理论[火用]分析在冷冻厂高温库中的应用

通过对一定环境温度条件下的高温冷库中的氨蒸汽压缩系统进行[火用]分析,利用线性拟合的方法对氨的物性进行模拟,并对定冷凝温度和变冷凝温度时,制冷系统的各部件的炯损失和系统的[火用]效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的[火用]损失最大,压缩机和冷凝器次之的结果。提出要对冷库氨蒸汽压缩系统的性能进行改进,必须首先考虑提高其蒸发器、压缩机和冷凝器的[火用]效率着手;认为在一定环境温度条件下,降低冷凝温度是提高[火用]效率的较好的改进措施之一．     

理论(焩)分析在冷冻厂高温库中的应用

通过对一定环境温度条件下的高温冷库中的氨蒸汽压缩系统进行(焩)分析,利用线性拟合的方法对氨的物性进行模拟,并对定冷凝温度和变冷凝温度时,制冷系统的各部件的(焩)损失和系统的(焩)效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的(焩)损失最大,压缩机和冷凝器次之的结果.提出要对冷库氨蒸汽压缩系统的性能进行改进,必须首先考虑提高其蒸发器、压缩机和冷凝器的(焩)效率着手;认为在一定环境温度条件下,降低冷凝温度是提高(焩)效率的较好的改进措施之一.     

过热和过冷对系统[火用]的影响分析

通过对定环境温度条件下的高温冷库中的氨蒸汽压缩系统进行(火用)分析,利用线性拟合的方法对氨的物性进行模拟,并对系统过冷度和过热度变化时,制冷系统的各部件的(火用)损失和系统的(火用)效率进行计算分析,得出在冷库氨蒸汽压缩系统中的蒸发器中的(火用)损失最大,压缩机和冷凝器次之的结果.提出定环境温度条件下,由于过热度越大,对系统越不利,过冷度越大,对系统越有利,提高系统性能可从减少过热度增大过冷度着手.     

水产品低温贮藏库的节能分析

通过利用线性拟合的方法对氨的物性进行模拟,在变冷凝温度和变冷间温度,以及在蒸发器和冷凝器压力降变化的条件下,分别对冷库中的氨双级蒸汽压缩系统进行能量分析,对系统各部件的炯损失和系统的炯效率进行计算分析,得出随着冷凝温度和冷间温度的改变,系统各设备的炯损失的排序变化的结果,以及随着压力降的变化系统的性能发生了变化,提出改进系统的性能可从减少冷凝传热温差和减少冷间传热温差,提高冷却水有效利用,改善蒸发器的压力降方面考虑。     

蒸汽压缩/喷射制冷系统喷射器设计及节能分析

蒸汽压缩/喷射制冷系统是一种有效的节能系统,可以减少节流膨胀损失,降低压缩机压力比,提高制冷系统效率。选择5种计算工况对蒸汽压缩/喷射制冷系统进行计算,研究喷射器结构与蒸发温度和冷凝温度的变化规律,并与普通蒸汽压缩系统对比,从制冷量、压缩机耗功、性能系数三个角度分析新系统的节能效果。计算结果表明蒸汽压缩/喷射制冷系统在低温工况条件下节能效果最优,制冷量最大可提高29%,压缩机耗功最大可降低65%,COP值最大可提高63%。     

跨临界二氧化碳蒸汽压缩/喷射循环的热力学分析

利用热力学第二定律的(火用)分析法,对跨临界二氧化碳蒸汽压缩／喷射制冷循环系统进行了仿真和分析。结果表明,放热压力存在最优值,升高气体冷却器出口温度和蒸发温度会降低系统火用效率;相对于简化循环,降低放热压力和蒸发温度能够增大系统火用效率的提高程度,而升高气体冷却器出口温度时,系统火用效率的提高程度将先增大,然后迅速减小。     

浸润式制冰系统和滑落式制冰系统能量分析

利用CoolPack软件对滑落式制冰系统和浸润式制冰系统进行分析,利用能量分析法对比评价两制冰系统中压缩机、冷凝器、节流阀、蒸发器的能量利用情况,并分析过冷度、过热度、蒸发温度、冷凝温度对整个系统损率和效率的影响。结果表明,浸润式制冰系统的效率较滑落式制冰系统提高约11.27%,制冷量提高约4.12%,适当降低蒸发器出口过热度、提高冷凝器出口过冷度、降低冷凝温度、提高蒸发温度均有利于提高机组性能。     

制冷系统中蒸发式冷凝器的性能优势

冷凝器是制冷系统主要的换热设备之一,其作用是将压缩机排出的高温过热制冷介质蒸汽冷却为液态。从20世纪70年代起,发达国家开始用蒸发式冷凝器代替水冷式冷凝器。而我国在近年也开始将蒸发式冷凝器应用于各类制冷系统中,其中包括冷库、中央空调、工业制冷机组、氨制冷系统等。蒸发式冷凝器的性能优势:(1)节水。蒸发式冷凝器充分利用水的汽化潜热,一般的水     

不同冷却方式制冷系统的热点问题分析

针对水冷系统和蒸发冷系统适用的蒸发器和螺杆式压缩机类型及2种系统的总体效率对比等相关热点问题进行分析,得出如下结论:降膜式或满液式蒸发器和半封闭螺杆式压缩机不适用于蒸发冷系统而更适用于水冷系统,干式蒸发器和开启式螺杆压缩机更适用于蒸发冷系统;在大多数工程应用中,配置降膜式或满液式蒸发器+半封闭螺杆式压缩机+水冷式冷凝器+开式冷却塔+冷凝器在线清洗装置的水冷系统,总体效率高于配置干式蒸发器+开启式螺杆压缩机的蒸发冷系统;蒸发冷系统更适合严苛工况及特殊工程应用,水冷系统更适合常规工艺冷却应用。     

复叠式制冷系统中R744替代R23的理论分析

本研究对复叠式制冷系统R744/R404A和R23/R404A进行了理论与对比分析。分析了高低温压缩机的排气温度、压缩机的功耗、系统的COP、系统的火用率以及各个部件火用损失的变化规律。研究结果表明:复叠式制冷系统随着蒸发温度的升高,其最佳低温循环冷凝温度增大,且存在一个最佳的COPopt所对应的最佳低温循环冷凝温度T4 opt;高低温压缩机的排气温度随蒸发温度的升高而降低;系统的COP随蒸发温度的升高而增大;系统的火用效率随蒸发温度的升高而降低先增加后减小;系统的火用损失随蒸发温度的升高而降低。     

Exergy analysis of multistage cascade low temperature refrigeration systems used in olefin plants

This paper provides an exergy analysis for multistage cascade low temperature refrigeration systems used in olefin plants. The equations of exergy destruction and exergetic efficiency for the main system components such as heat exchangers, compressors and expansion valves are developed. The relations for total exergy destruction in the system and the system overall exergetic efficiency are obtained. Also, an expression for minimum work requirement for the refrigeration systems of olefin plants is developed. It shows that the minimum work depends only on the properties of incoming and outgoing process streams cooled or heated with refrigeration system and the ambient temperature. Using actual work input values, the exergetic efficiency of the low temperature cascade refrigeration system of a typical olefin plant is determined to be 30.88% indicating a great potential for improvements. The novelty of this paper includes the suggestions for increasing efficiencies, along with discussion about the reasons for deviation from reversible processes.     

氨压缩制冷循环的分析

依据热力学第二定律,建立了氨压缩制冷循环的T-S热力学分析模型,对系统的各部件进行了损失的计算分析,列出了各部分损失的大小比例,从而揭示了系统中能量损失的原因,提出了系统节能的有效途径,并为氨压缩制冷系统的优化设计积累了经验。     

复叠式低温制冷箱的(火用)分析

根据实验得到的低温箱降温过程和稳定工作过程状态点参数,以R502/R13复叠式低温制冷箱为例对低温箱系统进行了(火用)分析计算.计算得出系统能效系数和(火用)损失随时间变化情况,更好的考察了系统各部件能耗状况,得到其中高低温级压缩机和蒸发冷凝器的(火用)损失所占比重最大,从而为设备改进提供借鉴和参考.     

一种新型跨临界CO2冷电联供系统热力分析

提出一种新型跨临界二氧化碳（trans-critical carbon dioxide,TCO₂）再压缩循环和喷射器制冷循环耦合的冷电联供系统。该系统在输出电能的同时,利用低品位热能驱动喷射器工作输出冷量。以输出电量1 MW为设计目标,对比冷电联供系统和再压缩发电系统的性能,研究联供系统各部件（火用）损和主要热力参数对其性能的影响。结果表明：联供系统利用CO₂余热驱动喷射器输出冷量,循环热效率高于单一再压缩系统;加热器（火用）损所占比例最大,回热器次之;透平进口温度、压力和背压对联供系统工质流量、循环效率、输出功率、加热器功率、压缩机耗功及喷射器制冷量等参数影响较大;而冷凝温度和蒸发温度仅对制冷循环制冷量影响较大。在设定条件下,联供系统的循环热效率和（火用）效率可分别达到46.99%和47.21%。     

A theoretical study on a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed for the cogeneration, which combines the Rankine cycle and the ejector refrigeration cycle by adding an extraction turbine between heat recovery vapor generator (HRVG) and ejector. This combined cycle could produce both power output and refrigeration output simultaneously, and could be driven by the flue gas from gas turbine or engine, solar energy, geothermal energy and industrial waste heats. Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the performance and exergy destruction in each component for the combined cycle. The results show that the condenser temperature, the evaporator temperature, the turbine inlet pressure, the turbine extraction pressure and extraction ratio have significant effects on the turbine power output, refrigeration output, exergy efficiency and exergy destruction in each component in the combined cycle. It is also shown that the biggest exergy destruction occurs in the heat recovery vapor generator, followed by the ejector and turbine.     

Diagrams of entropy for ammonia–water mixtures: Applications to absorption refrigeration systems

The objective of this work is to calculate the entropy of ammonia–water mixture as a function of temperature, pressure, concentration, and other thermodynamic properties associated to absorption process, to support energy and exergy analysis of absorption refrigeration systems. This calculation is possible because a novel mathematical modelling was developed for this attempt. This determination will allow simulation and optimisation of absorption refrigeration systems, giving major importance in determining the values of thermodynamic properties of ammonia–water mixtures, such as enthalpy and entropy. A mathematical modelling for thermodynamics properties calculation at liquid and vapour phases of ammonia–water system is developed. The studies were based on the enthalpy vs. concentration diagram obtaining the enthalpy in the liquid phase corresponding at a temperature range from 80 °C to −40 °C. The mixtures enthalpy values were calculated for ammonia (h_1c) and water (h_2c) by using a non-linear regression program. The evaluation of thermodynamic properties in this work was discretised by formulating appropriate equations for each type of substance. However, thermodynamic properties of mixtures can be determined based on data from simple substances and mixing laws, or from an equation of state that considers the mixture concentration. The consistency of experimental data indicates the most suitable method to be used in entropy calculation.     

Exergy analysis of an ionic-liquid absorption refrigeration system utilizing waste-heat from datacenters

Ionic-liquid (IL) was introduced as an absorbent of an absorption refrigeration system designed for high power electronics cooling. IL is a salt in liquid-state, which is nonvolatile, thermally-stable, nonflammable, and environmentally-benign. It provides an alternative to the normally toxic working fluids, such as ammonia, also eliminates crystallization and metal-compatibility issues of the water/LiBr system. The performance of IL absorption refrigeration system was theoretically examined using exergy analysis. Various combinations of refrigerant and imidazolium-based ILs were chosen as working fluid pairs. The thermodynamic properties of ILs were evaluated using the correlations based on group contribution methods. A non-random two-liquid (NRTL) model was built and used to predict the solubility of the mixtures. Both the coefficient of performance (COP) and the exergetic coefficient of performance (ECOP) were evaluated. The effects of operating conditions on ECOP were explored. Also, the exergy destruction of each component was evaluated and discussed as a means to identify the critical component(s) of the system that would require optimization.     

Exergy analysis of gas turbine trigeneration system for combined production of power heat and refrigeration

A conceptual trigeneration system is proposed based on the conventional gas turbine cycle for the high temperature heat addition while adopting the heat recovery steam generator for process heat and vapor absorption refrigeration for the cold production. Combined first and second law approach is applied and computational analysis is performed to investigate the effects of overall pressure ratio, turbine inlet temperature, pressure drop in combustor and heat recovery steam generator, and evaporator temperature on the exergy destruction in each component, first law efficiency, electrical to thermal energy ratio, and second law efficiency of the system. Thermodynamic analysis indicates that exergy destruction in combustion chamber and HRSG is significantly affected by the pressure ratio and turbine inlet temperature, and not at all affected by pressure drop and evaporator temperature. The process heat pressure and evaporator temperature causes significant exergy destruction in various components of vapor absorption refrigeration cycle and HRSG. It also indicates that maximum exergy is destroyed during the combustion and steam generation process; which represents over 80% of the total exergy destruction in the overall system. The first law efficiency, electrical to thermal energy ratio and second law efficiency of the trigeneration, cogeneration, and gas turbine cycle significantly varies with the change in overall pressure ratio and turbine inlet temperature, but the change in pressure drop, process heat pressure, and evaporator temperature shows small variations in these parameters. Decision makers should find the methodology contained in this paper useful in the comparison and selection of advanced heat recovery systems.