DIESEL + WATER HEAT EXCHANGER CALCULATION

[takiyasamsama]

Hi,

If we have a stream that contains diesel and water, which physical properties shall we consider in sizing of heat exchanger?
Do we use water since it's heavier than diesel? or do we use diesel since the viscosity affects the sizing as well?

On the top of my head was that using HTRI, I would go on specifying PROPERTIES MIXTURE assigning Diesel and Water with respect to their mass fraction then run the sizing and whatever the properties are on the TEMA result sheet would be the mixture properties.

Any advise is much appreciated

 

[lukaiENG]

This is interesting given that diesel and water do not mix well.

For a more typical HVAC scenario, when using a water/glycol mixture you can get physical properties of the blended mix from the manufacturer. Example
This basically follows the logic you outline.

I don't have experience of flow of mixed water/hydrophobic fluid flow, let alone through a heat exchanger. a few thoughts:
[ol 1]
[li]Is there any sort of surfactant in use to make the fluids mix well?[/li]
[li]what % of each are we talking? if it is 90% diesel (or water) then applying your logic is probably pretty safe. Mixes closer to 50/50 may more difficult to guess.[/li]
[li]what sort of heat exchanger are you using? is there a chance of getting pockets of the 'carried' fluid getting stuck in pockets of the heat exchanger? (in the same way that bubbles of air can get trapped in a plate and frame HX in a CHW system). These pockets of fluid could be an impediment to flow and decrease your heat transfer[/li]
[li]if it is a plate and frame heat exchanger, make sure you specify a frame with extra capacity (50%?) just in case you need to add more plates in the future to get your capacity [/li]

[/ol]

good luck!

 

[LittleInch]

I'm stifling to think why you would want to heat or cool a mixture of diesel and water unless one is 5% or so. Stratification inside the exchanger would seem to be a big issue as would any slugs of more percent water than the normal mixture.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[lukaiENG]

I would agree. definintely not a common HVAC application.

A quick google found this which might be useful reading (I didn't read it for you)

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322012000200008

 

[takiyasamsama]

Hi LukaiENG & LittleInch,

Thanks for your replies. I've worked with water-glycol heaters and coolers before, yes they're quite difficult in determining the physical properties but the properties were defined as mixture properties.

However in this current case I'm in, the fluid (diesel & water) are defined separately i.e. the datasheet specify the diesel and water flowrates, MW, density, specific heat, viscosity, and thermal conductivity separately. Thus in order for me to find the duty, reynolds number, etc is quite difficult.

I would think that in order for it to work I could add i.e. density for diesel & water and find the average but again I don't find it correct somehow. One method I saw yesterday was that they find the mass flow rate fraction then they multiply by that fraction then add them all up e.g. diesel flowrate fraction is 0.6 and water flowrate fraction is 0.4, then they multiply diesel density, 60.5 lb/cu-ft by 0.6 and water density of 20 lb/cu-ft by 0.4 then finally they add all those number to find the mixture properties.

If anyone ever saw this method and it does actually worked kindly let me know. Thank you and have a good day!