Dynamic Analysis of the Discharge Valve of the Rotary Compressor

Transcription

1 Purdue Unversty Purdue e-pubs Internatonal Compressor Engneerng Conference School of Mechancal Engneerng 8 Dynamc Analyss of the Dscharge Valve of the Rotary Compressor Bo Huang Shangha Htach Electrcal Applances Co. Fe Xe Shangha Htach Electrcal Applances Co. Follow ths and addtonal works at: Huang, Bo and Xe, Fe, "Dynamc Analyss of the Dscharge Valve of the Rotary Compressor" (8). Internatonal Compressor Engneerng Conference. Paper hs document has been made avalable through Purdue e-pubs, a servce of the Purdue Unversty Lbrares. Please contact epubs@purdue.edu for addtonal nformaton. Complete proceedngs may be acqured n prnt and on CD-ROM drectly from the Ray W. Herrck Laboratores at Herrck/Events/orderlt.html

2 118, Page 1 Dynamc Analyss of the Dscharge Valve of the Rotary Compressor Bo Huang, Fe Xe* Shangha Htach Electrcal Applances Co., Ltd., R&D Center, Shangha, Chna , Xef1@shec.com.cn ABSRAC Dscharge valve s very crtcal component n rotary compressor, and t s a reed valve whch conssts of valve seat, valve slce and retaner. he moton characterstcs of valve slce greatly nfluence the flowng loss and lfe of valve. he paper presents a mathematcal model to smulate thermodynamc process and moton of the valve smultaneously. Based on the thn-plate theory, the fnte element model of the valve slce s bult up, and the soparametrc element of eght nodes s adopted whch has good adaptablty to shape of the valve slce. he valve seat and retaner are taken as statonary boundary condtons. he gas flow through the sucton and dscharge ports, and the thermodynamcs of real refrgerant have been taken nto consderaton. he Runge-Kutta method and the Newmark method have been taken to solve the equatons. In ths paper, the nfluence of the dscharge valve wth same valve slce and dfferent retaner on the compressor s effcency and reed valve s dynamc stress has been analyzed. he analyss results matches wth the expermental results. he proper retaner can be desgned to optmze the effcency and relablty of the valve. 1. INRODUCION Rotary compressor has been wdely used n room ar-condtoners. Dscharge valve s a crtcal component, whch conssts of valve seat, valve slce and retaner, as shown n Fgure 1. Fgure shows the geometry of the valve slce. Fgure 1: Schematc dagram of dscharge valve Fgure : Schematc dagram of valve slce Ensurng the hgh effcency and relablty of the compressor has become more and more mportant wth ncreasng requrements of the customer and polcy. he dscharge loss nfluences the effcency a lot, as we all know, through ncreasng the lft of the retaner, the effcency wll ncrease much, but the relablty wll decrease. So mostly, there s a conflct between hgh effcency and hgh relablty. Relablty has been nfluenced by a lot of factors, such as materal, manufacturng, abnormal operatng condton, and desgn. he effect of profle of retaner upon the fatgue lfe has been studed by Jan-Shew, 199. Based on the commercal fnte element method software ANSYS, the natural frequences and statc stresses of valves wth dfferent retaners have been analyzed. he research found that small defect on profle of retaner due to manufacturng carelessness may result n valve fracture (Jan-Shew, 199). Influences of valve on pressure pulsaton n sucton manfold and dscharge muffler have also been studed respectvely (Jeong 6; Yka Yuan, 6). Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8

3 118, Page In ths paper, based on the dynamc analyss of the valve, the nfluences of valve on performance and relablty have been conducted.. NUMERICAL MODEL he fnte element method has been conducted to smulate the motonal behavor of the valve. he effcency and the stress dstrbuton of the valve slce whle openng have been calculated by couplng the thermodynamc analyss of the practcal refrgerant and the dynamc analyss of the valve..1 Dynamc analyss of the valve Based on the thn-plate theory, the fnte element model of the valve slce s bult up, and the so-parametrc element of eght nodes s adopted whch has good adaptablty to shape of the valve slce, as shown n Fgure 3. he shape functon can be obtaned as Equaton (1). he schematc dagram of the fnte element dscretzaton of the valve s shown n Fgure 4., 1/ ,,3,4, 1/1 1 5,7 (1), 1/1 1 6, Fgure 3: he so-parametrc element of eght nodes Fgure 4: Fnte element dscretzaton of the valve slce Dsplacement stuaton of any pont on the thn-plate can be descrbed as vector w, x, y ; therefore, dsplacement n X, Y, Z drectons can be expressed as Equaton (). he moton equaton of the valve slce can be deduced as Equaton (3) u z, vz, w w x, y () y x M q KqFgas M s the mass matrx, K s the stffness matrx, q w,,, F Where q x y gas (3) s vector of dsplacement of node, s gas force actng on the valve slce, s the rotatonal angle of the shaft. he valve seat and retaner have been treated as statc boundary of the moton of the valve. he curve of the retaner conssts of a straght lne and an arc as shown n Fgure 5, and ts lft H( x) can be descrbed as Equaton (4) wth ts orgn at start of the arc. After the valve hts the valve seat or retaner wth a certan velocty, t wll come back n opposte drecton wth less velocty. As shown n Equaton (5), nstantaneous dsplacement of the node s lft of the retaner, the rebound velocty s the mpactng velocty multpled by rebound coeffcent. Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8

4 118, Page 3 Fgure 5: Valve retaner H( x) r r x (4) h H( x) (5) v CR v Where, r s radus of the arc, CR s rebound coeffcent. he moton equaton of valve slce has been solved by Newmark method, and then coupled wth the thermodynamc process by Runge-Kutta method through the relatonshp between moton of the valve and dscharge mass. he Newmark method s expressed as followng. Assume, qqt qttq t (6) Integratng Equaton (6) yelds, 1 qttqttqt qtq tt t (7) We can solve, qtta1qttqtaq ta3q t (8) Where, a1 a a3 1 t t Substtutng Equaton (8) nto Equaton (6), we can obtan, K qttfgasttftt (9) Where, K a1 MK F M a q a q a q. hermodynamc analyss 1 t t 3 t he Runge-Kutta method has been used to solve the thermodynamc equatons. he dscharge mass flow equatons have a relaton wth the moton equaton of the valve slce...1 Energy equaton. Governng equatons of the thermodynamc model have been derved from mass and energy conservaton equatons wth the equaton of state for real refrgerant R. he energy equaton wth respect to rotatonal angle s shown as Equaton (1). d 1 1 h P dm h P dv { ( Q hm ) [ hv( ) v ( ) ] [( ) v( ) ] } (1) d c vm s v v d v v d Where m and Q represent the mass flow rate and heat flow rate enterng or extng the governng volume, respectvely. Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8

5 118, Page 4.. Dscharge mass flow equatons. Dscharge process has been taken as one-dmensonal compressble flow through nozzle. he mass flow rate wth respect to rotatonal angle can be descrbed as dm Au/ (11) d v d Where, area of valve clearance Av Ddhv, Dd s the dameter of the dscharge port, k 1 k P 1 k k Velocty of flow u, k1 v1 P P, cr; k P1 P 1 k 1 k cr. k 1 P k 1, cr. k1 P1 hv s lft of the valve, 3.1 Phenomenon of the Valve Fracture 3. ANALYSIS OF HE VALVE FRACURE In order to mprove the performance of the compressor, the valve s lft has been ncreased from 1.97mm to.8mm through changng the retaner. After operatng for average tme of one month, the compressors were locked or couldn t buld the pressure dfference between sucton and dscharge. hrough dsassemblng these compressors for nspecton, we found valve fracture occurred as shown n Fgure 6. he factors that nfluence the relablty of the valve are ncludng materal, manufacture procedure, assemblng, abnormal workng condton, desgn and so on. hrough mprovng manufacture procedure and optmzng the shape of retaner, the problem has been solved. In ths paper we only theoretcally analyze the motonal behavor of the valve, and optmze the retaner s shape to meet wth the requrements of the performance and relablty. 3. he heoretcal Analyss of Valve Fracture Fgure 6: Valve fracture Before usng the model to solve practcal problems, we must ensure the valdty of the program. herefore, durng developng the program, we compared the statc deformaton and natural frequency of the valve slce wth commercal software ANSYS to verfy the model Regardng to the valve fracture, the nfluence of the dscharge valve wth same valve slce and dfferent retaner on the compressor s effcency and reed valve s dynamc stress has been analyzed. Dfferent shapes of the retaners and calculaton results have been presented n able 1. In case 1, the mass producton retaner wth lft of 1.97mm was analyzed; n case, the retaner whch caused the valve fracture was also analyzed; and n, the latest optmzed retaner has obtaned. he calculaton results show that the retaner n not only mproves COP, but also decreases the maxmum dynamc stress of the valve slce. Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8

6 .able 1: Geometrcal parameter of the retaners and calculaton results 118, Page 5 Retaner Case 1 Case Case 3 Valve s lft at center of the dscharge port /mm Radus of arc /mm Length of the straght lne /mm Maxmum stress /MPa heoretcal COP Varaton of gas pressure n governng volume s shown n Fgure 7, the over-compresson loss n case 1 s maxmum, the dscharge pressure pulsaton n case s maxmum because of flutter of the valve slce. Varaton of valve s lft at center of the dscharge port, whch s shown n Fgure 8, represents that the flutter of the valve slce n case s most serous, maybe that s the reason to cause the valve fracture. Varaton of the maxmum stress of valve slce s shown n Fgure 9, the stress value n case s maxmum and the ampltude of fluctuatng stress n case s also the maxmum. hat confrms that possblty of fatgue falure n case s largest. Fgure 1 represents at whch nodes of valve slce the maxmum stress occurs; through that we can fnd whch ponts are most vulnerable to falure. he numberng nodes are shown n Fgure 4. Based on the results, we can fnd the maxmum stress concentraton on node 6 or node, the maxmum stress at node 6 only appears nstantly when the valve slce reaches the maxmum deformaton, the maxmum stress at node appears for a long tme. So the most probable poston for fatgue falure s at node, the neck of the valve slce, just as practcal fracture shown n Fgure 6. Stress dstrbuton when the maxmum stress occurred n case s shown n Fgure Pressure /MPa caae 1 case lft of the valve /mm case 1 case.5. stress /MPa Fgure 7: Varaton of gas pressure case 1 case Fgure 9: Varaton of maxmum stress Fgure 8: Varaton of valve s lft at center of the dscharge port number of the node case 1 case Fgure 1: Node numbers correspondng maxmum stress Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8

7 118, Page 6.15 str1/pa Rotatonal Angle of the Shaft: wdgth/m.1. axal length/m Fgure 11: stress dstrbuton when the maxmum stress occurred n case 4. CONCLUSIONS In ths paper, the valve slce s moton behavor and stress varaton have been studed though dynamc analyss of the valve slces. Properly desgnng the valve slce and retaner can mprove the performance and ensure the relablty. We only demonstrate nfluence of the dfferent retaner on the system n ths paper; actually, we can also analyze the nfluence of the shape, thckness, stffness (materal) on performance and relablty of the compressor. he valve slce s moton behavor not only nfluences the performance and relabllty of the compressor, but also nfluences the dscharge pressure pulsaton to excte the nose. hat s our next research. NOMENCLAURE A v Area of valve clearance emperature A s Area of sucton port Rotatonal angular velocty s Coeffcent of sucton flow h Valve s lft or enthalpy d Coeffcent of dscharge flow P Pressure Rotatonal angle of shaft D d Dameter of the dscharge port REFERENCES Danqng Wu, Jngtong Cong, 1993, Mathematcal Smulaton and Desgn of Reed Valve of Compressor, Chna Machne Press. Jeong I.P, Nasr B., Douglas E.A., 6, Development of a wo-dmensonal Fnte Element Model of a Sucton Valve for Reducton of Pressure Pulsaton n the Sucton Manfold of a Mult-Cylnder Automotve Compressor, Internatonal Compressor Engneerng Conference at Purdue, C9 Yka Yuan, Janhua Wu, 6, Investgaton on the Pressure Pulsaton n the Dscharge Muffler of Rotary Compressors. Internatonal Compressor Engneerng Conference at Purdue, C3 Jan-Shew Ho, Re-Yan Chen, 199, the Effect of Profle of Backng Plate Upon the Fatgue Lfe of a Cantlever Dscharge Valve Reed, Internatonal Compressor Engneerng Conference at Purdue: p Janhua Wu, 1998, Study on Performance and Dynamcs of Inverter Controlled Rotary Compressor, Doctor s hess. Internatonal Compressor Engneerng Conference at Purdue, July 14-17, 8