凹版印刷机烘干系统的热力学分析

目的研究凹版印刷机热风干燥系统热能流向与品质,为烘干系统的设计与优化提供理论依据,提高干燥热效率,促进国内凹印机能量审计进一步发展。方法对凹印机烘干系统进行热力学分析,进行能耗计量。结果经计算,凹印机烘干系统的热效率只有9.21%,而62.29%高热量气体被直接排出系统,没有得到有效的利用。干燥介质在经过烘箱时,产生的不可逆损失为86.96%,而加热纸张的不可逆损失占到整个烘箱不可逆损失的24.21%。结论回收利用系统废气热量是提高凹印机烘干系统热效率最有效的途径;此外,降低热风与纸张的换热过程产生的不可逆能量损失也会直接提高凹印机烘干系统热能的品质。     

凹版印刷工业的绿色节能技术

针对当前凹版印刷设备存在的耗能大、尾气排放污染等问题,通过对凹版印刷机热风干燥系统节能、印刷有机废气(VOCs)综合治理和凹印企业主要热源余热循环利用等主要相关技术的探讨,提出了切实可行的节能减排方案.在此基础上,进一步将热力燃烧式氧化器与热水二段型溴化锂机组相结合,解决了热力燃烧式氧化器运行成本较高的问题.研究结果表明,从热风干燥系统、有机废气综合利用、主要热源余热循环利用3个方面入手实施的节能减排方案,可以降低凹版印刷工业运行能耗的20%~40%.     

芒果热泵干燥生命周期成本建模与效益分析

目的 对比研究芒果果脯热泵干燥过程与传统化石能源热风干燥的成本效益，为企业生产提供科学指导。方法 在芒果果脯干燥动力学模型基础上，为芒果果脯的干燥生产过程建立生命周期成本与效益分析模型，辅以芒果热泵干燥实验数据，验证模型的正确性，并用该模型对芒果果脯热泵干燥企业的生产成本进行预测分析，比较采用热泵干燥和传统热风干燥方法的能耗、成本效益。结果 在热泵干燥条件下，不同高度层的芒果受热均匀，可以精准调控果干温度。相较于燃煤锅炉加热干燥，采用热泵干燥可以降低17.1%的生产成本，有利于减轻企业的经济负担。与传统锅炉加热干燥方法相比，采用热泵干燥方法可使生产能耗下降30.17%，二氧化碳排放量减少了32%，符合我国节能减排发展战略。结论 证明了热泵技术在芒果果脯干燥生产上的优越性。该模型方法还可用于龙眼、荔枝等同类农副产品生产中，为果脯果干生产企业的生产成本控制提供测算方法。     

Comparison of total energy systems using gas turbines and diesel engines for combined cooling

A gas turbine engine was used to drive the compressor of a vapour compression cycle so that the usually wasted energy in the exhaust gases was partially recovered and used in the generator of an absorption cycle. The cooling effect was therefore boosted. The degree of energy utilization was further enhanced when the energy released from the absorber and condenser of both cycles was recovered in the form of hot water, which could be used for different applications. The performance parameters for this combined system, such as the cooling effect, total heat recovered and performance effectiveness ratio, were calculated for various evaporator and condenser temperatures. It was found that a system driven by a gas turbine gives a better performance than a diesel engine system under similar operating conditions.     

Analysis of energy efficient and environmentally friendly technologies in professional laundry service

Professional laundry service (i.e., doing laundry for hospitals, hotels, production plants, dormitories, and students cafeterias) is an industrial, energy intensive process. Electrical energy and natural gas are commonly used to heat water and drying air. However, much of the energy leaves the process in waste flows completely without any profit. Professional laundry service has also direct impact upon environment. Waste water is often contaminated with laundry detergents and natural gas flue gas is used as drying medium. Therefore, it is an energy intensive process and its energy consumption and related environmental impact are worth researching. This article presents the concept of professional laundry service and main energy efficiency measures that may be relevant for the process. Impacts of laundry process on environment along with financial aspects are assessed in this article, too. Financial parameters of any measure are crucial for laundry operators. However, every assessment of profitability of particular measure has to be substantiated by source operational data. These may significantly vary depending on local prices of energy, water, and human labor. This fact is presented using case study where the difference between real operational costs in three European countries is evaluated (Germany, France, and the Czech Republic). Successful research and development of energy efficient and environmentally friendly technologies must encompass three aspects of every technology, i.e., energy intensity, environmental impact, and financial aspects. This three-component approach and its application in laundry service are unique and since they have not subject to any academic research yet, they are discussed in the conclusion of this article. Article is basically an overview of energy efficient and environmentally friendly technologies in professional laundry service and it must be asserted that it is a first of a kind in this area.     

Numerical analysis on the heat and work transfer due to shear in a hot cascade Ranque–Hilsch vortex tube

Cascading of vortex tubes is a possible implementation to extract significantly larger amount of useful work. A hot cascade-type RHVT makes use of the cold gas for cooling purposes while improving the heating capacity of the hot gas. In a vortex tube inflow pressure is the only source of energy which converts into thermal energy. The conversion of pressure energy into thermal energy is associated with the heat and work transfer due to shear along the radial, axial and tangential directions. In this paper, the physics of fluid flow and thermal separation are studied based on the heat and work transfer due to shear along all three directions. The work transfer due to the action of tangential shear is always from the cold to hot fluid layers and is the most dominant factor in the thermal separation process. The contribution increases considerably with hot cascading. However, the process of thermal separation degrades due to the effect of sensible heat transfer.     

循环加热式热泵热水机性能评价系统研究

对国家标准中循环加热热泵热水机性能评价方法的研究,结合主流性能评价系统存在的不足,给出提高性能评价系统精度及可行性的思路:一是尽可能的减少热量损失所占机组总加热的比重,二是简化精确计算热量损失方法。PPR管件替换钢制管件可以有效减少评价系统热损,热损修正函数的引入使热损计算更加准确、易行,使得循环加热式热泵热水机组制热量的计算也更加准确,性能系数的得出更加可靠,从很大程度上促进了热泵热水机行业的性能改善与研发进程,加速热泵热水机替换传统热水器的进程,为国家的低碳节能与可持续发展有一定促进。     

Analysis of the energy input during wire coating from a cylindrical magnetron source

In order to deposit thin films on a substrate several techniques can be used, e.g. chemical vapour deposition, atomic layer deposition or sputter deposition, depending on their specific advantages and disadvantages due to the related application. A significant parameter is the energy incident upon the substrate by the specific technique, especially when the heat capacitance of the substrate is low. Within this paper we analyse the energy transported into a thin wire (few 10 μm in diameter) during a dynamic inline aluminium sputter process in a cylindrical magnetron source. The evoked heating is important for the tensile strength of the wire and uniformity of the sputtered layer. Therefore, mathematical models were created to estimate the energy input into the wire supported by monte-carlo-simulations of the sputtering process using the TRIM-simulation (Transport and Range of Ions in Matter). Measurements with a Langmuir probe and the corresponding deposition rate were used to quantify these models, showing that at an aluminium coating process of a gold wire, the significant energy input is only due to electrons and ions of the processing gas (argon). Using the heat equation based on the sputtering apparatus' parameters, it was also possible to determine the energy input into the wire with in situ electrical resistance measurements. Both methods did show similar results, whereby the resistance results were more stable. The determined energy input made it possible to calculate the temperature profile during the wire-coating process which can be useful for estimations about film diffusion and process optimisation.     

Synthesis of ceramic oxide powders by microwave plasma pyrolysis

Ceramic powders prepared pyrolytically exhibit homogeneity and, in most cases, small grain sizes. The energy efficiency of electrically heated systems performing the pyrolysis in a stream of carrier gas is poor. Similar considerations concerning energy demand are valid for spray drying of suspensions. This situation can be improved using a microwave plasma as a source for thermal energy. The process described in this paper works with any aqueous solution of salts used as starting material in ceramics. The process was demonstrated by the synthesis of alumina, zirconia, and zirconia-based ceramic powders; where an energy efficiency of more than 80% was found. For the powder synthesis, aqueous solutions of the nitrates were used as starting materials. Through proper selection of conditions for synthesis, it is possible to obtain nanocrystalline powders, as demonstrated by electron microscopy. Because of the extreme conditions associated with plasma during synthesis, it is possible to prepare nonequilibrium structures and solid solutions in systems in which nearly no equilibrium solubility exists.     

CO2-heat pump water heater: characteristics, system design and experimental results

CO₂ is one of the few non-toxic and non-flammable working fluids that do not contribute to ozone depletion or global warming, if leaked to the atmosphere. Tap water heating is one promising application for a trans-critical CO₂ process. The temperature glide at heat rejection contributes to a very good temperature adaptation when heating tap water, which inherits a large temperature glide. This, together with efficient compression and good heat transfer characteristics of CO₂, makes it possible to design very efficient systems. A heating-COP of 4.3 is achieved for the prototype when heating tap water from 9°C to 60°C, at an evaporation temperature of 0°C. The results lead to a seasonal performance factor of about 4 for an Oslo climate, using ambient air as heat source. Thus, the primary energy consumption can be reduced with more than 75% compared with electrical or gas fired systems. Another significant advantage of this system, compared with conventional heat pump water heaters, is that hot water with temperatures up to 90°C can be produced without operational difficulties.     

Numerical analysis of drying characteristics of frozen material immersed in fluidized bed at low temperature under reduced pressure

A spherical frozen material was dried in a fluidized bed of inert particles at a low temperature (lower than the melting point of water) under reduced pressure. To evaluate the drying characteristics of the frozen material, the heat and mass transfers in the material during the drying process were calculated using one-dimensional differential equations. The fitting parameters (accommodation coefficient of internal sublimation and heat transfer coefficient at the surface of the material) were determined to fit the calculation results and the experimental data. Drying characteristics, such as the distributions of moisture content and temperature in the material during drying, were calculated. Operational conditions, such as bed temperature, humidity, and heat transfer coefficient (gas velocity) at the surface of the material were varied in the calculation, and the effects on the end time of drying were estimated. Sublimation in the interior of the material governs the drying characteristics. The dry region in the material became resistant to heat transfer. The calculation results are reasonable for expressing the drying characteristics of freeze-drying, that is, our calculation method can be used to estimate the drying characteristics of frozen material in a fluidized bed.     

Research on microwave drying technology in the procedure of preparation of V2O5 from ammonium polyvanadate (APV)

High-quality vanadium pentoxide powder is an important product of the vanadium industry and was usually prepared from ammonium polyvanadate (APV) using a roasting process combined with a drying pretreatment. Conventional hot air drying is usually used for the drying of APV, the heat transfer of which is from outside to inside thus limited the efficiency of the drying pretreatment. In the present paper, microwave heating was applied as an alternative heating method for the drying of APV because of its advantages including selective heating, high heating efficiency, low energy consumption, and green environmental protection. An experimental comparison between hot air drying and microwave drying is provided, and the results show that microwave drying is more energy-saving and faster. The drying characteristics of APV under the irradiation of microwave energy were investigated. The influences of factors including microwave power, material quality, and initial moisture content on microwave drying were studied. The results show that the microwave power, initial moisture content, and initial mass are positively proportional to the microwave drying efficiency of APV. Additionally, the Page model was robust in describing the kinetics of microwave drying and hot air drying of APV. This study provides fundamental knowledge on the microwave drying process and provides the trial for the industrial applications of microwave heating on the preparation of V₂O₅.     

Thermal seawater desalination based on self-heat recuperation

Recently a novel self-heat recuperation (SHR) technology has been developed for energy saving. In the SHR process, both sensible heat and latent heat are circulated by compression work. Energy consumption is thereby drastically reduced. Using this technology, a new thermal desalination process is developed for reducing energy consumption. The energy required for this SHR-based process is explained by process simulation. It requires ~1/4 the energy of the conventional multi-stage flash desalination process, which is the most widely used thermal desalination. Thus, the proposed thermal desalination process is promising for application in industrial plants.     

The oxidation behaviour of metals and alloys at high temperatures in atmospheres containing water vapour: A review

The kinetics of oxide formation in the presence of water vapour are discussed and compared with oxidation in dry atmospheres. The main protective oxide systems are considered, i.e. alumina, chromia, silica, titania and iron and nickel oxides, and with the possible exceptions of alumina and nickel oxide, oxidation rates are increased by the presence of water vapour. Scale morphology is also influenced by water vapour, and an important observation is that whisker formation is encouraged; this is believed to be due to the more rapid dissociation of water vapour compared to oxygen. In general, water vapour promotes the formation of a more porous scale. This is related to an increase in cation diffusion and consequent vacancy condensation, thereby developing a porous structure. The thermochemistry of oxide formation is discussed, and here oxide stability and hydroxide formation are considered. A significant observation is that where hydroxides or oxyhydroxides form, they generally have higher volatility than the corresponding oxide, and this leads to loss of protection.The effect of water vapour on oxide growth processes is considered. It is demonstrated that all aspects of oxide growth including adsorption, dissociation and diffusion of reactants are altered in the presence of water vapour compared with similar processes in dry conditions. The important first stages of the reaction involving adsorption and dissociation are controlled by the catalytic activity and acid base nature of oxides. For oxides formed at high temperatures very limited information is available, but, in general, data obtained at room temperature is confirmed and strongly suggests that dissociation of any gas molecule is favoured by defects in the surface. Dissociation of water seems to be more rapid at lower temperatures than, for example, oxygen, but this difference may be less pronounced at higher temperatures. Fast diffusion of water in oxides is possible due to “proton hopping”, in which protons localised at oxide ions move by transfer from one oxygen to another. Since the OH⁻ ion concentration is increased there is a resultant increase in cation vacancies, and this, in part, is responsible for the observed increase in oxidation rates. A further factor to consider is the possibility of molecular diffusion, and it has been demonstrated that where pores or voids are present in the scale, and the void contains both hydrogen and water vapour, oxidation of the surface nearest the metal will occur by reaction with water to form new oxide and the reaction product hydrogen, while a reduction reaction occurs at the surface of the void nearest the gas phase to produce water vapour. Thus it can be seen that this process provides for rapid inward diffusion of oxygen while the void gradually moves outwards from the metal/oxide interface to the oxide/gas interface.Finally, the review considers the effect of water vapour on the mechanical properties of the scale. Scale adhesion can be improved (iron oxides) or made worse (alumina and chromia) by the presence of water vapour. It is shown that while there is experimental evidence for altered mechanical behaviour, there is very little data on relevant mechanical properties. It is possible, therefore, that water vapour either alters mechanical properties of some oxides, or, as has been demonstrated, the oxide growth process has been changed. Alternatively, at least for the cases where increased oxidation rates were caused by the presence of water vapour, the observed differences between wet and dry behaviour may simply be a function of the greater scale thickness. A significant effort has been made to develop models that can be used to predict the onset scale spallation observed in industrial boilers using process steam. The further development of these models is strongly dependent upon obtaining relevant input data, and this is considered a major challenge for materials scientists.Some areas for future research are proposed.     

Low-temperature solar-plate-assisted heat pump: A developed design for domestic applications in cold climate

Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature.     

吸收式热泵余热回收先进技术综述

热力发电厂余热资源丰富,且存在锅炉烟气排入大气环境导致的"白羽"现象。为此,国内外学者对烟气余热利用展开了大量研究,其中吸收式热泵作为余热驱动的能级提升装置被广泛应用于区域集中供热和供冷领域。针对目前余热回收领域中应用的回热、多效、多级和压缩-吸收复合的吸收式热泵技术进行综述,并提出一种由双级吸收热泵、升温型压缩吸收耦合热泵和三级烟气换热器组成的烟气余热全热回收系统。该系统基于烟气余热能量梯级利用原理,将烟气由145℃降为40℃以下,同时制取70℃以上的一次热网供暖热水,有效地提升能源利用效率,减少"白羽"现象的产生。     

基于COMSOL的纸浆模塑干燥模拟及验证

目的 研究采用COMSOL Multiphysics模拟纸浆模塑干燥效率及厚度变化的可行性。方法 基于多孔介质理论,应用有限元仿真软件COMSOL Multiphysics建立纸浆模塑干基含水率随时间变化的热湿、水分流动、非等温流动多物理场耦合模型,考虑干燥中含湿多孔介质的湿空气热对流及多孔基体的热传导,模拟在热板加热条件下纸浆模塑的干燥效率和厚度的变化,并与实验结果进行比较。结果 模型内域探针所得模拟结果与实验结果具有良好的一致性,在干燥后期厚度预测误差范围为0.4%～7.7%,干燥效率预测差异值最低为4.3%。结论 采用COMSOL Multiphysics模拟纸浆模塑干燥过程可行。     

升华干燥过程的动力学机理研究

本文采用传热与传质耦合的动力学模型了单一加热方式和混合加热方式的升华干燥过程机理,并分析了升华干燥过程中物料温度、升华面温度和升华面水汽通量等参数对于燥过程的影响。     

New absorption chiller and control strategy for the solar assisted cooling system at the German federal environment agency

Typically the cooling capacity of absorption chillers is controlled by adjusting the driving hot water temperature according to the load. Meanwhile the cooling water temperature is controlled to a constant set value. In order to increase the solar cooling fraction and/or to decrease the operating costs of solar assisted cooling systems (SAC-systems) a new control strategy has been developed which controls hot and cooling water temperature simultaneously. Hereby the specific cost of cold – generated from solar or conventional heat – can be reduced. The basic concept of the strategy is explained and results are shown for the SAC-system at the Federal Environment Agency in Dessau, Germany. Here a recently developed absorption chiller is now used instead of a former adsorption chiller. With the new absorption chiller and the control strategy the seasonal energy efficiency ratio SEER is above 0.75, electric efficiency is 35% higher and water consumption is reduced by 70%.     

关于家用CO2热泵热水器设计思路的探讨

CO2放热过程中的温度滑移与热水形成很好的温度匹配,使得家用CO2热泵热水器在生产高温热水方面的优势明显,借鉴日本的标准,可达到65℃。但我国大部分地域水质较硬,较高的出水温度会加剧气冷器管道中的结垢现象;并且由于幼儿和老人对高温热水不敏感,容易造成热水烫伤。通过理论分析和试验验证发现降低出水温度后,CO2系统仍然具有明显的性能优势。综合考虑家用CO2热泵热水器在我国实际使用过程中系统性能、水质情况、防高温烫伤三方面的限制和影响,推荐其设计出水温度以不高于45℃为宜。