RESEARCH ARTICLE. Copyright 2011 American Scientific Publishers All rights reserved Printed in the United States of America

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1 Copyright 2011 American Scientific Publishers All rights reserved Printed in the United States of America Computational Study of the High Temperature Heat Transfer Coefficient for Different Cutting Fluids Wisansart Satana 1, Karuna Tuchinda *1, Anantawit Tuchinda 1, Surachet Chutima 1 1 King Mongkut s University of Technology Thonburi 126 Prachautid Rd., Tungkru, Bangmod, Bangkok Thailand The aim of this research is to study the heat transfer coefficient of the cutting fluids with different viscosity at high temperature using computation fluid dynamics (CFD). Three different groups of cutting fluid domestically available, which are oil based (MEGACUT N911), emulsion with water based (BIOCOOL EPS) and semi-synthetic with water based (BIOBAN 2000 EP), were studied. The experiment designed to determine the heat transfer coefficient of the cutting fluids at different surface temperatures of the workpieces in cutting processes employed in the previous work was modeled. In the experiment, the specimens were heated to different temperatures, i.e. with surface temperature of 300 C C. The cutting fluids were then ejected from the nozzle at a short distance above the top surface of the specimen. The copper plate was located at a short distance below the bottom surface of the specimen. The surface temperature at the center of the specimen and the copper plate were measured and used to determine the heat transfer coefficient of the cutting fluid. In this work, the two-dimensional (2D) plane strain computational model was developed and used to predict the heat transfer coefficient of different type of cutting fluid at different surface temperature. It could be seen that the surface temperature has a much stronger effect on the heat transfer coefficient of the water based cutting fluid (low viscosity) than the oil based type (high viscosity) with higher value at higher surface temperature. Similar observations were experimentally obtained. The research results suggest that CFD modeling can be used to capture the effect of different fluid parameter, i.e. fluid viscosity, and surface temperature on the heat transfer behavior of the cutting fluid. The model was then used to investigate the effect of fluid velocity on the heat transfer coefficient of the cutting fluids. Strong fluid velocity effect was observed for the semi-synthetic with water based cutting fluid with minimum heat transfer coefficient at 0.05m/s and higher value at lower and higher fluid velocity. For the emulsion with water based and the oil based cutting fluids, it could be seen that higher fluid velocity result in lower value of the heat transfer coefficient up to 0.03m/s while insignificant effects of fluid velocity were found at higher fluid velocity. The results would be very useful in the study of the effect of cutting fluid on the cutting tool performance during cutting process. Keywords: Heat transfer coefficient, Cutting fluid, High temperature, CFD 1. INTRODUCTION Appropriate working temperature can significantly improve the wear performance of cutting tools 1. The working temperature usually depend on many process parameters such as cutting speed, feed rate, material properties and cutting fluid 2. Cutting fluids usually used in most cutting process to control the working temperature aiming to reduce tool wear. The heat transfer properties of cutting fluids were found to vary with many cooling conditions, for example fluid types, injection velocity and also injection direction 3. The density and the viscosity of cutting fluids have also been found to vary with working temperature in the previous work 4. In such work, the experiments were designed to determine the effect of surface temperature on the heat transfer coefficient of the cutting fluids. It has been found that change in the surface temperature which results in alteration of the working temperature, has a strong effect on the heat transfer performance of the cutting fluids due to change in fluid density and viscosity at different surface temperature. * Address: ikarisut@kmutt.ac.th Computational fluid dynamics (CFD) has extensively used to study fluid flow and the heat transfer behavior of many engineering applications including the cutting process 5. However, only few researches have employed CFD in the investigation of the effect of cutting fluid properties and other related process parameters on the heat transfer characteristic in wet cutting applications 6. In this work, the previous work 4 was extended in order to fully study the flow effect on the heat transfer performance of the cutting fluids with different viscosity at different surface temperature found during cutting process using computation fluid dynamics (CFD). The effect of the fluid velocity and the flow direction relative to the contacting surface were also investigated. The fluid velocity and surface temperature ranges corresponding to low pressure cooling system of the cutting process of stainless steel were studied, i.e. the maximum surface temperature and fluid velocity of 800 C and 0.08m/s. Three different groups of cutting fluid domestically available, which are oil based (MEGACUT N911), emulsion with water based (BIOCOOL EPS) and semi- 1

2 synthetic with water based (BIOBAN 2000 EP), were studied. The experiments were carried out. 2. EXPERIMENTAL DETAILS The experiment designed to determine the heat transfer coefficient of the cutting fluids at different surface temperatures of the workpieces in cutting processes employed in the previous work was modeled. The stainless steel, AISI 316L, blocks were heated to different temperature, i.e. with surface temperature of 300, 400, 500, 600, 700 and 800 ºC, covering the temperature range found 6. The cutting fluids were then ejected from the nozzle at located at the distance of 30mm above the top surface of the specimen. The copper plate was located at the distance of 10 mm below the bottom surface of the specimen. The surface temperature at the center of the specimen and the copper plate were measured by type K thermocouples. The thickness and top surface area of the stainless specimens and the thin copper sheet are 500 mm, 900 mm2 and 2.5 mm, 1.7 mm 2, respectively. The specimen and the copper plate were put in the cylindrical container with the diameter of 30 mm (see Fig. 1). The average total time for the cutting fluid to travel from the injector to the AISI 316L steel and to fill up the container up to the level of the top surface of the specimen is approx. 1 second and 5 second, respectively. This gives the average fluid velocity of approx. 0.03m/s Fig.1. Sketching of condition test. 3. COMPUTATIONAL FLUID DYNAMICS MODEL The model consists of an outlet, an inlet, container walls, and a nozzle with the cutting fluid, air, a stainless steel specimen and a copper plate. The system was modeled as pressure based transient two-dimensional plane strain analysis. The gravitational effect was also included. The rectangular four-node elements were employed with the total number of 8,824 elements. The average element size for AISI 316L steel specimen, the copper plate and the cutting fluid were set to be sufficiently small in all the contacting area to capture the flow behavior controlling the heat transfer behavior with the minimum and the maximum element length of 0.3 mm and 0.5 mm, respectively. The CFD model is given in Fig.2. The dynamic re-meshing techniques were also employed. Wall Outlet Nozzle: Fluid Cu AISI 316L Outlet Inlet Fig.2. CFD model used to study the heat transfer performance of the cutting fluids. The thermal and physical properties of AISI 316L steel and copper used are presented here in Table 1 and 2. Table1 Density of AISI 316L steel and copper 7. Materials Density (Kg/m3) AISI 316L 7,560 Cu 8,978 Wall Table2 Thermal properties of AISI 316L 7. Temperature ( C) Thermal conductivity (W/m-K) Specific heat (J/Kg-K) Table3 Thermal properties of copper 7. Temperature ( C) Thermal conductivity (W/m-K) Specific heat (J/Kg-K) Three different cutting fluids were selected from different types of cutting fluids domestically available which were experimentally study in the previous work. The cutting fluids studied include MEGACUT N911 (oil based), BIOCOOL EPS (emulsion with water based) and BIOBAN 2000 EP (semi-synthetic with water based). The density and dynamic viscosity of such three cutting fluids are given here in Fig.3 and 4 together with the other cutting fluids previously studied. Air 2

3 Cutting fluid e+08 Fig.3 The density of cutting fluids at various temperature 4. Table8 Thermal and physical properties of air (1 atm) 11 Thermal conductance Dynamic viscosity Density (Kg/m 3 ) Specific heat (J/Kg-K) x10-3 (W/m-K) x10-5 (N.s/m 2 ) 26.23(27 C) 1.95 (50 C) 1.09(50 C) 1010(100 C) 29.23(77 C) 2.38 (150 C) 0.95(150 C) 1010(200 C) 33.28(127 C) 2.57 (200 C) 0.84(200 C) 1020(300 C) 36.56(177 C) 2.75 (250 C) 0.75(250 C) 1040(400 C) 39.71(227 C) 2.93 (300 C) 0.68(300 C) 1070(500 C) 45.73(327 C) 3.25 (400 C) 0.62(400 C) 1090(600 C) 51.46(427 C) 3.55 (500 C) 0.53(500 C) 56.99(527 C) 5.04(1000 C) 0.46(1000 C) 62.37(627 C) 67.63(727 C) 72.81(827 C) 4. RESULTS AND DISCUSSION Fig.4 The dynamic viscosity of cutting fluids at various temperature 4. The other thermal and physical properties of the cutting fluids and air employed in the analysis are shown in Table 3-8. Note that the thermal conductivity, the specific heat, the molecule weight and the standard state entropy of water were assumed for the water based type of cutting fluid, i.e. BIOCOOL EPS and BIOBAN 2000 EPS. The capability of the CFD model developed to investigate the fluid flow and heat transfer behavior of the system was firstly validated based on the steady state temperature of the steel specimen. The temperature at the center of the top surface predicted by CFD for different initial surface temperatures with BIOBAN 2000 EP are shown in Fig.5 together with the experimental results. Good agreement between the CFD and the experimental results with a maximum difference of only 7.5 percent could be observed. Table4 Thermal conductivity of MEGACUT N Thermal conductivity at temperature of (W/m-K) 25 C 50 C 100 C 150 C 200 C 300 C Table5 Thermal conductivity of BIOCOOL EPS and BIOBAN 2000 EP 9. Thermal conductivity at temperature of (W/m-K) 27 C 52 C 72 C 100 C Table6 Specific heat of the cutting fluids. Cutting fluid Specific heat (J/Kg-K) MEGACUTN ,006(30-60 C) 3,025(100 C) 3 BIOCOOL EPS & BIOBAN 2000EP 9 4,118.8 (25-60 C) Table7 Thermal and physical properties of air and cutting fluid. 10 Fluid Molecule weight Standard state (kg/kgmol) entropy (J/kgmol) Air Fig.5 The surface temperature of steel specimen at different initial surface temperature with BIOBAN 2000 EP. The model was used to study the effect of the surface temperature on the heat transfer coefficient of the three cutting fluids, i.e. MEGACUT N911, BIOCOOL EPS and EPS BIOBAN 2000 EP. The results are shown in Fig. 6-8 together with the experimental results obtained in the previous work 4. It can be seen that the CFD results suggest similar relationship between the heat transfer coefficient, h, and the surface temperature for all type of cutting fluids. Discrepancy in the heat transfer coefficient values may be caused by the three dimensional effect of heat transfer system and environmental effect such as air

4 flow, heat loss and the surrounding temperature change due to heat transfer history of the system. Fig.10 Heat transfer coefficient of 3 cutting fluids at high temperature for parallel flow. Fig.6 Heat transfer coefficient of BIOBAN 2000 EP. Fig.7 Heat transfer coefficient of BIOCOOL EPS. Fig.8 Heat transfer coefficient of MEGACUT N911. In the cutting process, the cutting fluid is injected to the system and the fluid flow will initially strike the surface at different relative to the contacting surface depending on the injector, workpiece and tool arrangement. However, the first point of contact usually at a distance away from the critical area, i.e. the workpiece-cutting tool contact zone. Hence, the fluid flow usually parallel to the contacting surface in the critical area. The results given earlier were obtained at the point of first fluid-solid contact at which the fluid flow is perpendicular to the contacting surface as shown in Fig. 9. The effect of different fluid flow direction on the heat transfer coefficient of the cutting fluid was also studied. The average heat transfer coefficients for all cutting fluids obtained from the point at which the flow is parallel to the contacting surface were then repotted against the surface temperature and is presented in Fig.10. It can be seen from Fig.7-10 that the water based cutting fluid offer higher heat transfer coefficient than the oil based cutting fluid as expected due to lower viscosity resulting in higher relative velocity at the contacting zone (example is shown in Fig.11). However, the heat transfer coefficients of the water based cutting fluids were found to be very sensitive to the surface temperature and the higher value is obtained at higher surface temperature. The oil based cutting fluid was found to be almost independent on the surface temperature. This may be due to the character of fluid-solid interface. The oil based cutting fluid was observed offer better wettability due to higher viscosity. Higher values of heat transfer coefficient were observed for the fluid flow parallel to the contacting surface for all cutting fluids. BIOBAN 2000EP BIOCOOL EPS MEGACUT N911 Fig.11 Different cutting fluid flows with the initial surface temperature of 150 C and the fluid injection velocity of 0.03m/s. Air Cutting Fluid AISI 316L steel Point of parallel flow Point of perpendicular flow Fig.9 Illustration of fluid flow directions at different areas. 5 Effect of fluid injection velocity The effect of fluid injection velocity on the heat transfer performance will be discussed in this section. The fluid injection velocity of 0.01, 0.02, 0.03, 0.05 and 0.08 m/s corresponding to low pressure cooling system of the cutting process of stainless steel were studied. The surface temperatures were kept constant at 150 C. The results of heat transfer coefficient are plotted against the fluid injection velocity in Fig.12. 4

5 Fig.12 The heat transfer coefficient predicted at different fluid injection velocities at the surface temperature of 150 C. It can be seen that the fluid injection velocity has a strong effect on the heat transfer coefficient values for the semi-synthetic with water based cutting fluid with minimum heat transfer coefficient at 0.05m/s and higher value at lower and higher fluid injection velocity. For the emulsion with water based and the oil based cutting fluids, it could be seen that higher fluid velocity result in lower value of the heat transfer coefficient up to 0.03m/s while insignificant effects of fluid velocity were found at higher fluid velocity. The change in the value of heat transfer coefficient at different fluid injection velocity was found to depend strongly on the flow velocity. Higher flow velocity will result in higher value of h due to higher heat transfer rate (see Fig.13). Fig.13 Flow velocity of BIOBAN 2000EP at different fluid injection velocity with the initial surface temperature of 150 C. 6. CONCLUSIONS 0.01 m/s 0.05 m/s 0.08 m/s In this work, the heat transfer coefficient, h, of the three types of cutting fluid, i.e. oil based, emulsion with water based and semi-synthetic with water based were studied using CFD. The water based cutting fluid offer higher h value than the oil based cutting fluid as expected due to lower viscosity. The heat transfer coefficients of the water based cutting fluids were found to be higher at higher surface temperature while insignificant effect of surface temperature was observed for the oil based type. This may be caused by better wettability due to higher viscosity of the oil based cutting fluid. The findings were found to agree well with the experimental results observed in the previous work 4. The effects of fluid flow direction and injection velocity on the heat transfer coefficient were also investigated. Higher values of h were observed for the fluid flow parallel to the contacting surface for all cases. The injection velocity was found to has a strong effect on the heat transfer coefficient values. For the semi-synthetic with water based cutting fluid, the minimum value was found at 0.05m/s due to highest flow velocity with higher values at lower and higher fluid injection velocity. For the others, lower value of h were observed at higher injection velocity up to 0.03m/s while almost constant values of h were found at higher fluid injection velocity. ACKNOWLEDGMENTS This research was financially supported by the Thailand Research Fund (MTEC) and the NSTDA University Industry Research Collaboration (NUI-RC). REFERENCES [1] Cassin C. and Boothroyed G., 1965, Lubrication action of cutting fluids, J. of Mechanical Engineering Science 7 (1), pp [2] Rodrigo Daun Monici, Eduardo Carlos Bianchi, Rodrigo Eduardo Catai, Paulo Roberto de Aguiar, Analysis of the different forms of application and types of cutting fluid used in plunge cylindrical grinding using conventional and superabrasive CBN grinding wheels, Int. of Machine Tools and Manufacture, Volume 46, Issue 2, February 2006, Pages [3] Diniz A.E. and Micaroni R., 2007, Influence of the direction and flow rate of the cutting fluid on tool life in turning process of AISI 1045 steel, Int. of Machine Tools & Manufacture 47, Elsevier, pp [4] Tuchinda K. and Wathayu K., 2012 Experimental Study of Fluid Properties for Different Commercial Cutting Fluids, Submitted to Int. Con. on Advanced Design and Manufacturing Engineering [5] L.N. L opez de Lacalle, C. Angulo, A. Lamikiz, J.A. S anchez,,2006, Experimental and numerical investigation of the effect of spray cutting fluids in high speed milling, J. of Materials Processing Technology, 172,pp [6] Xaioping Le,1996, Study of the jet-flow rate of cooling in machining, J.of Material Processing Technology,pp [7] Satana W. and Tuchinda K., 2012, Performance of PVD TiAlN and TiN Coated Tungsten Carbide Tool in Hard Turning, Submitted to Int. Con. on Advanced Design and Manufacturing Engineering [8] Abdulagatova Z. Z., Abdulagatov I. M., Emirov S.N., 2010, Effect of pressure, temperature, and oil-saturation on the thermal conductivity of sandstone up to 250 MPa and 520 K, J. of Petroleum Science and Engineering, Volume73, pp [9] Ramesh K, Huang H., Yin L., 2004, Analytical and experimental investigation of coolant velocity in high speed grinding, Int.of Machine Tools & Manufacture, Volume 44, pp [10] ANSYS manual guild, version 11. [11] Kodoya K., Matsunaga N., and Nagashima A., 1985, Viscosity and Thermal Conductivity of Dry Air in the Gaseous Phase J.Phys. Chem. Ref. Data, Vol.14, No.4. Received: Accept 5

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