NEW ASPECTS of FLUID MECHANICS, HEAT TRANSFER and ENVIRONMENT

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1 Geneated by Foxit PDF Ceato Foxit Softwae Fo ealuation onl Nueical Siulation of Coplex Flow Field in Quenching Funace with Mixtue of Nitogen-spay Wate Eject Quenching unde Noal Pessue and High Velocity Baodong SHAO, Heing CHENG, Jianyun LI, Ziliang LI, Lijun HOU, Jie HOU, Lifeng WANG Faculty of Ciil and Achitectual Engineeing Kuning Uniesity of Science and Technology 118 postbox, Lianhua Capus, Kuning Uniesity of Science and Technology Kuning, China Abstact: - The flow field in quenching funace designed by us is coplex, and the fluid flow in funace is the ixtue of Nitogen and spay wate unde noal pessue and high elocity. The two-phase flow based on ixtue odel is siulated by CFD softwae. The elocity and pessue (static and dynaic) fields in funace ae gien. The siulation esults show that the flow field in funace is coplex as analysis. The esults also show that the alue of slip elocity between two phases has oe contibution to the ixtue elocity of the two-phase, and the funace designed can acceleate the elocity of flow field. Key-Wods: - Nitogen-spay wate ixtue Gas quenching Two-phase flow Nueical siulation 1 Intoduction As a quenching edia, the theal conductiity of gas is usually salle than that of oil and wate, but gas can adjust quenching pocess accoding to wopiece shape and specific equieent of ateial, and the theal conductiity of gas can be enhanced to the leel of oil and wate by inceasing elocity and pessue. Copaed with wate and oil quenching, gas quenching has any adantages, such as good unifoity, little defoation, no quenching spot, no enionent pollution, easy to contol techniques paaete, and low cost. Because acuu high pessue gas quenching has oe equieents fo equipent and cost, odinay pessue and high elocity gas quenching ay hae wide applications. CHENG et al. [1] designed the equipent of odinay pessue high elocity gas quenching by theseles and it has sae quenching effect as acuu quenching. Hec et al. [2] studied the gas flow field and siultaneous heat tansfe pocess in gas quenching by nueical siulation fo suface teatent of cylindical saple geoety. The ealuation of optiized flow conditions and nozzle aangeents to achiee a axiu oeall heat elease to axiize the quenching efficiency and a local sooth distibution of the cooling pocess fo aoidance of spatial hadness aiations by deiation of an optiized nozzle aangeent and appopiate opeation conditions of the gas jet aay with espect to the thee diensional saple geoety of a cylinde to be quenched. [3, 4] Soe eseaches showed that the cooling pefoance of ixed two gases is bette than single pue gas, thus it is ey ipotant to eseach quenching of ixtue of two gases. At pesent, studies of ixtue quenching ae liit to ixed gas of He, N 2, CO 2, A o H 2, and soe of gas is expensie, so cheap and high capability ixed gases ae needed. Quenching by spay wate jetted by ai is an effectie pocessing heat teatent technology. The heat tansfe echanis of spay wate jet quenching is ey coplex, pesent eseach is still exploed. MEI et al. [5] studied spay cooling heat tansfe coefficient on high tepeatue suface, and analyzed the effects of spay wate density, high suface tepeatue, doplet diension and doplet elocity on spay cooling heat tansfe coefficient. GAO et al. [6] inestigated nueically a doplet ipinging on a constant tepeatue flat suface by the ethod of Volue-of-Fluid (VOF), and the esults showed that when the initial size is salle and the ipact elocity is bigge, the cooling effectieness will be highe. LIU [7] expeientally studied the boiling citical heat flux by ist cooling, and found the coelations between CHF and the ist flow conditions, which consist of ass elocity of spay wate, ean diaete of spay wate doplets and ixed ipact elocity of doplets-ai. ZHANG et al. [8] inestigated the steady-state chaacteistics of the spay cooling syste, and analyzed the effects of the heat flux alue, the spay distance, the sin tepeatue, the subcooling degee of the etun liquid on the heat tansfe pefoance and the ISSN: ISBN:

2 Geneated by Foxit PDF Ceato Foxit Softwae Fo ealuation only. eapoation efficiency of the spay liquid. DU et al. [9] siulated the spay quenching pocess by establishing a nonlinea FEM odel copising aiable physical popety paaetes and phase tansfoation. Because the theal conductiity of Nitogen is bigge than that of ai and it is safe, abundant, cheap, inetia, if it is ixed with spay wate, the ixtue will has faoable cooling effect. Theefoe, odinay pessue and high elocity Nitogen and spay wate jet quenching is nueically siulated in this pape and the aiety of flow field in quenching funace with pessue and elocity of inlet and Nitogen-spay wate ixtue atio. 2 Nueical odel The configuation of quenching funace is shown in figue 1. The ixtue of Nitogen and spay wate is jetted into the outside caniste of funace with cetain elocity and pessue, and then into the inne caniste though hole of inne caniste, finally into outlet though collection loops, whee the wopiece is cooled. Because the ixtue atio of Nitogen and spay wate at inlet can be adjusted dynaically, the cooling pefoance can be adjusted between pue Nitogen and wate quenching to eet the equieent fo diffeent icostuctue. Fig.1 Diaga of quenching funace 1-outlet, 2-coe, 3-uppe coe, 4-outside caniste, 5-collection loop, 6-hole in side of inne caniste, 7- inne caniste, 8- hole unde inne caniste, 9-down coe, 10-inlet The flow field is eshed by hexahedon stuctual gid, and 3D gid of flow field in funace is shown in figue 2. In figue 2, the wopiece at outlet is consideed. Thee ae about eleents and nodes. The bounday laye is consideed at all the solid bounday Fig.2 3D eshed odel of quenching funace 3 Contol equation The two-phase flow in funace is siulated by Mixtue odel. The continuity equation fo the ixtue odel is ( ) + ( ) = & (1) t Whee is ass ean elocity, which can be expessed as n α = = 1 (2) Whee is ix density, which can be expessed as n = α (3) = 1 Whee α is the olue pecent of No. phase. The oentu equation fo the ixtue odel is + = p + µ + t g F α d, d, (4) T ( ) ( ) [ ( )] Whee n is nube of phase, F is olue foce, is iscosity of the ixtue d, n = 1 µ µ = α µ (5) is slip elocity of the second phase. ISSN: ISBN:

3 Geneated by Foxit PDF Ceato Foxit Softwae Fo ealuation only. = d, (6) 4 Pocess of nueical siulation The nueical siulation is conducted by CFD softwae Fluent6.3. The adius of inlet is 40, and the elocity of initial ixtue is about 100/s, and the iscosity of ixtue is about , so the appoxiate Re nube is about 8000, and the -ε (2 equations) odel is used fo tubulent analysis. By calculating cusoily, the Mach nube is lage than 0.3, so the ix fluid is teated as incopessible. Duing siulation, Nitogen is piay phase, and spay wate is seconday phase, and spay wate is teated as doplet which diaete is At inlet, diffeent elocities of Nitogen and spay wate ae set to gie a ixtue bounday condition. At outlet, the pessue is noal ai pessue. The iteatie nube is Fig.4 Velocity agnitude field of Nitogen 5 Results of nueical siulation Fig.3-Fig.7 is elocity and pessue fields when the elocity of Nitogen and spay wate at inlet of funace is 170/s and 150/s, espectiely. Because the density of spay wate is lage than that of Nitogen, the elocity of spay wate is quice than that of Nitogen, though the initial elocity of Nitogen is lage than that of spay wate. Fo Fig.3-Fig.5, when the initial elocity is about 150/s, the outlet elocity is about 400/s. The siulation esults show that the quenching funace can ipoe the elocity of quenching edia. Fig.4 and Fig.5 show the static and dynaic pessue in flow field, espectiely. The outlet pessue is less than enionental pessue. Fig.5 Velocity agnitude field of spay wate Fig.6 Static pessue field of ixtue Fig.3 Velocity agnitude field of ixtue ISSN: ISBN:

4 Geneated by Foxit PDF Ceato Foxit Softwae Fo ealuation only. Fig.7 Dynaic pessue field of ixtue Fig.8-Fig.12 shows the elocity and pessue fields when the elocity of Nitogen and spay wate at inlet of funace is 150/s and 100/s, espectiely. Copae with Fig.3, the axiu elocity agnitude in Fig.8 is less. One eason is that the inlet elocity is less, and anothe eason is that the slip elocity is lage. The lage slip elocity between two phases, the oe inetic enegy cost. The esults also show that the outlet elocity is lage than that of inlet, which eans the funace designed can quicen the elocity of flow field. Fig.9 Velocity agnitude field of Nitogen Fig.10 Velocity agnitude field of spay wate Fig.8 Velocity agnitude field of ixtue Fig.11 Static pessue field of ixtue ISSN: ISBN:

5 Geneated by Foxit PDF Ceato Foxit Softwae Fo ealuation only. Fig.12 Dynaic pessue field of ixtue 6 Conclusion The flow field in funace fo ixtue of Nitogen and spay wate ejecting quenching unde noal pessue and high elocity is coplex. In two-phase flow poble, the alue of slip elocity between two phases has oe contibution to the ixtue elocity of the two-phase. The nueical siulation esults show that the funace designed can acceleate the elocity of flow field. coefficient on high tepeatue suface, Enegy fo Metallugical Industy, Vol. 23, No. 6, 2004, pp [6] GAO Shan, QU Wei, YAO Wei, Flow and heat tansfe of doplet ipinging on hot flat suface duing spay cooling, Jounal of Engineeing Theophysics, Vol. 28, Suppl. 1, 2007, pp [7] LIU Zhenhua, Expeiental study on the boiling citical heat flux of ist cooling, Jounal of Shanghai Jiaotong Uniesity, Vol. 31, No. 2, 1997, pp [8] ZHANG Hongxing, MIAO Jianyin, YAO Wei, et al, Steady-state chaacteistics of a closed-loop spay cooling syste, Chinese Space Science and Technology, No. 4, 2009, pp [9] DU Fengshan, ZHANG Fang, HUANG Huagui, et al, Nueical siulation of spay quenching pocess fo lage-scale fogings, Metal Heat Teatent, Vol. 33, No. 5, 2008, pp Refeences: [1] CHENG Heing, XIE Jianbin, LI Jianyn, Copaison of popeties of 9SiC alloy steel in aious quenching edia afte quenching, Jounal of Aeonautical Mateials, Vol.24, No.4, 2004, pp [2] Hec U., Fitsching U., Bauchage K, Fluid flow and heat tansfe in gas jet quenching of a cylinde, Intenational Jounal of Nueical Methods fo Heat & Fluid Flow, Vol.11, No.1, 2001, pp [3] F. Faua, A. Capo, B. Zaoa, A ixtue of pue gases that poduce axiu heat tansfe chaacteistics fo quenching, J. Mate. Eng. Pef., Vol.7, No.3, 1998, pp [4] C. Lauen, S. J. Midea, T. Lubben, F. Hoffann and P. May, Measued heat tansfe coefficients by using hydogen as quenchant in copaison with heliu and nitogen, In SM heat teatent confeence. Acceleated Cooling/Diect Quenching of Steels, Indianapolis, Indiana, USA, 1997, pp [5] MEI Guohui, MENG Hongji, WU Rongyang, et al, Analysis of spay cooling heat tansfe ISSN: ISBN: