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Thermo-Mechanical Modeling in Ultrasonic Spot Welding of Dissimilar Metal Sheets
Published in Susanta Kumar Sahoo, Mantra Prasad Satpathy, Ultrasonic Welding of Metal Sheets, 2020
Susanta Kumar Sahoo, Mantra Prasad Satpathy
The motions of both upper and lower weld specimens are regulated by friction at the interface along with their contacts with the sonotrode and anvil tips. The coefficient of friction varies with the surface conditions as well as with the progression of weld time. Thus, it is difficult to measure the coefficient of friction precisely with respect to weld time. In the above-described model, the coefficient of friction at all contiguous surfaces is taken as constant: i.e., 0.6 for the surfaces between sonotrode and anvil tips with the weld specimens, and 0.2 at the weld interface. The contact surfaces in this model are defined in LS-DYNA with a keyword CONTACT _AUTOMATIC _ SURFACE _ TO _ SURFACE _ THERMAL. In the developed FE model, the central region under the sonotrode knurl pattern is considered the major source of heat flux. The thermal properties such as specific heat and thermal conductivity are applied for the respective components of the model. The AA5754 aluminum alloy weld sample has 926 J/kg K specific heat and 205 W/mK thermal conductivity values. In comparison, the steel tips of the sonotrode and anvil have 480 J/kg K specific heat and 50 W/mK thermal conductivity values. The coefficient of thermal contact conductance of 2000 W/m2K is also applied. The convective boundary condition is applied on the weld specimen surfaces that are exposed to air. Usually, the coefficient of convective heat transfer is considered to be 30 W/m2K.
Metal Foam Heat Exchangers
Published in Yasser Mahmoudi, Kamel Hooman, Kambiz Vafai, Convective Heat Transfer in Porous Media, 2019
Considering the thermal contact resistance, the description should start from the analysis of the current technology: most of the air-cooled heat exchanger in HAVA&R as well as in many other applications use louver fins as extended surfaces. Elsherbini et al. (2003) reported an average thermal contact conductance of 9.44 kW m−2 K−1 (press-fit) for a louvered-fin heat exchanger with collars. As the fin collars completely overlap the tubes, the resulting contact resistance for the louvered heat exchanger became 6.1 10−4 K/W. For a varying airside mass flow rate, the relative contribution of the contact resistance to the overall thermal resistance ranges from 7% to 11%. In general, it can be stated that an average thermal contact resistance for the louver-fin heat exchanger can be up to 15% of the overall one.
The Laws of Nuclear Heat Transfer
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
In practice, the flow of heat across a boundary between two material regions cannot be treated as if there is perfect contact between the regions. In fact, most boundaries are very rough at a microscopic scale—no matter how smooth they appear to be visually. In other words, an interface between two materials may contain pockets of air and other gases having different sizes and shapes. These air gaps and gas pockets offer some internal resistance to the flow of heat because of their low thermal conductivity. In fact, they sometimes behave as insulators. An interface having these properties is called a contact zone, and in conductive heat transfer, the thermal resistance per unit area across this contact zone is called the thermal contact resistance Rc. In general, the value of Rc is determined experimentally. Moreover, the value of hc, which is equivalent to the convective heat transfer coefficient, is called the thermal contact conductance of the interface, and it is often expressed in terms of the thermal contact resistance as
Interface heat transfer for hydronic heating: heating tests of concrete blocks and numerical simulations
Published in Experimental Heat Transfer, 2023
Gang Lei, Teng Li, Omid Habibzadeh-Bigdarvish, Xinbao Yu
Many studies have provided a comprehensive understanding of thermal contact theory [38–42]. A series of parameters, including surface morphology, gas rarefaction, thermal interface material, the microscopic distance between mean planes, and material hardness, have critical influences on thermal contact conductance. However, it is very difficult, or even impossible, to accurately measure the parameters mentioned above in laboratory tests. Therefore, a newly hypothesized thermal contact model was developed that simplifies the micro-contact heat transfer and the gaps between the concrete and the PEX pipe as a layer with no thickness. The governing equation at the contact surface is presented in Eq. (2). The heat rate is assumed to be zero in this study. Then this simplified model was applied in COMSOL models detailed in Section 3.2. The TCC involved in Eq. (2) was obtained using a thermal resistance model (TRM) described in this section. It should be noted that this study is the first attempt ever made to develop a thermal contact model for an internal heating system that can improve the accuracy of numerical analyses and obtain a more reasonable match with experimental measurements.
An improved interface temperature distribution in shallow hot mix asphalt patch repair using dynamic heating
Published in International Journal of Pavement Engineering, 2020
Juliana Byzyka, Mujib Rahman, Denis Albert Chamberlain
The inverse of thermal contact resistance is thermal contact conductance. Thermal contact conductance can be calculated by the ratio of the conductivity of the material over its thickness and it is expressed in W/m2 K. The higher the thermal conductance, the lower the thermal resistance at the interface. Thermal conductance is influenced by the characteristics of the two surfaces in contact such as surface deformation, surface cleanliness, surface roughness, waviness and flatness (Gilmore 2002), the contact pressure between the two bodies and any conducting fluid (fluids or gases) in the voids spaces of the bodies’ interface (Cooper et al. 1969).