Govt. Exams
Entrance Exams
ν = μ/ρ = 0.5/800 = 6.25×10⁻⁴ m²/s.
The Bernoulli equation is P + ½ρV² + ρgz = constant. P itself is pressure energy per unit volume (not P/ρ which is pressure head).
Tip speed = πDN/60 = π × 0.3 × 1500/60 = 23.56 m/s (where N is in RPM).
Hagen-Poiseuille equation (ΔP = 32μLV/D²) is specific for laminar flow. Darcy-Weisbach is general for both laminar and turbulent flows.
Re = (ρVD)/μ = VD/ν. Re = (2 × 0.1)/(1×10⁻⁶) = 0.2/(1×10⁻⁶) = 2×10⁵. Flow is turbulent.
Kinematic viscosity is dynamic viscosity divided by density. Its SI unit is m²/s (or Stokes in CGS, where 1 Stoke = 10⁻⁴ m²/s).
Condensation is phase change from vapor to liquid, releasing latent heat. This occurs when steam condenses on cooler tube surfaces. Pool boiling and convective boiling involve liquid-to-vapor phase change.
Q = hA·ΔT = 50 × 2 × (100-25) = 50 × 2 × 75 = 7,500 W = 7.5 kW
For fully developed laminar flow in a circular tube with constant wall temperature (thermal entry), Nu ≈ 4.36. For constant heat flux, Nu ≈ 3.66. The question refers to the thermally developed region.
Biot number classifies transient conduction regimes: Bi << 1 indicates uniform internal temperature (lumped model valid), while Bi >> 1 indicates significant spatial temperature gradients requiring solution of differential equations.
