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Total Flow Area TFA Calculation, Calculator, Chart

This article will handle the definition of the term Total Flow Area, how to calculate TFA, how to use the TFA chart to calculate bit total flow area and finally you can download its calculator for desktop and mobile.

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What Is The Drilling Bit Jet Nozzles?

Drilling Bit Jet Nozzles Total Flow Area chart calculation calculator

The part of the drilling bit includes a hole or opening for drilling fluid to exit. The hole is usually small (around 0.25 in. in diameter) and the pressure of the fluid inside the bit is usually high, leading to a high exit velocity through the total flow area of the nozzles that creates a high-velocity jet below the nozzles. This high-velocity jet of fluid cleans both the bit teeth and the bottom of the hole.Total flow area TFA calculations depend on The sizes of the nozzles that are usually measured in 1/32-in. increments (although some are recorded in millimeters) and are always reported in “thirty-seconds” of size (i.e., fractional denominators are not reduced), and usually range from 6/32 to 32/32.

Why Are This Drilling Bit jet Nozzles Necessary?

Drilling fluids circulate through a drill string to nozzles at the bit and back to the surface via the system annulus. They provide three crucial functions to drilling:

  • Cleaning of the cutting structure.
  • Cuttings removal from the hole bottom.
  • Efficient cuttings evacuation to the surface.

What is The Definition Of Total Flow Area (TFA) ?

This term is related to drilling bits jet nozzles which can be defined as the summation of all the areas of the drilling bit jet nozzles areas which fluid can go through while circulating.

How To perform TFA calculation Without Chart ?

So it is simple all you have to do is to count all the drilling bit jet nozzles. Accordingly, you can determine the flow area with a simple equation.

drilling bits total flow area tfa calculation equation

D is the diameter in inch,  Area in square inch   But we have to take in our consideration that diameter of the drilling bits jet nozzles is reported on xx/32 inch.  

The total flow area TFA calculations formula above can be simplified like this.

drilling bits total flow area tfa calculation equation

N is nozzle size in number/32 inch. Area in square inch


For Example, a drilling bit has 5 jet nozzles. 3 x 10/32 in & 2 x 12/32in . To calculate the total flow area of the drilling bit, we will use this equation for each nozzle size and then make a summation for all of them.

drilling bits total flow area calculation equation

Total Flow Area = ( 10^2 +10^2 +10^2 + 12^2+ 12^2 ) / 1303.8   So solving above equation we will have 0.451 inch2

Drilling Bits Nozzles Total Flow Area TFA Calculator Chart

In the below TFA chart, you can calculate it using both the number of nozzles and the nozzle size. just if you have 3 nozles of size 11 and 1 of size 13 you can get each one flow area then add them together to give you the total area.

Nozzles Total Flow Area TFA Chart and calculation definition
TFA Chart

Download Bit Nozzles Total Flow Area TFA Calculator Spreadsheet

This drilling software/ spreadsheet calculates it for a selection of up to 11 nozzle sizes.

TFA Calculator Application Download On Mobile 

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