International Communications in Heat and Mass Transfer

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Forced convective heat transfer of water/functionalized multi-walled carbon nanotube nano ﬂ uids in a microchannel with oscillating heat ﬂ ux and slip boundary condition☆

Zahra Nikkhah

^a

, Arash Karimipour

^a

, Mohammad Reza Safaei

^b,

⁎ , Pezhman Forghani-Tehrani

^a

, Marjan Goodarzi

^b

, Mahidzal Dahari

^c

, Somchai Wongwises

^d,

⁎

aDepartment of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Isfahan, Iran

bYoung Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

cDepartment of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia

dFluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab. (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangmod, Bangkok 10140, Thailand

a b s t r a c t a r t i c l e i n f o

Available online 4 September 2015 Keywords:

Convective heat transfer Nanoﬂuid

Microchannel Oscillating heatﬂux Slip velocity

In the present work, forced convective heat transfer of water/functionalized multi-walled carbon nanotube (FMWCNT) nanofluid in a two-dimensional microchannel is investigated. To solve the governing Navier–Stokes equations and discritization of the solution domain, the numerical method offinite volume and SIMPLE algorithm have been employed. Walls of the microchannel are under a periodic heatflux, and slip boundary conditions along the walls have been considered. Effect of different values of shear forces, solid nanoparticles concentration, slip coefficient, and periodic heatflux on theflow and temperaturefields as well as heat transfer rate has been evaluated. In this study, changes of the variables considered to be from 1 to 100 for Reynolds number, 0–25%

for weight percentage of solid nanoparticles, and 0.001–0.1 for velocity slip coefficient. Results of the current work showed good agreement with the numerical and experimental studies of other researchers. Data are presented in the form of velocity and temperature profiles, streamlines, and temperature contours as well as amounts of slip velocity and Nusselt number. Results show that local Nusselt number along the length of microchannel changes in a periodic manner and increases with the increase in Reynold number. It is also noted that rise in slip coefficient and weight percentage of nanoparticles leads to increase in Nusselt number, which is greater in higher Reynolds numbers.

1. Introduction

Recently,flow in small sizes has been widely considered and efforts have been made to make smaller and yet more efficient devices. One of the applications of microchannels is in the cooling of electronic chips, where heat transfer rate is of great importance[1–3]. Choi[4]was the first who gave the name of nanofluid to the suspension of nanoparticles in a hostfluid and showed considerable increase in their heat transfer coefficient. In recent years, CNTs have attracted many attentions due to their significant mechanical, electrical, and thermal properties.

These particles are cylindrical with a high length-to-width ratio and suspend well in water[5,6]. On the other hand, there has been a lot of research regarding energy transfer through microdevices like microchannels as well as thermal properties of nanoﬂuids.

Lately, microchannels with different cross-sections such as circular, rectangular, and trapezoidal have been used to evaluate the heat transfer and characteristics of nanofluids flow. Researchers found that Nusselt number increases by the increase in Reynolds number and that solid nanoparticles have significant effect on the fully developed thermal boundary conditions. They also showed that when the fluid temperature difference between the inlet and outlet of the microchannel is substantially high, temperature-related properties affect the augmentation of heat transfer[7–9]. Many investigators assessed the nanofluids thermal performance taking into account slip boundary condition and found that thermal performance of thefluid enhances by the rise in slip coefficient[10,11].

To better understand the role of liquid and solid phases on the heat transfer process, researchers have adopted a two-phase model for the nanofluidflow. They evaluated the temperature and velocity differences between the liquid and solid phases and observed that the relative velocity and temperature of phases are very small and therefore negli- gible[12–15]. Reviewing published articles, one can understand the significance of utilizing nanofluids in cooling applications[16,17].

☆ Communicated by W.J. Minkowycz.

⁎ Corresponding authors.

E-mail addresses:[email protected](M.R. Safaei),[email protected] (S. Wongwises).

Contents lists available atScienceDirect

International Communications in Heat and Mass Transfer

j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / i c h m t

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However, nanoﬂuids require more extensive research[18,19]. Besides, evaluation of the thermal performance of nanoﬂuids in devices of micro and nano sizes needs more attention[20].

In the present research, laminar forced convective heat transfer of water/FMWCNT nanofluid in a microchannel under periodic heatflux was numerically investigated. Slip boundary condition was taken into account. Thermal performance of nanofluid under the effect of shear force, nanoparticle concentration, velocity slip coefficient, and periodic heatflux has been studied. Obtained results from numerical solution of the problem have been presented by temperature lines, streamlines, and local and average Nusselt numbers. Data have been validated through comparison with the available results.

2. Problem statement

The investigated problem is a two-dimensional microchannel as illustrated inFig. 1. Nanofluid consists of water and FMWCNT solid nanoparticles. FMWCNT nanoparticles are all spherical with the same diameter of d_p= 30 ± 5nm. Cold nanofluid with the temperature of Tc= 306K and uniform velocity of ucenters the microchannel and exits from the other side after cooling the microchannels walls. The fluidflow inside the microchannel is considered as Newtonian, laminar, steady and incompressible. Thermophysical properties of water and FMWCNT at constant temperature of T = 33^∘C are tabulated in Table 1. A periodic heatflux of q″is imposed on the microchannel's walls. The amplitude of heat flux (q0″) is calculated using non- dimensional parameters of Eq.(5). Slip boundary conditions are also considered for the velocity at the walls. Reynolds number for the nanofluid at the inlet are considered equal to Re = 1, Re = 10, and Re = 100. Variation of slip coefficient is considered as B = 0.001, B = 0.01, and B = 0.1. The weight percentages of solid nanoparticles are also taken asϕ= 0 %, ϕ= 0.12 %, and ϕ= 0.25 %.

3. Governing equations

Governing 2-D Navier–Stokes equations in the Cartesian coordinate are shown below[21]:

Continuity equation:

∂u

∂xþ∂v

∂y¼0 ð1Þ

Momentum equation in X direction:

u∂u

∂xþv∂u

∂y¼− 1 ρn f

∂p

∂xþυn f ∂²u

∂x²þ∂²u

∂y²

!

ð2Þ

Momentum equation in Y direction: Energy equation:

u∂v

∂xþv∂v

∂y¼− 1 ρn f

∂p

∂yþυn f ∂²v

∂x²þ∂²v

∂y²

!

ð3Þ Nomenclature

FMWCNT Functionalized multi-walled carbon nanotube K Thermal conductivity, W/mk

Cp Speciﬁc heat, J/kgk dp Diameter of nanoparticle, m h Microchannel height, m

H non-dimensional microchannel height, H = h/h = 1 l Microchannel length, m

L non-dimensional microchannel length, m B non-dimensional slip coefﬁcient, B =β/h Re Reynold number, Re = u_ch/υf

Pr Prandtl number, pr =υf/αf

q′′ Heatﬂux, W/m²

q₀′′ Amplitud heatﬂux, W/m² x, y Cartesian coordinates, m

X, Y non-dimensional coordinates, X = x/h, Y = y/h T Temperature, K

Tc Cold temperature, K P Fluid pressure, pa

p Average pressure, p¼pþρcgy

P Non-dimensionalﬂuid pressure, P¼p=ðρn fu²_cÞ u, v Velocity components in x, y directions, ms⁻¹

U,V Non-dimensional velocity components, U = u/uc, V = v/u_c

us Slip velocity, ms⁻¹

uc Nanoﬂuid inlet velocity, ms⁻¹ U_s Non-dimensional slip velocity Nux Local Nusselt number Num Averaged Nusselt number

Greek symbols

α Thermal diffusivity, m²s⁻¹ β Slip coefﬁcient, m

φ Weight percentage of nanoparticles μ Dynamic viscosity, pas

ρ Density, kg m⁻³

λ Convection heat transfer coefﬁcient, W/m²k θ Non-dimensional temperature,θ= (T−Tc)/ΔT υ Kinematic viscosity, m²s⁻¹

Subscripts

f Fluid

nf Nanoﬂuid m Averaged value

Fig. 1.Schematic of analyzed conﬁguration.

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u∂T

∂xþv∂T

∂y¼αn f ∂²T

∂x²þ∂²T

∂y²

!

ð4Þ Non-dimensional used parameters in Eqs.(1) to (4)are as below[22]:

H¼h=h¼1; L¼l=h¼32 Y¼y=h; X¼x=h V¼v=uc; U¼u=uc

θ¼T‐Tc

ΔT; ΔT¼q⁰⁰₀h k_f P¼ P

ρn fu²_c; Re¼uch

νf ; Pr¼νf=αf

ð5Þ

Therefore, the non-dimensional governing equations can be expressed as: Non-dimensional continuity equation:

∂U

∂Xþ∂V

∂Y¼0 ð6Þ

Non-dimensional momentum equation in X direction:

U∂U

∂XþV∂U

∂Y¼−∂P

∂Xþ 1 PrRe

υn f

αf

∂²U

∂X²þ∂²U

∂Y²

!

ð7Þ

Non-dimensional momentum equation in Y direction:

U∂V

∂XþV∂V

∂Y¼−∂P

∂Yþ 1 PrRe

υn f

αf

∂²V

∂X²þ∂²V

∂Y²

!

ð8Þ

Non-dimensional energy equation:

U∂θ

∂XþV∂θ

∂Y¼αn f

αf

1 PrRe

∂²θ

∂X²þ∂²θ

∂Y²

!

ð9Þ

4. Boundary Conditions

Nanoﬂuid slip velocity on the moving wall is deﬁned by[23]:

us¼ β∂u

∂y

_y_¼₀_;_h ð10Þ

or in non-dimensional form:

Us¼ B∂U

∂Y

_y_¼₀_;₁ ð11Þ

Generally, governing dimensionless boundary conditions are:

U¼1;V¼0 and θ¼0 for X¼0 and 0≤Y≤1

V¼0 and ∂U

∂X¼∂θ

∂X¼0 for X¼32 and 0≤Y≤1 V¼0;Us¼B∂U

∂Y and ∂θ

∂Y¼2q₀^′′þq₀^′′sin πX

4 for Y¼0 and 0≤X≤32 V¼0;Us¼−B∂U

∂Y and ∂θ

∂Y¼2q₀^′′þq₀^′′sin πX

4 for Y¼1 and 0≤X≤32 ð12Þ Table 1

Experimental data for physical properties of FMWCNT nanoﬂuids at T = 33 °C[5,16].

Wt.%(FMWCNT/water) ρ(kg m⁻³) μ(Pas) K (W/mk) Cp(J/kgk)

0 995.8 7.65 × 10⁻⁴ 0.62 4178

0.12 1003 7.80 × 10⁻⁴ 0.68 4178

0.25 1008 7.95 × 10⁻⁴ 0.75 4178

Fig. 2.Comparing fully developed dimensionless velocity proﬁles with those of Raisi et al.

[31].

Fig. 3.Variation of heat transfer coefﬁcient with Re from present work versus of experimental study[5]for different values of bulk temperature.

Table 2

Grid independence tests for Re = 1 and Re = 10 atϕ= 0.12% and B = 0.001.

Grid points 400 × 40 500 × 50 600 × 60

Re = 1

Num 0.183 0.183 0.184

Uout(Y = H/2) 1.490 1.491 1.491

Re = 10

Num 0.836 0.835 0.835

Uout(Y = H/2) 1.489 1.490 1.490

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Oscillation heatﬂux applies on the whole length of top and bottom microchannel walls are given as:

q^′′ð Þ ¼X 2q₀^′′þq₀^′′sin πX

4 ð13Þ

Local Nusselt number along the microchannel walls can be expressed as[22]:

Nux¼λh

kf ð14Þ

λ¼ q₀^′′

Ts−Tc ð15Þ

Therefore, local Nusselt number can be achieved by using dimensionless parameters in the Eq.(5)as follows:

Nuxð Þ ¼X 1

θ^sð ÞX ð16Þ

By integrate local Nusselt number along heated surfaces, the average Nusselt number is calculated as follows:

Num¼1 L

Z L 0

Nuxð ÞXdX ð17Þ

5. Numerical solution

To solve the governing Navier–Stokes equations, theﬁnite volume method has been utilized [24,25]. In this method, conservation

Fig. 4.Streamlines (top) and isotherms (bottom) atϕ= 0.12 %, B = 0.1 and for different values of Re.

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equations are integrated over the grids, while these equations are valid in the entire computational domain. This is applicable in any number of nodes, even when the number of nodes is small[26–28]. To discretize all the equations terms, second-order upwind has been used and to couple the pressure and velocity, SIMPLE algorithm has been employed[29,30].

When the residuals of all parameters become lower than 10⁻⁸, the solution converges and the results can be obtained.

6. Validation of numerical solution

6.1. Comparison with the work of Raisi et al.[31]

In order to validate our results, developed velocity profiles of water– copper nanofluid in a microchannel were compared with the results presented by Raisi et al.[31]. Comparison is shown inFig. 2for different values of slip coefficient (B). Raisi et al.[31]numerically investigated laminar forced convectivefluidflow of water–copper nanofluid in a microchannel, considering slip and no slip boundary conditions. They evaluated the cooling capacity of pure water and nanofluid and also studied the effect of Reynolds number, volume percentage of nanoparticles, and slip coefficient on theflow domain and heat transfer.

6.2. Comparison with the experimental study of Amrollahi et al.[5]

Forced convective heat transfer coefficient at the inlet of a horizontal pipe for water/FMWCNTnanofluid inφ= 0.12 % and different bulk temperatures and Reynolds numbers were compared with the work of Amrollahi et al.[5]inFig. 3. Amrollahi et al.[5]experimentally mea- sured forced convective heat transfer coefficient of water/FMWCNT nanofluid in the inlet section of a horizontal pipe under constant heat flux in laminar and turbulentflow regimes. Reynolds number was considered to be in the range of 1592≤Re≤4778 and the experimental area was a pipe of 1 m length and 11.42 mm diameter. They were the first who examined the effect of Reynolds number, mass fraction, and temperature on the convective heat transfer coefficient at the inlet section. Their results revealed that compared to water, heat transfer coefficient of the nanofluid in laminar and turbulent regimes increases with the rise in nanoparticles concentration.

7. Mesh independent results

Table 2presents average Nusselt number of nanoﬂuid inside the microchannel for different grids of 400 × 40, 500 × 50, and 600 × 60at Reynolds numbers of Re = 1, Re = 10 inφ= 0.12 %, B = 0.001. It is observed that the difference between the two grids of 500 × 50, 600 × 60 is small; therefore the 500 × 50 grid was selected for the calculation.

8. Results and discussion

Forced convective heat transfer of water/FMWCNT nanofluid in a 2-D horizontal microchannel was numerically investigated. As shown inFig. 1, walls of microchannel were under sinusoidal heatflux q″. Thermophysical properties of water/FMWCNT nanofluid are presented inTable 1. Moreover, slip boundary conditions (Us) was considered along the microchannel's walls for different values of slip coefficient equal to B = 0.001, B = 0.01, and B = 0.1.

Fig. 5.Dimensionless velocity proﬁle of FMWCNT at central vertical cross-section of microchannel (X = L/2), atϕ= 0.12 %, Re = 10 and for different values of B.

Fig. 6.Dimensionless temperature proﬁles of FMWCNT at different cross-sections of the microchannel, atϕ= 0.12 %, B = 0.1 and for different values of Re.

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Effect of different values of Reynolds number on the streamlines and temperature lines of the nanofluid inφ= 0.12 %, B = 0.1 is displayed in Fig. 4. Based on the streamlines, it can be observed that for all the three Reynolds numbers,flow becomes fully developed after passing a small length further from the microchannel inlet. It is also found that the lower the Reynolds number, theflow would quicker become fully developed. Temperature lines show that nanofluid temperature increases along the length of the microchannel due to the heat from heatflux, which is higher in lower Reynolds numbers. It is also noted that as the Reynolds number becomes greater, it takes longer time for thefluidflow to become thermally fully developed. This is because of the higherfluid velocity and less heat transfer between the nanofluid and microchannel's walls.

Fig. 5demonstrates the effect of different values of B on the velocity profile (U) along the vertical centerline of microchannel (X = L/2) in φ= 0.12 %. As indicated inFig. 5, due to the slip boundary condition on the walls of microchannel, there is a velocity for the nanofluid on the walls and as slip coefficient increases, this velocity gets higher. The

maximum velocity across the vertical centerline of microchannel is also increased by the slip coefﬁcient.

Fig. 6displays non-dimensional temperature profiles,θ, at different cross-sections of microchannel inφ= 0.12 %, B = 0.1 for various values of Reynolds number. Temperature profiles at Re = 1 are almost uniform for different cross-sections due to the lowflow velocity and higher heat transfer between the nanofluid and microchannel's walls. As Reynolds number increases, considerable changes can be observed in temperature profiles. Nanofluid temperature in the fully developed region increases across the length of microchannel with the increase in cross- section. In X = 0.9 L, where flow is fully affected by the walls

Fig. 7.Variations of dimensionless velocity along the horizontal microchannel centerline (Y = H/2), atϕ= 0.12 %, B = 0.1 and for different values of Re.

Fig. 8.Variations of dimensionless velocity along the horizontal microchannel centerline (Y = H/2), atϕ= 0.12 %, Re = 10 and for different values of B.

Fig. 9.Variations of dimensionless temperature along the horizontal microchannel centerline (Y = H/2), at B = 0.1 for various Re andϕ.

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temperature, maximum temperature with a parabolic profile is observed. Temperature profiles show that nanofluid temperature is increased near the warm walls of microchannels.

Figs. 7 and 8illustrate the effects of different values of Re and B on the non-dimensional velocity (U) across the horizontal centerline of microchannel (Y = H/2), atφ= 0.12 %. Velocity profiles show that for all the considered Reynolds numbers, velocity increases with X in a short length from the microchannel inlet and then becomes constant whenflow becomes hydro-dynamically fully developed. It is also noted that in lower Reynolds number, transition to fully developed flow occurs in a shorter time.Non-dimensional velocity across the horizontal centerline of microchannel decreases with the slip coefficient.

This is because the velocity grows near the microchannel's walls as the slip coefﬁcient increases and based on the conservation of mass, velocity decreases across the horizontal centerline of microchannel.

Figs. 9 and 10show the effect of different values of Re, B, andϕon the non-dimensional temperature (θ) across the horizontal centerline of microchannel (Y = H/2). As it can be seen from temperature profiles, inlet temperature of the nanofluid periodically increases with the rise in X, because of the heat transfer with the microchannel's walls warmed by the periodic heatflux. The rate of this increment is higher in lower Reynolds numbers. The reason is that when the velocity is low, there

Fig. 10.Variations of dimensionless temperature along the horizontal microchannel centerline (Y = H/2), atϕ= 0.12 % for various Re and B.

0 2 4 6 8 10

0.0 0.2 0.4 0.6

0.8

^{B = 0.001}

B = 0.01 B = 0.1

Re = 1

U

_s

X

0 2 4 6 8 10

0.0 0.2 0.4 0.6

0.8

^{B = 0.001}

B = 0.01 B = 0.1

Re = 10

U

_s

X

0 2 4 6 8 10

0.0 0.2 0.4 0.6

0.8

^{B = 0.001}

B = 0.01 B = 0.1

Re = 100

U

_s

X

Fig. 11.Dimensionless slip velocity along the microchannel wall atϕ= 0.12 % for various Re and B.

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is enough time for the heat to be transferred between the nanofluid and microchannel's walls. It is clear inFig. 9that increasing the nanoparticles weight percentages results in the elevation in the non- dimensional temperature of the nanofluid due to the rise in the thermal conductivity of nanofluid. This augmentation is more evident in higher Reynolds numbers. One can observe fromFig. 10that with the decrease in slip coefficient, non-dimensional temperature of Nanofluid along the horizontal centerline of the channel increases. When Reynolds number grows, this temperature rise is more visible.

Shown inFig. 11is the effect of different values of B on the slip velocity U_sacross the length of microchannel for various values of Reynolds number atϕ= 0.12 %, B = 0.1. It is observed that with the rise in the slip coefficient,flow become closer to the slipflow and slip velocity across the walls increases. It is also seen that the slip velocity has the maximum value at the inlet of microchannel and decreases as

X increases within a short length from the inlet. Then it becomes constant and theﬂow begins to be fully developed. As the Reynolds number increases, it takes more time for the slip velocity to get fully developed.

To better study the mechanism of heat transfer in microchannel, values of local Nusselt number Nux, across the length of microchannel for various values of Re, B, andφare presented inFigs. 12 and 13.

Nusselt number has the highest value at the inlet of channel because of the maximum temperature difference between the nanoﬂuid and microchannel's walls. This value periodically decreases by X along the length of channel due to the increase in the nanoﬂuid temperature.

Nusselt number reduces more quickly in lower Reynolds numbers. At the outlet of channel, where temperatures of nanofluid and walls approach each other, Nusselt number turns to zero. As Reynolds number gets higher, nanofluid velocity near the walls increases and temperature difference between the nanofluid and walls becomes greater and therefore Nusselt number increases.

Fig. 12shows that in different Reynolds numbers, local Nusselt number grows as the nanoparticle weight fraction increases. The reason is that by increasing the weight percentage, nanoﬂuid thermal performance enhances due to the high thermal conductivity of nanoparticles.

Fig. 13reveals the effect of various values of B on the local Nusselt number across the length of microchannel atφ= 0.12 % for different Reynolds numbers. At Re = 1, local Nusselt number is not a function of slip coefficient and therefore when the slip coefficient increases, it remains unchanged along the length of the microchannel's wall. With the growth in Reynolds number, local Nusselt number increases with the slip coefficient, because the temperature gradient along the length of the warmed wall of the microchannel gets higher.

Values of Numon the channel wall for different values of B,ϕ, and Re are given inFig. 14. For all the Reynolds numbers, average Nusselt number increases with the rise inϕ. Because increasing the weight percentage of nanoparticle intensifies the thermal conductivity of the nanofluid. By the rise in Reynolds number and therefore nanofluid velocity, temperature difference of the nanofluid and channel wall increases. Then, average Nusselt number along the length of the channel wall enhances. It is observed that at Re = 1, Nusselt number remains unchanged by the slip coefficient. However, as Reynolds number increases, the average Nusselt number along the length of channel enhances with the growth in slip coefficient.

Fig. 12.Variations of local Nusselt number along the microchannel wall at B = 0.1 for various Re andϕ.

Fig. 13.Variations of local Nusselt number along the microchannel wall atϕ= 0.12 % for various Re and B.

Fig. 14.Variation of averaged Nusselt number withϕfor various Re and B.

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9. Conclusion

In the current research, forced convective heat transfer of water/

FMWCNT in a microchannel under periodic heatflux has been numerically evaluated. Slip boundary condition across the length of the channel walls for different slip coefficients equal to B = 0.001, B = 0.01, and B = 0.1 has been considered. Effect of weight percentage of nanoparticles, shear force, velocity slip coefficient, and periodic heatflux on theflowfield, temperature, and heat transfer rate has been investigated.

Key observations are summarized as follows:

1- Streamlines and temperature lines vary along the length of microchannel by the Reynolds number.

2- Velocity proﬁles on the vertical centerline of channel are constant for all Reynolds numbers and remain the same with the change in Reynolds number, notable changes are observed in temperature proﬁles.

3- Nanoﬂuid velocity on the channel walls increases with the rise in slip coefﬁcient.

4- Nanoﬂuid temperature across the length of microchannel increases by X, and the rate of this increment is higher in lower Reynolds numbers.

5- Increasing the slip coefﬁcient and weight percentage of nanoparticles, results in higher nanoﬂuid temperature across the horizontal centerline of microchannel.

6- Slip velocity begins at the channel entrance with the maximum value and gradually decreases by X to becomeﬁnally constant along the length of walls, whereﬂow becomes fully developed.

7- Augmentation of slip coefﬁcient signiﬁcantly increases the slip velocity.

8- The imposed periodic heatﬂux on the walls causes a periodic change for both non-dimensional temperature along the horizontal centerline and local Nusselt number along the length of microchannel walls.

9- Nusselt number is maximum at the inlet and decreases with X along the length of microchannel.

10- Nusselt number elevates with the rise in Reynolds number, weight percentage of nanoparticles, and slip coefﬁcient, and the maximum value occurs atφ= 0.25 %, B = 0.1 and Re = 100.

11- In low Reynolds numbers, Nusselt number is not affected by the slip coefﬁcient and remains constant.

Acknowledgements

The authors gratefully acknowledge High Impact Research Grant UM.C/HIR/MOHE/ENG/23 and Faculty of Engineering, University of Malaya, Malaysia, for support in conducting this research work. The seventh author would like to thank the National Science and Technology Development Agency (NSTDA 2013), the Thailand Research Fund (IRG5780005) and National Research University Project (NRU 2014) for the support.

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