Pressure-assisted thermal sterilization of soup

The overall efficiency of an existing scale-up pressure-assisted thermal sterilization (PATS) unit was investigated with regards to inactivation of Geobacillus stearothermophilus spores suspended in pumpkin soup. The PATS unit is a double pipe heat exchanger in which the soup is pumped into its inner high pressure tube and constrained by two high pressure valves, while steam is continuously passed through the annular region to heat the content. The technology is based on pressure generation by thermal expansion of the liquid in an enclosure. In this work, the addition of an air line to push the treated liquid food out of the existing PATS unit has improved the overall quality of the treated samples, as evidenced by achieving higher log reduction of the spores. Compared with thermal processing, the application of PATS shows the potential for lowering the thermal treatment temperature, offering improved food quality.     

高效传热管内凝结换热性能及阻力性能的实验研究

本文以ＨＦＣ１３４ａ和ＨＣＦＣ２２为工质对光管及两种不同槽型的强化传热管（ＤＡＥ－２管与ＤＡＥＣ管）的水平管内凝结换热进行了对比实验研究、研究发现,ＤＡＥ－２管平均换热系数比光管提高了１４０％～１７０％,而单位长度阻力损失增加了５０％～１００％,ＤＡＥＣ管平均换热系数比光管提高了１６０％～２００％,同时单位长度阻力损失增加了７０％～１３０％。此外,本文给出了ＤＡＥ－２管和ＤＡＥＣ管平均换热系数及阻力损失的计算关联式,可用于冷凝器设计。     

基于超材料的平板二维定向传热结构设计

基于变换热力学, 采用坐标斜变换和旋转变换得到定向传热结构单元的热导率分布表达式, 并利用隔热材料和铜分层排布实现了定向传热结构单元. 将定向传热结构单元周期性排列, 得到二维平板定向传热结构. 数值计算结果表明: 当外部热流流向该结构上表面时, 热量主要向两侧流动, 从而使上下表面保持低温. 与同厚度二氧化硅气凝胶隔热材料相比, 上表面温度降低33.3%, 下表面温度降低4.3%, 而侧面温度上升40.1%. 定向传热结构上表面温度的降低表明能够及时导走热量, 从而降低上表面的红外辐射; 下表面温度的降低说明定向传热结构比二氧化硅隔热材料具有更好的隔热效果; 上表面热量主要向两侧传输造成侧面温度急剧升高, 有利于热能的有效利用. 定向传热结构在红外隐身、热防护领域具有潜在的应用价值.     

Cogeneration: One way to use biomass efficiently

Cogeneration in district heating systems is the most energy-efficient way to convert biomass into heat and electricity with current or nearly commercial technologies. Methanol produced from biomass and used in vehicles instead of petrol or diesel could reduce carbon dioxide emissions nearly as much per unit of biomass as if the biomass were used to replace natural gas for cogeneration, but at some higher cost per unit of carbon dioxide reduction. The most energy-efficient way to use biomass for cogeneration appears to be combined cycle technology, and the world's first demonstration plant is now being built. Potentially, this technology can be used for electricity production in Swedish district heating systems to provide nearly 20% of current Swedish electricity production, while simultaneously reducing carbon dioxide emissions from the district heating systems by some 55%. The heat costs from cogeneration with biomass are higher than the heat costs from fossil fuel plants at current fuel prices. Biomass can only compete with fossil fuels if other advantages, for example a lower environmental impact, are considered.     

Isolated quantum heat engine

We present a theoretical and numerical analysis of a quantum system that is capable of functioning as a heat engine. This system could be realized experimentally using cold bosonic atoms confined to a double well potential that is created by splitting a harmonic trap with a focused laser. The system shows thermalization, and can model a reversible heat engine cycle. This is the first demonstration of the operation of a heat engine with a finite quantum heat bath.     

蓝宝石衬底上RF-MBE生长的GaN中的极性控制和螺旋位错的降低

近年来人们报道了用MBE方法生长GaN的飞速进展,利用RF-MBE方法可以获得高的GAN生长速率和高的电子迁移率.本文讨论了用RF-MBE方法在蓝宝石衬底上生长GaN过程中的极性控制和螺旋位错的降低.在充分氮化的蓝宝石衬底上直接生长GaN,使GaN的极性控制为N-极性,并用高温生长的AlN核化层实现GaN的Ga-极性.对于N-和Ga-极性的GaN这两种情况,高温生长的AlN中间迭层的引入,可以有效地抑制螺旋位错的扩散.位错的降低使GaN的室温电子迁移率得到提高,对于Ga-极性的GaN,其值为332cm²/V·s;而对于N-极性的GaN,其值为688cm²/V·s.     

Impact of new technologies on future heat exchanger design

Heat recovery technology has featured strongly in most major inductrial energy conservation programmes, and significant penetration of heat exchange equipment into processes, for the express purpose of energy efficiency, has been achieved. Barriers, both technical and economic, still exist however, preventing more widespread adoption of heat exchangers. Problems associated with fouling and corrosion remain, and the temptation to adopt more sophisticated energy recovery methods such as organic Rankine cycle machines had led to some overambitious installations with dubious economic benefits.The prospects for cost-effective low temperature heat recovery are improving due to a combination of developments, including the novel use of materials and new heat exchanger concepts. A number of peripheral aids, in particular improved design procedures including process integration, and the use of artificial intelligence techniques, can help users select appropriate state-of-the-art equipment.In this paper, the role of techniques for enhancing heat (and mass) transfer will be discussed. Process intensification, perhaps normally associated with compact chemical plant unit operations, has, the author believes, an important future role to play in enabling heat exchanger size and costs to be reduced. Enhancement of transport processes, by techniques which are largely established in other heat transfer areas or in other technologies, is a necessary step to achieving compact systems.     

英国冷库设计中的若干新技术剖析

根据现场考察和交流,介绍分析英国冷库氨制冷系统设计中的若干新技术.通过采用减少系统充氨量的系列新技术,可以使系统的充氨量大大减少,安全性大大提高.通过采用自动控制、高效热氨融霜、回收余热加热地坪、冷风机合理配置等新技术,可明显提高运行的能效.结合我国冷库情况,分析了适合我国借鉴的新技术.     

相变储热体释热强度研究

对相变储热体以导热为主的释热过程,可以应用一维相变导热模型描述。当进一步简化,认为散热表面的温度低于相变温度且保持不变,不考虑液相区的自然对流和固液两相有明确的分界面,利用Neuman解法求解出释热过程的热强度,并通过实验进行研究。理论与实验结果比较表明,其相对误差不大于5％,从而证明这种方法可作为这类储热体的设计基础。     

Isotropic Thermal Cloaks with Thermal Manipulation Function

By extending the conventional scattering canceling theory,we propose a new design method for thermal cloaks based on isotropic materials.When the objects are covered by the designed cloaks,they will not disturb the temperature profile in the background zone.In addition,if different inhomogeneity coefficients are selected in the thermal cloak design process,these cloaks can manipulate the temperature gradient of the objects,i.e.,make the temperature gradients higher,lower,or equal to the thermal gradient in the background zone.Therefore,thermal transparency,heat concentration or heat shield effects can be realized under a unified framework.     

RECIPROCATING IMPINGEMENT JET HEAT TRANSFER WITH SURFACE RIBS

This article presents the experimental heat transfer results of an impinging jet onto a flat surface with discrete ribs in a reciprocating confinement. The test flows were systemically varied from static to reciprocating conditions with oscillating frequencies of 0.83, 1.25, and 1.67 Hz. Parametric ranges of tests in terms of Reynolds, pulsating, and buoyancy numbers were 10,000-25,000, 0-0.15, and 0-4.12 x 10^-7, respectively. It was found that the nonreciprocating heat transfer close to and away from the stagnation point was respectively reduced and improved from the smooth-walled values, which led to the more spatially uniform heat transfer distribution. An empirical correlation was developed to permit the evaluation of nonreciprocating local Nusselt numbers. Under reciprocating environment with relatively weak pulsating force effects, a tendency of heat transfer deterioration from static reference developed, which trend could lead to about 20% of heat transfer reduction. Further increase of pulsating force ratio caused the subsequent heat transfer recovery, and the local reciprocating Nusselt number could be enhanced to a level about 240% of the equivalent static value at a pulsating number of 0.014. Considerable influence of reciprocating buoyancy interaction on heat transfer was detected to impede local heat transfer. As the present flow system in a reciprocating confinement could result in higher and more spatially uniform heat transfer rates in general, it could be an applicable cooling method for pistons.     

Periodic high-temperature heat pumps for industrial heat recovery—Part II. Example of application and design of apparatus

Using a drying process as an example, the use of a periodic high-temperature heat pump for industrial heat recovery is investigated. The investigation shows that by using a special control system and two buffer reservoirs, the thermal powers of adsorber, evaporator and condenser can be kept constant in time. The unit under investigation achieves a calculated power density of 6.8 kW/m³ at an effective capacity of 150 kW. A working cycle lasts 3.5 h and the heat ratio is 1.54. The technical design of an experimental unit in tower configuration is described in detail.     

Thermodynamic Analysis and Optimization of a Novel Power-Water Cogeneration System for Waste Heat Recovery of Gas Turbine

A power-water cogeneration system based on a supercritical carbon dioxide Brayton cycle (SCBC) and reverse osmosis (RO) unit is proposed and analyzed in this paper to recover the waste heat of a gas turbine. In order to improve the system performance, the power generated by SCBC is used to drive the RO unit and the waste heat of SCBC is used to preheat the feed seawater of the RO unit. In particular, a dual-stage cooler is employed to elevate the preheating temperature as much as possible. The proposed system is simulated and discussed based on the detailed thermodynamic models. According to the results of parametric analysis, the exergy efficiency of SCBC first increases and then decreases as the turbine inlet temperature and split ratio increase. The performance of the RO unit is improved as the preheating temperature rises. Finally, an optimal exergy efficiency of 52.88% can be achieved according to the single-objective optimization results.     

S波段超宽带高平均功率多注速调管的研制

介绍一种新型超宽带（相对带宽≥17%）S波段大功率多注速调管的研制过程及研制成果,该速调管首次在S波段实现了17%的相对带宽,带宽指标为国内宽带多注速调管首次实现。通过优化电子光学系统和高频段的参数设计、优化电子枪区的结构设计、优化整管散热系统设计等多项措施,提高电子注流通率及注波互作用效率,降低高频部分的散热压力,使该速调管仅在120 kW的峰值功率下实现了大于30%的效率及40 kW的平均功率。同时,通过近似连续波阴极发射电流密度的低阴极负荷设计、阴极区零部件多项预处理工艺措施等实现了3 ms脉宽的稳定工作及连续24 h稳定工作不打火。为实现3 min内满功率输出及2000 h的寿命,对阴极工作参数、电子枪区的工艺结构进行了反复优化。本项目在能够实现指标的前提下,进行了小批量的生产及车载环境的环境试验,并针对可能产生的不可靠性因素,进行了改进,使产品真正能实现工程化应用,为后续同类产品的设计提供有效的技术参考。     

Analysis of an existing heat exchanger network and effects of heat pump installations

The existing heat exchanger network (HEN) at a refinery is analysed and redesigned by grassroots as well as retrofit designs. The integration of heat pumps into the network is also investigated. The results indicate that the existing network consumes approximately 6% more energy than the optimum design. Retrofitting the existing network leads to a design similar to the optimal grassroots design. To achieve the energy saving, the heat exchanger area has to be increased by 9%. The estimated payback is 1.5 years if a large fraction of the existing heat exchanger area is reused. The effect of heat pump installations is considered and some alternative cases are presented. Significant energy savings could be achieved but the economics is open to discussion.     

航天相机主动热控测试系统设计

为了检测航天相机主动热控系统的功能、性能及可靠性,设计了主动热控仿真测试系统。依据传热学基本定律、航天器轨道理论和热控策略,给出了计算航天相机温度场的热网络数学模型,使主动热控系统能在模拟的空间热环境中连续工作,实现了对主动热控系统的闭环仿真测试。采用两个数字电位器相串联的方法模拟温度传感器的走势,得到的最大阻值为100 kΩ,精度达到10Ω,符合设计中对总电阻和电阻变化率的需求,实现了对主动热控系统的功能、性能以及可靠性的仿真测试。     

Experimental and Theoretical Studies on Filling a Stel a Rator with Laser-Produced Plasma

Experiments have been performed on filling a stellarator with a noncurrent-carrying laser-produced plasma. Simultaneous plasma production by means of pulsed laser beams at four separate positions on the toroidal magnetic axis has been found to drastically enhance the trapping efficiency of produced plasma by stellarator field, to as high as 50 percent in contrast with about 10 percent in the case of plasma production at one position. This figure of 50 percent could be further improved to nearly 75 percent by spatially isotropic plasma productions which could not be realized in the present experiments owing to technical restrictions on the stellarator employed. The enhancement of trapping efficiency may be attributed to the reduction of toroidal plasma drift due to rotational transform coming into effect earlier in the multiposition production case. Some approximate theoretical analyses and considerations on toroidal drift motion of laser-produced plasma stream within stellarator field have also been presented, and the theoretical prediction on these analyses appears to be consistent with experimental results obtained.     

多股流换热器的柔性特性及柔性设计研究

本文从换热器的运行和调节特性入手提出了换热器柔性的概念,探讨了柔性特性与换热器变工况运行的关系,指出:柔性特性直接关系到换热器的变工况的运行性能,并且进而改变了换热器的设计思想。在分析了换热器传统设计方法的基础上,本文提出了考虑变工况运行的柔性设计思想,分别对多工况点等权重设计条件和多工况点不等权重设计条件进行了具体分析,并且相应地提出了虚拟工况点设计方法和主要运行工况点决定设计工况的方法。     

级联积分球辐射源角度均匀性研究

为了设计和制造高角度均匀性的积分球辐射源,需要提供优化的设计参数。基于空腔的辐射传输理论,建立了基于级联积分球结构的发光单元光出射度分布的仿真模型,并获得了朗伯型发光单元安装位置和级联积分球辐射源角度均匀性之间的关系。仿真结果表明：理想情况下,采用2个朗伯型级联子球作为发光单元,对称安装在与级联积分球辐射源出光口法线方向成10°夹角位置时,通过球心与出光口法线方向成±20°夹角观测区域内的角度均匀性可以达到0.03%的水平。最后,通过实验测量级联子球在30°夹角位置时级联积分球辐射源的角度均匀性,发现实验结果与仿真结果接近一致。因此,通过优化发光单元的类型和安装位置,可以有效提升积分球辐射源的角度均匀性。     

一种用于船舶吸附制冷系统的单元管设计与实验

基于前人提出的利用船舶内燃机排气废热的吸附式制冷系统系统的设计思想,文中致力于应用在吸附床中的单元冷管的研究,进行了一种用于船舶吸附式制冷系统的单元冷管的结构设计、工质对选择等,并实验分析和研究了添加可膨胀石墨的吸附单元冷管的循环特性,文中研究为今后的单元和系统设计提供了一定的实践指导。