A series of tests in which water was heated while flowing through a 1-m-long electrically heated tube of 1.3-cm ID yielded the experimental pressure-drop data shown next.

Isothermal pressure-drop data for the same tube are given below in terms of the dimensionless friction factor ∫ = (Δp/pu̅²) (2D/L)_gc and Reynolds number based on the pipe diameter, Re_D = 4m^•/πDμ. The symbol u̅ denotes the average pipe velocity.

By comparing the isothermal with the nonisothermal friction coefficients at similar bulk Reynolds numbers, derive a dimensionless equation for the nonisothermal friction coefficients in the form

where μ_s = viscosity at surface temperature, μ_b = viscosity at bulk temperature, and n and m = empirical constants.

Transcribed Image Text:

Mass Flow Rate m (kg/s) 1.37 0.98 0.82 1.39 0.97 Fluid Bulk Tube Surface Temp Tb Temp Ts (°C) (°C) 32 45 36 37 42 52 94 104 120 140 Pressure Drop with Heat Transfer, Apht (kPa) 67 33 23 58 31