The authors of this paper have studied the dissipation of heat from the hot surfaces to the air current by natural convection passing through the narrow space between the two parallel walls facing each other. The amount of heat dissipated from any particular point on the hot surface is to be determined from the product of the temperature gradient in the boundary layer and the thermometric conductivity of the air film. The former was observed directly by the Schlieren method, and the latter by thermo-couples. This procedure of experiments enables us to determine the gradual variation of the capacity of heat dissipation from point to point along the radiating surface. The heat transfer coefficient at any point on the hot surface is affected by (1) the temperature difference between the hot surface and the cold air current at the entry. (2) the width of the passage of the air current between the two parallel walls. The results of the experiments are shown in several diagrams after the dimentional analysis.
In the periodic heat flow in solid, the initial temperature distribution is not given, and hence the ordinary methods of numerical analysis used in the steady or unsteady heat conduction cannot be applied to the periodic one. The only existing condition is the cyclic variation of temperature within the solid. By taking this periodic condition into consideration, the writers proposed two methods of numerical analysis of periodic heat conduction, the matrix and successive approximation. methods. In this paper the several examples of this method in one-dimensional heat flow were stated and the relative merit between the two methods was also discussed.
In this paper, the non-linear heat conduction problem in the semi-infinitive solid, having the thermal conductivity such as next type [numerical formula] is dealt. Using the moment method considered by H. Yamada, the temperature distribution is obtained by the polynomial semi-analytically and its result has the sufficient accuracy to be used for the practical application.
Although many researches have been made on the heat loss from the horizontal cylinder or vertical wall, very few on the heat loss from the inclined cylinder due to free convection and apparently the definite relations between the heat transfer coefficient, dimensions and inclinations of the cylinder in this case, have not been obtained as yet. From this point of view, measurements were carried out on the heat losses from the inclined circular cylinders in the still air the different cylinder temperatures, in which measurements diameter (d), length (l) and inclination (θ) of the cylinders were chosen as follows : d=3∼30mm, l/d=1∼200, θ=0∼90°C. From the results of experiments, the heat transfer coefficients by free convection (αc) were evaluated and shown by diagrams and then expressed by the following formulae ; [numerical formula] where λm, γm, μm and Tm are mean thermal conductivity, mean specific weight, mean viscosity and mean absolute temperature of surrounding gas, respectively, and ΔT is temperature difference between the cylinder surface and the gas and m, n, and K are constants depending on the inclination. The authors wish to thank Miss Y. Akashi, for her help in conducting the experiment. The authors are also glad to acknowledge that the research was carried out partly with the Grants-in-Aid for Scientific Research of the Ministry of Education.
This report is concerned with the heat transfer from a two-dimensional body placed in uniform stream. We calculated the temperature distribution in the boundary layer and the local heat-transfer coefficient on the body surface under the following assumptions : (1) The outer layer velocity U is expressed by [numerical formula] (2) The body surface temperature distribution A is expressed by [numerical formula] (3) Flow is incompressible. (4) The density ρis independent of temperature. (5) The kinetic viscosity νand the thermal diffusivity α are the linear functions of temperature.
Considering the variation of properties depending upon temperature, the auther calculated heat transfer and skin friction for a heated flat plate in longitudinal flow of water. The differential equations for laminar forced convection are solved by means of perturbation theory, using the Pohlhausen's solution for constant properties as 0 approximation. It is assumed that (1) density and specific heat are constant ; (2) viscosity varies in proportion to T-6, where T is absolute temperature ; and (3) thermal conductivity varies in proportion to Tm, where m varies with temperature of general flow. Fricton factor and Nusselt's number are given for the value of (T0-T1)/T1, where T0 and T1 are the absolute temperature of plate and general flow, respectively.
A general case was treated, in which surface temperature distribution of vertical and concentric pipe-walls with annular space varied axially. In theory, Fourier series, Bessel function and Hankel function with imaginary variable, Laplace transformation and homogeneous integral equation were used and, as a new attempt, method of numerical solution of Volterra's integral equation of the 2nd kind was used. Theory was compared with experiment of air, using the zero-approximation of theoretical solution calculable numerically and simply, partially experimental, and a partially theoretical solution, which showed the experimental results, was conducted. The influences of dimensions of every parts, temperatures and Grashof number, which influenced on heat transfer, were made clear and practical formulas were found.
It is one of the most effective methods for rising mechanical efficiency of engine, to reduee the thickness of piston ring thin. But we found the wavy defflection on extremely thin piston rings, which were tentatively applied to some engine. So we calculated elasticaly, to find the lateral stability of thin rings, and obtained the reasons why the wavy defflection was occurred. We are going to continue the test & analysis so that we may set a limit to the thickness of piston rings.
In the reciprocating machines, such as internal combustion engines and compressors, etc., the pressure distribution of the piston ring which exerts on the cylinder wall changes gradually due to wear of the cylinder wall and also the piston ring itself. Then, if we use the piston ring which exerts initially uniform pressure on the cylinder wall, the life of this piston ring for good action is not very long, causing gas leakage and increasing the consumption of lubricating oil owing to the decrease of the spring power near the gap ends of the piston ring by the local wear during operation. As the counter-measure for this, if we use the piston ring of the elliptical pressure distribution named E type ring, the spring power being more intense for the gap direction, the pressure distribution of the piston ring should be equalized by the local wear of the piston ring during operation, and then the spring power for the gap direction is decreased gradually. For these reasons, the life of the E type piston ring for good action becomes considerably long. In our researches, we measured peripheral forms of piston rings which were closed by using flexible steel bands with different sizes. From these results, the theoretical calculation was carried out concerning the pressure distribution of the E type piston ring on the cylinder wall, when the diameter of the piston ring is different a liitle from than of the cylinder bore. Moreover, it was made clear from our calculations that if we want to make such a piston ring as has the elliptical pressure distribution which exerts more intense pressure for the gap direction, we may make the diameter of the piston ring a little larger than that of the cylinder bore and further, the state of pressure distribution of the piston ring with normal size in the worn cylinder bore was also made clear.
The property of the coefficient of friction for the vapour-liquid mixture, which has been used to calculate the water circulation in boiler tubes in the previous report, is inquired, referring to Lockhart's method of calculating the pressure drop for two-phase, two component flows and also to Schurig's experimental data for air-water mixture. The ratio of the coefficient of friction for mixture to that for the liquid in the mixture (when only the liquid flow in the tube), is expressed as a function of the flowing ratio of both liquids. And this value for the mixture of saturated water and saturated steam of 1∼225 ata is shown. In the approximate calculation of water circulation in natural circulation boilers which pressure is above 10 ata, 1.5∼2.0 can be used as this value.
As a reliable analysis of the stress of the flat endplate supported by two eccentric circles (one of them is the flxing circle of the endplate to the shell and the other is to the flue) under the uniform pressure, like in the case of Cornish Boiler without gusset stay, has not been done ; the authors dealt with this problem theoretically using the bipolar co-ordinates, and obtained the satisfactory coincidence with the numerical calculation for the practical dimensions, and moreover comparing the values obtained by the approximate solution and its numerical results using the same data which were previously reported by one of the authors, the error of the approximate one was confirmed to be negligible.
This report deals with the unit fuel injector having a pintle nozzle, which was modified from the famous General Motors' unit injector with a flat type vale. Since the General Motors' diesel engine has a combustion chamber of direct injection type, so its injector has a spray tip with the multiples-holes. But instead of the type the author has adopted the pintle nozzle, because he intended to apply the injector to the precombustion chamber or turbulence chamber. As to this injector the author measured the rate of fuel discharge and observed the spray formation by means of the strobo-flash apparatus, and he also calculated the injection pressure according to the statical compression theorem. These calculated results agreed fairley well with the measurements.
In case of forced convection, the coefficient of surface heat transmission is different from the former case of the natural heat convection and depends increasingly on the stream velocity and peripheral velocity of the cylinder, but not on the temperature difference. The experiments are performed as same as the case of the natural heat convection which was already reported in the previous paper, and these results are shown graphically in figures 1∼5. From these figures we found that the experimental formula [numerical formula] is sound.
The aim of this study is to show more quantitatively the factors that affects the atomizing character of the high speed liquid jets, and to make better injection nozzles for internal combustion engines. In this paper, we observed the mechanism of dripping, laminar flow, turbulent flow and spray of issuing jets by means of ultra-rapid photography. Changing the kinds of liquid, many ultra-rapid pictures were taken for various issuing velocities, and the transition points of dripping, laminar flow, turbulent flow and spray were cleared. The empirical formula for the transition velocity from dripping to laminar flow is given by [numerical formula] from the consideration of dimensional relation.
Continued from the 1st report, we observed the mechanism of laminar flow, turbulent flow and spray of issuing liquid jets by means of ultra-ropid photography. The empirical formula for the jet length of laminar flow is given by [numerical formula]. The transition velocities from laminar to turbulent νc and turbulent to sprayνs are given by the equations [numerical formula], where μ/√(σρD)=stability number andνD/ν=Reynolds' number. The critical Reynolds' number (νcD/ν) of liquid with high stability number is smaller than the one with low stability number, i.e. the critical Reynolds' number of heavy oil is smaller than that of water. But the jet length of the heary oil is much longer than the water. The reason is that the jet length is nearly proportional to the issuing velocity ν, which takes a larger value for the larger kinematic viscosity ν. The spraying phenomena of viscous liquid has the so-called starting length. Near the nozzle, the flow is laminar. Apart from it, the flow becomes turbulent. Far from it, the flow spreads by the surface friction with air accompanying the thin liquid films.