Gas-diffusion layer's structural anisotropy induced localized instability of nafion membrane in polymer electrolyte fuel cell

The design of robust polymer electrolyte fuel cell requires a thorough understanding of the materials' response of the cell components to the operational conditions such as temperature and hydration. As the electrolyte membrane's mechanical properties are temperature, hydration and rate dependent, its response under cyclic loading is of significant importance to predict the damage onset and thus the membrane lifetime. This article reports on the variation in stress levels in the membrane induced due to the gas-diffusion layer's (GDL) anisotropic mechanical properties while accurately capturing the membrane's mechanical response under time dependent hygrothermomechanical conditions. An observation is made on the evolution of negative strain in the membrane under the bipolar plate channel area, which is an indication of membrane thinning, and the magnitude of this strain found to depend upon the GDL's in-plane mechanical properties. In order to come up with a strategy that reduces the magnitude of tensile stresses evolved in the membrane during the hygrothermal unloading and to increase the membrane's lifetime, we numerically show that by employing a fast hygrothermal loading rate and unloading rate strategy, significant reduction (in this study, nearly 100%) in the magnitude of tensile stresses is achievable. The present study assists in understanding the relation between materials compatibility and durability of fuel cell components.     

Finite element analysis of hygrothermal effects of angle-ply composite plates resting on elastic foundation

Analytical and numerical results on hygrothermal behaviors of angle-ply composite plates resting on elastic foundation are scarce in literature. To fill this gap, a higher-order global-local model (HGLMA) is proposed for hygrothermal analysis of angle-ply composite plates resting on elastic foundation. Based on the model HGLMA, a triangular plate element is formulated by using the refined element approach, in which a new finite element formulation including effects of elastic foundation has been developed. By analyzing hygrothermal response of composite plates with general configurations, the effects of elastic foundation parameters, lamination angles, boundary conditions, transverse normal strain, and hygrothermal expansion coefficients on the hygrothermal response have all been studied. Numerical results showed that elastic foundation has a significant impact on the behaviors of composite plates and models neglecting transverse normal strain fail to simulate the effects of the elastic foundation parameters on displacements and stresses of symmetric composite plates.     

通水除热管板应用于屋面结构中的模型实验研究

针对夏热冬暖地区的屋顶在夏季受太阳辐射强度大的问题,开发一种新型通水除热管板,将该通水除热管板应用于屋面结构中,构成新型通水除热屋面,可以有效改善夏热冬暖地区顶层屋面的热工性能,在间歇空调状况下,同时达到节能和舒适的目的。通过搭建模型实验台进行模型实验来研究通水除热屋面的隔热性能,得出主要结论如下:将铝制通水除热管板埋入屋顶找坡层,在17:00左右通水,此工况下对屋顶内表面有一定的降温效果,阻止晚间屋顶内表面温度的升高,降低了晚间空调的冷负荷,对夏热冬暖地区居住建筑有着重要的应用价值。     

Solar conversion under consideration of energy and entropy

With massive deployment of solar panels on the built environment expected in the future, it is anticipated that most of these panels, especially in new buildings, will be incorporated into the roof structure, rather than attached onto the roof, above an already existing conventional skin to protect against the weather. These panels have to fulfill the demand for comfort conditioning and to provide electrical power. When incorporated into the roof they also have to participate in providing mechanical strength and shielding the house from inclement weather. In addition it is essential that these solar panels are optimized with respect to their efficiency under consideration of energy, entropy and cost. In this paper, we have analyzed the intricate interconnection between the different components of a solar-fueled collection and conversion system, based on hybrid collectors, thermal storage and a heat pump.     

Field testing on nonsalt solar ponds

A new type of nonsalt solar pond was investigated by field testing. The roof of the solar pond was formed using a transparent double film. Three kinds of tests were carried out under the following conditions: (1) insulating pellets were packed between the layers of the transparent double film of the roof at sunset; (2) the water surface of the pond was insulated using only the two transparent films; (3) the water surface of the pond was covered by the double film with the top surface blackened on which solar energy can be collected, while pond water was circulated using a solar cell powered submerged water pump. The warm water stored in the solar pond by the above methods was utilized as a heat source for a gas engine powered heat pump used to heat a greenhouse. In this report, the results of the field tests on the above solar ponds and greenhouse heating system are discussed. Also the utility of a combination plant using a solar pond and underground borehole storage system is evaluated.Important conclusions on performance are as follows: (1) collection efficiencies of these solar ponds become 9–54% corresponding to the weather conditions and pond temperatures; (2) maximum temperature of the pond water under weather conditions at Osaka is about 80°C; (3) the solar pond can be effectively utilized for heating a greenhouse; (4) the combination plant using the solar pond and the underground storage layer can store heat of 1119 MJ m⁻² yr⁻¹.     

Methodologies for shortening test period of coupled heat-moisture transfer in building envelopes

Moisture movement and condensation through the building envelope can cause serious problems including reduction in thermal resistance of the wall, mold growth, and deterioration of the structural integrity of the wall. Full-scale tests are well suited to study these phenomena. However, a full-scale hygrothermal test requires a long testing period, typically from several months to a year, to study both wetting and drying processes. This paper presents methodologies whereby the test period is shortened to reduce cost and make large scale testing of building envelopes more affordable. A computer program for building heat-moisture simulation and test planning (BHMSTP) is developed using implicit finite-difference equations of coupled heat and moisture transfer in buildings. Two methodologies are proposed based on the analysis with the BHMSTP, shortening the test cycle from a year to a few months. In one method, indoor conditions are varied while maintaining climatic conditions constant; in the other method, weather conditions are varied, while indoor conditions are kept constant. The implementation of methodologies with the BHMSTP is demonstrated using Montreal (Canada) weather data.     

三峡库区秭归地区某碎石土岸坡稳定性分析及防治对策

为研究三峡库区岸坡在不同状态下的稳定性,选取三峡库区秭归地区某碎石土岸坡做了快剪试验,获得了该碎石土在天然状态和降雨状态下的抗剪强度指标,并运用SLOPE/W软件模拟边坡,采用Bishop方法计算了两种状态下的安全系数,发现天然状态下边坡稳定,降雨状态下边坡不稳定,进而采用抗滑桩模拟治理不稳定边坡的稳定性,并给出了抗滑桩的设计尺寸。     

Influence of external surface colour on the periodic heat flow through a flat solid roof with variable thermal resistance

In this research, the influence of external colour on the dynamics of the heat flow through a flat solid roof, with variable thermal resistance, has been studied analytically. The chromatic effect on the density of heat flow through the roof has been analysed using periodic solutions of the heat conduction equation, by means of Fourier analysis. The simulation has been carried out over a period of 24 h, for the summer design day of Campinas, in the State of São Paulo, Brazil, and its composite climate. An almost linear relationship between heat flow amplitudes (Δq_i) and the thickness of a concrete roof has been noticeable in the range from 5 to 14 cm for a grey coloured exterior surface and a corresponding white one. Conversely, from 15 cm and more, this relationship starts flattening. It may be concluded that as the thermal resistance of the concrete roof increases (>15 cm), the effect of the exterior colour surface on the periodic heat transfer through the roof is attenuated. As a consequence, the conflict between choosing colour for aesthetics and assuring energy efficiency of opaque building components in hot climates can be mitigated, if building designers make proper use of thermal inertia. Copyright © 2003 John Wiley & Sons, Ltd.     

Testing glare in universal space design studios in Al-Ain, UAE desert climate and proposed improvements

Previous studies by the author revealed several issues with regard to daylighting levels and glare problems in the new building of the architectural engineering department at UAE University and proposed solutions. This study investigates mainly the use of reflective light shelf to reduce glare problems and redistribute daylight in the ground floor studio space of the case study. Several slopes of light shelf along with other design parameters were tested on March 21 at 10:00AM using serial testing improvement approach, based on comparisons between pretest and posttest results. Other parameters were also tested, as ways to improving the performance of the light shelf, such as the height of the light shelf, the slope of the ceiling, and the type/existence of the front north partition. Both Radiance and Ecotect programs were used to simulate the required design configurations. The 5°-sloped roof performed better than the horizontal roof and improved the performance of the light shelf. Removing the north partition has the potential to improve glare on the rear space, yet it creates glare problems on the front side. Future testing is needed to investigate this problem.     

Investigation of building height and roof effect on the air velocity and pressure distribution around the detached houses in Turkey

Heat losses from buildings occur to a great extent through external walls. As compared to other types of buildings detached houses have fewer stories constructed in open places with less environmental shelter against wind. In urban and rural settlements, the wind effect on houses with roof remains as an important subject of study. More specifically, the role of roof as an insulator and the effect of roof on forced convection from buildings need to be considered in this context. In this study, we have investigated the potentials of roofs for reducing the wind effect on the detached houses during winter months in Kayseri, a midsize city in Turkey located at 38.44°N and 35.29°W Turkey.For this purpose, four different detached house scenarios are taken into account. They are (i) without roof and one storey, (ii) with roof and one storey, (iii) without roof and two storey and, (iv) with roof and two storey. For each scenario, air velocity and pressure distributions in front and back sides of the house are investigated using finite volume methods with FLUENT software. The evaluation of velocity and pressure distributions reveals the importance of roof in reducing the wind effect on houses.     

Comparative building simulation study utilising measured and estimated solar irradiance for Australian locations

The focus of this paper is to investigate the impact of using estimated solar irradiance data in building energy simulations. A series of annual weather files were developed with the estimates from two global and three diffuse/direct irradiance models for three locations in Australia. A weather file was also developed using the modelled values of global, diffuse and direct irradiance as estimated by EnergyPlus' (Version 7.0.0) auxiliary weather generator program. In addition weather files were generated with measured irradiance data and satellite derived irradiance data from the Australian Bureau of Meteorology. The influence of irradiance data was tested via the simulation of a simple 15 × 15 × 3.5 m building under two construction scenarios with varying window to wall ratios (WWR). This study indicates that the level of bias and uncertainty in the simulation results was low when global irradiance was measured and only diffuse and direct irradiance were estimated. However, when global irradiance was unknown the level of bias and uncertainty increased significantly and was shown to be highly dependent on the WWR, whilst only the level of bias was shown to be dependent on the building envelope construction. The results also indicated that the Skartveit diffuse/direct irradiance model used in combination with the BOM's satellite derived global irradiance data set achieved better results than the complete (global and direct) satellite derived irradiance data set from the BOM. The worst correlation in the simulation results occurred for the case where the irradiance data was estimated by EnergyPlus' auxiliary weather generator program.     

Carbon footprint of green roof installation on school buildings in Greek Mediterranean climatic region

Green roof installation in contemporary urban centres is increasing due to their numerous benefits, including microclimate improvement. However, the magnitudes of influence of the green roof design to energy savings is not fully clear, as well as the environmental benefit, in terms of reducing greenhouse gases emissions. The aim of this study was to estimate the effect of green roofs design on energy savings and their carbon footprint when installed on school buildings. The cooling and thermal insulation features of green roofs have been studied by using the TRNSYS simulation software. Different types of green roof systems (extensive and semi-intensive) and construction options are studied in four types of school buildings. Results showed that the estimated reduction in annual CO₂ emissions due to energy savings and CO₂ capture by plants was many times greater than the CO₂ emissions that caused from roof construction.     

Assesment of grid-connected photovoltaic systems in the Kuwaiti climate

Grid-connected photovoltaic (PV) systems is one of the most promising applications of PV systems. Till now, no detailed studies have been carried out to assess the potential of grid-connected systems in Kuwait. This work investigates the feasibility of implementing grid-connected PV systems in the Kuwaiti climate. The proposed system consists of crystalline solar modules mounted on the building roof and an inverter to convert PV dc output to ac voltage. The building receives electricity from both the PV array and the utility grid. In this system, the load is the total electrical energy consumption in the building.The objective of this work is to examine the performance as well as the economic feasibility of grid-connected PV systems in the Kuwaiti climate. A program is written to evaluate the performance as well as the economic feasibility of such systems in Kuwait. The input to the program is the weather data for Kuwait, time dependent building loads, as well as the utility rates for Kuwait. Weather data generator subroutine included in the program is used to generate hourly weather conditions from the monthly average values of daily radiation on horizontal surface, and ambient temperature available for Kuwait. The five-parameter PV model, which is applicable to both crystalline and amorphous PV modules, is used to determine the performance of the solar modules used in this study.The transient simulation program ( ) is used to link the components of the grid-connected PV system together. The inverter efficiency is represented as a linear function of input power. In this case, it is assumed that the AC output from the system will never be greater than the building load. Electricity tariffs will have an important impact on the cost-effectiveness of the system studied. The tariff used for electric utility is a flat rate per unit kWh of electrical energy. Simulations of the proposed system were carried out over the academic year.The building examined in this study is a flat roof building with a single story. The building roof area is large enough so that the PV arrays can be spaced widely to minimize shading losses. Different array slopes, and azimuth angles were studied to maximize the annual energy generated by the PV modules. Finally, the economic feasibility of grid-connected PV systems in Kuwait are examined.     

Hygrothermoelastic response in the bending analysis of elliptic plate due to hygrothermal loading

Abstract

This study investigates the theoretical outline to couple both classical Fourier’s and Fick’s laws to frame a new model of two-temperature hygrothermoelastic diffusion theory for a non-simple rigid material. Based on hygrothermoelasticity method, a system of linearly coupled partial differential equations for the thermal and moisture diffusion for the case of a non-simple medium is established. The transient response using the decoupled technique of a multilayered elliptic plate perpendicular to the axial axis, subjected to hygrothermal loading is considered, to derive closed-form expressions for temperature, moisture, deflection, bending moments, and hygrothermal stresses. The solutions to the governing coupled equations and its boundary conditions are solved by employing a new integral transform technique. The small deflection equation is found and utilized to preserve the intensities of bending moments and stresses, involving the Mathieu functions and its derivatives. Moreover, the elliptical region can be degenerated into a circular part by applying limitations. Numerical results of the transient response of hygrothermoelastic fields are established graphically for the better understanding the underlying elliptic structure, improved understanding of its relationship to circular profile, and better estimates of the effect of the associated hygrothermoelastic responses.     

屋顶光伏与建筑负荷之间的相互影响

建立了3种不同形式光伏屋顶和普通屋顶的一维非稳态模型,采用天津地区典型年的气象数据,考察了不同屋顶形式对建筑冷热负荷的影响,并对3种不同光伏屋顶系统中光伏组件的电性能进行了研究.研究结果表明:夏季采用带通风流道的光伏屋顶比较有利,而冬季则比较适宜采用封闭通风流道的光伏屋顶形式.     

轻钢彩板坡形屋面在小区住宅方面的尝试

轻钢彩板坡型屋面与传统屋面比较具有自己独特的优越性,本文通过其在哈尔滨通站小区的应用实例说明其在住宅小区建设中应用的尝试。     

Energetic and exergetic investigation of single slope solar still with sponge and circular hollow fins at different water depths

In this investigation, the experimental analysis of single slope solar still (SSSS) using hollow pin fins and sponge is done. The analysis of a SSSS using various sizes of water depth located in the basin was investigated based on energy and exergy analysis. The performance was estimated for the different water depths such as 15, 30, and 45 mm in basin. Four types are considered, type 1: traditional solar still (TSS), type 2: TSS with sponge, type 3: TSS with circular hollow fins and type 4: TSS with sponge and circular hollow fins. The effects of the sponge, water depth and the use of hollow pin fins were also examined. The performance was estimated for the variation of water depth such as 15, 30, and 45 mm in basin. The energy efficiency of Type 4 (TSS with sponge and circular hollow fins) is 20% higher than that of Type 3 (TSS with circular hollow fins), 38.47% higher than that of Type 2 (TSS with sponge) and 79.98% higher than that of Type 1 (TSS).     

Mixed-mode ventilation and air conditioning as alternative for energy savings: a case study in Beirut current and future climate

The aim of this work is to assess the use of mixed-mode ventilation for a typical office building in Lebanon and consequently reduce Heating Ventilation and Air Conditioning (HVAC) energy consumption in the observed current and under the future projected climatic conditions. Mixed-mode cooling is considered a compromise between the insufficient natural ventilation and the expensive year round-operated HVAC. A control algorithm is set for windows and HVAC system to ensure mixed-mode operation. Dynamic simulations are performed on a typical office building in Beirut City under the mixed-mode operation in the present and the future using commercial IES-VE software. The results of the software were validated against measured HVAC and total energy consumption of the typical office base case with conventional mechanical system. The results of the simulations are evaluated in terms of potential reduction in energy consumption under the present and the future weather data. Finally, a lifecycle cost analysis is performed for the proposed system, and its payback period is computed. Under present construction practices and weather data, 31% annual energy savings were achieved using mixed-mode system. Under future 2050s projected weather data, annual energy savings of 21% was attained with a payback period of 3.8 years.     

Optimum collector slope for residential heating in adverse climates

Optimum collector slope for a liquid base active solar heating system employing flat-plate collectors was investigated. The optimum collector slope was studied as a function of (a) collector area, (b) yearly total heating load and (c) the ratio of space heating load to service hot water load. Collectors facing equator only were considered. Such a system was studied in four different Canadian locations having widely different climates. Under the above conditions, optimum collector slope varied with the amount of collector area employed. The optimum collector slope was invariant with the yearly total load itself, or the space heating to hot water load ratio. Contrary to the widely held belief, for the four locations investigated, the optimum collector slope varied from lat. ? 10° to lat. + 15°; depending upon f_y, the fraction of load supplied by the solar system. When f_y is in 10–20 per cent range, optimum collector slope is lat. ? 10° and increases almost linearly to lat.+ 15° at f_y in 80 per cent range. Consequently, when the fraction of load by the solar system is low, a flat roof may be profitably employed. On the other hand, when the fraction by the solar system is high, a south facing (for northern hemisphere) vertical wall may be profitably employed.     

A study of Canadian diffuse and total solar radiation data—II Monthly average hourly horizontal radiation

Optimum collector slope for a liquid base active solar heating system employing flat-plate collectors was investigated. The optimum collector slope was studied as a function of (a) collector area, (b) yearly total heating load and (c) the ratio of space heating load to service hot water load. Collectors facing equator only were considered. Such a system was studied in four different Canadian locations having widely different climates. Under the above conditions, optimum collector slope varied with the amount of collector area employed. The optimum collector slope was invariant with the yearly total load itself, or the space heating to hot water load ratio. Contrary to the widely held belief, for the four locations investigated, the optimum collector slope varied from lat. − 10° to lat. + 15°; depending upon f_y, the fraction of load supplied by the solar system. When f_y is in 10–20 per cent range, optimum collector slope is lat. − 10° and increases almost linearly to lat.+ 15° at f_y in 80 per cent range. Consequently, when the fraction of load by the solar system is low, a flat roof may be profitably employed. On the other hand, when the fraction by the solar system is high, a south facing (for northern hemisphere) vertical wall may be profitably employed.