4 replies to this topic

[erwinfs]

Dear All,

 

I was once using HTRI in my college for shell & tube heat exchanger sizing excercise. When I checked the datasheet, there are "Actual U" and "Required U" terms in the datasheet. 

I currently still can't find satisfying explanation about "Actual U" and "Required U" terms in this software.

 

Can anyone explain about this?

 

Thank You

[Pradeepy]

Actual U is based on heat transfer area provided or heat transfer area provided including overdesign.
And U required means heat transfer area provided in case of overdesign factor is zero percent

Edited by Pradeepy, 30 May 2018 - 11:25 PM.

[kingnumberone]

Heat transfer through a surface like a wall can be calculated as

q = U A dT                        (1)

where

q = heat transfer (W (J/s), Btu/h)

U = overall heat transfer coefficient (W/(m²K), Btu/(ft² h ^oF))

A = wall area (m², ft²)

dT = (t₁ - t₂)

     = temperature difference over wall (^oC, ^oF)

You can find the review article example,

as well as more details about Overall Heat Transfer on this site https://www.engineer...ient-d_434.html.

[kingnumberone]

This calculator can be use to calculate the overall heat transfer coefficient and the heat transfer through a multi-layered wall. The calculator is generic and can be used for metric or imperial units as long as the use of units is consistent.

[ankitmalhotra]

This is applicable to a rating case in HTRI.

Required U is the heat transfer coefficient which HTRI calculates based on the basic equation Q = U A Delta-T. This implies the U which the exchanger is supposed to deliver as a minimum to do the required duty.

Actual U is based on the heat transfer coefficients of shell side, tube side and fouling factors. HTRI calculates this based on the fluid physical properties, fluid conditions, fouling factor and exchanger geometry. This is the U the exchanger will be able to deliver. 

A ratio of the two is the overdesign % reported by HTRI, which basically means if the exchanger will be able to do the required duty, under the given conditions, only if this is > 0%.