自然工质低温复叠式制冷循环的热力学分析与比较

介绍了用于低温环境下采用自然工质CO2、NH3和R2903的复叠式制冷循环，介绍和分析了CO2、R290和NH3的物性特征，并且进行了复叠式制冷循环的热力学理论分析，通过计算得出了不同蒸发温度下的最佳低温循环的冷凝温度和最流量比。通过CO2－NH3，CO2－R290和NH3－NH3复叠式循环的比较，可以看出CO2－NH3、CO2－R290的复叠式制冷循环在低温制冷条件下有明显优势。     

地下环境CO2盐水溶液密度的变化及状态方程

利用可以在高温高压条件下，对密闭容器内的流体密度进行直接测量的电磁悬浮式天平对地下盐水的密度进行了测量。实验结果表明，在CO2地下储存30～50℃、10～20MPa时，CO2盐水溶液的密度随着温度的升高而减小，随着CO2的质量分数的增加而增大，随着压力的增加呈线性增加。CO2盐水溶液密度与盐水密度之比与压力无关，但随着CO2的质量分数的增加而增大，随着温度的升高而减少。     

正庚烷均质压燃燃烧反应化学动力学数值模拟研究

应用零维详细化学反应动力学模型，对正庚烷均质压燃燃烧反应的化学反应动力学过程进行了数值模拟研究，分析了在内燃机边界条件下影响其燃烧反应的关键基元反应、关键中间产物以及自由基。结果表明，正庚烷的燃烧过程由高温反应和低温反应两个阶段组成，高温反应阶段又可以分为蓝焰反应和热焰反应两个阶段。正庚烷氧化反应首先经过脱氢反应，第一次加氧异构化后的第二次加氧是低温反应的必经途径，其产物的两次分解是低温反应阶段OH自由基的主要来源；蓝焰反应阶段主要是甲醛氧化成CO的过程，H2O2的热分解是控制该阶段反应最重要的基元反应，也是OH自由基的主要来源；热焰反应主要是CO氧化成CO的过程；CO的生成途径是：低温反应生成的甲醛(CH2O)脱氢生成HCO，HCO氧化生成CO，OH是CO氧化为CO2和正庚烷脱氢反应最重要的自由基。     

CO2跨临界循环地源热泵的研究

给出了CO2跨临界循环地源热泵的系统流程，并在考虑输气系数和绝热效率的基础上，与R22和R134a等进行了循环性能比较。结果表明，用于需要较高供水温度的空调系统或热水供应系统时，CO2可具有和常规工质相当的性能。同时对于一特定的CO2地源热泵，分析了在热水流量和热水温度变化时的运行特性，并讨论了CO2地源热泵容量调节的方法。     

CO2跨临界循环吸热过程换热性能理论分析

通过对两相流型和干涸现象进行分析，发现CO2在吸热沸腾过程中，环状流是主要的流型，液滴夹带和沉降是支持环状流最可能的机理。与其他制冷剂相比，CO2出现环状流以及发生干涸时的干度值要低得多。并且干涸前和干涸后的传热特点，以及关联式形式存在很大差别，应该区分对待。因此，研究能淮确描述CO2流动沸腾换热关联式，为CO2跨临界制冷循环蒸发器的优化设计提供理论依据，是非常必要的。     

进气含有高浓度CO2的柴油机的燃烧特性

在一台可以拍摄缸内混合气形成和燃烧过程的发动机上，在进气中加入不同浓度的二氧化碳（CO2）气体，研究其对柴油机的燃油束发展、混合气形成、着火、燃烧过程所带来的影响，同时采用三基色法对测出的燃烧温度场分布进行计算分析。拍摄的工况是在不同发动机转速以及不同的CO2浓度的情况下进行。拍摄到的图像经分析和计算表明，加入不同浓度的CO2后，燃油束的喷雾及混合过程没受影响，但使着火滞后期延长、燃烧持续期缩短，并降低了燃烧温度，特别是降低了最高燃烧温度。研究结果还表明，加入CO2过多时则会影响燃烧稳定性。     

生物质合成气的化学当量比调整

针对生物质气化气中硫化物少、V（H2／CO）低和V（CO2）高的特点，采用气化炉内铁系高温变换催化剂和气化炉外钛促进的钴钼耐硫催化剂进行水煤气变换调整H2／CO比，添加部分沼气重整过量CO2，对生物质合成气化学当量比调整进行了实验研究。结果表明：气化炉内铁系催化剂调整效果不明显；在高温低硫的生物质气化气中，钛促进的钴钼耐硫催化剂具有较高的变换活性，CO转化率达到80％以上，合成气H2／CO比在1-8范围内可调；在V（CH4，CO2）=1、常压、750℃和镍基催化剂作用下沼气重整过量CO2，制备出宽V（H2／CO）、V（CO2）和V（CH4）均低于5％（摩尔百分比）的合成气；通过水煤气变换过程结合沼气重整过程，可依据目的产物合成的要求，制备合适化学当量比、高碳转化率的生物质合成气。     

CO2跨临界循环膨胀特性及机理

介绍了采用膨胀机的CO2跨临界循环的系统流程及典型工况，详细分析了膨胀中经历的亚稳态过程的成因和机理，指出气化的滞后对系统的危害，并对相变膨胀过程中的成核现象进行了热力学分析，在此基础上，结合CO2超临界膨胀过程的特点，阐明了气液相变介质中声速的确定方法，认为CO2超临界膨胀过程可近似按照经典热力学的准静态理论进行分析。     

模型化合物吡啶加热氧化规律研究

为研究煤中吡啶型氮的氧化规律，选取吡啶为煤的含氮模型化合物，采用傅立叶红外光谱仪(Ft-Ir)和烟气分析仪连用，在600—1400℃温度范围内，对其氧化产物进行研究．实验结果表明，吡啶氧化产物主要是NO、NO2、N2O、CO和CO2．N2O在750～900℃生成量最大；氧气量大于或等于理论氧气量的76％时，CO在650℃存在一个高峰，NOx随着温度升高而增加；氧气量等于理论氧气量的59％时，生成大量CO，抑制了NOx的生成．     

边界条件对正庚烷均质压燃燃烧过程的影响

应用零维详细化学反应动力学模型，对不同边界条件下正庚烷（n—heptane）均质压燃燃烧反应的化学反应动力学过程进行了数值模拟研究，得出了以初始温度和燃料当量空燃比这两类边界条件为函数，压缩比为17，转速为1400r／min的HCCI全工况解。结果表明：HCCI燃烧分为完全燃烧区域、低温反应和蓝焰反应区域、仅发生低温反应区域和失火区域；不发生热焰反应的关键是反应H＋O2=O＋OH进行程度浅，不能生成足够的OH自由基使CO氧化成CO2；蓝焰反应也不发生而仅发生低温反应的关键是H2O2分解反应的进行程度浅，H2O2只有在缸内温度达到1000K时才能快速分解，这就不能生成足够的OH自由基使甲醛转化成CO2低温反应和蓝焰反应区域是高CO排放区，仅发生低温反应的区域是高甲醛排放区。     

Study on carbon dioxide gas cooler heat transfer process under supercritical pressures

In carbon dioxide transcritical air‐conditioning and heat pump systems, the high‐pressure‐side heat exchanger operating at supercritical pressures is usually called as gas cooler. The carbon dioxide gas cooler displays much difference from the traditional heat exchangers employing constant property fluids. The commonly used logarithmic mean temperature difference (LMTD) and effectiveness—heat transfer unit (ε‐NTU) fail for the gas cooler design calculation as the carbon dioxide properties change sharply near the critical or pseudo‐critical point in the heat transfer processes. The new effective heat transfer temperature difference expression for variable fluid property derived by the authors is verified by numeric simulation of the carbon dioxide gas cooler. Moreover, the available correlated models for the cooled carbon dioxide supercritical heat transfer are used to simulate the gas cooler. Detail analysis is made for the deviations among the different models, and for the distributions of local convective coefficient, heat flux, and local temperature of carbon dioxide along the flow path in the gas cooler. Copyright © 2002 John Wiley & Sons, Ltd.     

Optimizing environmental insulationthickness of buildings with CHP-based district heating system based on amount of energy and energy grade

The increase of insulation thickness (IT) results in the decrease of the heat demand and heat medium temperature. A mathematical model on the optimum environmental insulation thickness (OEIT) for minimizing the annual total environmental impact was established based on the amount of energy and energy grade reduction. Besides, a case study was conducted based on a residential community with a combined heat and power (CHP)-based district heating system (DHS) in Tianjin, China. Moreover, the effect of IT on heat demand, heat medium temperature, exhaust heat, extracted heat, coal consumption, carbon dioxide (CO₂) emissions and sulfur dioxide (SO₂) emissions as well as the effect of three types of insulation materials (i.e., expanded polystyrene, rock wool and glass wool) on the OEIT and minimum annual total environmental impact were studied. The results reveal that the optimization model can be used to determine the OEIT. When the OEIT of expanded polystyrene, rock wool and glass wool is used, the annual total environmental impact can be reduced by 84.563%, 83.211%, and 86.104%, respectively. It can be found that glass wool is more beneficial to the environment compared with expanded polystyrene and rock wool.     

Thermal analysis of slurry ice production system using direct contact heat transfer of carbon dioxide and water mixture

This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between − 15 and − 60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well.     

跨临界CO2热泵热水器的应用研究

分析CO2在热泵热水器中跨临界循环的原理及特点,阐述了CO2用于热泵热水器的优势,概述了国内外跨临界CO2热泵热水器的应用情况及关键零部件的研究开发。     

Power-based performance comparison between carbon dioxide and R125 transcritical cycles for a low-grade heat source

In order to compare the power output of the carbon dioxide transcritical cycle and the R125 transcritical cycle for a low-grade heat source of about 100 °C, the two cycles were optimized for power output using a simulation method. In contrast to conventional approaches, each working fluid’s heat transfer and pressure drop characteristics within the heat exchangers were taken into account by using a discretized heat exchanger model. To fairly compare the power output of the cycles by using different working fluids, the inlet temperatures and the flow rates of both the heat source and the heat sink were fixed. The cycle minimum temperature was not given, but was determined by the heat sink conditions and the working fluid’s heat transfer and pressure drop characteristics, as it is in actual practice. The total heat transfer area was fixed, whereas the allocation of the heat-exchanger area between the vapor generator and the condenser was optimized in the simulation. The R125 transcritical cycle produced 14% more power than did the carbon dioxide transcritical cycle. Even though the carbon dioxide cycle shows better heat transfer and pressure drop characteristics in the heat exchangers, the high pumping power required to manage the large pressure head degrades the cycle’s power output. Based on this study, the R125 transcritical cycle is recommended for heat sources of about 100 °C.     

Investigation of convection‐based energy systems using supercritical carbon dioxide as a working fluid

Carbon dioxide is the best retrofit to meet the future demand on long‐term environmental friendly working fluids. The volumetric efficiency of supercritical carbon dioxide is very high, which makes it a promising working fluid in convection‐based energy systems with high efficiency and small volume. Here, the natural convection of supercritical carbon dioxide driven only by temperature difference is studied in circulation loops. The Reynolds number of the flow is about 10⁴ when the temperature difference is only 20 K, about two orders of magnitude greater than that of water. Furthermore, the heat transfer rate is about 3 times as great as that of water. These results demonstrate the potential of carbon dioxide as a working fluid in solar thermal conversion, nuclear power and waste heat utilization, etc. The influence of the tube diameter on the flow and heat transfer characteristics is discussed. Both the velocity and the Nusselt number are greater in the loop with a larger tube diameter where flow reversal occurs periodically. It is found that flow reversal degrades the system efficiency of the natural circulation loop. Therefore, the optimization about the geometric configuration of convection‐based energy systems using carbon dioxide as a working fluid does exist and is very important for their safe and effective operation. Copyright © 2010 John Wiley & Sons, Ltd.     

国内外熔融高炉渣显热回收方法

分析了熔融高炉渣显热回收的必要性。因为熔渣的物理性质和高炉出渣不连续性,导致熔渣显热回收存在困难。介绍了滚筒法、搅拌法、风淬法、连铸法、离心粒化和反应热法显热回收工艺,并指出甲烷-二氧化碳重整法有很好的发展前途。     

铜渣催化甲烷二氧化碳重整的热力学及动力学分析

以铜渣作为甲烷二氧化碳重整的催化剂及热源,考察其催化重整活性,并对铜渣进行了XRD,SEM,BET,H2-TPR分析表征。实验结果表明,铜渣在高温段具有较高的催化活性,当铜渣温度为1 200℃时,甲烷、二氧化碳转化率分别为87.5%和85.2%。同时,对铜渣催化甲烷二氧化碳重整进行了热力学及动力学分析,得出铜渣从1 200℃降至600℃过程中余热利用率为22.93%,铜渣催化该重整反应的活化能为213.90 k J·mol~(-1),反应速率常数k=2.19exp(-213.90/RT)。     

Investigation of turbulent convective heat transfer and pressure drop of TiO2/water nanofluid in circular tube

Turbulent heat transfer behavior of titanium dioxide/water nanofluid in a circular pipe was investigated experimentally where the volume fraction of nanoparticles in the base fluid was less than 0.25%. The experimental measurements have been carried out in the fully-developed turbulent regime for various volumetric concentrations. The results indicated that addition of small amounts of nanoparticles to the base fluid augmented heat transfer remarkably. There was no much effect on heat transfer enhancement with increasing the volume fraction of nanoparticles. The measurements also showed that the pressure drop of nanofluid was slightly higher than that of the base fluid and increased with increasing the volume concentration. In this paper, experimental results have been compared with the existing correlations for nanofluid convective heat transfer coefficient in turbulent regime. Finally, a new correlation of the Nusselt number will be presented using the results of the experiments with titanium dioxide nanoparticles dispersed in water.     

Thermal performance of a packed bed reactor for a high‐temperature chemical heat pump

The thermal performance of a chemical heat pump that uses the reaction system of calcium oxide/lead oxide/carbon dioxide, which is developed for utilization of high‐temperature heat above 800°C, is studied experimentally. The thermal performance of a packed‐bed reactor of a calcium oxide/carbon dioxide reaction system, which stores and transforms a high‐temperature heat source in the heat pump operation, is examined under various heat pump operation conditions. The energy analysis based on the experiment shows that it is possible to utilize high‐temperature heat with this heat pump. This heat pump can store heat above 850°C and then transform it into a heat above 900°C under an approximate atmospheric pressure. An applied system that combines the heat pump and a high‐temperature process is proposed for high‐efficiency heat utilization. The scale of the heat pump in the combined system is estimated from the experimental results. Copyright © 2001 John Wiley & Sons, Ltd.