The dynamic response of towed thermometers

1968 ◽  
Vol 34 (3) ◽  
pp. 449-464 ◽  
Author(s):  
A. G. Fabula
Keyword(s):  
Heat Transfer ◽  
Dynamic Response ◽  
Diffusion Layer ◽  
Water Layer ◽  
Heat Transfer Process ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Small Scale ◽  
Layer Model ◽  
Buoyant Plumes

Small-scale temperature fields in water were used to test the dynamic response of towed thermometers of the platinum film resistance type. Laminar buoyant plumes rising from submerged heaters below the line of motion were the test temperature fields. The analysis of results was based on an approximate ‘diffusion-layer’ model of the dynamic heat-transfer process occurring near the platinum film on the probe tip. The model represents the linear heat transfer into a two-layer semi-infinite medium, with the platinum thin film located at the interface between a water layer of thickness Δ and a semi-infinite substrate of glass. The differences of the thermal properties of water and glass were found to be negligible. The characteristic time Δ2/D, where D is the thermal diffusivity of water, was determined by the ratio of actual to film-indicated plume-peak temperature, assuming a sinusoid approximation to the plume profile. The frequency response for the same operating conditions as the plume tests could then be obtained from the diffusion-layer model.

Direct numerical simulation of a turbulent jet impinging on a heated wall

2015 ◽  
Vol 764 ◽  
pp. 362-394 ◽  
Author(s):  
T. Dairay ◽  
V. Fortuné ◽  
E. Lamballais ◽  
L.-E. Brizzi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
Direct Numerical Simulation ◽  
Temperature Fields ◽  
Heated Wall ◽  
Small Scale ◽  
Turbulent Regime ◽  
High Heat Transfer ◽  
Radial Evolution

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

Heat Transfer Process Computer Simulation and Microstructure Prediction During Crystallization of Metal Alloys

2013 ◽  
Vol 43 (1) ◽  
pp. 71-78
Author(s):  
Georgi Evt. Georgiev ◽  
Sasho Popov ◽  
Valentin Manolov ◽  
Rositsa Dimitrova ◽  
Pavel Kuzmanov
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Cast Iron ◽  
Aluminum Alloys ◽  
Transfer Process ◽  
Heat Transfer Process ◽  
Metal Alloys ◽  
Temperature Fields ◽  
Microstructure Prediction ◽  
Process Computer

Abstract Processes of crystallization during casting formation from aluminum alloys, steel and cast iron have been studied using 3-D com- puter simulation. Temperature fields of castings have been obtained and the microstructure distribution of these castings has been predicted. A comparison between numerical results and experimental measurement has been performed. It is proved, that the proposed approach is suitable for investigation and analysis of casting technologies.

Predicting Heat Transfer From Unsteady Synthetic Jets

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Mehmet Arik ◽  
Tunc Icoz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operating Conditions ◽  
Small Scale ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Synthetic jets are piezo-driven, small-scale, pulsating devices capable of producing highly turbulent jets formed by periodic entrainment and expulsion of the fluid in which they are embedded. The compactness of these devices accompanied by high air velocities provides an exciting opportunity to significantly reduce the size of thermal management systems in electronic packages. A number of researchers have shown the implementations of synthetic jets on heat transfer applications; however, there exists no correlation to analytically predict the heat transfer coefficient for such applications. A closed form correlation was developed to predict the heat transfer coefficient as a function of jet geometry, position, and operating conditions for impinging flow based on experimental data. The proposed correlation was shown to predict the synthetic jet impingement heat transfer within 25% accuracy for a wide range of operating conditions and geometrical variables.

Determination of Key Parameters Required to Optimize Calcination Process in Ferrous Metallurgy Heating Plants

2021 ◽  
Vol 316 ◽  
pp. 282-287
Author(s):  
Boris Yur'ev ◽  
Vyacheslav Dudko
Keyword(s):  
Heat Transfer ◽  
Ferrous Metallurgy ◽  
Construction Material ◽  
Heat Transfer Process ◽  
Operating Conditions ◽  
Shaft Kiln ◽  
Thermal Calculations ◽  
Carbonate Decomposition ◽  
Rotary Kilns

Lime is the product of calcination. Its formation is always related to removal of carbon dioxide generated in the course of carbonate decomposition. Ferrous metallurgy, construction material, chemical and food industry companies account for about 90 % of lime produced in the country. Ferrous metallurgy is the major consumer of commercial lime using up to 40 % of all produced lime. Currently, despite occurrence of new binding and artificially produced chemical compounds, lime remains the major chemical compound produced by the industry in terms of output. Various units (shaft, rotary tubular kilns and fluidized bed kilns) are used for calcination. Shaft kilns are used the most widely. Considering continuously growing demand for lime, the need occurs for intensification of the burning process and optimization of the shaft kiln operating conditions. This requires knowledge of calcination physicochemical and heat transfer process mechanisms. Thus, the work deals with the issues related to determination of the optimal specific fuel consumption for burning of limestone from a particular deposit. It may be done only basing on thermal calculations for an operating shaft kiln, what, in its turn, causes the need for determination of the whole set of limestone and lime heat transfer properties. The obtained work results may be used to optimize the operating conditions of not only shaft but also rotary kilns intended for limestone heat treatment.

Flow and heat transfer in a closed loop thermosyphon Part II – experimental simulation

2007 ◽  
Vol 18 (4) ◽  
pp. 41-48 ◽  
Author(s):  
J.C. Ruppersberg ◽  
R.T. Dobson
Keyword(s):  
Heat Transfer ◽  
Closed Loop ◽  
Cooling System ◽  
Operating Conditions ◽  
Experimental Simulation ◽  
Theoretical Modelling ◽  
Working Fluid ◽  
Small Scale ◽  
System A ◽  
Test Loop

A closed loop thermosyphon is an energy transfer device that employs thermally induced density gra-dients to induce circulation of the working fluid thereby obviating the need for any mechanical moving parts such as pumps and pump controls. This increases the reliability and safety of the cool-ing system and reduces installation, operation and maintenance costs. These characteristics make it a particularly attractive option for the cavity cooling system of the Pebble Bed Modular Reactor (PBMR). Loop thermosyphons are however, known to become unstable under certain initial and operating conditions. It is therefore necessary to conduct an experimental and theoretical study of the start-up and transient behaviour of such a system. A small scale test loop was built representing a section of a concept cooling system. A number of representative yet typical experimental temperature and flow rate curves for a range of initial and boundary condi-tions were generated, plotted and are given as a function of time. These curves show that oscillatory temperature and flow occurred that was dependent on the differing design and operating conditions. A number of theoretical modelling and actual cooling system design problem areas were identified. These problem areas need to be addressed if more accu-racy is required to capture the erratic and ostensibly chaotic heat transfer behaviour of the loop.

A Study of the Heat Transfer Mechanisms in Horizontal Flame Propagation

1980 ◽  
Vol 102 (2) ◽  
pp. 357-363 ◽  
Author(s):  
S. R. Ray ◽  
A. C. Fernandez-Pello ◽  
I. Glassman
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Conduction ◽  
Flux Distribution ◽  
Heat Transfer Process ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Gas Velocity ◽  
Field Temperature ◽  
Transfer Mechanisms

An experimental study is performed on the magnitude of the different mechanisms by which heat is transferred from the flaming region to the unburnt fuel ahead of the flame for flames propagating horizontally over the surface of a solid fuel. Measurements of the gas velocity field, temperature fields and radiant flux distribution in a particular case of laboratory scale flame spread over a thick fuel are used to determine the magnitude of the heat fluxes ahead of the flame. The results show that, for this particular case, although heat conduction through the solid is dominant, radiation from the flame contributes significantly to the heat transfer process. An analysis of the development of the fire indicates that there is a transition in the mechanisms of heat transfer as the fire grows. While in the early stages of the fire, heat conduction through the solid is dominant, radiation from the flame becomes of increased importance as the size of the fire increases.

scholarly journals Turbulent Flow and Heat Transfer in Gas Turbine Blade Cooling Passages

1992 ◽  
Author(s):  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Air Cooling ◽  
Turbine Blade Cooling ◽  
Gas Turbine Blades ◽  
Analysis Methodology

A numerical analysis methodology has been created to predict the heat transfer within the air cooling passages of gas turbine blades. In this paper, the turbulent flow heat convection with developed velocity and temperature fields is studied for cavities with turbulators. The influence of Coriolis forces and rotational buoyancy effects were also included. The k-equation turbulence model was employed over most of the cross section while a modified Van Driest’s version of the mixing length hypothesis is used in the near-wall sublayer. This methodology was successfully benchmarked against experimental results for air cooling passages of turbine blades. Analytical results are presented in terms of the Reynolds, Rossby and rotational Rayleigh numbers for realistic operating conditions.

scholarly journals Conjugate Heat Transfer of an Internally Air-Cooled Nozzle Guide Vane and Shrouds

2014 ◽  
Vol 6 ◽  
pp. 146523 ◽  
Author(s):  
Leiyong Jiang ◽  
Xijia Wu ◽  
Zhong Zhang
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Conjugate Heat Transfer ◽  
Guide Vane ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Pressure Side ◽  
Cooling Flow ◽  
Nozzle Guide Vane ◽  
Nozzle Guide

In order to assess the life of gas turbine critical components, it is essential to adequately specify their aerothermodynamic working environments. Steady-state analyses of the flow field and conjugate heat transfer of an internally air-cooled nozzle guide vane (NGV) and shrouds of a gas turbine engine at baseline operating conditions are numerically investigated. A high-fidelity CFD model is generated and the simulations are carried out with properly defined boundary conditions. The features of the complicated flow and temperature fields are revealed. In general, the Mach number is lower and the temperature is higher on the NGV pressure side than those on the suction side. There are two high temperature regions on the pressure side, and the temperature across the middle section is relatively low. These findings are closely related to the locations of the holes and outlets of the cooling flow passage, and consistent with the field observations of damaged NGVs. As a technology demonstration, the results provide required information for the life analysis of the NGV/shrouds assembly and improvement of the cooling flow arrangement.

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