Effect of Surface Curvature on Contact Resistance Between Cylinders

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Michael Mayer ◽  
Marc Hodes ◽  
Toby Kirk ◽  
Darren Crowdy
Keyword(s):  
Boundary Condition ◽  
Contact Resistance ◽  
Full Range ◽  
Constant Heat Flux ◽  
Contact Spot ◽  
Outer Radius ◽  
Spreading Resistance ◽  
Single Cylinder ◽  
Flat Base ◽  
Circular Contact

Due to the microscopic roughness of contacting materials, an additional thermal resistance arises from the constriction and spreading of heat near contact spots. Predictive models for contact resistance typically consider abutting semi-infinite cylinders subjected to an adiabatic boundary condition along their outer radius. At the nominal plane of contact, an isothermal and circular contact spot is surrounded by an adiabatic annulus and the far-field boundary condition is one of constant heat flux. However, cylinders with flat bases do not mimic the geometry of contacts. To remedy this, we perturb the geometry of the problem such that, in cross section, the circular contact is surrounded by an adiabatic arc. When the curvature of this arc is small, we employ a series solution for the leading-order (flat base) problem. Then, Green's second identity is used to compute the increase in spreading resistance in a single cylinder, and thus the contact resistance for abutting ones, without fully resolving the temperature field. Complementary numerical results for contact resistance span the full range of contact fraction and protrusion angle of the arc. The results suggest as much as a 10–15% increase in contact resistance for realistic contact fraction and asperity slopes. When the protrusion angle is negative, the decrease in spreading resistance for a single cylinder is also provided.

Exhaust-Pipe Effects in a Single-Cylinder Four-Stroke Engine

1940 ◽  
Vol 143 (1) ◽  
pp. 109-127 ◽  
Author(s):  
G. F. Mucklow
Keyword(s):  
Full Range ◽  
Exhaust Pipe ◽  
Valve Timing ◽  
Pipe Length ◽  
Exhaust Port ◽  
Single Cylinder ◽  
Wide Range ◽  
Different Diameters ◽  
Theoretical Considerations ◽  
Stroke Engine

The paper deals with an investigation of the fluctuations of pressure, due to piston motion on the exhaust stroke, which occur in the exhaust pipe of a single-cylinder four-stroke engine. Indicator diagrams of exhaust-port and of cylinder pressure, and measurements of air consumption were recorded, using exhaust pipes of three different diameters at three standard engine speeds; the exhaust pipe length was varied over a wide range in each case. In the light of the data thus obtained, the effects on air consumption of progressive alterations in valve timing were studied under known conditions of exhaust port pressure. Further trials were then carried out in which the valve timing which gave the maximum air consumption was determined for the full range of conditions of speed and exhaust pipe dimensions. The experimental results are discussed, and a method is derived by which the pressures in the exhaust port throughout the cycle may be obtained from theoretical considerations; the method is also directly applicable to induction pipe conditions.

The role of source boundary condition in spreading resistance calculations

1978 ◽  
Vol 21 (7) ◽  
pp. 933-941 ◽  
Author(s):  
M.S. Leong ◽  
S.C. Choo ◽  
L.S. Tan
Keyword(s):  
Boundary Condition ◽  
Spreading Resistance

Thermal and Fluid Dynamic Model for Capillary-Driven Heat Pipe With Closed-Form Solution

2017 ◽  
Author(s):  
Jesse Maxwell
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Closed Form ◽  
Heat Pipe ◽  
Closed Form Solution ◽  
Constant Heat Flux ◽  
Form Solution ◽  
Constant Heat ◽  
Micro Channels ◽  
Flow Through

A model is derived for the steady state performance of capillary-driven heat pipes on the basis treating fluid flow through miniature- and micro-channels and applied as bulk properties to a large aspect ratio quasi-one-dimensional two-phase system. Surface tension provides the driving force based on an equivalent bulk capillary radius while laminar flow through micro-channels and the vapor core are treated. Heat conduction is accounted for radially while isothermal advection is treated along the axis. A closed-form solution is derived for a steady state heat pipe with a constant heat flux boundary condition on the evaporator as well as a constant heat flux or a convective boundary condition along the condenser. Two solution methods are proposed, and the result is compared to empirical data for a copper-water heat pipe. The components of the closed-form solution are discussed as contributors to driving or frictional forces, and the existence of an optimal pore radius is demonstrated.

On Effects of Temperature Boundary Conditions on Heat Transfer in Turbulent Low-Prandtl-Number Flows

2020 ◽  
Author(s):  
Ivan Otic
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Large Eddy ◽  
Heat Flux Boundary Condition ◽  
Effects Of Temperature

Abstract One important issue in understanding and modeling of turbulent heat transfer is the behavior of fluctuating temperature close to the wall. Common engineering computational approach assumes constant heat flux boundary condition on heated walls. In the present paper constant heat flux boundary condition was assumed and effects of temperature fluctuations are investigated using large eddy simulations (LES) approach. A series of large eddy simulations for two geometries is performed: First, forced convection in channels and second, forced convection over a backward facing step. LES simulation data is statistically analyzed and compared with results of direct numerical simulations (DNS) from the literature which apply three cases of heat flux boundary conditions: 1. ideal heat flux boundary condition, 2. non-ideal heat flux boundary condition, 3. conjugate heat transfer boundary condition. For low Prandtl number flows LES results show that, despite very good agreement for velocities and mean temperature, predictions of temperature fluctuations may have strong deficiencies if simplified boundary conditions are applied.

Numerical Study of Flow and Heat in Long Micro and Nano Channels

2008 ◽  
Author(s):  
Masoud Darbandi ◽  
Shidvash Vakilipour
Keyword(s):  
Boundary Condition ◽  
Numerical Study ◽  
Slip Flow ◽  
Constant Heat Flux ◽  
Gas Flows ◽  
Transfer Rates ◽  
Compressibility Effect ◽  
Momentum And Heat Transfer ◽  
Compressibility Effects ◽  
Early Transition

In this work, we extend a numerical tool capable of solving compressible and incompressible gas flows to study the momentum and heat transfer rates in micro/nano channels with high aspect ratio (L/H = 8000), where the compressibility effect is dominant. The constant heat flux thermal boundary condition is firstly applied at the wall. Next, the flow regime is extended to the early transition regime employing a high order slip velocity boundary condition based on the kinetic theory assumptions. The accuracy of the present results in the slip flow regimes is evaluated against other available theoretical and experimental results. The thermal and compressibility effects on the pressure and Knudsen number distribution are extensively studied along the channel at early transition regimes up to Kn = 0.5. Likely, this Knudsen is the highest one to be reached via applying the foregoing boundary conditions.

Study of the MHD Flow of Casson Nanofluid in the Presence of Oxides Nanoparticles Based C2H6O2/H2O Under Constant Heat Flux Boundary Condition

2021 ◽  
Vol 15 (3) ◽  
pp. 149
Author(s):  
Feras M. Al Faqih ◽  
Mohammed Z. Swalmeh ◽  
Sulaiman Mohammed Ibrahim ◽  
Hebah G. Bani Saeed ◽  
Hamzeh T. Alkasasbeh ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Mhd Flow ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Casson Nanofluid ◽  
Heat Flux Boundary Condition
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