I've completed this problem and received the below feedback but have gone to a state of complete loss on what to do to amend. Can anyone provide a prompt ?
Heat transfer coefficient is correct. But heat transfer rate is wrong - the question says Heat transfer per UNIT AREA, so why would you multiply your heat flux by AREA??
Liquid ammonia is heated as it flows at a mean velocity of 2 m s-1 through a circular pipe. The pipe, which has an internal diameter of 75 mm, is at a uniform temperature of 27°C, and the ammonia at a section 1.2 m from the inlet to the pipe has a temperature of -23°C.
Use the following information to estimate the local heat transfer flux at l = 1.2 m. Note, the properties of ammonia liquid have been taken at -23°C, except where stated.
Liquid ammonia properties:
ρ Density=600 kg m^(-3)
C_p Specific heat capacity=4.86 kJ kg^(-1) K^(-1)
μ Dynamic Viscosity (at 27°C)=1.19∙10^(-4 ) kg m^(-1) s^(-1)
μ Dynamic Viscosity= 2.05∙10^(-4 ) kg m^(-1) s^(-1)
k Thermal conductivity= 5.11∙10^(-4 ) kW m^(-1) s^(-1)
The Attempt at a Solution
Heat transfer correlations:
N_u=1.86 〖R_e〗^(1/3) 〖P_r〗^(1/3) 〖(d/l)^(1/3) (μ/μ_w )〗^0.14for laminar flow
N_u=0.023 〖R_e〗^0.8 〖P_r〗^0.33 for turbulent flow.
Determining the Reynolds number,
Determining the Prandtl number,
Re > 2600, so flow is turbulent