Uncertainties on HTC Measurement of Water Spray Quenching of Aluminum Alloys

2011 ◽  
Author(s):  
S. Bikass ◽  
B. Andersson ◽  
A. Pilipenko
Keyword(s):  
Heat Transfer ◽  
Computer Simulation ◽  
Surface Temperature ◽  
High Strength ◽  
Sample Surface ◽  
Temperature History ◽  
Water Spray ◽  
Uncertainty Sources ◽  
Transfer Equations ◽  
Accuracy And Repeatability

Water spray cooling of profiles right after extrusion is critical for control over the mechanical properties of high strength alloys. To design the optimum distribution of spray, computer simulation is a powerful tool. For that purpose a quantification of the heat-transfer boundary conditions is challenging, especially as the heat transfer coefficient (HTC) changes with the surface temperature. It is possible to record temperature history during the quenching in laboratory/plant experiments and then HTC values can be calculated by means of inverse modeling. These values are applicable only if they are accurate enough. In this paper, it is assumed the maximum allowed tolerance for calculated HTC to be 5%. This work is based on the computer simulation of the real experiments with thermocouples installed inside the sample to estimate the heat flux at the surface of the sample as well as the sample surface temperature using heat transfer equations. Error sources are typically: inaccurate thermocouple positioning and contact quality, sample geometry, thermocouple accuracy and repeatability, thermal properties, initial temperature and etc. In this study, some of these errors and uncertainty sources are selected and their impact on calculated HTC values is investigated. Finally, maximum allowance for every parameter to achieve calculated HTC within ±5% is calculated. Since HTC is not constant but a curve vs. temperature, the calculated HTC values must be between two parallel curves which represent +5% and −5% of nominal HTC.

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.

Experimental Investigation on Heat Transfer of Water Spray Cooling by Addition of n-Butanol

2020 ◽  
Author(s):  
Chang Cai ◽  
Hong Liu ◽  
Han Chen ◽  
Chuanqi Zhao ◽  
Jiuliang Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Heat Dissipation ◽  
Absolute Error ◽  
Spray Cooling ◽  
High Heat Flux ◽  
Water Mixture ◽  
Water Spray ◽  
Maximum Absolute Error ◽  
Water Spray Cooling

Abstract Heat transfer characteristics of water spray cooling with n-butanol additive were experimentally studied in this paper. The results indicated that adding n-butanol can effectively enhance the heat dissipation and control the surface temperature. The optimal concentration of n-butanol corresponding to the best heat transfer performance is 0.5 vol%. The experimental Nusselt numbers also agree well with a previous correlation with Weber, Prandtl, Jacob and Reynolds numbers, evidenced by a maximum absolute error of 6.34%. The measurement also showed that the decrease of surface tension and contact angle of the n-butanol-water mixture is the main mechanism to enhance the spray cooling heat transfer, while other physical properties also play an important role. The surface temperature non-uniformity in the radial direction is more apparent at a high heat flux while the addition of different contents of n-butanol has a negligible effect.

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.

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.

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.

Heat Transfer Through Metal-Foam Heat Exchanger at Higher Temperature

2013 ◽  
Author(s):  
P. Hafeez ◽  
J. Esmaeelpanah ◽  
S. Chandra ◽  
J. Mostaghimi
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Surface Temperature ◽  
Heat Exchangers ◽  
Metal Foam ◽  
Spray Deposition ◽  
Nickel Foam ◽  
High Strength ◽  
Heating System ◽  
Higher Temperature

Open pore metal foams are lightweight and offer high strength, rigidity, and a large heat transfer area per volume. They make efficient heat exchangers because of high thermal conductivity and high permeability. These heat exchangers made of nickel foam are suitable for high temperature application. They can be manufactured by shaping the foam into any desired configuration and depositing metal skins on it using thermal spray deposition method. Combustion based heating system that burns natural gas is designed to understand the heat transfer through metal foam heat exchanger at higher temperature. A test rig has been fabricated to perform heat transfer experiments. The rig is capable of generating hot combustion gases through methane-oxygen premixed combustion chamber. The design of the rig allows exposure of the thermally sprayed nickel foam to hot gases and finally, cooling the metal foam by circulating air through it. The experiments were performed on metal foam and hollow channel to measure the heat transfer enhancement of the metal foam. The surface temperature measurements were done for different flow rates of cooling air. A significant decrease in surface temperature of metal foam was observed.

An Inverse Analysis Method for Estimation of Heat Flux and Temperature-Dependence of Heat Transfer Coefficient

2011 ◽  
Author(s):  
Shiro Kubo ◽  
Seiji Ioka
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Inverse Method ◽  
Thermal Stresses ◽  
Temperature History ◽  
Inner Surface ◽  
History Of ◽  
Transient Thermal ◽  
The Relationship ◽  
Inverse Analysis Method

Transient thermal stresses develop in pipes during start-up and shut-down. In previous papers the present authors [1–4] proposed an inverse method for determining the optimum thermal inlet liquid temperature history which reduced the maximum transient thermal stress in pipes. The papers considered multiphysics including heat conduction, heat transfer, and elastic deformation. The inverse method used the relationship between inner surface temperature history, transient temperature distribution and transient thermal stresses. The coefficient of heat transfer plays an important role in the evaluation of thermal stress. In this study an inverse method was developed for estimating heat flux and temperature-dependence of the coefficient of heat transfer from the history of the outer surface temperature and the liquid temperature. The method used the relationship between the outer surface temperature and the inner surface temperature. For the regularization of solution the function expansion method was applied in expressing the history of flux on the inner surface. Numerical simulations demonstrated the usefulness of the proposed inverse analysis method. By examining the effect of measurement errors of temperature on the estimation, the robustness of the method was shown.

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

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
James L. Rutledge ◽  
Jonathan F. McCall
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Random Noise ◽  
Computational Simulation ◽  
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.

Estimation of Flash Temperatures in Dry Sliding

1984 ◽  
Vol 198 (2) ◽  
pp. 91-97 ◽  
Author(s):  
S Lingard
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Cold Work ◽  
Dry Sliding ◽  
Metallic Contacts ◽  
Direct Measurements ◽  
Transfer Equations

The paper develops expressions for the flash temperatures experienced by contacting surface asperities during dry sliding. The analysis is based on the heat transfer equations of the Jaeger—Archard theory but additional terms are introduced to allow for the effects of junction growth and cold work in plastic conjunctions. Results of direct measurements of surface temperature in metallic contacts are also given which are in approximate accord with the theory.

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.

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