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分析了低温换热器中传热过程的热力学特性,定义了低温换热器传热效率,得到了效率的计算式。讨论了传热单元数、介质热容量比等参数对低温换热器效率的影响,比较了各种流型低温换热器效率的相对大小,给出了使效率达最大值的最佳热容量比的计算方法。 相似文献
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低温换热器的Yong效率分析 总被引:4,自引:0,他引:4
分析了低温换热器中传热过程的热力学特性,定义了低温换器传热Yong效率,得到了Yong效率的计算式,讨论了传热单元数,介质热容量比等参数对低温换热器Yong效率的影响,比较了各种流型低温热器Yong效率的相对大小,给出了使Yong效率达最大值的最佳热容量比的计算方法。 相似文献
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以锥形螺旋弹性管束(conical spiral elastic tube bundle, CSETB)换热器为研究对象,通过在换热器内增设脉动/引流折流板,以期获得具有更高传热性能的弹性管束换热设备。通过采用双向流固耦合计算方法,研究了不同壳程入口流速和不同结构方案下CSETB换热器的振动强化传热性能。研究表明,CSETB的振幅随流速的增加而增加,仅增设脉动折流板可使CSETB表现为相对大幅高频振动,同时增设脉动、引流折流板可使CSETB表现为相对大幅低频振动。增设折流板可使流体流动的规律性和温度场分布的层次性增强,且能使换热器的壳程传热能力获得大幅提高。振动能够实现强化传热,这种强化传热的程度在高流速时更明显,且增设折流板能明显提高CSETB的振动强化传热性能。此外,引流折流板的存在使换热器的综合传热性能降低。 相似文献
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用有限时间热力学方法分析实际隐态制冷装置性能,导出了恒温和变温热源条件下实际闭式回热式布雷顿制冷循环制冷率与压力比和制冷系数与压力比之间的解析关系。考虑了不可逆性包括高,低温侧换热器和回热器的不可逆传热损失,压缩机和膨胀机中的非等熵压缩和膨胀损失,以及管路系统中的压力损失,通过优化两个换热器和回热器之间的热导率分配或传热面积分配可得循环最优性能,由数值算例给出了各项损失对循环制冷率和制冷系数的影响。 相似文献
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空分主换热器温差分布的计算与分析 总被引:1,自引:1,他引:0
简述了Praxair 2000m^3/h内压缩流程空分设备主换热器的流程和参数,利用数字计算机软件Maehcad7.0计算并作出了主换热器内部的传热温差分布曲线图,分析以主换热器内的温差分布情况,最后简单讨论了传热温差与不可逆损失的关系。 相似文献
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简述了Praxair 2 0 0 0 0m3/h内压缩流程空分设备主换热器的流程和参数 ,利用数字计算机软件Maehcad7 0计算并作出了主换热器内部的传热温差分布曲线图 ,分析以主换热器内的温差分布情况 ,最后简单讨论了传热温差与不可逆损失的关系。 相似文献
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汽车空调换热器(冷凝器和蒸发器)是汽车空调系统的董要组成部分,换热器的性能优化直接影、响空调系统的性能,并影响整车的紧凑型。针对蒸气压缩式汽车空调系统,总结其换热器的发展分类及各自结构特点,同时回顾国内、外对汽车空调换热器性能研究的发展,指出采用计算机辅助模拟技术来开发具有更好传热效果且结构更为紧凑可靠的换热器是汽车空调换热器的研究发展趋势。 相似文献
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为改进换热器内螺旋传热元件的振动均匀性及提高换热器的综合传热性能,提出一种带有螺旋折流板(hollow helical baffle, HHB)的中空换热器,采用双向流固耦合计算方法,研究了入口流速及折流板安装位置对换热器振动及传热特性的影响。结果表明:带螺旋折流板的中空换热器可有效均衡振动特性,提高传热特性;增加入口流速,传热元件振动幅值和换热系数增大;折流板安装在换热器上部时,平均振动幅值最大,平均传热系数最小,传热均匀性最好;带螺旋折流板中空换热器的PEC(performance evaluation criteria)值大于1,实现了强化传热的效果,折流板安装在换热器的下部、上部、左部和右部时换热器的PEC值比传统螺旋弹性管束换热器的PEC值分别提高了2.04%,7.87%,1.32%和0.03%,折流板安装在上部时PEC值最大,综合传热性能最好。 相似文献
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网络方法是便于计算机模拟复杂结构换热器特性的有效方法。减少轴向导热量是提高换热器效率的有效措施之一。以填料间壁式换热器的热网络模型为基础 ̄[1],定量地分析了轴向导热对换热器性能的影响,确定了轴向导热对换热器性能影响最为严重的部位;为设计和制造高效率的填料间壁式换热器提供依据。 相似文献
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Mixed Refrigerant-Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. The temperature glide effect is one of the major features of using mixed refrigerants since a recuperative heat exchanger in a MR-JT refrigerator is utilized for mostly two-phase flow. Although a pressure drop estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in MR-JT refrigerator heat exchanger designs, it has been rarely discussed so far. In this paper, macro heat exchangers and micro heat exchangers are compared in order to investigate the pressure drop characteristics in the experimental MR-JT refrigerator operation. The tube in tube heat exchanger (TTHE) is a well-known macro-channel heat exchanger in MR-JT refrigeration. Printed Circuit Heat Exchangers (PCHEs) have been developed as a compact heat exchanger with micro size channels. Several two-phase pressure drop correlations are examined to discuss the experimental pressure measurement results. The result of this paper shows that cryogenic mixed refrigerant pressure drop can be estimated with conventional two-phase pressure drop correlations if an appropriate flow pattern is identified. 相似文献
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The effectiveness of counterflow heat exchangers using normal hydrogen at cryogenic temperatures has been evaluated by a numerical method. 相似文献
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Prabhat Kumar Gupta P.K. Kush Ashesh Tiwari 《International Journal of Refrigeration》2009,32(5):960-972
The aim of present experimental research is to find out the suitable correlations for designing the coiled finned-tube heat exchangers used in cryogenic applications. In order to conduct above experimental study, cross-counter-flow coiled finned-tube heat exchangers were developed in our lab and used in actual refrigeration cycle. The experiments were conducted in the range of effective Reynolds number 500–1900. The effect of diametrical clearance on the prediction of overall heat transfer coefficient is also investigated experimentally. The results from present study were compared in the form of overall heat transfer coefficient. Results of present experimental research indicate that different correlations selected in the study can be used with reasonable accuracy for designing the coiled finned-tube heat exchangers, if they are applied with suitable method of calculation of free-flow cross-sectional area. A more accurate new correlation has also been proposed that fitted experimental data within ±10% error band. 相似文献
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Woven wire screen matrix heat exchanger (WSMHE) is a kind of compact, light-weight and high-efficiency matrix heat exchanger (MHE) for cryogenic applications. This paper presented a numerical model for the design and thermal analysis of WSMHE. The influence of wall thermal resistance, axial conduction, parasitic heat load and properties variation was taken into account, which is neglected in the traditional effectiveness-NTU method but important for compact cryogenic heat exchangers. The proposed numerical method is verified by effectiveness-NTU method under specific conditions, then it is tested according to experiment data, and a well agreement was obtained. Based on this model, a detailed analysis was performed on WSMHEs. The analysis results show that the axial conduction might result in evident decrease of effectiveness at low flow rate region; the effectiveness of WSMHEs with large flow rate could be remarkably enhanced by increasing its length; the influence of parasitic heat load varied little throughout of the flow rate region. Furthermore, the numerical model presented in this paper can be developed to the design and thermal analysis of small partition wall type heat exchangers. 相似文献
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《低温学》2017
Experimental investigations are carried out using a specially developed three-layer plate fin heat exchanger (PFHE), with helium as the working fluid cooled to cryogenic temperatures using liquid nitrogen (LN2) as a coolant. These results are used for validation of an already proposed and reported numerical model based on finite volume analysis for multistream (MS) plate fin heat exchangers (PFHE) for cryogenic applications (Goyal et al., 2014). The results from the experiments are presented and a reasonable agreement is observed with the already reported numerical model. 相似文献
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Heat exchangers are the main components in cryogenic processes. Thermo-economic considerations set the need for high-effectiveness equipment and accurate models. This situation is challenging due to the complex operating conditions and the fact that some physical effects, such as changes in fluid properties, flow maldistribution, axial conduction and heat leakage, cannot be neglected.In this work a systematic review of the state of art and challenges in modeling cryogenic heat exchangers is presented. They include lumped parameters, distributed parameters and stream-evolution models. These formulations fail to take all relevant effects into account.A general discussion on the performance of the reviewed models is presented. In general, more effects are included in the framework of numerical solution of discretized energy balance equation. Two main points stand out as not considered by the present models, namely the effects of pressure drop on heat transfer and the existence of partial flow mixing. These two effects are highly relevant for two-phase flow and multi-component applications, as in LNG processes. 相似文献
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A heat exchanger model that includes axial conduction, parasitic heat loads, and property variations
G.F. Nellis 《低温学》2003,43(9):523-538
High performance heat exchangers are a critical component in many cryogenic systems and the performance of these devices is typically very sensitive to axial conduction, property variations, and parasitic heat losses to the environment. This paper presents a numerical model of a heat exchanger in which these effects are explicitly modeled. The governing equations are derived, nondimensionalized, discretized, and solved on an exponentially distributed grid. The resulting numerical model is simple to implement and computationally efficient and can therefore easily be integrated into complex system models. The numerical model is validated against analytical solutions in the appropriate limits and then used to investigate the effect of heat exchanger end conditions (adiabatic vs fixed temperature) and radiation parasitics. The numerical model, which explicitly considers the combined effect of several loss mechanisms as they interact, is compared to simple models that consider these effects separately. Finally, the model is applied to an example heat exchanger core under a specific set of operating conditions in order to demonstrate its utility. This numerical model may also be used to examine the effect of property variations including temperature driven changes in specific heat capacity, metal conductivity, parasitic heat load, and heat transfer coefficients and is therefore useful in the design of a variety of cryogenic system components including counter- and parallel-flow heat exchangers for gas liquefaction, mixed-gas refrigeration, and reverse Brayton systems. 相似文献
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A. A. Vasserman S. V. Bodyul E. S. Bodyul 《International Journal of Thermophysics》2004,25(2):371-377
An automated system for calculating thermophysical properties of gases and liquids over a wide range of parameters has been developed. On the basis of values of the properties, the processes of isothermal compression, adiabatic throttling, polytropic expansion, heat exchange in two- and multi-stream heat exchangers, separation of vapor-liquid mixtures in the liquid vessel, and rectification in an air separation plant can be analyzed. For a specified structure scheme of a cryogenic plant, optimization of a corresponding thermodynamic cycle can be fulfilled. 相似文献