Dear All,

I have two questions related to Lockhart-Martinelli two phase flow calculation. For 2 phase flow, the flow modulus factor, X, is calculated using the equation provided below.

X^2 = (delP,liq / delP,gas)

Once this is calculated the next step (ref: Emergency Relief System Design using DIERS tech) is to calculate the phi (gas) using the equation provided below.

(phi,gas)^2 = (1 + X^(2/n))^n

where n =4 for turbulent flow in gas and liq phase, 2.88912 for viscous flow in gas and liq phase and 3.5 for the rest.

Assuming the flow of gas and liquid phase are transitional by nature, based on the statement above, n should be 3.5. With reference to Ludwig, Martinelli correlation considers transitional flow as turbulent flow.

My question is the factor of 3.5 is applicable for which flow type?

Secondly, for vertical upward flow, GPSA provided Flanigan's equation to calculate the elevation pressure drop. In some tech notes, vertical upward 2 phase pressure drop is calculated based on the equation provided below.

delP,e = rho x gravity x H x sin(theta).

For elevation 2 phase pressure drop, which correlation is correct?

Appreciate your advice on this matter.