scholarly journals Advanced Modeling of Enclosed Airspaces to Determine Thermal Resistance for Building Applications

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7772
Author(s):  
Hamed H. Saber ◽  
David W. Yarbrough
Keyword(s):  
Heat Flow ◽  
Aspect Ratio ◽  
Thermal Resistance ◽  
Flow Direction ◽  
Total Heat Transfer ◽  
Temperature Variations ◽  
One Dimensional ◽  
Heat Flow Direction ◽  
R Value ◽  
The Impact

Enclosed airspaces to reduce heat flow have been recognized for well over 100 years. Airspaces with one or more reflective surfaces define reflective insulation (RI) assemblies, a product type used in walls, roofs, windows with multiple panes, curtain walls and skylights. The thermal resistance (R value) of airspaces depends on the emittance of all surfaces, airspace dimensions and orientation, heat flow direction and surfaces temperatures. The modeling of RI now includes CFD coupled with radiation to quantify the total heat transfer. This study compares a validated model for airspace R values with existing methods such as ISO 6946 and hot-box results that provide the R values in the ASHRAE Handbook of Fundamentals. The existing methods do not include an airspace aspect ratio. This study showed that the aspect ratio can impact the R value by a factor of two. The impact of aspect ratio was calculated for double airspaces variation such as that for single airspaces. The present calculations are two-dimensional and also consider all the bounding airspace surfaces, while previous methods are one-dimensional and do not include surface temperature variations or detailed radiative transport.

scholarly journals Evaluation and use of airspaces for thermal resistance in buildings

2021 ◽  
Vol 2069 (1) ◽  
pp. 012098
Author(s):  
H H Saber ◽  
D W Yarbrough
Keyword(s):  
Thermal Resistance ◽  
Flow Direction ◽  
Energy Performance ◽  
Building Envelope ◽  
Surface Radiation ◽  
Air Infiltration ◽  
Aspect Ratios ◽  
Heat Flow Direction ◽  
R Value ◽  
Bounding Surfaces

Abstract The thermal resistance (R-value) of airspaces depends on the emittance of surfaces around the airspace, dimensions, heat-flow direction, and the temperatures of bounding surfaces. Assessing the energy performance of building envelope components and fenestration systems requires accurate results for the R-values of any enclosed spaces. The evaluation of reflective insulation R-values has evolved to include use of computational fluid dynamics and surface-to-surface radiation to quantify convective and radiation contributions to the heat transfer across airspaces of all types. This paper compares an advanced and validated computational tool for calculating enclosed airspace R-values with the widely-used ISO 6946 and airspace R-values in the ASHRAE Handbook-Fundamentals. The tool evaluates construction defects, air-infiltration impact, and dimensional aspect ratios that 1-D methods do not address. The differences between the methods that are currently being used to evaluate the R-value and the advantages of the advanced method for evaluation of reflective insulation applications are discussed.

Practical correlation for thermal resistance of 45° sloped-enclosed airspaces with upward heat flow for building applications

2021 ◽  
pp. 174425912110099
Author(s):  
Hamed H Saber
Keyword(s):  
Heat Flow ◽  
Aspect Ratio ◽  
Thermal Resistance ◽  
Accurate Determination ◽  
Thin Sheet ◽  
Energy Performance ◽  
Operating Conditions ◽  
Building Components ◽  
R Value

Assessing the energy performance of building components with enclosed airspaces requires accurate determination of the thermal resistance ( R-value) of the airspaces. The R-value of enclosed airspace depends on its size and orientation, direction of heat transfer through the airspace, and temperatures and emissivities of all surfaces that define the airspace. In previous studies, practical correlations were developed to determine the R-values for vertical enclosed airspaces, horizontal enclosed airspaces with upward heat flow and downward heat flow, and 30° and 45° sloped-enclosed airspaces with downward heat flow. However, to the authors’ best knowledge, there is no such practical correlations available to determine the R-values for wide ranges of dimensions and operating conditions for 30° and 45° sloped-enclosed airspaces with upward heat flow. This paper focused on the thermal performance of 45° sloped-enclosed airspaces with upward heat flow, and the predicted R-values were compared with the R-values provided in ASHRAE Handbook of Fundamentals at different conditions. The dependence of the R-value on the aspect ratio of the enclosed airspaces was also investigated. As well, considerations were given to quantify the potential increase in the R-value of enclosed airspace when a thin sheet having different values of emissivity on both sides was placed in the middle of the airspace. The results showed that depending on the value of the effective emittance and the thickness of the airspace, the R-value could be tripled by incorporating thin a sheet in the middle of the enclosed airspace. Finally, practical correlation were developed to determine the effective R-values of 45° sloped-enclosed airspaces with upward heat flow for wide ranges of aspect ratio, temperature difference across the airspace, mean temperature, and effective emittance. The results showed that the calculated R-values using this correlation were in good agreement with the predicted R-values.

scholarly journals Influence of heat flow direction on solder ball interfacial layer

2018 ◽  
Vol 69 (4) ◽  
pp. 305-310 ◽  
Author(s):  
Alexandr Otáhal ◽  
Ivan Szendiuch
Keyword(s):  
Heat Flow ◽  
Flow Direction ◽  
Intermetallic Layer ◽  
Point Of View ◽  
Infrared Heating ◽  
Root Mean Square Roughness ◽  
Sac305 Solder ◽  
Heat Flow Direction ◽  
Solder Balls ◽  
Bga Package

Abstract This paper deals with the research of an intermetallic layer of SAC305 solder balls soldered from three directions of the heat flow in the ball-attach process for BGA package. From the point of view of the heat flow direction, the samples were soldered by infrared heating. The heat sources were placed on the top, bottom and both lateral sides of the BGA package. After the solder balls-attach process, a metallographic cross-section was performed, followed by selective etching to visualize the relief of the intermetallic layer. Images of the interfacial between the solder and solder pad were taken from the created samples, followed by measurement of the average thickness and root mean square roughness of the intermetallic layer. The results showed changes in the intermetallic layer. The largest thickness of the intermetallic layer was observed on samples soldered from the top and both sides. Soldering with the bottom infrared heater resulted to the smallest thickness of the intermetallic layer. The same trend was in the roughness of the IMC layer. The greatest roughness was found for samples soldered by the top and both side heaters. The top soldered samples exhibit the smallest roughness.

scholarly journals Orientation and Microstructure Evolution of Al-Al2Cu Regular Eutectic Lamellar Bifurcating in an Abruptly Changing Velocity under Directional Solidification

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1004
Author(s):  
Ka Gao ◽  
Zan Zhang ◽  
Junliang Zhao ◽  
Dejian Sun ◽  
Fu Wang
Keyword(s):  
Heat Flow ◽  
Directional Solidification ◽  
Flow Direction ◽  
Solidification Rate ◽  
Lateral Diffusion ◽  
Interfacial Instability ◽  
Growth Orientation ◽  
Al2cu Phase ◽  
Heat Flow Direction ◽  
Solidification Microstructures

In an abruptly changing velocity under directional solidification, microstructures and the growth orientation of Al-Al2Cu eutectic lamellar were characterized. The change in solidification rate led to an interfacial instability, which results in a bifurcation of the eutectic lamella into new, refined lamellae. The growth orientation of the eutectic Al2Cu phase was also only in its (001) direction and more strongly oriented to the heat flow direction. The results suggest that the eutectic lamellar Al-Al2Cu bifurcation and the spacing adjustment may be caused by the rate determining lateral diffusion of the solutes after interfacial instability.

The importance of heat flow direction for reproducible and homogeneous freezing of bulk protein solutions

2013 ◽  
Vol 29 (5) ◽  
pp. 1212-1221 ◽  
Author(s):  
Miguel A. Rodrigues ◽  
Gustavo Balzan ◽  
Mónica Rosa ◽  
Diana Gomes ◽  
Edmundo G. de Azevedo ◽  
...  
Keyword(s):  
Heat Flow ◽  
Flow Direction ◽  
Protein Solutions ◽  
Heat Flow Direction ◽  
Homogeneous Freezing

scholarly journals Mathematical apparatus for determination of homogenous scalar medium thermal resistance

Vestnik MGSU ◽  
2019 ◽  
pp. 1037-1045
Author(s):  
Tatiana A. Musorina, ◽  
Michail R. Petritchenko ◽  
Daria D. Zaborova
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Thermal Resistance ◽  
Heat Conducting ◽  
Heat Flow Rate ◽  
Conductivity Equation ◽  
Total Thermal Resistance ◽  
Active Resistance ◽  
One Dimensional

Introduction: the article suggests a method for determining a thermal resistance of small and large-sized areas (one-dimensional and multidimensional problems) of wall enclosure. The subject of the study is the thermal resistance of homogeneous scalar medium (homogeneous wall enclosure). The aim is the determination of thermal resistance of a wall structure for areas of arbitrary dimension (by the coordinates xi, where 1 ≤ i ≤ d and d is the area dimension) filled with a scalar (homogeneous and isotropic) heat-conducting medium. Materials and methods: the article used the following physical laws: Fourier law (the value of the heat flow when transferring heat through thermal conductivity) and continuity condition for the heat flow rate leading to the thermal conductivity equation. Results: this method extends the standard definition of thermal resistance. The research proved that the active thermal resistance does not increase with increasing of the area dimension (for example, when switching from a thin shell or plate to a rectangle with length and width of the same order of magnitude). That is the sense of geometric inclusion, i.e., increase of the dimension of an area filled with a homogeneous isotropic medium. Evident expressions are obtained for the determination of active, reactive, and total thermal resistance. It is proved that the total resistance is higher than the active resistance since the reactive resistance is positive, and the wall possesses an ability to suppress the temperature fluctuations and accumulate/give up the heat. Conclusions: the appearance of an additional wall dimension (comparable length-to-thickness ratio) does not increase its active resistance. In the general case, the total thermal resistance exceeds the active thermal resistance no more than four times. Geometric inclusions must be considered in the calculation of wall enclosures that are variant from one-dimensional bodies.

scholarly journals Analysis of Temperature Field, Heat and Fluid Flow of Two-Phase Zone Continuous Casting Cu–Sn Alloy Wire

2016 ◽  
Vol 16 (1) ◽  
pp. 33-40 ◽  
Author(s):  
J. Luo ◽  
X. Liu ◽  
X. Wang
Keyword(s):  
Temperature Field ◽  
Fluid Flow ◽  
Heat Flow ◽  
Continuous Casting ◽  
Flow Direction ◽  
Phase Zone ◽  
Two Phase ◽  
Alloy Wire ◽  
Heat Flow Direction ◽  
Heat And Fluid Flow

Abstract Cu–4.7 wt. % Sn alloy wire with Ø10 mm was prepared by two-phase zone continuous casting technology, and the temperature field, heat and fluid flow were investigated by the numerical simulated method. As the melting temperature, mold temperature, continuous casting speed and cooling water temperature is 1200 °C, 1040 °C, 20 mm/min and 18 °C, respectively, the alloy temperature in the mold is in the range of 720 °C–1081 °C, and the solid/liquid interface is in the mold. In the center of the mold, the heat flow direction is vertically downward. At the upper wall of the mold, the heat flow direction is obliquely downward and deflects toward the mold, and at the lower wall of the mold, the heat flow deflects toward the alloy. There is a complex circular flow in the mold. Liquid alloy flows downward along the wall of the mold and flows upward in the center.

Aerodynamics of Darrieus Wind Turbines Airfoils: The Impact of Pitching Moment

2016 ◽  
Vol 139 (4) ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari
Keyword(s):  
Flow Direction ◽  
Pitching Moment ◽  
Aerodynamic Coefficients ◽  
One Dimensional ◽  
High Incidence ◽  
The Impact ◽  
Starting Torque ◽  
Very High ◽  
Selection Of ◽  
The Revolution

Recent studies have demonstrated that, when rotating around an axis orthogonal to the flow direction, airfoils are virtually transformed into equivalent airfoils with a camber line defined by their arc of rotation. In these conditions, the symmetric airfoils commonly used for Darrieus blades actually behave like virtually cambered ones or, equivalently, rotors have to be manufactured with countercambered blades to ensure the attended performance. To complete these analyses, the present study first focuses the attention on the airfoils' aerodynamics during the startup of the rotors. It is shown that, contrary to conventional theories based on one-dimensional aerodynamic coefficients, symmetric airfoils exhibit a counterintuitive nonsymmetric starting torque over the revolution. Conversely, airfoils compensated for the virtual camber effect show a more symmetric distribution over the revolution. This behavior is due to the effect of the pitching moment, which is usually neglected in lumped parameters models. At very low revolution speeds, its contribution becomes significant due to the very high incidence angles experienced by the blades; the pitching moment is also nonsymmetric between the upwind and the downwind zone. For upwind azimuthal positions, the pitching moment reduces the overall torque output, while it changes sign in the downwind section, increasing the torque. The importance of accounting for the pitching moment contribution in the entire power curve is also discussed in relationship to the selection of the best blade–spoke connection (BSC) point, in order to maximize the performance and minimize the alternate stresses on the connection due to the pitching moment itself.

Thermoelectric Power of Gradient Fex(Al2O3)100-x Composite Films

2015 ◽  
Vol 233-234 ◽  
pp. 694-698 ◽  
Author(s):  
Oleg Stognei ◽  
Ahmed Al-Maliki ◽  
Alexander Sitnikov ◽  
Vladimir Makagonov
Keyword(s):  
Heat Flow ◽  
Temperature Gradient ◽  
Thermoelectric Power ◽  
Concentration Gradient ◽  
Flow Direction ◽  
Composite Films ◽  
Sputter Deposition ◽  
Deposition Technique ◽  
Opposite Edge ◽  
Heat Flow Direction

Nanocomposite Fex(Al2O3)100-x films with concentration gradient along the long axis of the samples (40 mm) have been obtained by sputter deposition technique and investigated. Based on the electric and magnetoresistive investigations the gradient Fex(Al2O3)100-x samples in which concentration of one edge of the sample is smaller than concentration of a percolation threshold while concentration of opposite edge of this sample is upper the threshold have been determined. Influence of the heat flow direction on the thermoelectric power of the gradient samples has been investigated. Hysteresis of the thermoelectric power is observed when temperature gradient direction is changed.

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