Results 1 - 10 of 135
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[en] An instability theoretical model for multi-channel system had been developed by building one-dimensional homogeneous model and adopting nonlinear analysis for two-phase flow in vertical single pipe, supplied by Clausse and Lahey. With the same parameters as the experiment, two-phase flow density wave oscillation in parallel inclined inner ribbed pipes was analyzed and solved in this paper. The variation of the working fluid inlet velocity perturbation with time was found using the time domain method. The criteria of density wave oscillation were defined according to the convergence or divergence of the velocity. The pulse cycle of calculated results was mostly between 5 and 16 seconds, which was quite similar to the data between 7 and 19 seconds in the experiment. It is shown that the calculated results have a good agreement with the experimental data. Therefore, the method can be used to determine whether the incidence of density wave instabilities. It can also provide a reference for the safety parameters of the water wall in the supercritical pressure boiler. (authors)
[en] Several sites were visited to monitor stonemason exposure to respirable crystalline silica (RCS), inhalable dust and respirable dust. At all sites, exposure to RCS exceeded the Workplace Exposure Limit of 0.1 mg/m3 8-hour TWA. There was therefore a continuing high risk of workers developing silicosis unless the appropriate measures were instigated to prevent or control exposure. Exposure control was ineffective at all sites e.g. water wall extraction systems were not well designed. There was evidence that foreign workers were at a greater exposure risk. But even with appropriate controls to mitigate exposure to RCS it may not be possible to sustain exposure to below 0.1 mg/m3 8-hour TWA without on-going HSE intervention.
[en] The paper presents the results of numerical investigations for determining the relationship between the replacement factor of heat load of passive solar heating passive systems and the thermal resistance of their collecting-accumulating walls. The calculations are carried out by using average daily meteorological information. (author)
[en] Supercritical Circulating Fluidized Bed (CFB) boiler becomes an important development trend for coal-fired power plant and thermal-hydraulic analysis is a key factor for the design and operation of water wall. According to the boiler structure and furnace-sided heat flux, the water wall system of a 600 MW supercritical CFB boiler is treated in this paper as a flow network consisting of series-parallel loops, pressure grids and connecting tubes. A mathematical model for predicting the thermal-hydraulic characteristics in boiler heating surface is based on the mass, momentum and energy conservation equations of these components, which introduces numerous empirical correlations available for heat transfer and hydraulic resistance calculation. Mass flux distribution and pressure drop data in the water wall at 30%, 75% and 100% of the boiler maximum continuous rating (BMCR) are obtained by iteratively solving the model. Simultaneity, outlet vapor temperatures and metal temperatures in water wall tubes are estimated. The results show good heat transfer performance and low flow resistance, which implies that the water wall design of supercritical CFB boiler is applicable. - Highlights: → We proposed a model for thermal-hydraulic analysis of boiler heating surface. → The model is applied in a 600 MW supercritical CFB boiler. → We explore the pressure drop, mass flux and temperature distribution in water wall. → The operating safety of boiler is estimated. → The results show good heat transfer performance and low flow resistance.
[en] In order to solve the problem of removing inhaled particle caused by the combustion source, the dynamics characteristics of the inhaled particle in additional temperature field have to be studied. The dynamics characteristics of the inhaled particle in temperature field are measured in designed and processed a rectangle experiment channel by the PDA instrument. This method is visual. The dynamic characteristic of the particle at 0.15 mm near by water wall surface in boundary layer can be measured through the direction change of beam of PDA light. The movement rules of the inhaled particle in the additional temperature field are obtained through the experiment. The experiment results show that the thermophoresis force has strong influence on the particle which diameter is about 6 μm and the experience formulas are put forward to calculate the thermophoresis deposition efficiency. The thermophoresis deposition efficiency formulas obtained from this experiment is consistent with Batchelor and Shen formulas. The research shows that the PM2.5 thermophoresis deposition efficiency is direct proportion to the temperature ratio between the inlet temperature and the water wall surface but is not the temperature difference in the rectangle channel
[en] Highlights: • Heat transfer of spiral water wall tube in an ultra-supercritical boiler is investigated for fast response-characteristic. • The safe range of mass fluxes and heat fluxes is investigated. The tube metal temperature is safe from 30% to 90% BMCR. • The Fr number can give a convincing prediction on the effect of flow stratification in the tested pressure range 12–18 MPa. • Four selected heat transfer correlations are assessed against our experiment data obtained under designed operating loads. • Natural convection influences heat transfer in the low and pseudo-critical enthalpy region significantly. - Abstract: Nowadays, heavy peak-shaving task requires ultra-supercritical boilers having fast and flexible response-characteristic. Wide operating loads and quick load-change mode ask for better flow and heat transfer characteristics of the water wall. Under the above backgrounds, heat transfer to water flowing upward in an inclined smooth bare tube was experimentally investigated under the operating conditions of an ultra-supercritical boiler. The experimental results show that the metal temperature of the tested water wall tube is safe from 30% to 90% BMCR. The heat transfer coefficient of single-phase water at bottom side is 1–2 times bigger than that at the top. The Fr number put forward by Kefer et al. can give a convincing prediction on the effect of flow stratification in the tested pressure range 12–18 MPa. The calculated steam quality difference with the Kefer et al. correlation is an average-value prediction on axial length of the transitional region. At supercritical pressures, four widely used heat transfer correlations are evaluated with the experimental data. The comparison results demonstrate that Swenson et al. correlation gives the best prediction on heat transfer. The effect of flow stratification is evaluated by the modified correlation of Petukhov and Popov, which demonstrates that the effect of flow stratification can be neglected in the high enthalpy region.
[en] Two types of phase change materials were used as storage media in a Trombe Wall; namely paraffin wax (N-Eicoseue C20 H42) and Glaubers Salt (Na2SO410H2O). To investigate the performance of these materials, a theoretical model and a simulation programme were developed. The wall temperature, the amount of heat stored, and the optimum wall thickness were calculated for both types. The study found that using two sheets of glass on the outside wall increased the surface wall temperature by around 50 degree C. It also found that Glauber salt was a much better storage material than paraffin wax. For a selected winter day at a location of 32 oN latitude, the storage capacity of the salt was more than twice that of the paraffin wax. The salt storage capacity was 32816 kJ/m3 at an optimum wall thickness of 16 cm. this value for paraffin was 14464 kJ/m3 at 13 cm optimum thickness. The study also concluded that according to this high heating value the wall uses, Glauber salt as a storage medium could supply its heat to the surrounding for a much longer period at night
[en] Introduction of a radioactive nuclide into the water offers a rapid procedure for diagnosing the functioning and properties of industrial boilers without altering the phenomena to be measured. The choice of radionuclide must satisfy strict criteria; after a large number of trials, a mixture of 186Re and 188Re obtained by neutron irradiation of natural rhenium was chosen. The background noise is measured at the time of the trials with the help of a system of three tubes placed in front of the boiler, or of one tube placed in an inspection chamber. The density of the emuision (water- steam) can be measured with an accuracy of between 10% and 15%. Trials were carried out on a boiler with a capacity of 3 tons of water operating under a pressure of 10kg/cm2 at 180°C. The emulsion density in several water-wall tubes was compared for different vapour flows, the density being measured along the whole length of the tube, which gives information on the thermal exchanges between the furnace and this tube. Trials will very soon be carried out on a power boiler belonging to Electricité de France (Creil Power Station). The personnel working around the boiler run no risk of irradiation since the quantities of radionuclide (10 to 25 μCi/litre of water) are small. The complete calculation of the isodose curves, verified by dosimetric measurements, shows that the dose 20 cm outside the boiler is below 90 mrads after 210 h, which is 6 or 7 times lower than the maximum tolerable dose. The dose is even smaller in the case of a large boiler. (author)
[fr]L'incorporation du radioélément émetteur dans l'eau offre un procédé rapide de diagnose du fonctionnement et des propriétés des chaudières industrielles, et ne perturbe pas les phénomènes à mesurer. Le choix du radioélément doit répondre à des critères impératifs: après un grand nombre d'essais le mélange 186Re et 188Re, obtenu par irradiation neutronique du rhénium naturel, a été retenu. Le bruit de fond est mesuré, au moment même des essais, à l'aide d'un système de trois tubes placés devant la chaudière, ou à l'aide d’un tube placé dans un regard. La précision de la mesure de la densité de l’émulsion (eau-vapeur) varie entre 10% et 15%. Des essais ont porté sur une chaudière d’une capacité de 3 t d'eau fonctionnant sous une pression de 10 kg/cm2, à 180°C. On a comparé la densité de l'émulsion dans plusieurs tubes écrans, pour différents débits de vapeur, et on a mesuré là densité tout le long du même tube, ce qui renseigne sur les échanges thermiques entre le foyer et ce tube. Des essais vont être très prochainement réalisés sur une chaudière de puissance de l’Electricité de France (Centrale de Creil). Le personnel travaillant autour de la chaudière ne court aucun risque d'irradiation, les quantités de radioélément (10 à 25 pCi par litre d'eau) étant faibles. Le calcul complet des courbes isodoses, vériffé par des mesures dosimétriques, montre que la dose à 20 cm à l’extérieur de la chaudière est inférieure à 90 mrad au bout de 210 h, ce qui est 6 à 7 fois plus faible que la dose maximale tolérable. Cette dose est encore plus faible dans le cas d’une grande chaudière. (author)
[en] Absorption heat pumps, first developed in the 19th century, have received renewed and growing attention in the past two decades. With the increasing cost of oil and electricity, the particular features of this heat-powered cycle have made it attractive for both residential and industrial applications. Solar-powered air conditioning, gas-fired domestic cooling and waste-heat-powered temperature boosters are some of the applications on which intensive research and development has been conducted. This paper describes the operation of absorption systems and discusses several practical applications. It surveys recent advances in absorption technology, including the selection of working fluids, cycle improvements and multi-staging, and fundamentals of the combined heat and mass transfer in absorption processes. (author)
[en] After the Great East Japan Earthquake, tsunami disaster mitigation has become more important for disaster prevention. As for tsunami sea walls installed along coastal line, the supposition that tsunami may overflow the seawalls are required. The tsunami force acting on the land structure is generally estimated based on the maximum passing inundation depth with the water depth coefficient but the estimation methods were proposed in the non-overflow condition, and the estimation method of the tsunami force verified for the overflow case is needed. In case of overflowing the seawall compared with the non-overflow case, the pressure acting area decreases because of the insufficient seawall height and the acting pressure itself also decreases because of the overflow. In this study, mainly for the seawalls, the physical model tests were conducted to examine the tsunami force characteristics when tsunami overflows the structure, and the estimation method of the tsunami force acting on land structures by the overflow tsunami was proposed and verified. (author)