共查询到19条相似文献,搜索用时 337 毫秒
1.
本文以去离子水为工质,实验研究了竖直矩形窄通道内少量残余不凝性气体对蒸汽凝结换热特性的影响。采用热阻分离法得到凝结侧换热表面传热系数,分析了不凝性气体的含量、冷却水质量流速、进口温度和热流密度对蒸汽凝结侧表面传热系数的影响。结果表明:当热流密度为1.668 kW/m~2,即蒸汽质量流速较小时,2%体积分数的不凝性气体使凝结侧表面传热系数下降了33%,但当热流密度为3.887 kW/m~2,蒸汽质量流速较大时,2%体积分数的不凝性气体仅使凝结侧表面传热系数降低了14%,此外,凝结换热表面传热系数随冷水质量流速和不凝性气体分数的增加而变小,随冷水进口温度和热流密度的增加而变大。 相似文献
2.
3.
4.
5.
6.
采用硅灰、氯化钙和碳酸锂等外加剂分别对物理发泡水泥混凝土的凝结硬化性能进行单一和复合改进试验。结果表明,氯化钙能够有效促进水泥泡沫混凝土的凝结与硬化,当氯化钙掺量为2%(36 g)时,混凝土的初凝和终凝时间均缩短了11 h,7 d抗压强度增加了0.8 MPa;硅灰对水泥泡沫混凝土凝结硬化有一定的促进作用;碳酸锂促凝效果不明显;硅灰和氯化钙复掺没有表现出较大的复合效应。 相似文献
7.
8.
甲烷气在V型纵槽管上凝结换热强化 总被引:1,自引:0,他引:1
主要研究甲烷气膜状凝结过程及强化。建立了甲烷气膜状凝结试验台,进行了甲烷在光管和V型纵槽管上膜状凝结换热试验。结果表明光管的数据与Nuselt解基本一致,而V型纵槽管上膜状凝结换热系数较光管提高了3~8倍。 相似文献
9.
R134a在水平强化管外凝结换热的实验研究 总被引:2,自引:0,他引:2
对氟利昂R134a在水平单管外的凝结换热性能进行了试验研究,试验管为光管和三根强化管,采用热阻分离法得到蒸气侧凝结换热系数。试验结果表明:光管管外Nusselt理论值与实验数据偏差小于10%。强化管No.1-3的传热性能均好于光管,当Re=40000时,No.1-4管的总传热系数分别为:5295,5818,5904,1502W/m2.K。在相同热流密度条件下,No.1-3管的管外换热系数分别是光管的7.0-8.8倍,9.0-10.8倍,9.9-12.0倍。管外强化后,管内外的换热系数已比较接近。 相似文献
10.
随着NH3/CO2复叠式制冷系统的推广应用,开发高效复叠换热器对于提高整个系统的性能至关重要.通过对一台NH3/CO2复叠式制冷系统进行实验研究,分析运行工况和传热管数量对复叠换热器的传热温差、热流密度和换热系数等性能参数的影响规律;获得了NH3/CO2复叠换热器在工程设计中的换热系数取值范围为1987~2378W/(m2.K);通过实验得到了复叠换热器的改进方案,使其传热面积减少了60%,有效地降低了复叠换热器的制造成本. 相似文献
11.
12.
本文选择不凝气体氮气作为添加剂加入到CO2跨临界制冷循环系统中,通过理论分析和计算仿真研究氮气对系统制冷性能的影响。首先分析CO2工质和氮气的基本物性参数,N2的加入会改变CO2工质物性参数,本文通过计算得出添加剂使CO2工质的饱和压力和液体比热提高,粘度系数、表面张力、液/汽密度比和导热系数降低。同时分析N2在蒸发器内可作为汽化核心,实现非均匀核化过程,从而降低成核温度,提高换热系数。同时N2的加入会降低压缩机排气温度,减小压缩机功率,从而提高系统制冷性能,并随浓度的增加而增加。本文为跨临界CO2制冷循环系统高效应用研究提供理论依据。 相似文献
13.
Assessment of condensation heat transfer correlations in the modelling of fin and tube heat exchangers 总被引:1,自引:1,他引:0
F. Vera-García J.R. García-Cascales J.M. Corbern-Salvador J. Gonzlvez-Maci David Fuentes-Díaz 《International Journal of Refrigeration》2007,30(6):1018-1028
This is the second paper of a series that assesses the performance of a refrigeration system model by means of cycle parameters. In this case, the condensation temperature is the parameter to study and it is focused on fin and tube condensers. It also studies the influence of the heat transfer models on the estimation of this refrigeration cycle parameter and different correlations for the heat transfer coefficients have been implemented in order to characterise the heat transfer in the heat exchangers. The flow inside the heat exchangers is considered one-dimensional as in previous works. In the cycle definition, other submodels for all the cycle component have been taken into account to complete the system of equations that characterises the behaviour of the refrigeration cycle. This global system is solved by means of a Newton–Raphson algorithm and a known technique called SEWTLE is used to model the heat exchangers. Some experimental results are employed to compare the condensation temperatures provided by the numerical procedure and to evaluate the performance of each heat transfer coefficient. These experimental results correspond to an air-to-water heat pump and are obtained by using R-22 and R-290 as refrigerants. 相似文献
14.
提出R404A直接接触凝结换热的制冷循环,分析R404A直接接触凝结制冷循环的热力性能,并与常规双级压缩制冷循环的性能进行对比。得出结论:在一定的冷凝温度、蒸发温度和过冷液体的过冷度下,直接接触凝结制冷循环存在最佳的饱和液体温度,并在此最佳的饱和液体温度下,获得最优的性能和最小的冷凝热负荷,随着过冷液体的过冷度增大和蒸发温度升高,直接接触凝结制冷循环的性能系数增加、冷凝热负荷减少,获得最优性能的最佳饱和液体温度值提高。过冷液体的过冷度为25℃时,直接接触凝结制冷循环的最佳性能系数较双级压缩制冷循环的最佳性能系数提高6.2%。直接接触凝结制冷循环的最小冷凝热负荷较双级压缩制冷循环的最小冷凝热负荷减小1.8%。 相似文献
15.
16.
Numerous mixed-gases refrigeration cycle configurations based on Joule-Thomson effects were developed in the past several decades. In this paper, comprehensive thermodynamic analyses were made on two typical cycle configurations to learn their performance for cooling fixed-temperature heat loads. One is the single-stage cycle without phase separators; the other is the auto-cascade refrigeration cycle which has at least one phase separator. An exergy model was developed to analyze the thermodynamic performance of those refrigeration cycles. Comprehensive comparisons were made on the performance of the recuperative throttling cycles using multicomponent mixture as refrigerant, including extensive simulations and optimizations of mixtures and cycle configurations. The results show that the auto-cascade cycle can improve thermodynamic performance in the case of using mixtures with increased fraction of high-boiling components, however, degrade the performance when using mixtures with increased fraction of low-boiling components. The results also show that the mixed refrigerant is the most important designing parameter in the design of such mixed-gases refrigeration system. Different cycle configuration has different optimal mixture composition. When using optimal mixtures, both cycles (separation and non-separation) can provide approximately equal performance. 相似文献
17.
宋传友 《制冷与空调(北京)》2012,(6):61-64
分析不凝性气体进入制冷系统的主要途径,重点研究不凝性气体对R290制冷系统的燃烧爆炸性、传热性能、饱和蒸气压和黏性的影响,最后阐述阻止不凝性气体进入系统的措施和判断方法。 相似文献
18.
系统介绍了自复叠制冷循环的工作原理、发展和主要研究方向,对几种典型的自复叠制冷系统进行了分析比较,介绍了一种带有精馏装置的新型自复叠制冷系统,最后提出了自复叠制冷系统设计需要考虑的一些关键问题。 相似文献
19.
提出一种新型水冷自复叠制冷循环方式,用冷凝分离器代替传统循环的冷凝器和相分离器,在冷凝分离器中同时完成了高沸点工质的冷凝及高沸点工质与低沸点工质的分离。对采用这种冷凝分离器的水冷自复叠制冷循环方式的R22/R23、R290/R170、R134a/R23、R134a/R170四种工质对进行了循环特性研究。在自行搭建的水冷自复叠制冷系统实验台上进行了R22/R23、R134a/R23两种工质对的实验研究。结果表明,在相同工况下,R22/R23自复叠制冷系统的COP要高于R134a/R23自复叠制冷系统;和传统的自复叠系统相比,采用冷凝分离器的水冷自复叠制冷循环COP明显提高,提升率达到60%~100%。 相似文献