Sadanari Mochizuki

Comparison between laminar and turbulent heat transfer in a stationary square duct with transverse or angled rib turbulators

Abstract Heat transfer in a rib-roughened duct was numerically simulated by using the second-order finite difference method in coordinates fitted to transverse or angled ribs. Turbulent and laminar cases of which Reynolds numbers were 350 and 50, respectively, were computed for rib angles of 60° and 90°. The present turbulent results clearly showed the locally high heat transfer spots at several locations. The comparison between the laminar and turbulent results showed clear differences in heat transfer distribution because the higher momentum fluid of the turbulent case was more disturbed by the ribs as compared to the laminar case.

Large eddy simulation with a dynamic subgrid-scale model of turbulent heat transfer in an orthogonally rotating rectangular duct with transverse rib turbulators

Abstract In order to investigate the effects of transverse ribs, the Coriolis force, and cross-sectional aspect ratios on turbulence, the large eddy simulation was performed changing the rotation number and the aspect ratio. The results reproduced the experimentally observed high heat transfer areas: in front of the rib on the rib-roughened walls and around the rib on the smooth side walls. In the rotating case, an interesting dissimilarity between the velocity and temperature fields was seen. The heat transfer enhancement caused by the rotation was larger for the higher aspect ratios because of the intensified Coriolis induced secondary flow.

Effect of cross-sectional aspect ratio on turbulent heat transfer in an orthogonally rotating rectangular smooth duct

Abstract In order to investigate the effects of the Coriolis force and the duct cross-sectional aspect ratio on turbulent heat transfer, the large eddy simulation was performed changing the aspect ratio and the rotation number in the range, 0.25–4.0 and 0–5.0, respectively, while the turbulent Reynolds number was 350. In the results, both direct and indirect influences of the Coriolis force on the turbulence were seen. The relative intensity of these influences depended on the aspect ratio. The Colburn’s j factor showed a higher value for a larger aspect ratio because of larger heat transfer enhancement on the pressure and side surfaces.

Detailed measurements of local heat transfer coefficients in turbulent flow through smooth and rib-roughened serpentine passages with a 180° sharp bend

Abstract An experimental study is performed to investigate heat transfer and fluid flow in two straight, rectangular channels with a 180° sharp bend. Ribs are attached to two opposite walls with an angle of 90° or 60° to the flow. More than 450 thermocouples are used to monitor detailed distributions of local heat transfer coefficients over the four wall surfaces of the entire flow channel. Flow visualization tests are performed which reveal the generation of secondary flows. The impacts of their interaction on heat transfer enhancement and the rib arrangement which gives the highest heat transfer performance are disclosed. Applications to the internal cooling of gas turbine blades are discussed.

Effects of Rib Arrangements on Heat Transfer and Flow Behavior in a Rectangular Rib-Roughened Passage: Application to Cooling of Gas Turbine Blade Trailing Edge

Experimentation was conducted to examine the heat transfer and pressure drop characteristics in a rib-roughened rectangular passage with aspect ratio 2:1 for four rib configurations: 90 deg, 75 deg, 60 deg and 45 deg oblique ribs. The ribs were attached to two opposing long side walls instead of short side walls. In this study the oblique ribs were intended to function as secondary flow inducers as well as turbulators to improve the heat transfer of the bottom wall (one of the short side walls)

TRANSPORT PHENOMENA IN STACKS OF INTERRUPTED PARALLEL-PLATE SURFACES

A scale-up model of interrupted fin surfaces in compact exchanger cores is employed for pressure loss and heat transfer study in a wind tunnel. Offset strip- and slotted-type interruptions are cons...

Effect of centrifugal buoyancy on turbulent heat transfer in an orthogonally rotating square duct with transverse or angled rib turbulators

Abstract The effect of the Coriolis and buoyancy forces on the turbulent heat transfer disturbed by rib turbulators was numerically investigated by using the large eddy simulation (LES). The computational condition was as follows: the turbulent Reynolds number of 350, the rotation number of 1.0, the rib angles of 90° and 60°, and the Rayleigh number from −5×10 4 to +5×10 4 . The heat transfer was enhanced and suppressed by the buoyancy-induced aiding and opposing flows, respectively. The friction factor was dominated by the form drag, and the results of 90° and 60° rib showed different behavior for the Rayleigh number change.

Effect of cross-sectional aspect ratio on turbulent heat transfer in an orthogonally rotating rectangular duct with angled rib turbulators

Abstract Heat transfer in a rotating rib-roughened rectangular duct was numerically simulated by using the large eddy simulation with a Lagrangian dynamic subgrid-scale model. The rotation number and the duct cross-sectional aspect ratio (0.25, 0.5, 1.0, 2.0, and 4.0) were varied for a friction Reynolds number of 350 and rib angle of 60°. The present results clearly showed the locally high heat transfer at several locations and how it was changed by the duct aspect ratio. The dissimilarity between the streamwise velocity and temperature was observed for all the aspect ratio cases in the rotating case.

A kinematic investigation of mandibular border movement by means of an electronic measuring system. Part I: Development of the measuring system

S ince the middle of the nineteenth century, there have been numerous studies analyzing mandibular movement. Many of these studies were successful when targets were attached in the incisal area where direct measurement was feasible.‘-’ However, the motion of the condyles was not successfully studied because it had to be measured indirectly from the outside of the face owing to the difficulty of placing targets inside the condyles.“’ Because the data obtained from these studies could not be accurately analyzed to determine the true movement of the condyles, the exact movement of the condyles is still not known. If the assumption is made that a human mandible is indeformable, mandibular movement may be treated as the movement of a “rigid body.” In order to describe the three-dimensional movement of a rigid body, it is necessary to measure the two-dimensional movement of three points fixed on the rigid body. These points should not be on a straight line. Then all six independent unknowns can be used to calculate the exact movement of a predetermined point fixed on the mandible. In this regard movement of a rigid body has six degrees of freedom. This measurement, however, requires only complicated calculations. If movement of the mandible can be measured with six degrees of freedom, if a vast amount of measured data can be recorded and stored, and if the great amount of calculations required can be accomplished, then movement of any point on the mandible, such as a condylar point, can be described as accurately as if it were measured directly inside the condyle. Studies of mandibular movement by means of elec-

Local heat transfer measurements of an orthogonally rotating square duct with angled rib turbulators

Abstract The effect of angled rib turbulators on the heat transfer of an orthogonally rotating square duct were experimentally investigated. The Reynolds and rotation numbers were varied in 10,000–20,000 and 0–0.08, respectively. The leading and trailing walls were rib-roughened with angles of 90° and 60°. The results showed that the rotation induced a peripheral variation of the heat transfer and the higher heat transfer was seen using the 60° angled rib; judging from the local heat transfer variation, the skewed secondary flow induced by the angled rib seemed to result in additional heat transfer enhancement.