论文中英文摘要

附件2论文中英文摘要作者姓名：陶于兵论文题目：CO2家用空调系统实验研究及换热器强化换热数值模拟作者简介：陶于兵，男，1979年11月出生，2003年9月师从于西安交通大学何雅玲教授，攻读硕博连读博士学位，于2008年6月获博士学位。

中文摘要近年来全球环境与能源问题日益严重，臭氧层破坏、温室效应以及能源危机已成为人类面临的主要挑战。

现有制冷空调等工业大量使用的氯氟烃类制冷工质，不仅会对臭氧层造成破坏，而且它们本身也是一种温室气体。

积极寻找制冷剂的替代工质，已成为目前制冷工业迫在眉睫的任务，CO2以其良好的热物性和对环境的无害性，已逐渐引起了各界的广泛关注。

另一方面，随着能源需求与日俱增、化石能源的大量消耗，排放了大量的温室气体，使得大气层的温室效应日益显著，人类正面临着全球能源日益枯竭和环境污染日益严重的问题，如何有效利用能源和保护生态环境是各国面临的重大课题。

因此，对在各领域大量应用的换热设备，进行强化换热及节能减阻研究显得至关重要。

本文针对国际上普遍关注的制冷工质替代及换热器强化换热、节能减阻问题，开展实验及理论研究。

实验方面，搭建了国内首台CO2家用空调系统性能测试实验台，对系统的COP 以及工质在换热器内的流动与换热特性随运行工况的变化规律进行了实验研究，探讨了提高系统性能的可靠方案；对带有内部回热器的CO2跨临界循环的节流损失及其主要影响因素，节流损失对系统COP 的影响进行了实验分析，指出了减小系统节流损失、提高系统性能的可靠途径。

理论方面，提出了适体坐标和块结构化相结合的复合网格生成方法，自行开发了三维适体坐标下的网格生成程序及SIMPLE算法程序，并运用该程序对工业领域及空调系统常用的翅片管换热器进行了大量数值模拟研究，分析了几何参数对波纹翅片管换热器的总体换热及阻力性能、翅片效率等的影响规律，并从场协同原理的角度对研究结果进行了合理解释。

同时，考察了平直翅片和波纹翅片表面的局部换热系数和翅片效率分布情况，并在此基础上进行了新型高效换热器的设计开发。

具体内容及结论如下：在CO2家用空调系统实验研究方面：（1）搭建了国内首台CO2家用空调系统性能测试实验台。

目前国际上，CO2作为天然制冷剂，已经在汽车空调、热水热泵及商业制冷等系统得到了成功应用，然而在家用空调方面还处在实验探讨阶段。

为了促进CO2制冷剂在家用空调系统的应用，本文考虑到CO2跨临界循环的高压侧压力非常高（7.0-12.0MPa）存在爆炸及容易泄露等问题，自行设计了实验系统方案，搭建了系统性能测试实验台，系统的设计方案及实验结果的精度和可靠性得到了日方合作伙伴详细验证及充分肯定。

在实验台上，分析了家用空调系统的工况参数对蒸发器和气体冷却器内部的流动和换热性能以及整个系统的总体性能的影响，实验结果发现，CO2家用空调系统的COP通常在2-3之间，略低于常规空调系统；气体冷却器的冷却效果是影响系统COP的主要因素，因此，强化冷却器的冷却效果是提高系统COP的有效手段；通过对循环进行优化、对冷却器采取强化换热措施可以使CO2系统的COP达到与常规空调系统相当的水平，从而证明了CO2天然制冷剂用于家用空调系统的可行性。

（2）分析了带有内部回热器的CO2跨临界循环的节流损失、节流损失对COP 的影响、影响节流损失的主要因素。

结果表明，内部回热器可以在很大程度上减小节流损失，然而带有内部回热器的跨临界循环，节流过程中仍然有5%的冷量损失，并造成系统COP减小近20%；进一步对影响节流损失的主要因素进行了分析研究，发现冷却器的冷却效果是影响节流损失的主要因素，冷却效果越好，节流损失越小，系统COP越高。

在换热器的强化换热及节能减阻性能研究方面：（3）提出了适体坐标和块结构化相结合的复合网格生成方法，自行开发了三维适体坐标下的网格生成程序及基于SIMPLE算法的数值模拟程序。

目前空调领域大量使用的都是波纹翅片管换热器，波纹翅片管换热器翅片表面之间是波纹形通道，另外还有管子的存在，结构非常复杂，网格生成困难，因此对其三维数值模拟研究迟迟未能展开。

本文提出了适体坐标和块结构化相结合的复合网格生成方法，开发了适体坐标下的网格生成程序和基于SIMPLE 算法的流动换热过程的三维数值模拟程序，所开发的程序可用于三维复杂区域的网格生成及流动与换热问题的数值求解，可以获得换热区域的总体换热及阻力性能，以及局部换热系数、局部温度场、流场的分布特性，并在其基础上对换热设备表面的形状和尺寸进行优化，从而实现换热设备的高效强化换热和节能减阻设计。

而且该模拟程序可以有效处理计算区域中同时存在流体和固体的流固耦合问题。

（4）基于自行开发的三维适体坐标下网格生成程序及SIMPLE算法程序，对三角形波纹翅片管换热器空气侧层流流动与换热特性进行了三维数值模拟研究。

重点考查了空气流动的雷诺数、翅片间距、翅片波纹倾角、管排数对流动与换热性能的影响规律，并从场协同角度分析讨论了这些参数的改变引起对流换热效果强化或恶化的物理本质。

研究结果表明，随流速增加、波纹倾角增加、翅片间距减小、管排数减小，换热器的换热特性得到强化，与此同时阻力损失也增加。

基于场协同原理，建立了单位体积换热量和全场平均协同角之间的对应变化关系。

采用之，对波纹翅片圆管及椭圆管换热器的换热特性随几何参数的变化关系给予了合理解释，使场协同原理可以更方便地应用于指导换热器结构的优化设计。

（5）分析了波纹翅片的翅片效率及翅片表面平均温度随雷诺数、波纹翅片倾角、翅片间距、翅片厚度及横向管间距的变化规律。

结果表明，随着雷诺数、波纹倾角、翅片间距、横向管间距的增加以及翅片厚度的减小，翅片表面温度逐渐降低，翅片效率逐渐减小；针对文献中常用的忽略翅片效率及翅片厚度的等温模型假设，指出在翅片材料的导热系数较高，空气流速相对较小的情况下，几何参数对翅片效率的影响较低，因此在精度要求不高的条件下，可以采用忽略翅片效率的等温模型；但是翅片厚度对换热及阻力性能的影响较大，在翅片厚度和翅片间距的比值不是很小的情况下，应该考虑翅片厚度的影响。

（6）进一步考察了波纹翅片表面的局部换热系数及局部翅片效率分布，获得了节能减阻型换热器的设计原理。

波纹翅片管换热器由于结构复杂，三维数值模拟工作开展较少，特别是波纹翅片表面局部换热系数及局部翅片效率分布的研究尚未见报道，而这些局部参数又是设计高效节能型换热器所必需的，因此，开展这方面研究非常必要。

本文采用数值模拟的方法获得了波纹翅片表面的局部换热系数及局部翅片效率的分布特性。

结果表明，局部换热系数沿空气流动方向逐渐减小；在波峰和波谷的位置，由于波峰破坏边界层，波谷处存在回流涡，局部换热系数的变化曲线出现波动；流速越高、波纹倾角越大，波动越明显；局部翅片效率沿流动方向逐渐增加，其分布特性主要依赖于翅片表面的温度分布。

获得了节能减阻型换热器的设计原理：在流速较低时，翅片管换热器的对流换热主要发生在入口区域，出口部分的波纹对换热的强化很小，却极大地增加了阻力损失，因此适当增加波纹翅片管换热器入口区域的翅片换热面积及波纹倾角，减小出口部分的换热面积及波纹倾角，可以达到强化换热、减少阻力、节省耗材的目的。

（7）设计了新型的局部波纹翅片形状，并进行了数值模拟验证。

传统的换热器强化换热措施，在强化换热的同时，往往都会引起阻力的大幅增加，而且通常都是阻力增加的百分比大于换热强化的百分比。

本文基于局部换热系数的模拟结果及节能减阻型换热器的设计原理，设计了波纹翅片位于上游，平直翅片位于下游的新型翅片形式，并且将该新型翅片的换热及阻力特性同现有的波纹翅片和平直翅片进行了对比研究。

对比结果表明，相对于原来的波纹翅片，新型翅片的换热性能仅仅减小4%，而阻力损失却减小了18%；相对于平直翅片，新型翅片的换热性能增加了45%，而阻力损失仅增加了26%，换热的强化大于阻力的增加，证明了新型翅片结构具有很好的强化换热及节能减阻性能。

（8）提出了椭圆管波纹翅片的换热器结构形式，数值研究了椭圆管波纹翅片换热器的流动与换热特性。

结果表明，椭圆管布置相对于圆管布置，可以在压降仅增加10%的条件下，使换热性能强化30%，因此椭圆管代替圆管，可以达到较好的强化换热和节能减阻的综合效果。

随着椭圆管向心率、翅片间距、横向管间距的增加以及翅片厚度的减小，椭圆管波纹翅片换热器的换热系数减小，同时阻力因子也减小。

（9）进一步分析了椭圆管的横截面形状对换热及阻力性能的影响。

将5种不同管截面形状的波纹翅片管换热器的换热和阻力性能进行了对比研究，结果表明，4种椭圆管的换热性能都比圆管好，分别平均强化了17.0%，16.9%，14.6%，12.3%；和圆管具有相同最窄空气流通截面的椭圆管的平均阻力损失比圆管高7.1%，其他3种椭圆管的阻力性能都比圆管好，分别减少了23.9%，20.7%，17.0%；从换热的角度，和圆管具有相同当量直径的椭圆管的强化换热效果最好；而从减阻的角度看，则是和圆管具有相同管周长的椭圆管的减阻效果最好，在实际应用时可以根据具体强化换热与节能减阻要求加以合理选择。

关键词：CO2制冷剂；跨临界循环；流动与换热；强化换热；场协同原理Experimental Study on CO2 Residential Air-condition System and Numerical Simulation on Enhanced Heat Transfer of Heat ExchangersTao YubingABSTRACTIn recent years, the problems of environment and energy have been more and more serious. Ozone depletion, greenhouse effect and energy crisis have become the main challenges for human being. The refrigerants used in refrigeration and air-condition systems not only make ozonosphere destroyed seriously but also cause great greenhouse effect. Looking for alternative refrigerant has become an exigent task for refrigeration industry. Due to the favorable thermophysical properties and benign environment effects, CO2 has attracted extensive attentions in recent years. On the other hand, the requirement for energy is more and more increasing and the combustion of fossil energy exhausts a large amount of greenhouse gas which aggravates the greenhouse effect. We are facing the threats of fossil energy drying up and environmental pollution. How to effectively utilize energy and efficiently protect ecological environment has become the key issue for all the countries. So it is very important to study the enhanced heat transfer and decreased pressure drop characteristics of the heat transfer equipments which are widely used in many fields.The objectives of present dissertation are focused on the alternative refrigerants of air-condition system and energy saving of heat transfer equipments. The corresponding experimental and theoretical studies are performed. In the experimental study, the domestic first test rig for the performance of CO2 residential air-condition system is set up. The effects of operating conditions on the heat transfer and fluid flow performances of heat exchangers and the system total performances are experimentally investigated. The throttling loss, effect of throttling loss on COP and influencing factors on throttling loss are analyzed for the CO2 transcritical cycle with an inner heat exchanger. Some reliable approaches to reduce throttling loss and improve the system performance are presented. In the theoretical analysis, a hybrid grid generation technology is proposed based on body fitted coordinates and block structured grid generation method, three-dimensional grid generation and numerical simulation codes are developed. Then the heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchangers which are widely used in industry fields and air-condition systems are numerically studied. The effects of geometric parameters and operating conditions on the total heat transfer and fluid flow performance and fin efficiency of the heat exchanger are examined. Then the distributions of local heat transfer coefficient and fin efficiency on the plain plate fin and wavy fin surface are examined. Based on thedistribution results, a new type of high efficient heat exchanger is designed and the performance is investigated. The detailed contents and findings of the present dissertation are as follows.Experimental study on CO2 residential air-condition system:(1) The domestic first test rig for the performance study of CO2residential air-condition system is set up. At present, CO2 as a natural refrigerant had been successfully used in automobile air-condition, heat bump hot water and commercial refrigeration systems. However, the applications of CO2 refrigerant in residential air-condition system are still in the experimental validation period. In order to promote the application of CO2 in residential air-condition, the experimental system is designed and the test rig is developed based on the theoretical analysis which fully considers the higher pressure in the gas cooler side (about 7.0-12.0MPa) and existing explosion and leakage problems. The design of the experimental system and the precision and reliability of the experimental results have been fully validated and affirmed by the Japanese cooperators. Then, the effects of operating conditions on heat transfer and fluid flow performance of evaporator and gas cooler and the total performance of the air-condition system are experimentally investigated. The experimental results show that COP of the CO2 residential air-condition system generally locates between 2 and 3, which is a bit lower than that of traditional air-condition system. The cooling effect of gas cooler is the main influencing factor for COP, so enhancing the cooling effect of the gas cooler is an effective approach to improve the system performance. The COP of the CO2 system can achieve the level of traditional air-condition system by cycle optimization and adopting proper enhanced heat transfer method to the gas cooler. The experimental results of present dissertation demonstrate that the natural refrigerant CO2 is applicable to the residential air-condition system.(2) Throttling loss of the transcritical cycle, effect of throttling loss on COP and the influencing factors on throttling loss are analyzed based on the CO2transcritical air-condition experimental system with an inner heat exchanger. The results show that the inner heat exchanger can decrease throttling loss in a large degree, but it can not eliminate throttling loss. To the cycle with an inner heat exchanger, there is still 5% cooling capacity loss in throttling process, which decreases COP about 20%. The further studies on the influencing factors to throttling loss are performed and it is found that the cooling effect of gas cooler is the major influencing factor for throttling loss. The throttling loss decreases and the COP increases with the improvement of the cooling effect.Numerical study on enhanced heat transfer and decreased pressure drop characteristics of wavy fin-and-tube heat exchangers:(3) A hybrid grid generation method based on body fitted coordinates and block structured grid generation method is proposed. At present, heat exchangers used in air-condition system are mostly wavy fin-and-tube pattern. There are wavy channels and tubes between two fins. Due to the complicated geometric configuration, the grid generation is very difficult, so three-dimensional numerical simulations on wavy fin-and-tube surface have not been opened out until recent years. In present dissertation, a hybrid grid generation method is proposed, and then three-dimensional gridgeneration code and numerical simulation code based on SIMPLE algorithm are developed in body fitted coordinates. The codes can be used to simulate the heat transfer and fluid flow problems in complicated three-dimensional regions and derive the total heat transfer and fluid flow performances of the computational region and the distributions of local heat transfer coefficient, temperature field and fluid field. And then, the configurations and dimensions of the heat transfer surface can be optimized and validated and the enhanced heat transfer and decreased pressure drop characteristics of the heat transfer equipments can be achieved in virtue of the simulation code. And the simulation code can efficiently deal with the fluid-solid conjugated problem.(4) Based on the self-developed grid generation and numerical simulation codes, the three-dimensional numerical studies on the air-side laminar flow and heat transfer performances of the wavy fin-and-tube heat exchangers are performed. The effects of Reynolds number, fin pitch, wavy angle and tube row number on heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchangers are investigated. And the effect mechanism of the parameters on heat transfer performance are discussed and well explained from the point of view of field synergy principle. The numerical results show that with the increases of Reynolds number, wavy angle and the decrease of fin pitch, tube row number, heat transfer performance of the heat exchanger is enhanced, but at the same time the pressure drop is increased. Then, correlation between the unit volume heat transfer capacity and the whole field average synergy angle is set up. The effects of the parameters on heat transfer characteristics of wavy fin heat exchanger with circular or elliptic tubes can be properly revealed by the correlation. The correlation can make the field synergy principle used in the design optimization of heat exchanger configuration more conveniently.(5) Effects of Reynolds number, wavy angle, fin pitch, fin thickness and transverse tube pitch on fin efficiency of wavy fin surface are analyzed numerically. The results show that with the increases of Reynolds number, wavy angle, fin pitch, transverse tube pitch and the decrease of the fin thickness, average temperature on fin surface decreases which leads to the decrease of fin efficiency. In a lot of the published papers, the isothermal model is adopted which neglects the fin efficiency and fin thickness and the fin is simplified as an isothermal surface without thickness. The present paper show that when the thermal conductivity of the fin material is relatively high and the velocity of the air is relatively small, the effects of geometric parameters on fin efficiency is very weak. And the isothermal model without thinking about the fin efficiency is applicable if the precision requirement is not high. But the fin thickness has obvious effects on the heat transfer and fluid flow performance. So if the ratio of the fin thickness and fin pitch is not very small, the fin thickness must be taken into account even to the isothermal model.(6) Local heat transfer coefficient and fin efficiency distributions on wavy fin and plate fin surfaces are investigated numerically and the design principle for the high efficient heat exchanger is derived. Due to the complicated configuration of the wavy fin-and-tube heat exchanger, the studies on the distributions of local heat transfer coefficient and fin efficiency on the wavy finsurface have not been reported in the published papers. However, these local distribution characteristics of the parameters are indispensable for the design of high efficient heat exchangers. So, it is very important to perform those studies. In present dissertation, the distribution characteristics of the local heat transfer coefficient and fin efficiency on wavy fin surface are derived by numerical method. The results show that local heat transfer coefficient generally decreases along air flow direction. At the locations of wave crest, the flow and heat transfer boundary is broken by the wave crest and the local heat transfer coefficient presents an obviously increasing tendency. At the locations of wave trough, there exist circumfluence and the vortexes are formed, so the local heat transfer coefficient presents a sharply decreasing tendency. The larger the air velocity and wavy angle, the more obvious the fluctuation. Local fin efficiency increases along air flow direction, its distribution characteristics basically depends on the distribution of temperature. Then the design principle for the high efficient heat exchanger is derived that convective heat transfer mostly occurs at the inlet region for the fin-and-tube heat exchangers when the air velocity is lower, so the corrugations at outlet region have little effects on heat transfer but greatly increase pressure drop. If we properly augment the heat transfer area and wavy angle at the inlet region and reduce them at the outlet region, the goals of enhanced heat transfer, decreased pressure drop and saving material can be realized.(7) A new type of local wavy fin is designed and its performances are validated. The traditional enhanced heat transfer approaches for heat exchanger always cause the great increase of pressure drop. And the increase percentage for the pressure drop is usually higher than the enhanced percentage of heat transfer performance. In this dissertation, on the basis of the above design principle, a new type of wavy fin pattern is designed which has wavy fin in the upstream and plain plate fin in the downstream. Then the comparison studies on the heat transfer and fluid flow performances of the new type fin pattern and the traditional plate fin and wavy fin patterns are performed. The simulation results show that the heat transfer coefficient for the new fin pattern only decreases 4%, but friction factor decreases 18% compared with traditional wavy fin; the heat transfer coefficient increases about 45% and friction factor only increase 26% compared with plain plate fin. The enhancement of heat transfer is larger than the increase of pressure drop. So the new fin pattern has better enhanced heat transfer and decreased pressure drop characteristics.(8) Wavy fin heat exchanger with elliptic tubes is proposed and numerical studies on the heat transfer and fluid flow performance are performed. The results show that the elliptic tube arrangement can enhance heat transfer up to 30% and only increase friction factor about 10% compared with circular tube. So the goal of enhanced heat transfer and decreased pressure drop can be achieved by replacing the circular tube with elliptic tube. And with the increases of ellipse centrality, fin pitch, transverse tube pitch and the decrease of fin thickness, both the heat transfer coefficient and the friction factor of the elliptic tube heat exchanger decrease.(9) Effects of elliptic tube cross-section pattern on heat transfer and fluid flow characteristicsof wavy fin-and-tube heat exchangers are investigated. Contrastive study on the performances of five tube cross-section patterns are performed. The results show that heat transfer performances of all the four elliptic tube patterns are better than that of circular tube; the enhanced percentages are 17.0%, 16.9%, 14.6% and 12.3% respectively. The friction factor of the elliptic tube with the same minimum airside free-flow area as circular tube is about 7.1% larger than that of circular tube. However, the friction factors of the other three elliptic tubes are smaller than that of circular tube, the friction factors are decreased about 23.9%, 20.7% and 17.0% respectively. From the point of view of enhanced heat transfer, the elliptic tube with the same hydraulic diameter as circular tube has the best heat transfer performance and from the point of view of decreased pressure drop, the elliptic tube with the same perimeter as the circular tube has the smallest pressure drop. In practical applications, we can choose different tube cross-section patterns according to different enhanced heat transfer and decreased pressure drop needs.Key words: CO2refrigerant; Transcritical cycle; Fluid flow and heat transfer;Enhanced heat transfer; Field synergy principle。