Modeling the gas flow in a cyclone separator at different temperature and pressure

Abstract

The gas flow field in a cyclone separator, operated within a temperature range of 293 K – 1373 K and a pressure range of 0.1 – 6.5 MPa, has been simulated using a modified Reynolds-stress model (RSM) on commercial software platform FLUENT 6.1. The computational results show that the temperature and pressure significantly influence the gas velocity vectors, especially on their tangential component, in the cyclone. The tangential velocity decreases with an increase in temperature and increases with an increase in pressure. This tendency of the decrease or increase, however, reduces gradually when the temperature is above 1000 K or the pressure goes beyond 1.0 MPa. The temperature and pressure have a relatively weak influence on the axial velocity profiles. The outer downward flow rate increases with a temperature increase, whereas it decreases with a pressure increase. The centripetal radial velocity is strong in the region of 0 – 0.25D below the vortex finder entrance, which is named as a short-cut flow zone in this study. Based on the simulation results, a set of correlations was developed to calculate the combined effects of temperature and pressure on the tangential velocity, the downward flow rate in the cyclone and the centripetal radial velocity in the short-cut flow region underneath the vortex finder.

Key words： cyclone separator; high temperature; high pressure; flow field; numerical simulation

Acknowledgments

The authors gratefully acknowledge the financial assistance from the National Key Project of Basic Research of the Ministry for Science and Technology of China (No. 2005CB22120103).

Notation
a	inlet height
b	inlet width
C	vortex coefficient
Ci	inner-vortex coefficient
C0	outer-vortex coefficient
D	diameter of the cyclone, mm
KA	cylinder-to-inlet area ratio, K_{\mathrm{A}}={\displaystyle \frac{\mathrm{\pi }}{\mathrm{4}}}{D}^{\mathrm{2}}/ab
m	empirical exponential
n	vortex exponential
ni	inner-vortex exponential
n0	outer-vortex exponential
P	pressure, Pa
P0	normal pressure, Pa
Qi	inlet flow rate, m3/s
Qd	downward flow rate, m3/s
qd	dimensionless flow rate,q_{\mathrm{d}}=Q_{\mathrm{d}}/Q_i
R	radius of the cyclone, mm
\tilde{r}	dimensionless radius, \tilde{r}=r/R
{\tilde{r}}_{\mathrm{t}}	dimensionless radius boundary between the inner and outer vortex, {\tilde{r}}_t=r/R
{\tilde{r}}_{Z\mathrm{0}}	dimensionless boundary between the upward and downward flow, {\tilde{r}}_{Z\mathrm{0}}=r_{Z\mathrm{0}}/R
T	temperature, K
T0	room temperature, K
Vi	inlet gas velocity, m/s
Vt	tangential velocity, m/s
{\tilde{V}}_t	dimensionless tangential velocity, {\tilde{V}}_t=V_t/V_i
Vtm	maximum radial velocity, m/s
{\tilde{V}}_{tm}	dimensionless maximum tangential velocity, {\tilde{V}}_{tm}=V_{tm}/V_i
Vr	radial velocity, m/s
Vrm	maximum radial velocity, m/s
{\tilde{V}}_{rm}	dimensionless maximum radial velocity, {\tilde{V}}_{rm}=V_{rm}/V_i
Vz	axial velocity, m/s
{\tilde{V}}_{\mathrm{z}}	dimensionless axial velocity, m/s
X,Y,Z	coordinates, mm
\tilde{Z}	dimensionless axial position, \tilde{Z}=Z/D
Greek symbols
m0	gas viscosity at normal condition, Pa·s
mT	gas viscosity at given temperature T, Pa·s
r0	gas density at normal condition, kg/m3
rTP	gas density at given temperature T and pressure P, kg/m3

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