Numerical Study On Local Entropy Generation In Compressible Flow Through A Suddenly Expanding Pipe

This study presents the investigation of the local entropy generation in compressible flow through a suddenly expanding pipe. Air is used as fluid. The air enters into the pipe with a turbulent profile using 1/7 th power law. The simulations are extended to include different expansion ratios reduced gradually from 5 to 1. To determine the effects of the mass flux, φ" the ambient heat transfer coefficient, hamb, and the inlet temperature, Tin, on the entropy generation rate, the compressible flow is examined for various cases of these parameters. The flow and temperature fields are computed numerically with the help of the Fluent computational fluid dynamics (CFD) code. In addition to this CFD code, a computer program has been developed to calculate numerically the entropy generation and other thermodynamic parameters by using the results of the calculations performed for the flow and temperature fields. The values of thermodynamic parameters in the sudden expansion. (SE) case are normalized by dividing by their base quantities obtained from the calculations in the uniform cross-section (UC) case. The contraction of the radius of the throat (from 0.05 to 0.01 m) increases significantly the maximum value of the volumetric entropy generation rate, (about 60%) and raises exponentially 11 times the total entropy generation rate with respect to the its base value. The normalized merit number decreases 73% and 40% with the contraction of the cross-section and with the increase of the ambient heat transfer coefficient (from 20 to 100 W/m2-K), respectively, whereas it rises 226% and 43% with the decrease of the maximum mass flux (from 5 to 1 kg/m2-s) and with the increase of the inlet temperature (from 400 to 1000 K), respectively. Consequently, the useful energy transfer rate to irreversibility rate improves as the mass flux decreases and as the inlet temperature increases.

[1]  Mohammad T. Khasawneh,et al.  Entropy generation due to laminar forced convection in the entrance region of a concentric annulus , 2004 .

[2]  Ammar Ben Brahim,et al.  Entropy generation in Poiseuille–Benard channel flow , 2003 .

[3]  Ramazan Kahraman,et al.  Entropy generation in a rectangular packed duct with wall heat flu x , 1998 .

[4]  Bekir Sami Yilbas,et al.  A laminar swirling jet impingement on to an adiabatic wall ‐ Effect of inlet velocity profiles , 2001 .

[5]  Bekir Sami Yilbas,et al.  Entropy Analysis for Non-Newtonian Fluid Flow in Annular Pipe: Constant Viscosity Case , 2004, Entropy.

[6]  Bekir Sami Yilbas,et al.  Thermal Analysis in Pipe Flow: Influence of Variable Viscosity on Entropy Generation , 2004, Entropy.

[7]  A. Sahin,et al.  A second law comparison for optimum shape of duct subjected to constant wall temperature and laminar flow , 1998 .

[8]  S. Orszag,et al.  Renormalization group analysis of turbulence. I. Basic theory , 1986, Physical review letters.

[9]  Gautam Biswas,et al.  Second-Law Analysis of Heat Transfer in Swirling Flow Through a Cylindrical Duct , 1987 .

[10]  A. Sahin,et al.  Entropy generation in turbulent liquid flow through a smooth duct subjected to constant wall temperature , 2000 .

[11]  Bekir Sami Yilbas,et al.  Entropy analysis of conjugate heating in a pipe flow , 2002 .

[12]  B. S. Yilbas,et al.  Confined swirling jet impingement onto an adiabatic wall , 2003 .

[13]  S. G. Penoncello,et al.  Thermodynamic Properties of Air and Mixtures of Nitrogen, Argon, and Oxygen From 60 to 2000 K at Pressures to 2000 MPa , 2000 .

[14]  Bekir Sami Yilbas,et al.  Flow through a protruding bluff body–heat and irreversibility analysis , 2001 .

[15]  Bekir Sami Yilbas,et al.  Local entropy generation in an impinging jet: minimum entropy concept evaluating various turbulence models , 2001 .

[16]  S. Orszag,et al.  Renormalization group analysis of turbulence. I. Basic theory , 1986 .

[17]  Roydon Andrew Fraser,et al.  Thermodynamic analysis of flow and heat transfer inside channel with two parallel plates , 2002 .

[18]  Nafiz Kahraman,et al.  Study on transient local entropy generation in pulsating fully developed laminar flow through an externally heated pipe , 2006 .

[19]  Enzo O. Macagno,et al.  Computational and experimental study of a captive annular eddy , 1967, Journal of Fluid Mechanics.

[20]  Robert J. Poole,et al.  Turbulent flow of viscoelastic liquids through an axisymmetric sudden expansion , 2004 .

[21]  D. F. Fletcher,et al.  Heat and mass transfer computations for laminar flow in an axisymmetric sudden expansion , 1985 .

[22]  A. Sahin,et al.  The effect of variable viscosity on the entropy generation and pumping power in a laminar fluid flow through a duct subjected to constant heat flux , 1999 .

[23]  Ahmet Z. Sahin,et al.  Irreversibilities in various duct geometries with constant wall heat flux and laminar flow , 1998 .

[24]  Ahmet Z. Sahin,et al.  Second Law Analysis of Laminar Viscous Flow Through a Duct Subjected to Constant Wall Temperature , 1998 .

[25]  Ahmet Z. Sahin,et al.  Entropy generation and pumping power in a turbulent fluid flow through a smooth pipe subjected to constant heat flux , 2002 .

[26]  K Abu-Hijleh,et al.  Numerical prediction of entropy generation due to natural convection from a horizontal cylinder , 1999 .

[27]  Bekir Sami Yilbas,et al.  Second law analysis of a swirling flow in a circular duct with restriction , 1999 .

[28]  Zhen-Xiang Gong,et al.  Entropy Generation Minimization , 1996 .

[29]  Bekir Sami Yilbas,et al.  Entropy analysis of a flow past a heat-generated bluff body , 1999 .

[30]  H. Yapici,et al.  Numerical study on transient local entropy generation in pulsating turbulent flow through an externally heated pipe , 2005 .

[31]  Sassi Ben Nasrallah,et al.  Numerical study of a piston-driven laminar flow and heat transfer in a pipe with a sudden expansion , 2003 .

[32]  Steven Beyerlein,et al.  A thermodynamic property formulation for air , 1992 .

[33]  Wolfgang Nitsche,et al.  Experimental investigation of the flow through axisymmetric expansions , 1989 .

[34]  A. Bejan.  Entropy generation minimization: The new thermodynamics of finite-size devices and finite-time processes , 1996 .

[35]  Bekir Sami Yilbas,et al.  Investigation into a confined laminar swirling jet and entropy production , 2002 .

[36]  Fernando T. Pinho,et al.  A general correlation for the local loss coefficient in newtonian axisymmetric sudden expansions , 1998 .

[37]  Roydon Andrew Fraser,et al.  The second law analysis in fundamental convective heat transfer problems , 2003 .

[38]  Leslie M. Smith,et al.  Renormalization group analysis of turbulence , 2003 .

[39]  Akira Nagashima,et al.  Viscosity and thermal conductivity of dry air in the gaseous phase , 1985 .

[40]  Panagiotis Neofytou,et al.  Non-Newtonian flow instability in a channel with a sudden expansion , 2003 .

[41]  Hüseyin Yapıcı,et al.  Numerical calculation of local entropy generation in a methane–air burner , 2005 .