Comprehensive Studies on Rarefied Jet and Jet Impingement Flows with Gaskinetic Methods

2017 ◽  
Vol 22 (3) ◽  
pp. 712-741 ◽  
Author(s):  
Chunpei Cai ◽  
Xin He ◽  
Kai Zhang
Keyword(s):  
Heat Flux ◽  
Flat Plate ◽  
Surface Properties ◽  
Knudsen Number ◽  
High Speed ◽  
Direct Simulation Monte Carlo ◽  
Jet Impingement ◽  
The Moment ◽  
Plate Center ◽  
Comprehensive Studies

AbstractThis paper presents comprehensive studies on two closely related problems of high speed collisionless gaseous jet from a circular exit and impinging on an inclined rectangular flat plate, where the plate surface can be diffuse or specular reflective. Gaskinetic theories are adopted to study the problems, and several crucial geometry-location and velocity-direction relations are used. The final complete results include flowfield properties such as density, velocity components, temperature and pressure, and impingement surface properties such as coefficients of pressure, shear stress and heat flux. Also included are the averaged coefficients for pressure, friction, heat flux, moment over the whole plate, and the averaged distance from the moment center to the plate center. The final results include complex but accurate integrations involving the geometry and specific speed ratios, inclination angle, and the temperature ratio. Several numerical simulations with the direct simulation Monte Carlo method validate these analytical results, and the results are essentially identical. Exponential, trigonometric, and error functions are embedded in the solutions. The results illustrate that the past simple cosine function approach is rather crude, and should be used cautiously. The gaskinetic method and processes are heuristic and can be used to investigate other external high Knudsen number impingement flow problems, including the flowfield and surface properties for high Knudsen number jet from an exit and flat plate of arbitrary shapes. The results are expected to find many engineering applications.

Experimental and Numerical Investigations of Jet Impingement Cooling of Flat Plate for Controlling the Non-Tail Pipe Emissions From Heavy Duty Diesel Engines

2006 ◽  
Author(s):  
Sandeep Kumar Goyal ◽  
Avinash Kumar Agarwal
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Flat Plate ◽  
Diesel Engines ◽  
High Speed ◽  
Jet Impingement ◽  
Heavy Duty ◽  
Heavy Duty Diesel ◽  
Oil Jet

The continuous increase in power density has led to higher thermal loading of pistons of heavy duty diesel engines. Material constraints restrict the maximum operating temperature of a piston. High piston temperature rise may lead to engine seizure because of piston warping. To avoid this, pistons are usually cooled by oil jet impingement from the underside of the piston in heavy duty diesel engines. Impingement heat transfer has been used extensively because of the high rates of cooling it provides. The associated high heat transfer rate is due to the oil jet that impacts hot impingement surface at high speed. However, if the temperature at the underside of the piston, where the oil jet strikes the piston, is above the boiling point of the oil, it may contribute to the mist generation. This mist significantly contributes to non tail-pipe emission (non-point source) in the form of unburnt hydrocarbons (UBHC’s). This paper presents and discusses the results of a numerical and experimental investigation of the heat transfer between a constant heat flux flat plate and an impinging oil jet. Piston boundary conditions are applied to the flat plate. Using the numerical modeling, heat transfer coefficient (h) at the underside of the piston is calculated. This predicted value of heat transfer coefficient significantly helps in selecting right oil grade, oil jet velocity, nozzle diameter and distance of the nozzle from the underside of the piston. It also helps to predict whether the selected grade of oil will contribute to mist generation. Using numerical simulation (finite element method) temperature profiles are evaluated by varying heat flux. Infrared camera is used to investigate and validate the temperature profile of the flat plate. High speed camera is used to capture the mist generation and oil jet breakup due to impinging jet.

Submerged Jet Impingement Boiling on a Polished Silicon Surface

2011 ◽  
Author(s):  
Preeti Mani ◽  
Ruander Cardenas ◽  
Vinod Narayanan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Silicon Surface ◽  
High Speed ◽  
Jet Impingement ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Submerged Jet ◽  
Jet Impingement Boiling

Submerged jet impingement boiling has the potential to enhance pool boiling heat transfer rates. In most practical situations, the surface could consist of multiple heat sources that dissipate heat at different rates resulting in a surface heat flux that is non-uniform. This paper discusses the effect of submerged jet impingement on the wall temperature characteristics and heat transfer for a non-uniform heat flux. A mini-jet is caused to impinge on a polished silicon surface from a nozzle having an inner diameter of 1.16 mm. A 25.4 mm diameter thin-film circular serpentine heater, deposited on the bottom of the silicon wafer, is used to heat the surface. Deionized degassed water is used as the working fluid and the jet and pool are subcooled by 20°C. Voltage drop between sensors leads drawn from the serpentine heater are used to identify boiling events. Heater surface temperatures are determined using infrared thermography. High-speed movies of the boiling front are recorded and used to interpret the surface temperature contours. Local heat transfer coefficients indicate significant enhancement upto radial locations of 2.6 jet diameters for a Reynolds number of 2580 and upto 6 jet diameters for a Reynolds number of 5161.

Aerothermodynamic correlations for high-speed flow

2017 ◽  
Vol 821 ◽  
pp. 421-439 ◽  
Author(s):  
Narendra Singh ◽  
Thomas E. Schwartzentruber
Keyword(s):  
Heat Flux ◽  
Stagnation Point ◽  
High Speed ◽  
Direct Simulation Monte Carlo ◽  
Local Heat ◽  
High Speed Flow ◽  
Speed Flow ◽  
Wide Range ◽  
Correlation Parameters ◽  
Stagnation Point Heat Flux

Heat flux and drag correlations are developed for high-speed flow over spherical geometries that are accurate for any Knudsen number ranging from continuum to free-molecular conditions. A stagnation point heat flux correlation is derived as a correction to the continuum (Fourier model) heat flux and also reproduces the correct heat flux in the free-molecular limit by use of a bridging function. In this manner, the correlation can be combined with existing continuum correlations based on computational fluid dynamics simulations, yet it can now be used accurately in the transitional and free-molecular regimes. The functional form of the stagnation point heat flux correlation is physics based, and was derived via the Burnett and super-Burnett equations in a recent article, Singh & Schwartzentruber (J. Fluid Mech., vol. 792, 2016, pp. 981–996). In addition, correlation parameters from the literature are used to construct simple expressions for the local heat flux around the sphere as well as the integrated drag coefficient. A large number of direct simulation Monte Carlo calculations are performed over a wide range of conditions. The computed heat flux and drag data are used to validate the correlations and also to fit the correlation parameters. Compared to existing continuum-based correlations, the new correlations will enable engineering analysis of flight conditions at higher altitudes and/or smaller geometry radii, useful for a variety of applications including blunt body planetary entry, sharp leading edges, low orbiting satellites, meteorites and space debris.

Numerical Simulation of a Novel Jet-Impingement Micro Heat Sink With Cross Flow Under Non Uniform Heating Condition

2011 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flat Plate ◽  
Heat Sink ◽  
Cross Flow ◽  
Jet Impingement ◽  
Jet Flow ◽  
Maximum Temperature ◽  
Cooling Performance

A novel micro heat sink applying the jet-impingement and cross flow is proposed to dissipate the heat from the electrical devices. Six hotspots of 2 mm × 2 mm are positioned on a flat plate of 25.4 mm × 25.4 mm. The area of flat plate except the hotspots is provided a constant heat flux of 20 W/cm2 as background heating source among cases. Four heat fluxes from 40 to 100 W/cm2 on the hotspots are tested to simulate the different operation conditions. The cross flow is used to remove the background heat flux and jet flow is supplied into the swirl microchannel, located at the right top of hotspot, to dissipate the large heat flux from hotspots. The channel depth is 0.5 mm and the width of swirl microchannel is 0.38 mm. The cross flow and jet flow velocity vary from 0.1 m/s to 0.5 m/s and from 0.5 m/s to 2 m/s, respectively. The effects of cross flow and jet flow on the cooling performance are investigated by numerical simulation. The local heat transfer coefficient and Nusselt number are calculated to evaluate the cooling performance of proposed micro heat sink for the targets of low maximum temperature, temperature gradient and pressure drop. The results show that the maximum temperature of the proposed design occurred at the outlet is approximately 65 °C among tested cases. The corresponding pressure drop is 5.5 kPa. The overall thermal resistance reaches as small as 0.23 K/W.

Gaskinetic Solutions for High Knudsen Number Planar Jet Impingement Flows

2013 ◽  
Vol 14 (4) ◽  
pp. 960-978 ◽  
Author(s):  
Chunpei Cai ◽  
Chun Zou
Keyword(s):  
High Speed ◽  
Rarefied Gas ◽  
Direct Simulation Monte Carlo ◽  
Jet Impingement ◽  
Gas Flows ◽  
Free Jet ◽  
Planar Jet ◽  
Rarefied Gas Flows ◽  
Analytical Results ◽  
Good Agreement

AbstractThis paper presents a gaskinetic study and analytical results on high speed rarefied gas flows from a planar exit. The beginning of this paper reviews the results for planar free jet expanding into a vacuum, followed by an investigation of jet impingement on normally set plates with either a diffuse or a specular surface. Presented results include exact solutions for flowfield and surface properties. Numerical simulations with the direct simulation Monte Carlo method were performed to validate these analytical results, and good agreement with this is obtained for flows at high Knudsen numbers. These highly rarefied jet and jet impingement results can provide references for real jet and jet impingement flows.

Surface properties for rarefied circular jet impingement on a flat plate

2011 ◽  
Vol 23 (2) ◽  
pp. 027102 ◽  
Author(s):  
Khaleel Khasawneh ◽  
Hongli Liu ◽  
Chunpei Cai
Keyword(s):  
Flat Plate ◽  
Surface Properties ◽  
Jet Impingement

Measuring hoof slip of the leading limb on jump landing over two different equine arena surfaces

2012 ◽  
Vol 8 (1) ◽  
pp. 33-39 ◽  
Author(s):  
O. Orlande ◽  
S.J. Hobbs ◽  
J.H. Martin ◽  
A.G. Owen ◽  
A.J. Northrop
Keyword(s):  
Surface Properties ◽  
High Speed ◽  
Surface Hardness ◽  
Horizontal Displacement ◽  
Jump Landing ◽  
Reference Marker ◽  
Surface Wax ◽  
Significant Difference ◽  
Wax Content ◽  
The Moment

The amount of hoof slip at the moment of impact can cause musculoskeletal injuries to the horse. Risk of injury is influenced by surface properties, however there is limited understanding of the effect on hoof slip during jump landing. The objectives of this study were to compare hoof slip on two different surfaces and investigate relationships between hoof slip and surface properties. A contact mat and hoof reference marker were designed and validated, the former to indicate the moment of impact and the latter to provide a visible reference marker on the lateral hoof wall. The leading right forelimb of six horses was recorded during jump landing on two different surfaces. Five trials, plus one where the forelimb landed on a contact mat were recorded at 500 Hz using a calibrated high speed camera positioned perpendicular to landing. Surface hardness, penetrability and traction were measured between horses. Horizontal displacement of the hoof reference marker was plotted and smoothed with a Butterworth filter at 25 Hz cut-off. Hoof slip was measured from impact to mid-stance. Data were analysed using ANOVA and Pearson correlations. A significant difference in hoof slip (10% wax = 4.9�2.1 cm and 3% wax = 7.4±3.6 cm) was found between the two surfaces (P<0.01). In addition, hoof slip was correlated with all surface measurements (hardness, penetrability and traction) on the 10% wax surface, but none on the 3% wax surface. Wax content appears to influence hoof slip during jump landing as greater hoof slip was measured on a 3% wax surface and variability on this surface was greater for the group. The results suggest that wax content had an effect on surface properties and greater variability in hardness and traction on the 3% wax surface influenced the consistency with which the horses jumped upon it.

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