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

2013 ◽  
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.

Simplified Procedure for Prediction of Asphalt Pavement Subsurface Temperatures Based on Heat Transfer Theories

1997 ◽  
Vol 1568 (1) ◽  
pp. 114-123 ◽  
Author(s):  
Lisheng Shao ◽  
Sun Woo Park ◽  
Y. Richard Kim
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Air Temperature ◽  
Asphalt Pavement ◽  
Prediction Method ◽  
Point Of View ◽  
Temperature History ◽  
Climatic Regions ◽  
Simplified Procedure ◽  
Subsurface Temperatures

Surface deflection measurements and backcalculation of layer moduli in flexible pavements are significantly affected by the temperature of the asphalt concrete (AC) layer. Correction of deflections or backcalculated moduli to a reference temperature requires determination of an effective temperature of the AC layer. For routine deflection testing and analysis in state highway agencies, it is preferable, from a practical point of view, to use a nondestructive prediction method for determining the effective AC layer temperature instead of measuring the temperature directly from a small hole drilled into the AC layer. A simplified procedure to predict asphalt pavement subsurface temperatures is presented. The procedure is based on fundamental principles of heat transfer and uses the surface temperature history since yesterday morning to predict the AC layer mid-depth temperature at the time of falling weight deflectometer (FWD) testing today. The surface temperature history is determined using yesterday’s maximum air temperature and cloud condition, the minimum air temperature of today’s morning, and surface temperatures measured during FWD tests. FWD tests and temperature measurements have been conducted on seven pavement sections with varying structural designs located in three different climatic regions of North Carolina. The field temperature records from these pavements have provided values of pavement thermal parameters and coefficients in temperature functions that are needed in the prediction procedure. A set of verification results are presented using examples with different climatic regions, changing AC layer thicknesses, and varying weather patterns in different seasons.

Transient Heat Transfer in a Vapor-Heated Heat Exchanger With Arbitrary Timewise-Variant Flow Perturbation

1964 ◽  
Vol 86 (2) ◽  
pp. 133-142 ◽  
Author(s):  
Wen-Jei Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Amplitude Ratio ◽  
Perturbation Technique ◽  
Transient Heat Transfer ◽  
Coolant Temperature ◽  
Flow Perturbation

An analysis is made of transient heat transfer in a vapor-heated heat exchanger with an arbitrary timewise-variant flow perturbation. The heat-transfer coefficient between the tube and coolant is assumed to vary like the n power of the coolant velocity. Results are obtained through the use of the perturbation technique. General relations are presented in closed form and their application is illustrated by carrying out some typical examples: step, linear, exponential, and sinusoidal transients in the coolant flow velocity. The influence of the system parameters on the variation of the coolant temperature is investigated. A phenomenon of resonance in the amplitude-ratio and phase-shift is disclosed for the oscillating flow transient. This phenomenon is explained by analyzing the enthalpy change of the coolant particle in the heat exchanger. The results are also compared with the analyses that have assumed a constant heat-transfer coefficient. Heat exchangers to which these results apply include the double-pipe and shell- and-tube type heat exchangers.

Transient Method for Convective Heat Transfer Measurement With Lateral Conduction—Part I: Application to a Deposit-Roughened Gas Turbine Surface

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
J. Bons
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Rough Surface ◽  
Convective Heat ◽  
3D Model ◽  
Temperature History ◽  
Surface Model ◽  
Transient Method ◽  
Transfer Measurement ◽  
1D Model

The effect of lateral conduction on convective heat transfer measurements using a transient infrared technique over a rough surface is evaluated. The rough surface is a scaled model of gas turbine surface deposits. Comparisons are made between a full 3D finite volume analysis and a simpler 1D transient conduction model. The surface temperature history was measured with a high resolution infrared camera during an impulsively started hot gas flow over the rough test plate at a flow Reynolds number of 750,000. The boundary layer was turbulent with the peak roughness elements protruding just above the boundary layer momentum thickness. The 1D model underestimates the peak to valley variations in surface heat flux by up to a factor of 5 compared with the 3D model with lateral conduction. For the area-averaged surface heat flux, the 1D model predicts higher values than a 3D model for the same surface temperature history. This is due to the larger surface area of the roughness peaks and valleys in the 3D model, which produces a larger initial input of energy at the beginning of the transient. For engineering purposes, where the net heat load into the solid is desired, this lower 3D model result must be multiplied by the wetted-to-planform surface area ratio of the roughness panel. For the roughness model in this study, applying this correction results in a 25% increase in the area-averaged roughness-induced Stanton number augmentation for the 3D rough surface model compared with a flat 1D surface model at the same Reynolds number. Other shortcomings of the transient method for rough surface convective heat transfer measurement are identified.

Determination of Time-Resolved Heat Transfer Coefficient and Adiabatic Effectiveness Waveforms With Unsteady Film Cooling

2012 ◽  
Author(s):  
James L. Rutledge ◽  
Jonathan F. McCall
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Random Noise ◽  
Temperature History ◽  
Flow Conditions ◽  
Adiabatic Effectiveness

Traditional hot gas path film cooling characterization involves the use of wind tunnel models to measure the spatial adiabatic effectiveness (η) and heat transfer coefficient (h) distributions. Periodic unsteadiness in the flow, however, causes fluctuations in both η and h. In this paper we present a novel inverse heat transfer methodology that may be used to approximate the η(t) and h(t) waveforms. The technique is a modification of the traditional transient heat transfer technique that, with steady flow conditions only, allows the determination of η and h from a single experiment by measuring the surface temperature history as the material changes temperature after sudden immersion in the flow. However, unlike the traditional transient technique, this new algorithm contains no assumption of steadiness in the formulation of the governing differential equations for heat transfer into a semi-infinite slab. The technique was tested by devising arbitrary waveforms for η and h at a point on a film cooled surface and running a computational simulation of an actual experimental model experiencing those flow conditions. The surface temperature history was corrupted with random noise to simulate actual surface temperature measurements and then fed into an algorithm developed here that successfully and consistently approximated the η(t) and h(t) waveforms.

TRANSIENT HEAT TRANSFER IN CHANNEL FLOW WITH STEP CHANGE IN INLET TEMPERATURE

1986 ◽  
Vol 9 (5) ◽  
pp. 619-630 ◽  
Author(s):  
R. M. Cotta ◽  
M. N. Özişik ◽  
D. S. McRae
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Step Change ◽  
Transient Heat Transfer ◽  
Inlet Temperature

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

1994 ◽  
Vol 29 (4) ◽  
pp. 277-283
Author(s):  
R. O. C. Guedes ◽  
M. N. Ozisik ◽  
J. P. Bardon
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Step Change ◽  
Transient Heat Transfer ◽  
Inlet Temperature

scholarly journals DETERMINING HEAT TRANSMISSION RESISTANCE OF ENCLOSING STRUCTURES

2018 ◽  
Vol 61 (1) ◽  
pp. 47-59 ◽  
Author(s):  
B. M. Khroustalev ◽  
V. D. Sizov
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Thermal Resistance ◽  
Surface Temperature ◽  
Rate Of Change ◽  
Temperature History ◽  
Transfer Coefficients ◽  
Thermophysical Characteristics ◽  
Time Intervals ◽  
Relative Temperature

Fulfillment of the activities aimed to an increase of the thermal resistance of enclosing structures requires the determination of their thermophysical characteristics with the use of the determination method based on the solution of problems of heat conduction, establishing the con- nection between the spatial and temporal temperature changes under the effect of heat source. This work uses the solution of the problem under nonstationary heating of the enclosing structure in the form of unrestricted plate with boundary conditions of the III kind. According to the known relations and graphs alterations in surface temperature depending on warm-up time, on thermal resistance of constructions and on arguments of Fo and Bi, i. e. initial and boundary conditions are determined. The graphic dependencies that have been obtained show that the surface temperature depends on the thermal resistance, while the temperature at the opposite surface during heat expo- sure remains practically unchanged during t = 5 h. Thus, if the outside air temperature is altered, then the rate of change of surface temperature or relative temperature q make it possible to deter- mine the thermophysical characteristics by solving the inverse problem of thermal conductivity with the use of the converted ratio to determine R as a function R = f(q, t). If the constructed graphic dependencies R = f(q, t) are used at different heat transfer coefficients, then according to the measured temperatures at different time intervals it is possible to determine thermal resistance in the same time intervals and, according to their average value, determine the required resistance to heat transfer R. The estimated ratio of analytical and graphic dependencies that we have obtained demonstrate the adequacy of the conducted full-scale measurements, if the areas with homogeneous temperature field and temperature history are chosen, and they can be used in determining the heat resistance of the enclosing structure in the form of unrestricted plate with boundary conditions of the III kind.

Numerical Simulation of the Transient Phase Change Heat Transfer in a Pressurized Water Reactor Core During a Loss-of-Coolant Accident

2011 ◽  
Author(s):  
Soo W. Jo ◽  
Yong K. Lee ◽  
Jong C. Jo
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Transient Heat Transfer ◽  
Coolant Temperature ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Water Reactor ◽  
The Core ◽  
Loss Of Coolant Accident ◽  
Loss Of Coolant

Temperature of pressurized water reactor (PWR) core is a key parameter used widely for judging the initiation of emergency operating procedures and severe accident management. Since direct measurement of the fuel cladding surface temperature using thermocouples is not practicable currently, the coolant temperature at the core exit locations is monitored instead. Several experimental researches showed that the CET rise during a loss of coolant accident (LOCA) and its magnitudes were always lower than the actual fuel rod cladding temperature at the same time. In this regard, a theoretical analysis of the transient heat transfer of coolant flow in a PWR core is needed to confirm the findings from the previous experimental works. This paper addresses numerical simulation of the transient boiling-induced multiphase flow through a simplified PWR core model during a LOCA by a commercial computational fluid dynamics (CFD) code. The calculated results are discussed to understand the transient heat transfer mechanism in the core and to provide useful technical information for reactor design and operation.

Transient Heat Transfer for Carbon Dioxide Flowing Over a Horizontal Plate With Exponentially Increasing Heat Input

2008 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Heat Generation ◽  
Numerical Solutions ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Horizontal Plate ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Transient heat transfer coefficients for carbon-dioxide gas flowing over a horizontal plate (ribbon) at various periods of exponentially increasing heat input was experimentally and theoretically studied. In the experimental studies, transient heat transfer coefficients were measured under various velocities and periods. The platinum plate with a thickness of 0.1 mm was used as test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocities ranged from 1 to 3 m/s, the gas temperatures ranged from 313 K to 353 K, and the periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature and heat flux increase exponentially as the heat generation rate increases with the exponential function. 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. In the theoretical study, forced convection transient heat transfer was numerically solved based on a conventional turbulent flow model. The temperature within the boundary layer around the heater increases with the increase of the surface temperature. It is understood that the gradient of the temperature distribution near the wall of the plate is higher at a higher surface temperature difference. The values of numerical solutions for the heat fluxes agree well with the experimental data, though the numerical solutions for surface temperatures show some differences with the experimental data.

The Application of Thin Film Gauges on Flexible Plastic Substrates to the Gas Turbine Situation

1995 ◽  
Author(s):  
S. M. Guo ◽  
M. C. Spencer ◽  
G. D. Lock ◽  
T. V. Jones ◽  
N. W. Harvey
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Surface Temperature ◽  
Guide Vane ◽  
Single Layer ◽  
Temperature History ◽  
Plastic Substrates ◽  
Free Stream Turbulence ◽  
Thermal Boundary Conditions ◽  
Nozzle Guide

Thin film heat transfer gauges have been instrumented onto flexible plastic substrates which can be adhesively bonded to plastic or metal models. These new gauges employ standard analysis techniques to yield the heat flux to the model surface and have significant advantages over gauges fired onto machinable glass or those used with metal models coated with enamel. The main advantage is that the construction of the gauges is predictable and uniform, and thus calibration for thickness and geometric properties is not required. The new gauges have been used to measure the heat transfer to an annular turbine nozzle guide vane in the Oxford University Cold Heat Transfer Tunnel. Engine-representative Mach and Reynolds numbers were employed and the free-stream turbulence intensity at NGV inlet was 13%. The vanes were either precooled or preheated to create a range of different thermal boundary conditions. The gauges were mounted on both perspex and aluminium NGVs and the heat transfer coefficient was obtained from the surface temperature history using either a single layer analysis (for perspex) or double layer (for aluminium) analysis. The surface temperature and heat transfer levels were also measured using rough and polished liquid crystals under similar conditions. The measurements have been compared with computational predictions.

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