Begell House Inc.
Heat Transfer Research
HTR
1064-2285
40
4
2009
Numerical Investigation of Heat Transfer in Friction Welding of Cylindrical Tubes
281-291
Yilmaz
Can
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Trakya University, 22030, Edirne, Turkey
Kamil
Kahveci
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Trakya University, 22030, Edirne, Turkey
Ahmet
Cihan
Department of Mechanical Engineering, Faculty of Engineering and Architecture, Trakya University, 22030, Edirne, Turkey
Heat transfer in friction welding of cylindrical tubes is considered in the present study and the governing equations are solved numerically using an explicit finite difference technique to determine the temperature field. The values of the radius ratio in the problem are selected as rr = 0.25, 0.50, and 0.75. Results show that the temperature of tubes increases with increasing radius ratio. In addition, as the generated heat is proportional to the interface radius, the temperature increases from the inner surface but drops slightly towards the periphery due to the convection effect. The temperature field is of a similar form for all values of the radius ratio, but the radial and axial temperature gradients change at certain amounts.
Optimal Running Conditions of Cooling Systems of the Gas-Main Pipeline Compressor Stations
293-304
I.
Cherednichenko
St. Petersburg State Polytechnic University, 29 Politekhnicheskaya Str., St. Petersburg, Russia
E.
Khodak
St. Petersburg State Polytechnic University, 29 Politekhnicheskaya Str., St. Petersburg, Russia
A. I.
Kirillov
Saint-Petersburg State Polytechnic University, Saint-Petersburg, Russia
N.
Zabelin
St. Petersburg State Polytechnic University, 29 Politekhnicheskaya Str., St. Petersburg, Russia
The article is dealing with the analysis and optimization of conditions of running the gas-main pipeline compressor station cooling systems. It is shown that at a given temperature of natural gas leaving the compressor station (the first phase of optimization) a significant saving rate can be achieved by selecting an optimal ratio of acting fans and extent of bypass. The results of experiments carried out by the authors on two operating compressor stations showed the influence of contamination of heat-exchange surfaces on operating costs of cooling systems.
Expanded Lumped Model for the Algebraic Evaluation of the Total Heat Rejection from a Large Plate Immersed in a Fluid during a Period of Time
305-319
Antonio
Campo
Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
Luis E.
Herranz
CIEMAT, Department of Nuclear Fission, Avenida Complutense 22, 28040 Madrid, Spain
Estimates of the total heat transfer from large plates by forced convection to neighboring fluids during a certain period of time has been traditionally obtained from the classic GrĂ¶ber chart. This paper proposes a simple composite lumped model of the unidirectional heat conduction equation that articulates a handful of algebraic expressions. It is demonstrated that simple composite lumped model is a capable predictive tool in the entire range of the dimensionless Bi number. A compact correlation for the so-called mean "internal Nusselt number" varying with the dimensionless time has been developed. With this information, the total heat transfer can be evaluated effortlessly by algebraic means at all dimensionless times x. The accuracy provided by the expanded lumped model exceeded expectations.
Temperature Oscillation of mLHP with Flat Evaporator
321-332
Dongxing
Gai
Wuhan Institute of Technology
Wei
Liu
School of Energy and Power Engineering, Huazhong University of Science & Tecnology, 1037 Luo Yu Rd. Hongshan District, Wuhan 430074, China
Zhichun
Liu
School of Energy and Power Engineering, Huazhong University of Science & Tecnology, 1037 Luo Yu Rd. Hongshan District, Wuhan 430074, China
Jinguo
Yang
Huazhong University of Science and Technology (HUST), 1037 Luoyu Rd., Hongshan District, Wuhan 430074, China
Loop heat pipes (LHPs) are heat transfer devices whose operating principle is based on evaporation and condensation of a working fluid, and which use the capillary pumping forces to ensure fluid circulation. Temperature oscillations are a rather wide-spread phenomenon accompanying the operation of miniature loop heat pipes (mLHP), which depends on the charging ratio of the working fluid, the device orientation in the gravity field, and the conditions of the condenser cooling, and so on. Intense oscillation, whose amplitude may exceed tens of centigrade degrees and the period may be equal to tens of minutes, arises from the lack of a working fluid in a mLHP when a hot condensate or vapor bubbles periodically penetrate into the compensation chamber and act on the vapor phase in it, thus increasing its temperature and volume. Changes in the external conditions, for instance, the LHP arrangement in an unfavorable orientation or applied heat load with respect to the conditions for which the filling volume is optimal, also contribute to initiation of intense temperature oscillation. All in all, the heat leak from the evaporator to the compensation chamber, the heat loss to the ambient, and the temperature and rate of subcooled liquid dictate the vapor bubble condition inside the compensation chamber, and the rate of the vapor bubble growth or dissipation inside the compensation chamber dictates the nature of temperature oscillation. The effects of different liquid charging ratios and the tilt angles to the temperature oscillation are studied in detail.
Efficiency Determination of Radiators with Temperature-Dependent Thermal Conductivity Using Two He's Methods
333-349
Zaman Ziabakhsh
Ganji
Department of Mechanical Engineering, Babol University of Technology, P. O. Box 484, Babol, Iran
Davood
Ganji (D.D. Ganji)
Babol University
Abdolhosein
Fereidoon
Department of Mechanical Engineering, Faculty of Engineering, Semnan University, Iran
Yasser
Rostamiyan
Department of Mechanical Engineering, Islamic Azad University-Semnan Branch-Iran
Variational iteration method (VIM) and homotopy perturbation method (HPM) have been used to evaluate the efficiency of pipe/fin with temperature-dependent thermal conductivity and to determine the temperature distribution within the pipe/fin. These methods are useful and practical for solving the nonlinear heat transfer equation, which is associated with variable thermal conductivity condition. VIM and HPM provide an approximate analytical solution in the form of an infinite power series. The pipe/fin efficiency of the radiators with temperature-dependent thermal conductivity has been obtained as a function of thermo-geometric fin parameter and the thermal conductivity parameter describing the variation of the thermal conductivity.
A Nonlinear Stability Analysis of a Rotating Double-Diffusive Magnetized Ferrofluid Saturating a Porous Medium
351-378
Sunil
Department of Mathematics, National Institute of Technology, Hamirpur, (H.P.) 177005, India
Poonam
Sharma
Department of Applied Sciences, National Institute of Technology, Hamirpur, 177 005, India
Amit
Mahajan
Department of Applied Sciences, National Institute of Technology, Hamirpur, 177 005, India; Department of Mathematics and Statistics, University of Windsor, Windsor, Ontario, N9B3P4, Canada
Thermal stability in a layer of a double-diffusive ferrofluid rotating about an axis orthogonal to the layer in the direction of gravity saturated by a porous medium for the stress-free boundaries is investigated by nonlinear analysis. A rigorous nonlinear stability result is derived by introducing a generalized energy functional. A comparison with the linear instability theory shows that there is a considerable difference between the critical values of magnetic thermal Rayleigh numbers and thus indicates the possibility of subcritical instabilities. However, it is noted that, in case of non-ferrofluid, the global nonlinear stability Rayleigh number is exactly the same as that for linear instability. For lower values of magnetic parameters, this coincidence is immediately lost. The effect of the magnetic parameter, M3, solute gradient, Sf, Taylor number, TA1, and Darcy number, Da, on the sub-critical instability region have also been analyzed. We also demonstrate coupling between the buoyancy and magnetic forces in the nonlinear energy stability analysis.