A New Theoretical Equation for Effective Thermal Conductivity of Cellular Concrete

2011 ◽  
Vol 71-78 ◽  
pp. 1228-1232
Author(s):  
Xiang Yu Li ◽  
Xiao Long Zhao ◽  
Xiang Yong Guo ◽  
Li Qiang Cao
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Property ◽  
Effective Thermal Conductivity ◽  
Transfer Mechanism ◽  
Theoretical Equation ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
New Equation ◽  
Cellular Concrete

A new theoretical equation that represents the thermal conductivity of two-phase composite has been proposed. The Cheng-Vachon equation has been modified by introducing a new parameter that is the corrected porosity. It was found that the new equation can describe the thermal conductivity of cellular concrete very accurately. Development of the equation is helpful to understanding heat transfer mechanism and improving thermal property of cellular concrete.

scholarly journals Design and Implementation of a Laboratory Equipment for Studying Heat Transfer by Conduction

2019 ◽  
Vol 11 (1) ◽  
pp. 153-156
Author(s):  
István Padrah ◽  
Judit Pásztor ◽  
Rudolf Farmos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Thermal Conduction ◽  
Transfer Mechanism ◽  
Measuring Instrument ◽  
Heat Transfer Mechanism ◽  
Laboratory Equipment ◽  
Insulating Materials ◽  
Design And Implementation

Abstract Thermal conduction is a heat transfer mechanism. It is present in our everyday lives. Studying thermal conductivity helps us better understand the phenomenon of heat conduction. The goal of this paper is to measure the thermal conductivity of various materials and compare results with the values provided by the manufacturers. To achieve this we assembled a measuring instrument and performed measurements on heat insulating materials.

scholarly journals Change in Conductive–Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation—Experimental and Simulated Investigations

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2626
Author(s):  
Aurelia Blazejczyk ◽  
Cezariusz Jastrzebski ◽  
Michał Wierzbicki
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Expanded Polystyrene ◽  
Transfer Mechanism ◽  
Total Thermal Conductivity ◽  
Heat Transfer Mechanism

This article introduces an innovative approach to the investigation of the conductive–radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14–17 kg·m−3) in the form of panels (of thickness 0.02–0.18 m) was tested with 1–15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity “thickness effect” is proposed. The conductive–radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m−1·K−1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the “grey” EPS insulating layer, with respect to “dotted” EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

New theoretical equation for effective thermal conductivity of two-phase composite materials

2012 ◽  
Vol 28 (5) ◽  
pp. 620-626 ◽  
Author(s):  
X Y Li ◽  
X L Zhao ◽  
X Y Guo ◽  
Z M Shao ◽  
M X Ai
Keyword(s):  
Thermal Conductivity ◽  
Composite Materials ◽  
Effective Thermal Conductivity ◽  
Theoretical Equation ◽  
Two Phase

Heat Transfer Characteristics in a Slug Unit

2010 ◽  
Author(s):  
Valery Babin ◽  
Dvora Barnea ◽  
Lev Shemer
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Slug Flow ◽  
Video Camera ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Vertical Pipe ◽  
Two Phase ◽  
Taylor Bubble ◽  
Hydrodynamic Parameters

Heat transfer mechanism in two-phase flows and particularly in vertical slug flow is of high interest both for basic hydrodynamic research and for industrial applications. Two-phase slug flow is highly complicated and only a limited number of heat transfer studies have been carried out. The flow field around a single Taylor bubble propagating in a vertical pipe can be subdivided into three distinct hydrodynamic regions: the gas bubble surrounded by a thin liquid film, a highly turbulent liquid wake in the vicinity of the bubble bottom, and the far wake region. Experimental and theoretical works have been presented during the last decades investigating the hydrodynamic parameters in each region. Due to the complexity and intermittent nature of slug flow the existing data on the heat transfer in slug flow is limited to a narrow range of operational conditions. To improve the understanding of the heat transfer mechanism in slug flow a new experimental setup was constructed. A part of the vertical pipe wall was replaced by a thin metal foil heated by electrical current. An IR video camera was used to determine the temporal variation of the instantaneous temperature field along the foil. The video camera was synchronized with a sensor that determined the instantaneous location of the Taylor bubble. The results of the instantaneous heat transfer measurements along the liquid film and in the wake of the Taylor bubble can be correlated with the detailed velocity measurements carried out in the same facility (Shemer et al. 2007). The effect of the local hydrodynamic parameters on the heat transfer coefficient in each region is examined.

Heat Transfer Mechanism and Flow Pattern During Flow Boiling of Water in a Vertical Narrow Channel: Experimental Results

2006 ◽  
Author(s):  
Ewelina Sobierska ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Transfer Mechanism ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
Mass Fluxes

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooling conditions with deionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single-and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg/m2s) and heat fluxes (30–110, 35–150 and 65–200 kW/m2, respectively) during two-phase flow. The fluid temperature at the inlet was about 50 °C what corresponds to inlet subcooling, depending on flow pressure conditions, from 34 °C to 57 °C. The visual observations were used to obtain a better insight about the heat transfer mechanism.

scholarly journals Thermoactivated heat transfer mechanism in molecular crystals: Thermal conductivity of benzophenone single crystals

AIP Advances ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 015121 ◽  
Author(s):  
A. Jeżowski ◽  
M. A. Strzhemechny ◽  
A. I. Krivchikov ◽  
O. S. Pyshkin ◽  
O. O. Romantsova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Single Crystals ◽  
Molecular Crystals ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism
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