江榮霞 謝秀娟 鄧筆財(cái),3 楊少柒
(1航天推進(jìn)劑技術(shù)國家重點(diǎn)實(shí)驗(yàn)室 北京 100190) (2中國科學(xué)院理化技術(shù)研究所 北京 100190) (3中國科學(xué)院大學(xué) 北京 100049)
江榮霞1,2,3謝秀娟1,2鄧筆財(cái)1,2,3楊少柒1,2
(1航天推進(jìn)劑技術(shù)國家重點(diǎn)實(shí)驗(yàn)室 北京 100190) (2中國科學(xué)院理化技術(shù)研究所 北京 100190) (3中國科學(xué)院大學(xué) 北京 100049)
液氦溫區(qū)大型低溫系統(tǒng)流程圖如圖1所示。系統(tǒng)由一個(gè)壓縮機(jī)(C1),6個(gè)換熱器(HEX1-6),2個(gè)透平膨脹機(jī)(E1、E2),1個(gè)節(jié)流閥(JT)和1個(gè)杜瓦瓶(Dewar)構(gòu)成。高純氦氣從緩沖罐被吸入壓縮機(jī)中,被壓縮機(jī)壓縮后經(jīng)三級油過濾器過濾后進(jìn)入冷箱,經(jīng)過液氮預(yù)冷,透平膨脹機(jī)膨脹后經(jīng)節(jié)流閥進(jìn)入杜瓦瓶,杜瓦瓶蒸發(fā)的氦氣再次經(jīng)冷箱中的換熱器,回到壓縮機(jī),完成工作循環(huán)。
圖1 液氦溫區(qū)大型低溫制冷系統(tǒng)的流程圖Fig.1 Process flow diagram of large-scale helium cryogenic system
mN2exNIN+mGex10+mex2+mLex1+mW1exW1+mW2exW1=
m1ex9+mex1+mN2exNOUT+mw1exw2+
mW2exw2+ExDest,coldbox
(1)
(2)
(3)
(4)
2.2 獨(dú)立參數(shù)的選取[7]
氦制冷系統(tǒng)設(shè)計(jì)計(jì)算過程中涉及到很多參數(shù),但是不同參數(shù)之間相互聯(lián)系。通過對氦制冷系統(tǒng)的熱力分析,得到各個(gè)參數(shù)間的關(guān)系,并且找出關(guān)鍵獨(dú)立參數(shù)。
對于系統(tǒng)給定的制冷量和液化率:Q@4.5 K+mLLHe,故T9=T10=4.5 K。壓縮機(jī)的吸氣壓力一般選為略高于大氣壓:P1=0.105 MPa,氮?dú)馀欧艍毫σ策x為略高于大氣壓:PNOUT=0.105 MPa。但透平膨脹機(jī)T1和T2串聯(lián)的中間壓力P5-1要根據(jù)循環(huán)的計(jì)算來定。
對于整個(gè)循環(huán),可用式(5)表示獨(dú)立變量之間的關(guān)系:
f(Q,m1,m,mL,P2,ηHEX6,ηHEX5,ηT2,ηHEX4,
ηHEX3,ηT1,ηHEX2,ηHEX1,PLN,T2,T3,ηC)=0
(5)
在這17個(gè)變量中,Q和mL是制冷機(jī)的設(shè)計(jì)參數(shù),它們表征了制冷機(jī)的容量大小,需要根據(jù)負(fù)載的熱負(fù)荷來確定。根據(jù)壓縮機(jī)、透平膨脹機(jī)的制造工藝水平給出效率:ηC=0.55,ηT1=ηT2=0.68。其中T2往往是環(huán)境溫度,通常取300 K;T3為液氮預(yù)冷后的溫度,通常取80 K;PLN為N2入口壓力,通常取0.3 MPa。這樣確認(rèn)制冷循環(huán)的獨(dú)立參數(shù)還剩下11個(gè):Q,m1,m,mL,P2,ηHEX1-6。
(6)
因此,獨(dú)立參數(shù)可化簡為壓縮機(jī)出口壓力,透平分流率和換熱器的效率。
3.1 壓縮機(jī)排氣壓力對循環(huán)性能的影響
圖2 冷箱效率、壓縮機(jī)效率和循環(huán)效率隨壓縮機(jī)排氣壓力的變化Fig.2 Effect of variation of compressor discharge pressure on cycle performance
因此,不管在制冷模式還是液化模式下,在制造工藝水平允許的范圍內(nèi),換熱器的效率越高越好,這里選取0.97。
圖3 在不同換熱器效率下,冷箱的效率隨著壓縮機(jī)出口壓力的變化Fig.3 Effect of compressor discharge pressure on cold box exergy efficiency at different exchangers efficience
圖4 在不同透平流量下,冷箱的效率隨著壓縮機(jī)出口壓力的變化Fig.4 Effect of compressor discharge pressure on cold box exergy efficiency at different expander mass flow rate
圖5 部件的損失占冷箱輸入的比隨著透平膨脹機(jī)分流率的變化Fig.5 Effect of variation in flow through expanders on exergy destruction in cold box components
對改進(jìn)Claude循環(huán)的液氦溫區(qū)低溫制冷系統(tǒng)進(jìn)行獨(dú)立參數(shù)選取并優(yōu)化,得出了以下結(jié)論:
(2)分析了換熱器效率隊(duì)循環(huán)性能的影響。發(fā)現(xiàn)在制造工藝允許的情況下,換熱器效率越高越好,這里選取0.97。
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Effect of independent variables on cycle exergy efficiency of helium cryogenic refrigeration system
Jiang Rongxia1,2,3Xie Xiujuan1,2Deng Bicai1,2,3Yang Shaoqi1,2
(1State Key Laboratory of Technologies in Space Cryogenics Propellants,Beijing 100190, China) (2Technical Institute of Physics and Chemistry,Chinese Academy of Sciences,Beijing 100190,China) (3University of Chinese Academy of Sciences,Beijing 100049,China)
Energy balance eqation of the modified Claude cycle of large helium cryogenic refrigeration system was established,and the computational formula of cycle exergy efficiency was obtained. Through the thermal analysis of the refrigeration mode and liquefaction mode of helium refrigerator,the relation between parameters of the cycle was determined and the key independent variables:compressor discharge pressure,the turbine expander flow rate and heat exchanger efficiency were extracted. Based on static model of the modified Claude cycle of large helium cryogenic refrigeration system,the effect of compressor discharge pressure,the turbine expander flow rate and heat exchanger efficiency on cycle exergy efficiency was studied,and the optimize design parameters was obtained.
helium cryogenic refrigeration system;independent variables;exergy efficiency
2016-08-10;
2016-11-03
航天低溫推進(jìn)劑技術(shù)國家重點(diǎn)實(shí)驗(yàn)室基金課題(SKLTSCP1502)資助。
江榮霞,女,25歲,碩士研究生。
TB611
A
1000-6516(2016)06-0024-05