Numerical Studies on Laminarization of Heated Turbulent Gas Flow in Annular Duct.

Int Jnl of Num Meth for HFF

2000

A theoretical study is performed to investigate transport phenomena in channel flows under uniform heating from either both side walls or a single side. The anisotropic t " P À 4 t heattransfer model is employed to determine thermal eddy diffusivity. The governing boundary-layer equations are discretized by means of a control volume finite-difference technique and numerically solved using a marching procedure. It is found that under strong heating from both walls, laminarization occurs as in the circular tube flow case; during the laminarization process, both the velocity and temperature gradients in the vicinity of the heated walls decrease along the flow, resulting in a substantial attenuation in both the turbulent kinetic energy and the temperature variance over the entire channel cross section; both decrease causes a deterioration in heat transfer performance; and in contrast, laminarization is suppressed in the presence of one-sideheating, because turbulent kinetic energy is produced in the vicinity of the other insulated wall.

“…A similar numerical study has been reported by Fujii et al (1991), who employ three difference turbulence models, i.e. k-4Y k À 4 À uv, and k À kL À uv.…”

supporting

confidence: 62%

Thermal‐fluid transport phenomena in strongly heated channel flows

Int Jnl of Num Meth for HFF

2000

“…(3), λ t is directly related to k, ε, t 2 , and ε t as depicted in Eq. (8). Hence, substantial reductions in the turbulent kinetic energy and temperature variance result in attenuation in the Stanton number, as shown in Fig.…”

Section: Resultsmentioning

confidence: 86%

“…Both the criteria for its occurrence and its heat-transfer characteristics have been reported by several investigators. 1−6 To investigate an effect of passage geometry on an occurrence of the laminarizing gas flow, Torii et al 7 and Fujii et al 8 deal with the thermal-fluid transport phenomena in concentric annuli under high heat flux heating. They disclosed that 1) when the gas flow is strongly heated with the same heat-flux level from inner and outer tube walls, the local heat-transfer coefficients on both walls approach the laminar values along the flow, that is, the laminarization takes place; 2) the existing criteria of laminarization for circular tube flows can be applied to annular flows as well if the occurrence of laminarization is estimated using a dimensionless heat-flux parameter q + w ; and 3) annular flows heated strongly from only one side are less vulnerable to laminarization even if the usual criteria are satisfied.…”

Section: Nomenclaturementioning

confidence: 99%

Effect of Heat Flux Ratio on Two-Dimensional Horizontal Channel Flow

Journal of Thermophysics and Heat Transfer

2004

Numerical analysis is performed to investigate thermal fluid-flow transport phenomena in channel under asymmetrical heat flux from both side walls. Emphasis is placed on an effect of heat-flux ratio from both sides on the velocity and thermal fields. The low-Reynolds-number k-ε turbulence model and the two-equation heat-transfer model are employed to determine turbulent viscosity and thermal eddy diffusivity, respectively. It is found that 1) under strong heating from both walls, laminarization, that is, a substantial deterioration in heat-transfer performance, occurs as in the circular tube flow case; 2) during the laminarization process, both the velocity and temperature gradients in the vicinity of the heated walls decrease along the flow, resulting in a substantial attenuation in both the turbulent kinetic energy and the temperature variance over the entire channel cross section; and 3) in contrast, laminarization is suppressed in the presence of one-side heating because turbulent kinetic energy is produced in the vicinity of the other insulated wall. Therefore, an occurrence of laminarization in the channel is affected by the ratio of heat flux from both side walls.

“…3, λ t is directly related to k, ε, t 2 and ε t as depicted in Eq. (8). Hence, substantial reductions in the turbulent kinetic energy and temperature variance result in attenuation in the Stanton number, as shown in Fig.…”

Section: Resultsmentioning

confidence: 86%

“…Both the criteria for its occurrence and its heat transfer characteristics have been reported by several investigators [1][2][3][4][5][6]. In order to investigate an effect of passage geometry on an occurrence of the laminarizing gas flow, Torii et al [7] and Fujii et al [8] deal with the thermal-fluid transport phenomena in concentric annuli under high heat flux heating. They disclosed that (i) when the gas flow is strongly heated with the same heat flux level from inner and outer tube walls, the local heat transfer coefficients on both walls approach the laminar values along the flow; that is, the laminarization takes place; (ii) the existing criteria of laminarization for circular tube flows can be applied to annular flows as well if the occurrence of laminarization is estimated using a dimensionless heat flux parameter q + w ; but (iii) annular flows heated strongly from only one side are less vulnerable to laminarization even if the usual criteria are satisfied.…”

Section: Introductionmentioning

confidence: 99%

Effect of Heat Flux Ratio from both Side-walls on Thermal-fluid Flow in Channel

8th AIAA/ASME Joint Thermophysics and Heat Transfer Conference

2002

Numerical analysis is performed to investigate transport phenomena in channel flows under uniform heating from both side-walls. Emphasis is placed on an effect of heat flux ratio from both sides on the velocity and thermal fields. The twoequation heat-transfer model is employed to determine thermal eddy diffusivity. It is found that (i) under strong heating from both walls, laminarization, i.e., a substantial deterioration in heat transfer performance occurs as in the circular tube flow case, (ii) during the laminarization process, both the velocity and temperature gradients in the vicinity of the heated walls decrease along the flow, resulting in a substantial attenuation in both the turbulent kinetic energy and the temperature variance over the entire channel cross section and (iii) in contrast, laminarization is suppressed in the presence of oneside-heating, because turbulent kinetic energy is produced in the vicinity of the other insulated wall. Therefore, an occurrence of laminarization in the channel is affected by the ratio of heat flux from both side-walls.