基于遗传算法的CO2热泵热水器系统优化研究

本文提出一种基于遗传算法的跨临界CO_2热泵热水器系统的优化方法。采用固定压缩机排气压力的方式,使用MATLAB对热泵热水器系统建立了仿真模型,并以实测数据验证了该模型的可靠性。以系统性能系数COP为目标函数,选择制冷剂质量流量M_r,气冷器管长L_g以及蒸发器管长L_e为优化变量,在不同的工况下采用遗传算法对原实验用CO_2热泵热水器系统进行优化,结果表明,该优化方法可以优化原设备管长,提高系统COP。     

PAG润滑油对超临界CO_2换热性能影响的研究

综述了润滑油在气冷器中对超临界CO_2换热特性影响的国内外研究现状,进行了润滑油对超临界CO_2换热性能影响的实验研究,以实验装置为物理原型建立了换热模型,编写了模拟程序,并根据实验得到的结果验证了模拟程序,模拟得出:随着CO_2压力增大,油膜增厚,换热系数反而也增大;随着CO_2质量流量增大,局部换热系数增大。可通过在管道内促进形成无源扰动、管道中设置扰流原件,设计气冷器时适当缩小后半段CO_2换热管管径等方法强化换热。     

利用LNG冷能与工业余热跨临界循环参数分析

针对一种利用LNG冷能与工业烟气余热的单级跨临界循环展开研究,采用乙烷为循环工质,分析冷凝温度、蒸发压力、冷凝器夹点温差及烟气出口温度4个主要运行参数对循环性能(热效率、火用效率、净功率输出、乙烷及烟气质量流量)的影响。介绍LNG冷能与工业烟气余热单级跨临界循环模型,给出典型工况下各节点的参数。进行热力学分析,得到循环的热效率及火用效率表达式。采用Matlab软件中的遗传算法工具箱进行优化。热效率和火用效率随着冷凝温度的升高而降低,随着蒸发压力的增大而增大;随着冷凝温度的降低及蒸发压力的升高,循环系统净功率输出都增加;火用效率曲面和热效率曲面存在交叉线,热效率在蒸发压力较低而冷凝温度较高时低于火用效率;烟气的质量流量明显大于乙烷的质量流量,且都随着冷凝温度和蒸发压力的增大而增大。热效率和火用效率随着夹点温差的升高而降低,随着烟气出口温度的增大,热效率不变而火用效率降低,且火用效率曲面和热效率曲面存在交叉线;净功率输出随夹点温差的增大而降低,随烟气出口温度的改变而不变;烟气及乙烷的质量流量随夹点温差的增加都降低;随烟气出口温度的增加,乙烷质量流量不变而烟气质量流量增加。火用效率和净功率输出随着蒸发压力的升高,先增大再减小,存在最佳的蒸发压力(8 MPa左右),使得火用效率及净功率输出最大,而热效率随着蒸发压力的增大而增大;随着烟气出口温度的增加,热效率及净功率输出不发生变化,火用效率逐渐降低;蒸发压力升高,烟气及乙烷的质量流量都降低;烟气出口温度增大,乙烷质量流量不变而烟气质量流量增加。     

LNG富氧燃烧电厂[火用]及[火用]经济分析

利用[火用]及[火用]经济分析方法,应用Aspen Plus模拟软件定量研究H_(2)O和CO_(2)作为稀释剂时对LNG富氧燃烧系统(O_(2)/H_(2)O燃烧系统和O_(2)/CO_(2)燃烧系统)的能耗及经济性的影响。结果表明:O_(2)/CO_(2)燃烧系统的总[火用]效率为51.12%,高于O_(2)/H_(2)O燃烧系统的36.35%;O_(2)/CO_(2)燃烧系统可避免[火用]损率为19.97%,远高于O_(2)/H_(2)O燃烧系统的11.99%。从系统整体而言,在保持系统进料及燃烧条件相同的条件下,O_(2)/CO_(2)燃烧系统[火用]效率更高,从能耗角度来讲,CO_(2)更适合作为LNG富氧燃烧系统的稀释剂,以CO_(2)作为稀释剂可以提高富氧燃烧系统各个组件的优化潜力。     

换热装置对一二级侧流量不匹配适应性分析

结合工程实例,在相同供热能力条件下,计算板式换热器、溴化锂吸收式换热机组的火积耗散,定量评价两种换热装置对热力站一二级侧流量不匹配工况的适应性。溴化锂吸收式换热机组的火积耗散为板式换热机组的49.7%,其更适用于热力站一二级侧流量不匹配的工况。     

热学参数在建筑热湿环境营造过程中的适用性分析

比较了两类热学参数--(火用) (或熵)、(火积)在分析建筑热湿环境营造过程时的适用性.(或熵)是研究热功转换过程的热学参数,参考状态的选取对分析所得结论的影响很大.介绍了(火积)的物理概念及其在传热领域的应用,尝试利用(火积)作为热学参数对以热量、质量传递过程为主的热湿环境营造过程进行研究.分析了典型热湿环境营造案例...     

带膨胀机CO2跨临界热泵系统运行特性

建立了带膨胀机CO2跨临界热泵系统的数学模型,将模拟计算结果与实验测量结果进行了比较,验证了模型的准确性。利用数学模型分析了冷却水进口温度和质量流量、冷冻水进口温度和质量流量对带膨胀机CO2跨临界热泵系统的制冷性能系数及最佳高压侧压力的影响。降低冷却水进口温度和提高其质量流量不仅有利于提高制冷性能系数,而且能降低最佳高压侧压力。提高冷冻水进口温度及质量流量有利于提高制冷性能系数,对最佳高压侧压力影响不大。     

地下水源热泵系统的(火用)分析

对地下水源热泵系统中蒸发器、压缩机、冷凝器、节流阀及系统进行了火用分析,给出火用效率、单位时间火用损、火用损系数的计算公式。结合工程实例,对某地下水源热泵系统进行了火用分析,压缩机的单位时间火用损最大。     

燃料电池与传统发电方式的热力学分析

从系统熵和火用的角度,对传统方式发电和燃料电池发电机理进行热力学分析,通过对两种发电过程中的火用损、熵增以及热力学效率的比较得出:传统发电装置在发电过程中,高温烟气在推动热机做功发电之前,由于升高自身温度所耗能量已造成较高的火用损;而燃料电池将燃料的化学火用,即吉布斯自由能直接转化为电能,火用损失明显减少,提高了热力学效率,因此燃料电池发电技术具有较为明显的优势。     

非均匀受火下约束型钢混凝土柱力学性能研究

为了解不同受火条件下型钢混凝土柱截面温度场,同时考察受火方式、火灾荷载比、荷载偏心率、约束刚度比等参数对型钢混凝土柱抗火性能的影响,进行了14个包括四面、三面、相对两面、相邻两面、单面受火条件下轴向约束型钢混凝土柱的抗火性能试验。试验结果表明：受火面数量、受火方位对 型钢混凝土柱截面温度分布有显著影响,升温时间相同时,四面受火、三面受火、两面受火、单面受火试件截面相同位置处所经历的最高温度依此降低;距试件表面距离相同时,型钢翼缘外侧受火面温度比型钢腹板外侧受火面温度略高。受火方式、火灾荷载比、荷载偏心率、约束刚度比对升降温全过程下型钢混凝土柱轴向变形和轴力发展有显著影响,试件受热膨胀变形和降温压缩变形随受火面数的增多而增大;轴向膨胀变形随火灾荷载比的增大而减小,随荷载偏心率的增大而增大;荷载比越大,试件由轴向拉伸状态转为轴向压缩状态的时间越短,压缩程度越高。定义试验实测轴力与初始施加轴力的比值为轴力变化系数,四面受火、三面受火、两面受火、单面受火时,试件升降温后期的轴力变化系数依此递减,轴力变化系数峰值随荷载偏心率和轴向约束刚度比的增大而增大,随火灾荷载比的增大而减小。     

Thermodynamic analysis of designed and fabricated shell- and tube-type heat exchanger by DSTHE software: Kern method

In this research work, shell- and tube-type heat exchanger has been designed by Kern method. To eliminate design problems, computer software (DSTHE software) has been developed. All design parameters have been calculated by this method with the help of DSTHE software such as number of tubes, shell diameter, pipe pitch and pitch ratio. And then velocity of the tube side fluid, convective heat transfer coefficients for tube and shell side fluids and overall heat transfer coefficient have been calculated. By developed DSTHE software, tube side and shell side fluids pressure drops, entropy generation and entransy dissipation have also been found. Shell- and tube-type heat exchanger has been fabricated with calculated parameters. At various operating conditions, a number of experiments have been performed. For each condition, entropy generation analysis, entransy dissipation analysis and entransy-based thermal resistance analysis have been done. Maximum value of effectiveness, minimum values of entropy generation, entransy dissipation and entransy-based thermal resistance have been found and that actual operating conditions have been identified.     

Application of entropy and entransy concepts to design shell and tube type surface condenser at different 4L/D ratios for Maral Overseas Ltd

ABSTRACT

The optimisation of heat exchanger is an important issue. So, the optimum size of counter flow surface condenser is found in this research work for Maral Overseas Ltd by entropy, exergy and entransy theories. In this work, effectiveness of heat exchanger, number of transfer units, entropy generation, entransy dissipation, entransy dissipation-based thermal resistance, entransy dissipation number and entransy effectiveness for hot/cold fluid sides with outlet temperatures of fluids are found for various 4L/D ratios. And then the optimum value of 4L/D ratio is found for the surface condenser. Entransy dissipation number and entransy-based thermal resistance both must be as low as possible for proper design. It is observed that when 4L/D ratio increases then EDN, entransy dissipation-based thermal resistance, outlet temperature of hot fluid and entropy generation decrease but NTU, effectiveness and outlet temperature of cold fluid increase. This research work is concluded as when 4L/D ratio increases with one unit, EDN values decrease with 0.05–0.02, but after some time, when 4L/D ratio increases with ten units, EDN values decrease with only 0.01. Finally, the optimum condition of 4L/D ratio for surface condenser is found, which is 40. Computer software is also developed to eliminate hectic calculations and human errors for performance analyses of heat exchangers.     

Comparative performance analysis of concentric-tube-type heat exchanger at various operating conditions with copper and aluminium tube materials

Concentric-tube-type heat exchanger is selected as a thermodynamic system for this research work. Different materials (copper and aluminium) are used for tube of heat exchanger. Entropy generation, exergy destruction, entransy and entransy-based thermal resistance are evaluated at different mass flow rates/inlet temperatures/specific heats of working fluids (hot/cold fluids). In addition, different tube materials and various outer/inner tube diameters of heat exchanger are also taken as parameters. And then combined effects of all these parameters are analysed. Finally, performance characteristic charts are generated. Analyses are done for counter flow heat exchanger as well as for parallel flow heat exchanger. Computer software is developed and all these analyses are done using prepared computer software. These evaluations are important to identify those operating conditions at which the heat exchanger’s performance is best and optimised.     

CO2跨临界循环中气体冷却器的熵产分析

指出CO2跨临界制冷循环中的放热设备是气体冷却器,CO2在整个放热中并无相变,其状态主要是超临界流体,针对超临界流体的特殊性质,用熵产分析研究气体冷却器的换热问题;在此基础上,提出了气体冷却器优化设计的原则与方法。     

Energy and exergy analysis of compression ignition engine fuelled with rice bran biodiesel blends

The present study aims to investigate a four-stroke single cylinder, water-cooled compression ignition (CI) engine coupled with an eddy current dynamometer. The rice bran oil biodiesel blends of B10, B20, B30 and pure diesel are tested for its performance in the engine. Energy and exergy analysis is carried out for the biodiesel blends and pure diesel. The experimental data were collected using steady-state tests which enable accurate measurements of air, fuel and cooling water flow rates, engine load and all the relevant temperatures. The performance parameters, energy and exergy efficiencies were computed for each fuel operation and compared with each other. The energy and exergy analysis has made to find input availability, brake power availability, cooling water availability and exhaust gas availability. From the exergy analysis, component of major exergy destruction was found. Balances of energy and exergy rates for the engine were also computed.     

地铁用间接蒸发冷却器换热性能影响因素

为解决地铁站冷却塔设置难题,提出了一种采用低速电机驱动旋转布水装置的间接蒸发冷却器,在两种布置方式下,对其换热性能进行了单因素实验,并运用正交实验法对较优布置方式下影响换热器换热的因素进行了分析。结果表明:两种布置方式下,喷嘴与蒸发冷却器的间距、两组换热管束间距均存在最佳值,喷嘴双侧旋转布水优于单侧旋转布水;换热器平行气流布置且喷嘴双侧旋转布水为较优布置方式,此时,换热器换热量随喷水量、转速、空气速度、冷却水进口温度的增加以及喷水温度、空气温度的降低而增大,其中,冷却水进口温度对换热器换热影响最为显著,其他因素对其换热的影响从主到次顺序为:喷水量、空气温度、空气速度、喷水温度、转速、冷却水流量。     

Performance characteristics of a two-stage transcritical N2O refrigeration cycle with vortex tube

ABSTRACT

The thermodynamic analysis has been presented in this article using nitrous oxide as the refrigerant in a two-stage transcritical cycle with the vortex tube (TSTCVT) instead of the expansion valve and its results are compared with the two-stage transcritical cycle with the expansion valve (TSTCEV). The evaporator and the gas cooler temperature ranges in both the cycles have been considered between ?55°C to 5°C and 35°C to 60°C for the analysis. Gas cooler and intercooler pressures are simultaneously optimised to obtain the maximum cooling coefficient of performance (COP). The COP of the TSTCVT improves by 1.97–27.19% in comparison to TSTCEV. A decrease in evaporator temperature and an increase in gas cooler exit temperature reduce the COP of TSTCVT. The comparison of refrigerants N₂O and CO₂ in TSTCVT shows that N₂O exhibits higher cooling COP, higher second law of efficiency and lower optimum gas cooler pressure under the considered operating conditions.