Pressure

A 60 kg person standing in flat shoes exerts about 30,000 pascals on the floor. The same person in stiletto heels (tiny contact area) exerts over 1,000,000 pascals through the heel tips. Same force, wildly different pressure. The floor under the stiletto might crack; the flat shoe is fine.

Pressure is force distributed over an area: P = F/A, measured in pascals (Pa), where 1 Pa = 1 newton per square meter. Concentrating the same force on a smaller area increases pressure. Spreading it over a larger area decreases it.

Pressure governs three critical energy systems. In steam turbines, high-pressure steam (6-25 MPa in modern plants) pushes turbine blades. Higher pressure means more force per unit area on the blades, which means more work extracted per kilogram of steam. In natural gas pipelines, gas is compressed to 5-10 MPa to push it through thousands of miles of pipe. The pressure differential between the inlet and outlet drives the flow. In hydraulic fracturing (fracking), fluid is injected at extreme pressure (40-80 MPa) to crack rock formations and release trapped oil and gas.

Worked Example

A steam turbine inlet receives steam at 15 MPa (about 150 atmospheres). The steam exits at 0.005 MPa.

• Find the pressure drop. 15 - 0.005 = 14.995 MPa.

Why does the turbine need such a large pressure difference between inlet and outlet?

The pressure drop is what drives the steam through the turbine blades. Greater pressure difference means more energy extracted per kilogram of steam. The exhaust is kept at near-vacuum (0.005 MPa) specifically to maximize this differential. A steam turbine's efficiency depends directly on the ratio of inlet to outlet pressure.

Pressure is the physical quantity that connects force to the engineering of turbines, pipelines, and extraction processes.

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