Critical Heat Flux Densities and Grossmann Factor as Characteristics of Cooling Capacity of Quenchants

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1 Critical Heat Flux Densities and Grossann Factor as Characteristics of Cooling Capacity of Quenchants N.I.KOBASKO 1, M.A. ARONO 1, MASAHIRO KOBESSHO, MAYU HASEGAA, KATSUMI ICHITANI,..DOBRYECHIR 3 1 IQ Technologies, Inc., Akron, USA Ideitsu Kosan Co., Ltd., Ichihara, Chiba, JAPAN 3 Intensive Technologies Ltd, Kyiv, UKRAINE Abstract:- In the paper, it is shown that critical heat flux densities and Grossann factor H, along with the cooling curves analysis, could be very iportant characteristics of different types of quenchants. On the basis of critical heat flux densities, it is possible to predict heat transfer odes taking place during quenching. hen the initial heat flux density (q in ) is less than the first critical heat flux density (q cr 1), a fil boiling ode of heat transfer is absent. hen q in is greater than q cr 1, the full fil boiling could occur. hen q in = q cr1 the local fil boiling is observed. The paper underlines that the Grossann factor H can correctly characterize a quenchant when the fil boiling is absent, or when both the fil boiling and the nucleate boiling are absent and direct convection takes place during quenching. Calculating ethods and software are proposed for evaluating of the critical heat flux densities and Grossann factor H. Exaples of calculations are provided. Key ords:- Critical heat flux density, Grossann factor, Quenchant, Software, Calculation, Cooling capacity. 1. Introduction A classical cooling curve during quenching of steel parts represents three stages of cooling: a fil boiling, nucleate boiling and convection. It is still questionable whether fil boiling can be absent when quenching parts having a teperature of o C in cold water or water solutions. At the first glance, one thinks that the fil boiling stage during such condition ust exist. However, in any cases fil boiling is absent due to the following reasons: Prior to boiling, the cold liquid should be heated to the saturation teperature. During this period of tie, the teperature of the steel part surface decreases alost to the saturation teperature due to a very high value of the specific heat of water and aqueous salt solutions [1]. hen quenching in water and aqueous salt solutions, a double electrical layer is established between the part surface and the quenchant, which eliinates fil boiling [1]. Recent studies show that initial heat flux density fro the part surface to the quenchant at the very beginning of iersion is a finite value that is often less than the first critical heat flux density [1, ]. Coputational fluid dynaics (CFD) odeling has shown that during quenching in an agitated water, the teperature of the boundary layer reains below the saturation teperature []. It has been discovered that the shock boiling increases the critical heat flux density and the part surface superheat [1]. ISBN:

2 Acoustical analyses have provided evidence that the fil boiling is absent [3]. These all factors show that fil boiling can be absent in any cases. hen fil boiling is absent the cooling curve and cooling rate look like it is shown in Fig. 1 below (see curve 1). q cr λ = v (1) a S q cr 0. () q cr1 here q cr1 is the first critical heat flux density (/ ); qcr is the second critical heat flux density (/ ); λ is heat conductivity (/ K); a is theral diffusivity ( /s); is a volue of the probe ( 3 ); S is a surface of the probe ( ); v is an average cooling rate of the probe ( o C/s). The ratio /S for a spherical probe is R/3, where R is a radius of the sphere. The heat conductivity and theral diffusivity of the aterial should be taken at the transition teperature fro fil boiling to nucleate boiling. In our case, it is 35 o C. The theral properties of silver and Inconel 600 are provided in Table 1 and Table. Fig. 1 Cooling rate vs. surface teperature: 1, fil boiling is absent;, cooling rates of a silver spherical probe of 0- diaeter after iersion in still water at different teperatures when fil boiling exists [1].. Procedures for the evaluation of the critical heat flux density and Grossann factor H A procedure for the evaluation of the critical heat flux density and Grossann factor H is as follows. To evaluate critical heat flux densities, the full fil boiling ode of heat transfer ust exist and a transition fro the fil boiling to nucleate boiling ust be clearly seen (see Fig. 1 curves ). For exaple, for water of 40 o C the transition fro fil boiling to nucleate boiling occurs at the teperature of 35 o C when the cooling rate is 118 o C/s. Knowing these data, it is possible to evaluate the first and second critical heat flux densities using the following equations [1, 4]: Table 1 Theral conductivity of silver, AISI 304 steel and Inconel 600 in / K vs. teperature ( o C) Teperature Silver AISI Inconel Table Theral diffusivity of silver, AISI 304 steel and Inconel 600 in /s vs. teperature ( o C). Teperature 100 o C o C Silver, Steel 304, 10 6 Inconel 600, ISBN:

3 Having theral properties of silver, it is very easy to deterine critical heat flux densities by using silver probes. As an exaple, let s consider a spherical probe of 0 diaeter. Soe experiental data are presented in Fig. 1. Let s calculate critical heat flux densities for the water at 0 o C. As one can see fro Fig. 1, the cooling rate of the spherical silver probe is 161 o C/s when cooling in water at 0 o C. For these conditions, the transition fro fil boiling to nucleate boiling occurs at 400 o C. The theral properties of silver at this teperature are as follows: λ = 365 and 4 a= and their K s λ ratio is =,401, For the spherical probe of a 0 diaeter, the ratio /S is R 0.01 = = = S 3 3 According to the obtained data and Eq. (1), the critical heat flux density q cr is equal to q cr =,401, = 1,88, q According to Eq. (), cr M qcr 1 = = Siilar calculations can be conducted for the water at the teperature of 40 o C where cooling rate is 115 o C/s and λ = 371 ; K λ =,48,485. a 4 a= ; s Following the sae procedure as described above, M we obtain: q cr = and M q cr 1 = Table 3 Coparison of q cr1 [M/ ] obtained by author s ethod and equations of Tolubinsky and Kutateladze [5, 6] Underheat, o C Tolubinsky Kutateladze Authors In practice, it is necessary to quantify quenching conditions. A paraeter used by heat treaters for this purpose is the Grossann quench severity factor H. The H value is deterined fro hardness easureents of a series of cylinders quenched in oil or water like those shown in Fig. and Fig. 3. In the chart shown in Fig., the Du/D values on the y- axis represent a ratio of the diaeter of the center portion that reains unhardened (Du) to the full diaeter (D) for several of the bars of the cylinder series. Measured values of Du/D can be plotted against the D values on a transparent paper with the sae coordinates. Soe results of such an approach are provided in Table 3 [7]. Fig. Chart for estiating Grossann H values fro a cylinder series [7]. Let s copare obtained results with the data which can be derived fro the equations of Tolubinsky and Kutateladze [5, 6]. Soe results of the coparison are shown in Table 3. Fig. 3 [7]. Hardenability depending on cylinder size ISBN:

4 Fro the Grossann ethod consideration, it Du follows that is a function of a teperature D gradient in the cylindrical specien during its quenching, which is characterized by the Grossann factor H. On the other hand, the teperature gradient in the cylindrical specien is a function of the generalized Biot nuber Bi [8, 9]: T T sf T T = ( Bi + Bi + 1) (3) Du It eans that the ratio is a function of the D generalized Biot nuber Bi. Taking this consideration into account, the authors [10] cae to the conclusion that the generalized Biot nuber Bi and Grossann factor H are the sae value. Let s assue that this conclusion is true. Then equation (4) can be used for calculating the HTC (see Table 4) [10]: 5.783λH α = (4) D For Grossann factor H = 0.5: α = 0.5 = 1, K For Grossann factor H = 0.30: α = 0.3 K = 1, K These results of calculations are in very good agreeent with the results of solving an inverse heat conduction proble and of the Kondratjev ethod of calculation shown in Fig. 4. During quenching of cylindrical probes of 0 diaeter in water (H=0.9), the heat transfer coefficient (HTC) is equal: 0.9 K α = = 5, K This value of HTC agrees well with the data presented in Fig. 6 (see curve 1). According to Grossann, during quenching of cylindrical probes of 0 diaeter in brine solutions, the HTC is equal: K α = = 1, K These results correlate well with the results presented in Table 3. According to Grossann, for a violent agitation, the HTC can be: 5 K α = = 31, K This value of HTC can be achieved in high velocity quench systes during quenching of steel parts in water flow of about 7 8 /s [1]. Table 4 Original Grossann s factor H depending on type of quenching and severity of agitation [7] Agitation Oil ater Brine None Mild Moderate Good Strong iolent Developed ethod of calculations allows engineers to use Grossann factors H to develop recipes for conventional and intensive quenching processes and can be also used during designing of quenching systes. For getting ore detail inforation on quenching processes, conducting of accurate experients are needed where teperature is easured on the part surface or near the surface. By solving an inverse heat conduction proble, it is possible to evaluate a real HTC. The obtained values of HTC can be used for calculations of ISBN:

5 teperature fields and residual stresses to optiize quenching processes. The Grossann factor H can be calculated using a theory of regular conditions since the generalized Biot nuber in the regular area can be calculated fro the following equations [1, 8, and 9]: akn v= ( T T ) (5) K Bi Kn = (6) ( Bi Bi + 1) 0. 5 Fig. 4 HTC vs. surface teperature for oil MZM-16 at 61 o C: 1 is HTC as a function of the surface teperature received by solving an inverse proble; is an average effective HTC received by Kondratjev ethod [1]. Table 5 Universal correlation Kn = ψbi of regular condition theory. Bi ψ Kn Bi ψ Kn Fig. 4 indows for software IQ Manager. On the basis of the theory of the regular theral condition, a software IQ Manager was developed by Intensive Technologies Ltd. of Kyiv, Ukraine to calculate the critical heat flux densities and Grossan factor H. The notion in this software is that there is no need to evaluate a point of the transition teperature fro fil boiling to nucleate boiling and a axiu cooling rate during quenching. The Grossann factor evaluation approach is very effective for intensive quenching ISBN:

6 when a direct convection ethod of cooling is applied [1, 11, 1]. During a nucleate boiling process, the Grossann factor H takes into account an effective HTC, which is an average value. The average HTC can be used for calculations of the cooling rate, cooling tie at the core teperature of steel parts [1, ]. The Grossann factor H is calculated using data fro the experient at the point (a) and point (b) as shown in Fig. 1 (see curve 1). The ain goal of the joint project initiated by IQ Technologies, Ideitsu Kasan Co., Ltd. and Intensive Technologies, Ltd is developing special additives to different kinds of quenchants to eliinate local fil boiling and full fil boiling during quenching. Critical heat flux densities should be included into a global database for different types of quenchants [3, 13, 14]. 3. Suary 1 Methods for calculation of the critical heat flux densities and Grossann factor H are proposed and software IQ Manager is designed to siplify significantly calculations during testing of quenchants. The ai of joint investigations is developing special additives for different types of quenchants to eliinate full fil boiling and local fil boiling, which are ajor reasons for excessive distortion of steel parts and low aterial echanical properties after quenching. References: [1] Kobasko, N.I., Aronov, M.A., Powell, J.A., and Totten, G.E., Intensive Quenching Systes: Engineering and Design, ASTM International, est Conshohocken, 010, 5 pages. [] Krukovskyi, P.G., Kobasko, N.I., and Yurchenko, D., Generalized equation for cooling tie evaluation and its verification by CFD analysis, Journal of ASTM International, ol. 6, No 5,009. [3] Kobasko, N.I., Discussion of the proble on Designing the Global Database for Different Kinds of Quenchants, In a book: Recent Advances in Fluid Mechanics, Heat & Mass Transfer and Biology, Zelliak, A., Mastorakis, N. (Eds.), SEAS Press, Athens, 011, pp [4] Kobasko, N.I., Aronov, M.A., Powell, J.A., Ferguson, B.L., Dobryvechir,.., Critical heat flux densities and their ipact on distortion of steel parts during quenching, In a book: New Aspects of Fluid Mechanics, Heat Transfer and Environent, SEAS Press, Athens, 010, pp [5] Tolubinsky,. I., Teplooben pri kipenii (Heat transfer at boiling), Naukova Duka, Kyiv, [6] Kutateladze, S. S., Fundaentals of Heat Transfer, Acadeic Press, New York, [7] Lyan, T.Ed., Metals Handbook: 1948 Edition, Aerical Society for Metals, Cleveland, OH, [8] Kondratjev, G.M., Regular Theral Mode, Gostekhizdat, Moscow, [9] Kondratjev, G.M., Theral Measureents, Mashgiz, Moscow, [10] Aronov, M.A., Kobasko, N.I., Powell, J.A., and Hernadez Morales, J.B., Correlation between Grossann H-Factor and Generalized Biot Nuber Bi, Proceedings of the 5 th SEAS International Conference on Heat and Mass Transfer (HTM 08), Acapulco, Mexico, January 5 7, 008, pp [11] Kobasko, N.I., US Patent # 6,364,974B1 [1] Kobasko, N.I., Intensive Steel Quenching Methods, In a Handbook: Theory and Technology of Quenching, B.Liscic, H.M.Tensi, and.luty (Eds.), Berlin, Springer erlag, 199, p [13] Liščić, B., Filetin, T., Global Database of Cooling Intensities of Liquid Quenchants, Proceedings of the European Conference on Heat Treatent 011, Quality in Heat Treatent, els, Austria, 011, pp [14] Kobasko Nikolai I., Intensive Steel Quenching Methods, In a book: Quenching Theory and Technology, Second Edition, Liščić Bozidar, Tensi Hans M., Canale Lauralice C.F., Totten George E. (Eds.), CRC Press, Boca Raton, London, New York, 010, pp ISBN: