压缩式制冷空调机组壳管式换热器的传热强化研究进展

冷凝器和蒸发器是压缩式制冷空调机组中的重要设备,其传热系数的高低直接影响机组的效率和成本.采用强化传热技术是提高冷凝器与蒸发器传热性能的关键.对于管外冷凝传热强化,在Turbo-C管的基础上,将翅片从翅顶到翅根完全割裂,形成断裂的三维翅片管,以减少表面张力作用下冷凝液在传热管表面粘滞特性对传热的影响.采用螺旋隔板替代冷凝器和干式蒸发器的弓型隔板,能改善壳程流体的流动与传热性能;针对降膜蒸发器的降膜蒸发区与满液蒸发区的不同特点,应分别采用不同类型的强化管,以提高蒸发器传热系数.     

强化传热技术在空调中的应用

众所周知,提高空调机热力循环过程中制冷剂的蒸发温度、降低其冷凝温度均能提高空调器的制冷系数。但是随着冷凝温度的降低和蒸发温度的提高,空调器的传热温差将会随之降低,蒸发器和冷凝器的传热条件恶化。虽然增大蒸发器、冷凝器的换热面积能解决这一矛盾,但是由此必然导致空调器体积增大、能重比降低。解决这一矛盾最为明智的方法就是利用现有的传热强化技术、强化冷凝器和蒸发器的传热实现空调机蒸发器、冷凝器的低温差传热。本文将简要介绍强化传热技术及几种能在空调设计中应用的强化传热管。     

压缩式制冷空调机组壳管式换热器的传热强化研究进展

冷凝器和蒸发器是压缩式制冷空调机组中的重要设备,其传热系数的高低直接影响机组的效率和成本。采用强化传热技术是提高冷凝器与蒸发器传热性能的关键。对于管外冷凝传热强化,在Turbo-C管的基础上,将翅片从翅顶到翅根完全割裂,形成断裂的三维翅片管,以减少表面张力作用下冷凝液在传热管表面粘滞特性对传热的影响。采用螺旋隔板替代冷凝器和干式蒸发器的弓型隔板,能改善壳程流体的流动与传热性能;针对降膜蒸发器的降膜蒸发区与满液蒸发区的不同特点,应分别采用不同类型的强化管,以提高蒸发器传热系数。     

R245fa传热性能实验

蒸发器和冷凝器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素,为了提高中低温余热在热泵机组和地热双工质发电系统中的利用效率,本文选用R245fa循环工质,对满液式蒸发器和冷凝器进行实验研究,分别讨论热水温度进口温度对蒸发器和冷凝器的传热系数、蒸发压力和冷凝压力的影响。研究结果表明,在工质流量和冷却水流量保持不变的条件下,蒸发器传热系数随着热水进口温度和温差的增大而减小,冷凝器的传热系数随着热水进口温度的增加先增大后减小,蒸发器传热系数可以达到2500 W/(m2?℃);蒸发器压力和汽轮机前后的压差随着热水出口温度的增加而增加,热水流量对蒸发压力和冷凝压力的变化浮动较小。     

R245fa传热性能实验研究

蒸发器和冷凝器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素,为了提高中低温余热在热泵机组和地热双工质发电系统中的利用效率,本文选用R245fa循环工质,对满液式蒸发器和冷凝器进行实验研究,分别讨论热水温度进口温度对蒸发器和冷凝器的传热系数、蒸发压力和冷凝压力的影响。研究结果表明,在工质流量和冷却水流量保持不变的条件下,蒸发器传热系数随着热水进口温度和温差的增大而减小,冷凝器的传热系数随着热水进口温度的增加先增大后减小,蒸发器传热系数可以达到2500 W/(m2·℃);蒸发器压力和汽轮机前后的压差随着热水出口温度的增加而增加,热水流量对蒸发压力和冷凝压力的变化浮动较小。     

不同循环冰箱的性能比较

本文讨论了两种双蒸发器冰箱的节能效果,一种是将两个蒸发器串联,另一种是将两个蒸发器各自构成独立的循环,两个独立循环可用电磁阀切换,或两循环采用各自的压缩机、冷凝器而构成彼此完全独立的循环.分析和试验表明,在研究的工况下,与单蒸发器冰箱相比,串联蒸发循环可节能20%,而电磁阀控制的交替蒸发循环比串联循环节能12.3%;彼此完全独立的双循环冰箱,与美国现行标准相比节能13.8%.     

制冷剂充注量对冷藏车用制冷机组性能的影响

为了研究制冷剂充注量对冷藏车用制冷机组性能的影响,在数值模拟得到的制冷剂标准充注量的基础上,试验研究制冷剂充注量对压缩机吸/排气压力、吸/排气温度、蒸发器出口过热度、冷凝器出口过冷度及制冷能力的影响。研究表明,数值模拟方法得到的制冷剂标准充注量适用于实际制冷机组。     

小型太阳能气泡泵吸收式制冷机研究

本文确定了设计计算参数下小型太阳能气泡泵吸收式制冷机制冷循环中各状态点参数,进行了发生器、冷凝器、蒸发器、吸收器、溶液热交换器的热负荷计算和加热热水、冷水、冷却水、稀溶液等循环介质的流量计算.进行了发生器、冷凝器、蒸发器、吸收器、溶液热交换器等换热设备所需的传热面积计算.根据求得的传热面积确定了各换热设备的传热管数,计算了热水进出口配管、冷却水进口配管、冷媒水进口配管的内径尺寸,为开发小型吸收式制冷机提供了一定的理论和实践基础.     

非共沸混合制冷剂组分对冷凝器换热特性的影响

为了揭示非共沸混合工质在冷凝器内的换热特性,探明非共沸混合工质组分对制冷剂和换热流体间沿程温度的影响,通过建立冷凝器换热模型,对不同沸点差的二元环保型非共沸混合工质进行了理论分析.结果表明:由于非共沸混合工质比焓值与温度的非线性关系,换热流体间的沿程传热温差出现极值点;混合工质中富含低沸点组分时,冷凝器内部存在最小传热温差;反之,存在最大传热温差;混合工质沸点差增加,滑移温度的限制条件之差增大,窄点现象增强.     

排气冷却R290/CO_2复叠式制冷系统性能分析

通过对带排气冷却器的R290/CO_2复叠式制冷系统的性能分析,以及与不带排气冷却器的R290/CO_2复叠式制冷系统的性能进行比较,得出在相同的运行工况下,当排气冷却器的热负荷为1.4 kW,低温循环的冷凝温度为-20℃,制冷量为10kW时,排气冷却器在降低冷凝蒸发器CO_2的入口温度方面起到显著作用,高温循环制冷剂R290的质量流量减少11.4%,相应的高温循环压缩机的功耗和冷凝器的热负荷均降低11.4%,R290/CO_2复叠式制冷系统的COP提高8.8%。     

Stepped pressure cycle – A new approach to Lorenz cycle

Refrigerant vapor-compression cycle usually works with variable temperature heat sources in reality, which causes remarkable irreversible losses in heat exchange process. This paper proposed the stepped pressure cycle to modify the vapor-compression cycle using refrigerant, particularly pure refrigerant. Refrigerant is designed to flow through a series of heat transfer units with stepped pressures so that the irreversible losses can be reduced. Theoretical proof confirmed the stepped pressure cycle with pure refrigerant can approach the Lorenz cycle, the most efficient cycle under variable temperature heat sources. Numerical analysis on cycle performance demonstrated that a dual-step suction and discharge pressure cycle using R32 can achieve 11.5% cooling COP improvement for residential air conditioner, while a dual-step discharge pressure cycle using R134a can bring 9.8% heating COP increase for heat pump water heater. A pilot system was made and preliminarily tested. Compared to the single cycle system, 12.3% and 18.7% COP increase were achieved in the pilot system by applying dual and triple subcycles, respectively.     

自然冷却技术应用于数据中心的方案分析

自然冷却技术是实现数据中心节能减排的重要途径。对于风冷冷水机组,采用冷冻水末端存在水进入数据中心的安全隐患,采用热管背板末端存在二次换热及蒸发温度低的问题。热管型冷水机组结构简单,具备小压比、变容量功能,机组配合风冷、水冷及蒸发冷等形式的选择及综合利用,可以发挥较好的节能效益;热管型制冷剂机组不仅可以解决水进入数据中心的安全隐患,而且可以解决多次换热性能效率低下以及分液不均的问题,提高系统蒸发温度,拓宽自然冷却利用时间,为大型数据中心全年冷却提供新的思考与方向。     

Capacity-controlled ground source heat pumps in hydronic heating systems

The objective of this study was to investigate the energy-saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps. Variable-speed capacity control is commonly used in air-to-air heat pumps, but not in ground source heat pumps for hydronic heating systems, even though the energy-saving potential may be greater for this application. A theoretical analysis indicates how the energy efficiency is influenced by variable-speed capacity control of the compressor. The analysis shows that, to take full advantage of the capacity control, care should be taken to achieve the correct relationship between refrigerant flow and heat transfer media flows. Intermittent control and variable-speed capacity control were compared by laboratory tests on two capacity-controlled heat pumps and one standard heat pump with a single-speed compressor. Test data were then used for seasonal performance factor (SPF) calculations. The SPF calculations show that despite improved performance at part load the variable-speed controlled heat pump did not improve the annual efficiency compared to the intermittently operated heat pump. This is mainly due to inverter and compressor motor efficiencies and the need for improved efficiency and control of pumps used in the heating and ground collector systems.     

湿风冷却分体式单冷空调器的试制与综合性能试验研究

针对风冷型分体空调器在酷暑的高气温、强辐射等恶劣气候条件下制冷运行时,经常出现制冷能力不足、压缩机连续运行时间过长以及易出现过压、超温保护故障等现象,提出了采用湿帘加湿产生湿风来改善空调器冷凝换热效果的措施,并设计、试制了湿风冷却小型家用分体单冷空调器样机;利用环境试验室条件和焓差法测量制冷量方法,测试和分析研究了该样机在不同室外环境工况、相同室内环境工况下的综合能效比.结果表明:在标准工况下,湿风冷却空调器与同类型传统风冷空调器相比,其综合能效比可提高约15%,在高温工况下,湿风冷却措施不但可大大提高空调器在高温工况下的运行可靠性,而且其节能效果明显,为进一步研发节能型分体单冷空调器提供了一种有益的参考.     

减压发生喷射吸收复合制冷原理与经济分析

为了提高制冷效率,降低换热器的热负荷,减少热能对制冷系统的注入,采用减压发生和液体喷射泵来推动制冷剂的循环,从而使整个制冷流程处在较低焓值下循环.无须给系统注入温度较高的热能,而只是利用吸收循环热,在降压条件下进行发生,大大降低了单位制冷量的能耗量,这优越于当前各类气体喷射吸收复合式制冷技术和其他各类制冷技术,其经济性是显而易见的,流程是简便易行的.     

两级双效溴化锂制冷-热泵复合循环

在热电冷联产系统中,溴化锂吸收式制冷机在制冷过程中排放了大量的废热,这些废热品味低,难以直接回收利用。在此提出了两级双效溴化锂制冷-热泵复合循环,该循环具有冷凝温度较高的特点,便于直接回收冷凝排放热。系统以背压汽轮机的背压蒸汽为热源,制冷的同时利用循环所排出的废热加热锅炉补充水至较高温度。以具有相同功效的双效溴冷机与单效溴化锂热泵联合运行作为对比循环,制冷-热泵复合循环系统省去了一台蒸发器与冷凝器,减少了两个换热温差,并且通过热力计算、能量分析和分析表明,该循环的能量利用率与效率均有很大的提高,效率比对比循环提高了45%。     

Investigation on gradient thermal cycle for power and refrigeration cogeneration

In order to improve energy utilization efficiency of low grade heat, a novel gradient thermal cycle for power and refrigeration cogeneration is proposed. The cycle is cascaded with two stages based on different thermal driven temperature. The first stage is pumpless Organic Rankine Cycle (PRC) while the second stage is two-stage sorption refrigerator. R245fa is selected as the working fluid of PRC, whereas CaCl₂-BaCl₂-NH₃ working pair is chosen for two-stage sorption refrigerator. Different heat source temperatures from 80°C to 95°C are adopted for analysis and comparison. Results indicate that the highest average power output and cooling effect are able to reach 204 W and 0.91 kW under the condition of 95°C heat source temperature and 10°C refrigeration temperature. For different heat source temperatures, total energy and exergy efficiency of the gradient thermal cycle for power and refrigeration cogeneration range from 9.49% to 9.9% and 10.9% to 11.8%, respectively. For gradient thermal cycle exergy efficiency of heat utilization ranges from 24% to 18.8% which is 126.5% and 70.9% higher than the PRC and two-stage sorption refrigerator, respectively, when the heat source temperature is 80°C.     

Methodology for thermal design of novel combined refrigeration/power binary fluid systems

Refrigeration cogeneration systems which generate power alongside with cooling improve energy utilization significantly, because such systems offer a more reasonable arrangement of energy and exergy “flows” within the system, which results in lower fuel consumption as compared to the separate generation of power and cooling or heating. This paper proposes several novel systems of that type, based on ammonia–water working fluid. Importantly, general principles for integration of refrigeration and power systems to produce better energy and exergy efficiencies are summarized, based primarily on the reduction of exergy destruction. The proposed plants analyzed here operate in a fully-integrated combined cycle mode with ammonia–water Rankine cycle(s) and an ammonia refrigeration cycle, interconnected by absorption, separation and heat transfer processes. It was found that the cogeneration systems have good performance, with energy and exergy efficiencies of 28% and 55–60%, respectively, for the base-case studied (at maximum heat input temperature of 450 °C). That efficiency is, by itself, excellent for cogeneration cycles using heat sources at these temperatures, with the exergy efficiency comparable to that of nuclear power plants. When using exhaust heat from topping gas turbine power plants, the total plant energy efficiency can rise to the remarkable value of about 57%. The hardware proposed for use is conventional and commercially available; no hardware additional to that needed in conventional power and absorption cycles is needed.     

Numerical optimisation of a two-stage ejector refrigeration plant

Jet-refrigeration cycles seem to provide an interesting solution to the increasing interest in environment protection and the need for energy saving due to their low plant costs, reliability and possibility to use water as operating fluid. A steam/steam ejector cycle refrigerator is investigated introducing a two-stage ejector with annular primary at the second stage. The steady_state refrigerator, exchanging heat with the water streams at inlet fixed temperatures at the three shell and tube heat exchangers, evaporator, condenser and generator, is considered as an open system. Heat transfer irreversibilities in the heat exchangers and external friction losses in the water streams are considered, ignoring the internal pressure drop of the vapor. A simulation program numerically searches the maximum COP at given external inlet fluid temperatures as a function of mass flows, dimensions and temperature differences in the heat exchangers. The code gives the ejector and heat exchangers design parameters.     

Study on an Energy-saving System for a Hydraulic Excavator′s Boom

To improve the energy efficiency of a hydraulic boom,a new energy-saving system adopting a hydraulic accumulator is proposed.First,the principle of the system is presented.Then,the dynamic simulation is introduced.Finally,the conclusions are given based on the analysis of simulation data.In Summary,the innovative energy-saving system combines flow regeneration and potential energy recovery,runs steadily and comfortably,saves energy remarkably and has good potential for improving energy utilization of a hydraulic excavator.