratio Couette–Taylor system: numerical simulations

2015 ◽  
Vol 771 ◽  
pp. 57-78 ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang ◽  
Innocent Mutabazi
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Convective Cell ◽  
Base Flow ◽  
Large Aspect Ratio ◽  
Radial Temperature ◽  
Instability Modes ◽  
Momentum And Heat Transfer

We have performed numerical simulations of the flow in a large-aspect-ratio Couette–Taylor system with rotating inner cylinder and with a radial temperature gradient. The aspect ratio was chosen in such a way that the base state is in the conduction regime. Away from the endplates, the base flow is a superposition of an azimuthal flow induced by rotation and an axial flow (large convective cell) induced by the temperature gradient. For a fixed rotation rate of the inner cylinder in the subcritical laminar regime, the increase of the temperature difference imposed on the annulus destabilizes the convective cell to give rise to co-rotating vortices as primary instability modes and to counter-rotating vortices as secondary instability modes. The space–time properties of these vortices have been computed, together with the momentum and heat transfer coefficients. The temperature gradient enhances the momentum and heat transfer in the flow independently of its sign.

Sign in / Sign up

Export Citation Format

Share Document