Recently the damages in the tubes of heat exchanger of sea water cooling type have frequently been experienced and the damaged condition could be noticed either from corrosion and erosion on the inner surface of tubes or from pin holes in the tubes. The damages are considered to have been caused directly from accumulation of marine growth such as sea shells on the inner surface of tubes and from suction of foreign stuff like mud or sand to the heat exchanger. On the other hand, the unbalancing stream condition in tubes is considered to be the indirect cause of damage. To investigate the cause, the tank experiment was carried out using a 1/10 scale model to confirm the effect of the unbalanced stream condition of cooling water in tubes and water chambers of main condenser and also in scoop pipe. In consequence of the above test, we have found out the following: Extent of unbalance of stream in tubes is rather small despite of some flactuational pressure existing in cooling water inlet chamber of main condenser, however, the phenomenon of cavitation was found to occure around the outlet of inner surface on the tubes near upper part of tube nest located within main stream area when the cooling water velocity in tubes exceeds some limited speed point. In the light of above experiment, we have confirmed that the excessive cooling water velocity could cause not only inlet-attack but also erosion occurring around the outlet of inner surface on tubes.
Heat transfer of film condensation is of interest in many industrial application, and many paper, concerned with laminar film condensation on a isothermal surface, have been reported. However, in the majority of cases when film condensation occurs, the surface temperature decreases along the surface in the direction of condensate flowing down. This paper describes an analytical and experimental study of laminar film condensation on nonisothermal vertical plate, of which one side condensation occurs, and the other cooling water passes with constant heat transfer coefficient. The results of analysis based on Nusselt theory indicate that distribution of surface temperature, heat flux and heat transfer coefficient can be approximated to the power law variation, xn, wherexis a distance along with the surface in the direction of condensate flowing down andnis the value varies with the ratio of steam side thermal resistance to all except steam side. Experimental results are good agreement with those distributions, while average heat transfer coefficient defined on the basis of the integrated mean temperature is about 13% above the theoretical value and the same results are obtained in the experiment of isothermal case.
A number of marine geared diesel engines have been widely used in recent years for the car ferries, the car carriers and the general cargo boats. As the reduction system for the engines, the epicyclic gear reducers have also been widely used because of their many advantages such as light-weight, compactness, concentricity of input and output shaft. IMT epicyclic gear reducers developed in our country utilizes two fundamental functions to balance the load on each gear. One is the oil film function of the floating intermediate rings between the planet gear and the planet gear shaft, and the other is spring function of the balance pins between the double internal gear and the internal gear retainer. A recent research of torsional vibration analysis of shafting system with IMT epicyclic gear reducer tells the IMT epicyclic gear reducer has a good chance of avoiding torsional vibration.
Where the torsional vibration in a marine propulsion system with reduction gears is calculated, it is usually assumed that the gear assembly is torsionally rigid, i.e. the torsional rigidity of tooth and gear backlash are neglected. With regard to the turbine-propulsion installations, however, especially during astern maneuvering, the gear tooth does not always keep the contact with each other. Then it is necessary to take into account of nonlinear behaviour due to gear backlash combined with torsional rigidity of tooth for the calculation of the torsional vibration. In this paper, the turbine-propulsion installation is simulated as a 5-masses gear-branched system with gear backlash. The calculation of the above system is carried out by the use of hybrid computer. The effect of the mass moment of inertia in the free running branch, the damping coefficient of the lubricating oil film between gear teeth and the amplitude of the excitation propeller torque to the vibrating torque in shafts and the impact loads at gear teeth are quantitatively obtained. Where the 2nd natural frequency is far away from the 1st one, the hysteresis phenomenon appears and at the same time the random impact loads at the gear tooth occur on free running branch. On the contrary, where the two natural frequencies are close, the hysteresis phenomenon does not appear and the vibrating torque in the shaft of the free running branch is strongly suppressed by the other branch which acts such as a dynamic damper.