STEADY-STATE AND TRANSIENT HEAT TRANSFER PHENOMENA OF WATER: AN EXPERIMENTAL AND THEORETICAL INVESTIGATION AT NEAR-CRITICAL PRESSURES

2018 ◽  
Author(s):  
Tobias Gschnaidtner ◽  
Andreas Kohlhepp ◽  
Gerrit A. Schatte ◽  
Christoph Wieland ◽  
Hartmut Spliethoff
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Theoretical Investigation ◽  
Transient Heat Transfer

scholarly journals Heat Exhaustion

2002 ◽  
Vol 124 (07) ◽  
pp. 50
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Catalytic Cracking ◽  
Slide Valve ◽  
Refining Process ◽  
Cooling Time ◽  
Transient Heat Transfer ◽  
Heat Exhaustion ◽  
Fluidized Catalytic Cracking ◽  
Operating Temperatures

This article focuses on fluidized catalytic cracking, which is a slide valve that controls the catalyst flow in hydrocarbon refining process. The valves are typically installed in refractory lined piping approximately 5 feet in diameter. Operating temperatures inside the valve range from 900°F to 1,400°F and, occasionally, go as high as 1800°F. Replacements require a shutdown that can run into days just for cooling time and then reheating. A major Houston-based manufacturer of slide valves, Tapco International, came up with a design that would eliminate bolts to make the valve last longer. The company asked BES Engineering of Houston to analyze the stresses due to steady-state and transient heat transfer, and to evaluate their effects. Tapco has about two dozen of the boltless valves in the field. The reliability of the new design can save hundreds of thousands of dollars by eliminating unscheduled shutdowns and unexpected maintenance.

Assessment of a Computationally Efficient Method for Industrial Simulations of Transient Heat Transfer During Autoclave Curing

2021 ◽  
Author(s):  
Iacopo Catalani ◽  
Francesco Balduzzi ◽  
Stefano Mariani ◽  
Giovanni Ferrara ◽  
Alessandro Bianchini
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Computational Cost ◽  
Numerical Approach ◽  
Curing Temperature ◽  
Transient Heat Transfer ◽  
Computationally Efficient ◽  
It Industry ◽  
Autoclave Curing ◽  
Cfd Analyses

Abstract A numerical approach for transient CFD analyses of autoclave curing process is presented, aimed at finding a trade-off between accuracy and computational cost that can make it industry-affordable. A steady-state, conjugated heat transfer (CHT) analysis is carried out for the simultaneous simulation of solid and fluid regions to obtain a spatial distribution of the heat-transfer coefficient (HTC). This distribution and the curing temperature diagram are then used as boundary conditions for a transient heat-transfer simulation of the solid parts only. Results are compared to both experiments and coupled fluid-solid steady-state CHT simulations, proving that the proposed methodology is accurate and less computationally expensive than a fully-coupled, fluid-solid simulation.

Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger

2015 ◽  
Author(s):  
Hailu Tadesse ◽  
Christian Rakut ◽  
Mathias Diefenthal ◽  
Manfred Wirsum ◽  
Tom Heuer
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Steady State ◽  
Transient Heat Transfer ◽  
Inlet Temperature ◽  
Boost Pressure ◽  
Turbine Inlet Temperature ◽  
Temperature Level ◽  
Turbine Wheel ◽  
Turbine Inlet

Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle. The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the turbine as well as material and surface temperatures of the turbine wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.

Transient Heat Transfer From a Horizontal Cylinder in the Low-Reynolds-Number Flow of Helium Gas

2002 ◽  
Author(s):  
Qiusheng Liu ◽  
Katsuya Fukuda ◽  
Koichi Hata
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Heat Input ◽  
Low Reynolds Number ◽  
Horizontal Cylinder ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Helium Gas ◽  
Low Reynolds

The knowledge of forced convection transient heat transfer at various periods of exponentially increasing heat input to a heater is important as a database for understanding the transient heat transfer process in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity. In this study, the transient heat transfer coefficients for Helium gas flowing perpendicular to a horizontal cylinder were measured in the low-Reynolds-number region. The platinum heater with a diameter of 1.0 mm was heated by electric current with an exponentially increasing heat input of Q0exp(t/τ). It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ over around 1 s, and it becomes higher for the period of τ shorter than about 1 s. The transient heat transfer shows less dependent on the gas flowing velocity when the period becomes very short. Based on the experimental data, the ratio of transient heat transfer to the quasi-steady-state one was correlated as a function of Reynolds number of the gas flow and the non-dimensional period of increasing heat input. For the non-dimensional period larger than about 300, the transient heat transfer approaches the steady-state one, and shows no dependence on the Reynolds number.

Transient Heat Transfer for Parallel Flow of Helium Gas Over a Horizontal Plate

2007 ◽  
Author(s):  
Qiusheng Liu ◽  
Katsuya Fukuda ◽  
Makoto Shibahara ◽  
Shingo Kikumoto
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Steady State ◽  
Heat Generation ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Horizontal Plate ◽  
Heat Generation Rate ◽  
Helium Gas

Forced convection transient heat transfer for helium gas at various periods of exponentially increase of heat input to a horizontal plate (ribbon) was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over a horizontal plate under wide experimental conditions. The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate, τ, ranged from 46 ms to 17 s. The pressures were from 400 to 800 kPa. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was obtained that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The values of numerical solutions for surface temperature and heat flux at the velocity of 6 m/s agree well with the experimental data, though they show some differences at other velocities.

Transient Heat Transfer for Helium Gas Flowing Over a Horizontal Flat-Plate With Different Widths

2013 ◽  
Author(s):  
Zhou Zhao ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Heat Generation ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Heat Generation Rate ◽  
Helium Gas ◽  
The Heat Transfer Coefficient

This study is aimed to clarify transient heat transfer process between the surface of solid and the neighboring helium gas in Very High Temperature Reactor (VHTR) or intermediate heat exchanger (IHX). In this paper a series of platinum heaters with different widths under different pressures inside a circular channel have been tested for forced convection flow. The heat generation rate of the platinum heater was increased with a function of Q0exp(t/τ) (where t is time and τ is period of heat generation rate or e-fold time). The heaters were platinum plates with a thickness of 0.1 mm and widths of 2 mm, 4 mm and 6 mm. In the present study, the heat flux, surface temperature, and transient heat transfer coefficients were measured for helium gas passing by horizontal plates under wide experimental conditions such as velocities, pressures and periods of heat generation rate. It was clarified that the heat transfer coefficient approaches the quasi-steady-state when the period is more than around 1 s and it becomes higher when the period shorter than around 1 s. Based on the experimental data, empirical correlations for both quasi-steady-state heat transfer and transient state one at various plate-widths were obtained. It was also found that the heat transfer coefficient becomes higher with the increases of gas pressure.

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