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Pressure loss in hot fluid. question

Pressure loss in hot fluid. question

Pressure loss in hot fluid. question

(OP)
I wonder what would happen if i begin pumping a saturated liquid on a pipeline with huge friction loss?.

Because in my Hypothetical design i´m pumping saturated liquid Ammonia and i have like 70 bar of friction preassure drop.

Thank you!

RE: Pressure loss in hot fluid. question

Welcome to eng-tips, Demo369.

It's a good idea if you take a minute to read through the Forum Policies. Number 4 is a good place to start.

Posting the same query in more than one forum generates confusion. You will have two threads going that will keep other members from seeing the whole discussion. That is very confusing for members who belong to both forums and you will not benefit from the whole group.

Thanks!

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Pressure loss in hot fluid. question

In your hypothetical design, how much of this 70 bar loss occurs in the suction line, and how much occurs in the discharge line. You may want to Google NPSH, and study up on it. Not enough NPSH and your pump is doomed! And, how did you calculate this 70 bar loss - as a liquid, as a vapor, as flashing, two-phase flow? You need to supply more details before you can get a good answer. As it stands now, the answer is "it depends".

Good luck,
Latexman

RE: Pressure loss in hot fluid. question

Demo, come back with some more specifics on your system.

RE: Pressure loss in hot fluid. question

(OP)
Hi Latexman.
Thank you for your answer.

Sorry, your right, i'll give more details.

In our system we are cooling an exothermic reaction in a batch reactor, so we put 300 meter coil inside the reactor where it flows SATURATED liquid ammonia -32 °C , 1 bar (refrigeration cycle), but when we calculated the friction loss and is about 70 bar, as a mix of liquid and vapor, so i argue with my college mate that, we have to change the design because so many preassure drop will make liquid change to vapor while flows in the coil, and the efficency of heat exchange will decrease , and he says that this state change to vapor won't happen from friction loss because of the compressor work supplied oppose that change . what´s the truth here?

Thank you.!

RE: Pressure loss in hot fluid. question

I have no experience in cooling reactors but I'm going to question a 300m coil (this is a single coil, one start, one end?).

I'm assuming you've done some sort of heat transfer calculation which has lead you to the 300m coil to get the necessary surface area, is that correct? If you are using ammonia as the cooling agent (you've stressed it's saturated liquid) then you almost certainly plan on vaporing the ammonia and utilizing the latent heat to cool the reactor? That gives you a flow rate which when you put it through your coil (considering the vapor generated) is generating an unreasonable pressure drop, you need to drop the velocity which means a larger diameter coil or parallel paths or both.

What about a cooling jacket on the outside of the reactor to allow the ammonia to boil and remove the heat?

RE: Pressure loss in hot fluid. question

(OP)
TD2K.

Exactly ,we did that, this is our first design aproximation, we calculated the Surface area exchange, and we decided to start with a 300 meter, Diameter 1 1/4 BWG 11 single coil to cover that Surface Area. your right , the idea is utilizing the latent heat to cool the reactor, we are going to consider changing the design to what do you suggest, what preassure drop do you think it will be reasonable?.

Thanks for reply, very helpfull.

RE: Pressure loss in hot fluid. question

What temperature profile is the reation media? For example, it may start out cool, it gets heated, it undergoes reaction, and then it gets cooled. Something like that. It may be different.

This is a real world or school design problem?

Good luck,
Latexman

RE: Pressure loss in hot fluid. question

(OP)
We are dealing right now with equipment Design , it's for the Chemical Plant project for graduating (Chemical Engineer).

The reaction begins at 25°C (ambient temperature) and we have to cold and maintain it at 5 ° C. We use a TC (temperature controller) to control the ammonia flow.

RE: Pressure loss in hot fluid. question

Were you given a PFD/P&ID or do you have to develop? If you have, please attach. The more info. the better.

Good luck,
Latexman

RE: Pressure loss in hot fluid. question

(OP)
We had to choose a product where involves Unit Operations and some Chemical Reaction and design the whole plant , we ended up with Atrazine production(herbizide) , everything is patented and secret, we only found one LAB experiment where we had some experimental data, and one block process diagram patent ( from year 1960-70), we had to begin from scratch, it had been like 6 months so far, so how you can see this is not a real life design , at least as good as possible..

I would like to know what preassure drop would be reasonable in the cooling coil.

I'll try to put more info soon.

Thank you.

RE: Pressure loss in hot fluid. question

(OP)

I can add something, we don't care the condition of the ammonia in the exit of the coil as long it had utilized completly or most of his latent heat for cooling (idealization).

Sorry for my English, I'm from Argentina =).

RE: Pressure loss in hot fluid. question

"we put 300 meter coil inside the reactor where it flows SATURATED liquid ammonia -32 °C , 1 bar (refrigeration cycle),"

"i´m pumping saturated liquid Ammonia and i have like 70 bar of friction preassure drop."

You have 1 bar, but there is 70 bar of friction preassure drop. This is not only unreasonable; it is impossible.

Have you considered a brine circulation cooling loop? Or 50/50 ethylene glycol and water (FP = -30 C). You could chill the brine or EG/water with ammonia refrigeration and then pump it through the RX and back to the chiller - a loop. A total pressure drop (chiller + piping + RX + return piping) of 2-4 bar would be reasonable. in my opinion.

Have you considered using a half-pipe jacketed RX. If you can get enough heat transfer area with a jacket, the RX can be smaller by the volume displaced by the coils you would use.

Just some ideas.

Good luck,
Latexman

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