Calculating minor losses for pipe fittings in AioFlo


In order to calculate the minor losses (i.e. pressure drops in fittings and valves) for a pipe it is necessary to give details of the start of the line, the end of the line, and all the fittings and valves in the line. AioFlo therefore breaks up the data input into these categories to make it logical and easy to check that everything has been covered.


Defining the start of the line

AioFlo Start of Line fittings

In the AioFlo model a pipe can start as the outlet from a tank or vessel, or it can be a continuation from another pipe.

The outlet from a tank can either be flush with the side of the tank, or it can project into the tank (sometimes known as a "Borda" entrance). The radius of the joint between the tank and a flush entrance can vary because a well radiused entrance has a very much lower resistance coefficient than a square outlet.

Because AioFlo is designed for pipes of a single diameter, any change in diameter must occur at either the start or end of the line. The change in diameter can be either an increase or a decrease from the previous section, and it can be implemented as a sudden expansion or contraction, or as a conical reducer, or as a standard pipe reducer. The diameter of the previous section can be keyed in as a numeric value, or it can be selected from the built in pipe dimension tables. The resistance coefficients for the changes in diameter are calculated using the Hooper Method.

Specifying elbows and tees for the calculation of minor losses

Specifying elbows and tees for the calculation of minor losses

A variety of threaded, welded (or flanged) and mitered fittings is included.

The second page covers elbows and tees. The resistance coefficients (K values) for the elbows and tees are calculated using the Darby 3-K Method which allows accurate calculation of pressure drops in the fittings for laminar and turbulent flow. This gives better accuracy than using equivalent lengths or fixed K values.

Where applicable, the details of the fittings are selected from drop down lists, and the number of fittings is keyed in.

Specifying valves and orifices for the calculation of minor losses

Specifying valves and orifices for the calculation of minor losses

A wide variety of generic valves is included, and there is the option of adding specific details for calculating losses in control valves and orifices.

The third page covers valves and orifices. The resistance coefficients for the generic valve types are calculated using the Darby 3-K Method which allows accurate determination of losses for laminar and turbulent flow. These K values are based on average values found in the open literature and catalogs and will be sufficiently accurate in most cases. However, if you have specific data for a valve you can enter that as a separate K value.

The control valve resistance is specified by entering a Cv value in the US, British or European form. Thin, sharp edged orifices as well as thick orifices are included. The permanent pressure loss through the orifices is calculated using the Hooper Method.

Generic resistance coefficient (K value) data is included for gate valves, globe valves, ball valves, plug valves, diaphragm valves, butterfly valves, Y-type strainers and a selection on non-return (check) valves.

Defining the end of the line

AioFlo End of Line fittings

In the AioFlo model a pipe can end in the same diameter as the main pipe line, or there can be an increase or decrease in diameter. The acceleration or exit loss can be included if the pipe discharges to the atmosphere or to an open tank, or the loss can be ignored if the pipe joins onto another section.

At the end of a pipe the kinetic energy due to the fluid velocity is lost if the fluid discharges to an unpressurized zone, or it can be retained if the fluid remains in another pipe (or if it is a gas discharged to a pressurized zone). This loss of kinetic energy is known as the "Exit Loss". This is an either-or selection in AioFlo.

In the same way as a change of diameter is allowed at the start of the line, there can be a change of diameter at the end as well. The change in diameter can be either an increase or a decrease to the downstream section, and it can be implemented as a sudden expansion or contraction, or as a conical reducer, or as a standard pipe reducer. The diameter of the downstream section can be keyed in as a numeric value, or it can be selected from the built in pipe dimension tables. The resistance coefficients for the changes in diameter are calculated using the Hooper Method.