An experimental study of corrugated steel sheet solar water heater

An analysis of the heat transfer process in the corrugated steel sheet solar water heater and a simplified test procedure for determining the collector efficiency equation are presented. By experiment, the collector efficiency equation is found to be , the efficiency factor of collector is over 0.94, and the space temperature is 7°C higher than the collector temperature. The efficiency equation obtained by the simplified procedure coincides with that obtained by the standard procedure.     

带排挤管的真空管太阳能热水器实验研究

用排挤管装入真空管的内管内 ,使真空管内的储水大大地减少 ,减少了能量损失 (实际是提高了水箱内的水温 ) ,经多次实验和计算证明 ,改装后的真空管太阳能热水器的热效率有较大提高 ,经济效益明显     

生物质颗粒链条锅炉降低一氧化碳排放技术的数值模拟研究

生物质颗粒的挥发分含量远高于煤炭,导致燃烧后产生的烟气中一氧化碳含量严重超标。采用在链条锅炉喉口处增设二次风,在炉膛内设置双层炉拱等措施,一方面能加强炉内的氧气与不完全燃烧物质充分反应,另一方面可以有效延长烟气在炉膛中的停留时间,极大促进烟气中一氧化碳的燃尽,进一步提高锅炉出力及热效率。采用Fluent计算软件,针对采用此种改进结构的生物质颗粒链条锅炉进行了数值模拟。主要对炉内气流分布规律、气流充满度等进行了分析和探究,并通过热态实验加以验证。发现采用增设二次风和加装双层炉拱等措施后烟气中一氧化碳含量显著下降(达到国家排放标准),从而验证了此种改进措施的有效性。所得出的结论可以用来指导实际工程设计。     

An experimental study on the pressure drop of nanofluids containing carbon nanotubes in a horizontal tube

This article reports an experimental study on the flow characteristics of the aqueous suspensions of carbon nanotubes (CNTs). Stable nanotube suspensions were made for pressure drop measurements by two different methods. One of them is to disperse nanotubes using a surfactant, and the other is to introduce oxygen-containing functional groups on the CNT surfaces by acid treatment. The pressure drops in a horizontal tube and viscosities of nanofluids were measured and the effects of CNT loading and different preparation methods were investigated. Viscosity measurements show that both CNT nanofluids prepared by two methods are shear thinning fluids and at the same volume fraction, the nanofluids prepared by the acid treatment have much smaller viscosity than the ones made with surfactant. Under laminar flow conditions, the friction factor of CNT nanofluids stabilized by adding surfactant is much larger than that of CNT nanofluids prepared by acid treatment, and both nanofluids show larger friction factors than distilled water. In contrast to this, under turbulent flow conditions, the friction factors of both nanofluids become similar to that of the base fluids as the flow rate increases. It is also shown that as CNT loading is increased, laminar regime of nanofluids has been extended to further higher flow rates, therefore, nanofluids could have low friction factors than pure water flows at certain range of flow rates.     

全玻璃真空管太阳热水器数值模拟研究

基于FLUENT软件及TECPLOT软件,通过对均匀加热条件下的全玻璃真空管太阳热水器内流场及温度场的数值模拟,研究了热水器的对流换热与传质过程;分析了集热管倾角、真空管双面受热对热水器内流场及温度场的影响和真空管与水箱连接处、垂直等温面上的流体速度、温度分布。结果表明,在真空管与水箱连接处出现随机的涡流和真空管内出现分段的小环流,对传热传质过程不利,特别是对于带反射板的双面受热的集热器,应采取措施确保管内对流换热流动的有序性。建议加装导流板,并初步探讨了导流板的长度,确立了最佳板长模拟结构,为后续的理论研究与试验打下基础。     

真空管式太阳热水器得热量的实验研究

对某型号真空管式太阳热水器进行多天的热性能测试,采用最小二乘法拟合出太阳热水系统能量方程系数,求出该型号太阳热水器的能量方程,同时进行误差和敏感性分析,指导试验设计.     

An experimental study of heater size effect on micro bubble generation

An experimental study of the heater size effect on micro boiling is reported in detail. Using a 1.66-ms-wide heating pulse, boiling in subcooled water was investigated on a series of micron/submicron thin film Pt heaters with various feature sizes ranging from 0.5 μm to 70 μm. It was found that there existed a critical heater size (10 μm): single spherical bubble generation with heater’s feature size less than 10 μm; oblate vapor blanket on the heater surface with the size larger than 10 μm. The bubble dynamics was studied by the visualization of the bubble nucleation process with a high-speed CCD. The onset bubble nucleation temperature was measured by using each Pt heater as a resistive temperature sensor. The formation of the oblate vapor blanket was attributed to the condensation effect of the vapor outside the superheated zone. The analysis was further validated by generating spherical bubble on heater with size larger than 10 μm with a longer heating pulse.     

可随时上水的全玻璃真空管太阳热水器

全玻璃真空管太阳热水器当前在我国已经得到普及应用,按结构型式分它主要有普通式和外置辅助水箱式两种。这两种热水器分别有：易产生“炸管”现象,前后出水温差较大,甚至在无自来水的情况下不能     

全玻璃真空管太阳能热水器影响因素的数值模拟研究

利用热能工程专业基础知识和场协同原理,结合计算流体力学配套商业软件,对反光板、倾斜角度、辐照强度、集热管尺寸和水箱大小等因素,影响全玻璃真空管太阳能热水器的传热传质特性进行了数值模拟研究和可视化分析,通过数值模拟研究给出了全玻璃真空管太阳能热水器的的最佳条件。     

Shallow solar pond water heater: An analytical study

This paper presents a simplified analytical model to predict the performance of a shallow solar pond water heater which combines both collection and storage in a single unit. Essentially, the water heater consists of a metallic (G.I.) tray, whose inner and bottom surfaces are blackened, and is covered with a transparent sheet at the top; the sides and bottom surfaces of the assembly are well insulated. The unit stores a substantial amount of heat for the next day morning's use when the top cover is insulated during the off-sunshine hours. The performance of the water heater, both during the day and night time, can satisfactorily be predicted by this theoretical model. The theoretical calculations are found to be in good agreement with the experimental observations reported earlier.     

An experimental study on the design parameters of a counterflow vortex tube

In this experimental study, the design parameters and performances of counterflow vortex tubes are investigated. Under different inlet pressures, the thermal performance as a function of the following geometrical parameters is studied: the length of the vortex tube, the diameter of the inlet nozzle and the angle of the control valve. Three different working gases are comparatively tested: air, oxygen and nitrogen. Temperatures, pressures and mass flow rates for the inlet and hot/cold exits, and temperature distributions at the wall are measured. On the optimum geometry, flow visualizations are also conducted in order to have more information about the flow inside the tube. It is disclosed that the inlet pressure and the cold fraction are the important parameters influencing the performance.     

结构参数对全玻璃真空管太阳热水器夜间热损失的影响研究

文章建立了三维非稳态的全玻璃真空管太阳热水器的数值模型,分析了夜间散热时,该热水器内的流动和传热特征,并且在夜间同一工况下,模拟研究了贮热水箱保温材料的导热系数、保温厚度,以及真空管涂层的发射率对贮热水箱温度、真空管温度和该热水器夜间热损失的影响。分析结果表明:随着散热过程的持续进行,全玻璃真空管太阳热水器内温度分层情况越来越明显,内部流体的流速越来越小,真空管内静滞区域自下往上逐渐扩大;当贮热水箱保温材料的导热系数由0.035 W/(m·℃)减小至0.020 W/(m·℃)时,该热水器的夜间热损失减少了8.5%;当贮热水箱保温厚度由50 mm增加至60 mm时,该热水器的夜间热损失减少了5.0%;当真空管涂层的发射率由0.06减小至0.05时,该热水器的夜间热损失减少了4.0%。     

带内集管的分体式太阳能热水器及其实验研究

为了实现太阳能热水器和建筑的结合,设计了一种分体式全玻璃真空管太阳能热水器。它由集热器、室内储水箱、上升管和下降管组成,其集热器的每根真空管内有一个分水管,分水管通过集箱内的集管与下降管相连。与已有的太阳能热水器相比,其分水管把真空管内的冷、热水流道分开,减少了冷热水流相互干扰,提高了热水器效率,同时实现了分体式太阳能热水器系统的自然循环。实验表明,带内集管的分体式太阳能热水器比不带内集管的分体式太阳能热水器有更高的效率。     

An experimental study on a finned type and non-porous type solar air heater with a solar simulator

The results of experiments performed on two non-porous solar absorber solar air heaters with and without fins have been reported in this communication. The experiments were performed under laboratory conditions. Air heaters with fins are seen to be more efficient in comparison to the air heater without fins for air flow rates ≤0.0388 kg/sec per m². The experimental results have been used to validate a simple theoretical model.     

Measured performance of a solar water heater with a parallel tube polymer absorber

We performed calibrated side-by-side measurements of the thermal performance of solar water heaters with spaced polypropylene tube absorbers in identical glazed and insulated collector boxes. This was to determine the influence of tube spacing and tube height above the back insulation. A low flow rate (4.32 g s⁻¹ m⁻²) was used. As the number of tubes (spaced over the same aperture) is increased by 76.3% (from 38 to 67), the mean mid day efficiency increases by only 12.9% (7.4 percentage points), from 57.2% to 64.6%. It may therefore be more cost effective to use fewer, more widely spaced tubes. As tube height h above the insulation increased from the lowest value (3 mm) to the next (8 mm), the thermal efficiency dropped 1.4 percentage points. From h = 8 to 28 mm, the efficiency was almost independent of h.     

Theoretical and experimental investigations of a two-phase thermosyphon solar water heater

This article experimentally and theoretically investigates a two-phase thermosyphon solar water heater. The performance of this innovative solar water heater at different solar radiation intensities and tilt angles are experimentally discussed. The results show the best charge efficiency of the system is 82%, which is higher than the conventional solar water heaters. The theoretical model is also developed using the thermal resistance-capacitor method. The simulation predictions agree well with the experimental data within an average error deviation of ±6%. Two methods for improving the performance of this heater, double fin tubes and nano particle, are proposed. The results show that charge efficiencies can increase 3% and 4%, respectively, according to the theoretical model.     

An experimental study of rupture dynamics of evaporating liquid films on different heater surfaces

Experimental data were obtained to reveal the complex dynamics of thin liquid films evaporating on heated horizontal surfaces, including formation and expansion of dry spots that occur after the liquid films decreased below critical thicknesses. The critical thickness of water film evaporating on various material surfaces is measured in the range of 60–150 μm, increasing with contact angle and heat flux while decreasing with thermal conductivity of the heater material. In the case of hexane evaporating on a titanium surface, the liquid film is found resilient to rupture, but starts oscillating as the averaged film thickness decreases below 15 μm.     

An experimental investigation into the performance of a domestic thermosyphon solar water heater under varying operating conditions

An experimental investigation has been carried out on a thermosyphon solar water heater. The system consisted of a flat-plate collector of 1.5 m² absorber area with 21 tubes/m width and storage tank of 125 litre capacity. Experiments were carried out for both cloudy and clear weather conditions in winter and summer. The hourly system performance was evaluated for all test conditions. The final mean tank temperature was measured daily which enabled the calculation of the possible contribution of solar energy for domestic hot water supply in Basrah, Iraq (latitude 30.76°N). The system was tested at both no-load and loading conditions. Intermittent and continuous load was imposed, and system performance was evaluated for each condition.     

Influence of hydrogen and carbon monoxide on reduction behavior of iron oxide at high temperature: Effect on reduction gas concentrations

The purposes of this study are to reduce Fe₂O₃ using hydrogen (H₂) and carbon monoxide (CO) gases at a high temperature zone (500 °C–900 °C) by focusing on the influence of reduction gas concentrations. Reduction behavior of hematite (Fe₂O₃) at high temperature was examined using temperature programmed reduction (TPR) under non-isothermal conditions with the presence of 10% H₂/N₂, 20% H₂/N₂, 10% CO/N₂, 20% CO/N₂ and 40% CO/N₂. The TPR_CO results indicated that the first and second reduction peaks of Fe₂O₃ at a temperature below 660 °C appeared rapidly when compared to TPR_H2. However, TPR_H2 exhibited a better reduction in which Fe₂O₃ entirely reduced to Fe at temperature 800 °C (20% H₂) without any remaining of wustite (FeO) whereas a temperature above 900 °C is needed for a complete reduction in 10% H₂/N₂, 10% and 20% CO/N₂. Furthermore, the reduction of hematite could be improved when increasing CO and H₂ concentrations since reduction profiles were shifted to a lower temperature. Thermodynamic calculation has shown that enthalpy change of reaction (ΔHr) for all phases transformation in CO atmosphere is significantly lower than in H₂. This disclosed that CO is the best reductant as it is a more exothermic, more spontaneous reaction and able to initiate the reduction at a much lower temperature than H₂ atmosphere. Nevertheless, the reduction of hematite using CO completed at a temperature slightly higher compared to H₂. It is due to the presence of an additional carburization reaction which is a phase transformation of wustite to iron carbide (FeO → Fe₃C). Carburization started at the end of the second stage reduction at 600 °C and 630 °C under 20% and 40% CO, respectively. Therefore, reduction by CO encouraged the formation of carbide, slower the reduction and completed at high temperature. XRD analysis disclosed the formation of austenite during the final stage of a reduction under further exposure with high CO concentration. Overall, less energy consumption needed during the first and second stages of reduction by CO, the formation of iron carbide and austenite were enhanced with the presence of higher CO concentration. Meanwhile, H₂ has stimulated the formation of pure metallic iron (Fe), completed the reduction faster, considered as the strongest reducing agent than CO and these are effective at a higher temperature. Proposed iron phase transformation under different reducing agent concentrations are as followed: (a) 10% H₂, 20% H₂ and 10% C; Fe₂O₃ → Fe₃O₄ → FeO → Fe, (b) 20% CO; Fe₂O₃ → Fe₃O₄ → FeO → Fe₃C → Fe and (c) 40% CO; Fe₂O₃ → Fe₃O₄ → FeO → Fe₃C → Fe → F,C (austenite).     

A theoretical and experimental investigation of a novel built-in-storage solar water heater

In this work, a novel built-in-storage type solar water heater of about 87 l capacity has been investigated theoretically and experimentally for the case of no draw-off. The solar water heater which performs the dual function of absorbing and storing hot water is made of 5 pipes, each of length 1.8 m and diameter 12 cm. A baffle plate is placed inside each pipe. The experiments have been performed inside the laboratory using an artificial Sun consisting of 27 lamps. The water temperatures have been measured at various locations in the system. In the theoretical study, transient performance of the system is predicted by solving the mathematical model consisting of energy balance equations written for each control volume comprising one length of pipe. These equations are converted to finite difference form and then solved by a personal computer. The experimental results have been compared with the numerical model and a good agreement has been found between the experimental results and the theoretical predictions.