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In order to simplify condensation heat transfer calculations for feed water heaters, one dimensional (1D) analyses were compared with three dimensional (3D) analyses. The results showed that average condensation heat transfer coefficients by I D analyses with 1/2 rows of heat transfer tubes agreed with those by 3D analyses within 7%. Using the 1D analysis model, effects of the pitch of heat transfer tubes were evaluated. The results showed that the pitch did not affect much on heat transfer rates and that the size of heat transfer tube bundle could be decreased by a small pitch.

In this study, experiments were conducted in order to investigate the effect of noncondensable gas on the condensation heat transfer in a feed-water heater under the conditions of inlet quality 13-100% and inlet air molar fraction 0-1.2%. The thermal resistance on condensation surface was found to be proportional to the local air molar fraction. A transport equation of noncondensable gas and the experimental equation of thermal resistance on condensation surface were added to the previously developed program with a two-fluid model and condensation heat transfer model. Feed-water heater calculations indicated that the effect of noncondensable gas on the heat transfer was negligibly small under the operation conditions of about 30 ppm in a power plant. Keywords: Noncondensable Gas, Condensation Heat Transfer, Feed Water Heater

Detailed gas-liquid two-phase flow prediction is required for development of high performance components of nuclear reactors and oil power generation plants, while performance components of nuclear reactors and oil power generation plants, while accelerated calculation method was developed by combining gas and liquid velocity accelerated calculation method was developed by combining gas and liquid velocity unified volumetric velocity of two-phase mixture was calculated instead of individual phase velocities and the calculation process became simpler. Velocity calculation error for a phase of small fraction could be reduced in convergence criteria of mass conservation because acceleration slip was obtained exactly from the momentum balance equations. Calculation time for two-phase flow in a chimney of a natural circulation reactor was about a half of the previous calculation method.

In order to evaluate the heat transfer performance in a feed water heater, a three-dimensional analysis for the heater of a power plant was conducted with a computational code for two-phase flow using a two-fluid model. In a conventional feed-water heater which was divided into six sections in the axial direction. the steam flowed mainly into both end sections. Therefore the overall heat-transfer coefficient was large there. Based on the calculated results, an improved feed-water heater was proposed in which the support plate had a hole leading the steam into the neighboring sections. In the improved feed-water heater, the steam flowed from the steam inlet section to the neighboring sections through the hole in the support plate, and the steam velocity was generally larger than that in the former heater. Therefore the overall heat-transfer coefficient was also larger.

A water wall type passive containment cooling system with an outer pool surrounding the suppression pool is one passive containment cooling system. In the system, a baffle plate in the suppression pool mitigates thermal stratification formed at the vent tube outlet level and enlarges the heat transfer area. The effectiveness of the baffle plate in mitigating thermal stratification was experimentally confirmed; the heat transferred to the outer pool increased about 50% due to a larger high temperature region and a longer effective heat transfer length. The experimental analysis was performed using a three-dimensional thermal-hydraulic analysis program. In the analysis, a laminar flow model and slip conditions on structural walls were used, and the calculated temperature profiles and natural circulation flow rates along the baffle plate agreed with measurements. The model was then judged as a valid and practical tool to evaluate global natural circulation and temperature distributions in a large pool. And i...

A multidimensional analysis code for two-phase flow using a two-fluid model was improved by taking into consideration the condensation heat transfer, film thickness, and film velocity, in order to develop an evaluation method for two-phase flow and heat transfer in a feed-water heater. The following results were obtained by a two-dimensional analysis of a feed-water heater for a power plant. (1) In the model, the film flowed downward in laminar flow due to gravity, with droplet entrainment and deposition. For evaluation of the film thickness, Fujii's equation was used in order to account for forced convection of steam flow. (2) Based on the former experimental data, the droplet deposition coefficient and droplet entrainment rate of liquid film were determined. When the ratio at which the liquid film directly flowed from an upper heat transfer tube to a lower heat transfer tube was 0.7, the calculated total heat transfer rate agreed with the measured value of 130 MW. (3) At the upper region of a heat transfer tube bundle where film thickness was thin, and at the outer region of a heat transfer tube bundle where steam velocity was high, the heat transfer rate was large.

A three-dimensional computational analysis program of gas-liquid two-phase flow is developed in order to simulate fuel flow in the intake menifold of an automobile fuel supplier. This program considers physical models as follows: (a) movement of fuel droplets and their deposition on the manifold wall; (b) temperuture change and evaporation of the droplets: (c) evaporation of fuel deposited on the wall: (d) transport of fuel vapor evaporated from the wall: and (e) force of the droplets' influence upon air. Calculated results show that all fuel droplets injected from the fuel injector deposit on the wall, and when the wall temperatures are 20°C and 80°C, 95% and 37% of the injected fuel flow into the cylinders in the state of liquid film, respectively. The remaining fuel flows into the cylinders as vapor.

A heating, ventilating and air conditioning (HVAC) system is installed on the operation floor of a BWR reactor building for temperature control and dust protection in work areas. In the current HVAC system, it is necessary to ensure that its exhaust ducts do not interfere with other structures and pipes, since pipings are buried under the floor.In this study, air velocity and temperature distributions and heat removal rate were analytically and experimentally investigated, and duct arrangements without the buried exhaust ducts were evaluated. In the analysis, a three-dimensional thermal hydraulic analysis computer program for incompressible viscous fluid was applied, and a laminar flow model and slip condition on the wall surface were used, based on a comparison of calculated results with measured ones. In the experiments, a one-twentieth scale model was used, and the temperature distribution was measured by thermocouples. Furthermore an airflow distribution was visualized and three-dimensional flow path lines were obtained by computer-aided image processing. The proposed HVAC system uses a rising current of air on the hotter surface of the reactor refueling pool and spent fuel pool, and exhausts air through exhaust ducts on the ceiling. Consequently, it is confirmed that the new HVAC system can be realized, which increases the removal heat capability on condition of the same ventilation rate as the current system.