Help with Calculating Wall Temperature of Air Cooled Condenser

[ank59]

Hey my problem is related to air cooled condenser

The condenser is for removing 5MW thermal power from steam at 350 C, the pressure is 170 kg/cm2. The average temperature of outside air is 95 C(inlet at 45 C and outlet at 145 C).
the data is as follows:

no of tubes : 182
tube od =25.4 mm
tube id= 20.58mm
no of fins= 196.5 /m
effective length of one tube = 6.074m
fin tip diameter=57.15 mm
material conductivity = 26.57 W/mK

I want to calculate the wall temperature so that condensation heat transfer coefficient can be obtained by Nusselt equation but I am getting a wrong answer again and again, can anybody please help me in this problem. The correct answer is 197.5 C.

Generally the film resistance of steam is takes as negligible so can anybody comment on this, and is there any separate formula for finned tube to calculate the wall temperature.

 

[Achy47]

Hi there,

Thank you for sharing your problem related to air cooled condenser. I would like to offer some suggestions and insights to help you solve your problem.

Firstly, it is important to understand that the wall temperature of the condenser is influenced by several factors such as the geometry of the tubes, the material properties, and the operating conditions. In your case, the outside air temperature, the steam temperature, and the pressure are the key factors that affect the wall temperature.

To calculate the wall temperature, you can use the overall heat transfer coefficient equation which takes into account the heat transfer coefficient on both the inside and outside of the tubes. This equation is given by:

1/U = 1/hi + δ/k + 1/ho

where U is the overall heat transfer coefficient, hi is the heat transfer coefficient on the inside of the tubes, δ is the thickness of the tube wall, k is the thermal conductivity of the tube material, and ho is the heat transfer coefficient on the outside of the tubes.

To calculate the heat transfer coefficient on the outside of the tubes, you can use the Nusselt equation for forced convection, which is given by:

Nu = 0.023(Re)^0.8(Pr)^0.4

where Nu is the Nusselt number, Re is the Reynolds number, and Pr is the Prandtl number. The Reynolds number can be calculated using the following equation:

Re = ρVd/μ

where ρ is the density of air, V is the air velocity, d is the tube diameter, and μ is the dynamic viscosity of air.

Once you have calculated the Nusselt number, you can use it to calculate the heat transfer coefficient on the outside of the tubes using the following equation:

ho = (Nu*k)/d

where k is the thermal conductivity of air and d is the tube diameter.

Next, you can calculate the heat transfer coefficient on the inside of the tubes using the Dittus-Boelter equation, which is given by:

Nu = 0.023(Re)^0.8(Pr)^0.3

where Nu is the Nusselt number, Re is the Reynolds number, and Pr is the Prandtl number. The Reynolds number can be calculated using the following equation:

Re = ρVd/μ

where ρ is the density of steam, V is the steam velocity, d is the