Thermosyphon reboiler height calcuation and htri quesiton

[hswang2]

I have a thermosypon reboiler, two-phase flow problem. The fluid flow from C to D
Is reboiler tube side, In this flow zone, 25% by weight of circulated fluid is vaporized.
And we need to find out the liquid level height LF. The segments between point C,D and E will be two phase flow. We use trial-and error to solve this. First, assume luquid level height LF. The LF is measure to the face of the bottom of tube bundle point C.
The reason is that vertical height of B to C and B to A tend to cancel each other.
Reboiler size required
*920 tube, inside diameter 0.57 in
*Tube length 8 ft
*One tube pass
Since the tubes are 8 ft long, and allowing 7 ft for the exchanger head, pipe outlet riser, and 4ft is vertical vapor space for the column bottoms section.
The first LF estimate is 11 ft (8+(7-4)=11)
My question is that
1. I don’t quite follow why they use 7(the pipe outlet riser height)-4 ( the bottom vapor space section height)
2. What kind of software do we can use to estimate pipe section loss, for example HTRI is good choice or not.
Thank you very much for your kindly help.

 

[dcasto]

first you need to look at the static pressure heads of each leg of the fluids. The fluid in has 8 feet + UNK feet at density X. The return has 7 feet minus UNK feet at density Y. This will get you the static distance.

Next calculate pressure drop while flowing and instaed of using an average density, integrate the density as the temperature changes and the amount of vapor is increasing.

I'd just look at 1 foot intervals going down the pressure leg inside column and the every foot going up through the reboiler.