Extended Thermodynamic Approach for Non-Equilibrium Gas Flow

2013 ◽  
Vol 13 (5) ◽  
pp. 1330-1356 ◽  
Author(s):  
G. H. Tang ◽  
G. X. Zhai ◽  
W. Q. Tao ◽  
X. J. Gu ◽  
D. R. Emerson

AbstractGases in microfluidic structures or devices are often in a non-equilibrium state. The conventional thermodynamic models for fluids and heat transfer break down and the Navier-Stokes-Fourier equations are no longer accurate or valid. In this paper, the extended thermodynamic approach is employed to study the rarefied gas flow in microstructures, including the heat transfer between a parallel channel andpressure-driven Poiseuille flows through a parallel microchannel andcircular microtube. The gas flow characteristics are studied and it is shown that the heat transfer in the non-equilibrium state no longer obeys the Fourier gradient transport law. In addition, the bimodal distribution of streamwise and spanwise velocity and temperature through a long circular microtube is captured for the first time.

Author(s):  
X. J. Gu ◽  
B. John ◽  
G. H. Tang ◽  
D. R. Emerson

A high-order moment method is employed to construct the transport model for non-equilibrium gas flow in micro-scale geometries. The motion of a gas in a two-dimensional square micro-cavity is solved using the 26 moment equations for low Reynolds and Mach number flows in the early transition regime. The computed velocity and temperature fields are compared with data obtained from the direct simulation Monte Carlo method. It is found that the 26 moment equations are able to capture the non-equilibrium phenomena in a driven micro-cavity, such as counter-gradient heat transfer, which are not embedded in the Navier-Stokes-Fourier equations.


2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.


2015 ◽  
Author(s):  
K. Farber ◽  
P. Farber ◽  
J. Gräbel ◽  
S. Krick ◽  
J. Reitz ◽  
...  

2018 ◽  
Vol 93 ◽  
pp. 326-333 ◽  
Author(s):  
Vadiraj Hemadri ◽  
G.S. Biradar ◽  
Nishant Shah ◽  
Richie Garg ◽  
U.V. Bhandarkar ◽  
...  

Author(s):  
O. Rovenskaya ◽  
G. Croce

Numerical investigation of a gas flow through microchannels with a sharp, 90 degrees bend is carried out using Navier-Stokes (N-S) equations with the classical Maxwell first-order slip boundary condition, including the tangential gradient effect due to the wall curvature, and Smoluchowski first order temperature jump definition. The details of the flow structure near the corner are analyzed, investigating the competing effects of rarefaction and compressibility on the channel performances. The flow characteristics in terms of velocity profiles, slip velocity distribution along inner and outer wall, pressure, average Mach number along central line of the channel have been presented. The results showed that impact of the bend on the channel performances is smaller at high rarefaction levels. The behaviour of pressure and velocity away from the bend is similar to that of a straight microchannel; however, the asymmetry in the flow at the bend, with high velocities and high velocity gradients on its inner side, has a strong impact on wall slip velocities. The presence of a recirculation is detected on both the inner and outer walls of the corner for larger Reynolds. However, rarefaction may delay the onset of recirculation. It is also observed that the mass flux through a bend microchannel can even be slightly larger than that through a straight microchannel of the same length and subjected to the same pressure difference.


2015 ◽  
Vol 26 (08) ◽  
pp. 1550087 ◽  
Author(s):  
Mojtaba Balaj ◽  
Hassan Akhlaghi ◽  
Ehsan Roohi

In this paper, we investigate the effects of convective heat transfer on the argon gas flow through micro/nanochannels subject to uniform wall heat flux (UWH) boundary condition using the direct simulation Monte Carlo (DSMC) method. Both the hot wall (q wall > 0) and the cold wall (q wall < 0) cases are considered. We consider the effect of wall heat flux on the centerline pressure, velocity profile and mass flow rate through the channel in the slip regime. The effects of rarefaction, property variations and compressibility are considered. We show that UWH boundary condition leads to the thermal transpiration. Our investigations showed that this thermal transpiration enhances the heat transfer rate at the walls in the case of hot walls and decreases it where the walls are being cooled. We also show that the deviation of the centerline pressure distribution from the linear distribution depends on the direction of the wall heat flux.


foresight ◽  
2015 ◽  
Vol 17 (1) ◽  
pp. 74-84
Author(s):  
Štefan Volner

Purpose – New non-equilibrium systems theory is a very important theoretical and methodological base of survey and understanding of contemporary economic systems and processes. Equilibrium is considered one of the basic conditions of existence and evolution of natural and social systems, according to scientific literature. Generally speaking, it can be presented as true. But the problem is that classical imagination perceives equilibrium as something real and stable – something more stable than basic condition of evolution of systems. Non-equilibrium state was usually understood as something negative, something destructive and something which has to be eliminated. Non-equilibrium state was understood as an anomaly, as an expression of weakening of system security and as a road to extinction. Thermodynamics comes with an idea that equilibrium is a “short” state of the system, equilibrium is very relative and all systems try to meet it, but they will never reach it. Equilibrium is usually connected with classical science and non-equilibrium state is connected with thermodynamics paradigm, with a new methodology of science. Non-equilibrium state is often seen as a basic condition – as an internal source of system evolution and its activities. Non-equilibrium state is a base of new arrangement of systems. Misunderstanding of contemporary non-equilibrium state theory and new expressions or aspects of dynamic processes can bring about negative impacts on the survey and establishment of new global economic system, e.g. new national and local economic systems. Therefore, the non-equilibrium state theory is a methodological base of new perception and survey of contemporary economic systems. Design/methodology/approach – A study of non-equilibrium thermodynamics. Findings – Irreversibility and non-equilibrium, occurring in each process and evolutionary phase of economic systems, are connected with accidents and openness. Openness of systems enables (and causes) diversification toward wider system or environment and penetration of external elements and processes to internal structure of the system. A system like this is more sensitive to external and internal changes. Considering this, it is very important to be aware of the fact that entropy has different behavior in “closed” systems – different from behavior in open systems. Open economic systems communicate with external environment, interact with external systems and they exchange the energy. They consume energy of external environment and penetrate it. Elements, nodes and joints in open systems can communicate, connect and integrate with elements, nodes and joints from external systems. The growth of entropy is “smoother” and equilibrium of the system, its sub-systems and elements proceeds despite the non-equilibrium state of elements of the own system. They have to communicate and exchange the energy with external environment. This is because of the non-equilibrium state. Originality/value – This is an original thermodynamic approach to the importance of non-equilibrium in the development of economic systems.


Author(s):  
Hadi Ghezel Sofloo ◽  
Alireza Shams ◽  
Reza Ebrahimi

This paper deals with simulation of transport phenomena in micro and nano pores. The number of cavities and the cavity radius were estimated by using Henry’s law for adsorption of Argon onto ZSM-5 and NaX zeolites. This work showed both of zeolites have pores with average size less than 1 nm. Then with using micro-nano channel assumption instead of micro-nano pores, gas flow and heat transfer were investigated. Subsonic nonideal gas flow and heat transfer for different Knudsen number are investigated numerically using the Direct Simulation Monte Carlo method modified with a consistent Boltzamnn algorithm. The collision rate is also modified based on the Enskog theory for dense gas. It is shown that nonideal gas effect becomes significant when the gas becomes so dense that the ideal gas assumption breaks down. The results also show that the nonideal gas effect is dependent not only on the gas density, but also the channel size. A higher gas density and a smaller channel size lead to a more significant nonideal gas effect. The nonideal gas effect also causes lower skin friction coefficients and different heat transfer flux distributions at the wall surface.


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