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341.
Predicting particle deposition on HVAC heat exchangers 总被引:2,自引:0,他引:2
Jeffrey A. Siegel William W Nazaroff 《Atmospheric environment (Oxford, England : 1994)》2003,37(39-40):5587
Particles in indoor environments may deposit on the surfaces of heat exchangers that are used in heating, ventilation and air conditioning (HVAC) systems. Such deposits can lead to performance degradation and indoor air quality problems. We present a model of fin-and-tube heat-exchanger fouling that deterministically simulates particle impaction, gravitational settling, and Brownian diffusion and uses a Monte Carlo simulation to account for impaction due to air turbulence. The model predicts that <2% of submicron particles will deposit on heat exchangers with air flows and fin spacings that are typical of HVAC systems. For supermicron particles, deposition increases with particle size. The dominant deposition mechanism for 1–10 μm particles is impaction on fin edges. Gravitational settling, impaction, and air turbulence contribute to deposition for particles larger than 10 μm. Gravitational settling is the dominant deposition mechanism for lower air velocities, and impaction on refrigerant tubes is dominant for higher velocities. We measured deposition fractions for 1–16 μm particles at three characteristic air velocities. On average, the measured results show more deposition than the model predicts for an air speed of 1.5 m s−1. The amount that the model underpredicts the measured data increases at higher velocities and especially for larger particles, although the model shows good qualitative agreement with the measured deposition fractions. Discontinuities in the heat-exchanger fins are hypothesized to be responsible for the increase in measured deposition. The model and experiments reported here are for isothermal conditions and do not address the potentially important effects of heat transfer and water phase change on deposition. 相似文献
342.
运用LCA技术可从全过程的视角识别和比较不同城市污水处理工艺在其生命周期各个阶段的能耗,并在此基础上提出改善其能效的措施。运用LCA方法对AB活性污泥法处理系统从其原材料开采和加工开始直到污水厂施工建设、处理运行以及废弃拆除的LC全过程能耗进行了识别和量化分析,并与普通活性污泥法进行了平行对照。研究结果表明,AB法的LC能耗在微孔和穿孔管两种曝气条件下可双普通活性污泥法分别节省9.5%和15.8%,但由于污水中有机物大部分转化为污泥形态,其比能耗仅与普通活性污泥法相当。AB法处理系统污泥的稳定化处理已成为提高其能效的重要途径。 相似文献
343.
二氧化碳储存技术的研究现状和展望 总被引:19,自引:0,他引:19
为了减少因温室效应造成的危害,必须大量减少CO2的人为排放.将化石燃料燃烧产生的CO2进行储存(尤其是地下储存)能够长期、有效地阻止大气中CO2浓度的增加.通过对CO2储存技术研究现状的介绍,对中国今后开展CO2地下储存技术提出了建议和研究方向. 相似文献
344.
When a chemical tank fire happens in a storage area, it is very important to protect adjacent tanks so as to decrease fire accident losses. In this paper, a new thermal protection method was put forward based on a PPH (potassium polyacrylate & hectorite) thermal insulation composite material spraying on an adjacent tank under fire. Firstly, the PPH material was prepared successfully by a polymerization reaction of potassium acrylate, hectorite, NaHSO3 and (NH4)2S2O8. Secondly, thermal insulation performance of the PPH material was characterized by heat transfer process at high incident heat flux using cone calorimeter. The results show that thermal insulation performance of the PPH material is affected by a content change of (NH4)2S2O8, NaHSO3 and hectorite in formulations. The content of (NH4)2S2O8 0.14 wt%, NaHSO3 1.38 wt% and hectorite 1.4 wt% was an optimum formulation ratio to obtain best thermal insulation performance. Finally, possible thermal insulation mechanisms of the PPH material were presented using SEM, TG and TG-IR techniques. One of the thermal insulation mechanisms is the incident heat flux absorbed by water evaporation from the PPH material. Another is the thermal protection of the char formed from the PPH material at high incident thermal radiation, which can prevent heat and mass transfer. 相似文献
345.
《京都议定书》的生效、CDM项目活动在全球的广泛开展为发展中国家寻求经济和环境的共赢发展带来了前所未有的机遇,中国的经济正处于高速发展中,在未来的国际CDM市场中必将扮演重要的角色。虽然我国在开发CDM项目、促进温室气体减排方面做出了突出的贡献,但仍然存在项目分布不合理、信息不对称、偏离方法学等明显问题。面对未来可以预见的国际环境压力,我们应当加强管制,充分利用好CDM的机遇。在借鉴印度、巴西等其他发展中国家的做法、总结自身经验和不足的基础上,提出CDM项目的管制建议,在政策引导、宣传培训、项目选择和方法学应用等方面调整CDM项目的发展策略,为我国的参与CDM带来更为巨大的商机和活力。 相似文献
346.
347.
348.
Michael J. Scott James A. Dirks Katherine A. Cort 《Mitigation and Adaptation Strategies for Global Change》2008,13(4):307-339
US residential and commercial buildings were responsible for about 41 exajoules (EJ) of primary energy use per year in 2002,
accounting for approximately 9% of the world fossil-fuel related anthropogenic carbon (C) emissions of 6.7 Gt that contribute
to climate change. US Government-sponsored building energy efficiency research and implementation programs are focused on
reducing energy consumption in US residential and commercial buildings and reducing these carbon (C) emissions. Although not
specifically intended for adaptation to a warmer climate and less effective than under today’s cooler climate, these programs
also could help reduce energy demand in a future warmer world. Warming scenarios projected by the United Nations Intergovernmental
Panel on Climate Change (IPCC) in 2001 imply net overall decreases in both site energy and primary energy consumption in US
residential and commercial buildings, largely because of the reduced need for heating. However, there would be as much as
a 25% increase in building space cooling demand and a significant part of the increase could be offset by energy-efficiency
improvements in buildings. Overall, in the US, buildings-related energy efficiency programs would reduce site energy consumption
in buildings in the US by more than 2 EJ in 2020 and primary energy by more than 3.5 EJ, more than enough to offset the projected
growth in cooling energy consumption due to climate change and growth in the US building stock. The savings would have an
estimated annual net value at 2005 energy prices of between $45.0 and $47.3 billion to consumers.
相似文献
Michael J. ScottEmail: |
349.
Green sea turtles (Chelonia mydas) are renowned for their long-distance migrations but have less fame for short-distance migrations or non-migratory behavior. We present satellite telemetric evidence from Cocos (Keeling) Islands, Indian Ocean for the first predominantly non-migratory green sea turtle (C. mydas) population. The mean migration distance from the nesting beach to the foraging grounds was 35.5 km with a maximum mean transit time of 3.4 days. The behavior of this population has major implications for our general understanding of green turtle behavior and their life cycle and for conservation. Firstly, these results indicate a level of juvenile or adult non-breeding homing behavior from the open ocean to foraging grounds adjacent to their natal nesting beach. Secondly, a non-migratory breeding phase reduces the consumption of reproductive energy utilized, potentially resulting in higher fecundity for this population. Thirdly, the close proximity of the nesting and foraging habitats allows for uniformity in management and conservation strategies rarely possible for wide-ranging green turtle populations. 相似文献
350.
We examined the risk-sensitive foraging behaviour of the round-eared elephant shrew by open-economy choice experiments, in which animals were deprived of food immediately prior to experiments but given food ad libitum afterwards, to test the energy budget rule. The energy budget rule states that if an animal's (daily) energy budget is negative it should behave in a risk-prone manner. A risk-prone elephant shrew should select food from a more variable rather than a constant feeding station, although both feeding stations yield the same average return. The choice of a variable station can indicate the degree to which an animal is an energy-shortfall minimizer. Elephant shrews running below energy requirement did not choose feeding stations in accordance with the rule. Under laboratory conditions, approximating either average summer or winter temperatures, elephant shrews showed risk-averse behaviour. A polycyclic activity profile, the ability to switch the diet, and greater than expected physiological control over energy balance, may favour a continuously foraging animal such that short-term energy deficits are minimized. We argue that, under these conditions, a risk-averse response to reward-size variance is expected, because an elephant-shrew may not reliably perceive those circumstances under which risk-prone behaviour should be adopted. 相似文献