浅析液体CO2冷藏车的运行经济性

以液体CO2为代表的第三代新冷源的开发与利用成为冷藏运输技术发展的重要研究课题.液体CO2冷藏车与机械式、冷板冷藏车相比,无论在经济上还是环保性能上都有较大的优势.对以上三种冷藏方式从初投资、设备折旧和维修费以及能耗费几个方面进行了运行经济性分析,得出机械冷藏车的制冷费用比液体CO2冷藏车的高42%;冷板式的制冷费用比液体CO2式高28%.     

小型空调装置毛细管长度计算方法研究

通过分析比较,选择根据动量方程导出的壅塞流判据作为确定毛细管合理长度的判据,选择了用于计算机模拟计算的两相区毛细管长度计算数学模型;计算毛细管长度的计算机程序基于Matlab软件进行编译。通过分析制冷剂通量、毛细管管径、制冷剂冷凝压力对毛细管长度的影响,总结得出了制冷剂通量、毛细管管径、制冷剂冷凝压力对毛细管长度的影响规律。编写的计算机程序可方便、快速、准确确定不同制冷量下小型空调装置的毛细管参数,为设计高效空调装置提供便利。     

RC270在冷冻冷藏箱系统中最佳充注量实验分析

在BCD-228冷冻冷藏箱系统中采用新型替代制冷剂环丙烷（RC270）进行了实验研究,测试不同充灌量、不同毛细管长度下的耗电量,确定了最佳充灌量,并在实验结果的基础上对毛细管长度进行优化设计,为环丙烷在冷冻冷藏箱中的推广应用提供了一定参考。     

粘度国家计量基准

国家标准物质研究中心自1965年建立了粘度临时工作基准以来，又经过扩大章程、测量自动化的研究等技术改造，1986年批准为粘度国家计量基准。粘度国家计量基准用于复现和保存液体运动粘度单位，对粘度一级标准物质定值并传递粘度量值，以及高准确度的粘度测试。本基准由27支毛细管，内径分别为：0．35mm，0.45mm,0．55mm，0．95mm，1．75mm，2．75mm，3．90mm，5．10mm，6．90mm，基准毛细管粘度计以及精密恒温槽、精密测温设备、精密计时器等辅助设备组成。其测量原理是基于泊氏公式，即测量一定体积的液体流经毛细管的时间求粘度。计算公…     

确定毛细管尺寸的当量方法研究

在类比法和当量法基础上，提出多根毛细管之间长度、内径相互转换的当量方法。指出毛细管的摩擦系数对当量转换公式有直接的影响。计算表明，当N／Neq=1．5时，采用不同毛细管摩擦阻力系数进行毛细管当量长度的计算结果差别在6％以内。以制热量为8．5kW和9．85kW的空调机组采用的毛细管为基准，通过类比方法和笔者提出的当量方法计算制热量18kW的空调机组应采用的毛细管的几何尺寸。实验表明：以8．5kW机组为基准时，毛细管内径和长度的计算值和实验值分别相差-7．2％和2．9％；以9．85kW机组为基准时，毛细管内径和长度的计算值和实验值分别相差-6．5％和12．7％。实验说明笔者提出的方法可以用来指导空调机组的毛细管匹配实验。     

一种新型水产品冷藏运输车的可行性实验

首先对以液体CO2为冷源的这种新型水产品冷藏运输车的保温性能进行了实验,可以看出相同液体CO2及环境温度下,厢温维持在0℃的时间比维持在-18℃时延长了80%,每打开一次厢门,要用约20min的时间使厢温降到设定温度;接着对三种水产品冷藏运输车的运行经济性进行了比较,结果是液体CO2冷藏车的运输费用是机械冷藏车的70.4%,是冷板冷藏车运输费用的88.1%.因此,这种新型水产品冷藏运输车具有很好的开发价值与市场前景.     

跨临界CO_2制冷(热泵)系统中毛细管研究进展

毛细管应用于CO2跨临界循环时,其内部流动不同于普通CFCs和HCFCs,针对毛细管作为跨临界CO2制冷(热泵)系统节流机构的研究进行了回顾。主要从CO2毛细管模型、实验研究、临界流以及毛细管对系统的影响4个方面详细介绍了国内外的研究进展。阐述了目前研究存在的几个问题,并探讨了这一领域内研究的发展方向。     

烯丙基功能化离子液体的制备及其分离CO_2性能

合成了一系列烯丙基修饰的咪唑类离子液体,使用FT-IR和1 H-NMR对产物结构进行表征。在常温、常压下,对合成的离子液体进行分离CO2性能研究。结果表明,烯丙基修饰的咪唑类离子液体捕获CO2容量高、速度快,与烷基修饰咪唑类离子液体比较,CO2捕获容量提高15%~50%,捕获速度提高30%~60%。     

毛细管粗糙度对空调器性能影响的试验研究

针对不同长度、不同粗糙度的毛细管,测试其流量,同时测试装有不同毛细管的空调器制冷量及能效比(EER),分析毛细管长度和加工粗糙度对系统温度、制冷量及能效比的影响。结果表明,由毛细管内径不一致引起的毛细管粗糙度的不同对系统影响最大,毛细管内径减小可导致系统能效比降低0.1以上,对整机制冷量的影响达到5.5%。     

以跨临界CO_2-离子液体[bmim]PF_6为工质对的吸收式制冷循环性能分析

选择跨临界CO2-[bmim]PF6作为新型的吸收式制冷工质对,考察了CO2在离子液体[bmim]PF6中的溶解度和CO2-[bmim]PF6工质体系的热物性.计算了在给定工况下循环的制冷特性并对结果进行了分析与讨论.     

A study of transcritical carbon dioxide flow through diabatic capillary tubes

An experimental and theoretical study of the diabatic flow of carbon dioxide through lateral capillary tube suction line heat exchangers is outlined. The influence of both operating conditions (capillary tube inlet and outlet pressures, capillary tube inlet temperature and suction line inlet temperature) and tube geometry (heat exchanger length and position, suction line diameter and capillary tube length) on the heat and mass flow rates was experimentally evaluated using a purpose-built testing facility. In total, 75 tests were carried out with heat fluxes spanning from 1 to 11 kW m⁻² and refrigerant mass flow rates ranging from 12 to 26 kg h⁻¹. In addition, the mathematical model of Hermes et al. (2008) was adapted to run with carbon dioxide as working fluid. The model was validated against experimental data, and a good agreement between the experimental and calculated mass flow rates was achieved with 85% and 98% of the data points being within ±5% and ±10% error bounds, respectively.     

A study of transcritical carbon dioxide flow through adiabatic capillary tubes

This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO₂) through adiabatic capillary tubes. The influence of both operating conditions (inlet and exit pressures, inlet temperature) and tube geometry (capillary diameter and tube length) on the CO₂ mass flow rate was experimentally evaluated using a purpose-built testing facility with a strict control of the measured variables. A dimensionless correlation to predict the refrigerant mass flow rate as a function of tube geometry and operating conditions was developed. In addition, a theoretical model was put forward based on the mass, energy and momentum conservation principles. The model results were compared with experimental data, when it was found that the model predicts 95% of the measured refrigerant mass flow rate within an error band of ±10%. The model was also employed to advance the knowledge about the transcritical carbon dioxide flow through adiabatic capillary tubes.     

Characteristics of evaporative heat transfer and pressure drop of carbon dioxide and correlation development

Carbon dioxide among natural refrigerants has gained considerable attention as an alternative refrigerant due to its excellent thermophysical properties. In this study, transcritical refrigeration cycle using carbon dioxide is of great interest, and the evaporation process is investigated by experiment and analysis. This paper presents the measured heat transfer coefficients and pressure drop during evaporation process of carbon dioxide in a horizontal smooth tube. The test section was made of a seamless stainless steel tube with the inner diameter of 7.53 mm, and length of 5 m. Heat is provided by a direct heating method to the test section. Experiments were conducted at saturation temperatures of −4 to 20 °C, heat fluxes of 12 to 20 kWm⁻² and mass fluxes of 200 to 530 kgm⁻² s⁻¹. A comparison of different heat transfer correlations applicable to evaporation of carbon dioxide has been made. Based on the experiments for the evaporation heat transfer, useful correlation is developed.     

The electrical resistivity of liquid carbon under rapid heating of dense isotropic graphite in different media

Experiments are considered which involve pulsed heating of graphite (in several microseconds) and registering of electrical resistance of liquid carbon. Samples of MF-307 dense (2 g/cm³) isotropic graphite with a cross section of ∼0.3 × 0.3 mm and 10–15 mm long are heated in water or in thick-walled (outside diameter D ∼ 10 mm, inside diameter d ∼ 0.5 mm) sapphire capillary tubes. It is confirmed that the heating in water at atmospheric pressure does not enable one to obtain and investigate liquid carbon: at best, only the beginning of the liquid state region is attained. The heating in sapphire tubes causes the emergence of pulsed pressure (up to ten kilobars) after expanding graphite comes against the tube wall. This growing pressure (within several microseconds) enables one to investigate the liquid state of carbon in a confined volume. The isochoric heating provided the possibility of measuring the electrical resistivity of liquid carbon at high specific energies (up to ∼32 kJ/g) and high pressures; such measurements are quite expensive in the case of stationary investigations.     

A generalized correlation for the characteristics of adiabatic capillary tubes

The capillary tube is often served as an expansion device in small refrigeration and air-conditioning systems. In this paper, a generalized correlation for predicting the refrigerant mass flow rate through the adiabatic capillary tube is developed with approximate analytic solutions based on the extensive data for R12, R22, R134a, R290, R600a, R410A, R407C, and R404A, in which a homogeneous equilibrium model for two-phase flow is employed, and there is a subcooled liquid or saturated two-phase mixture at the inlet of the capillary tubes. The collected database about capillary tubes covers the inner diameter from 0.5 mm to 2 mm, the tube length from 0.5 m to 5 m, the condensing temperature from 20 °C to 60 °C, the subcooling from 0 °C to 20 °C, and the quality from 0 to 0.3 at the inlet. Assessments for the correlation are made with some experimental data for R12, R22, R134a, R290, R407C, R410A, and R404A obtained from the open literature and some existing correlations based on the experimental database also. The present correlation yields an average deviation of −0.83% and a standard deviation of 9.02% from the database.     

Capillary tube selection for HCFC22 alternativesSélection de capillaires pour les frigorigènes de remplacement du HCFC22

In this paper, pressure drop through a capillary tube is modeled in an attempt to predict the size of capillary tubes used in residential air conditioners and also to provide simple correlating equations for practicing engineers. Stoecker's basic model was modified with the consideration of various effects due to subcooling, area contraction, different equations for viscosity and friction factor, and finally mixture effect. McAdams' equation for the two-phase viscosity and Stoecker's equation for the friction factor yielded the best results among various equations. With these equations, the modified model yielded the performance data that are comparable to those in the ASHRAE handbook. After the model was validated with experimental data for CFC12, HFC134a, HCFC22, and R407C, performance data were generated for HCFC22 and its alternatives, HFC134a, R407C, and R410A under the following conditions: condensing temperature; 40, 45, 50, 55°C, subcooling; 0, 2.5, 5°C, capillary tube diameter; 1.2–2.4 mm, mass flow rate; 5–50 g/s. These data showed that the capillary tube length varies uniformly with the changes in condensing temperature and subcooling. Finally, a regression analysis was performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and subcooling. Thus determined simple practical equations yielded a mean deviation of 2.4% for 1488 data obtained for two pure and two mixed refrigerants examined in this study.     

变径毛细管在R410A冷暖空调器中的流量特性

为减少变径毛细管在R410A冷暖空调器应用中的匹配实验工作量,利用节流元件制冷剂流量测试台对多个结构尺寸规格的变径毛细管进行了R410A制冷剂流量测试,建立了基于阻抗计算方法的流量特性经验模型。利用该模型计算出KFR-32GW冷暖空调器所需变径毛细管的初步结构尺寸,并在该冷暖型空调器上进行精确匹配实验,确定最佳变径毛细管结构尺寸。实验结果表明:采用变径毛细管节流的空调器相对采用毛细管组件节流的空调器,制冷量减少0.3%,制冷能效比不变,制热量增加0.5%,制热能效比减少0.3%,两者的性能指标基本相同。因此变径毛细管可以代替毛细管组件应用于R410A冷暖空调器,且通过实验方法建立的变径毛细管R410A制冷剂流量特性经验模型精度较高,可以满足实际工程应用。     

水平管外二氧化碳膜状凝结传热分析

综述了水平低翅片管外凝结传热的基本模型,阐述了二氧化碳制冷剂的物性特点,讨论了表面张力与凝液滞留角及二氧化碳管外凝结换热系数的关系,分析了翅片密度、环形翅片管尺寸对翅片效率、滞留角、凝结换热系数以及传热增强比的影响,优化了外翅片管的齿高与齿距,并求得相应的强化传热增强比.结果表明,对于根径为20mm的低翅片管,最佳翅片密度为每米435个翅片,最佳齿高为5.1mm,最佳齿距2.3mm.