The ratios of the laminar hydrodynamic boundary layer thickness

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The ratios of the laminar hydrodynamic boundary layer thickness to thermal boundary layer thickness of flows of two fluids P and Q on a flat plate are 1/2 and 2 respectively. The Reynolds number based on the plate length for both the flows is 10⁴. The Prandtl and Nusselt numbers for P are 1/8 and 35 respectively. The Prandlt and Nusselt numbers for Q are respectively

1. 8 and 140
2. 8 and 70.
3. 4 and 70
4. 4 and 35

Correct Option: A

	δ_t	=	1	× P_r^-1/3
	δ		1.026

For fluid Q: 1/2 =	δ_t	=	1	× P_r^-1/3
	δ		1.026

⇒ P_r = 8
For fluid P: Laminar flow over flat plate Nu = 0.664 Re_L^1/2 P_r^1/3 = 35
Similarly for fluid Q: Nu = 0.664 Re_L^1/2 P_r^1/3
= 0.664 (10⁴)^1/2 8^1/3 ≃ 140