I have to extract heat from a surface by cooling pipes of 6mm diameter with water flow.I wish to know whether the water inside the pipes will boil and cause Nucleate boiling effect as in case of heat exchangers in Powerplants. How can I calculate the amount of pressure required to pump the water through the pipes to overcome this effect.My mass flow rate is around 0.02kg/s and I need to extract 10kW heat from the conical surface.
I suppose you mean 400 C. It would be unambiguous to add degrees Celsius.
I have a few questions in answering which the solution will become self evident. (1) How did you determine that the maximum temperature of the surface (outer?) is 400 C? Or is it the maximum temperature of the outer medium? (2) What is on the outside? Is it gas, plasma or perhaps liquid metal? If it is is gas or plasma, the major temperature drop will be on the side of gas/plasma and the wall will run cool and Michal's suggestions will serve you well. On the other hand, it it is a liquid metal, you need to pressurize the water to a level where bulk boiling will not occur. Bubbles formed locally will condense in the main flow and the mean temperature at exit can be kept below the saturation temperature.
This question is another example in a long series of questions on Research Gate where it is not posed clearly enough to enable good answers. I keep imploring: Please don't pose the question as it comes into your mind. Reconsider if it is likely to be clear to the reader. Even better, bounce it on a couple of friends/colleagues and see if it is clear to them.
Before getting into advanced non-linear mathematics, do the simple calculations.
First, what is the heat transfer rate to and through pipe walls, and is it sufficient?
Second, at 20 g/s, you would need to heat the water by about 120 C to remove 10 kW. Tripling the flow rate would get you to a nice 40 C temperature difference, which can be readily handled at normal pressures with normal materials.
I agree with Michal. Figure out the quality of the mixture coming out of your pipes. Based on this, you can calculate velocities and kinetic energies. Find out what regime you'll be in (bubbly, slug, churn, annular) and there are pretty good dP/dx correlations available that will get you in the right ball park.
I suppose you mean 400 C. It would be unambiguous to add degrees Celsius.
I have a few questions in answering which the solution will become self evident. (1) How did you determine that the maximum temperature of the surface (outer?) is 400 C? Or is it the maximum temperature of the outer medium? (2) What is on the outside? Is it gas, plasma or perhaps liquid metal? If it is is gas or plasma, the major temperature drop will be on the side of gas/plasma and the wall will run cool and Michal's suggestions will serve you well. On the other hand, it it is a liquid metal, you need to pressurize the water to a level where bulk boiling will not occur. Bubbles formed locally will condense in the main flow and the mean temperature at exit can be kept below the saturation temperature.
This question is another example in a long series of questions on Research Gate where it is not posed clearly enough to enable good answers. I keep imploring: Please don't pose the question as it comes into your mind. Reconsider if it is likely to be clear to the reader. Even better, bounce it on a couple of friends/colleagues and see if it is clear to them.
Although it is not clearly posed, a calculation path may hel Bharat.
If you have given heat exchange and flow rate, the first thing you should calculate is the exit quality or exit temperature (of liquid or superheated vapour). By the way, you need to know an approximate pressure.
According to this result, you should use a flow pattern map and then a pressure drop correlation, as Kris mentioned.
Finally, check that the calculated absolute pressure is consistent with your assumption.
Nucleate boiling can be avoided alltogether if your tube wall inside temperature is kept below the saturation temperature (or more accurately: saturation temperature plus a few Kelvin due to the surface tension effects of a curved bubble interface). Your maximum wall temperature is at the tube exit conditoin, hence calculating the heat transfer coefficient (from suitable correlation) and fluid bulk temperature (frpom an energy balance) would provide you with a good estimate. If the tube inner wall temperature is 400 C, boiling will occur nonetheless, and you need to figure out the vapor generation and the pressure drop from suitable models for this (which can be tricky in the subcooled region).
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