R22替代工质蒸发器的性能研究

基于湿球温度效率法,建立了蒸发器的稳态分布参数模型。分别以R22及其3种替代产品(R407C,R410A,R134A)为工质,运用该模型详细比较了在流量变化及风量变化两种情况下2排管蒸发器的换热和流动特性。结果表明：当迎风面风速不变时,随着管内冷媒流量的增大,各种工质蒸发器总换热量、显热换热量、潜热换热量均增大,但潜热换热量增大得更快。压降亦随着管内流量的增大而增大。当管内冷媒流量不变时,随着蒸发器迎风面风速的增大,各种工质蒸发器总换热量、显热换热量均增加,潜热换热量下降,同时压降亦下降,但下降的趋势随着风速的增大而最终趋于平缓。四种工质中,R134A性能较好,但其压降也最大,R410其次,压降最小,但其蒸发压力比R22高出60％左右。R407C与R22在换热量及压降方面最为接近,是其理想的替代产品。     

流程布置对R407C冷凝器性能的影响

本文基于传热单元法，建立了冷凝器的分布参数模型。以R407C为工质，运用该模型详细分析了四种不同流程布置两排管冷凝器的换热和流动特性，并与以R22为工质的冷凝器进行了性能比较。结果表明：采用R407C为工质时，四种流程布置中，无论是随着管内冷媒流量的变化，还是随着冷凝器迎风面风速的变化，逆流布置换热效果都是最好，换热量比顺流高约5％-40％，压降比顺流高约3％-10％，其次是错流布置，顺流布置最差。在与以R22为工质的冷凝器性能比较中，无论是随着管内冷媒流量的变化，还是随着迎风面风速的变化，R407C冷凝器换热量都比R22冷凝器高约3％-5％，压降低约5％-10％，是其理想的替代产品。     

风速对不同流程数CO2蒸发器性能的影响

为研究迎面风速对不同流路数CO₂翅片管蒸发器性能的影响,本文建立分布参数模型对蒸发温度为-25℃,风速为0.5～4 m/s条件下5种流路数CO₂翅片管蒸发器的制冷剂压降、换热量、温度分布及传热系数的变化进行分析,并通过实验验证了蒸发器模型的可靠性。蒸发器模型的换热量、制冷剂压降和风侧压降等参数模拟值与相同工况下实验值的误差均在±4%以内。结果表明:同一流路数蒸发器的换热量、制冷剂压降及传热系数均随风速的增大而增大,而其涨幅随风速增大而减小,综合考虑换热效果和能耗可得最佳风速范围为2.5～3.5 m/s;在一定风速条件下,蒸发器设计时在合理范围内选择较多流路数可有效提升蒸发器换热性能并增强换热均匀性,本次实验中24流路蒸发器为最佳设计方案。     

二氧化碳翅片管式蒸发器模拟与分析

运用分布参数法建立采用CO2的翅片管式蒸发器的数学模型，分析制冷剂侧和空气侧温度、压力和换热的变化情况。同时讨论迎面风速和制冷剂质量流量对蒸发器换热和流动性能的影响，结果表明提高迎面风速可以增加换热效果，但增加的趋势趋于平缓。制冷剂侧压降则成近似线性增大；随着管内工质流量的增大，蒸发器总换热量和制冷荆侧压降都成近似线性增大。这些工作有助于进一步了解CO2在翅片管式蒸发器中的换热和流动特性，并为换热器的优化设计和系统的匹配提供理论依据。     

流路布置对R22替代工质冷凝器性能的影响研究

基于相关文献提出的冷凝器分布参数模型,分别以R22的3种替代产品（R407C,R410A,R134A）为工质,分析了4种不同流路布置的2排管冷凝器的换热和流动特性,并与以R22为工质的冷凝器进行了性能比较。结果表明：采用R22的3种替代工质时,冷凝器性能的变化规律基本一样,4种流路布置中,在随着管内冷媒流量的变化和随着冷凝器迎风面风速的变化两种工况下,逆流换热效果最好,其次是错流,顺流最差;在与R22为工质的冷凝器性能比较中,采用3种替代工质的冷凝器换热量及进出口压降的变化趋势基本一样;在3种替代工质中,R410A性能较好,换热量最大、压降最低,但其冷凝压力比R22高出60%左右,R134A压降较大,这两种都不是理想替代物,而R407C与R22在换热量及压降方面最为接近,是其理想的替代工质。     

冷凝器流程布置方案的研究与探讨

基于传热单元法，建立了冷凝器的稳态分布参数模型。经与前人的实验研究结果进行对比，数值模拟结果与实验结果吻合良好。运用该模型详细分析了六种不同流程布置的二排管冷凝器的换热和流动特性。研究结果表明：单回路冷凝器中，逆流布置换热最好，错流其次，顺流最差；对任一流程布置的冷凝器，当风量不变时，必然存在一最佳冷媒流量使冷凝器性能达到最佳；当冷媒流量保持不变时，也相应存在一个最佳风量，使冷凝器性能最佳。冷凝器流路布置中，重力的影响不可忽略。针对单回路冷凝器进出口总压降过大，沿程压降、热阻及换热系数分布不均匀，提出了一些实用性的分流原则，如双“N”流路，相变点分流等并进行了深入细致的讨论。该研究方法为冷凝器流程布置的优化设计提供了理论基础和指导方向。     

不同空气侧风速下微通道蒸发器换热特性实验研究

搭建微通道蒸发器性能实验台,采用控制变量法研究不同空气侧风速下微通道蒸发器表面温度分布、制冷剂进出口压力的变化规律,计算换热量和换热系数,从而分析空气侧风速对微通道蒸发器的流量分配特性和换热效果的影响。结果表明,随着风速增大,微通道蒸发器制冷剂流量分配不均匀性增大,进出口压力波动振幅和周期增加,压降增大,风速2 m/s时微通道蒸发器换热效果最佳。     

流程布置对R410A冷凝器性能的影响研究

本文基于效率-传热单元法,建立了空冷式冷凝器的分布参数模型.以R410A为工质,运用该模型详细分析了四种不同流程布置两排管冷凝器的换热和流动特性,并与以R22为工质的冷凝器进行了性能比较.结果表明采用R410A为工质时,四种流程布置中,无论是随着管内制冷剂流量的变化,还是随着冷凝器迎风面风速的变化,逆流布置换热效果最好,换热量比顺流高约5～15%,压降比顺流高约3～20%,其次是错流布置,顺流布置最差.在与以R22为工质的冷凝器性能比较中,无论是随着管内制冷剂流量的变化,还是随着迎风面风速的变化,R410A冷凝器换热量都比R22高约6～15%,压降低约30～50%.本研究结论为冷凝器流程布置的优化和设计提供了一定的理论基础和指导方向.     

R22替代工质冷凝器的性能研究

本文基于传热单元法,建立了冷凝器的稳态分布参数模型.分别以R22及其3种替代产品(R407C,R410A,R134A)为工质,运用该模型详细比较了在流量变化及风量变化两种情况下2排管冷凝器的换热和流动特性.结果表明:无论是随着管内冷媒流量的变化,还是随着迎风面风速的变化,换热量及进出口压降的变化趋势基本一样.四种工质中,R410A性能较好(换热量最大,压降最低),但其冷凝压力比R22高出60%左右,R134A由于压降较大,两者都不是R22的理想替代物.R407C与R22在换热量及压降方面最为接近,是其理想的替代工质.     

基于NSGA-III算法的小管径翅片管式蒸发器高维多目标优化

以稳态分布参数法和NSGA-III算法为基础，提出一种翅片管式蒸发器结构参数与流路参数混合寻优的方法，并依此展开小管径蒸发器结构和流路参数的影响分析与流路的高维多目标设计优化。建立的小管径翅片管式蒸发器模型与实测数据的误差在4%以内，可以较好地用于小管径翅片管式蒸发器的计算。基于该模型进一步建立以结构参数与流路参数为自变量，换热量、制冷剂侧压降、空气侧压降以及成本为因变量的神经网络模型，并利用NSGA-III算法对模型进行优化求解，得到小管径翅片管式蒸发器在一定的结构参数变化范围内的最优结构参数及最佳流路。研究结果显示：管外径对小管径翅片管式蒸发器的换热量、制冷剂侧压降以及成本的影响程度最大；翅片间距对小管径翅片管式蒸发器的空气侧压降影响程度最大；翅片厚度对换热量、制冷剂侧压降、空气侧压降以及成本的影响程度均最小；流路主要影响蒸发器的换热量及制冷剂侧压降；制冷剂流路为二支路、三支路和四支路时，模型可输出综合性能最优的结构及流路特征。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...