# 7.11 Flat heating Coils - Water

Water at 80 degrees Celsius flows through a flat heating coil at a rate of 60 L/min. There are 7 180 degree bends in it. The coil is 8 m long, with 0.5 m of straight length on the inlet and exit. The r/D of the bends is 4. The pipe is schedule 40, 25 mm pipe.

    [1]:

    from math import *
    from fluids.units import *
    from thermo.units import Chemical

    water = Chemical('water', P=2*u.bar, T=80*u.degC) # P assumed
    rho = water.rho
    mu = water.mu

    Q = 60*u.L/u.min
    L = (1*8 + 0.5*2)*u.m

    NPS, D_pipe, Do_pipe, t = nearest_pipe(Di=25*u.mm)
    v = Q/(pi/4*D_pipe**2)
    Re = Reynolds(rho=rho, mu=mu, D=D_pipe, V=v)
    fd = friction_factor(Re=Re, eD=0.0018*u.inch/D_pipe)

    K_elbow = bend_rounded(Di=D_pipe, angle=180*u.degrees, fd=fd, bend_diameters=5)
    K_friction = K_from_f(fd=fd, L=L, D=D_pipe)

    K_tot = 7*K_elbow + K_friction
    dP = dP_from_K(K=K_tot, rho=rho, V=v)
    print('Pressure drop = %s' %dP.to(u.Pa))

    Pressure drop = 61330.665674 pascal

The value presented in the solution is 19609 Pa. They chose a constant friction factor of 0.024 in this calculation. If this were used, the result compares much better. Their friction factor can be obtained at a roughness of 0.05 mm.

    [2]:

    fd = 0.024
    K_elbow = bend_rounded(Di=D_pipe, angle=180*u.degrees, fd=fd, bend_diameters=5)
    K_friction = K_from_f(fd=fd, L=L, D=D_pipe)

    K_tot = 7*K_elbow + K_friction
    dP = dP_from_K(K=K_tot, rho=rho, V=v)
    print('Pressure drop = %s' %dP.to(u.Pa))

    Pressure drop = 18539.7300274 pascal