Stress analysis in cylindrical pressure vessels with loads applied to the free end of a nozzle

This paper contains a stress analysis of a cylindrical pressure vessel loaded by axial and transverse forces on the free end of a nozzle. The nozzle is placed such that the axis of the nozzle does not cross the axis of the cylindrical shell. The method of finite elements was applied to determine the state of stress in the cylindrical shell. The values obtained for stress in the nozzle region were used to determine the following: envelopes of maximum stress values; maximum values on these envelopes; and distances between maximum values on envelopes and the outer edge of the nozzle. Algebraic functions were determined, which enable easy and simple determination of these numerous stress values. The stress values obtained from the algebraic function were within −12.5 and +12.8% of those from finite elements. The difference between stresses deduced from strain gauge readings on experimental and calculated stresses was a maximum of 12%.     

Energy-Efficient Building Envelopes with Phase-Change Materials: New Understanding and Related Research

Thermal performance of building envelopes is important in improving building energy efficiency. This paper includes three parts: (1) It introduces our new understanding of developing optimized or ideal building envelopes based upon inverse problems and their solutions, which is helpful for energy efficient building envelope structure design and material development. (2) It reviews our recent research on developing energy-efficient building envelopes with phase-change materials, including the optimized thermal mass characteristics of building wall, novel phase-change material development, measurement method for thermal physical properties of phase-change material, and application of some prototype energy efficient building envelopes. (3) It puts forward some limitations of the available works and related research topics for future study.     

Optical collection efficiencies of arrays of tubular collectors with diffuse reflectors

The fractions of solar radiation collected by arrays of cylindrical absorbers with diffuse reflectors of various shapes have been found using a Monte-Carlo ray tracing technique. The results for configurations with black absorbers with no outer glass envelopes and various shapes and positions of the diffuse reflector show that there is little to be gained in having curved diffuse reflectors when the finite absorptance of the reflector is included, and that there is an optimum position for a planar diffuse reflector.The fractions of solar radiation collected for arrays of modules with outer glass envelopes and selective absorbers, situated above a plane diffuse reflector, have been calculated for variable module spacings in the range 1.5-3 absorber tube diameters. The calculations include the effects of polarisation and angle of incidence on the reflectance of the outer envelope and the selective absorber, and the effect of absorption in the glass envelope and by the reflector. Multiple reflections or second chance effects play an important role in increasing the fraction absorbed over what is predicted with simple theories.The curves derived for the model with realistic properties of the components are useful for designing collectors. Tube spacings less than two diameters produce only small increases in collector performance. Collectors made with the modules aligned E-W rather than N-S will be less efficient, but the difference will be small ( 5 per cent).     

Numerical assessing energy performance for building envelopes with phase change material

In hot climate, phase change material (PCM) can be incorporated into building envelopes to reduce heat gain through the building envelopes and therefore reduce its cooling demand. In this study, the energy performance of building envelopes integrated with PCM has been explored using a popular dynamic building performance simulation package, EnergyPlus, and the energy saving mechanism of PCM was investigated. The simulation results reflected that PCM could effectively help to reduce the building's annual energy consumption by 20.9% for Guangzhou, China. In addition, for the Guangzhou city, 27°C transition temperature, smaller thermal conductivity of roof, and higher amount of PCM can all help to improve the building's energy performance. Additionally, it is suggested that in real building development/retrofit projects, the selection of PCM needs to be based on both their thermal properties and the local climatic conditions of the building.     

Analysis of design approaches to improve the comfort level of a small glazed-envelope building during summer

An architect applies glazing to a building envelope to express an expansiveness and hi-tech quality through transparency. However, in small over-glazed buildings, the glazed envelopes often lead to an inadequate comfort level in summer, when much cooling energy is needed to improve the comfort level and occupants are forced to avoid the use of glazed envelopes. This paper presents the results of comfort survey and measurements on the indoor environment of an architecturally significant small glazed-envelope building that has received many awards for its architectural design quality, and analyzes design approaches to improve the comfort level of its occupants. During the late summer of 2002, the comfort survey was conducted, polling responses from 57 office workers, while simultaneously measuring air/surface temperatures and daylight factors. Numerical simulations were performed to investigate 13 design approaches for the improvement of the comfort level. From the temperature/daylight factor measurements, the indoor air temperature did not maintain the set-point temperature of 24.0 °C even with the operation of the air-conditioning system. When using the roller shades, the intensities of illumination and luminance on each measured desk surface were unevenly distributed from 650 Lux and 51 cd/m² to 6291 Lux and 310 cd/m². From the survey, office workers suffered thermal discomfort and uncomfortable glare from high or non-uniform brightness distributions in the working areas. From the numerical analyses using computer simulations, the double-skin envelopes with the sufficient intermediate space and shading devices were suggested to improve the comfort level.     

Application of infrared thermography for the determination of the overall heat transfer coefficient (U-Value) in building envelopes

Infrared (IR) thermography constitutes a reliable measurement method for the determination of spatially resolved surface temperature distributions. IR thermography may be used for several research problems, applications, and measurement environments with a variety of physical arrangements. In this work the results of the determination of the overall heat transfer coefficient (U-Value) with the use of IR thermography for building envelopes are presented. The obtained U-Values are validated by means of measurements performed with the use of a thermohygrometer for two seasons (summer and winter), as well as with the notional results provided by the relevant EN standard. Issues related to the applicability of the method due to the non-steady heat transfer phenomena observed at building shells are also discussed. A more precise validation of the proposed technique was also performed with the use of heat flux meters. The percentage absolute deviation between the notional and the measured U-Values for IR thermography is found to be in an acceptable level, in the range of 10–20%. Finally, a sensitivity analysis is conducted in order to define the most important parameters which may have a significant influence on the measurement accuracy.     

An image processing technique for automatically detecting forest fire

In this paper we present an automatic system for early smoke source detection through the real time processing of landscape images. The first part describes the segmentation technique we use to extract persistent dynamical envelopes of pixels into the images. We describe the temporal algorithm at the pixel level (filtering) and the spatial analysis to bring together connected pixels into the same envelopes (object labeling). The second part deals with the method we use to discriminate the various natural phenomena that may cause such envelopes. We describe the image sequence analysis we developed to discriminate distant smokes from other phenomena, by extracting the transitory and complex motions into little pre-processed envelopes. We present then our main criterion for smoke recognition based on the analysis of the smoke plumes velocity.     

Sensitivity analyses of convective and diffusive driving potentials on combined heat air and mass transfer in hygroscopic materials

ABSTRACT

The focus of this paper was to examine the contribution of two key mechanisms—moisture convection and diffusion–on heated air and moisture transfer in porous building envelopes and to define the validity of the sub-models. A numerical simulation was performed and is focused on the one-dimensional problem for drying test boundary conditions. Thereafter, a detailed parametric analysis was carried out in order to investigate the influence of typical nondimensional parameters. Results show that convection is a prominent driving potential with respect to the diffusion process when the hygric state is stable between the environment and the envelope.     

Diagnosis of fuel cells using instantaneous frequencies and envelopes extracted from stack voltage signal

The work carried out aims to diagnose fuel cells with reduced instrumentation and computation times. The article describes a non-intrusive, application-oriented diagnostic tool, based on the sole measurement of the stack voltage and requiring no specific external excitation of the electrochemical generator. The adopted data-driven method relies on well-suited signal analysis techniques (fast calculations of relevant fault signatures based on envelopes and instantaneous frequencies) and information processing (pattern recognition). A wide range of operating regimes can be identified (variations in flow rates, pressures, temperatures; combinations of simultaneous faults), even when they correspond to small deviations from nominal conditions. The portability of the method has been studied on two PEMFC stacks, designed for different applications: transport and stationary. Correct classification rates close to 98% are obtained in both cases.     

Soot formation, spray characteristics, and structure of jet spray flames under high pressure

Coaxial jet spray flames of kerosene and oxygen are experimentally studied over a pressure range of 0.1–1.0 MPa to determine the relationship between flame structure, droplet behavior, and soot formation region, which varies with changes in pressure. The direct images and chemiluminescence spectra show that the spray flames have three regions: the blue flame region, which has a peak of CH* and C₂* radical chemiluminescence, luminous flame region caused by soot emission, and blue emission region caused by CO₂ emission. With increase in ambient pressure, the flame length shortens drastically, the luminous flame region envelopes the blue flame region, and the blue emission becomes more intense. The result of phase-Doppler anemometry shows that a large number of small droplets evaporate and disappear near the burner, and the evaporation of large droplets also occurs rapidly under high pressure. The result of temperature measurements shows that high-temperature regions appear near the burner. The flame temperature drastically decreases along the central axis, and a minimum temperature point appears. This point moves upstream with increase in ambient pressure because evaporation of the droplets occurs further upstream. A laser-induced incandescence measurement shows that the soot volume fraction does not monotonously increase or decrease with increase in ambient pressure. The soot volume fraction at the central axis becomes low upstream and high downstream. As pressure increases, the vertical position at which the peak of soot volume fraction appears at the central axis moves upstream.     

Angular dependence of optical efficiency of evacuated tubular collectors with antireflection coatings and stationary specular reflectors

The efficiencies of η₀ of arrays of evacuated tubular collectors with non-imaging specular reflectors have been determined experimentally using a calorimetric technique and theoretically using a Monte-Carlo ray tracing technique. Results have been obtained for collectors incorporating reflectors of two concentrations, and efficiencies are compared with and without antireflection coatings on the glass envelopes for sunlight incident at angles 0–70°. The reflective properties of all optical components have been modelled in detail for the ray tracing calculations. Experimental and theoretical efficiencies agree within 0.02 for a wide range of angles of incidence. Antireflection coatings which increase the normal transmittance through a glass envelope by 5% result in an increase of 0.025 (about 4%) in collector efficiency. A theoretical study of the dependence of collector efficiency on absorptance of the absorber tube and specular reflectance of the reflectors is also discussed. Experimental and theoretical results have also been obtained for a collector incorporating a specular reflector with an accumulated dust cover. In this system, the reflector exhibits both specular and diffuse components of reflectance.     

Energy efficiency in building envelopes through ground integration

Energy efficiency in building envelopes is still a matter of great concern for designers, users, and Governments all over the world. It will become all the more important due to shortages of conventional energy in the foreseable future. A study sponsered by the Commission of the European Communities (CEC) at the Bartlett School of Architecture and Planning, University of London, UK, examines the building envelope of houses common in the Delhi region of India. The thermal environment in a traditional building envelope is determined, an index quantifying thermal discomfort is established, and thermal discomfort is calculated. Design options with different degrees of ground integration of building envelopes are considered. The thermal discomfort is quantified as a function of ambient climate and the extent of ground integration. The Methodology of computer simulation is used to determine the thermal performance of different design options. It is concluded that thermal discomfort in a building envelope with ground integration may be reduced by up to 13.3 Kelvin hours (Kh). It signifies that an occupant will have lesser discomfort equivalent to 1°C for 13.3 hours.     

The thermal storage performance of monobasic, binary and triatomic polyalcohols systems

Energy storage of phase change materials used in the building envelopes such as the wall or the floor is more and more valuable. Polyalcohols solid–solid phase change materials have become important because of its advantages. In this paper, the phase change temperatures and phase change heats of monobasic, binary and triatomic systems consisting of neopentylglycol, pentaerythritol and trihytdroxy methyl-aminomethane with different component were studied experimentally by differential scaning calorimeter (DSC). Feasibility of materials used in the building envelope was analyzed. The research is to find suitable polyalcohols mixtures with different composition used in the building envelope. Results can provide the basis for the application of solid–solid phase change materials in the building fields.     

Passive options for thermal comfort in building envelopes—An assessment

Building envelopes that have been developed so far often require mechanical systems involving expensive equipment utilising fuel and electrical energy for thermal comfort. These sophisticated systems (active systems) cannot be adopted by an average person in developing countries because it is difficult to afford and to maintain them. A study conducted by the author in a Ph.D. programme at the Bartlett School of Architecture and Planning, University of London, U.K., examines the building envelope of houses common in the Delhi region of India. The thermal environment in a traditional building envelope is determined, an index quantifying discomfort is established, and the degree of discomfort calculated. A vailable passive options for modifying the internal climate of building envelopes are considered one by one and an attempt is made to examine how far the thermal discomfort can be controlled with each of these options. The extent of the integrated effect of passive options is also established. The methodology of computer simulation is used to determine the thermal performance of different alternatives. It is concluded that two-thirds of the discomfort can be eliminated by the judicious use of simple passive options based on thermophysical properties and configuration of building envelopes.     

Reducing energy use in the buildings sector: measures, costs, and examples

This paper reviews the literature concerning the energy savings that can be achieved through optimized building shape and form, improved building envelopes, improved efficiencies of individual energy-using devices, alternative energy using systems in buildings, and through enlightened occupant behavior and operation of building systems. Cost information is also provided. Both new buildings and retrofits are discussed. Energy-relevant characteristics of the building envelope include window-to-wall ratios, insulation levels of the walls and roof, thermal resistance and solar heat gain coefficient of windows, degree of air tightness to prevent unwanted exchange of air between the inside and outside, and presence or absence of operable windows that connect to pathways for passive ventilation. Provision of a high-performance envelope is the single most important factor in the design of low-energy buildings, not only because it reduces the heating and cooling loads that the mechanical system must satisfy but also because it permits alternative (and low-energy) systems for meeting the reduced loads. In many cases, equipment with significantly greater efficiency than is currently used is available. However, the savings available through better and alternative energy-using systems (such as alternative heating, ventilation, cooling, and lighting systems) are generally much larger than the savings that can be achieved by using more efficient devices (such as boilers, fans, chillers, and lamps). Because improved building envelopes and improved building systems reduce the need for mechanical heating and cooling equipment, buildings with dramatically lower energy use (50–75% savings) often entail no greater construction cost than conventional design while yielding significant annual energy-cost savings.

新建建筑不同设置围护结构的热质耦合传递对建筑负荷的影响Ⅱ:冬季湿负荷

传统建筑室内湿负荷的计算大多不考虑围护结构内表面的散湿量,而围护结构内表面的散湿量尤其是新建节能建筑对室内湿负荷的影响是很大的。以哈尔滨地区为例,分析了严寒地区典型新建建筑不同设置的多层围护结构在最初四年内热质耦合传递对模拟房间湿负荷的影响,并与文献[5]的模拟结果进行对比。分析结果表明：新建建筑围护结构内表面粘贴墙纸或降低围护结构主体砌块的初始含湿量能够降低模拟房间冬季湿负荷;而保温层内侧隔汽层以及围护结构外表面釉面砖的使用都会增加新建建筑的模拟房间冬季湿负荷,但若延后釉面砖的粘贴时间会有所好转。     

分户计量供暖系统室内温度波动规律研究

本文旨在研究采暖房间室温的波动幅度和规律,从而对合理确定分户计量供暖系统的采暖热负荷提供参考意见。为此笔者根据用户调节时室温变化的特点,提出一种应用简化计算数学模型对非稳态传热过程进行模拟的方法。并应用这种模拟方法对不同围护结构条件下典型房间的室内温度变化进行了模拟,得到一系列室温波动曲线。根据这些曲线分析供热附加率、外围护结构条件及房间在建筑中所处位置等因素对室温的影响。     

Studies concerning charged nickel hydroxide electrodes: Part V. Voltammetric behaviour of electrodes containing β-Ni(OH)2

The first oxidation wave for aged β-Ni(OH)₂ normally occurs simultaneously with oxygen evolution, and by measuring the oxygen evolved the active material oxidation current may be determined. Oxidation of aged, ?-Ni(OH)₂ (phase U) to ?-NiOOH (phase V) reaches a maximum at about 0.59 V with respect to Hg/HgO/7M KOH whilst further oxidation to the γ phase (V₁) takes place at higher potentials (0.66 V).By restricting the anodic limit (0.55 – 0.6 V) the system can be constrained largely within the β-phase. At low oxidation states (2.1 – 2.2) a single reduction peak appears at ～ 0.4 V due to the reduction of phase V to phase U. If the oxidation state is increased to 2.7 by repetitive cycling or by single potentiostatic steps the reduction peak appears at progressively less cathodic potentials in the range 0.35 – 0.3 V. Cyclic oxidation reduction is found to “activate” the β-Ni(OH)₂ starting material allowing reoxidation to occur at lower anodic potentials (～ 0.46 V).Shifts in cathodic potential are found to relate directly to a decrease in quasi-reversible potential by ～ 70 mV for the species present at the peak maxima. The broad reduction envelopes are considered to be related to differences in free energy between different pairs of coexisting phases, U and V, which are present within the β-phase layer lattice system. The previous charging history critically influences the extent to which the quasi-reversible potential (E_r) value changes. Additional kinetic factors also appear to influence the precise shape and position of the first oxidation wave for β-Ni(OH)₂ which has been aged in hot 7M KOH.     

An investigation of the potential for natural ventilation and building orientation to achieve thermal comfort in warm and humid climates

The aim of this study was to analyze the most important factor, the climatic conditions with respect to thermal comfort in buildings. The impact of building location and climate and orientation on thermal comfort were investigated.With the help of dynamic computer simulations the different hourly weather data were analyzed. First of all the climate determines the amount of solar radiation and mean outside temperature that a building is exposed to. The climate also influences the amount of energy that is used for heating and cooling but also the amount of energy that is used for lighting. There is solar excess which determines the amount of solar energy that is unwanted in the building. With growing amounts of glass and a glazing system that allows large solar heat gains,the impact of orientation is substantial. A detailed analysis was conducted to evaluate the potentials for improving thermal comfort. Detailed results are given in sample graphics and tables in the study. In a tropical climate the improvement in comfort by NV range between 9% and 41% (Kuala Lumpur in April). For a subtropical climate the improvements vary between 3% and 14%. In a temperate climate the improvements vary between 8% and 56%. The results showed that NV has a good potential in tropical and temperate climates but not in subtropical climates. Especially in Hong Kong it seems to be very difficult to apply NV. The results showed that in particular in the hottest period (summer) the potential for comfort improvements is rather small. The design of climate responsive building envelopes should take this into consideration.     

Numerical investigation of subsonic hydrogen jet release

A buoyant round vertical hydrogen jet is investigated using Large Eddy Simulations at low Mach number (M = 0.3). The influence of the transient concentration fields on the extent of the gas envelope with concentrations within the flammability limits is analyzed and their structure are characterized. The transient flammable region has a complex structure that extends up to 30% beyond the time-averaged flammable volume, with high concentration pockets that persist sufficiently long for potential ignition. Safety envelopes devised on the basis of simplified time-averaged simulations would need to include a correction factor that accounts for transient incursions of high flammability concentrations.