Effects of temperature-dependent thermo-physical properties on hydrodynamic swirl decay in microtubes

2018 ◽  
Vol 233 (3) ◽  
pp. 427-435 ◽  
Author(s):  
Sukumar Pati ◽  
Vishwanath Kumar
Keyword(s):  
Physical Properties ◽  
Swirling Flow ◽  
Slip Length ◽  
Temperature Fields ◽  
Temperature Dependent ◽  
Swirl Number ◽  
Constant Property ◽  
Swirl Velocity ◽  
Inlet Swirl ◽  
Thermo Physical Properties

In this paper, the influence of temperature-dependent thermo-physical properties is investigated on the decay of swirl in a laminar swirling flow of liquid through a heated microtube. The conservation equations for mass, momentum, and energy are numerically solved to obtain the velocity and temperature fields. The decay of swirl is quantified by the variation of the ratio of swirl number at a section to that at the inlet ( S/ S0) along the flow. The results reveal that constant property simulations result in faster swirl decay as compared to the variable-property simulations. Further, the implications of slip length, inlet swirl number, inlet swirl velocity profile, and Reynolds number on the swirl decay are presented. The results of the present analysis bear significant technological consequences in the design of micro-heat exchangers with intrinsic rotationalities.

scholarly journals Dynamics of Rising Bubbles in a Quiescent Slag Bath with Varying Thermo-Physical Properties

2020 ◽  
Vol 51 (6) ◽  
pp. 2843-2861
Author(s):  
D. Obiso ◽  
D. H. Schwitalla ◽  
I. Korobeinikov ◽  
B. Meyer ◽  
M. Reuter ◽  
...  
Keyword(s):  
Physical Properties ◽  
Bubble Dynamics ◽  
Fluid Dynamic ◽  
Temperature Gradients ◽  
Slag Bath ◽  
Bubble Motion ◽  
Temperature Dependent ◽  
Slag Properties ◽  
Temperature Dependent Properties ◽  
Thermo Physical Properties

AbstractThe motion of bubbles in a liquid slag bath with temperature gradients is investigated by means of 3D fluid dynamic computations. The goal of the work is to describe the dynamics of the rising bubbles, taking into account the temperature dependency of the thermo-physical properties of the slag. Attention is paid to the modeling approach used for the slag properties and how this affects the simulation of the bubble motion. In particular, the usage of constant values is compared to the usage of temperature-dependent data, taken from models available in the literature and from in-house experimental measurements. Although the present study focuses on temperature gradients, the consideration of varying thermo-physical properties is greatly relevant for the fluid dynamic modeling of reactive slag baths, since the same effect is given by heterogeneous species and solid fraction distributions. CFD is applied to evaluate the bubble dynamics in terms of the rising path, terminal bubble shape, and velocity, the gas–liquid interface area, and the appearance of break-up phenomena. It is shown that the presence of a thermal gradient strongly acts on the gas–liquid interaction when the temperature-dependent properties are considered. Furthermore, the use of literature models and experimental data produces different results, demonstrating the importance of correctly modeling the slag’s thermo-physical properties.

Effect of geometrical and temperature-dependence parameters on forced convection of a nanofluid in a micro-channel heat sink

2016 ◽  
Vol 13 (5) ◽  
pp. 399-406 ◽  
Author(s):  
Rabah Nebbati ◽  
Mahfoud Kadja
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Physical Properties ◽  
Forced Convection ◽  
Heat Sink ◽  
Volume Fraction ◽  
Micro Channel ◽  
Temperature Dependent ◽  
Content Type ◽  
Thermo Physical Properties

Purpose The purpose of this study is the numerical prediction of the thermal and hydraulic characteristics (Nusselt number and shear stress) of a forced convection laminar flow through a rectangular micro-channel heat sink, using constant and temperature-dependent thermo-physical properties. The effects of the solids volume fraction and the size of the micro-channel on heat transfer enhancement have also been investigated. Design/methodology/approach The authors use the flow of a water-Al2O3 nanofluid and a single-phase approach. The equations are solved using the commercial code Fluent Version 6.3. This code uses the finite volume approach to solve the equations subject to the boundary conditions, which govern three-dimensional conjugate convection-conduction heat transfer model. The physical domain was meshed using the code GAMBIT. The mesh used is non-uniform and was obtained by sweeping in the Z direction an X-Y surface meshed with QUAD/pave type cells. Findings The results clearly show that the inclusion of nanoparticles produces a considerable increase in the heat transfer. Also, the temperature-dependent models present higher values of local and average Nusselt number than in the case of constant thermo-physical properties, and an increase in the channel dimensions leads to an important increase in heat transfer. Consequently, we ensure a better cooling of the base of the micro-channel heat sink. Research limitations/implications Because of the settling of nanoparticles, the research results may not be generalized to high values of solids volume fraction. Therefore, researchers are encouraged to find other techniques of cooling when the heat loads exceed values that cannot be dissipated using nanonofluids. Practical implications The paper includes implications for the miniaturization of electronic devices such as in microprocessors or those used in robotics and automotive industries, where continually increasing power densities are requiring more innovative techniques of heat dissipation from a small area and small coolant requirements. Originality/value This paper shows the implementation of variable property nanofluid models in CFD commercial codes.

Strut Losses in a Diverging Annular Diffuser With Swirling Flow

2006 ◽  
Author(s):  
G. K. Feldcamp ◽  
A. M. Birk
Keyword(s):  
Total Pressure ◽  
Swirling Flow ◽  
Pressure Recovery ◽  
Swirl Number ◽  
Pressure Losses ◽  
Swirl Angle ◽  
Wide Range ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
The Ideal

An experimental investigation into the overall influence of struts spanning a double divergent annular diffuser followed by a straight cored annular diffuser has been undertaken in order to determine the performance of various strut configurations over a wide range of inlet swirl conditions. Two strut profiles have been investigated in four and eight strut configurations. Results have shown that the presence of struts under no swirl conditions have a relatively small effect on the overall total pressure loss. Increasing the inlet swirl angle to 20° has shown that the struts are able to assist in recovery of the swirling flow such that the pressure recovery nearly approaches that without struts, despite increased total pressure losses. Performance at 40° swirl is highly dependent on strut profile; the higher thickness-to-chord ratio strut configurations show minimal decrease in pressure recovery compared to 20° swirl, while the lower thickness-to-chord ratio configurations experiences a significant decrease as the result of significant flow separation from the struts. The exit swirl number has been shown to correlate strongly with the strut profile shape, while the number of struts had only a secondary influence. The exit velocity profiles show significant distortions at 40° swirl, and as a result the ideal pressure recovery calculated from the inlet and exit profiles change with strut configuration at 40° swirl.

Influence of High Temperature Heat Sources on the Moisture and Temperature Distribution in a Real/Virtual Foundry Sand Mould

2016 ◽  
Vol 7 ◽  
pp. 69-83
Author(s):  
Paweł Popielarski ◽  
Zenon Ignaszak
Keyword(s):  
Cast Iron ◽  
Physical Properties ◽  
Rapid Heating ◽  
Temperature Fields ◽  
Coupled Modeling ◽  
Molding Sand ◽  
Mould Material ◽  
Sand Mould ◽  
Thermal Phenomena ◽  
Thermo Physical Properties

The problem described in the paper concerns the thermo-physical properties of the green mould material to which the cast iron is most often poured. The study includes the experiment of pouring the cast iron plate into green bentonite-sand mould. The temperature fields of casting and in different zones of the mould were recorded. The goal of the study was to determine the substitute thermo-physical properties of mould sand containing the over-moisture zone by means of simulation tests (inverse problem). An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, by application of the substitute thermal coefficients without using the coupled modeling. In the simulation tests in order to achieve the effect of rapid heating of the mould (below temperatures 100 °C) by poured cast iron (T>1300 °C), the function of the latent heat source and the modified values of substitute thermal conductivity and substitute specific heat of the molding sand were used. In order to facilitate the solution, the mould was divided into zones, in which different starting humidity of molding sand was assumed.

Improved Lumped Model for Transient Heat Conduction in a Heat Generating Cylinder With Temperature-Dependent Thermophysical Properties

Volume 4 ◽  
2004 ◽  
Author(s):  
Auro C. Pontedeiro ◽  
Renato M. Cotta ◽  
Jian Su
Keyword(s):  
Heat Conduction ◽  
Physical Properties ◽  
Transient Heat Conduction ◽  
Reactor Accident ◽  
Temperature Dependent ◽  
Lumped Model ◽  
Average Temperature ◽  
Lumped Models ◽  
Testing Case ◽  
Thermo Physical Properties

This paper presents improved lumped-differential formulations for one dimensional transient heat conduction in a heat generating cylinder with temperature-dependent thermo-physical properties. Two points Hermite approximations for integrals (H1,1/H1,1) are used to approximate the average temperature and the heat flux in the radial direction. As a testing case, transient heat conduction in a nuclear fuel rod was computed with the thermo-physical properties represented by correlations from MATPRO — a Library of Materials Properties for Light-Water-Reactor Accident Analysis. The problem was formulated and solved using the symbolic/numerical computation software system MATHEMATICA. The solution of the proposed improved lumped models is validated by a numerical solution of the original distributed parameter formulation.

scholarly journals A new method for the characterization of temperature dependent thermo-physical properties

2018 ◽  
Vol 124 ◽  
pp. 98-109 ◽  
Author(s):  
T.R. Pavlov ◽  
D. Staicu ◽  
L. Vlahovic ◽  
R.J.M. Konings ◽  
P. Van Uffelen ◽  
...  
Keyword(s):  
Physical Properties ◽  
New Method ◽  
Temperature Dependent ◽  
Thermo Physical Properties

Effective Modeling of Phenomena in Over-Moisture Zone Existing in Porous Sand Mould Using the Simplified Simulation Systems Applied in Foundry

2015 ◽  
Vol 365 ◽  
pp. 200-206
Author(s):  
Zenon Ignaszak ◽  
Paweł Popielarski
Keyword(s):  
Physical Properties ◽  
Temperature Fields ◽  
Mould Material ◽  
Technological Tool ◽  
Sand Mould ◽  
Thermal Phenomena ◽  
Simulation Systems ◽  
Thermo Physical Properties ◽  
Auxiliary Role

The problem concerns the thermo-physical properties of the mould material to which the liquid metal is poured (foundry industry). In the foundry processes the sand mould fulfils an auxiliary role only as technological tool, but its physical and technological properties determine the quality of the casting. The study includes the iron plate casting experiments poured in multi-component porous sand mould. The temperature fields of casting and in different zones of the mould were recorded. The determining of the thermo-physical properties of mould sand in over-moisture zone using simulation tests in Procast system was the goal of our study. An originality of the related research is an attempt to take into account the effects of the global thermal phenomena occurring in the quartz sand bonded by bentonite-water binder, using the apparent thermal coefficients. The majority of foundry simulation systems are not capable to modeling the phase transformation of water into vapor, vapor transport and its condensation in porous media (mould). In these cases the application of apparent coefficients is an effective way.

Sign in / Sign up

Export Citation Format

Share Document