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.     

Experimental investigation on radiation heat transfer properties degradation of (black nickel-coated aluminium) solar receiver tube material

In our previous research, we have studied the surface property degradation of the uncoated receiver tubes of solar water heater at elevated temperatures Logesh et al. [2017. “Experimental Investigation on Radiation Heat Transfer Properties Degradation of Aluminium Solar Receiver Tube Material.” International Journal of Ambient Energy 1–6]. In this study, the investigation is extended to property degradation of selective surface, black nickel-coated aluminium material. The selective surface has been investigated for its absorptivity (α) and emissivity (?) changes due to its exposure to sunlight at elevated temperatures. The duration of exposure ranges from 240 to 960?h; the properties are measured at four intervals in the selected range of exposure. The investigation is also carried out to find the temperature dependence nature of the heat transfer properties. The properties are measured at 10 temperature intervals for every period of exposure. The absorptivity (α) is found to be increased for the coated surface than the uncoated, whereas the emissivity (?) gets decreased for the same period of exposure.     

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.     

Effect of an Absorptive Coating on Solar Energy Storage in a Thrombe wall system

An analysis is undertaken to show the effects of a range of coating absorptivity values on the improvement of heat transfer across a Trombe wall (which is used for passive solar heating) and to its enclosure. The analysis shows that enhanced heat delivery to the enclosure of a Trombe wall system is feasible with the application of an absorptive coating of a superior nature – characterized by high absorptivity and very low emissivity – on the heat-receiving surface of the wall and thus can be seen as a heat transfer enhancement technique.     

佛甲草辐射特性的研究

在对植被屋顶进行热工性能研究时,绿化植物的发射率、长波辐射吸收率和太阳辐射吸收率是3个基本参数,对分析和计算植被屋顶的能量平衡有着重要意义。然而,目前学术界缺少常用绿化植物辐射特性的基本数据。本文研究了国内最常见的绿化物种——佛甲草的辐射特性,测得佛甲草叶片对太阳辐射的吸收率为0.67～0.69,发射率为0.81～0.84;同时利用太阳辐射传感器现场测得单位土地面积上密植的佛甲草草坪对太阳辐射的吸收率为0.83,估算得到其长波辐射吸收率约为1,在无进一步实验结果之前,可暂时认为单位土地面积上密植的佛甲草草坪发射率等同于叶片的发射率(0.83)。     

Heat transfer enhancement of the AISI stainless steel 304 elliptical annular fin coated with the carbon nanotube

In this work, experimental heat transfer enhancement investigation on the AISI stainless steel 304 (AISI SS 304) elliptical annular fin with nano-coating of multi-walled carbon nanotubes (MWCNTs) and without nano-coating was carried out. The parameters, such as temperature distribution, thermal conductivity, convective heat transfer coefficient, shaped tube efficiency and fin effectiveness, are compared for different heat inputs. The result shows that the thermal conductivity of the stainless steel (AISI SS 304) was increased by 21.1% with MWCNTs coating. The surface temperature of the fin decreases with coating as thermal conductivity increases. Also, the convective heat transfer coefficient of the coated fin increased by 7%. The fin-shaped tube efficiency was increased by 6.2% and the fin effectiveness was increased by 21.8%. The uncertainty of the performance parameters was also determined, the values were±5%.     

The effect of surface roughness and emissivity on radiator output

The effect of altering the emissivity and the roughness of a wall behind a radiator on the radiator heat output has been studied experimentally and by using computational fluid dynamics.The results of a 3D RNG k–? turbulent model agree well with, and have the same trend as, the experimental results. The results indicate that the presence of large scale surface roughness and a high emissivity surface increases both the heat flow rate and the air velocity behind the radiator compared to a smooth shiny surface. The former increases the wall surface emissivity which causes the surface temperature of the wall to increase, effectively creating additional convective heat transfer surface. The surface roughness will increase both the surface area for heat transfer and the turbulent intensity which increase the mass transfer and free convective heat flux through the air gap.The results indicate that the heat transfer can be increased by about 26% through the use of a high emissivity saw-tooth surface compared to a smooth shiny one. This means that using a wall surface with high roughness and emissivity behind the radiator will increase the heat output from the radiator.     

Experimental Study on Downslope Fire Spread over a Pine Needle Fuel Bed

The downslope fire represents a percentage of wildland fireline while the heat transfer mechanism of this process is poorly understood. In this study, the experiments were carried out in a fuel bed of dead pine needles with the slopes of ??30°, ??20°, ??10° and 0° for 0.4 and 0.8 kg/m² fuel loads. Flame length, flame angle, temperatures over the fuel bed, flow speed at the fuel bed surface, radiation heat flux near the end of the fuel bed were measured. The rate of spread shows a parabolic shape which decreases firstly and then increases from 0° to ??30°. The combustion interface, reconstructed from the temperature histories of two vertical thermocouples, was perpendicular to the fuel bed under all slope conditions for two fuel loads. The measured radiation heat flux is higher at ??30° slope than level ground, which is attributed to higher flame emissivity. A quasi-physical model was developed to describe the heat transfer mechanism of downslope fire spread. The calculation results show that the flame radiation dominated the downslope fire spread process and the combustion zone radiation should not be neglected in the near flame region.     

Effect of aspect ratio of footing on behavior of two closely-spaced footings on geogrid-reinforced sand

This paper presents the results of laboratory model tests carried out on two closely-spaced interfering footings resting on the surface of geogrid-reinforced and unreinforced sand bed. The effect of aspect ratio (or shape) of the footing on interference behavior is studied by adopting three pairs of model footings of different sizes. The length (L) to width (B) ratio (i.e., aspect ratio) of the footings is varied from 1.0 to 2.0. The effects of single layer of geogrid on footing interference and bearing capacity improvement are investigated. The optimum depth of the geogrid layer for both interfering and isolated footings is found to be one-third of the footing width and it is not dependent on the aspect ratio of the footing. The optimum spacing between the interfering footings is found to be 1.5 times the width of the footing. Lower efficiency factor is observed for interfering footings resting on the reinforced sand compared to the unreinforced sand. Higher bearing capacity ratio (BCR) is observed for isolated footing than that of interfering footings when BCR is measured based on ultimate bearing capacity values of reinforced and unreinforced cases and BCR value increases as the aspect ratio of the footing increases.     

Influence of soaking and polymerization conditions on the properties of polymer concrete

An experimental investigation was conducted to study the effect of soaking time and polymerization temperature on the mechanical and physical properties of polymer-impregnated concrete. Soaking time was controlled in 4, 8, 12, 16, 20 and 24 h, polymerization temperature was set at 70, 80 and 90 °C for 0.5, 1, 2, 4, 6, 12 and 24 h in impregnation process, respectively. Cylindrical concrete specimens with water/cement ratios of 0.45 and 0.65 were impregnated with methyl methacrylate (MMA) and benzoyl peroxide (BPO) mixtures. The polymer loading increases as immersion time increases until 12 h. Based on compressive strength and surface absorption, optimum polymerization temperature is 70 °C for Mix A (high cement content) and 80 °C for Mix B (low cement content). Polymer impregnation not only increases concrete strength and resistivity but also greatly decreases surface absorption comparing with normal concrete. SEM and MIP observations indicate that the micro-pores and meso-pores of PIC specimens are filled with PMMA and the total pore volume and maximum pore size are reduced significantly.     

Corrosion behaviour of a new low-nickel stainless steel in saturated calcium hydroxide solution

Corrosion behaviour of low-nickel stainless steel (SS), AISI 304 SS and carbon steel was studied using cyclic anodic polarization curves and electrochemical impedance spectroscopy (EIS). Saturated calcium hydroxide (Ca(OH)₂) solution was used to simulate a concrete pore solution at room temperature. The effect of up to 5.0% sodium chloride (NaCl) concentration in the test solution on the passivity of the alloys was studied. Experimental results showed that low-nickel SS exhibits similar behaviour to conventional AISI 304 SS, with E_corr and R_ct values of the same order and higher corrosion resistance than traditional carbon steel.     

Diffusion‐controlled reference material for VOC emissions testing: effect of temperature and humidity

A polymethylpentene film loaded with toluene is being developed as a reference material to support the reliable measurement of volatile organic compound emissions from building materials using environmental chambers. Earlier studies included the measurement of the material‐phase diffusion coefficient (D) and material/air partition coefficient (K) at 23°C. A fundamental mass‐transfer model can then be used to predict toluene emissions from the reference material at 23°C, serving as a reference for validating chamber‐measured emission profiles. In this study, the effect of temperature and humidity on performance of the reference material was investigated. Reference material emissions were measured at 10, 23, and 30°C and at different relative humidity (RH) levels. D and K at different temperatures and RH were determined using an independent method. Results showed that RH does not significantly affect D and K and had no effect on emissions. However, emissions increased substantially at elevated temperatures due to the relationship between D and temperature. A statistical analysis shows good agreement between model‐predicted and measured gas‐phase concentrations, indicating that the model can accurately predict emission profiles as a function of temperature. The reference material can therefore be applied to a wide range of emission chamber testing conditions.     

Experimental study of SS304L cylindrical shell with/without cutout under cyclic combined and uniaxial loading

In this research, ratcheting behavior of SS304L cylindrical shells under cyclic combined and uniaxial loadings was studied. Experimental tests were carried outby a servo-hydraulic INSTRON 8802 machine and the shells were fixed normal and oblique at angle of 20° with respect to the longitudinal direction of the shell. Force-control loadings were applied and the effect of length, angle of cylindrical shell and loading history on ratcheting behavior were examined.It was shown as the angle of cylindrical shell increases, due to increase of bending moment, accumulation of plastic deformation increases.Also, linear relation was observed between plastic energy and rate of plastic deformation which shows the rigidity of fixtures used in tests. Cutout effect on cylindrical shells under these kinds of loading has been studied and it was observed that creating cutout increases the plastic deformation and its rate.     

多孔金属板燃气灶燃烧性能数值模拟

应用FLUENT软件对影响多孔金属板燃气灶燃烧性能的多个参数进行了控制变量的数值模拟,对各参数进行归一化处理与敏感性分析,探讨各参数对灶具燃烧性能的影响。简化模拟计算,取多孔金属板上的一个单火孔的一半作为数值模拟对象并划分网格进行模拟。得出以下结论:火焰中心位置随板面表面发射率的增大而上升,表面发射率的增大使氮氧化物体积分数峰值出现下降,降幅约7.9%。表面发射率的增大在维持火焰温度基本不变且氮氧化物排放降低的情况下,提升了火焰位置,因此为提升灶具热效率,应将主要优化方向集中在通过表面处理以提高板面的表面发射率。灶具热负荷和火孔内直径的增加对上板面温度的提升有明显的促进作用,当热负荷从3.1 kW增加至3.9 kW时,火焰中心温度增幅为5.3%,同时氮氧化物排放量随之增大。内直径对上板面温度的提升作用在其值大于1.10 mm后开始显现,内直径的增加会明显提高氮氧化物的排放。因此在适当考虑烟气中氮氧化物排放的范围内,可提高灶具的热负荷和火孔内直径。在灶具热负荷较小时,孔隙率不可过大,但随着热负荷的增加,孔隙率可适当增大。鉴于板面厚度增加会明显增加达到稳态所需的时间,因此不宜采用过厚板面,以3.00~4.00 mm为宜。     

Emissivity considerations in building thermography

In the last 25 years, there have been considerable efforts put into the use and development of infrared thermography on buildings and large structures. As a result, nowadays, there are systems that can be used effectively in outdoor and/or indoor building surveys; indication and monitoring of problems such as voids, detached areas, deposits of humidity, etc. However, the principal problem where infrared thermographic measurements are concerned is the emissivity—emittance of the material(s). Given that an infrared camera detects the radiation emitted by a material under investigation and renders this energy to a temperature—thermal image, the feature that describes the relation between the emitted radiation and the material’s temperature, is termed as emissivity. Emissivity is actually a surface property that states the ability of the investigated material to emit energy. Correct emissivity values could provide valuable information concerning the interpretation of thermal images obtained from thermographic surveys. There is a considerable amount of work that has been published on emissivity of different materials and under various circumstances (i.e. temperature, surface condition, wavelength). In this work, a review on emissivity measurement techniques and the importance of emissivity values on building diagnostics was materialised. Furthermore, the emissivity of selected building materials were determined at a variety of temperatures, in the mid and long wavelength regions of the infrared spectrum, using different approaches and were discussed and explained in terms of the approach used, the wavelength and temperature effects, as well as the materials surface state.     

Experimental analysis of heat transfer through multiple reflecting bodies in a reactor-based cooling vault

In a nuclear reactor power plant, massive amount of heat generated in the reactor core causes the Reactor vault (RV) temperature to rise, which should be maintained at a permissible temperature range of 65°C–80°C. In order to address this issue we propose to incorporate thermal insulation, which consists of thin stainless steel (SS) sheets of 0.1?mm-thick stacked with uniform gap between them, introduced between the core and RV. The SS sheets (emissivity?=?0.05) are of highly polished, reflective type (mirror finish conforming to No. 8 as per ASTM A480/480M), which are made in the form of panels of suitable size and shape covering the entire outer contour. These types of insulations work on the principle of thermal radiation shielding Heat radiations from the reactor core falling on these reflective plates are reflected back thereby restricting the heat flux into the RV concrete. In order to estimate the effectiveness, 10 such plates are arranged over a length of 150?mm inside a casing made of an insulating material. A plate heater attached at the one end produces the desired heat transfer to analyse the thermal behaviour of the reflective plates. Thermocouples are attached to each plate to understand the temperature distribution in the system. Solidworks simulation and numerical calculations will be carried out.     

Effects of blends on the physical properties of bioethanol produced from selected Nigerian crops

Bioethanol fuel was synthesised from various Nigerian crops (palm (Elaeis Guineensis) wine, raffia (Raphia vinifera) trunk and sugar cane (Saccharum L.)) to serve as alternative fuels for internal combustion engines. Bioethanol was obtained through fermentation and distillation from these selected Nigerian crops and was then purified. Physical properties of the bioethanol and various petrol–bioethanol blends such as vapour pressure, octane number, flash point, heating values, auto ignition temperature and density were evaluated using the American Society for Testing and Materials methods. The calorific value of petrol decreased from 44.40 to 44.22 MJ/kg with a blend of 10% of alcohol (E₁₀). The calorific value of the produced ethanol (E₁₀₀) is 29.78 MJ/kg. The research octane number (RON) of petrol increased from 91 to 94 with a blend of 10% of alcohol (E₁₀). The RON of the produced ethanol (E₁₀₀) is 114. The flash point increased from -40°C at E₁₀ to 12.6°C at E₁₀₀. The results showed that the addition of bioethanol to petrol increases the octane number, flash point and auto ignition temperature, but on the other hand reduces the calorific value of the produced blend. The optimal petrol–bioethanol blends of E₂₀ and below were recommended for vehicles running on spark ignition engines.     

Photoinactivation of virus on iron-oxide coated sand: enhancing inactivation in sunlit waters

Adsorption onto iron oxides can enhance the removal of waterborne viruses in constructed wetlands and soils. If reversible adsorption is not coupled with inactivation, however, infective viruses may be released when changes in solution conditions cause desorption. The goals of this study were to investigate the release of infective bacteriophages MS2 and ΦX174 (two human viral indicators) after adsorption onto an iron oxide coated sand (IOCS), and to promote viral inactivation by exploiting the photoreactive properties of the IOCS. The iron oxide coating greatly enhanced viral adsorption (adsorption densities up to ∼10⁹ infective viruses/g IOCS) onto the sand, but had no affect on infectivity. Viruses that were adsorbed onto IOCS under control conditions (pH 7.5, 10 mM Tris, 1250 μS/cm) were released into solution in an infective state with increases in pH and humic acid concentrations. The exposure of IOCS-adsorbed MS2 to sunlight irradiation caused significant inactivation via a photocatalytic mechanism in both buffered solutions and in wastewater samples (4.9 log₁₀ and 3.3 log₁₀ inactivation after 24-h exposure, respectively). Unlike MS2, ΦX174 inactivation was not enhanced by photocatalysis. In summary, IOCS enhanced the separation of viruses from the water column, and additionally provided a photocatalytic mechanism to promote inactivation of one of the surrogates studied. These qualities make it an attractive option for improving viral control strategies in constructed wetlands.     

Effects of boundary conditions on the energy absorption of thin-walled polymer composite tubes under axial crushing

Polymer composite tubes can be designed to absorb high levels of impact energy by progressive crushing. When a tube is crushed onto a flat platen, energy is absorbed by bending failure of the plies, delamination and friction mechanisms. In the present work, significant increases in energy absorption are shown when a shear mode of failure is initiated by crushing the tube onto a radiused plug (or initiator). A study of plug radius, R, normalised with respect to the tube wall thickness, t, in the range of 0R/t5 for circular tube diameter/thickness ratios of 10<D/t<33 was undertaken with continuous filament random mat glass/polyester composite. Different radii plugs lead to significantly different deformed shapes and crush zone morphologies. Large radius initiators (R/t>2) cause the tubes to split and energy is absorbed primarily through friction and axial splitting. As the initiator radius decreases, the amount of through-thickness shear damage in the fronds increases along with specific energy absorption (SEA). When the plug radius becomes small compared to the wall thickness (R/t<0.75) a debris wedge forms between the initiator and the tube and acts like a larger radius initiator. The highest energy absorption was seen to occur at R/t1 when through-thickness shear damage was induced. In this range, under static loading conditions, SEA was seen to be higher than that for tubes crushed onto a flat platen.