Ikuo Tokura

Study on Properties and Growth Rate of Frost Layers on Cold Surfaces

Etude experimentale des proprietes et de la vitesse de croissance de couches de givre sur une plaque verticale refroidie dans un ecoulement de convection naturelle. Deduction, par analyse dimensionnelle, de parametres sans dimension permettant la prevision des densites et des conductivites thermiques du givre et de ses vitesses de croissance

Relationship Between Some Physico-Mechanical Properties and Numerical Indexes of Graphite Shape in Compacted-Vermicular Graphite Cast Irons

The main purpose of this paper is to present some data on the mechanical and physical properties of compacted-vermicular graphite cast iron and to give a reasonable interpretation to the characteristics by using numerical indexes indicating the shape of graphite flakes in the structure. After describing the preparation of the material and a new method for measuring thermal diffusivity of the iron, the influence of kind and amount of alloy added for treatment and of cooling rate upon the graphite shape is discussed by using the indexes of the structure. The thermal diffusivities and mechanical characteristics such as tensile strength and hardness are shown as functions of the indexes to clarify the relationship between them. Furthermore, the present indexes are compared with those proposed earlier to find which is most suitable for the cast iron treated in this work. Authors propose a definition of compacted-vermicular graphite cast iron, which is reasonable from the physico-mechanical point of view, and also show some typical mechanical properties and measures required to produce such cast iron with desirable features.

Flashing phenomena of depressurized liquid nitrogen in a pressure vessel. Part 2: Mist formation and behavior of the liquid surface in the early depressurization process

Flashing of liquid nitrogen in a pressure vessel (cryostat) was observed at depressurization rates from 0.01 to 4.0 MPa/s. The explosive boiling behavior was observed by using a video camera. Pressure and temperature changes in the pressure vessel were measured. In the case of high depressurization rates, mist formation was observed in the vapor phase near the vapor—liquid interface in the early stages of the depressurization process. The mist layer became more dense as the depressurization rate increased. Observations of mist formation and the estimated temperature drop of the vapor under an adiabatic expansion process show that mist formation depends on the vapor expansion and boiling near the liquid surface. Mist formation in flashing phenomena plays an important role in the relaxation of thermal nonequilibrium states between the subcooled vapor and the superheated liquid generated by depressurization.

An experimental study on natural convective heat transfer from a vertical wavy surface heated at convex/concave elements

Natural convective heat transfer from a vertical wavy surface has been studied experimentally. The wavy surface has isothermally heated convex or concave semicircular cylinders. Such a problem involves the effect of complex geometries and heat conduction in unheated elements on natural convection flow. In this problem, the clarification of the interaction between the fields of fluid convection and heat conduction in the unheated elements is the most important part of explaining the heat transfer behavior. Therefore, a new proposed parameter S (= BR/GrD14) was introduced through a vectorial dimensional analysis, taking into account the thermal properties of the material of the unheated elements. Heat transfer characteristics for cases of both convex and concave heating surface are discussed on the basis of the parameter S and visual observations of the velocity and temperature fields. Empirical formulas for the cases of convex and concave heating have been derived to correlate the heat transfer characteristic Nu/GrD14 and the parameter S.

Visualization of Natural Convection Heat Transfer from a Vertical Wavy Surface Composed of Isothermally Heated Convex

Visualization of Natural Convection Heat Transfer from a Vertical Wavy Surface Composed of Isothermally Heated Convex/Concave Semicircular Cylinders.by Koki Kishinami *, Hakaru Saito *, Ikuo Tokura t, Norihiro Bando ** Natural convective heat transfer from a vertical wavy surface having heated convex/concave semicircular cylinders has been studied experimen-tally, considering the effect of heat conduction in unheated elements.Heat transfer characteristics are discussed based on visual observations of the velocity and temperature fields by using micro-particle trajectories and a Mach-Zehnder interferometer.The parameter S (= B R / Gro1/4 ) was introduced through a vectorial di-mensional analysis and clarified that it indicates to play an important role in the interaction between the fields of fluid convection and the heat con-duction regions.

An experimental study on free convection heat transfer from vertically lined horizontal cylinders set between parallel walls.

Experiments have been carried out on the free convection heat transfer from horizontal cylinders in array of staggered arrangements. Average heat transfer coefficients of individual cylinders and whole cylinder arrays were measured in order to clarify dependabilities of those coefficients upon the geometric figures including spacing and off-set distance between two cylinder lines, . Visualization of flow fields around the array has also been tried to explain the heat transfer behavior of cylinders in array. The experiments showed that there exist some optimum values of cylinder spacings and the off-set distances to increase the heat transfer coefficients and that the promoting effect in heat transfer can be expected especially when the array is set between parallel walls.