Entropy Generation of Hydrogen Flow in a Curved Annular Duct

Abstract

The main objective of this study is to numerically investigate the entropy generation of both hydrodynamically and thermally fully developed laminar flow of hydrogen gas under various operating pressures and temperatures in the concentric curved annular ducts with rectangular cross section. In this regard, the solutions of discretized continuity, momentum and energy equations have been obtained using elliptic Fortran Program based on the SIMPLE algorithm. The solutions have been achieved for (1) Dean numbers ranging from 2.3 to 202.9, (2) Annulus dimension ratios of 5.5, (3) Operating pressures of 0.101325, 1, 10, 40, 70 and 100 MPa, (4) Core wall temperature of 50 and 80 °C, (5) Duct wall temperature of 25 °C. In this regard, overall entropy generation in the whole flow field has been analyzed in detail. Moreover, the effects of Dean number, operating pressure and core wall temperature on entropy generation arising from the flow and heat transfer have been investigated. Accordingly, it is concluded that the effect of volumetric entropy generation that is a result of fluid flow can be neglected as compared with volumetric entropy generation due to heat transfer. When Dean number, operating pressure and core wall temperature increase the total volumetric entropy generation goes up. Thus, it is expected that this study will contribute to develop the energy efficient-hydrogen gas heaters for practical applications including hydrogen exchangers, PEMFC applications, hydrogen gas turbines, chemical mixing processes and hydrogen gas dryers in hydrogen industry.

Nomenclature

a:

Width or height of the curved channel, m

A:

Duct cross section area, m²

b:

Width or height of core, m

Be:

Bejan number

dP/dz:

Axial pressure gradient, Pa m⁻¹

dT/dz:

Axial temperature gradient, K m⁻¹

De:

Dean number

D_h :

Hydraulic diameter, m

k:

Thermal conductivity, W m⁻¹ K⁻¹

P:

Pressure, Pa

Re:

Reynolds number

R:

Radius of curvature of a curved channel, m

S ^′′′ _P :

Volumetric entropy generation rate due to friction, W m⁻³ K⁻¹

S ^′′′ _T :

Volumetric entropy generation rate due to heat transfer, W m⁻³ K⁻¹

S ^′′′ _gen :

Total volumetric entropy generation rate, W m⁻³ K⁻¹

T:

Temperature, K

u, v, w:

Velocity components in x-, y- and z-directions, m s⁻¹

x, y, z:

Cartesian coordinates, m

α:

Thermal diffusivity, m² s⁻¹

μ:

Dynamic viscosity, kg m⁻¹ s⁻¹

ν:

Kinematic viscosity, m² s⁻¹

ρ:

Density, kg m⁻³

ϕ :

Irreversibility distribution ratio

ave:

Average

c:

Cold

h:

Hot

i:

Inner

o:

Outer