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Diffusivity in Drying of Porous Media
Published in Peng Xu, Agus P. Sasmito, Arun S. Mujumdar, Heat and Mass Transfer in Drying of Porous Media, 2020
Chien Hwa Chong, Chung Lim Law, Adam Figiel, Tommy Asni
The transport of heat in the drying process occurs primarily by conduction and convection, though radiation heat transfer may occur for certain types of drying such as infrared or solar drying. Heat transfer takes place due to the temperature gradient. Heat transfer through conduction occurs through the contact of two different solid material or two regions of the same material with different temperature (Eq. 2.3).
Metal Forming
Published in Sherif D. El Wakil, Processes and Design for Manufacturing, 2019
Before being subjected to hot-forming processes, ingots (or billets) should be uniformly heated throughout their cross sections, without overheating or burning the metal at the surface. This is particularly important when forming steels. Attention must also be given to the problems of decarburization and formation of scale in order to bring them to a minimum. The thermal gradient is another important factor that affects the soundness of the deformed part. If the temperature gradient is high, thermal stresses may initiate and can cause internal cracks. This usually happens when a portion of the metal is above the critical temperature of metal (AC1 or AC3) while the rest of the billet is not. The larger the cross section of the billet and the lower its coefficient of thermal conductivity, the steeper the temperature gradient will be, and the more liable to internal cracking during heating the billet becomes. In the latter case, the rate of heating should be kept fairly low (about 2 hours per inch of section of the billet) in order not to allow a great difference to occur between the temperatures at the surface and the core of the billet. The metal must then be “soaked” at the maximum temperature for a period of time long enough to ensure uniformity of temperature.
Drying
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
Drying is described as a process of simultaneous heat and mass transfer. Heat transfer proceeds from the product surface in contact with the drying medium at a higher temperature (Th) to the core of the food product and also from one point to another within the product. Consequently, a temperature gradient is created between the product and water surface at some location within the product. This temperature gradient acts as the driving force for the heat transfer phenomenon which occurs by one or a combination of the conduction, convection, and radiation mechanisms (Figure 10.3). The abovementioned mechanisms vary with respect to the type of drying medium, mode of contact between the product and drying medium, the scale of heat transfer within the product, i.e., molecular or bulk transport, and the direction of heat transfer.
Thermal fracture analysis of a two-dimensional decagonal quasicrystal coating structure with interface cracks
Published in Mechanics of Advanced Materials and Structures, 2023
Minghao Zhao, Xin Zhang, Cuiying Fan, Chunsheng Lu, Huayang Dang
In recent years, extensive research has been done on preparation and enhancement of QC TBCs [25–29]. Owing to mismatch between the material constants of the coating and substrate, pores and microcracks inevitably appear at the interface [30]. Crack propagation may lead to failure of a structure, especially in extreme environments, such as a rocket launch. An extreme temperature gradient may result in rapid crack propagation. Understanding the characteristics of crack propagation can avoid irreversible consequences caused by sudden failure of a coating [31, 32]. Some preliminary studies on crack propagation characteristics of QC coatings have been carried out under anti-plane and plane mechanical loads [22, 33]; however, to the best of our knowledge, there is still lack of research on the thermal fracture analysis of a 2D decagonal QC coating structure.
Transient response analysis of a spherical shell embedded in an infinite thermoelastic medium based on a memory-dependent generalized thermoelasticity
Published in Journal of Thermal Stresses, 2019
Tianhu He, Pei Zhang, Chi Xu, Yan Li
Nevertheless, composite structures often contain imperfections at the interface, which significantly affect the material properties [23, 24]. For instance, thermal-contact resistance lying in the interface between two dissimilar media significantly influences the performance of laminated materials [25, 26]. High temperature gradient can cause thermal damage or even failure if the temperature difference at the interface is large. Thus, matching materials with proper thermal properties is crucial, especially in the design of microstructures. Towards this end, Lor and Chu [25] analyzed the effect of interfacial thermal resistance upon heat transfer in a two-layered composite material structure by using the hyperbolic heat conduction equation. Li et al. [27] studied the thermal shock resistance of ceramics. Rossikhin and Shitikova [28] concerned the vibrations and stability of a cylindrical shell embedded in an unbounded thermoelastic medium.
Numerical research on carbon activity, fuel utilization, chemical reaction, and temperature distribution for IT single planar SOFC
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
Dingwen Kang, Jie Yu, Guoqiang Lv, Wenhui Ma, Xin Gu, Chao Xiong, Hui Liu
It can be clearly seen from Figures 6 and 7 that the maximum thermal stress occurs at the interface between the anode/cathode and the electrolyte, where heats of both electrochemical reactions and chemical reactions generate. Thermal stress of the inlet is higher than that of the outlet, which is caused by the temperature gradient. Thermal stress increases with temperature gradient.