Numerical Simulation of Heat Transfer Tube Characteristics of Refrigeration and Air Conditioning Based on Mixed Fractional Model

The main parameters affecting the heat transfer performance of heat transfer tube heat exchanges include fin shape, fin spacing, fin thickness, tube row arrangement, tube diameter, dry and wet bulb temperature and flow rate. The air side heat transfer performance of heat transfer tube heat exchange and the influence of velocity field and temperature field distribution on heat transfer effect have been the focus of domestic and foreign scholars. In this paper, based on the mixed fraction model, CFD software is used to simulate the absorption process of gravity falling film outside the heat transfer tubes of refrigeration and air conditioning, and to study the flow and heat transfer characteristics of the process. The results show that, for the heat transfer tubes with the selected structure, the heat transfer capacity increases with the increase of water flow velocity, and the heat transfer enhancement effect of turbulence is enhanced. The heat transfer tubes have better comprehensive heat transfer performance than smooth tubes with the same diameter.

Effects of Non-Condensable Gas on Characteristics of Natural Circulation Flow of Isolation Condenser

An isolation condenser (IC) is a passive core cooling system in boiling water reactors. The cooling performance of IC is deteriorated when hydrogen generated in the core flows into the IC pipes. In this study, we conducted high pressure experiments using natural circulation loop with non-condensable gas injection, where helium was used to simulate hydrogen effect on the IC. The reaching distance of steam in the heat transfer tube was estimated by observing the region where nucleate boiling occurred on the outer surface of the heat transfer tube, and the heat transfer coefficient was estimated. The heat transfer coefficient hardly changed when helium was injected to the loop that indicates injected helium was not accumulated in the heat transfer tube. The system pressure at quasi-steady state increased with increasing amount of the injected helium. Since the differential pressure at the down comer section increased by helium injection, the injected helium may be accumulated in the section, leading to increment of the system pressure.

Influence of steam heat transfer tube damage characteristics on burst pressure

The corrosion damage and leakage of heat transfer tube of steam generator were important factors of nuclear power accident, which is closely related to the national nuclear power production safety and people's life and property. The influence of the size change of cylindrical defect on burst pressure of inconel690 alloy heat transfer tube was studied by finite element simulation and experimental measurement. According to the simulation and test data, the relationship between burst pressure and damage parameter is established. The results show that for cylindrical defects with small depth, there is an extreme point of cylinder damage diameter b which makes the damage maximum, which makes the burst pressure at a minimum. The research results can provide reference for accurate evaluation of residual life of heat transfer tubes.

A heat transfer tube wear reliability analysis method based on first-order reliability method

The heat transfer tube is one of the most essential components of the nuclear power plant as the boundary between the first and second circuit pressures. The wear between the heat transfer tube and the support plate or the anti-vibration strip is one of the essential reasons for its failure. Based on a heat transfer tube wear analysis method, combined with the reliability analysis theory, the calculation scheme of tube wear failure probability is proposed in this paper. In the analysis and calculation process, the key factors affecting the reliability are determined, including the baffle thickness B and the aperture difference Ce. In the manufacturing process, these key factors can be controlled, which is instructive for engineering practice.

Experiment and Analysis on Isolation Condenser Simulator Using Pressurized Steam

Isolation condensers (ICs) are important passive cooling systems in BWRs. After the Fukushima Daiichi Nuclear Power Station accident, concerns if the IC was able to restart with the inflow of hydrogen were arose. Because ICs lose heat removal ability when non-condensable gas inflow occurs, accurate evaluation of the effect is necessary. To develop analysis methods, as an initial stage, experiments and analyses considering only high-pressure steam and water were conducted. The experiment was done by an isolation condenser simulator which contains an accumulator with heaters inside, and a heat transfer tube. From the experiment, all steam was condensed at the heat transfer tube and the approximate position of complete condensation was confirmed from the temperature distribution and the observation. The experiment provided data such as temperature distribution, natural circulation flow rate, and pressure to compare with the analysis. The analyses were conducted for 4 cases of void fraction values at the heat transfer tube inlet and found that it has a high sensitivity to condensation. The reason is estimated to be the difference in inflow velocity that strongly depends on the void fraction even if the mass flow rate is constant. And the initial condition of the liquid film also affected condensation process. Heat removal at the section before the heat transfer tube should be considered to adjust void fraction at the inlet of heat transfer tube.

Melting Behavior of Phase Change Material in a Solar Vertical Thermal Energy Storage with Variable Length Fins added on the Heat Transfer Tube Surfaces

This paper investigates the melting behaviour of phase change material (PCM) in a vertical thermal energy storage system with provision of thin rectangular fins of uniform and variable lengths on the heat transfer tube surfaces. The selected PCM and heat transfer fluid (HTF) are paraffin wax and water, respectively. The HTF is passed through the helically coiled copper tube of 10 mm diameter to melt the PCM. The time required to complete the melting of PCM in the system with fins is found to be five hours, whereas for the system without fins it is five hours and forty minutes, for the same conditions of constant water temperature of about 70°C and flow rate of 0.02 kg/s. HTF tube with fins is observed to be more effective with a 13.33% faster rate of melting when compared to that of the HTF tube without fins. Such a fast charging process will be helpful in storing maximum energy within a short period/duration of time shorter duration in for solar thermal and heat recovery applications during lean production times. ©2020. CBIORE-IJRED. All rights reserved