Dynamic shear stress and heat transfer of solid hydrogen, deuterium, and neon

2012 ◽  
Vol 111 (8) ◽  
pp. 083513 ◽  
Author(s):  
Jacob Leachman ◽  
John Pfotenhauer ◽  
Greg Nellis
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Solid Hydrogen ◽  
Dynamic Shear ◽  
Hydrogen Deuterium

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

Enhanced Heat Transfer and Shear Stress Due to High Free-Stream Turbulence

1995 ◽  
Vol 117 (3) ◽  
pp. 418-424 ◽  
Author(s):  
K. A. Thole ◽  
D. G. Bogard
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Skin Friction ◽  
Free Stream ◽  
Surface Heat ◽  
Wall Region ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Free Stream Turbulence ◽  
Wall Interaction

Surface heat transfer and skin friction enhancements, as a result of free-stream turbulence levels between 10 percent < Tu > 20 percent, have been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulence levels, the skin friction and heat transfer enhancements scale best using parameters that are a function of turbulence level and dissipation length scale. However, as turbulence levels approach Tu = 20 percent, the St′ parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles, the maximum streamwise rms value in the near-wall region, which is needed for St′, is the same as that measured in the free stream at Tu = 20 percent. Analogous to St′, a new parameter, Cf′, was found to scale the skin friction data. Independent of all the correlations evaluated, the available data show that the heat transfer enhancement is greater than the enhancement of skin friction with increasing turbulence levels. At turbulence levels above Tu = 10 percent, the free-stream turbulence starts to penetrate the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction. Although inactive motions do not contribute to the shear stress, these motions are still active in removing heat.

Condensation of a Vapor Flowing Inside a Horizontal Rectangular Duct

1995 ◽  
Vol 117 (2) ◽  
pp. 418-424 ◽  
Author(s):  
Q. Lu ◽  
N. V. Suryanarayana
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Interfacial Shear Stress ◽  
Interfacial Shear ◽  
Rectangular Duct ◽  
Interfacial Waves ◽  
Condensate Film

Condensation of a vapor flow inside a horizontal rectangular duct, using the bottom plate as the only condensing surface, was experimentally investigated. The experimental measurements included condensate film thickness and heat transfer coefficients with R-113 and FC-72. The condensate film thickness, measured with an ultrasonic transducer, was used to obtain the local heat transfer coefficient. The heat transfer coefficient increased with increasing inlet vapor velocity. The rate of increase was enhanced noticeably after the appearance of interfacial waves. Within the limited range of the experimental variables, a correlation between St and RegL was developed by a linear regression analysis. However, because of the effect of the interfacial waves, instead of a single correlation for the entire range of RegL, two separate equations (one for the wave-free regime and another for the regime with waves) were found. Analytical predictions of heat transfer rates in the annular condensation regime require the proper modeling of the interfacial shear stress. A properly validated interfacial shear stress model with condensation is not yet available. The measurement of condensate film thickness at several axial locations opens the door for determining the local interfacial stress and, hence, a model for the interfacial shear stress.

Microwave Enhanced Hydrogenation Reactions using Solid Hydrogen, Deuterium and Tritium Donors

1998 ◽  
pp. 400-401 ◽  
Author(s):  
Mohammed H. Al-Qahtani ◽  
Nicola Cleator ◽  
Timothy N. Danks ◽  
Russell N. Garman ◽  
John R. Jones ◽  
...  
Keyword(s):  
Solid Hydrogen ◽  
Hydrogenation Reactions ◽  
Hydrogen Deuterium

scholarly journals MODELING HEAT EXCHANGE DEPENDING ON THE PRANDTL NUMBER FOR VARIOUS GEOMETRIC AND REGIME PARAMETERS

2020 ◽  
Vol 46 (4) ◽  
pp. 91-101
Author(s):  
I. E. Lobanov
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Prandtl Number ◽  
Energy Equation ◽  
Transport Model ◽  
Reynolds Numbers ◽  
Structured Grids ◽  
Shear Stress Transport Model ◽  
Small Reynolds Numbers ◽  
Prandtl Numbers

Objectives. The aim is to study the dependency of the distribution of integral heat transfer during turbulent convective heat transfer in a pipe with a sequence of periodic protrusions of semicircular geometry on the Prandtl number using the calculation method based on a numerical solution of the system of Reynolds equations closed using the Menter’s shear stress transport model and the energy equation on different-sized intersecting structured grids.Method. A calculation was carried out on the basis of a theoretical method based on the solution of the Reynolds equations by factored finite-volume method closed with the help of the Menter shear stress transport model, as well as the energy equation on different-scaled intersecting structured grids (fast composite mesh method (FCOM)).Results. The calculations performed in the work showed that with an increase in the Prandtl number at small Reynolds numbers, there is an initial noticeable increase in the relative heat transfer. With additional increase in the Prandtl number, the relative heat transfer changes less: for small steps, it increases; for median steps it is almost stabilised, while for large steps it declines insignificantly. At large Reynolds numbers, the relative heat transfer decreases with an increase in the Prandtl number followed by its further stabilisation.Conclusion. The study analyses the calculated dependencies of the relative heat transfer on the Pr Prandtl number for various values of the relative h/D height of the turbulator, the relative t/D pitch between the turbulators and for various values of the Re Reynolds number. Qualitative and quantitative changes in calculated parameters are described all other things being equal. The analytical substantiation of the obtained calculation laws is that the height of the turbuliser is less for small Reynolds numbers, while for large Reynolds numbers, it is less than the height of the wall layer. Consequently, only the core of the flow is turbulised, which results in an increase in hydroresistance and a decrease in heat transfer. In the work on the basis of limited calculation material, a tangible decrease in the level of heat transfer intensification for small Prandtl numbers is theoretically confirmed. The obtained results of intensified heat transfer in the region of low Prandtl numbers substantiate the promising development of research in this direction. The theoretical data obtained in the work have determined the laws of relative heat transfer across a wide range of Prandtl numbers, including in those areas where experimental material does not currently exist. 

The Reynolds Analogy Applied to a Cylinder Rotating in Air

1954 ◽  
Vol 58 (519) ◽  
pp. 205-208 ◽  
Author(s):  
Y. R. Mayhew
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Flow ◽  
Solid Surface ◽  
Fluid Flows ◽  
Flat Plates ◽  
Reynolds Analogy ◽  
Transfer Data ◽  
Turbulent Fluid ◽  
Flow Through

When a turbulent fluid flows past a solid surface whose temperature differs from that of the fluid, the shear stress at the surface and the heat flow from it can be related by means of the Reynolds analogy. This analogy has been improved by Prandtl, Taylor, von Kármán and others, and its validity has been tested for flow through tubes and past flat plates by several investigators. In this note the analogy is checked against shear stress data and heat transfer data for a cylinder rotating in “still” air, when the flow is turbulent.

scholarly journals Effects of Nanoparticle Enhanced Lubricant Films in Thermal Design of Plain Journal Bearings at High Reynolds Numbers

Symmetry ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 1353 ◽  
Author(s):  
Abdollahzadeh Jamalabadi ◽  
Alamian ◽  
Yan ◽  
Li ◽  
Leveneur ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Temperature Rise ◽  
Rotational Speed ◽  
Volume Fraction ◽  
Journal Bearings ◽  
Thermal Design ◽  
Average Shear Stress ◽  
Average Shear ◽  
Dissipation Power

Performance investigation of oil journal bearings is of particular importance given the growing use of them as a support for rotary components in a wide range of industrial machines. Frictional forces and shear stresses, which are proportionate to the velocity of lubricating layers at different points in the bearing space, provide the basis for changing temperature conditions. Various factors such as rotational velocity increase, slip width reduction, and small heat transfer coefficient of lubricant cause intensification of lubricant temperature changes. In the present study, with using computational fluid dynamic (CFD) thermohydrodynamic (THD) numerical simulations, the effect of nanoparticles on the performance features of plain journal bearings is evaluated. Particularly, 3D simulation of a journal bearing is implemented using CFD which considerably improves the accuracy of results, coupled with conjugate heat transfer model for metal parts of bearings. Reynolds equation model is used to calculate the oil-film pressure developed in hydrodynamic journal bearings by applying the nano-based lubricants. The configuration of thrust bearing consists of six pads in this study. In order to reduce the modeling complexity and computational cost and because of the symmetrical geometry of the pads, simulation of a single pad is considered instead of the entire domain. In this study, TiO2 nanoparticle with different volume fraction percentages are used. The parameters that are changed to evaluate the performance of the bearing include volume fraction percentage of the nanoparticle, type of lubricant, and rotational speed. Based on the results, for all different lubricant types, the dissipation power, average shear stress, and temperature rise are increased with augmenting the rotational speed. By increasing the rotational speed from 500 to 1500 rpm, the average shear stress increases by more than 100%, 120%, and 130% for DTE 26, DTE 25, and DTE 24 lubricant types, respectively. Moreover, by increasing the rotational speed from 500 to 1500 rpm, the dissipation power, and temperature rise are increased around 600% and 800%, respectively. Furthermore, increasing nanoparticles volume fraction from 0% to 10%, increases all parameters by approximately 10% for all lubricant types and in all rotational speeds.

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