The drying process of a macrolayer on a 15 mm diameter boiling surface was observed with high speed video in the region of nucleate and of transition boiling close to the critical heat flux (CHF). It was found that the macrolayer rests beneath a large vapor mass. It partially dries in nucleate boiling and completely dries in transition boiling at the detachment of the vapor mass. The macrolayer thickness at CHF and in transition boiling was determined on the basis of the energy balance relation proposed by Katto and Yokoya. The macrolayer thickness at low heat flux was obtained by decreasing CHF with downward-facing heating surfaces and agreed well with the correlation proposed previously by the present authors. The macrolayer thickness in transition boiling with a vertical surface also agrees fairly well with the correlation, when the heat flux at macrolayer formation, given on the nucleate boiling curve, is extrapolated to surface superheat of transition boiling and when the surface temperature at macrolayer formation is equal to a time-averaged value. © 1998 Scripta Technical, Heat Trans Jpn Res, 27(2): 155–168, 1998
To visualize heat transfer distributions in systems with complex internal geometries, an experimental technique using a combination of the transient method and the hysteresis effect of thermopaint was developed. A mercury compound based thermopaint was used as a temperature indicator. Features of the paint are its reusability and its hysteresis nature. Isothermal lines visualized by the thermopaint are preserved after the experiment by utilizing the hysteresis nature. Also heat transfer on those parts that are hidden behind other parts can be visualized. Effects of initial and air temperature on the measurement uncertainty were evaluated. With this method, local heat transfer coefficients were obtained on the model scroll of a single can type combustor. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(3): 229–242, 1998
Experiments were carried out to determine the effect of flow separation on freezing heat transfer characteristics along a horizontal cooled flat plate immersed within a rectangular duct. The flow separation was induced by a vertically situated thin plate placed against the flow at the leading edge of a uniformly cooled plate. The degree of flow separation was altered by employing vertical plates of various heights. The Reynolds number and the cooling temperature ratio ranged from 5.6 x 102 to 8.4 x 104 and from 3.0 to 10.0, respectively. The measurements showed that the flow separation exerts a marked influence on the local ice formation characteristics. Two kinds of ice formation of convex and concave profiles were observed to occur as a function of the Reynolds number, as well as of the cooling temperature ratio. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 43–56, 1998
In order to clarify the daily effects of increasing carbon dioxide level on the regional thermal environment, a two-dimensional numerical analysis was carried out on unsteady heat and mass-transfer. The results indicate a large surface temperature change in the nighttime and in the summer. The nighttime change is proportional to the change in infrared radiation flux from the atmosphere. An interaction between the effects of water vapor and those of carbon dioxide is found only in the daytime. When carbon dioxide is released from an urban surface, the vertical distributions of the air temperature and the pollutant concentration are affected in urban areas. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(4): 299–311, 1998
In the present report, first, heat transfer coefficients of oscillatory flow at inner surfaces of the heating and cooling regions of oscillation controlled heat transport tubes (OCHTs) are investigated numerically. The numerical simulation is conducted under the following three conditions for the tube walls at the heating and cooling regions : isothermal, extremely thin and actual wall systems. Based on the numerical results and Hausen's correlating equation for laminar flow heat transfer in tubes, a correlating equation of the heat transfer coefficient is developed which can be generally applied to these three conditions. Next, using this correlating equation and the author's simplified model of overall thermal resistance in OCHTs, heat transport rates are predicted, and it is found that the predicted results are in good agreement with the numerical results. Finally, numerical simulation is conducted also to compare the heat transport rates of OCHTs with those of the conventional forced circulation type under the same pumping power. The results indicate that there exist oscillatory flow regions in which the heat transport rate of the phase shifted OCHTs is larger than that of the conventional circulation type.
