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.     

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.     

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     

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.

     

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%。     

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.     

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 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.     

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。     

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.     

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.     

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.     

Exergetic analysis and evaluation of coal-fired supercritical thermal power plant and natural gas-fired combined cycle power plant

The present work has been undertaken for energetic and exergetic analysis of coal-fired supercritical thermal power plant and natural gas-fired combined cycle power plant. Comparative analysis has been conducted for the two contestant technologies. The key drivers of energetic and exergetic efficiencies have been studied for each of the major sub-system of two contestant technologies. Overall energetic and exergetic efficiency of coal-fired supercritical thermal power plant are found to be 43.48 and 42.89 %, respectively. Overall energetic and exergetic efficiency of natural gas-fired combined cycle power plant are 54.47 and 53.93 %, respectively. The major energetic power loss has been found in the condenser for coal-fired supercritical thermal power plant. On the other hand, the major energetic power loss has been found in both the condenser and heat recovery steam generator for gas-fired combined cycle thermal power plant. The exergetic analysis shows that boiler field is the main source of exergetic power loss in coal-fired supercritical thermal power plant and combustion chamber in the gas-fired combined cycle thermal power plant. It is concluded that natural gas-fired combined cycle power plant is better from energetic and exergetic efficiency point of view. These results will be useful to all involved in the improvement of the design of the existing and future power plants.     

A continuum thermodynamic analysis of cohesive zone models

A global thermodynamic analysis of the running crack problem is presented. The crack is modeled as an evolving partially cohesive interface endowed with a thermodynamic structure distinct from that of the surrounding body. Constitutive relationships for the cohesive part of the crack surface are formulated in a general way that allows one to account for various dissipative mechanisms and to recover most of the cohesive zone models available from the literature. Particular attention is focused on some of the fundamental and necessary requirements for formulating cohesive zone models. The relationship between such requirements and the interface evolution is discussed and analysed.     

Equilibrium, kinetic and thermodynamic studies on the adsorption of phenol onto chitin

The adsorption of phenol onto chitin, a naturally occurring material was studied as a function of initial pH, temperature and initial phenol concentration. The highest phenol adsorption capacity was determined as 21.5 mgg(-1) for 300 mgdm(-3) initial phenol concentration at pH 1.0 and 40 degrees C. Adsorption data were well described by the Freundlich Model, although they could be modeled by the Langmuir equation. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second-order kinetic model provided the best correlation of the experimental data compared to the pseudo-first-order model. The thermodynamic constants of the adsorption process; DeltaG degrees , DeltaH degrees and DeltaS degrees were evaluated as -19.4 kJmol(-1) (at 40 degrees C), 10.2 kJmol(-1) and 0.093 kJmol(-1)K(-1), respectively. These showed that adsorption of phenol on chitin was endothermic and spontaneous.     

Equilibrium,kinetic and thermodynamic studies on the adsorption of phenol onto graphene

Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.