数据中心冷却用动力型热管的实验研究

为研究用于数据中心的动力型热管系统性能,本文在焓差法实验室对三类压缩机性能进行了实验研究,结果表明:1)带气泵功能的压缩机具备低压缩比运行能力,可根据室外环境温度以及室内负荷不同分别切换不同工作模式,简化系统配置,具有很好节能效益,其中变频转子压缩机COP可以超过20,变频涡旋压缩机COP接近20,可以较好的替代液泵; 2)中小型机房空调领域,综合利用气相动力型热管与压缩制冷技术,拓宽了自然冷却利用时间,全年能效比AEER远高于常规机房空调,配合运用地域性风冷、水冷、蒸发冷等节能方式,为现代数据中心节能减排提供了新的思路; 3)大型数据中心空调领域,磁悬浮压缩机COP超过20,具有较高的节能效益,但与液泵相比仍具有一定差距,同时离心式压缩机作为气泵运用存在循环不畅的现象,需要液泵进行压头补偿。     

Performance evaluation of a CO2 heat pump system for fuel cell vehicles considering the heat exchanger arrangements

A novel CO₂ heat pump system was provided for use in fuel cell vehicles, when considering the heat exchanger arrangements. This cycle which had an inverter-controlled, electricity-driven compressor was applied to the automotive heat pump system for both cooling and heating. The cooling and heating loops consisted of a semi-hermetic compressor, supercritical pressure microchannel heat exchangers (a gas cooler and a cabin heater), a microchannel evaporator, an internal heat exchanger, an expansion valve and an accumulator. The performance characteristics of the CO₂ heat pump system for fuel cell vehicles were analyzed by experiments. Results for steady and transient state performance were provided for various operating conditions. Furthermore, experiments to examine the arrangements of a radiator and an outdoor heat exchanger were carried out by changing their positions for both cooling and heating conditions. The arrangements of the radiator and the outdoor heat exchanger were tested to quantify cooling/heating effectiveness and mutual interference. The improvement of heating capacity and coefficient of performance (COP) of the CO₂ heat pump system was up to 54% and 22%, respectively, when using preheated air through the radiator instead of cold ambient air. However, the cooling capacity quite decreased by 40–60% and the COP fairly decreased by 43–65%, for the new radiator-front arrangement.     

基于制冷剂泄出的涡旋压缩机容量调节技术

具有固定内容积比的涡旋压缩机存在当外压缩比小于其内压缩比时内容积效率较快下降的问题,由于空调制冷(热泵)系统大部分时间运行在偏向小室内外温差工况即小压缩比工况下,此时压缩机处于过压缩工况,故制冷(热泵)系统的效率低下;同时,随着系统压缩比的减小,会出现建筑的供冷/供热负荷下降和系统的供冷/供热能力上升的矛盾,系统存在降容的需求。为解决小压缩比工况下压缩机效率降低和系统容量过大的问题,提出一种带制冷泄出功能的涡旋压缩机制冷系统,采用模拟分析和实验测量方法,对其技术可行性进行研究,结果显示:合理适度的制冷剂泄出能有效提高压缩机在过压缩工况下的内容积效率,提高系统的COP并减小制冷系统的制冷/制热能力,是一项极具潜力的制冷系统调节技术。     

Compressor driven metal hydride cooling systems—mathematical model and operating characteristics

A detailed mathematical model of a compressor driven metal hydride (CDMH) cooling system is presented. The model takes into account the transient characteristics of the coupled metal hydride reactors with external fins, reciprocating compressor and conditioned space. The model can be used for predicting the system performance during the initial pull-down as well as the stable cycling periods. Results are obtained for a 1 kW capacity air conditioning system using optimized reactors packed with Zr_0.9Ti_0.1Cr_0.55Fe_1.45 hydride. The COP's obtained are in the range of 1.7–2.2 depending on operating conditions while the specific cooling power obtained is about 600 kJ kg alloy⁻¹ h⁻¹. It is shown that in order to make these systems commercially viable it is important to select suitable materials with fast reaction kinetics. Since, system performance parameters can be predicted more effectively, the model can be used for design of optimized systems.     

低温热泵用涡旋压缩机性能的试验研究

制定低温热泵用涡旋压缩机试验方案,对研制的原型机进行性能测试。试验结果表明：在冷凝温度不变的情况下,随着蒸发温度的降低,原型机的制热量有所减少,但减少的速度低于普通热泵系统用涡旋压缩机;压缩机的电功率有所增加,但增加的幅度不大,且压缩机的排气温度也有所降低,故在低温工况下采用准二级压缩热泵用涡旋压缩机比采用普通热泵用涡旋压缩机可以更有效地提高空气源热泵的低温制热性能,是寒冷地区用小型空气源热泵比较适宜采用的压缩机。     

电动汽车空调热泵型涡旋压缩机结构分析

为了解决电动汽车空调系统冬季采暖问题,针对冬季空调工况下压缩机单级压比增大的运行特性,以涡旋压缩机制热性能系数为热力学优化目标函数,确定了制冷剂循环系统中的最佳补气压力,优化了涡旋压缩机静涡旋盘上的中间补气口的几何位置和形状,使其具备了准双级压缩功能。将研发的热泵型电动涡旋压缩机安装于电动汽车空调系统,利用空气焓差法对系统进行了制热、制冷性能实验。实验结果表明,静涡旋盘结构优化后的热泵型电动涡旋压缩机,其制热和制冷能力可以满足5人座电动汽车司乘人员的冬季和夏季舒适性要求,并且具有较高的制热和制冷性能系数,从而提升了汽车空调系统热泵循环和制冷循环的热经济性,达到了节能的目的。     

Modeling and performance study of a water-injected twin-screw water vapor compressor

Due to the reason of water injection, twin screw water vapor compressor can realize higher pressure ratio and saturated temperature lift of compressed vapor. Its application in mechanical vapor compression (MVC) heat pump systems has drawn much attention recently because of the great energy-saving potential and reliability. In this paper, a thermodynamic model of the working process in water injected twin screw water vapor compressor is established, in which heat and mass transfer between water liquid and vapor are considered. Its accuracy is validated by the experimental recorded p–V indicator diagrams. With the proposed model, the compressor performance is simulated and studied. According to the simulation results, water injection can increase the volumetric efficiency 5% and adiabatic indication efficiency 6%. Once the discharged vapor has been cooled to saturation, the shaft power of the compressor will increase while the adiabatic indication efficiency and the volume flow rate together with the volumetric efficiency change little with the continuous increase of injected water. Since the sensible heat of water is much smaller than latent heat, the temperature of injected water has little effect on the performance. Both the volume flow rate and shaft power increase linearly with the rotor speed. In addition, the volume flow rate of injected water should be adjusted with the regulation of rotor speed to guarantee a saturate discharge temperature. The volumetric efficiency will increase and the adiabatic indication efficiency will decrease slowly with the rise of rotor speed. Due to the cooling and evaporation effects of liquid water at the discharge chamber, the adiabatic indication efficiency does not decline when it operates at under compression condition. Water injection can greatly improve the compressor performance when the compressor operates at under compression or over compression condition, especially where a high saturated temperature lift of compressed vapor is in demand.     

Heating performance enhancement of a CO2 heat pump system recovering stack exhaust thermal energy in fuel cell vehicles

A CO₂ heat pump system using recovered heat from the stack coolant was provided for use in fuel cell vehicles, where the high temperature heat source like in internal combustion engine vehicles is not available. The refrigerant loop consists of an electric drive compressor, a cabin heater, an outdoor evaporator, an internal heat exchanger, an expansion valve and an accumulator. The performance characteristics of the heat pump system were investigated and analyzed by experiments. The results of heating experiments were discussed for the purpose of the development and efficiency improvement of a CO₂ heat pump system, when recovering stack exhaust heat in fuel cell vehicles. A heater core using stack coolant was placed upstream of a cabin heater to preheat incoming air to the cabin heater. The performance of the heat pump system with heater core was compared with that of the conventional heating system with heater core and that of the heat pump system without heater core, and the heat pump system with heater core showed the best performance of the selected heating systems. Furthermore, the coolant to air heat pump system with heater core showed a significantly better performance than the air to air heat pump system with heater core.     

Semi-empirical modeling and analysis of oil flooded R410A scroll compressors with liquid injection for use in vapor compression systems

Oil flooding is a technique that can be utilized in compression systems to achieve near-isothermal compression. This can lead to a boost in system efficiency and a reduction in compressor power consumption. In this paper a semi-empirical model for oil flooded compressors using liquid injection was developed. The model is validated with experimental data and integrated into a thermodynamic model of a vapor compression system with oil flooding and regeneration. The performance of the heat pump system is predicted and the semi-empirical model is used to identify and estimate the magnitude of the irreversibilities during the compression process. A method for generalizing the model for different working fluids is also presented. Using this model, design recommendations are made to improve the efficiency of the studied liquid flooded compressors for heat pump applications.     

Investigation of R-744 Voorhees transcritical heat pump system

Using economizer in R-744 heat pump cycle is an effective way to improve the heating capacity in cold climates. In this paper, a modification construction of reciprocating compressor with economizer port, a Voorhees compressor was introduced and the heat pump cycle with Voorhees economizer was compared with the traditional screw or scroll economizer cycles. Both the R-744 transcritical heat pumps with and without Voorhees economizer were tested at the same conditions with different air mass flow rates and different evaporating temperatures. The results show that the heating capacity of the heat pump with Voorhees economizer can be two times higher than the transcritical heat pump without economizer at low evaporating temperature conditions. At the same capacity operation conditions, the efficiency of the heat pump with Voorhees economizer is higher at high refrigerant mass flow rate conditions. The optimum discharge pressure of the heat pump with Voorhees economizer is found to be higher than the heat pump without economizer at the same ambient conditions. For mobile heat pump application, CO₂ transcritical heat pump with Voorhees economizer demonstrates better performance comparing to the conventional transcritical CO₂ heat pump without economizer when the evaporating temperature is lower than −20 °C, or when the mobile is idling with low compressor RPM.     

Experimental analysis of a novel cooling system driven by liquid refrigerant pump and vapor compressor

This study introduced a novel energy saving cooling system, i.e. a combined cycle coupled with a traditional vapor compression cycle with a pumped liquid two-phase cooling cycle. The system has two operation modes, i.e. the compression cycle mode driven by compressor and the pump cycle mode driven by refrigerant pump. A multi-purpose test bench was constructed to experimentally evaluate the performance of the integrated cycle system under various operation conditions. The effects of cycle working condition and the shift temperature between the two operation modes on the overall cycle performance were investigated in detail. It is found that the novel cycle system has a higher EER compared to the traditional compressor system when the ambient temperature is relatively low. The further experimental results and comparative annual energy saving analysis also indicated that the proper shift temperature is about −5 °C from the system EER and cooling capacity point of view.     

阀门控制的金属氢化物制冷系统的热力学分析

建立了阀门控制的金属氢化物制冷系统的动态性能模型，针对阀门控制的金属氢化物制冷系统，分析了热源温度、反应器的比热、氢化物与反应器质量比、传热系数等对系统动态性能的影响。结果表明：中温热源温度的增高将会降低COP、炯效率和制冷率；反应器的比热容对COP、炯效率和制冷率影响较小；增加氢化物与反应器质量比时COP、炯效率将增加，但制冷率将下降；增加传热流体与反应床表面的传热系数将会较明显提高COP、炯效率和制冷率。根据计算结果提出了改善系统动态性能的措施。     

Thermodynamic based comparison of sorption systems for cooling and heat pumping: Comparaison des performances thermodynamique des systèmes de pompes à chaleur à sorption dans des applications de refroidissement et de chauffage

A comparison of thermodynamic performances of sorption systems (liquid absorption, adsorption, ammonia salts and metal hydrides) is carried out for typical applications (deep-freezing, ice making, air-conditioning and heat pumping) with either air-cooled or water-cooled heat sink. The results are given in terms of cooling coefficient of performance (COP) (heating COP or coefficient of amplification (COA) for the heat pump), cooling (heating) power versus reactor volume or weight and thermodynamic efficiency. LiBr–water systems show the best results for air-conditioning except when small units are required (metal hydride systems lead to more compact units). Other systems, however, show better results for other applications (chemical reaction with ammonia salts for deep-freezing, adsorption for heat pumping).     

Using an air cycle heat pump system with a turbocharger to supply heating for full electric vehicles

Air cycle heat pump has large potentials in heating applications. However, a key challenge faced nowadays is the matching problem between its expander and compressor. This paper presents the performance evaluation of an air cycle heat pump system integrated with a turbocharger, a blower and a regenerated heat exchanger. A thermodynamic model for this system is first developed and the relationships between the system performance and the operating parameters are investigated. Then, the performance of three different air cycle heat pumps with a blower installed before the compressor, and a blower installed before the turbine, and with an expander, are numerically simulated. The results indicated that the blower installed before the compressor can achieve a higher heating capacity and thus a higher COP. Finally, the heating power consumption of air cycle heat pump was compared with the PTC and the vapor compression heat pump of the full electric vehicle.     

Thermodynamic analyses on an ejector enhanced CO2 transcritical heat pump cycle with vapor-injection

In this paper, an ejector enhanced vapor injection CO₂ transcritical heat pump cycle with sub-cooler (ESCVI) for heating application in cold regions is proposed. The thermodynamic analysis using energetic and exegetic methods is carried out to predict the performance characteristics of the ejector enhanced cycle, and then compared with those of the conventional vapor injection heat pump cycle with sub-cooler (SCVI). The simulation results demonstrate that the ejector enhanced cycle exhibits better performance than the conventional vapor injection cycle under the specified operating conditions. The improvements of the maximum system COP and volumetric heating capacity could reach up to 7.7% and 9.5%, respectively. Exergetic analysis indicates that the largest exergy destruction ratio is generated at the compressor followed by the evaporator and gas cooler. Additionally, the exergy efficiency of the ejector is introduced to quantify the effectiveness of the exergy recovery process, which may be a new criterion to evaluate the performance of the ejector enhanced vapor compression cycle.     

Optimization study of the compression/absorption cycle

For each external situation optimum working conditions for the compression/absorption cycle can be found. The improvement in cycle performance which is gained by optimizing the temperature gradient in the absorber is considerable, particularly for situations with small external temperature gradients. Theoretically, the external and internal temperature gradients should be equal to maximize the cycle performance. The introduction of a solution loop, however, changes this and the optimum internal temperature gradient is always larger than the external gradients. The optimum point of operation is found by studying the changes in the compressor and pump and the heat loss obtained in the solution heat exchanger with the working conditions. A comparison of a compression/absorption cycle, using NH₃-H₂O, and a compression cycle working with pure R12, always results in a higher coefficient of performance for the former. The capacity of the NH₃-H₂O system is also considerably higher.     

可变内容积比螺杆式压缩机的性能分析

随着冷水机组、单元式空调机和水源热泵机组等产品的能效指标从名义工况EER或COP发展到IPLV或ICOP,机组的变容量或变工况性能主要取决于压缩机的变容量或变工况性能。固定内容积比的螺杆式压缩机如果在偏离设计工况下工作,效率下降,进而导致整个机组的性能下降。本文研究变内容积比螺杆式压缩机,内容积比可变化,使得压缩机内压比与外压比与工况相适应,可提升压缩机效率及机组性能。应用于冷水机组、水源热泵机组时,水源热泵机组在制冷工况时能效比可提高14.1%～35%,冷水机组的IPLV可提高7.2%左右。     

Experiments on a metal hydride cooling system working with ZrMnFe/MmNi4.5Al0.5 pairEtude d'un système de refroidissement à hydrure métallique utilisant un couple actif ZrMnFe/MmNi4,5Al0,5

Experimental studies are carried out on a metal hydride cooling system working with ZrMnFe/MmNi_4.5Al_0.5 pair. The effects of operating parameters such as heat source, heat sink and refrigeration temperatures, and half-cycle times on the system performance are obtained. The experimental results are compared with an analytical model proposed earlier by the authors, and a satisfactory agreement is found between the two.     

Two-stage heat pump system with vapor-injected scroll compressor using R410A as a refrigerant

Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both flash tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.     

Performance characteristics of a simultaneous cooling and heating multi-heat pump at partial load conditions

A simultaneous cooling and heating multi-heat pump can improve thermal comfort and energy efficiency through heat recovery at partial load conditions. The performance of a simultaneous heating and cooling multi-heat pump with four indoor units was measured by varying the compressor speed, EEV opening, and fan speed at full and partial load conditions in five operating modes. In the cooling-only and heating-only modes, the heating and cooling capacities were properly controlled by varying the compressor speed. However, in the cooling-main and heating-main modes under partial load conditions, a large imbalance between the cooling and heating capacities was observed even though the compressor speed was optimized. This capacity imbalance under partial load conditions was optimized by adjusting the EEV openings in the mode change unit and the outdoor unit. In addition, in the entire-heat recovery mode, rating compressor speed ratios were proposed under the full and partial load conditions.