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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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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DOI: https://doi.org/10.1007/s40997-018-0270-x