skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: CFD simulation of simultaneous monotonic cooling and surface heat transfer coefficient

Abstract

The monotonic heating regime method for determination of thermal diffusivity is based on the analysis of an unsteady-state (stabilised) thermal process characterised by an independence of the space-time temperature distribution on initial conditions. At the first kind of the monotonic regime a sample of simple geometry is heated / cooled at constant ambient temperature. The determination of thermal diffusivity requires the determination rate of a temperature change and simultaneous determination of the first eigenvalue. According to a characteristic equation the first eigenvalue is a function of the Biot number defined by a surface heat transfer coefficient and thermal conductivity of an analysed material. Knowing the surface heat transfer coefficient and the first eigenvalue the thermal conductivity can be determined. The surface heat transport coefficient during the monotonic regime can be determined by the continuous measurement of long-wave radiation heat flow and the photoelectric measurement of the air refractive index gradient in a boundary layer. CFD simulation of the cooling process was carried out to analyse local convective and radiative heat transfer coefficients more in detail. Influence of ambient air flow was analysed. The obtained eigenvalues and corresponding surface heat transfer coefficient values enable to determine thermal conductivity of the analysedmore » specimen together with its thermal diffusivity during a monotonic heating regime.« less

Authors:
;  [1]
  1. Institute of Construction and Architecture, Slovak Academy of Sciences, Dubravska cesta 9, 845 03 Bratislava (Slovakia)
Publication Date:
OSTI Identifier:
22608488
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1752; Journal Issue: 1; Conference: THERMOPHYSICS 2016: 21. international meeting on thermophysics, Terchova (Slovakia), 12-14 Oct 2016; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AIR FLOW; AMBIENT TEMPERATURE; BOUNDARY LAYERS; COOLING; EIGENVALUES; HEAT FLUX; HEAT TRANSFER; HEATING; LONG WAVE RADIATION; REFRACTIVE INDEX; SIMULATION; SPACE-TIME; SURFACES; TEMPERATURE DISTRIBUTION; THERMAL CONDUCTIVITY; THERMAL DIFFUSIVITY

Citation Formats

Mihálka, Peter, E-mail: usarmipe@savba.sk, and Matiašovský, Peter, E-mail: usarmat@savba.sk. CFD simulation of simultaneous monotonic cooling and surface heat transfer coefficient. United States: N. p., 2016. Web. doi:10.1063/1.4955251.
Mihálka, Peter, E-mail: usarmipe@savba.sk, & Matiašovský, Peter, E-mail: usarmat@savba.sk. CFD simulation of simultaneous monotonic cooling and surface heat transfer coefficient. United States. doi:10.1063/1.4955251.
Mihálka, Peter, E-mail: usarmipe@savba.sk, and Matiašovský, Peter, E-mail: usarmat@savba.sk. 2016. "CFD simulation of simultaneous monotonic cooling and surface heat transfer coefficient". United States. doi:10.1063/1.4955251.
@article{osti_22608488,
title = {CFD simulation of simultaneous monotonic cooling and surface heat transfer coefficient},
author = {Mihálka, Peter, E-mail: usarmipe@savba.sk and Matiašovský, Peter, E-mail: usarmat@savba.sk},
abstractNote = {The monotonic heating regime method for determination of thermal diffusivity is based on the analysis of an unsteady-state (stabilised) thermal process characterised by an independence of the space-time temperature distribution on initial conditions. At the first kind of the monotonic regime a sample of simple geometry is heated / cooled at constant ambient temperature. The determination of thermal diffusivity requires the determination rate of a temperature change and simultaneous determination of the first eigenvalue. According to a characteristic equation the first eigenvalue is a function of the Biot number defined by a surface heat transfer coefficient and thermal conductivity of an analysed material. Knowing the surface heat transfer coefficient and the first eigenvalue the thermal conductivity can be determined. The surface heat transport coefficient during the monotonic regime can be determined by the continuous measurement of long-wave radiation heat flow and the photoelectric measurement of the air refractive index gradient in a boundary layer. CFD simulation of the cooling process was carried out to analyse local convective and radiative heat transfer coefficients more in detail. Influence of ambient air flow was analysed. The obtained eigenvalues and corresponding surface heat transfer coefficient values enable to determine thermal conductivity of the analysed specimen together with its thermal diffusivity during a monotonic heating regime.},
doi = {10.1063/1.4955251},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1752,
place = {United States},
year = 2016,
month = 7
}
  • Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingementmore » plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.« less
  • Spray cooling is an integral part of many manufacturing processes and is particularly relevant to high-temperature process. It may be used to simply allow the survival of a unit or to insure that a unit operates at an acceptable temperature. A more recent trend is to use spray cooling to control the final properties of the product. Particular problems are experienced when cooling from the high temperature, stable film boiling regime through Leidenfrost to nucleate boiling. In this case, the published relationships between spray impact density (liters/s/sq meter) and heat transfer coefficient (HTC) are of little use, becoming very inaccuratemore » as cooling proceeds. Mathematical models of cooling are well developed and reliable but need accurate information on the heat removal conditions at the surface of the stock. A test apparatus using a stainless steel specimen cooled from 1,200 C to ambient has been used to investigate the HTC`s from various types of spray, both pressure atomized and air mist, by a transient method. The temperature history is supplied to a mathematical model which works in a reverse iterative manner but with a convergence function. This gives a relationship between HTC and stock temperature over the entire temperature range. Relationships between impact density and HTC are presented for various nozzles and suggestions for further work are made.« less
  • The local heat transfer inside the entrance to large-scale models of film cooling holes has been measured using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models. Full distributions of local Nusselt number were calculated based on the cooling passage centerline gas temperature ahead of the cooling hole. The circumferentially averaged Nusselt number was also calculated based on the local mixed bulk driving gas temperature to aid interpretation of the results, and to broaden the potential application of the data. Data are presented for a single film cooling holemore » inclined at 90 and 150 deg to the coolant duct wall. Both holes exhibited entry length heat transfer levels that were significantly lower than those predicted by entry length data in the presence of crossflow. The reasons for the comparative reduction are discussed in terms of the interpreted flow field.« less
  • SPRAY cooling has become an integral part of the steel industry. Applications include secondary cooling of continuous casting strands, roll cooling and plate cooling. Manufacturers offer many types of spray nozzles including both hydraulic and air mist. Knowledge of heat removal performance of these sprays is vital in making the correct choice and the use of mathematical modeling of cooling demands a precise understanding of the capability of the nozzle. The methods of nozzle testing, including the determination of heat removal characteristics are presented and discussed in this article. A test apparatus, using a stainless steel specimen cooled from 1,200more » C to ambient, has been used to investigate the heat transfer coefficients (HTCs) from various types of spray, both pressure atomized and air mist. It is a transient method with the temperature history being supplied to a mathematical model. The model is iterative but with a convergence function which gives the relationship between HTC and stock temperature over the entire temperature range. Relationships between impact density and HTC are presented for various nozzles.« less