scholarly journals Velocity and temperature profiles, wall shear stress and heat transfer coefficient of turbulent impinging jets

2017 ◽  
Vol 107 ◽  
pp. 846-861 ◽  
Author(s):  
J.B.R. Loureiro ◽  
A.P. Silva Freire
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Impinging Jets ◽  
Temperature Profiles ◽  
Wall Shear

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.

Effect of Particle Migration on Flow and Convective Heat Transfer of Nanofluids Flowing Through a Circular Pipe

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
M. M. Heyhat ◽  
F. Kowsary
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Particle Migration ◽  
Circular Pipe ◽  
Wall Shear

This paper aims to study the effect of particle migration on flow and heat transfer of nanofluids flowing through a circular pipe. To do this, a two-component model proposed by Buongiorno (2006, “Convective Transport in Nanofluids,” ASME J. Heat Transfer, 128, pp. 240–250) was used and a numerical study on laminar flow of alumina-water nanofluid through a constant wall temperature tube was performed. The effects of nonuniform distribution of particles on heat-transfer coefficient and wall shear stress are shown. Obtained results illustrate that by considering the particle migration, the heat-transfer coefficient increases while the wall shear stress decreases, compared with uniform volume fraction. Thus, it can be concluded that the enhancement of the convective heat transfer could not be solely attributed to the enhancement of the effective thermal conductivity, and beside other reasons, which may be listed as this higher enhancement, particle migration is proposed to be an important reason.

Experimental Results of Local Shear Stresses and Friction Torque in an Open Rotor-Stator Disc System

2021 ◽  
Author(s):  
Alexander Kuntze ◽  
Stefan Odenbach ◽  
Wieland Uffrecht
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Friction Torque ◽  
Tangential Displacement ◽  
Torsion Spring ◽  
Moment Coefficient ◽  
Open Rotor

Abstract This contribution presents experimental investigations of friction torque in an open rotor-stator disc system by using two different measuring procedures. The first procedure based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is firstly calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow. The second measuring procedure based on the tangential displacement of the stator disc due the friction torque. The disc is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disc. Both measuring procedures are compared and agree well with each other. The used test rig has the possibility of reaching rotational Reynolds numbers representative for instance of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disc rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disc and can be converted into moment coefficient. Moment coefficient on stator as well as measured pressure distributions are presented.

Experimental Results of Local Shear Stresses and Friction Torque in an Open Rotor-Stator Disc System

2020 ◽  
Author(s):  
Alexander Kuntze ◽  
Stefan Odenbach ◽  
Wieland Uffrecht
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Friction Torque ◽  
Tangential Displacement ◽  
Torsion Spring ◽  
Moment Coefficient ◽  
Open Rotor

Abstract This contribution presents experimental investigations of friction torque in an open rotor-stator disc system by using two different measuring procedures. The first procedure based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is firstly calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow. The second measuring procedure based on the tangential displacement of the stator disc due the friction torque. The disc is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disc. Both measuring procedures are compared and agree well with each other. The used test rig has the possibility of reaching rotational Reynolds numbers representative for instance of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disc rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disc and can be converted into moment coefficient. Moment coefficient on stator as well as measured pressure distributions are presented for different gap ratios and rotational Reynolds number.

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.

scholarly journals Local Heat Transfer Coefficient and Adiabatic Wall Temperature Measurement Beneath Arrays of Staggered and Inline Impinging Jets

1994 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Zuolan Wang ◽  
Peter T. Ireland ◽  
Terry V. Jones ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Impinging Jets ◽  
Hole Diameter ◽  
Channel Height ◽  
Published Data ◽  
Target Plate ◽  
Adiabatic Wall

Recent work, Van Treuren et al. (1993), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000–40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is confined on three sides and spent flow is allowed to exit in one direction. Local values are averaged and compared with previously published data in related geometries. The current data for a staggered array is compared to those from an inline array with the same hole diameter and pitch for an average jet Reynolds number of 10,000 and channel height to diameter ratio of one. A comparison is made between intensity and hue techniques for measuring stagnation point and local distributions of heat transfer. The influence of the temperature of the impingement plate through which the coolant gas flows on the target plate heat transfer has been quantified.

Sign in / Sign up

Export Citation Format

Share Document