Heat Transfer Rate & Estimation in Air-Steam Flow System

[dj_silver]

Thought this would be the most appropriate forum to ask for help

Air flows through a copper inside tube and is heated by saturated steam condensing on the outside of the tube.

1. Determine the rate of heat transfer to the air at 3 different flow rates of the air (rotameter readings 10, 20 and 30).
For each air flow rate:
2. Experimentally determine the overall heat transfer coefficient based on the outside area of the pipe.
3. Estimate the inside (air) film heat transfer coefficient assuming that the resistances of the copper wall and steam film are small compared to the resistance of the air film.
4. Predict the film heat transfer coefficient using the Dittus-Boelter equations.
5. Compare the film heat transfer coefficients from the experiments with those calculated from the Dittus-Boelter equation. Comment on the comparison.
6. Estimate the steam consumption, stating assumptions.

The schematic is attached.

The dimensions of central copper tube are:
Length: L = 300 mm
Inside diameter: di = 4.5 mm
Outside diameter: do = 6.3 mm

Just wondering what the best way to approach this is, and how to answer all the questions, what measurements to make etc?

Any links or straight out advice?

Thanks very much

 

[FredGarvin]

Develop the energy balance for the system. What comes in is what goes out in some form or another. Ask yourself what those different ways energy can be manifested. I would suggest to look at simple heat exchanger theory for hints since that's what this is.

 

[ravenprp]

Hello, thank you for posting your question in this forum. This is indeed a suitable place to seek help for your heat transfer problem.

To determine the rate of heat transfer to the air at different flow rates, you will need to measure the inlet and outlet temperatures of the air, as well as the flow rate (using the rotameter readings). With this information, you can use the equation Q = m * Cp * (T2-T1) to calculate the heat transfer rate, where Q is the heat transfer rate, m is the mass flow rate of air, Cp is the specific heat of air, and T2 and T1 are the outlet and inlet temperatures, respectively.

To experimentally determine the overall heat transfer coefficient, you will need to measure the condensing steam temperature and the air temperature at different points along the length of the tube. You can then use the log-mean temperature difference (LMTD) method to calculate the overall heat transfer coefficient, using the equation U = Q/(A*ΔTlm), where U is the overall heat transfer coefficient, Q is the heat transfer rate, A is the outside area of the tube, and ΔTlm is the log-mean temperature difference.

To estimate the inside film heat transfer coefficient, you can use the equation h = k/di, where h is the inside film heat transfer coefficient, k is the thermal conductivity of air, and di is the inside diameter of the tube.

To predict the film heat transfer coefficient using the Dittus-Boelter equation, you will need to calculate the Reynolds number (Re) and Prandtl number (Pr) of the air flow. Then, you can use the equation Nu = 0.023*Re^0.8*Pr^0.4 to calculate the Nusselt number (Nu), and finally use the equation h = k*Nu/di to calculate the film heat transfer coefficient.

After obtaining the experimental and predicted film heat transfer coefficients, you can compare them and comment on the comparison. If they are close, it indicates that the Dittus-Boelter equation is a suitable model for estimating heat transfer in this system.

To estimate the steam consumption, you will need to make assumptions about the steam flow rate and the heat transfer rate from the steam to the air. You can then use the equation Q = m * hfg, where Q is the heat transfer rate, m is the mass flow rate of steam, and h