混合制冷剂制冷工艺在石油伴生气液化上的应用

小型天然气液化装置的制冷循环以带膨胀机的制冷循环和单级混合制冷剂循环为主,目前随着单级混合制冷剂流程研究的深入和使用的增多,装置越来越简单,投资越来越少,相对于膨胀循环流程的劣势很小,而能耗比膨胀循环更是要低40%左右,可有效降低系统的运行费用。石油伴生气的组份特点使得烃类制冷剂容易获得,应该优先采用单级混合制冷剂循环。在液化系统中设置分离塔,利用混合制冷剂本身就是混合物质的特点,不需要将各种冷剂提纯,就可以组合成多种冷剂配制方法,还可以根据不同的气源条件进行优化设计,解决了以往采用混合冷剂制冷循环的冷剂配比、采购、储运问题。     

Heat transfer research on vapor‐gas mixture with condensation in a vertical tube

The convection‐condensation heat transfer of vapor‐gas mixtures in a vertical tube was studied theoretically and experimentally. The effects of the condensation of a small amount of water vapor (8 to 20%) on heat transfer in a vertical tube were discussed. Comparisons show that theoretical solutions obtained through modified film model and experimental results are in good agreement. The results show that the condensation heat transfer of a small amount of water vapor and single‐phase convection heat transfer in the vapor‐gas mixtures are of the same order of magnitude, and these two modes of heat transfer could not be neglected. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 531–539, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10055     

A comparative study of an absorber heat recovery cycle for solar refrigeration using NH3-refrigerant with liquid/solid absorbents

This paper presents an investigation on using an ammonia refrigerant with liquid/solid absorbents in an absorber heat recovery cycle where heat released during the absorption process is used to heat up the strong solution coming out of the absorber, thereby reducing the generator heat input and hence improving the coefficient of performance. A comparative thermodynamic study is made with NH₃-H₂O and NH₃-LiNO₃ pairs as working fluids for both conventional absorption and absorber heat recovery systems. It is found that an improvement of about 10 per cent in COP for the absorber heat recovery cycle is achieved over the conventional absorption cycle and the NH₃-LiNO₃ system yields a higher COP than for NH₃-H₂O over a wide range of generator temperatures and condenser/absorber temperatures. A detailed parametric study is also presented in this paper.     

天然气锅炉烟气换热特性的分析

天然气锅炉的排烟温度一般在160～240℃，烟气中水蒸汽约占20％，它是烟气热量的主要携带者，若回收烟气余热，锅炉效率可大大提高。在回收余热过程中，由于凝结换热的存在，在不同换热截面上烟气侧换热系数及物性参数发生很大的变化，导致换热性能改变。利用传热传质理论对烟气倒换热进行研究，提出了新的换热系数计算方法。通过与实验值及文献数据的比较，获得满意的结果，为强化换热及设计出高效换热器提供了依据。图9参11     

自然工质低温复叠式制冷循环的热力学分析与比较

介绍了用于低温环境下采用自然工质CO2、NH3和R2903的复叠式制冷循环，介绍和分析了CO2、R290和NH3的物性特征，并且进行了复叠式制冷循环的热力学理论分析，通过计算得出了不同蒸发温度下的最佳低温循环的冷凝温度和最流量比。通过CO2－NH3，CO2－R290和NH3－NH3复叠式循环的比较，可以看出CO2－NH3、CO2－R290的复叠式制冷循环在低温制冷条件下有明显优势。     

微型压缩机驱动的单级与自复耦合系统的实验研究

搭建了微型压缩机驱动的单级与自复叠耦合系统的实验台,以单级制冷系统对自复叠系统进行预冷的方式获得更低的蒸发温度。高温级工质选用R404A,低温级工质选用R290/R170/R14组成的混合工质(充注质量比为0.33/0.17/0.50),在25 ℃环境温度,获得了系统的运行特性以及环境温度和高温级预冷温度对系统性能的影响。研究表明:在157 min的降温时间内,蒸发器进口温度达到-112 ℃,出口温度达到-111 ℃并保持稳定;环境温度从15 ℃升高到32 ℃,系统所能达到的最低温度由-116.68 ℃升高到-95.31 ℃;高温级预冷温度从-27 ℃降低到-37 ℃,系统蒸发器进口温度由-91.18 ℃降低到-112.7 ℃。     

天然气热风冲击换热在织物干燥中的节能应用

对某保温材料生产企业的织物干燥系统进行了改造,将原电加热干燥系统改造为天然气热风干燥系统.采用天然气燃烧后产生的高温烟气与空气混合,形成干燥介质.通过高速热风冲击换热,加速织物中水分扩散传质过程.通过改造,热风温度可降低至110℃运行,并且使干燥系统产能增加24％,织物干燥成本降低39.1％,仅3个月即可回收改造成本,达到显著的节能效果.采用清洁燃料天然气代替电能,单条生产线每年可减少耗电量70.8万kWh.     

联合循环在输气增压站中应用的研究

通过对联合循环增压站进行技术经济分析,提出在“西气东输”管线下游用联合循环为增压站提供动力的设想,进而对联合循环的设备选型,负荷调节,运行方式进行了初步的探讨。     

“球囊夹紧法”取出锁骨下动脉支架推送杆断裂残端一例

针对水平光滑管和微肋管,基于FLUENT平台对制冷剂管内沸腾传热特性进行了数值模拟,研究质量流量、热流密度及干度等因素对制冷剂R245fa沸腾换热系数的影响。模拟结果表明:沸腾换热系数随着制冷剂质量流速与热流密度的增加而提高;随着干度的增加,换热系数先增加再降低,并在x=0.7时达到极大值;相比光滑管,微肋管内制冷剂的沸腾传热系数能提高10%~25%。     

分液冷凝强化传热的实验验证

阐述了分液冷凝强化冷凝传热的原理,从理论上分析了该技术能同时实现强化传热和降低压降的可行性。该结论在微通道平行流冷凝器上得到了实验证实:与常规的微通道平行流冷凝器(PFMC)对比表明,在当量直径为1.05 mm、管内工质的质量流量为633~770 kg/(m~2·s)的微通道中,当冷凝温度分别为45和50℃时,微通道分液冷凝器(LSMC)的管内传热系数分别提高了3.7%~6.7%和2.3%~6.1%,压降分别降低了45.5%~49.5%和51.9%~52.6%,惩罚因子(Fp)分别降低了46.5%~52.7%和52.6%~56.7%。当进口流量达到一定值时,分液冷凝技术器能同时实现强化传热和降低流阻,有较好的综合热力性能。     

Prediction of heat exchanger capacity by thermal network method (Influence of thermal conduction in fins on capacity of a condenser)

This paper describes the influence of heat flow from high‐temperature refrigerant to low‐temperature refrigerant through fins by thermal conduction. To estimate that influence, we applied a thermal network method that can consider refrigerant quality distribution in the heat exchanger. At the same time, for verifying the estimation, an experiment was performed with a two‐row, two‐pass heat exchanger. Prediction shows that the heat transfer capacity of a condenser is reduced by 3% for a simple two‐row, two‐pass heat exchanger by heat conduction in fins. Comparison of experimental results and predicted results proves that the prediction error was within 1% for condenser capacity. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(2): 101–114, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20184     

Optimization of a two-phase flow evaporator by varying the channel cross section

Evaporation heat transfer coefficients depend on the mass flux and quality. When a non-azeotropic mixture is used as a working fluid, this dependence is significant due to the suppression of nucleate boiling. It is possible to improve the heat transfer performance if the channel cross-sectional area is enlarged at the latter part of the evaporator, namely, the mass flux is reduced in the high-quality region where the pressure drop is large. This work involves an analytical investigation on the enhancement effect by varying the channel cross section. It was assumed that the working fluid was a mixture of refrigerants R123 and R134a, and that the tubes used were smooth or spirally grooved. As a result, the heat transfer area and the channel volume were reduced by more than 20% with a permissible pressure drop. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(3): 143–158, 1997.     

强化管外CFC11与HCFC123凝结换热系数的对比试验研究

以目前某一大型冷冻机上实际使用的外径为19．2mm的压制浅肋强化管为试验元件,分别采用CFC11与HCFC123为工质进行了凝结换热系数试验,得出了各自的凝结换热系数,并对结果进行了分析与比较。