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中高温热泵工质应用的现状与选择 总被引:1,自引:0,他引:1
为了消除现有热泵技术利用温度比较低,对于高温的工业余热和地热尾水利用率低的问题,指出中高温热泵工质技术替代常温热泵技术的必要性。介绍热泵系统的组成部分、中高温热泵工质的循环特性、热泵工质对环境的影响以及中高温热泵工质的研究现状。中高温热泵提高了热泵的工作温度,扩大了低位热能资源的回收和供热范围。 相似文献
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针对普通R134a热泵制取中高温热水过程中存在的冷凝压力过高、系统效率低、不环保及无法直接替代等问题,提出一种新型中高温热泵混合工质R13I1/R290/R600a。建立基于该工质的热力循环模型,计算该循环的热力特性。结合气象数据,对其进行多工况计算并与已有的工质R134a、MIX1和MIX2对比分析。研究结果表明该新型混合工质的循环性能与同模型常温热泵工况下R134a的循环性质大致相同,且其环境性能优良:ODP为零,GWP小于20,温度滑移小于4℃。单位容积制热量略低于R134a,分别比MIX1和MIX2平均高16.7%、1.3%;COP分别比R134a、MIX1和MIX2平均高9.2%、4.1%和0.7%。综合循环性能较对比工质更优越,适用于冷凝温度为70~90℃,循环温升低于75℃的热泵工况。 相似文献
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文章提出了一种利用海洋温差能和风能联合发电的方法及装置。利用海洋表层的热海水加热低沸点工质,使之蒸发.送入汽轮机推动汽轮发电机组做功发电,汽轮机排出的工质乏气用海洋深层的冷海水冷凝为液态,再用热海水加热,送入汽轮机,使之蒸发,推动汽轮机发电机组做功发电,如此循环,持续发电;并且利用洋面风力发电,并用该电力驱动热泵装置.由热泵装置的媒质将工质的温度进一步提高.增大工质体积膨胀率;由热泵装置的媒质将冷海水的温度进一步降低.再用该低温海水去冷凝工质乏气,增强对工质乏汽的冷凝效果。该装置既需要用到小型透平,又需要用到风力发电装置.十分适合公司发展。 相似文献
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The effect of sensible heating of the phase-change material (PCM) before melting and subcooling after solidification, on the performance of the latent heat storage system (LHSS), is studied in terms of first- and second-law efficiencies for the overall charge–discharge cycle. The external heat transfer irreversibilities on account of the interaction between the heat transfer fluid and the storage element are characterized and the optimum phase-change temperature for maximum second-law efficiency is studied. The performance of the LHSS operation is assessed with and without sensible heating before melting and subcooling after solidification. It is observed that the optimum phase-change temperature is higher, and, the overall second-law efficiency is greater for LHSS with sensible heating and subcooling beyond a certain phase-change temperature compared to latent heat storage alone. In addition, the first-law overall efficiency is found to exhibit a minimum and a pre-heated discharge stream is shown to result in a substantial improvement of the second-law efficiency. © 1998 John Wiley & Sons, Ltd. 相似文献
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A new approach to improve the performance of supercritical carbon dioxide Rankine cycle which uses low temperature heat source is presented. The mechanical pump in conventional supercritical carbon dioxide Rankine cycle is replaced by thermal driven pump. The concept of thermal driven pump is to increase the pressure of a fluid in a closed container by supplying heat. A low grade heat source is used to increase the pressure of the fluid instead of a mechanical pump, this increase the net power output and avoid the need for mechanical pump which requires regular maintenance and operational cost. The thermal driven pump considered is a shell and tube heat exchanger where the working fluid is contained in the tube, a tube diameter of 5 mm is chosen to reduce the heating time. The net power output of the Rankine cycle with thermal driven pump is compared to that of Rankine cycle with mechanical pump and it is observed that the net power output is higher when low grade thermal energy is used to pressurize the working fluid. The thermal driven pump consumes additional heat at low temperature (60 °C) to pressurize the working fluid. 相似文献
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The energy needs of a typical one-family house in the Thessaloniki area for heating, cooling and domestic hot water production are calculated. The calculations are based on the typical average daily consumption of hot water and on the degree-day method for heating and cooling. The results are finally translated into thermal energy consumption, assuming the typical Greek situation (heating with diesel oil boilers and conventional radiators, cooling with local air-to-air split-type heat pumps and hot water production with electric heaters). The same energy needs are assumed to be covered by a vertical closed loop ground heat exchanger combined with a water-to-water heat pump system with fan-coils for heating and cooling and a thermosyphonic solar system for domestic hot water production. The ground heat exchanger/heat pump system efficiency is determined using data from an existing and continuously monitored similar system installed in the broader area of Thessaloniki. The solar system load coverage is calculated using the f-chart method. The energy consumption of the renewable energy systems is calculated and compared to that of the conventional system. The results prove that significant energy savings can be achieved. 相似文献
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When a vapour compression heat pump is used to heat a fluid over a range of temperatures the refrigerant cycle may be fundamentally different from a standard Rankine cycle which operates only between isothermal reservoirs. This paper considers two strategies for heating fluids: in one approach the fluid is heated in a single pass condenser; in the other the body of fluid is kept fully mixed at all stages of the heating process. An isothermal source reservoir is assumed and the performance of nine common refrigerants is examined. In the ideal limit the mixed fluid process has a higher COP than the single pass method. But in practice there is likely to be no clear advantage in using a fully mixed sink fluid, especially where the temperature lift is greater than 50°C. The single pass heating process has an advantage under these conditions that lower peak condensing temperatures may generally be achieved than for the mixed fluid heating process. 相似文献
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Improved underground heat exchanger by using no-dig method for space heating and cooling 总被引:2,自引:0,他引:2
Yasuhiro Hamada Makoto Nakamura Hisashi Saitoh Hideki Kubota Kiyoshi Ochifuji 《Renewable Energy》2007,32(3):480-495
This paper describes experiments and analyses on an improved underground heat exchanger by using a no-dig method for the purpose of the cost reduction of a space heating and cooling system using underground thermal energy. First, the improved underground heat exchanger was installed on the campus of Hokkaido University, and it was shown that a ground source heat pump system utilizing the heat exchanger was sufficient for space heating and cooling. Second, evaluation program of the heat exchanger was developed, and the program was verified to give good predictions by comparing with experimental results. As a result of system simulations, an energy reduction for a system installation relative to a conventional vertical earth heat exchanger reached 78%. The primary energy reduction rate including the system installation and operation relative to a typical air source heat pump was 29%. 相似文献
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采用压缩机变频、设置回热器与气液分离器辅助加热等技术途径,设计与构建一种供暖用CO2空气源热泵系统。在此基础上,建立响应面模型对供暖用CO2空气源热泵的压缩机运行频率进行优化,以提高供暖用CO2空气源热泵的低温性能。响应曲面法分析结果表明,低温环境下压缩机合理升频运行可有效提高供暖用CO2空气源热泵制热量,虽压缩比增大,但仍能保证压缩机稳定运行。为提高供暖用CO2空气源热泵的性能系数(COP),在低温环境下压缩机可分段变频运行。当环境温度依次为-5、-10及-15℃时,COP最大时对应的压缩机运行频率分别为55、58及60 Hz。 相似文献
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随着热泵空调的普及,热泵空调的能耗占比不断增大,其节能问题成为了关注焦点。换热器对系统性能有着重要的影响,如何通过改进换热器来提升系统性能则成为了研究的热点。其中分液冷凝器作为一种新型的换热设备,能对系统制冷性能产生积极影响。但热泵空调系统在制热工况下,分液冷凝器变成气液分离式蒸发器,其系统制热性能尚未可知。通过实验研究,调整毛细管长度和制冷剂充注量,发现在国家标准工况下分液热泵空调系统的最大制热量比原系统高4.50%,C OP比原系统高7.93%,所对应的毛细管长度为700 mm,制冷剂充注量为700 g。且制冷剂过充注的情况下,分液热泵空调系统的制热性能比较稳定。 相似文献
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Urban heating in northern China accounts for 40% of total building energy usage.In central heating systems,heat is often transfened from heat source to users by the heat network where several heat exchangers arc installed at heat source,substations and terminals respectively.For given overall heating capacity and heat source temperarure,increasing the terminal fluid temperature is an effective way to improve the thermal performance of such cascade heat exchange network for energy saving.In this paper,the mathematical optimization model of the cascade heat exchange network with three-stage heat exchangers in series is established.Aim at maximizing the cold fluid temperature for given hot fluid temperature and overall heating capacity,the optimal heat exchange area distribution and the medium fluids' flow rates are determined through inverse problem and variation method.The preliminary results show that the heat exchange areas should be distributed equally for each heat exchanger.It also indicates that in order to improve the thernmal performance of the whole system,more heat exchange areas should be allocated to the heat exchanger where flow rate difference between two fluids is relatively small.This work is important for guiding the optimization design of practical cascade heating systems. 相似文献