Flammability limits of five selected compounds each mixed with HFC-125

Flammability limits of five selected combustible gases each mixed with 1,1,1,2,2-pentafluoroethane (HFC-125) were investigated. Actually, the investigation was made for methane, propane, propylene, methyl formate, and 1,1-difluoroethane (HFC-152a). The observed data were analyzed using the extended Le Chatelier's formula. As a result, the HFC-125 mixing effect on the flammability limits of individual gases was found to be adequately interpreted using the extended Le Chatelier's formula. However, contrary to the cases of nitrogen and carbon dioxide dilutions, it was not possible to appropriately interpret the HFC-125 mixing effects on all five gases simultaneously using a common set of parameter values. This fact suggests that the reaction of HFC-125 in flame is different if the coexisting fuel is different.     

On the pressure dependence of flammability limits of CH2=CFCF3, CH2F2 and methane

Flammability limits of CH₂=CFCF₃ (HFO-1234 yf), CH₂F₂ (HFC-32), and methane were measured at pressures from ambient to 2500 kPa in a 5 l stainless-steel spherical vessel. For HFO-1234 yf, as the pressure rises from ambient, the lower flammability limit is shifted downward and the upper limit is shifted upward. The changes to the lower flammability limits are, in general, small compared to the upper flammability limits. Both the lower and upper flammability limits of this compound can be approximated by simple logarithmic functions of pressure. For HFC-32, the behavior of lower flammability limit is similar to that for HFO-1234 yf, but the behavior for the upper limit is rather complicated. As the pressure is increased, it begins to rise upward gradually. Then, as the pressure becomes larger than about 1000 kPa it begins to rise upward rapidly, and then the change becomes moderate again. This must be due to a change of combustion reaction mechanism below 1000 kPa and above 1500 kPa in the upper flammability limit region for this compound. On the other hand, both the flammability limits of methane change almost linearly with pressure, at least in the pressure region considered.     

利用管状火焰燃烧器测量混合气惰化体积分数的技术 --关于可燃混合气易燃极限测试方法的研究

为了评价卤代烷替代灭火剂的灭火性能，对传统的使用爆炸量管的惰化体积分数的测试方法进行了理论和实际的探讨，指出传统方法测试的是点火界限而非灭火界限，其测试结果受众多因素的影响可信度差，操作繁杂不利于获取数据。作为传统方法的替代，该研究试制了管状火焰燃烧器测试装置，利用其测量了各种卤代烷替代灭火剂对不同可燃混合气的惰化体积分数。结果表明，该方法具有理论合理、操作简便、数据可靠等优点，适用于各种可燃性混合气的可燃区域的测试及气体灭火剂的灭火性能的评价。     

Corn's cob as a potential ecological thermal insulation material

Tabique construction is one of the main Portuguese traditional building techniques that use earth based building materials. It is peculiar building technique which uses corn's cob as a filling material for the external tabique walls. The existing tabique construction in Trás-os-Montes e Alto Douro region of northeast Portugal was studied to learn from it for modern day construction. The research showed that corn's cob, an agricultural waste, has the potential to be used as a sustainable building material for thermal insulation. An experimental work concluded that there are significant similarities between the corn's cob and the extruded polystyrene (XPS) material in terms of microstructure and chemical composition. Furthermore, the results obtained from an expeditious experimental thermal procedure indicate that the corn's cob may have adequate thermal properties for building purpose.     

A new virtual sphere method for estimating the role of thermal mass in natural ventilated buildings

The role of thermal mass is very important in natural ventilated buildings. Thermal mass can be classified as external thermal mass and internal thermal mass. In this paper, a heat balance model for naturally ventilated building is developed. The effect of external thermal mass is introduced by harmonic response method, and the effect of internal thermal mass is calculated by virtual sphere method which can lump different shapes and types into one virtual sphere. The effective convection heat transfer coefficient is presented to represents the effect of uneven distribution of internal thermal mass temperature. Through comparison with Li's model [1] and numerical calculation, it was found that the model is more suitable than the others, especially in estimating decrement factor of indoor air temperature. The errors of time lag become smaller when the fluctuation of indoor air temperature is smaller. Based on the model, a simple tool is developed to evaluate the indoor air temperature and required internal thermal mass for certain naturally ventilated buildings.     

Extreme value theory applied to the definition of bathing water quality discounting limits

The European Community Bathing Water Directive (European Parliament, 2006) set compliance standards for bathing waters across Europe, with minimum standards for microbiological indicators to be attained at all locations by 2015. The Directive allows up to 15% of samples affected by short-term pollution episodes to be disregarded from the figures used to classify bathing waters, provided certain management criteria have been met, including informing the public of short-term water pollution episodes. Therefore, a scientifically justifiable discounting limit is required which could be used as a management tool to determine the samples that should be removed. This paper investigates different methods of obtaining discounting limits, focusing in particular on extreme value methodology applied to data from Scottish bathing waters. Return level based limits derived from threshold models applied at a site-specific level improved the percentage of sites which met at least the minimum required standard. This approach provides a method of obtaining limits which identify the samples that should be removed from compliance calculations, although care has to be taken in terms of the quantity of data which is removed.     

The HC value: A method for estimating the flammability of mixtures of combustible gases

The authors discuss the use of the ratio of gas concentration to its lower flammable limit in estimating the flammability of combustible gas mixtures.     

A new predictive index for evaluating both thermal sensation and thermal response of the human body

About 20 years ago, Ring and de Dear [Ring JW, de Dear R. Temperature transients: A model for heat diffusion through the skin, thermoreceptor response and thermal sensation. Indoor Air 1991; 1(4):448–56] introduced a thermal response index (R) for evaluating the cutaneous thermoreceptor response and thermal sensation. Although the mentioned index possesses the advantages of simplicity and sensitivity, it has not been commonly used over the years. The main reason for this infrequent using is that the mentioned index is not in conformity with the ASHRAE standard thermal sensation scale. To remedy this deficiency we try to present a new predictive index by finding a relationship between the thermal response index (R) and ASHRAE thermal sensation scale. In the present study, a new thermal response index, TRESP, is introduced on the basis of Ring and de Dear model. The TRESP index has been verified by extensive comparisons with the published analytical and experimental results where a good agreement was found under both steady-state and transient conditions. Results indicate that the new index can accurately predict the thermal sensation with average absolute errors of 0.19 and 0.28 under steady-state and transient conditions, respectively.     

Application of human thermal load into unsteady condition for improvement of outdoor thermal comfort

Human thermal comfort is studied as a countermeasure to the thermal stress in outdoor urban space. Outdoors, people experience the strong impact of solar radiation in states that are unsteady and non-uniform. The feeling of comfort is a mixed sensation that can be easier to improve overall, as compared with a global large-scale effort, and can lead to improved ways of saving energy and reducing costs. Moreover, this can be directly beneficial to human experience and fulfill natural human desires. Since a thermal comfort index is a useful tool for understanding the present state and evaluating the impact of countermeasures, we examine the effects of the human thermal load, which is a thermal comfort index based on the energy balance of the human body. In a steady state, and even in an unsteady state with its variations in weather and human factors, thermal comfort values can generally be obtained by using the overall human thermal load. The reason for this is that the human thermal load takes physiological factors in account as well as weather parameters. This leads to the idea that thermal sensations follow from the human thermal load, which can then well describe a given human environment. As a result, human sensations as expressed by the human thermal load pave the way to the creation of comfortable urban spaces that require minimum expense and energy as an example of simple heat transport model focusing on urban outer structure.     

A new model based on experimental results for the thermal characterization of bricks

The development of fast and reliable protocols to determine the characteristics of building materials is of importance in order to develop environmentally friendly houses with an efficient energy design. In this article heat flux evolution on different types of clay and concrete bricks has been studied using a guarded hot-plate. The studied bricks were purchased from local commercially available sources and included a solid face brick and a range of honeycombed and perforated bricks. From the data collected a new model to study heat flux is proposed. This model is based on the shape of the typical sigmoidal curves observed for the time dependent heat flux evolution. The model allows the calculation of the thermal resistance (R) and the heat flux in the steady-state (φ_∞). The model also calculates two new parameters, t_B and τ_B. t_B represents the time at which half φ_∞ is attained. This parameter (t_B) has additionally been found to be dependent on the thermal diffusivity and the geometric characteristics of the brick.     

AC类基质沥青混合料最大理论相对密度分析

对AC类基质沥青混合料最大理论密度与计算最大理论密度进行了分析,结果表明:两种最大理论密度之间有着很好的相关性,同时对同一个试件进行了空隙率计算,结果相差甚小,为缺乏试验仪器且试验量较大的沥青路面工程的体积参数计算提供参考.     

A study on the thermal comfort in sleeping environments in the subtropics—Developing a thermal comfort model for sleeping environments

In the subtropics, air conditioning serves to maintain an appropriate indoor thermal environment not only in workplaces during daytime, but also at night for sleeping in bedrooms in residences or guestrooms in hotels. However, current practices in air conditioning, as well as the thermal comfort theories on which these practices are based, are primarily concerned with situations in which people are awake in workplaces at daytime. Therefore, these may not be directly applicable to air conditioning for sleeping environments. This paper, reports on a theoretical study on a thermal comfort model in sleeping environments. A comfort equation applicable to sleeping thermal environments was derived by introducing appropriate modifications to Fanger's comfort model. Comfort charts which were established by solving the comfort equation, and can be used for determining thermally neutral environmental conditions under a given bedding system have been developed. A related paper reports on an experimental study on measuring the total thermal insulation values of a wide range of bedding systems commonly used in the subtropics, which are an essential input to the comfort equation developed and reported in this paper.     

谈对混凝土拌和物工作性的认识

对混凝土拌和物的工作性及其测定作了论述,并分析了影响混凝土拌和物工作性的主要因素,在此基础上提出了改善混凝土拌和物工作性的措施,以使硬化后的混凝土满足设计强度及耐久性要求。     

沥青混合料的施工配合比设计

结合工程实践,对沥青混合料的配合比组成设计进行了总结,从各种材料的准备和选用、沥青混合料的目标配合比设计及生产配合比设计三个方面进行了深入探讨,从而优化沥青混合料的配合比,保证工程质量.     

沥青混合料不均匀性的原因分析及防治措施

从原材料、生产配合比、拌和、运输、摊铺等几个环节详细分析了沥青混合料不均匀性产生的原因及所采取的有效防治措施，以期最大限度减少沥青混合料不均匀性的产生。     

A criterion for the assessment of the reliability of ASHRAE conduction transfer function coefficients

This paper presents a new mathematical approach, which, when applied to conduction transfer functions (CTFs) of a multi-layered wall, is able to predict the reliability of building simulations. This new procedure can be used to identify the best set of CTF coefficients, which are a critical point at the core of the ASHRAE calculation methodology founded on the transfer function method. To evaluate the performance of different CTF coefficient sets, the authors performed a large number of thermal simulations on the multi-layered walls included in the ASHRAE Handbook, volume fundamentals, and on other walls typical of Mediterranean building heritage. Those data were employed to test an algorithm able to assess the reliability of the simulations. The numerical results show that it is possible to select the optimal number of coefficients on the basis of the size of the poles of a CTF. The proposed criterion, which employs a pole threshold value, is highly accurate, fast and easy to integrate in the most diffuse building simulation tools.     

Formal and statistical aspects of estimating Okun's law at a regional level

The paper challenges the common practice of estimating Okun's law at a regional level and investigates the mathematical and statistical model valid for regional applications. Confining to the difference version of Okun's law, the paper demonstrates that if a trade-off between output fluctuations and fluctuations in the labour market is to hold on an economy-wide level, a completely different specification of Okunian equations ensues for regions than is currently considered in research studies on the topic. An econometric approach is proposed to provide estimates of Okunian equations compliant with the disaggregation model, and the issue is demonstrated for Italian regions.     

基于关联规则的儿童户外活动空间偏好 研究——以杭州三个社区公园为例

社区公园是儿童户外活动的重要承载空间。研究儿 童在社区公园的行为偏好及空间需求对增加儿童户外活动机 会、提升社区公园品质和促进环境公平具有重要意义。以杭州 市3个社区公园为研究对象,采用行为注记法获取儿童活动空 间分布特征,运用关联规则、核密度分析和多因素方差分析等 方法,研究儿童户外活动与社区公园空间和环境要素之间的关 系。研究发现,社区公园中儿童不同活动类型对空间的偏好度 存在显著差异：自然活动对特定空间的偏好度最高,主要集中 在有沙、水体和草坪的空间;功能活动和规则活动的空间偏好 度次之,多发生在器械区、广场等设施丰富或面积较大的场 地;休闲活动与大部分空间都具有关联性,分布较均衡。设 施、基底类型和植被覆盖等环境要素与儿童活动空间选择的关 联性较强。以此为基础,提出以儿童活动偏好为导向的社区公 园规划设计建议。     

A new thermal performance index for dwelling roofs in the warm humid tropics

This research aims to find a scientific rating scheme for roof system for the warm humid tropics. The overall air-to-air thermal transmittance (U-value) or thermal resistance (R-value) of roof are most widely used properties, but these are based on steady-state heat conduction and do not respond to changing conditions of climate, design and comfort needs. The paper presents a new thermal performance index, which is based on thermal comfort and actual thermal performance of a roof design option. It provides a basis for identifying the optimum roof design for unconditioned and acclimatised regimes. A review of the acceptable limits of ceiling surface temperature is presented. The mathematical modelling for predicting performance of roof based on admittance procedure and derivation of thermal performance index is described. In the proposed scheme the galvanized iron roof is given 0% rating and the roof satisfying the comfort needs for the given climate is rated as 100%. Illustrative examples of built roofs or design options are taken from India and Australia. It clearly shows that the roofs with the highest thermal resistance are not necessarily optimum solutions.     

沥青混合料剪切性能影响因素研究

采用单轴贯入试验和无侧限抗压试验,分别对沥青类型、级配类型、油石比对沥青混合料剪切性能的影响进行研究,结果表明:沥青的类型会直接影响到混合材料所具备的剪切性能,不同沥青类型的混合料的内摩擦角、粘聚力C以及剪切强度三个指标方面相差较大;级配类型对沥青混合料剪切性能具有很大的影响,特别是对沥青混合料的粘聚力C和剪切强度影响很大。