Analytical simulation models for solar heating system design

Presented here is a method of simulating the performance of solar heating systems which can be incorporated into a microcomputer-based system design and sizing procedure. A general analytical solution to the storage energy balance is presented, and a scheme for varying the parameters of the general solution to represent changes in the operating mode and the driving forces is detailed. Three different simulation methods which employ the general solution are described. Two of these methods use hourly data and the third uses daily data. Measured results from an actual system are compared with simulated results to validate the models. Also, simulated results and computing speeds are compared with the general simulation model TRNSYS. Finally, an example of a microcomputer application is discussed.     

蒸汽供热管网运行工况的水力计算与分析

以节点连续方程为基础对蒸汽供热管网运行工况进行了水力模拟计算,编制了3个枝状蒸汽供热管网的水力工况模拟计算软件,对某现有蒸汽供热管网的实际运行工况进行了计算与分析,给出了经济运行工况,并在对蒸汽供热管网实际运行进行预测的同时指出了蒸汽供热管网节能改造的方向。程序具有可再植入性,能够适应因管网改造导致的数据库中管段信息的更改。     

High temperature solar heated seasonal storage system for low temperature heating of buildings

A preliminary study of a solar-heated low-temperature space-heating system with seasonal storage in the ground has been performed. The system performance has been evaluated using the simulation models TRNSYS and MINSUN together with the ground storage module DST. The study implies an economically feasible design for a total annual heat demand of about 2500 MWh. The main objective was to perform a study on Anneberg, a planned residential area of 90 single-family houses with 1080 MWh total heat demand. The suggested heating system with a solar fraction of 60% includes 3000 m² of solar collectors but electrical heaters to produce peak heating. The floor heating system was designed for 30°C supply temperature. The temperature of the seasonal storage unit, a borehole array in crystalline rock of 60,000 m³, varies between 30 and 45°C over the year. The total annual heating costs, which include all costs (including capital, energy, maintenance etc.) associated with the heating system, were investigated for three different systems: solar heating (1000 SEK MWh⁻¹), small-scale district heating (1100 SEK MWh⁻¹) and individual ground-coupled heat pumps (920 SEK MWh⁻¹). The heat loss from the Anneberg storage system was 42% of the collected solar energy. This heat loss would be reduced in a larger storage system, so a case where the size of the proposed solar heating system was enlarged by a factor of three was also investigated. The total annual cost of the solar heating system was reduced by about 20% to about 800 SEK MWh⁻¹, which is lower than the best conventional alternative.     

Enhanced performance of nanostructured thin film anode through Pt plasma enhanced atomic layer deposition for low temperature solid oxide fuel cells

Thin-film electrode deposited by sputtering has drawn attention due to high surface area and density of reaction sites for low-temperature solid oxide fuel cells. However, the nano-column structure of the sputtered film on the nanoporous anodic aluminum oxide (AAO) substrate has been showing low performances, possibly originated from low in-plane electrical connectivity and limited reaction area at electrolyte/electrode interface. We report here that application of 10 nm thickness of Pt plasma-enhanced atomic layer deposition (PEALD) on the nanoporous Ni-based anode and Gd doped ceria (GDC) deposited by sputtering dramatically enhances anodic reactions, significantly reduces ohmic and polarization resistances (25% reduction in ohmic, 50% reduction in polarization resistances), and improves the power density over 60% compared to the bare cells. It is noteworthy that Pt PEALD deposited on the nanoporous GDC layer shows much-improved performance compared to that deposited on the nanoporous anode structure. This is attributed to the enhanced contact area at Pt/GDC interface by exceptional conformal deposition of Pt PEALD and improved reaction sites from surface of GDC anode interlayer.     

Different anode catalyst for high temperature polybenzimidazole-based direct ethanol fuel cells

Five different bimetallic catalyst formulations (PtRu/C, PtSn/C, PtW/C, PtRh/C and PtOs/C) were prepared by reduction with sodium borohydride, and physico-chemically characterized by X-Ray Diffraction, Transmission Electron Microscopy, Temperature Programmed Reduction and X-Ray Photoelectron Spectroscopy. It was observed that in the case of the PtRu/C and PtRh/C a large fraction of the second metal enters the platinum lattice structure. The remaining metal, and in those catalysts in which no alloy was formed, its deposition was in a mixed metallic (Os) and/or oxide form, as TPR and XPS results displayed. Crystal sizes were in the range 3–5 nm, except for the case of the PtW/C in which there was a large agglomeration of platinum particles, as the TEM images confirmed. Electrochemical half-cell tests demonstrated the better performance of these bimetallic catalysts in terms of ethanol oxidation, with lower onset potential and larger current densities, particularly in the case of the PtOs/C, PtRu/C and PtRh/C materials, and to a lower extent in the case of the PtSn/C. Actual fuel cell tests at high temperature (150 and 200 °C) confirmed the beneficial effects of increasing the temperature in terms of cell performance, with an increase in the performance, particularly in the cases of PtOs/C and PtRu/C. Finally, the product distribution was also assessed, observing a large conversion to CO₂ by operating at high temperatures, particularly for PtRh/C at low current density, and for Pt/C at high current density (up to 35%), although acetaldehyde remained as the main oxidation product for all the catalysts.     

Industrial waste heat utilization for low temperature district heating

Large quantities of low grade waste heat are discharged into the environment, mostly via water evaporation, during industrial processes. Putting this industrial waste heat to productive use can reduce fossil fuel usage as well as CO₂ emissions and water dissipation. The purpose of this paper is to propose a holistic approach to the integrated and efficient utilization of low-grade industrial waste heat. Recovering industrial waste heat for use in district heating (DH) can increase the efficiency of the industrial sector and the DH system, in a cost-efficient way defined by the index of investment vs. carbon reduction (ICR). Furthermore, low temperature DH network greatly benefits the recovery rate of industrial waste heat. Based on data analysis and in-situ investigations, this paper discusses the potential for the implementation of such an approach in northern China, where conventional heat sources for DH are insufficient. The universal design approach to industrial-waste-heat based DH is proposed. Through a demonstration project, this approach is introduced in detail. This study finds three advantages to this approach: (1) improvement of the thermal energy efficiency of industrial factories; (2) more cost-efficient than the traditional heating mode; and (3) CO₂ and pollutant emission reduction as well as water conservation.     

Induction heating apparatus for high temperature testing of thermo-mechanical properties

A low cost high temperature test facility designed and built for the purpose of thermo-mechanical testing is described. An induction heater provides variable heating rates, simple operation and easy access for temperature and strain measurement. Specially designed high temperature specimen grips with water-cooling allow for testing over long periods of time. Contact temperature and strain measurements are utilised to provide accurate and reliable results. Detail is given on the experimental procedure including calibration of the thermocouple temperature measurement. A validation study of the thermal expansion and tensile Young’s Modulus of carbon steel 1020 at temperatures up to 850 °C proves the accuracy of the test set-up and procedure. Results are given for the stress–strain curves of aluminium alloy 7000 T4 at various temperatures to further demonstrate the capabilities of the test facility. The measured thermo-mechanical properties of these materials were used to develop high temperature constitutive models for implementation in finite element thermal–structural analysis of hypersonic structures.     

翼片超塑性等温精锻时加热装置的设计与计算

本文分析了大型翼片件采用超塑性等温精锻成型的可行性。并叙述了内加热装置的热力学计算和电热元件的设计。通过工艺试验表明,内加热装置适用于大型锻件的等温加热。     

Nano Ni layered anode for enhanced MCFC performance at reduced operating temperature

Nanoparticles of Ni and Ni–Al₂O₃ were coated on a molten carbonate fuel cell (MCFC) anode by spray method to enlarge the electrochemical reaction sites at triple phase boundaries (TPBs). Both nano Ni coated anode and nano Ni–Al₂O₃ anode exhibited significant reduction of anode polarization, thanks to smaller charge transfer resistance. The maximum power density of nano Ni coated anode was 159 mW cm⁻² at current density of 300 mA cm⁻² operating at 600 °C. This is about 7% increase from the standard cell performance tested and compared in the study. Although low performance of nano coated Ni–Al₂O₃ cell is observed due to electrolyte consumption, the stability of cell performance during operation time is more favorable in MCFCs operation.     

Optimal temperature control of solar heating systems

Temperature control systems based on solar and wind energy differ in two important ways from existing fossil fuel systems. One is that solar systems, at least active solar systems, all have some kind of energy storage, the other is that the source of energy in a solar and wind energy system is variable and uncontrollable. Because of these added complications and the high capital investment required for solar and wind energy systems, considerably more sophisticated techniques are required for the design of those systems. In this study, a new technique is applied to the optimal control problem of solar heating systems.     

Experimental characterization of anode heating by electron emission from a multi-walled carbon nanotube

The steady-state temperature distribution in a thin anode bombarded by an electron beam field emitted from an individual multi-walled carbon nanotube is measured with an infrared camera, and this distribution is compared to that predicted by a numerical model. By assuming the electron distribution in the beam follows a Gaussian distribution, a good fit to the anode temperature profile is obtained and this fit provides an estimate of the beam spreading radius. Results indicate the electron beam narrows as the emission current increases. A heat flux on the anode surface as high as 0.35 W/cm² has been measured, corresponding to an electron beam radius of approximately 1.22 mm.     

Advanced models of fuel droplet heating and evaporation

Recent developments in modelling the heating and evaporation of fuel droplets are reviewed, and unsolved problems are identified. It is noted that modelling transient droplet heating using steady-state correlations for the convective heat transfer coefficient can be misleading. At the initial stage of heating stationary droplets, the well known steady-state result Nu=2 leads to under prediction of the rate of heating, while at the final stage the same result leads to over prediction. The numerical analysis of droplet heating using the effective thermal conductivity model can be based on the analytical solution of the heat conduction equation inside the droplet. This approach was shown to have clear advantages compared with the approach based on the numerical solution of the same equation both from the point of view of accuracy and computer efficiency. When highly accurate calculations are not required, but CPU time economy is essential then the effect of finite thermal conductivity and re-circulation in droplets can be taken into account using the so called parabolic model. For practical applications in computation fluid dynamics (CFD) codes the simplified model for radiative heating, describing the average droplet absorption efficiency factor, appears to be the most useful both from the point of view of accuracy and CPU efficiency. Models describing the effects of multi-component droplets need to be considered when modelling realistic fuel droplet heating and evaporation. However, most of these models are still rather complicated, which limits their wide application in CFD codes. The Distillation Curve Model for multi-component droplets seems to be a reasonable compromise between accuracy and CPU efficiency. The systems of equations describing droplet heating and evaporation and autoignition of fuel vapour/air mixture in individual computational cells are stiff. Establishing hierarchy between these equations, and separate analysis of the equations for fast and slow variables may be a constructive way forward in analysing these systems.     

蒸汽供热管网水力计算的简易算法

针对蒸汽在供热管道流动过程中密度不断发生变化的问题,用连续性方程、动量方程推导出适合于蒸汽供热管网的水力计算公式,实例验证其与文献提供的计算公式对比具有较好的计算精度,水力计算误差平均减少5.6%。     

On the complexity of radiation models for PV energy production calculation

Several authors have analysed the changes of the probability density function of the solar radiation with different time resolutions. Some others have approached to study the significance of these changes when produced energy calculations are attempted. We have undertaken different transformations to four Spanish databases in order to clarify the interrelationship between radiation models and produced energy estimations. Our contribution is straightforward: the complexity of a solar radiation model needed for yearly energy calculations, is very low. Twelve values of monthly mean of solar radiation are enough to estimate energy with errors below 3%. Time resolutions better than hourly samples do not improve significantly the result of energy estimations.     

Three-dimensional FE model for calculation of temperature of a thermosensitive disc

An effect of variations of the temperature-dependent thermophysical properties of materials of a pad and a disc on the temperature generated due to friction was studied. A three-dimensional boundary-value problem of heat conduction of the disc heated locally within the contact area by the moving with the constant deceleration heat flux and the intensity proportional to the specific capacity of friction was formulated. An issue was solved numerically using the finite element method (FEM). The experimental dependences curves of the thermal conductivity and the thermal diffusivity on the temperature ranging from 20 to 500 °C indispensable for the calculations were approximated using Chichinadze's methodology. The comparative analysis of temperature values on the contact surface of the disc obtained with and without influence of temperature dependence of the four different pad and the same quantity of the disc materials was carried out. It was demonstrated that apparent temperature differences arose for each friction couple combining temperature-dependent and constant properties of materials, however, the largest observed discrepancy (13.7%) occurred for the disc made of aluminium alloy series Al MMC. Other disc materials i.e. iron alloy series FCD50, cast iron ChNMKh and steel EI-696 revealed relatively equal temperature differences of order of 6.4%. Furthermore incorporated in the formula for the heat partition temperature variability of the thermophysical properties of materials affected the resulting contact temperature of the disc for friction couple combined exclusively with the titanium pad VT-14 (3.1%).     

Simulation of solar air heating at constant temperature

Solar space heating with warm air in typical air collectors and rock bed storage systems involves constant air flow rates and varying the temperature of supply to rooms and to storage. This practice results in undesirable fluctuations in comfort levels in the living space, excessive storage size, useful but inaccessible heat in storage, and unnecessarily high energy consumption for air circulation and auxiliary heat. These drawbacks can be avoided by use of a practical controller and variable speed fan to provide heated air from the collector at constant temperature and a continually varying flow rate. Collector manufacturer's data, confirmed by seasonal tests on a solar air heating system in Solar House II at Colorado State University, have been used in simulations at constant hot air supply temperatures of 40°, 50°, and 60°C, and at one typical constant flow rate of 49 kg/h per m² through a 50 m² collector and rock bed storage unit, providing approximately half the seasonal heating requirements of a residential building. Auxiliary heat requirements and fan power use in the 40°C and 50°C constant temperature operations were significantly reduced from the levels prevailing under constant flow conditions. Collection efficiency and solar heat supply at constant flow were slightly higher than values at the 60°C constant temperature level.     

经皮经脾碘油门静脉造影——肝内占位性病变的平片和 CT 观察

碘油门静脉造影以往多采用剖腹门脉置管来实现。笔者对18例肝内占位性病变患者采用经皮穿刺脾静脉灌注碘油的方法,完成门静脉造影,造影全部成功。术后没有发生脾破裂,脾出血及明显肝功能损害;18例肝肿瘤(直径1～18 cm)平片和 CT 扫描,瘤内及瘤周没有发现碘油沉积。笔者推测这是瘤内、瘤周的门脉分支高压或存在离肝血流的结果;本法有3例3 cm 以下的小结节灶检测数比常规 CT多,提示本法的敏感性可能与动门脉 CT 相似,从平片和 CT 观察瘤内及瘤周并没有象肝动脉灌注碘油那样有碘油充盈,而是呈充盈缺损,相反,正常肝组织分布碘油,这使得笔者对门脉置管化疗栓塞治疗肝癌的作用产生疑虑。     

Effects of temperature dependent properties in electromagnetic heating

Electromagnetic heating such as microwave processing and radio frequency heating becomes very popular because of its non-contact, pollution free and fast distribution of thermal energy within the object of interest. In electromagnetic heating, the temperature distribution within a sample greatly depends on the dielectric properties which are functions of electromagnetic frequency, temperature and the composition of the object. There are many experimental and numerical investigations on electromagnetic heating because of its widespread use in food and other industries, but only few researchers have looked at this problem from analytic point of view specifically for the temperature dependent properties. In this paper, we developed an analytic expression for temperature distribution in a three dimensional rectangular object under electromagnetic heating and presented a method to incorporate temperature dependent properties of the object in determining the temperature distribution at different times. A simplified Maxwell’s equation is solved for plane wave to obtain electric field distribution in the body, and the electromagnetic power absorption is computed from the electric field distribution which was then used as a source term in the energy equation. Next an unsteady, three dimensional, non-homogenous energy equation is solved by integral transform technique to obtain temperature distribution. Finally, this closed form analytical solution is used to study the effects of electromagnetic frequency, dielectric properties, and heat transfer coefficient on temperature distribution in a rectangular salmon fillet. It is found that incident frequency, sample thickness and processing time have significant influence on the heating pattern. For radio frequency heating, the temperature dependent dielectric properties influence the temperature distribution significantly, but the effect of temperature dependent dielectric properties is less dominant for the microwave frequency used in the household microwave oven. Our results also show that microwave heating provides heterogeneous temperature distribution with alternate hot and cold spots. On the other hand, the radio frequency heating allows almost uniform temperature distribution within the body, which makes it a better choice for quick and convenient heating process especially for commercial and industrial heating.     

Constant temperature control of tundish induction heating power supply for metallurgical manufacturing

The tundish induction heating power supply (TIHPS) is one of the most important equipment in the continuous casting process for metallurgical manufacturing. Specially, the constant temperature control is greatly significant for metallurgical manufacturing. In terms of the relationship between TIH load temperature and output power of TIHPS, the constant temperature control can be realized by power control. In this paper, a TIHPS structure with three-phase PWM rectifiers and full-bridge cascaded inverter is proposed. Besides, an input harmonic current blocking strategy and a load voltage feedforward control are also proposed to realize constant temperature control. To meet the requirement of the system, controller parameters are designed properly. Experiments are conducted to validate the feasibility and effectiveness of the proposed TIHPS topology and the control methods.     

A simplified method for direct calculation of the annual load fraction of solar systems for space heating

Availability of data about long-term system performance is a first step towards economic analysis and optimization of solar systems. The use of detailed computer simulation techniques or even design methods such as the f-chart for evaluating system performance may be cumbersome for engineers and architects. In this paper, we present a simplified method to predict the annual system performance. The method allows direct calculation of the annual solar load fraction, for a specific location, as a function of collector area and design parameters. This method is based on a correlation of data generated by using the f-chart method. Because of its simplicity and excellent agreement with f-chart calculations, the present method should be a useful design aid for sizing and selecting solar systems for space heating.