Help with Calculating Wall Temperature of Air Cooled Condenser

In summary: Finally, you can use the overall heat transfer coefficient equation to calculate the wall temperature, which is given by:Tw = Ti + (U*A*dT)/Qwhere Tw is the wall temperature, Ti is the inlet temperature of the steam, U is the overall heat transfer coefficient, A is the surface area of the tubes, dT is the temperature difference between the steam and the outside air, and Q is the heat transfer rate.In summary, with the given data, you can use the overall heat transfer coefficient equation and the Nusselt equation for forced convection to calculate the wall temperature of the condenser. I hope this helps you in solving your problem. Best of
  • #1
ank59
2
0
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.
 
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  • #2


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
 

FAQ: Help with Calculating Wall Temperature of Air Cooled Condenser

1. How is wall temperature of an air cooled condenser calculated?

The wall temperature of an air cooled condenser can be calculated by using the heat transfer equation Q = U*A*ΔT, where Q is the heat transfer rate, U is the overall heat transfer coefficient, A is the surface area of the condenser, and ΔT is the temperature difference between the air and the wall. This equation can be rearranged to solve for the wall temperature.

2. What factors affect the wall temperature of an air cooled condenser?

The wall temperature of an air cooled condenser is affected by several factors including the heat transfer coefficient of the air, the surface area of the condenser, the temperature difference between the air and the wall, and the material properties of the wall.

3. How does air flow affect the wall temperature of an air cooled condenser?

Air flow plays a critical role in determining the wall temperature of an air cooled condenser. Higher air flow rates result in a higher heat transfer coefficient, which leads to a lower wall temperature. Lower air flow rates can result in higher wall temperatures and reduced heat transfer efficiency.

4. Can the wall temperature of an air cooled condenser be controlled?

Yes, the wall temperature of an air cooled condenser can be controlled by adjusting the air flow rate, the surface area of the condenser, and the temperature difference between the air and the wall. Changes in any of these factors will impact the overall heat transfer rate and therefore the wall temperature.

5. What are some common methods for measuring the wall temperature of an air cooled condenser?

There are several methods for measuring the wall temperature of an air cooled condenser, including using thermocouples or infrared thermometers. Some manufacturers also have built-in temperature sensors on their condensers. It is important to ensure that the measurement method is accurate and representative of the overall wall temperature.

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