The Exergy Analysis Of Gas Cooler In CO 2 Heat Pump System

Transcription

1 Available onle at Procedia Environmental Sciences 11 ( e Exergy Analysis Of Gas Cooler In CO 2 Heat Pump System Ygbai Xie a, Zicao Wang b, Kuikui Cui c, Xuedong Zang d Scool of Energy & Power Engeerg,Nort Ca Electric Power University, 62 Mailbox, Baodg, Ca a xieyb@ncepu.edu.cn, b wzcmonkey@163.com, c cuikk_27@126.com, d kouyizan@163.com Abstract e (HCFC-pase- and te fear for future problems for oter syntetic workg fluids, because of teir known and unknown impact on te environment, ave troduced a risg terest environmentally safe natural workg fluids. CO2 is one of te few non-toxic and non-flammable workg fluids tat do not contribute to ozone depletion or global warmg, if leaked to te atmospere. Because te critical temperature of CO2 is only 31.1 C, te transcritical cycle can be used to improve te coefficient of performance of te system. o te gas cooler of transcritical CO2 eat pump system for termodynamics analysis and test results sow tat gas cooler on te system's performance as a great fluence, so need to te performance analysis of te gas cooler. Analytical process sould be taken to account evaporation temperature,gas cooler let temperature and pressure, usg exergy analysis metod to eat excanger performance analysis. 211 Publised by Elsevier Ltd. Selection and/or peer-review under responsibility of te Intelligent Information 211 Publised ecnology by Elsevier Application Ltd. Selection Researc and/or Association. peer-review under Open responsibility access under CC BY-NC-ND of [name organizer] license. Keywords-:CO 2; transcritical carbon dioxide cycle; exergy efficiency; teoretical analysis; experimental results 1.Introduction Alternative refrigerants request satisfy te ozone layer protection and stop global warmg up te dual requirement. e former IIR cairman G. Lorentzen [1]is te first to advance te CO2 transcritical cycle, and tk tat CO2 is "te most prospects refrigerant of te 21st century." CO2 as a refrigerant, as its unique advantages [2], but te COP of te transcritical system is not ig because of teir lower critical temperature (31. erefore, te key to promote te CO2 transcritical cycle is to improve te efficiency of te system. Natural refrigerants are creasgly becomg te refrigerant of coice to replace te environmentally armful CFCs and (HCFCs. CO2 is te most friendly wit te environment, it is one of te refrigeration laser as many advantages: 1ODP =,GWP =1 ; 2it is abundant, non-flammable, non-toxic and its cost is fairly low. 3it is compatible wit standard materials and lubricants and is not armful to te environment. 4it as potentially favorable termodynamics and transports properties. 5its termo pysical properties are well known even te supercritical area. 2.Experimental Apparatus and Procedures est device troduced Publised by Elsevier Ltd. Selection and/or peer-review under responsibility of te Intelligent Information ecnology Application Researc Association. Open access under CC BY-NC-ND license. doi:1.116/j.proenv

2 1556 Ygbai Xie et al. / Procedia Environmental Sciences 11 ( Figure 1. e test device cludes tree sub-systems: carbon dioxide eat pump system, coolg water system and cilled water system. e core part wic carbon dioxide eat pump system cludes compressor, gas cooler, previa evaporator, evaporator, value, ternal eat excanger, gasliquid separator and oil elimator etc. Matematical model Fundamental assumption In order to simplify te calculation wic te gas cooler is workg under supercritical pressure lead to carbon dioxide large temperature canges, make te followg assumptions [3]: 1e mass flow rates of refrigerant and water is steady gas cooler, and eac side tube ave similar refrigerant. 2If one-dimensional flow te tube, ten circumferential and axial flow of bot side fluid are ignored. 3Refrigerant and water is steady flow. 4Pressure drop te gas cooler is negligible. 5Heat transfer wit te ambient is negligible; Model simplification [4-6] e gas cooler transcritical carbon dioxide cycle is tube eat excanger. e model for exergy analysis followg: Ex c, Ex Gas cooler Ex c c c, Ex Figure 2. exergy analysis of gas cooler e average constant pressure specific eat capacity of coolg water and carbon dioxide are C pa and C pb.because te temperature of medium is varied, so micro-unit equation is coosed. dex = m ( d - ds Constant pressure process d = C pd,

3 Ygbai Xie et al. / Procedia Environmental Sciences 11 ( d ds = C p Δ 2 d Ex = m 1 C pd C p = mc ( ln 2 p Supply exergy for carbon dioxide: Δ E xa = E x E x = m C ( ln A pa Atta exergy for coolg water: Δ E xb = Exc Exc Partial energy equilibrium equation: m A C pa (( = m B C pb ( c c So exergy efficiency for gas cooler m ( ln c B C pb c c c ex = m C ( ln A pa 3.Gas Cooler effect of system pressure on exergy By te above analysis we can see, we need temperature pressure and mass flow bot coolg water and carbon dioxide [7]. Figure 3 sows te variation te exergy efficiency for te system pressure creases. Results sow tat te variation te maximum exergy efficiency for te evaporatg temperature =5. eoretical analysis and experimental trend of te curve is basically te same system pressure/mpa (a eoretical analysis

4 1558 Ygbai Xie et al. / Procedia Environmental Sciences 11 ( actual system pressure/mpa (b Experimental results Figure 3. Variation of exergy efficiency wit system pressurev 4.Gas Cooler effect of coolg water on exergy As sown Figure 4, te exergy efficiency improvement creases wit te crease of gas cooler let temperature. In o te 34 C, te gas exergy efficiency appears flection pot tat presents ascendant trend. eory analysis and experimental get curve te cange trend of basic same, but due to te system operation process exists some irreversible loss obtaed ave certa deviation [8] gas cooler let temperature / o C (a eoretical analysis actual gas cooler let temperature / o C

5 Ygbai Xie et al. / Procedia Environmental Sciences 11 ( (b Experimental results Figure 4. Variation of exergy efficiency wit coolg water temperature 5.Gas Cooler effect of coolg water flow on exergy coolg water flow /m/l (a eoretical analysis actual coolg water flow /m/l (b Experimental results Figure 5. Variation of exergy efficiency wit coolg water flow Figure 5 reflects te coolg water flow cange on gas exergy efficiency effects. Between 24-31L/m, gas cooler of exergy efficiency is a lear rise. 6.Conclusions o te gas cooler termodynamic analysis and experimental researc of transcritical carbon dioxide eat pump system sows tat teory analysis and experimental get curve te cange trend of basic same, but due to te system operation process exists some irreversible loss obtaed ave certa deviation. Wen te gas cooler and evaporation let temperature constant, gas cooler exergy efficiency wit ig pressure measurg pressure creasg gradually decreases; wen te evaporation temperature and ig pressure side constant, gas cooler exergy efficiency slow cange quickly after risg wit gas cooler let temperature wit a certa range creased; wen te evaporation and condensg temperature constant, gas cooler of exergy efficiency lear growt. In system design process sould be taken to te system pressure, gas cooler exit temperature and coolg water flow of gas exergy efficiency and reduce te fluence of system operation process of irreversible loss to make te system designg optimal.

6 156 Ygbai Xie et al. / Procedia Environmental Sciences 11 ( Acknowledgment References is work was supported by te Fundamental Researc Funds for te Central Universities (9MG32 [1] Hideaki Obana,Zongquan Xu translation, Heat excanger manual: Hydrocarbon processg press,1987 [2] Guancun Zao, Lilun Qian, Exergy analysis and te application, Beijg, Higer Education Press, 1984 [3] Ruui Li, Energy Effective Use Of Exergy,1992 [4] Sengcun Liu, Yitai Ma, Qiuju Liu. e Analysis And Experiment On CO2 Gas Cooler Wit Hydrocoolg, Refrigeration and Air- Conditiong,28,1(8,pp [5] Suangyg Wu, Zicai Mou, Zejun Liu. Exergy Economic Analysis On Heat Excanger, Journal of Engeerg for ermal Energy and Power,1999,14(6,pp [6] Mxia Li, Yitai Ma, Junlan Yang. Study On Gas Coller Of CO2 ranscritical Cycle Water Source Heat Pump.Acta Energiae Solaris Sica. 28,12(29:pp [7] unlan Yang, Yitai Ma,Gang Feng, Mxia Li.Performance Simulation and Optimization Calculation For CO2 Gas Cooler. Fluid Macery, 21,8(3:pp [8] Onder Ozgener, Arif Hepbasli. A review on te energy and exergy analysis of solar assisted eat pump systems[j]. Renewable and Sustaable Energy Reviews11 (