Int. J. Engg. Res. & Sci. & Tech. 2014 Kuber Dwivedi and Nilesh Mohan, 2014 Research Paper ISSN 2319-5991 www.ijerst.com Vol. 3, No. 4, November 2014 2014 IJERST. All Rights Reserved INFLUENCE OF GEOMETRICAL PARAMETERS OF MPFHS WITH FOUR FIN GEOMETRY (SQUARE, TRIANGULAR, CIRCULAR AND DIAMOND) ON THE THERMO HYDRAULIC CHARACTERISTICS Kuber Dwivedi 1 * and Nilesh Mohan 1 *Corresponding Author: Kuber Dwivedi kuber_dwivedi@rediffmail.com Computational studies were carried out by using the ANSYS FLUENT 14.0 to find the effects of various fin geometries (square, triangular, circular and diamond) with constant surface area on heat transfer and pressure drop in a finned micro channel heat sink. Simulation was performed with the Reynolds number in a range from 100 to 500 at constant boundary condition when Ag-water Nano fluid is used as a coolant, Boussines q approximation was used to get the buoyancy effect and N-S equations were used to solve for the fluid flow. From the studied it is illustrated that, diamond fins is dissipating more amount of heat after circular fins. It was also found that diamond fins gives minimum pressure drop compared to other finned heat sink and both triangular and square finned heat sink is having approximate same performance in thermal and hydraulic characteristics. Keywords: Heat Transfer, Fins, Nano Fluid, Computational Fluid Dynamic INTRODUCTION Rapid growth in electronic world, Micro-pin-fin heat sink is used for dissipating the heat from microelectronic chips, therefore provide larger heat transfer surface area in compact size for avoid the overheating problem. But due to small size of product, we need liquid forced convection mechanism for better heat transfer, but it also leads the pressure drop so geometry of fins is also imperative aspect for analysis because it plays a vital role in both the characteristics (thermal and hydraulic). Now the recent days for optimum performance in thermal point of view, Nano fluid is also used as a coolant in which Nano particle of metal or metal oxide are unvaryingly deferred into the base fluid for escalation in thermal conductivity of fluid. There are numerous investigators having their prime deliberation in the field of micro-electro-mechanical system to enhance the performance in respect of coolant, geometry of fins, configuration of fins, and shape of MCHS, etc. An experiment has been already 1 Scope College of Engineering, Bhopal, India. 21
performed for analysis of thermo-hydraulic behaviour of circular finned micro heat sink with Ag-H 2 o and Al 2 O 3 -water Nano fluid and founded that Ag-H 2 o Nano fluid perform better then Al 2 O 3 - water Nano fluid (Kuber et al., 2014). Mushtaq Ismael Hasan (2014) he has numerically deliberate the MPFHS with three fin geometries (square, triangular and circular) same in hydraulic diameter and boundary condition with two types of Nano-fluid (diamond-water and Al 2 O 3 -water) with (1-4)% volumetric concentration and founded that diamond-water Nano fluid is better than Al 2 O 3 - water from heat transfer point of view and circular fins give the higher heat transfer rate also square fins caused of higher pressure drop compared with other fin geometries. Alfaryjat et al. (2010) they are numerically investigated that influence of the geometrical parameters on the thermohydraulic behavior of the MCHS with three different channel shapes (hexagonal, circular, and rhombus) at the similar boundary condition and founded that the highest value of the top wall temperature, f riction factor and thermal resistance are found with the use of rhombus cross-section MCHS. And the smallest hydraulic diameter of the hexagonal cross-section MCHS has the highest pressure drop and heat transfer coefficient among other shapes. Paisarn Naphon and Lursukd Nakharintr (2013) they are deliberated the thermal behaviour of TiO 2 -water Nano fluids cooling in the small-rectangular heat sink with three different channel heights. And they found that average heat transfer rates for Nano fluids as a coolant are higher than those for water. Hamid Reza Seyfand Morteza Feizbakhshi (2012) they observed from his experiment Nano fluid enhance the heat transfer instead of pure water and it is intensified with increase in volume fraction of Nano particles and Reynolds number, but it cause to increase the pressure drop and also it is noticed that decreasing the diameter of Nano particle enhances the nusselt number foral 2 O 3 - water Nano fluid while the trend is reverse for CuO-water Nano fluid John et al. (2010) they are performed the numerical analysis for the influence of thermal resistance and pressure drop of a micro pin-fin heat sink with single phase liquid flow and different pin-fin geometries (square shaped pin-fins and circular pin-fins) when subjected to several factors and concluded that with square pin-fins. The change in the axial pitch between the pin-fin structures show negligible effects on both the thermal and hydraulic behavior but for heat sinks with circular pins the thermal resistance of the device decreases as the axial pitch is decreased at the cost of increased pressure drop. Ricci and Montelpare (2006) they did examined experimentally the pin fin heat sink with fins in different shapes (circular, square, triangular and rhomboidal) arranged in-line with constant heat flux boundary condition and they found that, the triangular geometry is on an average the best with respect to the others. Soodphakdee et al. (2001) they investigated that the heat transfer performance of heat sink with commonly used fin geometries (round, elliptical and square) also the plate fins in staggered and inline arrangement. They found that, in all cases, staggered geometries perform better than inline, also at lower values of pressure drop and pumping power, elliptical fins work best. At higher values, round pin fin offer highest performance. Relation Involved in Study Following relationship has been used for analysis. 22
For calculating the properties of Nano fluid Thermal Conductivity: 1 1 1 K K SH K SH c K K nf K K SH K c K K p f f p f p f f p For spherical particle considered (SH=3) Table 1: Geometric Parameter S. No. Name of the Geometrical Specimens parameter 1 Base plate (heat sink) Length = 11.5 mm, Width = 6 mm, Thickness = 1mm 2 Square fins Width = 0.41 mm, Height = 0.5 mm 3 Triangular fins Width = 0.564 mm, Height = 0.5 mm 4 Circular fins Diameter = 0.5 mm, Height = 0.5 mm...(1) nf Viscosity : 1 2.5c...(2) f Density : c 1 c p...(3) nf p f Specific heat : 1 c cc c C...(4) pnf p p p f For calculating the velocity of flow w d R e i...(5) dh h 4a...(6) p Geometrical and Material Parameters Geometrical Parameter: In this study five 5 Diamond fins Diagonal Length = 0.81X0.3mm, Height = 0.5 mm specimens have been used for analysis. The nomenclatures and dimensions of the specimens are given in the Table 1. Material Parameter: Ag-water Nano fluid at 4% volumetric concentration are used as coolant and for heat sink and pin fins aluminium metal is considered. Following values of thermo physical properties of Nano fluid which is calculated by Equations 1, 2, 3 and 4, heat sink and fin, at the ambient temperature are taken for computational fluid dynamic analysis is shown in Table 2. Table 2: Material Parameter Material ( ) (C p ) (K) ( ) (kg/m 3 ) (J/kg-k) (W/m-k) (kg/m-s) Pure water 981.3 4189 0.643 0.000598 (c=0%) Ag 10500 235 429 - Ag-water 1362.048 4030.89 0.723 0.000657 (c=4%) Aluminium 2719 871 202.4 - where, Cp, K and are density, specific heat, thermal conductivity and dynamic viscosity, respectively. OBJECTIVE OF THE THESIS The present study approaches to examine the thermo-hydraulic behavior of micro pin fin heat sink with some more different shape of pin fins (square, triangular, circular and diamond) with constant surface area with Ag-H 2 O Nano fluids at 4% volumetric concentration at similar boundary condition and the range Reynolds number is 100 to 500 for further optimization of its performance. METHODOLOGY Modelling The geometry is modelled in NX 7.5. It is 23
consisting of 50 number of 3D micro pin fins of four shapes (square, triangular, circular, diamond) which are fixed in heat sink as shown in Figure 1. The pitch distance between the fins is 1 mm and these are arranged in staggered configuration which is better than inline configuration. From the heat transfer point of view as it is used by many references. Aluminium (Al) is used as material having thermal conductivity (K=202.4 w/m-k). Meshing Meshing of the specimen is generated by Meshing software of Ansys (Figure 2), it plays the important role in simulation. For the specimen programmable controlled meshing is generated with growth rate as 1.2, relevance and span angle center is kept fine. Edge sizing is done for fluid domain with bios factor is 7. Simulation To analyze the thermal behavior and other characteristics of Nano fluid and heat sink with different shapes of pin fins, after meshing of the all the specimen, output file has been created and further it was imported in fluent solver, where all the boundary conditions have defined for simulation. In this analysis one open domain has been created for fluid flow. Figure 1: Isometric View of Heat Sink with Different Profile of Pin Fins 24
Figure 2: Mesh of Different Profile of Pin Fins with Heat Sink Flow analysis: Here domain properties and boundary condition are defined. The realizable laminar model was applied to all the simulations because of its numerical stability for analysis of fluid flow. Energy model is also used for analysis of heat flow. Viscosity and density of fluid is considered to be constant, i.e., the Nano fluid is Newtonian and incompressible. Boundary conditions: The two types of boundary condition are defined at inlet and outlet, at normal atmospheric operating condition. Inlet boundary: At the inlet the finite values of velocity and temperature was used at the lower surface of the heat sink the constant wall temperature boundary condition is used (T = 373 K) and velocity is w = w in, u = v = 0 which is calculated by eq. (5). Outlet boundary: At the outlet the flow is assumed to be fully developed, hence gauge pressure is taken zero at outlet. RESULTS AND DISCUSSION Solver solves the given problem and creates a result file, which has been analyzed in CFD-Post. Here temperature contour pattern and velocity contour pattern, etc., has been analyzed. The 25
values of heat transfer rate and pressure are predicted at different surfaces. Temperature Distribution of different Heat Sink with Ag-H 2 O Nano Fluid with Reynolds Number (Re=500) Figure 3 shows the temperature contour on longitudinal (x-y) plan at z = 0.0002165 m for heat sink with four fin geometries (square, triangular, circular and diamond) with Ag-water Nano-fluid with volumetric concentration (c=4%) at 500 respectively. It is inferred that the temperature is increasing along the flow direction due to heat transfer from lower wall with constant temperature. Velocity Distribution of different Heat Sink with Ag-H 2 O Nano Fluid with Reynolds Number (Re=500) Figure 4, shows the velocity profile on longitudinal (x-y) plan at z = 0.0002165 m for micro heat sink with four fin geometries (square, triangular, Figure 3: Temp. Contour of HS with Different Shape of pin fins with (Ag-water) Nano fluid (Re=500) 26
Figure 4: Velocity Contour of HS with Different Shape of pin fins with (Ag-water) Nano fluid (Re=500) circular and diamond) with Ag-water Nano fluid with volumetric concentration (c=4%) at Re = 500 respectively From the figure it can be observed that, velocity increases at side of wall along the flow and also it has seen that the shape of flow differ for every geometry and here circular finned heat sink gives the better mixing compared to other geometry. Validation of Result of Presented Model with (Kuber et al., 2014) For Pressure Drop and Heat Transfer Rate Figure 5 shows the comparison between result of presented numerical model and the data of Kuber et al. (2014) for pressure drop of circularfinned heat with Ag-water Nano-fluid respectively. From this figure it can be seen that, the value of present model and data of Kuber et al. (2014) is very near to close. The slightly difference in parameter (pressure drop) due to the difference in mesh and solving control method. Therefore the present numerical model is reliable and can be used to study the effect of geometry of fins and using of Nano fluid. Graphical Representation of Comparison of Heat Transfer Rate with Different Nano-fluid for Different Heat Sink Figure 6 shows the comparison of pressure drop with Reynolds number of different profile of heat sink with Ag-water Nano-fluid. From the figure, it has been illustrated that the triangular and square 27
Figure 5: Comparison of Pressure Drop Between the Presented Model and Result of [4] Figure 6: Comparison of Pressure Drop with Re of Different Heat Sink with Ag-water Nano-fluid finned-heat sink gives approximate same and maximum pressure drop with Ag-water Nano fluid and it is also observed that diamond finned heat sink is having the low pressure drop for both the Nano-fluid comparison with others profile. Figure 7 shows the comparison of heat transfer with Reynolds number of different profile of heat sink with Ag-water Nano-fluid. From the figure, it has been illustrated that the circular finned-heat sink gives maximum heat transfer rate due to create better mixing of fluid and after circular, diamond performs better in comparison with others. CONCLUSION AND FUTURE SCOPE Following points are worth observing from the present exploration. At the same boundary condition and constant heat transfer surface area, circular finned-heat sink gives the higher cooling rate compared to others finned heat sink for all values of Reynolds number.. Figure 7: Comparison of Heat Transfer Rate with Re of Different Heat Sink with Ag-water Nano-fluid After circular, diamond finned heat sink perform better in heat transfer point of view compared to others. Diamond finned heat sink gives minimum pressure drop at all values of Reynolds number and at same thermal boundary condition compared to others. Square and triangular finned heat sink approximately has same performance in heat transfer and pressure drop. SUGGESTIONS FOR THE FUTURE WORK In the present investigation work and on the basis of literature review, it was assumed that the rate 28
of will increase by considering the use of heat transfer fins and Nano-fluid as a coolant. Further from the computational analysis it was understood that the rate of heat transfer is increased by using the Nano-fluid but the pressure drop also increases, which is important parameter for pump work. The computational analysis did not indicate any particular shape of fins, which would give maximum heat transfer. It was only our presumption of considering only the commonly available shapes like square, triangular, circular and diamond. Although the current investigative study reveals that maximum heat transfer is gives by the circular fins and after it diamond fins performs better and also diamond fins gives the low pressure drop compared to others. Probably there would be other shapes of fins for which the rate of heat transfer would be maximum and pressure drop would be minimum. Current study also helped in finding the performance of Nano-fluid. In future study a similar exhaustive investigation may be performed for optimizing the result with respect to concentration of Nano-fluid, spacing between the fins and using different kind of Nano-fluid and shape of fins. REFERENCES 1. Alfaryjat A A, Mohammed H A, Nor Mariah Adam M K A, Ariffin M I and Najafabadi (2014), Influence of geometrical parameters of hexagonal, circular, and rhombus micro channel heat sinks on the thermo hydraulic characteristics, International Communications in Heat and Mass Transfer, Vol. 52, pp. 121 131. 2. Hamid Reza Seyf and Morteza Feizbakhshi (2012), Computational analysis of nanofluid ef fects on convective heat transf er enhancement of micro-pin-fin heat sinks, International Journal of Thermal Sciences, Vol. 58, pp. 168-179. 3. John T J, Mathew B and Hegab H (2010), Parametric study on the combined thermal and hydraulic performance of single phase micro pin-fin heat sinks part I: square and circle geometries, Int. J. Therm. Sci., Vol. 49, pp. 2177-2190. 4. Kuber Dwivedi, Rupesh Kumar Malviya and Rupesh Sinha (2014), Fvm Analysis for Thermal and Hydraulic Behaviour of Circular Finned Mpfhs by Using Ag-H 2 O Nano Fluid, Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 7( Version 2), pp. 64-68 5. Mushtaq Ismael Hasan (2014), Investigation of flow and heat transfer characteristics in micro pin fin heat sink with nanofluid, Applied Thermal Engineering, Vol. 63, pp. 598-607. 6. Paisarn Naphon and Lursukd Nakharintr Farkade (2013), Heat transfer of nanofluids in the mini-rectangular fin heat sinks, International Communications in Heat and Mass Transfer, Vol. 40, pp. 25 31. 7. Ricci R and Montelpare S (2006), An experimental IR thermo graphic method for the evaluation of the heat transfer coefficient of liquid-cooled short pin fins arranged in line, Exp.Therm. Fluid Sci., Vol. 30, pp. 381-391. 8. Soodphakdee D, Behnia M and Copeland D W (2001), A comparison of fin geometries for heat sinks in laminar forced convection: part 1- round, elliptical and plate fins in staggered and inline configuration, Int. J. Microcircuits Electron., Packag.24 (1). First Quarter. 29