Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
8
5
2016
MODELING THE DEGRADATION OF THERMAL DIFFUSIVITY OF CERAMIC MATRIX COMPOSITE UNDER AXIAL STRAIN
399-408
Abdulrahman
Alghamdi
Mechanical Engineering Department, Umm Al-Qura University, Makkah, Saudi Arabia
Abdulmajeed Saeed
Al-Ghamdi
Mechanical Engineering Department, College of Engineering, Umm Al-Qura University, Makkah, Saudi Arabia
In this paper, a multi-scale finite element modeling approach is adopted to predict the degradation of through-thickness thermal diffusivity of a ceramic matrix composite under uniaxial load. A tow model is constructed to predict its thermal conductivities for three different cases: (i) virgin tow, (ii) tow containing matrix cracks, and (iii) tow containing matrix cracks with different number of debonding fibers. These values of thermal conductivities are then incorporated into the composite unit cell to predict the degradation of thermal diffusivity of the composite with damage. The modeling results are in good agreement with the experimental results and the deviations are within the bounds of numerical error of 5%.
NUMERICAL STUDY OF COOLING ENHANCEMENT: HEAT SINK WITH HOLLOW PERFORATED ELLIPTIC PIN FINS
409-428
Fatima Zohra
Bakhti
University Med Boudiaf, Faculty of Technology, Mechanical Department 28000 M'sila, Algeria
Mohamed
Si-Ameur
LESEI Laboratory, Department of Mechanical Engineering, Technology Faculty, University of Batna 2, Algeria
A mixed convective heat transfer in hollow perforated pin fins array with inline arrangement subject to a vertical impinging flow is numerically investigated. The governing equations based on Navier−Stokes equations are solved by adopting a three-dimensional finite volume numerical model. The target heat sink is tailored on the basis of the experimental work of Deshmukh and Warkhedkar [Exp. Therm. Fluid Sci., vol. 50, pp. 61−68,2013]. Hence, the elliptic solid pin fin without perforation is preliminarily considered to validate the numerical procedure. The aim is to assess the thermal performance of the new heat sink (perforated pin fins) under several significant parameters such as geometrical position of the hole (ht = 10, 20, 30, 40 mm) and the Reynolds number (Re = 50−500). The effects of the height of the horizontal hole and the vertical perforation on the thermal dissipation rate and the pressure drop are explicitly undertaken and compared to the standard configuration (without perforation). It is shown that the optimal value of the geometrical coordinate of the hole is found at about ht = 10 mm, which enhances heat dissipation positively and consequently ensures a good cooling process of the system.
A NUMERICAL INVESTIGATION OF NEW FILM COOLING HOLE CONFIGURATION AT THE LEADING EDGE OF ASYMMETRICAL TURBINE BLADE: PART B
429-443
Mustapha
Benabed
Aeronautical Laboratory and Propulsive Systems, Faculte de Genie-Mecanique, Universite des Sciences et de la Technologie d'Oran, B.P. 1505 El-Mnouar, Oran, Algeria
The focus of the second part of this numerical study is, firstly, to investigate the effects of the third new configuration, the slot with cylindrical hole midway (SWC), generated from two previous configurations, developed in Part A, by the combination between two film cooling configurations: cylindrical hole and uniform slot and secondly, to establish a final comparison between the three configurations. Computational results are presented for a row of coolant injection holes in each side of an asymmetrical turbine blade model near the leading edge. For each configuration, three values of the radius are taken: R = 0.4, R = 0.8, and R = 1.2. All simulations are conducted for the same density ratio of 1.0 and the same inlet plenum pressure. The new parameter, Rc, is defined to measure the ratio of blade coverage by the film cooling. The best cooling performances are allotted to the configurations with the smallest hole (cases 1, 4, and 7).
COMPUTATIONAL STUDY OF NATURAL CONVECTION THERMAL RADIATION HEAT TRANSFER IN TIGHTLY COILED CURVED PIPE FOR SMALL RANGE OF PECLET NUMBER
445-456
Muhammad
Ashraf
Centre for Advanced Studies in Pure and Applied Mathematics, Bahauddin Zakariya University Multan, Pakistan
R.
Yasmeen
Department of Mathematics, Faculty of Science, University of Sargodha, Pakistan
Natural convection heat transfer in a tightly coiled curved pipe is studied using the Navier−Stokes equation in cylindrical coordinates system. Transverse and axial components of flow field, temperature field, heat transfer rate, transverse and axial components of skin friction are examined. The proposed model is solved for different ranges of curvature of the pipe δ angle α, radiation parameter Rd, and Peclet number Pe. In this study, the nonlinear differential equations are transformed into convenient form by using a group of transformations and then solved by using the finite difference scheme. Useful correlations are proposed graphically for the different ranges of parameters involved in the present problem.
ENTROPY ANALYSIS ON TITANIUM MAGNETO-NANOPARTICLES SUSPENDED IN WATER-BASED NANOFLUID: A NUMERICAL STUDY
457-468
Muhammad Mubashir
Bhatti
Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Yanchang
Road, Shanghai 200072, China;
Department of Mathematics, Shanghai University, Shanghai 200444, China
Tehseen
Abbas
Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan
Mohammad Mehdi
Rashidi
Tongji University
In this article, entropy generation on titanium magneto-nanoparticles suspended in water-based nanofluid through a porous medium has been investigated. The water-based nanofluid has TiO2 magneto-nanoparticles of cylindrical shape. Entropy generation is also taken into account. The governing problem consists of energy, linear momentum, and entropy equation, which is simplified with the help of similarity transformation variables. Numerical solution has been obtained for the resulting non-linear coupled partial differential equations by means of the successive linearization method (SLM) and Chebyshev spectral collocation method (CSCM). The impact of all the physical parameters such as Hartmann number, porosity parameter, suction parameter, nanoparticle volume fraction, Prandtl number, Brinkmann number, and Reynolds number is demonstrated graphically. In particular, we discuss their effects on velocity, temperature, and entropy profile. Moreover, the expression for skin friction coefficient and local Nusselt number are also presented with the help of a table.
NUMERICAL MODELING AND PERFORMANCE INVESTIGATION FOR COMPACT HEAT EXCHANGERS IN DIFFERENT FIN ARRANGEMENT AND FLUID FLOW CONDITIONS
469-482
Waleed
Abdelmaksoud
Assistant Professor at Jouf University
Mahmoud A.
Kassem
Mechanical Power Engineering Department, Cairo University, Egypt
This paper presents a computational fluid dynamics (CFD) parametric study to investigate the effect of various parameters such as the fin arrangement (or spacing) and the inlet flow conditions (velocity and temperature) on the performance of compact finned-tube heat exchangers, which can be found in many HVAC industrial applications. In the present study, the heat exchanger's performance is expressed in terms of heat transfer and pressure drop. Both heat transfer and pressure drop are presented here in dimensionless forms; the Nusselt number and the pressure coefficient. An additional factor, the ratio of the Colburn factor to friction factor, combining the effects of the heat transfer and the pressure drop, is also presented to complete the performance assessment. Several CFD cases were studied using a commercial software package for the investigation of flow and thermal behavior in the heat exchanger under various modeling conditions. To ensure accurate numerical results, grid independence analysis and model validation against previously published experimental data were performed. Using the results generated from the CFD cases, two useful mathematical correlations were developed and presented in the dimensionless form. These correlations can be used to predict the performance of typical heat exchangers.
NUMERICAL CALCULATION OF CONJUGATE HEAT TRANSFER IN END SEALS OF STEAM TURBINES
483-488
Svitlana
Alyokhina
A. M. Pidgorny Institute for Mechanical Engineering Problems of the National Academy of Sciences of Ukraine, Kharkiv, UA-61046, Ukraine; V.N. Karazin Kharkiv National University, Kharkiv, UA-61022, Ukraine
Andrii
Kostikov
A. M. Pidgorny Institute for Mechanical Engineering Problems of the National Academy of Sciences of Ukraine, Kharkiv, UA-61046, Ukraine; V.N. Karazin Kharkiv National University, Kharkiv, UA-61022, Ukraine
Marat
Satayev
M. Auezov South Kazakhstan State University, Shymkent, Kazakhstan
Abdilla
Saipov
M. Auezov South Kazakhstan State University, Shymkent, Kazakhstan
The results of the operation of some steam turbines showed that the cracks in the zone of end seals of the high-pressure cylinder arise after long-term operation. The defects could be caused by the cyclic changes of thermal stresses in rotor material, so it is very important to have detailed information about heat transfer conditions in those elements for the following numerical thermal stress calculations. The purpose of this work is the development of effective numerical methodology of definition of the heat exchange conditions in the end seals with thermal compensating grooves by modeling of thermal processes on the basis of solving conjugate heat transfer problems. The heat transfer coefficients on surfaces of the ledges, cavities, and thermal compensating grooves in the zone of the end seal were calculated based on the results of the conjugate heat transfer problem solving. The range of usage of the empirical dependence for the calculation of the heat transfer coefficients on surfaces of the end stepping seals was expanded. The influence of the frequency of rotor rotation on the value of the heat transfer coefficients on its surface was detected. The distribution of the heat transfer coefficients on the rotor surfaces in the zone of end seal during turbine startup was detected. The obtained results could be used for estimation of the service life of a steam turbine.