Koki Kishinami

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

Combined forced and free laminar convective heat transfer from a vertical plate with coupling of discontinuous surface heating

Combined free and forced laminar air convective heat transfer from a vertical composite plate with isolated discontinuous surface heating elements has been studied numerically and experimentally. The problem has been simplified by neglecting heat conduction in unheated elements of the plate to accomplish a better understanding of the complicated combined/complicated convection problem. In this study, it is most important in explaining the heat transfer behaviour to clarify the interactions between buoyancy and inertia forces in the convective field and also the coupling effects of unheated elements upon the combined flow fields. Therefore, the temperature distributions of the wall surface and local Nusselt number, obtained by numerical calculations and experiments, have been discussed based on the various parameters associated with the present convection problem, i.e., Grashof number GrL, Reynolds number ReL, geometry factor D/L and stage number N. Heat transfer characteristics Nut/Re1/2L of this combined...

Numerical study on laminar flow forced‐convection heat transfer for air in a channel with offset plates heated by radiation heat flux

A two‐dimensional numerical study was carried out to investigate laminar forced‐convection heat transfer characteristics of air flow in a two parallel plate channel with offset plates and heated by a radiation heat flux. The SIMPLE method was used for the numerical prediction of the flow and thermal fields. The flow field temperature boundary conditions were obtained by applying the energy balance equation to boundary elements. The ray tracing technique was used to obtain the net absorbed radiation fractions in the boundary elements. The numerical results were validated with measured temperature values and experimentally calculated values of local Nusselt number (Nux), and a reasonable agreement was shown. Then the numerical simulation was used to study effects of design parameters on the convective heat transfer coefficient. It was found that in Re numbers from 650 to 2,550, the optimum spacing of offset plates relative to the nearest channel wall was around one third of the channel height. Also, the optimum offset plates’ numbers can be calculated based on one offset plate length being equal to one and a half times the channel hydraulic diameter. A correlation of average Nusselt number between the flowing air and the offset plates was obtained as follows; —Nu = 1.81 Re 0.352Pr1/3(Dh/l)1/2.

Experimental study of laminar flow forced-convection heat transfer in air flowing through offset plates heated by radiation heat flux

An experimental study of the steady state laminar flow forced-convection heat transfer of air flowing through offset plates located between two parallel plates and heated by radiation heat flux was carried out. The ranges of parameters tested were incident radiation heat fluxes of 500, 700, and 1000 W/m2 . With Re ranging from 650 to 2560. the inlet air bulk temperatures changed from 18.2 to 70 °C and the tilting angel of the unit with the horizontal ranged from 0 to 90° respectively. The results show that the rate of the increase in the local Nusselt number was observed to be proportional with Re up to 1900, while it became less sensitive over Re range of 1900–2500. Also. in this range of Re, with the inlet air temperature of 20 °C, the angel of inclination of the unit has no effect on the local Nusselt number. Increasing the incident radiation heat flux in the case of higher values of Re leads to a slight decrease in the value of the local Nusselt number. The effect of the inlet air bulk temperature on the forced-convection heat transfer coefficient shows. in the case of the horizontal position. an increase in the inlet air bulk temperature leads to slight decreases in the value of the average Nusselt number. while it leads to a significant decreases in the value of the average Nusselt number as the tilting angle increases up to the vertical position. This effect is clearer in the case of Re = 650 rather than Re = 2550.

A fundamental study of combined free and forced convective heat transfer from a vertical plate followed by a backward step

Combined forced and free laminar convective heat transfer on a vertical plate with a backward‐facing step has been studied numerically and experimentally, considering the effects of the interaction between the buoyancy and inertia forces which play a significant role in this phenomenon with the step‐geometry factor of d/L. The convective heat transfer behavior in connection with the reattachment and recirculation flows appearing in the step region has been investigated based on the numerical calculations and Mach‐Zehnder interferometer measurement under the wide range of the thermal condition. The behaviors of local Nusselt number NuL, velocity and temperature boundary layers and streamline fields in the recirculating region have been discussed for the various parameters of Grashof number GrL, Reynolds number ReL and the geometry factor d/L. The characteristic behavior of this convection heat transfer, including the vortex flow mode in the recirculating region and the unstable fluctuating mode near the re...

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.

Natural convective heat transfer on a vertical plate with discontinuous surface-heating (Effect of the heat conduction of a plate)

Natural convective heat transfer along vertical plates with discontinuous heating elements has been studied by numerical computation and experiments. It has been found that the heat transfer on the surface of a plate and the temperature distribution of unheated elements change depending upon the ratio of the thermal conductivity of convective fluid and that of the unheated element material, the ratio of thickness and length of unheated elements, and the length and surface temperature of the heating elements. The heat transfer data are also found to be correlated by using a parameter S=B··Rλ/G1/4rL, presented in this paper through vectorial dimensional analysis, and the observation of convective behavior visualized by a Mach-Zehnder interferometer and computational results. An empirical formula has been presented to predict heat transfer coefficients of discontinuously heated plates based on the new parameter S.