Roughness Transfer Research Articles

A study of roughness and mass transfer enhancement for the rotating cylinder electrode

It is well established that enhanced mass transfer occurs at a rotating cylinder electrode operated in the turbulent regime when cathodically deposited metal grows in a rough powdery or dendritic manner. In the absence of quantitative data for the degree of roughness and the consequent increase in the friction factor, such enhancement has been expressed empirically as an increase in the power exponent of a simple mass transfer relationship K L = constant × U n where n is normally about 0.7 in turbulent flow for a smooth electrode. By using cylinder electrodes of known induced roughness, which can be characterized by a true surface area, topography etc., it is possible to distinguish between the effects of increased surface area and microturbulence, whence it becomes possible to recognize and devise optimal methods of increasing the surface roughness in order to maximize mass transfer. For the V-grooved cylinders investigated, the saturated or maximum enhanced mass transfer was correlated according to the power law relationship where n varied between 0.51 and 0.58. For six such cylinders the average increase in mass transfer at a high velocity, or degree of enhancement, was 80% relative to a smooth cylinder.

Proposal for wall function for friction and heat transfer in the presence of roughness and mass transfer

The heat transfer characteristics are predicted of a turbulent boundary layer over a rough porous wall through which mass is injected. A proposal is made for the wall function that accounts for the simultaneous influences of roughness and mass transfer. This proposal though has no strong theoretical foundation, appears justified by agreement with experiment. The problems considered include cases with and without unheated lengths of plate. The separate effect of roughness without mass transfer is also investigated. The predictions compare well with the measurements of Coleman et al. for uniform-grain elements under fully rough conditions.

熱伝達率の研究 : 突起物を有する外壁面の熱伝達特性に関する風洞実験

This paper concerns the relation between the distribution of wind velocity near the surface of a wall and its wall roughness and heat transfer characteristics. A test plate which formed part of a wind tunnel apparatus was used. To make clear the relation between wall roughness and heat transfer coefficient, we attached a fin-like projection to a test plate and examined the distribution of wind velocity, the turbulent intensity and the heat transfer characteristics. We also examined them when the projection is not used, and compared the former values with the latter. The experimental results show 1) that the heat transfer coefficint on the surface of a building wall is influenced by the distribution of wind velocity and the distribution of turbulent intensity, 2) that when a projection is attached to the surface of a wall, three regions, separated, reattached and redevelopment ones, are formed neat the surface of the wall behind the projection, and the heat transfer coefficient indicates different values in these regions, 3) that when a projection is attached to the surface of a wall, the maximum value is found in the reattached region and is 1.5 times as large as that of a wall without the projection.