Shoichiro Fukusako

Visual observation of natural convective flow in a narrow vertical cavity

Experimental visualization of natural convective flow was carried out by using several kinds of fluid contained in a narrow vertical rectangular cavity with one vertical wall heated, the opposing vertical wall cooled and the upper and lower walls insulated. The effects of the Prandtl number Pr of the working fluid and the width of the cavity W on the flow pattern are discussed qualitatively in the present paper. The occurrence of flow patterns consisting of unicellular flow, steady secondary flow, tertiary flow and transition (from laminar to turbulent) flow is categorically demonstrated by the photographs taken. Moreover, experimental measurements of the net heat transfer through the vertical fluid layer are given for aspect ratios of 6-30 and Prandtl numbers of 4-12 500.

Thermophysical properties of ice, snow, and sea ice.

The paper reviews and discusses data and information on the thermophysical properties of ice, snow, and sea ice. These properties include thermal conductivity, specific heat, density, thermal diffusivity, latent heat of fusion, thermal expansion, and absorption coefficient. The available data are shown graphically for convenience in conjunction with the recommended correlation equations.

Heat transfer in a confined rectangular cavity packed with porous media

Abstract This paper presents an experimental investigation of convective heat transfer in a confined rectangular cavity packed with porous media, on the opposing vertical walls of which different temperatures are imposed. Measurements are made for each of two kinds of solid particles using three kinds of fluids, i.e. water, transformer oil and ethyl alcohol. The present experiments cover a wide range of Rayleigh number Ra∗ between 1 and 105, Prandtl number Pr∗ between 1 and 200 and geometrical aspect-ratio H W between 5 and 26. The experimental results indicate that Nusselt number Nu∗ is correlated by the following relationship: Nu∗ = 0.627 Pr∗ 0.130 ( H W ) −0.527 Ra∗ 0.463

Forced Convection Heat Transfer on Heated Bottom Surface of a Cavity

Experiments to measure the heat transfer characteristics for various cavities situated at a duct-wall were performed. Flow visualization, measurements of pressure and temperature distributions on the heated bottom surface of cavity were carried out. It was observed that the effects of main flow stream, reattachment of separated flow, and vortex flow in the cavity on heat transfer unexpectedly large. It was found that heat transfer did not always decrease monotonously with an increase of aspect (depth-width) ratio D/W, in the flow range of laminar to turbulent. Correlations between Num and Rew were made in laminar and turbulent heat transfer ranges.

Recent advances in research on water-freezing and ice-melting problems

Abstract A comprehensive review of recent developments in research on a variety of water-freezing and ice-melting problems is presented that covers such subjects as analytical and numerical methods on freezing and melting problems, freezing of water with and without main flow, atmospheric and marine icings, and various types of melting ice. An attempt is also made to review the thermophysical properties of pure ice and sea ice.

Free convective heat transfer with density inversion in a confined rectangular vessel

An experimental and analytical investigation pertaining to the effect of density inversion on steady free convective heat transfer of water in a confined rectangular vessel in which different temperatures are imposed on the opposing vertical walls is carried out. Water, as a testing fluid, has its maximum density at 4‡C. Temperature of the cold wall is maintained at 0‡C, while that of the hot wall is varied from 1‡C to 12‡ C. Photographs and analytical descriptions of the flow patterns, temperature distributions and average Nusselt number are presented. Moreover, the effect of dimensions of a rectangular vessel on the average Nusselt number is investigated. From the present investigation, it can be demonstrated both experimentally and analytically that the density inversion of water have an influential effect on the free convection heat transfer in the prescribed water layer, moreover, the average Nusselt number is a peculiar function of temperature difference between the cold and the hot walls, unlike the previous results for common fluids without density inversion.ZusammenfassungDer Einflu\ der Dichteumkehr von Wasser auf die stationÄre freie Konvektion in einem geschlossenen rechtwinkligen BehÄlter, dessen gegenüberliegende senkrechte WÄnde auf verschiedenen Temperaturen gehalten werden, ist experimentell und analytisch untersucht. Wasser hat sein Dichtemaximum bei 4‡C. Die kalte Wand ist auf 0‡C gehalten, die Temperatur der warmen Wand liegt zwischen 1‡C und 12‡C. Die Strömungsform, die Temperaturverteilung und die mittlere Nu\elt-Zahl werden durch photographische Aufnahmen und analytische Rechnungen beschrieben. Auch der Einflu\ der BehÄlterdimensionen auf die mittlere Nu\eltZahl ist angegeben. Es zeigt sich, da\ die Dichteumkehr den WÄremübergang in der Wasserschicht grundsÄtzlich verÄndern kann und da\ die Nu\elt-Zahl in eigentümlicher Weise vom angelegten TemperaturgefÄlle abhÄngt, im Gegensatz zu Älteren Ergebnissen für übliche Flüssigkeiten ohne Dichteumkehr.

An Experimental Study of Free Corrective Heat Transfer in a Parallelogrammic Enclosure

Experimental measurements are presented for free convective heat transfer across a parallelogrammic enclosure with the various tilt angles of parallel upper and lower walls insulated. The experiments covered a range of Rayleigh numbers between 3.4 × 104 and 8.6 × 107 , and Prandtl numbers between 0.70 and 480. Those also covered the tilt angles of the parallel insulated walls with respect to the horizontal, φ, of 0, ±25, ±45, ±60, and ±70 deg under an aspect ratio of H/W = 1.44. The fluids used were air, transformer oil, and water. It was found that the heat transfer coefficients for φ = −70 deg were decreased to be about 1/18 times those for φ = 0 deg. Experimental results are given as plots of the Nusselt number versus the Rayleigh number. A correlation equation is given for the Nusselt number, Nu, as a function of φ, Pr, and Ra.

A Criterion of Onset of Free Convection in a Horizontal Melted Water Layer With Free Surface

The problem considered in this paper is the determination of the Rayleigh number marking the onset of free convection in a horizontal melted layer of ice heated from above under uniform radiant heat flux. In this analysis, linear perturbation techniques are used to derive a sixth-order differential equation subject to hydrodynamic and thermal boundary conditions. The series-solution method is utilized to obtain an eigenvalue equation for the case where the lower surface (ice surface) is kept at 0°C and the upper free surface is subjected to the general thermal conditions. An experimental determination of the onset of free convection, when the heat transfer mode changes from conduction to convection, is obtained from the fact that the temperature distribution in a melted water layer starts to deviate from its linear profile. At the same time, a peculiar variational inflection of the water-surface temperature occurs. From the present investigation, it can be demonstrated both analytically and experimentally that the critical Rayleigh number Ra c in a horizontal melted water layer with a density inversion is dependent on the free water-surface temperature T2 for T2 < 8°C, while Ra c for T2 ≧ 8°C is independent of T2 .

Melting heat transfer inside ducts and over external bodies

The recent literature dealing with melting heat transfer inside ducts and over external bodies is reviewed mainly in the context of its application to the latent heat-of-fusion thermal energy storage. The emphasis in the paper is on the fundamental, physical transport phenomena observed during melting of phase change material as well as snow layer and porous media. The important role played by buoyancy-driven fluid flow is in particular discussed and some promising areas for further research are also identified.

Numerical study on freezing heat transfer in water-saturated porous media

Numerical investigations have been carried out to examine the characteristics of unsteady freezing heat transfer in water-saturated porous media. As a physical model, a two-dimensional vertical cavity is considered. The temperature of the porous media is initially maintained at the temperature of the hot wall. The vertically opposite wall is abruptly cooled below the freezing temperature. The equation of momentum includes Forchheimers extension as the resistance to flow in the porous media. For the governing equations in the frozen and unfrozen porous layers, the transformations of variables are performed by the boundary fixing method, and the finite-difference equations are obtained by integrating the governing equations over the control volume. The successive overrelaxation method is utilized to solve the equations numerically. Modified Nusselt numbers are introduced to characterize the unsteady freezing heat transfer in water-saturated porous media. The flow patterns and the temperature distributions ...