基于最小熵产的地埋管换热器优化设计研究

对于地埋管换热器,综合考虑传热性能和消耗的功率,建立管内流体的熵产模型。考虑两支管间热短路影响,确定流体沿管长的温度分布。以最小熵产为目标,根据沿埋管深度的温度分布,在不同换热负荷条件下,确定地埋管换热器的最优长度和管径随流量的变化关系,换热负荷确定时,埋管的最优管长随流量增加而减小,地埋管的最优管径随流量的增加而增大。在流量一定的条件下,埋管的最优管长随换热负荷的增加而增加,最优管径随换热负荷的增加也相应增大。以青岛市某实验室土壤源热泵系统为例,分析最优长度和管径对换热效能及系统性能的影响。     

正压浓相气力输灰管径的选择研究

对正压浓相气力输灰系统的输灰管道的管径选择进行了研究。分析了影响输灰管道的管径选择的众多因素,采用理论与实际工程相结合的方式,利用理论上的公式推导和60个工程的实际统计数据进行研究,确定了关键参数的计算方法。并建立了相关的数学模型,最终得出了可用于指导工程设计的管径计算经验公式。为以后燃煤电厂正压浓相气力输灰系统的输灰管道管径选择提供了设计选型依据,填补了这方面的空白,具有重要的借鉴参考意义。     

自然循环平板式太阳能热水系统的设计计算

提出了一种自然循环平板式太阳能热水系统水流阻力的工程计算方法，对采用不同管径循环管，由1－10架铜铝复合和铝翼管集热器单排并联组成的自然循环系统,进行了水流阻力核算。并根据水流阻力核算结果，对较大集热面积自然循环平板式太阳能热水系统的设计进行了分析与讨论。     

定壁温水平传热管外降膜对流显热换热特性理论研究

采用层流模型对定壁温边界条件时水平管外垂降液膜的强制对流显热换热性能进行了数值计算。计算中对管顶部的冲击滞止区和管侧部的自由绕流区分别采用不同的坐标变换方法进行微分方程组筒化。根据滞止区计算结果确定自由烧流区的初始边界条件。计算结果证明管径对平均换热系数的影响不容忽视。定壁温条件时的平均换热系数比定热通量时约高12％到20％左右。     

基于多目标粒子群的抽水蓄能电站输水管径多目标优化研究

针对抽水蓄能电站在传统的输水系统管径设计过程中仅考虑经济因素,而缺乏对其他因素如能耗、环境相容性的考量的不足,结合惠州某抽水蓄能电站在建设期及运行期的实际情况,分别提出了以总投资最小和总能耗最小为目标函数的输水管径模型,同时引入了多目标粒子群算法,综合考虑投资和能耗对管径的影响,对输水系统管径进行多目标优化,并利用模糊隶属度函数来辅助确定满意度最高的最优管径。实例计算结果表明,经过多目标优化以后的输水系统管径比单一考虑经济因素的管径更科学、全面,可为类似工程提供参考。     

改进的汽轮机热力系统修正方法研究

汽轮机热力系统的修正对于验证汽轮机设计制造效果、确定汽轮机热耗率应达值具有重要的意义。常规的热力系统修正方法需要预先确定蒸汽在汽轮机内的膨胀过程线,而凝汽式汽轮机中蒸汽膨胀过程线存在较大的误差,从而引起热力系统修正计算结果产生较大的误差。为此,提出改进的热力系统修正方法,该方法基于蒸汽在汽轮机内等熵膨胀过程线进行热力系统的修正,避开了蒸汽在汽轮机内膨胀过程线的求取问题。实例计算结果表明:与常规的热力系统修正方法相比,改进的热力系统修正方法最大相对误差为0.123%。     

直流式系统中平板型太阳能集热器数值模拟研究

由于非稳态传热问题通过理论计算得到解析解较困难,本文运用数值模拟方法研究定温放水型直流式系统中平板型太阳能集热器的工作状况,讨论了集热器的管径和管中心距在非稳态传热条件下对集热器的效率和每平方米产水量的影响.可得到结论扁盒式集热器具有较高效率;相同条件下,管径越大集热器效率越高.该结果有利于优化直流式平板集热器的设计参...     

8230ZC柴油机增压系统的计算分析和试验研究

对8230ZC柴油机增压系统进行了深入的计算分析,提出了配气正时、排气管径等多个试验方案,并进行了试验研究,确定了8230ZC柴油机增压系统最佳的技术参数。试验结果表明,增压系统匹配良好,8230ZC 柴油机达到了预期的性能指标。     

氢在单壁碳纳米管中吸附的计算机模拟

采用巨正则系综蒙特卡罗(Grand Canonical Ensemble Monte Carlo，GCEMC)方法模拟了不同结构参数(管径和管间距)的单壁碳纳米管在不同操作工况(温度和压力)下的吸附储氢性能。由计算结果发现，在不同管间距的情况下，不同的管径对吸附性能的影响不同：在管间距较小的情况下，吸附储氢重量百分比和体积百分比均随管径的增大而增大；在管间距较大的情况下，吸附储氢的体积百分比却随管径的增大而减小。在不同的操作工况下，存在一个最优的管间距，能使吸附储氢的体积百分比达到最大值。通过模拟，得到77K下最接近DOE能量密度标准的碳纳米管结构参数和操作工况。     

天然气压力能回收的热力学分析与研究趋势

目前,对于天然气长输管线在门站节流降压过程中,压力能发电等机械功利用的研究比较少,缺乏系统解决方案。文章分析了透平膨胀过程中火用降的构成,从热力学第二定律角度,对管输天然气做功能力,做了理论分析和定量计算,得出了温度火用、压力火用、化学火用的计算方法和透平膨胀输出轴功极限能力的评价因子。结合天然气压力能利用的未来要求,从机电一体化角度,提出了该领域基于总能系统理论的多学科的研究思路。     

Exergy assessment of an optimized capillary tube‐based transcritical CO2 heat pump system

A capillary tube‐based CO₂ heat pump is unique because of the transcritical nature of the system. The transcritical cycle has two independent parameters, pressure and temperature, unlike the subcritical cycle. A comparative study for various operating conditions, based on system COP and exergetic efficiency, of a capillary tube and a controllable expansion valve‐based transcritical carbon dioxide heat pump systems for simultaneous heating and cooling at 73 and 4°C, respectively, is presented here. Two optimized capillary tubes having diameter of 1.5 and 1.6 mm are compared with an equivalent controllable throttle valve. Heat transfer and fluid flow effects are included in the gas cooler and evaporator model and capillary tube employs the homogeneous flow model to simulate two‐phase flow. Subcritical and supercritical thermodynamic and transport properties of CO₂ are calculated employing a precision in‐house property code. Optimization of effective distribution of total heat exchanger area ratio between gas cooler and evaporator is investigated. The exergetic efficiency is better in case of the capillary tube than that of a controllable throttle valve‐based system. Capillary tube‐based system is shown to be quite flexible regarding changes in ambient temperature, almost behaving to offer an optimal pressure control just like the controllable expansion valve yielding both, maximum system COP and maximum exergetic efficiency. Relatively at a smaller diameter, the capillary tube exhibits better exergetic efficiency. Capillary tube length is the critical parameter that influences system optimum conditions. The exergy flow diagram exhibits that compressor, gas cooler and capillary tube contribute a larger share, in that order, to system irreversibility. It is fairly established in this study that a capillary tube can be a good engineering option for small capacity systems in lieu of an expansion valve, which has been thought of as the only possible solution to attain the pressure optimization, an important feature of all transcritical CO₂ systems. Copyright © 2009 John Wiley & Sons, Ltd.     

An empirical model for predicting the length of a capillary tube

Any refrigerant device consists of several parts, and one of the most significant parts is the expansion device. This expansion device can be classified into several types according to the size of the refrigeration system. The capillary tube is used usually with a small refrigerant system size to reduce the higher pressure in the condenser into the low pressure in the evaporator. In this study, the effect of the capillary tube's diameter and that of the temperature of the condenser and evaporator on the length of such a device has been theoretically studied. Furthermore, a validation between the theoretical analysis and experimental findings from the literature review has been carried out. To achieve the theoretical aspect, MATLAB code has been developed. The results showed that the maximum difference between the theoretical and experimental results regarding temperature and pressure refrigeration is around 5% and 3.4%, respectively. Also, the results depict that the inner diameter and the condenser temperature have an effect on the length of the capillary tube. However, the effect of the inner diameter is higher compared with the condenser temperature. In addition, an equation to predict the length of the capillary tube has been developed with an accuracy of 98%. This equation is created as a function of the capillary tube's diameter and the temperature of the condenser and the evaporator. Moreover, this equation can be used to predict the length of the capillary tube for small refrigeration devices, especially those operating under 10 KW. The findings of this study can help make a mathematical approach used for the design of the capillary tube simpler and easier to apply.     

基于有限元法的抗性消声器声学性能分析

本文是针对不同结构常用摩托车抗性消声器做了有限元分析。在保持其它结构参数不变的情况下,分析了单节扩张腔消声器扩张腔的长度、直径以及进出口插入管对其声学性能的影响。首先建立单节扩张腔消声器的数学模型,然后采用有限元法对所建立的Helmholz方程进行求解。结果表明,插入管可以有效的改善单节扩张腔存在通过频率的缺点,且当进口插入管长度为l/2,出口插入管长度为l/4时消声量达到最大。分析结果为在短时间内选出最佳的消声器结构及相应的最佳尺寸参数提供了依据,而不必做大量的消声器加工和试验测试工作。     

基于有限元法的抗性消声器声学性能分析

本文是针对不同结构常用摩托车抗性消声器做了有限元分析。在保持其它结构参数不变的情况下,分析了单节扩张腔消声器扩张腔的长度、直径以及进出口插入管对其声学性能的影响。首先建立单节扩张腔消声器的数学模型,然后采用有限元法对所建立的Helmholz方程进行求解。结果表明,插入管可以有效的改善单节扩张腔存在通过频率的缺点,且当进口插入管长度为1／2,出口插入管长度为1／4时消声量达到最大。分析结果为在短时间内选出最佳的消声器结构及相应的最佳尺寸参数提供了依据,而不必做大量的消声器加工和试验测试工作。     

The effects of improper refrigerant charge on the performance of a heat pump with an electronic expansion valve and capillary tube

For inverter heat pumps and multi-type heat pumps, conventional expansion devices such as capillary tubes, short tube orifices, and thermostatic expansion valves (TXVs) are being gradually replaced with electronic expansion valves (EEVs) because of the increasing focus on comfort and energy conservation. In this study, the effects of off-design refrigerant charge on the performance of a water-to-water heat pump are investigated by varying refrigerant charge amount from −20% to +20% of full charge in a steady state, cooling mode operation with expansion devices of capillary tube and EEV. The characteristics of the heat pump with an EEV are compared with those with a capillary tube. The capillary tube system is more sensitive to off-design charge as compared with the EEV system. Cooling capacity and COP of the EEV system show little dependence on refrigerant charge, while those are strongly dependent on outdoor conditions. In general, for a wide range of operating conditions the EEV system shows much higher performance as compared with the capillary tube system. The performance of the EEV system can be optimized by adjusting the EEV opening to maintain a constant superheat at all test conditions.     

Correlations for sizing adiabatic capillary tubes

This paper presents new correlations for the practical sizing of adiabatic capillary tubes used as an expansion device in small refrigerating and air-conditioning systems. The governing equation based on conservation of mass, energy and momentum is modelled. The developed model is used as an effective tool for studying the effects of relevant parameters on capillary tube length and developing the correlation. In this model, Colebrook's equation is used to determine the friction factor. The two-phase viscosity models are varied depending on the type of refrigerant and are based on the recommendations from past research. By varying the model input parameters, it is possible to show that for all refrigerants, the length decreases as the mass flow rate increases, increases as subcooling increases, increases as tube diameter increases, decreases as tube roughness increases and increases as condensing temperature increases. After the developed model is validated by comparing with existing experimental data, correlations for sizing capillary tubes, which contains the relevant parameters, namely condensing temperature, degree of subcooling, refrigerant mass flow rate, capillary tube inner diameter and roughness, are presented. Different from previous studies, correlations are presented for an extensive number of refrigerants and a wide range of operations. The developed correlations are validated with previous studies and found to agree well with the experimental data. The correlations can be used to integrate with system models working with alternative refrigerants for practical design and optimization. Copyright © 2003 John Wiley & Sons, Ltd.     

虹吸管与辐射井相结合的尾矿坝排渗系统排渗效果分析

尾矿坝浸润面的位置直接影响坝体的稳定性。为快速有效地降低尾矿坝浸润面,提出了一种虹吸管与辐射井相结合的尾矿坝排渗系统,该系统利用自流式虹吸管代替排渗井中的抽水泵,以减少维护和运行费用、降低施工难度。进而以某尾矿坝工程为例,首先采用数学解析法计算了排渗井的渗透流量和虹吸管所需管径,初步确定了该系统的可行性;然后根据该工程尾矿料特性,建立了三维有限元渗流分析模型,利用子结构有限元法,对比分析了排渗井的排渗效果。结果表明,该排渗系统具有良好的排渗效果,并且虹吸管管径可满足工程施工要求。     

Measurements of flow parameters and decompression wave speed following rupture of rich gas pipelines,and comparison with GASDECOM

Measurements of flow parameters and decompression wave speeds in a conventional gas mixture and two other rich gas mixtures following rupture of a high-pressure pipe have been conducted. A test rig, consisting of a stainless steel expansion tube (internal diameter ∼50 mm), has been used to give a length to diameter ratio of 3440 representing a long section of a pipeline. Pressure– and temperature–time traces obtained with high-frequency response transducers have been collected at various locations close to rupture and along the length of the tube. Tests were conducted at three pressure levels: 10, 14 and 20 MPa and at temperatures as low as −25 °C. Results indicate good agreement between measured and predicted decompression wave speed by GASDECOM. Additionally, gas temperature–time traces were also measured at different locations along the expansion tube. Since the temperature probes are not as fast in their response, a technique has been developed to reconcile the actual gas temperature from the measured data. The paper presents example results for lean, medium and rich gas mixtures at different initial conditions.     

Numerical modeling of two-phase refrigerant flow through adiabatic capillary tubes

Literature shows that the homogeneous flow assumption has been commonly used in most of the adiabatic capillary tube modeling studies due to its simplicity. The slip effect between the two phases was often not considered in this small diameter capillary tube. This paper attempts to exploit the possibility of applying the equilibrium two-phase drift flux model to simulate the flow of refrigerant in the capillary tube expansion devices. Attempts have been made to compare predictions with experimental results. The details flow characteristics of R134a in a capillary tube, such as distribution of pressure, void fraction, dryness fraction, phase’s velocities and their drift velocity relative to the center of the mass of the mixture are presented.     

A new approach in evaluation of thermal contact conductance of tube–fin heat exchanger

This paper presents a new method in evaluating the thermal contact conductance (TCC) of tube–fin heat exchanger, which makes it possible to improve the tube–fin TCC performance at the stage of forming process design. Firstly, the tube–fin contact status is studied with a finite element (FE) model of tube expansion process. The simulation result shows that the tube–fin joining is far form full contact and a gap exists at the interface, which is confirmed by experimental observation. Distribution of the contact pressure along the tube–fin interface is obtained from the numerical results. Then, an experiment for the relationship between the contact pressure and the TCC is carried out. Combining the experiment result with the contact pressure distribution from the simulation, the tube–fin TCC can be evaluated. This evaluation results agree well with thermal measurement of the whole heat exchanger. Based on the method, effect of key factors of the expansion forming process, such as expanding ratio and die geometry, are optimized.