Heat Transfer and Forces on Concave Surfaces in a Free Molecular Flow

1973 ◽  
Vol 95 (1) ◽  
pp. 107-112 ◽  
Author(s):  
Chien Fan
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
Spherical Surface ◽  
Speed Ratio ◽  
Molecular Flow ◽  
Flow Conditions ◽  
Incident Flow ◽  
Half Angle ◽  
Drag And Lift ◽  
Good Agreement

A Monte Carlo modeling technique is described for mathematically simulating free molecular flows over a concave spherical surface and a concave cylindrical surface of finite length. The half-angle of the surfaces may vary from 0 to 90 deg, and the incident flow may have an arbitrary speed ratio and an arbitrary angle of attack. Partial diffuse reflection and imperfect energy accommodation for molecules colliding with the surfaces are also considered. Results of heat transfer, drag, and lift coefficients are presented for a variety of flow conditions. The present Monte Carlo results are shown to be in very good agreement with certain available theoretical solutions.

Coupling of Heat and Momentum Transfer Between Nanostructured Surfaces

2009 ◽  
Author(s):  
Alexander A. Donkov ◽  
Steffen Hardt ◽  
Sudarshan Tiwari ◽  
Axel Klar
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Numerical Solutions ◽  
Small Scale ◽  
Molecular Flow ◽  
Transition Regime ◽  
Free Molecular Flow ◽  
Direction Parallel ◽  
Nanostructured Surfaces

Heat transfer between nanostructured surfaces separated by a thin gas film is studied in the free-molecular flow and in the transition regime. Besides topographic features the surfaces are characterized by regions with different boundary conditions displaying either diffuse or specular reflection of the molecules. The thermal conductivity of the materials on both sides of the gas film is assumed to be very high such that isothermal conditions may be applied at both surfaces. We analyze the problem using a combination of analytical techniques in the free-molecular flow regime and Monte-Carlo simulations. Under certain conditions, when the surfaces are held at different temperatures heat transfer is accompanied by a transfer of momentum such that a force is created parallel to the surfaces. This force can be significant and vanishes in the classical regime when the continuum transport equations can be applied. It is only observed if the reflection symmetry in a direction parallel to the surfaces is broken. We derive an analytical expression for the thermally-induced force as a function of the geometric parameters characterizing the surface topography and compare the results to Monte-Carlo simulations. The latter provide numerical solutions of the Boltzmann equation both in the free-molecular flow and in the transition regime. The scenario studied points to a novel method for conversion of thermal into kinetic energy and may find applications in small-scale energy converters.

scholarly journals A numerical analysis of a convective straight fin with temperature-dependent thermal conductivity

2017 ◽  
Vol 21 (2) ◽  
pp. 939-952 ◽  
Author(s):  
Gokhan Sevilgen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Heat Transfer Characteristics ◽  
Temperature Dependent ◽  
Fin Efficiency ◽  
Conductivity Property ◽  
Temperature Dependent Thermal Conductivity ◽  
Good Agreement

In this paper, heat transfer characteristics of a straight fin having temperature-dependent thermal conductivity were computed by using 3-D CFD analysis and MATLAB differential equation solver. The computations were performed with two different cases having both constant and linear function for thermal conductivity property. The CFD and MATLAB results were in good agreement with the data available in the literature. With the help of using these numerical techniques, fin efficiency can be improved and heat transfer rate of fins can be augmented by changing fin materials with variable thermal properties and air-flow conditions. Application of the proposed method can be effectively extended to solve the class of similar non-linear fin problems in engineering and sciences.

scholarly journals Aerodynamic Performance of a High-Speed Train Passing through Three Standard Tunnel Junctions under Crosswinds

2020 ◽  
Vol 10 (11) ◽  
pp. 3664 ◽  
Author(s):  
Xiujuan Miao ◽  
Kan He ◽  
Guglielmo Minelli ◽  
Jie Zhang ◽  
Guangjun Gao ◽  
...  
Keyword(s):  
High Speed ◽  
Tunnel Junctions ◽  
Pressure Coefficient ◽  
Aerodynamic Performance ◽  
High Speed Train ◽  
Flow Conditions ◽  
Tunnel Wall ◽  
Drag And Lift ◽  
Flat Ground ◽  
Good Agreement

The aerodynamic performance of a high-speed train passing through tunnel junctions under severe crosswind condition was numerically investigated using improved delayed detached-eddy simulations (IDDES). Three ground scenarios connected with entrances and exits of tunnels were considered. In particular a flat ground, an embankment, and a bridge configuration were used. The numerical method was first validated against experimental data, showing good agreement. The results show that the ground scenario has a large effect on the train’s aerodynamic performance. The bridge case resulted in generally smaller drag and lift, as well as a lower pressure coefficient on both the train body and the inner tunnel wall, as compared to the tunnel junctions with flat ground and embankment. Furthermore, the bridge configuration contributed to the smallest pressure variation in time in the tunnel. Overall, the study gives important insights on complicated tunnel junction scenarios coupled with severe flow conditions, that, to the knowledge of the authors, were not studied before. Beside this, the results can be used for further improvements in the design of tunnels where such crosswind conditions may occur.

Model Configuration for the Validation of Thermal-Mechanical Fluid-Structure-Interactions

2012 ◽  
Author(s):  
Matthias C. Haupt ◽  
Daniel Kowollik ◽  
Peter Horst ◽  
Reinhold Niesner ◽  
Burkard Esser ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Modelling ◽  
Hypersonic Flow ◽  
Experimental Investigations ◽  
Fluid Structure Interactions ◽  
Flow Conditions ◽  
Fluid Structure ◽  
Model Configuration ◽  
Transfer Mechanisms ◽  
Good Agreement

A simple configuration is described and used for computational and experimental investigations including thermal and mechanical fluid structure interactions for hypersonic flow conditions. The numerical modelling includes all relevant heat transfer mechanisms, takes into account the changes due to the heated and deformed structure and shows a good agreement with experiments.

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