scholarly journals THE STRUCTURE OF MANTLE FLOWS AND STRESS FIELDS IN A TWO-DIMENSIONAL CONVECTION MODEL WITH NON-NEWTONIAN VISCOSITY

2014 ◽  
Vol 55 (7) ◽  
2016 ◽  
Vol 21 (1) ◽  
pp. 83-94 ◽  
Author(s):  
Imre Ferenc Barna ◽  
Gabriella Bognar ◽  
Krisztian Hriczo

We investigate Navier-Stokes (NS) and the continuity equations in Cartesian coordinates and Eulerian description for the two dimensional incompressible nonNewtonian fluids. Due to the non-Newtonian viscosity we consider the Ladyzenskaya model with a non-linear velocity dependent stress tensor. The key idea is the multidimensional generalization of the well-known self-similar Ansatz, which has already been used for non-compressible and compressible viscous flow studies. Geometrical interpretations of the trial function are also discussed. Our recent results are compared to the former Newtonian ones.


2020 ◽  
Vol 80 ◽  
pp. 103927
Author(s):  
Shanlong Yao ◽  
Michele Zappalorto ◽  
Wei Pan ◽  
Changzheng Cheng ◽  
Zhongrong Niu

2020 ◽  
Vol 37 (8) ◽  
pp. 2913-2938
Author(s):  
Rajul Garg ◽  
Harishchandra Thakur ◽  
Brajesh Tripathi

Purpose The study aims to highlight the behaviour of one-dimensional and two-dimensional fin models under the natural room conditions, considering the different values of dimensionless Biot number (Bi). The effect of convection and radiation on the heat transfer process has also been demonstrated using the meshless local Petrov–Galerkin (MLPG) approach. Design/methodology/approach It is true that MLPG method is time-consuming and expensive in terms of man-hours, as it is in the developing stage, but with the advent of computationally fast new-generation computers, there is a big possibility of the development of MLPG software, which will not only reduce the computational time and cost but also enhance the accuracy and precision in the results. Bi values of 0.01 and 0.10 have been taken for the experimental investigation of one-dimensional and two-dimensional rectangular fin models. The numerical simulation results obtained by the analytical method, benchmark numerical method and the MLPG method for both the models have been compared with that of the experimental investigation results for validation and found to be in good agreement. Performance of the fin has also been demonstrated. Findings The experimental and numerical investigations have been conducted for one-dimensional and two-dimensional linear and nonlinear fin models of rectangular shape. MLPG is used as a potential numerical method. Effect of radiation is also, implemented successfully. Results are found to be in good agreement with analytical solution, when one-dimensional steady problem is solved; however, two-dimensional results obtained by the MLPG method are compared with that of the finite element method and found that the proposed method is as accurate as the established method. It is also found that for higher Bi, the one-dimensional model is not appropriate, as it does not demonstrate the appreciated error; hence, a two-dimensional model is required to predict the performance of a fin. Radiative fin illustrates more heat transfer than the pure convective fin. The performance parameters show that as the Bi increases, the performance of fin decreases because of high thermal resistance. Research limitations/implications Though, best of the efforts have been put to showcase the behaviour of one-dimensional and two-dimensional fins under nonlinear conditions, at different Bi values, yet lot more is to be demonstrated. Nonlinearity, in the present paper, is exhibited by using the thermal and material properties as the function of temperature, but can be further demonstrated with their dependency on the area. Additionally, this paper can be made more elaborative by extending the research for transient problems, with different fin profiles. Natural convection model is adopted in the present study but it can also be studied by using forced convection model. Practical implications Fins are the most commonly used medium to enhance heat transfer from a hot primary surface. Heat transfer in its natural condition is nonlinear and hence been demonstrated. The outcome is practically viable, as it is applicable at large to the broad areas like automobile, aerospace and electronic and electrical devices. Originality/value As per the literature survey, lot of work has been done on fins using different numerical methods; but to the best of authors’ knowledge, this study is first in the area of nonlinear heat transfer of fins using dimensionless Bi by the truly meshfree MLPG method.


2007 ◽  
Vol 129 (2) ◽  
pp. 234-241 ◽  
Author(s):  
Dennis K. Williams

The mechanical roll expansion of heat exchanger tubes into tubesheets containing TEMA grooves, which are thought to aid in the mechanical integrity of the tube-to-tubesheet (TTT) joint, has for many years provided an acceptable means of completing a TTT joint. Inherent with the intentional roll expansion of the tube is the creation of a tensile residual stress field within the tube that is greatest in the transition region between the expanded and unexpanded zones of the tube. An additional complicating factor in the tube-to-tubesheet joint design is the choice of utilizing a seal weld or a “full strength” weld at the tube end in conjunction with a level of roll expansion quantified by the degree of tube wall reduction. This paper presents the results of an initial study of the mechanical roll expansion of 1in. diameter tubes into a typical TEMA-R designed tubesheet, utilizing two grooves in the tubesheet hole. Two combinations of tube and tubesheet materials are studied that include duplex stainless steel tubes and tubesheet, while the second combination includes type 321 tubes roll expanded into a 2‐1∕4 Cr-1 Mo tubesheet, clad with 321 SS overlay. The residual stress fields are calculated by the finite element method and employ a simplified two-dimensional nonlinear axisymmetric model.


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