The Refrigerator With a COP Greater Than One
Refrigerator COP is not the same as thermal efficiency. A COP above one can be completely consistent with the first law.
Exam: Fe
The Turbine That Produced 1.2 MW From an Enthalpy Drop
For an adiabatic steady-flow turbine, an enthalpy drop becomes shaft work when kinetic and potential changes are negligible.
The Sealed Tank That Reached 150 kPa, Not 133
A rigid tank does not keep pressure constant. For an ideal gas, pressure tracks absolute temperature when mass and volume are fixed.
The Channel That Carried 5.69 Cubic Meters per Second
Hydraulic radius is not automatically equal to flow depth. Manning discharge depends on area, wetted perimeter, roughness, and slope.
The Faster Pipe Section That Lost 16 kPa of Pressure
A horizontal pipe can still lose static pressure when the flow accelerates because velocity head increases.
The Pipe That Halved Its Diameter and Quadrupled Its Velocity
Halving pipe diameter reduces area to one-quarter, so constant-flow velocity becomes four times larger.
The Tank Gauge That Read 58.9 kPa at 6 m
Zero velocity does not mean zero pressure. A static water column develops pressure that increases with depth.
The Column That Buckled Near 497 kips
A slender column can lose stability before material strength is exhausted. Effective length enters Euler load as a squared term.
The Beam Moment That Peaked at 75 kip-ft, Not 300
The uniform load resultant is useful for reactions, but its moment about a support is not the beam’s maximum internal bending moment.
The Floor Beam That Was Loaded at 400 lb/ft, Not 50
A floor pressure cannot be applied directly as a beam line load. Tributary width converts psf into plf.