Turbulent transient heat transfer in channel flow with step change in inlet temperature

Transient heat transfer experiments were performed in a model of a multi-pass gas turbine blade cooling circuit. The inner surface of the Plexiglas model was coated with thermochromic liquid crystals in order to determine the internal heat transfer coefficients. A change in inlet temperature is applied using a pre-cooled heat exchanger. As for simple geometries the analytical solution of Fourier’s equation can often be directly used for data evaluation, one ought to pay attention to complex passages. The reason has to be seen that the flow in complex passages has to be characterized by local and time dependent fluid temperatures. As a direct consequence data evaluation might be limited to small evaluation areas especially far downstream. Otherwise the uncertainties in the heat transfer results will increase substantially. In the present study the sensitivity of the transient method for complex passages has been analyzed theoretically and applied experimentally.

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

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2015-43165 ◽

2015 ◽

Cited By ~ 1

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.

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Transient Heat Transfer Characteristics of Twisted Structure Heated by Exponential Heat Flux

Frontiers in Energy Research ◽

10.3389/fenrg.2021.771900 ◽

2021 ◽

Vol 9 ◽

Author(s):

Li Wang

Keyword(s):

Heat Transfer ◽

Penetration Depth ◽

Heat Generation ◽

Generation Rate ◽

Transient Heat Transfer ◽

Inlet Temperature ◽

Heat Generation Rate ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Wide Range

This study was conducted to investigate the transient heat transfer characteristics of a twisted structure. The twisted structure was heated according to exponential function (Q=Q0×exp(t/τ), where Q0 is the initial heat generation rate, W/m3; t is time, s; and τ is the period of heat generation rate). A wide range of τ from 37 ms to 14 s was applied for the experimental study. A platinum plate with five pitches (each was 180° twisted with 20 mm in length) was used in the experiment. Helium gas with inlet temperature of 298 K under 500 kPa was used as the coolant. The heat transfer coefficient is found to increase with the decrease of τ, and the transition point was estimated to be at τ≈1s, which means that, when the increasing ratio of heat generation rate satisfies dQdt≥Q0⋅et, the heat transfer enhancement phenomenon will be observed. The response analysis for transient heat transfer at fluid-solid interface was conducted by applying the concept of penetration depth. It is considered that, when the penetration depth is smaller than the thermal boundary thickness, the heat transfer from the interface (wall surface) to the fluid domain is not fully developed during the disturbance.

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An Inverse Heat Transfer Approach to Mitigating Sources of Experimental Error in Transient Heat Transfer Experiments

Volume 3C: Heat Transfer ◽

10.1115/gt2013-94583 ◽

2013 ◽

Cited By ~ 1

Author(s):

James L. Rutledge ◽

Jonathan F. McCall

Keyword(s):

Heat Transfer ◽

Surface Temperature ◽

Step Change ◽

Transient Heat Transfer ◽

Temperature History ◽

Coolant Temperature ◽

Gradual Change ◽

Transient Method ◽

Time Resolved ◽

Arbitrary Change

The Inverse Flux Solver for Arbitrary Waveforms (IFSAW) algorithm is a transient, simultaneous solution of time resolved adiabatic effectiveness, η(t), and heat transfer coefficient, h(t). Numerical simulations showed IFSAW maintained its high accuracy despite two experimental sources of error typically found when using a transient heat transfer method. The traditional transient method involves exposing a film cooled wind tunnel model at uniform temperature to a step change in freestream temperature. The experimental design results in nearly one-dimensional heat transfer and allows the surface to be modeled as semi-infinite. Typically, the surface temperature history is correlated to an analytical solution to the governing heat transfer equation (yielding η and h), but the required temperature step change is impossible to achieve in a laboratory. This paper first analyzed the error introduced by imperfect step changes and evaluated an alternative methodology, IFSAW, requiring only an arbitrary change in freestream temperature occurring at any rate. Secondly, severe error in h (found in locations where η is near unity because the surface temperature changes little from the initial temperature) was shown to be mitigated using IFSAW combined with a gradual change in coolant temperature at any point during measurement. With both complications, IFSAW maintains its ability to determine periodic η(t) and h(t) waveforms. In these ways, IFSAW is shown to be superior to the legacy transient method.

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