The Experts below are selected from a list of 54 Experts worldwide ranked by ideXlab platform

A Agwu G Nnanna - One of the best experts on this subject based on the ideXlab platform.

  • experimental estimation of the Phase Front under local thermal non equilibrium condition Phase Change phenomena in porous media
    Electronic and Photonic Packaging Electrical Systems Design and Photonics and Nanotechnology, 2002
    Co-Authors: A Agwu G Nnanna, A Hajisheikh, Kendall T Harris
    Abstract:

    A systematic experimental method of estimating the extent of the Phase Front under local thermal non-equilibrium condition in porous media saturated with Phase Change material has been developed. During Phase Change in porous medium, the solid matrix and the pore material are under thermodynamic non-equilibrium condition until the Phase Change process is complete. It is often hypothesized that the solid matrix and the pore material are in local thermal equilibrium (LTE) condition hence, the arrival of the Phase Front is predicted based on this hypothesis. An understanding of the rate of freezing and thawing in a porous medium undergoing the Phase Change process is important to permit proper implementation of procedures such as cryopreservation, cryosurgery, and to predict the thermal performance of passive cooling systems for electronic devices. In this paper, a systematic method of estimating the extent of the Phase Change Front is developed. Results show that during the Phase Change process the porous medium is far from local thermal equilibrium condition.Copyright © 2002 by ASME

  • Phase Change phenomena in porous media a non local thermal equilibrium model
    International Journal of Heat and Mass Transfer, 2001
    Co-Authors: Kendall T Harris, A Hajisheikh, A Agwu G Nnanna
    Abstract:

    Abstract An approximate theoretical enthalpy model is developed to study the Phase-Change process in porous media. During the melting or the freezing process, the interface within a pore remains at the Phase-Change temperature until the process is completed. Since the melting process is relatively slow, the assumption of local thermal equilibrium is not universally valid. This theoretical study leads to the development of working relations. An approximate two-temperature model is studied analytically. The results provide the parametric information concerning the Phase-Change Front. Also, the conditions that would assure the existence of local thermal equilibrium are presented.

Kendall T Harris - One of the best experts on this subject based on the ideXlab platform.

  • experimental estimation of the Phase Front under local thermal non equilibrium condition Phase Change phenomena in porous media
    Electronic and Photonic Packaging Electrical Systems Design and Photonics and Nanotechnology, 2002
    Co-Authors: A Agwu G Nnanna, A Hajisheikh, Kendall T Harris
    Abstract:

    A systematic experimental method of estimating the extent of the Phase Front under local thermal non-equilibrium condition in porous media saturated with Phase Change material has been developed. During Phase Change in porous medium, the solid matrix and the pore material are under thermodynamic non-equilibrium condition until the Phase Change process is complete. It is often hypothesized that the solid matrix and the pore material are in local thermal equilibrium (LTE) condition hence, the arrival of the Phase Front is predicted based on this hypothesis. An understanding of the rate of freezing and thawing in a porous medium undergoing the Phase Change process is important to permit proper implementation of procedures such as cryopreservation, cryosurgery, and to predict the thermal performance of passive cooling systems for electronic devices. In this paper, a systematic method of estimating the extent of the Phase Change Front is developed. Results show that during the Phase Change process the porous medium is far from local thermal equilibrium condition.Copyright © 2002 by ASME

  • Phase Change phenomena in porous media a non local thermal equilibrium model
    International Journal of Heat and Mass Transfer, 2001
    Co-Authors: Kendall T Harris, A Hajisheikh, A Agwu G Nnanna
    Abstract:

    Abstract An approximate theoretical enthalpy model is developed to study the Phase-Change process in porous media. During the melting or the freezing process, the interface within a pore remains at the Phase-Change temperature until the process is completed. Since the melting process is relatively slow, the assumption of local thermal equilibrium is not universally valid. This theoretical study leads to the development of working relations. An approximate two-temperature model is studied analytically. The results provide the parametric information concerning the Phase-Change Front. Also, the conditions that would assure the existence of local thermal equilibrium are presented.

A Hajisheikh - One of the best experts on this subject based on the ideXlab platform.

  • experimental estimation of the Phase Front under local thermal non equilibrium condition Phase Change phenomena in porous media
    Electronic and Photonic Packaging Electrical Systems Design and Photonics and Nanotechnology, 2002
    Co-Authors: A Agwu G Nnanna, A Hajisheikh, Kendall T Harris
    Abstract:

    A systematic experimental method of estimating the extent of the Phase Front under local thermal non-equilibrium condition in porous media saturated with Phase Change material has been developed. During Phase Change in porous medium, the solid matrix and the pore material are under thermodynamic non-equilibrium condition until the Phase Change process is complete. It is often hypothesized that the solid matrix and the pore material are in local thermal equilibrium (LTE) condition hence, the arrival of the Phase Front is predicted based on this hypothesis. An understanding of the rate of freezing and thawing in a porous medium undergoing the Phase Change process is important to permit proper implementation of procedures such as cryopreservation, cryosurgery, and to predict the thermal performance of passive cooling systems for electronic devices. In this paper, a systematic method of estimating the extent of the Phase Change Front is developed. Results show that during the Phase Change process the porous medium is far from local thermal equilibrium condition.Copyright © 2002 by ASME

  • Phase Change phenomena in porous media a non local thermal equilibrium model
    International Journal of Heat and Mass Transfer, 2001
    Co-Authors: Kendall T Harris, A Hajisheikh, A Agwu G Nnanna
    Abstract:

    Abstract An approximate theoretical enthalpy model is developed to study the Phase-Change process in porous media. During the melting or the freezing process, the interface within a pore remains at the Phase-Change temperature until the process is completed. Since the melting process is relatively slow, the assumption of local thermal equilibrium is not universally valid. This theoretical study leads to the development of working relations. An approximate two-temperature model is studied analytically. The results provide the parametric information concerning the Phase-Change Front. Also, the conditions that would assure the existence of local thermal equilibrium are presented.

Luiz C. Wrobel - One of the best experts on this subject based on the ideXlab platform.

  • Inverse analysis of continuous casting processes
    International Journal of Numerical Methods for Heat & Fluid Flow, 2003
    Co-Authors: Iwona Nowak, Andrzej J Nowak, Luiz C. Wrobel
    Abstract:

    This paper discusses an algorithm for Phase Change Front identification in continuous casting. The problem is formulated as an inverse geometry problem, and the solution procedure utilizes temperature measurements inside the solid Phase and sensitivity coefficients. The proposed algorithms make use of the boundary element method, with cubic boundary elements and Bezier splines employed for modelling the interface between the solid and liquid Phases. A case study of continuous casting of copper is solved to demonstrate the main features of the proposed algorithms.

  • tracking of Phase Change Front for continuous casting inverse bem solution
    Inverse Problems in Engineering Mechanics II#R##N#International Symposium on Inverse Problems in Engineering Mechanics 2000 (ISIP 2000) Nagano Japan, 2000
    Co-Authors: Iwona Nowak, Luiz C. Wrobel, Andrzej J Nowak
    Abstract:

    Publisher Summary This chapter discusses 2-D numerical solution of the inverse geometrical thermal problem consisting of an estimation of the position of the Phase Change Front in a continuous casting process. The continuous casting process of metals and alloys is frequently utilized in the metallurgical industry and in materials engineering in general. The liquid material flows into the mould having the walls cooled by flowing water. The solidifying ingot is pulled out by the withdrawal rolls. The side surface of the ingot below the mould is very intensively cooled by water flowing out of the mould and sprayed over the surface. The transport phenomena encountered in such solid-liquid Phase Change systems are of the great importance for fundamental research as well as for engineering and technological practice. Proposed algorithms utilize temperature measurements inside the solid Phase and the sensitivity coefficients. Solution procedure also involves the application of the Boundary Element Method, which simplifies modifications of numerical discretization when position of the Front is updated within the iterative process.

Pagnini G. - One of the best experts on this subject based on the ideXlab platform.

  • A generalized Stefan model accounting for system memory and non-locality
    International Communications in Heat and Mass Transfer, 2020
    Co-Authors: Garra R., Falcini F., Voller V.r., Pagnini G.
    Abstract:

    The Stefan problem, involving the tracking of an evolving Phase-Change Front, is the prototypical example of a moving boundary problem. In basic one- dimensional problems it is well known that the Front advances as the square root of time. When memory or non-locality are introduced into the system however, this classic signal may be anomalous; replaced by a power-law advance with a time exponent that differs from n = 1/2. Up to now memory treatments in Stefan problem models have only been able to reproduce sub-diffusive Front movements with exponents n 1/2. In the present paper, using a generalized Caputo fractional derivative operator, we introduce new memory and non-local treatment for Stefan problems. On considering a limit case Stefan problem, related to the melting problem, we are able to show that, this gen- eral treatment can not only produce arbitrary power-law in time predictions for the Front movement but, in the case of memory treatments, can also produce non-power-law anomalous behaviors. Further, also in the context of the limit problem, we are able to establish an equivalence between non-locality and a space varying conductivity and memory and a time varying conductivity