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Numerical Investigation of Heat Transfer of Non-Newtonian Power-Law Fluids Around a Triangular Prism in Time-Periodic Regime

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Abstract

Laminar heat transfer characteristics of non-Newtonian power-law fluids from a long (heated) triangular prism in the time-periodic regime have been explored. Momentum and energy equations were solved using finite volume methodology over the range of non-dimensional control parameters: Reynolds number (Re) = 50–150, Prandtl number (Pr) = 1–50 and power-law index (n) = 0.4–1.8. For the fixed Pr, the local and the time-averaged Nusselt numbers increase with rising Re irrespective of n. However, the local and the time-averaged Nusselt numbers decrease as the fluid nature alters from pseudo-plastic (n < 1) to dilatant (n > 1) for the fixed Re and Pr. Maximum enhancements in the values of time-averaged Nusselt numbers for Pr = 10, 20 and 50 with respect to Pr = 1 are observed to be approximately 180, 273 and 438%, respectively. Further, it is observed that for the fixed n and Pr, the Colburn heat transfer factor (or the jh factor) decreases with rising Re. Finally, the various values of the jh factor at different Re, n and Pr have been correlated via a simple expression, thus enabling its estimation in a new application.

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Abbreviations

b :

Equilateral triangular prism’s side (m)

C D :

Drag coefficient [= 2FD/(ρ\(U_{\infty }^{2}\)b)]

c p :

Specific heat (J kg−1 K−1)

Δt :

Dimensionless time step

f :

Body force (N m−1)

F D :

Drag force (N m−1)

h :

Local heat transfer coefficient (W m−2 K−1)

\(\overline{h}\) :

Mean heat transfer coefficient (W m−2 K−1)

H :

Domain height (m)

I 2 :

Second invariant of the strain tensor rate (s−2)

\(j_{\text{h}}\) :

Colburn heat transfer factor

k :

Thermal conductivity (W m−1 K−1)

L :

Domain length (m)

m :

Consistency index (Pa sn)

n :

Power-law index

n s :

Normal direction

N cell :

Overall cells in domain

Npa :

Overall CVs on each surface of the triangular prism

\(\overline{Nu}\) :

Time-averaged Nusselt number (= \(\overline{h}\)b/k)

Nu L :

Local Nusselt number (= hb/k)

Nu Z :

Normalized Nusselt number

p :

Pressure (N m−2)

Pr :

Prandtl number (\(= mc_{p} \left( {U_{\infty } /b} \right)^{n - 1} /k\))

Re :

Reynolds number (\(= \rho U_{\infty }^{2 - n} b^{n} /m\))

Re c :

Critical Re (for the onset of periodic behaviour)

t :

Time (s)

t′:

Time period for a cycle (s)

T :

Temperature (K)

\(T_{\infty }\) :

Inlet temperature (K)

\(T_{w}\) :

Prism’ surface temperature (K)

\(U_{\infty }^{{}}\) :

Inlet uniform fluid velocity (m s−1)

U x :

x-velocity (= U*x/\(U_{\infty }^{{}}\))

U y :

y-velocity (= U*y/\(U_{\infty }^{{}}\))

U *x , U *y :

x- and y-components of velocity, respectively (m s−1)

Xd, Xu :

Downstream and upstream distances, respectively (m)

x, y :

Coordinates (= \(x^{*} /b\), \(y^{*} /b\))

x*, y*:

Cartesian coordinates (m)

θ :

Dimensionless temperature (= (T − T)/(Tw − T))

ε :

Component of the strain tensor rate (s−1)

τ :

Shear stress tensor (Pa)

η :

Power-law viscosity (Pa s)

ρ :

Density (kg m−3)

δ :

Smallest grid size (m)

*:

Dimensional value

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The authors would like to thank the editor/reviewers for their valuable suggestions and helpful comments, which have enriched the present work for the wider readership.

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Correspondence to Amit Kumar Dhiman.

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Dhiman, A.K., Agarwal, R. Numerical Investigation of Heat Transfer of Non-Newtonian Power-Law Fluids Around a Triangular Prism in Time-Periodic Regime. Iran J Sci Technol Trans Mech Eng 44, 427–441 (2020). https://doi.org/10.1007/s40997-018-0270-x

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