空气制冷应用于空调系统的分析研究

随着CFCs 制冷工质替代技术的深入研究,由于空气作为制冷工质对环境的非污染的友好特性,所以以空气作为制冷工质的制冷系统的特性研究得到人们的青睐.从分析空气制冷循环的热力特性入手,对应用于空调系统的空气制冷循环进行了高压循环和真空循环性能理论计算与比较,讨论了开式循环和闭式循环的特点、空气制冷循环利用一次回风的特性以及在实际工程中的应用问题.     

Feasibility analysis of an OTEC plant as the bottom cycle of the third nuclear power plant

Abstract

A conceptual design, performance analysis, system optimization and simulation of an OTEC (Ocean Thermal Energy Conversion) power plant was carried out in the present study. The OTEC plant acts as the bottom cycle of the Third Nuclear Power Plant, utilizing the warm water discharged from the nuclear plant as the heat source and the cold deep seawater pumped from the nearby sea bottom as the heat sink. The nominal net power output from the OTEC plant is estimated to be 8.74 MWe. A plant simulation was further carried out to study the OTEC plant performance due to seasonal variation of the warm water temperature, which shows that the OTEC plant is able to deliver an electricity of 5.18×10⁷ kWH per year. The net power output in the winter season will be reduced to about one eighth of that in the summer season. The final discharged warm water temperature was shown to be below 29°C all year around, so that the current thermal pollution problem of the nuclear power plant can be eliminated. Additionally there is the side benefit of 8.74 MWe net power generation from ocean energy resource. This OTEC plant will become economically feasible if the installation cost is considered as a thermal pollution control investment.     

蒸汽双效吸收式制冷站的设计和运行调试

介绍了天津石化蒸汽双效吸收式制冷站的设计概况。针对不同季节制冷负荷的差异,采用不同的制冷方式。冷冻水系统采用闭式循环,蒸汽系统设置了减温减压装置。对凝结水回收器进行了改进,使之同时满足凝结水回收和减温水供给的需要。试运行期间,出现了水泵电机过载的问题,分析为实际工作状态点偏离设计状态点所至,比较了3种不同处理方案,即采用增大局部阻力、变频和叶轮切削后增加局部阻力的方法加以修正。另外还出现蒸汽关断阀不能正常动作的情况,原因是阀门执行机构工作特性与制冷机工作原理不匹配,更换执行装置后动作正常。合理应用蒸汽双     

Influence of the new refrigerant thermodynamic properties on some refrigerating turbocompressor characteristics

Comparison of the main geometrical and operating parameters of centrifugal compressors working with various refrigerants is realised in this paper. The interdependence between the centrifugal compressor pressure ratio, compression work, impeller peripheral speed, Mach number, compressor capacity, impeller diameter and width, speed of rotation, and refrigerant molecular mass, normal boiling temperature and specific volumetric cooling capacity for various refrigerants are shown and discussed. The flow phenomena in the turbocompressor flow field, caused by high Mach number and high pressure ratio, are analysed. Some theoretical observations for the influence of the substitute of the refrigerant on the turbocompressor performance characteristics are presented. The possibilities for the replacement of the refrigerant in the existing refrigerating machines are discussed.     

The efficiency of an optical heat pump in the inverse thermodynamic cycle

Proceeding from the first law of thermodynamics and the laws of radiation, an expression for the efficiency of an optical heat pump in the inverse thermodynamic cycle is derived in terms of the system parameters. Based on these relations, general requirements to the parameters of an optical heat pump are formulated that can be used in designing real devices.

     

某小型制氧制氮设备流程改进的探讨

某小型制氧制氮设备由于流程设计上存在的不足 ,存在冷损大、产品浪费大和氮纯度不及时反映工况等问题 ;针对问题 ,提出了改进措施     

Influence of the piston displacement profile on the performance of a refrigerating cycle equipped with an axial piston compressor

An extended analysis aiming to investigate the influence of the piston displacement in an axial compressor on the thermodynamic cycle of a refrigeration system was carried out. Axial piston compressors are commonly equipped with a rotating disk plate that guides the pistons along a sinusoidal displacement. A proper shape of the rotating disk can lead to a piston displacement that optimizes the power consumption and then the refrigeration cycle efficiency. In this paper, a sensitivity analysis on the compressor cycle characteristics by varying the piston displacement profile and the compressor operating conditions is presented. The mechanical analysis of the forces exerted by the piston on the rotating disk was also carried out to estimate the mechanical stresses acting on the rotating disk.     

SRMES: an expert system for performance analysis of small refrigerating machines

SRMES is a rule-based expert system designed for use in the refrigeration industry as an aid in diagnosing the most frequent malfunctions in small refrigerating machines of either the air- or water-cooled condenser type. Suitably expanded, it may cover other more complex types of refrigerating machine. The system could also be suitable for education and training. In the version described here, SRMES is intended to demonstrate that the use of expert system tools in the refrigeration industry may lead to higher efficiency and better performance. Although the version described in the paper has been optimized for off-line performance, its extension to on-line application may be justified by relevant experience gained through its practical operation. Particular attention is devoted in the paper to the development of the decision tree. It is shown that with computer hardware of limited capacity knowledge-based rules can be used to reach specific diagnoses of the performance of small refrigerating machines.     

循环周期对吸附制冷管性能的影响与分析

设计制作了一种类似于热管、以13X分子筛-水为工质对的吸附制冷单管,吸附制冷单管直径为19 mm,吸附制冷单管由吸附床段和蒸发\冷凝段组成,其中吸附床段长800 mm,蒸发冷凝段长260 mm。吸附制冷系统由吸附制冷单管、管式电炉和数据采集装置组成,利用本装置对影响吸附制冷单管性能的循环周期、吸/脱附时间比进行了一系列实验研究,并利用数值模拟对分析结果进行了理论分析。研究表明:当吸附时间和脱附时间相等时,在不同脱附温度下,循环周期存在一个相应的最佳值,脱附温度越高,相应的最佳循环周期越长;适当增加一个循环周期内吸附时间所占比例可有效提高单元管制冷功率。对于此吸附单元管,在脱附温度为310℃时,吸附时间35 min、脱附时间25 min时,吸附制冷单管制冷功率达到最大值4.97 W,其单位质量吸附剂的制冷功率SCP为57.73W/kg,比吸附时间和脱附时间均为30 min时的制冷功率提高6.65%。     

Application of an ejector in autocascade refrigeration cycle for the performance improvement

This paper presented a novel autocascade refrigeration cycle (NARC) with an ejector. In the NARC, the ejector is used to recover some available work to increase the compressor suction pressure. The NARC enables the compressor to operate at lower pressure ratio, which in turn improves the cycle performance. Theoretical computation model based on the constant pressure-mixing model for the ejector is used to perform a thermodynamic cycle analysis for the NARC with the refrigerant mixture of R23/R134a. The effects of some main parameters on cycle performance were investigated. The results show the NARC has an outstanding merit in decreasing the pressure ratio of compressor as well as increasing the COP. For NARC operated at the condenser outlet temperature of 40 °C, the evaporator inlet temperature of −40.3 °C, and the mass fraction of R23 is 0.15, the pressure ratio of the ejector reaches to 1.35, the pressure ratio of compressor is reduced by 25.8% and the COP is improved by 19.1% over the conventional autocascade refrigeration cycle.     

A thermodynamic analysis of the drying thermogram method

A thermodynamic analysis of dispersed particle drying is used to formulate the conditions which must be satisfied in order to correctly record and interpret drying thermograms.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 3, pp. 419–423, September, 1973.     

Selecting a thermodynamic cycle for the closed gas-turbine power plant of spacecraft in order to minimize surface of the cooler-radiator

The influence of the thermodynamic cycle scheme selected for a closed gas-turbine power plant of spacecraft on the specific surface of its cooler-radiator are evaluated. The dependence of the cooler-radiator characteristics on the regeneration, intermediate cooling, and heating of the working medium are analyzed.     

延长FN-800/70Y空分设备生产周期的实践

通过技术改造和加强管理 ,使两套FN - 80 0 / 70Y空分设备连续运转时间达 6 6 6 0 0小时以上 ,近 8年时间两套设备省电 1336 0 0kWh ,经济效益可观。     

盐冻循环条件下沥青高低温性能的灰关联熵分析

利用动态剪切流变仪(DSR)和弯曲梁流变仪(BBR)对冻融循环前后的三种沥青(沥青、苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)改性沥青、胶粉改性沥青)进行测试,比较分析不同冰冻温度、融雪盐浓度、冻融循环次数下三种沥青的高低温性能变化规律,并对环境因素进行灰熵分析。结果表明:在盐冻循环条件下对沥青复合模量G*影响最大的因素是融雪盐溶液浓度,其次是10℃延度;对沥青相位角δ影响最大的因素是软化点,其次是25℃针入度;对沥青蠕变劲度模量S影响最大的因素是融雪盐溶液浓度,其次是10℃延度;对沥青蠕变速率m影响最大的因素是试验温度,其次是冰冻温度。     

A thermodynamic analysis of rigid heat conductors

A thermodynamic approach to rigid heat conductors is proposed: it introduces the heat flux vector as independent variable while its temporal evolution is governed by a first order differential equation. The form of the second law is that proposed by Müller wherein the entropy flux and the entropy source are not given a priori but determined through constitutive equations. Restrictions on the constitutive equations are placed by the second law. Some properties, valid in the vicinity of equilibrium are established. In particular, it is shown that the present theory leads to a hyperbolic heat conduction equation, allowing for the propagation of heat as a thermal wave with a finite velocity. The concept of thermodynamic forces and fluxes is also introduced. The latter are seen to derive from a potential function plus an additional term. Finally, it is established under which conditions symmetry relations are satisfied.     

A detailed fractographic analysis of cleavage steps in silicon

A detailed analysis of cleavage steps present on fracture surfaces in pure silicon has been carried out using scanning electron microscopy. The results indicate that the mechanisms involved in both the formation of unfractured ligaments, produced when adjacent cleavage facets overlap, and the subsequent fracture of these ligaments to form cleavage steps, are quite complex. Specifically it is shown that, during ligament formation, the local crack fronts are deflected from their preferred (1 1 1) cleavage plane and that the fracture of these ligaments to form cleavage steps occurs in a very complex fashion producing very small microcleavage steps. It is shown that these latter steps are consistent with cleavage along both {1 1 1} and {0 1 1} planes.     

Potential energy of adsorption in A-type zeolites and adsorption thermodynamic characteristics of noble gases and methane

Simple models of the NaA and CaNaA lattice were developed and applied to the computation of the potential energy of interaction of Ar, Kr, Xe and CH₄ molecules with the zeolite lattice at many points in the large cavity. The corresponding potential reliefs have been constructed and are illustrated in this Paper. The spatial distribution of potential energy was used in molecular statistical computations of Henry constants and isosteric heats of adsorption in the low coverage region. Agreement between calculated and observed thermodynamic characteristics was achieved via selection of the most appropriate formula to calculate the constants of dispersion attraction.     

Dynamics of superconductors and minimum entropy production

A simple model of the resistive state in a superconducting channel with a periodic array of inhomogeneities is considered. It is shown that the dynamic equations for the resistive state in this channel do not, in principle, determine a unique value of the Josephson oscillation period in the resistive state, i.e., a unique value of the electric field in the channel at a given current. Such an ambiguity appears to be characteristic for the resistive state in narrow superconducting channels also in a quite general situation not restricted to any particular model. In the simplest case considered here it is shown, however, that fluctuation effects lead to relaxation of the system to the state that corresponds to the minimum possible electric field at a given current, i.e., to the state with the minimum entropy production.     

A model of discontinuous precipitation based on the balance and maximum production of the entropy

A model of discontinuous precipitation in supercooled binary polycrystalline alloys at reduced temperatures, taking place as a result of the diffusion-induced grain boundary migration, is constructed with allowance of grain boundary diffusion. The proposed approach allows independent determination of the main parameters, including the interlamellar distance, the maximum velocity of the phase transformation front, and the concentration jump at this boundary. This is achieved by using a set of equations for the (i) mass transfer in the moving interphase boundary, (ii) balance of the entropy fluxes at the phase transformation front, and (iii) maximum rate of the free energy release. The model uses a minimum of thermodynamic information on the two-phase system: the curvature of the Gibbs potential surface in the decomposing phase and the free energy of the interface between the new phases. Theoretical results are compared to the available experimental data.