Studies on the effect of temperature and time on the SS 304 surface for the properties degradation of the solar collector

The properties of emissivity (?) and absorptivity (α) of the surface of the material is an essential output for the solar collector. This paper highlights the work based on the RSM design expert, to study the effect of parameters’ temperature and time when the surface is exposed to sunlight and absorbing the properties of emissivity and absorptivity of the material SS 304. The temperature range of the SS 304 varied from 20°C to 356°C for various time intervals from 90 to 1100?h. From this experimental work, it is clearly seen that the emissivity rate increased when the surface is focused onto sunlight beyond the saturated level. The absorptivity of the surface of SS 304 increases till the optimum level and reaches the saturated level. As a result, after the optimum level, emissivity rate of the surface increases, and absorptivity of the surface decreases when it is focused onto sunlight.     

蒙脱石含量测定方法改进研究

用吸蓝量(MB)换算法测定蒙脱石含量,换算系数0.442不能用来准确计算其实际含量。由于吸蓝量和阳离子交换容量(CEC)与蒙脱石含量正相关,通过测定原矿、原矿提纯样以及提纯后杂质矿物的吸蓝量或CEC,进行加权或对比计算,即可得到原矿中蒙脱石的含量,这样可消除膨润土属性、属型等对测定结果的影响。改进的结果表明,不论加权法还是比值法,CEC也可用于测定蒙脱石含量;但加权法计算更为合理。蒙脱石、杂质矿物的纯度,以及它们的吸蓝量、CEC的精密度和准确度,是加权法测定准确与否的关键;比值法适用于细粒级或提纯后纯度较高情况下的测定。     

不同水胶比及养护条件对内养护混凝土吸水性能的影响

为了研究预湿轻骨料的内养护效率受混凝土自身水胶比和外界养护条件的影响，采用改进的ASTM 1585试验方法，开展了不同水胶比、不同养护条件（饱和石灰水养护、喷雾养护、密封养护、干燥养护）下普通混凝土及内养护混凝土毛细吸水试验。从混凝土的水化程度、混凝土孔隙率等角度，解释了水胶比、养护条件以及内养护材料对混凝土中水分传输的影响。结果表明：水胶比、养护条件以及内养护材料的掺入对混凝土中水泥的水化和混凝土材料的孔隙率有较大影响。高水胶比试件比低水胶比试件具有更大的累积吸水量及二次吸水率，水胶比为0.5的试件的累积吸水量及二次吸水率分别为水胶比为0.3的试件的1.4~2.1倍和3~4倍；预湿轻骨料的掺入对高水胶比试件的累积吸水量、初始吸水率和二次吸水率的改善作用并不明显，但可以显著降低低水胶比试件的吸水能力，对于水胶比为0.3的试件，其累积吸水量和二次吸水量的降低幅度分别为7.7%~18.6%和20.4%~27.4%；随着外界养护环境湿度的降低，低水胶比试件的初始吸水率变化较小，累积吸水量和二次吸水率有轻微的上升；预湿轻骨料在低水胶比、密封养护条件下内养护效率较高。     

粉煤灰加气混凝土吸水性能研究

试验表明,当粉煤灰加气混凝土在整体吸水时的吸水速度和吸水量明显大于粘土砖;粉煤灰加气混凝土一端吸水时的吸水性能与其成型时的膨胀方向密切相关,当吸水方向平行于加气混凝土膨胀方向时,粉煤灰加气混凝土的吸水速度和吸水量明显大于粘土砖;吸水方向垂直于加气混凝土膨胀方向时,粉煤灰加气混凝土的吸水速度和吸水量小于粘土砖。     

Experimental investigation on degradation of heat transfer properties of a black chromium-coated aluminium surface solar collector tube

ABSTRACT

In our earlier research, we have studied the surface radiation property degradation of the solar collector receiver tube material [Logesh, K., R. Ganesh, I. Saran Raj, V. Ramesh, and B. Tharun Raj. 2017. “Experimental Investigation on Radiation Heat Transfer Properties Degradation of Aluminium Solar Receiver Tube Material.” International Journal of Ambient Energy. doi:10.1080/01430750.2017.1335230]. In this study, the examination is expanded to degradation property of the selective surface, black chromium-coated aluminium material. Black chrome is mainly used for its high corrosion resistance. The selective surface has been examined for its emissivity (ε) and absorptivity (α) changes due to its sunlight exposure at elevated temperatures. The exposure duration ranges from 240 to 960?h. In the selected range of exposure, the properties are measured in four intervals. The emissivity (ε) is found to decrease, whereas the absorptivity (α) gets increased for coated than the uncoated surfaces for the same duration of exposure. The examination is also carried out to find the nature of the heat transfer properties determined by its temperature. For every duration of exposure, the properties are measured at 10 temperature intervals.     

Postflashover fires — an overview of the research at the national research council of Canada (NRCC), 1970–1985

The NRCC model of fully developed compartment fires is discussed. Although the mathematics involved is quite simple, it allows a rather comprehensive simulation of the fire process. The model offers an explanation for the findings that ventilation control is related to the pyrolysis mechanism and is not a result of scarcity of air in the fire compartment, and that thermal feedback is of secondary importance in the burning (pyrolysis) of cellulosic fuels. Another feature of the model is the introduction of the normalized heat load concept. The normalized heat load is a scalar quantity that depends on the total heat absorbed by the compartment boundaries during the fire incident, and is practically independent of the temperature history of the fire. A simple explicit formula has been proposed and proved experimentally to describe the normalized heat load for real-world fires with fair accuracy. The normalized heat load concept offers a simple means for converting fire severities into fire resistance requirements, and makes it possible to design buildings for prescribed levels of structural fire safety. The potential of fires to spread by convection and the expected characteristics of fires of noncharring plastics are also discussed. Reference: T. Z. Harmathy, Postflashover Fires—An Overview of the Research at the National Research Council of Canada (NRCC), 1970–1985,Fire Technology, Vol. 22, No. 3, August 1986, p. 210.     

室内音质设计中新材料应用实践

在室内音质设计中,吸声材料起到控制混响时间和吸声降噪的作用。近年来,随着声学材料水平和室内声学装修设计水平的大幅提升,越来越多兼具良好吸声性和美观性,且卫生环保的新型吸声材料进入声学装修市场。本文介绍了4种新型吸声材料通过混响室法测得的吸声特性,并结合实际工程项目,介绍了它们在室内音质设计中的应用效果。     

Experimental investigation on surface radiation properties’ degradation of solar collector receiver tube material

In this study, we have investigated the degradation characteristics of surface radiation heat transfer properties of stainless steel 304. The emissivity (ε) and absorptivity (α) of stainless steel has been measured for a surface unexposed to sunlight and that exposed to sunlight for various time intervals (240, 480, 720, and 960?h). The temperature dependence of these properties is also measured for the temperature range of 30–300°C at 10 equal intervals. It is observed that the emissivity of the material increased when it is exposed to sunlight and the temperature dependence is very strong beyond 180°C. The absorptivity of the material increases first and then starts to decrease with exposure time. The combined effect of decrease in absorptivity and increase in emissivity leads to reduction in aS/E ratio, which results in a higher rate of radiation loss for exposed surfaces when compared to that for the unexposed surfaces.     

Spectrally selective and adaptive surfaces for protection against radiative heating: ITO and VO2

Two surface materials for reducing absorptivity of heat radiation from fires have been investigated. The first is VO₂, which is a thermochromic material. When the temperature of a VO₂ surface increases over a certain temperature, it switches, ideally, from infrared (IR)‐absorbing to IR‐reflecting. VO₂ window coatings are still on a research level, yet to be commercialized. In this study, VO₂ powder available on the market was investigated. The thermochromic effect could be identified but was not large enough to significantly improve the fire properties of treated surfaces. Some thoughts concerning how to improve the performance of VO₂ are discussed. The second investigated material is indium tin oxide (ITO), which is a so called low‐e coating, which means that it has low emissivity and absorptivity in the IR part of the spectrum. ITO is spectrally selective in the sense that it transmits visible light while reflecting a large fraction of the IR radiation, which is a rare property for surfaces in general but a typical property of thin electrically conducting non‐metallic films. It is shown that the application of ITO to poly(methyl methacrylate) (PMMA) significantly improves its fire properties. ITO coating is a mature technology already in widespread use today in the electronics industry. Copyright © 2012 John Wiley & Sons, Ltd.