Nanofluid flow through non-corrugated and corrugated channels is studied using a 

two-dimensional (2D) and three dimensions (3D) numerical simplification. Due to the 

high computational costs of a full 3D grid model, the 2D approach offer a more practical 

advantage. However, little information about its validity is available. The aim of this 

study is to explore to which extent 2D simulations can describe the flow within a 3D 

geometry, and to investigate how effective the commonly used 2D numerical 

simplification is in nanofluid flow through non-corrugated and corrugated channels. A 

case study has implemented with 2D and 3D mesh models to compare their results 

taking into consideration the analysis of heat transfer and pressure drop. A simulation 

has been carried out using Ansys fluent software to compare the results for different 

Reynolds Numbers ranges from 10000 to 30000 and different geometries non�corrugated, semicircle and rectangular channels. The results show that for non�corrugated channel there is a slight difference between 2D and 3D results for all 

Reynolds number ranges, while for both semicircle and rectangular corrugated 

channels, the difference becomes larger for high Reynold’s Number

Kh. Abugnah, Elhadi

M. Elfaghi, Abdulhafid

Ngali, Zamani

Wan Salim, Wan Saiful-Islam

UTHM Institutional Repository

1st Biannual Post Graduate Conference 7th-10th May 2014, Seri Iskandar, Perak Flow Characteristics of 3-D Turning Diffuser  Normayati Nordin  Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia  Batu Pahat, Malaysia mayati@uthm.edu.my Zainal Ambri Abdul Karim  Department of Mechanical Engineering                   Universiti Teknologi Petronas Tronoh, Malaysia ambri@petronas.com.my Safiah Othman Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia  Batu Pahat, Malaysia safiah@uthm.edu.my Vijay R. Raghavan OYL Research & Development Centre OYL Research & Development Sdn Bhd  Sungai Buloh, Malaysia vijay@oyl.com.my  Abstract— It is often necessary in fluid flow systems to simultaneously decelerate and turn the flow. This can be achieved by employing turning diffusers in the fluid flow systems. The flow through a turning diffuser is complex, apparently due to the expansion and inflexion introduced along the direction of flow. The flow characteristics of 3-D turning diffuser by means of varying inflow Reynolds number are presently investigated. The flow characteristics within the outlet cross-section and longitudinal section were examined respectively by the 3-D stereoscopic PIV and 2-D PIV. The flow uniformity is affected with the increase of inflow Reynolds number due to the dispersion of the core flow throughout the outlet cross-section. It becomes even worse with the presence of secondary flow, 22% to 27% of the mean outlet velocity. The flow separation takes place within the inner wall region at the point very close to the outlet edge and the secondary flow vortex occurs dominantly within half part of the outlet cross-section.   Keywords—turning diffuser; flow characteristics; particle image velocimetry (PIV) I.  INTRODUCTION  It is often necessary in fluid flow systems to simultaneously decelerate and turn the flow. This can be achieved by employing turning diffusers in the fluid flow systems. A turning diffuser is characterised by its expansion directions into two types, namely, two dimensional (2-D) turning diffuser and three-dimensional (3-D) turning diffuser [1, 2, 3]. A geometric layout of a 90o turning diffuser is shown in Fig. 1. A 2-D turning diffuser expands its cross-section in either x-y or y-z axis plane, whereas a 3-D turning diffuser expands its cross-section in both x-y and y-z planes.   Chong et al. [4] designed a 90o turning diffuser with quadrants of circles at both the inner wall and centerline. The outer wall was shaped using circular arcs with the centers placed along the centerline and the circumferences tangent to the inner wall. It was designed such that equal area distributions  were  established  between  the  inner  and  outer                     Fig. 1. A geometric layout of a 90o turning diffuser  wall passages relative to the centerline. The gross geometry of a turning diffuser could be described in terms of four parameters, namely, the inner wall length to the inlet  throat width ratio (Lin/W1), the outlet area to the inlet area ratio (AR) , the outlet-inlet configurations (W2/W1, X2/X1) and the turning angle () [5].  The flow through a 90o turning diffuser is complex, apparently due to the expansion and sharp inflexion introduced along the direction of flow. The  inner  wall  is  subjected to curvature-induced effects where under a strong adverse pressure gradient, the boundary layer on the inner wall is likely to separate, and the core flow tends to deflect toward the outer wall region [2, 6]. Flow separation is basically undesirable as it would decrease the core flow area, induce the presence of secondary flow vortices and ultimately affect the flow uniformity [4]. The flow uniformity index (out) is used to measure the extent of dispersion of local oulet velocity from the mean outlet velocity. The out  was strongly dependent on the dispersion of core flow, y and the presence of secondary flow, Sout throughout the outlet cross-section [7].  1st Biannual Post Graduate Conference 7th-10th May 2014, Seri Iskandar, Perak  In the present work, the flow characteristics of 3-D turning diffuser of = 90o, AR= 2.16, W2/W1=1.440, X2/X1=1.500  and Lin/W1= 3.970 are experimentally investigated. The operating condition is varied within the range of inflow Reynolds number, Rein= 5.786E+04 - 1.775E+05. II. INSTRUMENTATION AND MEASUREMENT SETUP  The test rig shown in Fig. 2 was developed. A centrifugal blower controlled using a 3-phase inverter and calibrated previously  by  [8] was  installed  at the upstream end. The rig    Fig. 2. Test rig   Fig. 3. 3-D stereoscopic PIV setup   Fig. 4. 2-D PIV setup was incorporated with several wind tunnel features to produce a fully developed flow at the diffuser entrance [9]. The test section, with inlet cross-section of 13 cm x 5 cm and hydrodynamic entrance length of 28Dh featured no fittings. The outlet flow uniformity was examined using a 3-D stereoscopic PIV shown in Fig. 3. In order to allow shots of the entire outlet plane to be taken, the cameras were mounted at 30o angle each and leveled up within a satisfied-calibrated distance on the top of the target plane. A 2-D PIV was used to examine the flow characteristic at the center plane within the longitudinal section, with the camera arranged to be perpendicular to the target plane shown in Fig. 4. The results obtained were verified [10]. The flow uniformity index (out) was evaluated by calculating the mean standard deviation of outlet velocity. The least absolute deviation corresponds to the greatest uniformity of flow [12]:                                 21)(11 Nioutletiout VVN                                                  (1) where, N= number of measurement points Vi = local outlet air velocity (m/s) Vout = mean outlet air velocity (m/s)  The dispersion of core flow (y) was evaluated by calculating the standard deviation of axial velocity at the outlet [11]:  21)(11 Niyavgyy VVN                  (2) where, Vy = velocity in y-direction (m/s) Vy avg = average velocity in y-direction (m/s)  Secondary flow index (Sout) represents the percentage of secondary flow at the outlet. The outlet velocity is considered uniform only if secondary flow magnitude at the outlet is less than 10% of the mean outlet velocity [7]:  outNizxout VNVVS 1122                                                 (3) where, Vx = velocity in x-direction (m/s) Vz = velocity in z-direction (m/s) III. RESULTS ANALYSIS AND DISCUSSION  Contours as depicted in Fig. 5 exhibit the characteristic of the outlet flow. The core flow that is in y-direction is represented by colour-code. Whereas, the secondary flow resulting of the flows in x- and z-direction is represented by vector-arrows. In general, each contour shares almost the same characteristic with the rapid flow mostly occurring within  the outer wall region and  the  flow  deficit  is  seen   to  happen within  the inner wall region. There  are   presences   1st Biannual Post Graduate Conference 7th-10th May 2014, Seri Iskandar, Perak  (a)   (b)  (c)  (d)   (e)  Fig. 5. Characteristic of the core flow, Vy (represented by color-coded) and the resultant of secondary flows, Vx and Vz (represented by arrows) at the outlet by varying (a) Rein=5.786E+04 (b) 6.382E+04 (c) 1.027E+05 (d) 1.397E+05 (e) 1.775E+05   of  swirling secondary flow vortices throughout the outlet cross-section and reverse core flows close to the inner wall region in each case.   Velocity profiles are extracted across the center of the turning diffuser outlet at two (2) different planes as shown in Fig. 6. As depicted in Fig. 7, the profiles are obtained to be asymmetric in each case. In Plane A, the flows deflect much toward the outer wall due to the existence of reverse core flows within the inner wall region. In Plane B, the secondary flow vortex occurs dominantly within half part of the outlet, i.e. left side causing the flow area in that particular region is to decrease.    The out is affected with the increase of Rein as indicated in TABLE I mainly because of the dispersion of the core flow throughout the outlet cross-section, y. It becomes even worse with the presences of the secondary flow, Sout= 22% to 27% of the mean outlet velocity. The  secondary flow vortices throughout  the outlet cross-section together with the excessive flow separation within the inner wall region may occur under a very strong pressure gradient and these not only incur unfavorable flow performance but also considerable losses associated with form drag [13, 14].     Fig. 6. Velocity profile planes across the center of turning diffuser outlet  Inner wall Inner wall Inner wall Inner wall Outer wall Outer wall Outer wall Outer wall Outer wall Inner wall 1st Biannual Post Graduate Conference 7th-10th May 2014, Seri Iskandar, Perak (a)  (b) Fig. 7. Velocity profiles at (a) Plane A and (b) Plane B TABLE I.  FLOW PFERFORMANCE INDEXES Rein out y Sout 5.786E+04 1.82 1.90 0.268 6.382E+04 2.25 2.40 0.223 1.027E+05 2.70 2.93 0.243 1.397E+05 4.64 5.01 0.236 1.775E+05 5.05 5.74 0.254  Vector plots, as in Fig. 8, demonstrate the flow structures within the longitudinal section of turning diffuser taken at the center plane. Since the flow structures of each case are almost the same, in order to avoid repetition, only the flow structures of minimum and maximum Rein are included in the paper. The boundary layer in each case separates from the inner wall almost at the same point which is close to the outlet edge,  S= 0.9Lin/W1.      (a)  (b) Fig. 8. Flow structures within the longitudinal section of turning diffuser (a) Rein=5.786E+04 (b) 1.775E+05  IV. CONCLUSION  In conclusion, the current work managed to investigate the flow characteristics of 3-D turning diffusers by means of varying Rein= 5.786E+04 - 1.775E+05. The flow uniformity is affected with the increase of Rein mainly because of the dispersion of the core flow throughout the outlet cross-section. It becomes even worse with the presences of secondary flow, 22% to 27% of the mean outlet velocity. The secondary flow vortex occurs dominantly within half part of the outlet, i.e. left side causing the flow area in that particular region is to decrease.  The flow separation takes place within the inner wall region close to the outlet edge of approximately 0.9Lin/W1.     1st Biannual Post Graduate Conference 7th-10th May 2014, Seri Iskandar, Perak ACKNOWLEDGMENT  This work was financially supported by the Fundamental Research Grant Scheme (FRGS) of the Ministry of Higher Education, Malaysia. The experimental work was conducted in the Aerodynamics Laboratory, Universiti Tun Hussein Onn Malaysia (UTHM). REFERENCES [1] G. Gan and S.B. Riffat, “Measurement and computational fluid dynamics prediction of diffuser pressure-loss coefficient,” Applied Energy, vol. 54(2), pp. 181-195, 1996. [2] R.K. Sullerey, B. Chandra, and V. Muralidhar, "Performance comparison of straight and curved diffusers," J. of Def. Sci., vol. 33, pp. 195-203, 1983. [3] N. Nordin, V.R. Raghavan, S. Othman and Z.A.A. Karim,“Compatibility of 3-D turning diffusers by means of varying area ratios and outlet-inlet configurations", ARPN Journal of Engineering and Applied Sciences, Vol. 7, No. 6, pp 708-713, 2012. [4] T.P. Chong, P.F. Joseph and P.O.A.L. Davies, “A parametric study of passive flow control for a short, high area ratio 90 deg curved diffuser,” J. Fluids Eng., vol. 130, 2008. [5] C.J. Sagi and J.P. Johnson, “The design and performance of two-dimensional, Curved Diffusers,” J.  Basic Eng. ASME, vol. 89, pp. 715-731, 1967. [6] N. Nordin, V. R. Raghavan, S. Othman and Z. A. A. Karim, “Numerical investigation of turning diffuser performance by varying geometric and operating parameters”, Applied Mechanics and Materials Journal, Vol. 229-231, pp. 2086-2093, 2012.  [7] M. K. Gopaliya, P. Goel, S. Prashar, and A. Dutt, "CFD Analysis of performance characteristics of S-shaped diffusers with combined horizontal and vertical offsets," Computer & fluids, vol. 40, pp. 280-290, 2011.  [8] N. Nordin, Z.A.A. Karim, S. Othman and V.R. Raghavan, “Design & development of low subsonic wind tunnel for turning diffuser application”, Advanced Material Research Journal, Vol. 614-615, pp. 586-591, 2013. [9]N.Nordin, Z.A.A. Karim, S.Othman and V.R. Raghavan, “Verification of fully developed flow entering diffuser and particle image velocimetry procedures”, Applied Mechanics and Materials Journal, Vol. 465-466, pp. 1352-1356, 2014. [10] N. Nordin, S. Othman, V.R. Raghavan and Z.A.A. Karim, “Verification of 3-D stereoscopic PIV operation and procedures”, International Journal Engineering and Technology IJET/IJENS, , Vol. 12, Issue 4, pp. 19-26, 2012. [11] M.K. Gopaliya, M. Kumar, S. Kumar, and S. M. Gopaliya, "Analysis of performance characteristics of S-shaped diffuser with offset," Aerospace Science & Tech., vol. 11, pp. 130-135, 2007.  [12] W.A. El-Askary and M. Nasr, “Performance of a bend diffuser system: Experimental and numerical studies,” Computer & Fluids, vol. 38, pp. 160-170, 2009. [13] N.Nordin,  Z,A.A. Karim, S.Othman and V.R. Raghavan, The performance of turning diffusers at various inlet conditions, Applied Mechanics and Materials Journal, Vol. 465-466, pp. 597-602, 2014.  [14] N.H.N. Seth, N.Nordin, S.Othman and V.R. Raghavan, Investigation of flow uniformity and pressure recovery in a turning diffuser by means of baffles, Applied Mechanics and Materials Journal, Vol. 465-466, pp. 526-530, 2014.     

Comparison of 2D and 3D modelling applied to single phase flow of nanofluid through corrugated channels

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