Results 1 - 10 of 11591
Results 1 - 10 of 11591. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] Most of world power plant traditionally use the cooling with water, and the types of cooling system are different from each other. The 85% of cooling system are once-through cooling system and closed cycle wet cooling system. There are two dry cooling system which are direct and indirect cooling system. In direct type, turbine exhaust is directly cooled by air-cooled condenser. In indirect system, turbine steam is cooled by recirculating intermediate cooling water loop, then the loop is cooled by air-cooled heat exchanger in cooling tower. In this paper, the purpose is to remove MMR waste heat, 24 MWth by using newly designed tower. The possibility of enhancing cooling performance by solar energy is analyzed. The simple cooling tower and solar cooling tower are presented and two design should meet the purpose of removing MMR waste heat, 24 MW. In simple cooling tower, as the number of finned tube increase, the required chimney height decreased. In solar cooling tower, as the collector radius increased, the required chimney height is decreased. To optimized the solar cooling tower, the cost analysis was conducted to find low cost tower. To analyze solar cooling tower further, consideration of solar energy performance at night should be analyzed.
[en] This round table session on strategic energy planning comprises separate presentations by the two authors, with some general discussion. It is agreed that nuclear energy will be needed in the next century, and may double. Much of the expansion will occur in developing countries. Fossil fuels will come from increasingly 'dirty' sources such as lignite and tar sands, adding pollution problems to the concern posed by carbon dioxide. Renewable energy sources should be taken seriously. Any assessment of fusion energy must take account of the fact that problems of containment and radioactive waste will be more difficult for fusion than for fission. 7 figs
[en] This keynote address is based on the findings of the World Energy Council's Commission 'Energy for tomorrow's World'. Forecasts up to and beyond the year 2020 are provided for several different economic and ecological assumptions. It is predicted that fossil fuels will continue to dominate, that real pressures on petroleum and gas supplies will develop, that nuclear energy will grow, that beyond 2020 the 'new' renewable sources, particularly solar, will grow steadily, and that targets for limiting emissions of greenhouse gases are unattainable. 6 figs
[en] The dry cooling systems commonly use extended surface, called fin, to increase surface area and heat transfer performance. The finned surfaces ideally have zero thermal resistance and show uniform temperature distribution. Direct contact heat transfer is getting interests as innovative solution in the dry cooling system. Hot fluid flows into the air and heat transfer occurs without physical barrier between the fluid and air, thus the heat transfer performance is high. For getting large surface area in the direct contact heat transfer system, the hot fluid is emitted as small droplet shape or thin falling film. UCLA published the Direct Contact Liquid-on-String Heat Exchanger (DILSHE) that the hot fluid flows along strings, and is cooled by air. Drexel published Spray Freezing of Recirculating PCM system that the hot fluid is sprayed as droplet shape into air and the cooled fluid returns to the pool. In KAIST, dry cooled waste heat removal system that applies the direct contact heat transfer technology has been being designed. This study conducted analysis for direct contact heat transfer on the film along vertical straight string. Physical modeling on the film, heat transfer analysis and pressure loss, and cooling tower analysis were conducted. When the string radius is larger than 1 mm, the film along the string doesn't break and stable film forms. As the string radius increases, the required cooling tower height is increased but the increase is very small.
[en] The Supercritical Water Cooled Reactor(SCWR) is being developed with it's operational conditions of a pressure over 25MPa and temperature of 290∼550 .deg. C. Many experiments have observed that the heat transfer coefficient of a fluid in the pseudo-critical region shows a different behavior from that of the conventional forced convection. One very specific characteristic of the heat transfer is called the 'heat transfer enhancement', or 'normal heat transfer' which shows a larger heat transfer coefficient than the Dittus-Boelter correlation in a relatively low and moderate ratio of the wall heat flux to the mass velocity(q/G). At a high heat flux, the wall temperature increases sharply and the heat transfer coefficient becomes low. This phenomenon is called 'heat transfer deterioration'. This paper is focused on the prediction capability of the heat transfer deterioration. In order to examine the reliability of the embedded turbulence models of FLUENT at a supercritical pressure, a series of simulations for the vertical upward flow of water in a heated tube were performed
[en] Condensation phenomena occur during the PCCS operation cooling the containment through phase change heat transfer. Accordingly it is important to enhance the condensation heat transfer performance. Condensation mode is commonly classified as filmwise condensation (FWC) and dropwise condensation (DWC). DWC heat transfer performance has an order of magnitude higher than FWC heat transfer performance. In DWC process, condensed liquid droplets attach to the surface and prevent transfer of heat to the cooled surface. Generally the condensate is removed by gravity. When removal rate of condensate is high, DWC heat transfer performance will be enhanced. In terms of removal rate, superhydrophobic surface, which is recently in the spotlight, is expected to have capability to enhance the DWC heat transfer efficiency by reducing droplet size. In this study, we investigated condensation heat transfer performance on micro and nano structured superhydrophobic surface. Condensation experiments on the micro and nano structured superhydrophobic surface were carried out and compared with those on the smooth hydrophobic surface in terms of heat transfer performance and condensed droplet morphologies. Through the experiments, we found that superhydrophobicity disappeared under the condensation circumstance. As a result, heat transfer performance on the superhydro-phobic structured surface decreased compared with that on the smooth hydrophobic surface. In order to enhance the condensation heat transfer performance with superhydrophobic property, condensation mechanism on superhydrophobic surface and the conditions for sustaining superhydrophobicity should be studied more
[en] To increase heat transfer performance of dry cooling system, direct contact heat exchangers were considered. There is no thermal resistance by wall structure and it is easy to get large surface area. On the other hand the conventional system uses fin structure and heat transfer performance is reduced due to thermal conduction in the fins. In most cases, increasing heat transfer performance is able to be obtained by increasing Reynolds number. In this study, many types of direct contact heat exchangers were analyzed and the optimum heat exchanger type having high heat transfer performance and low pressure loss of the system was selected. In summary, the best type for direct contact heat exchanger is falling oil film along vertical strings. It is important to consider not only heat transfer performance of the heat exchanger but also frictional pressure loss. The range of Reynolds number in the direct contact heat exchangers are generally 100 to 10,000. Within this range, whole correlations used for this study are proven, thus the results are reliable. This study shows that straight flow of air on the flat surface is the best option for direct contact heat exchanger. The heat transfer performance on the wavy surface is high due to turbulence, but the frictional pressure loss is much large.
[en] KALIMER-600(Korea Advanced LIquid MEtal Reactor, 600MWe) is a pool type sodium-cooled liquid metal reactor. The NSSS is composed of three heat transfer systems of a PHTS(Primary Heat Transport System), a IHTS(Intermediate Heat Transport System) and a SGS(Steam Generation System). This paper is on the case study for the arrangement and structural evaluation of the KALIMER-600 IHTS piping system. The arrangement of piping system was carried out by considering the piping length, the number of curved pipings and the sizes of the components. The stress and strain for the structural integrity evaluation were calculated for each case of the piping arrangement by considering the material of the piping system
[en] The hydrogen production system coupled with a High Temperature Gas Cooled Reactor (HTGR) is considered as one of the most promising application to allow new processes of massive hydrogen production with economy and emission free. In the cavity of the HTGR which is the space between the reactor vessel and containment, a reactor cavity cooling system (RCCS) is equipped to remove the heat transferred from the reactor vessel to the structure of the containment. In the present study, a new concept of the RCCS for the HTGR named water pool type RCCS was proposed which is expected to have better cooling capability than air cooled type and simpler system configuration than water cooled type. Also the experimental results for the new RCCS were presented, which were performed to evaluate its cooling capability and understand the heat transfer phenomena in the system
[en] With projections of sharply rising energy consumption and continuing global dependence on fossil fuel sources, environmental pollution and greenhouse gas emission could reach severe damaging levels. The global challenge is to develop strategies that foster a sustainable energy future less dependent on fossil fuels. Low environmental impacts and a vast fuel resource potential should allow nuclear power to have a meaningful role in the supply of energy during the next century. Nuclear power for over 40 years has contributed significantly to world energy needs, currently providing more than 6% of primary energy and 17% of global electricity. Low environmental impacts and a vast fuel resource potential should allowed to contribute substantially to meeting the sustainable energy challenge.. Although there is some awareness on both the technical and political level of nuclear power's advantages, it is not a globally favored option in a sustainable energy future. A sizeable sector of public opinion remains hesitant or opposed to its increased use, some even to a continuation at present levels. This paper, after some discussion of the rising energy consumption, concentrates on a comparison of the environmental impacts of the available energy options. (author)