PHE problem 1

[danielruo]

Hi, everyone,

I am meeting one problem right now. I have one Alfa Laval PHE, the type is M6-MBASE that is two section cooler, and it cannot cool product to desired temperature and blown the gasket due to high pressure.

I checked the system and found the PHE installation is wrong. In the equipment description, product should flow from S4 to A14P and then from A14P to T4; tower water flow through section I that from A11V to S1 and ice water flows through section II that from T1 to A11. Section II has more heat transfer surface than Section I.

But actually the product flow through T4 to S4; tower water working in section II and ice water working in section I. so the ice water section is smaller than the tower water section.

That seems explain the reason why the product cannot cool to expecting temperature. But I want to know if the flow direction is reverse that means only the inlet and outlet is different than the original description but still in counter current flow mode, what is the affection for the pressure drop in the system. Is it possible to cause high pressure?

I appreciate for your suggestion.

 

[Montemayor]

Daniel:

The most fortunate position that you find yourself in is that you are the owner of a recognized quality product that has been traditionally backed up by its fabricator.

Your best strategy should be to refer back to Alfa Laval, explaining in detail what you have found and requesting their expert help. Some of us here on the Forum are familiar with Alfa Laval and their products - especially their Plate Heat Exchangers. However, we are only amateurs compared to the fabricator. Why waste time and effort in trying to obtain help from us when you have a presumed excellent technical back-up in the original supplier?

I believe your best success would be in contacting Alfa Laval.

 

[rmw]

Well said Art.

rmw

 

[danielruo]

I have measure the flow rate about 17,000l/h but it is in the outlet of PHE ice water section. And I know the ice water inlet pressure is 32psi. Is anyone know how to estimate the inlet flow rate?

Is the inlet flow rate higher than the outlet due to the PHE inside pressure drop?

Thanks for your suggestion.

 

[Montemayor]

Daniel:

I hate to have to be the one to level with you, but I might as well do it because you're going to get from the rest of the engineers who are on this Forum:

As any engineer knows, under the basis of steady state flow (and this heat exchanger is sized for steady state) "what goes in must come out". In other words, there is no accumulation. In simpler terms, the inlet mass flow rate better be the same as the outlet mass flow rate or you are defying the laws of nature - and that won't last very long.

 

[KiwiMace]

I'd start by re-piping the HE into the correct configuration. Your Alfa laval rep is only going to suggest re-piping it correctly anyway.

If you have a two-stage HE, are you getting counter-flow in both stages with the incorrect piping? If there is excessive pressure drop, the higher flow fluid might be flowing in the lower flow fluid section. Check the sandwich bolt torques after you re-pipe it. Usually PHEs are sized for similar flowrates.

 

[danielruo]

Montemayor,

Thank you for your reply.

Based on your reply, I can know the ice water inlet mass flow rate equal to outlet flow rate. I assume the density is same because the temperature difference is 5 deg C. So the flow rate is 17,000l/h.

I sent the data to PHE manufacturer because we don't want to change the ice water pump, etc.

The ice water pump is Armstrong 3x3x6, serial 4380, 3600rpm. The motor is 15HP. Regarding the pump curve, it can run 353usgpm at 100ft head.

I know the total system head has three parts: static head, elevation, and dynamic head. The static head and elevation is not change after system installation but dynamic head is change by the component add or reduce. The dynamic head losses are propotional to the square of the flow rate.

At present, I got the inlet pressure is 32psi and flow is 17,000l/h. Can i caculate the total dynamic pressure is p1^2/P2^2=V1/V2?

How can I estimate the pressure loss in valve and elbow? Is there any thumb rule can be used?

Regards,

 

[thermmech]

I know the total system head has three parts: static head, elevation, and dynamic head. ... (snipped)...
How can I estimate the pressure loss in valve and elbow? Is there any thumb rule can be used?

Your best bet is to obtain a copy of Crane Technical Paper No. 410 (TP-410). In there you will find how to calculate pressure drop in pipes.

You can get it from your local library if you are in US/Canada or buy it at:

http://www.tp410.com/tp410.htm