A: The tables exist specifically for water in steel pipe — they're faster and just as accurate for that exact scenario, so use them. The Darcy equation and Moody diagram are for everything else: different fluids, different pipe materials, unusual conditions where the table assumptions don't apply. Learn both, but reach for the table first when it fits.

A: The key distinction is whether you're dealing with NPSH available (NPSHA) or NPSH required (NPSHR) — one is a property of the system, the other is a property of the pump. NPSHA is what the system can provide to the pump inlet based on static head, vapor pressure, and friction losses; NPSHR is what the pump manufacturer specifies as the minimum needed to avoid cavitation. Match the formula to what you're solving for.

A: Yes, that's exactly a swamp cooler — the direct evaporative cooler equation uses entering dry-bulb and wet-bulb temperatures for air, while the open cooling tower equation substitutes entering and leaving water temperatures. The structure of both equations is the same; just be clear about what fluid's temperatures are going into each one and don't mix them up.

A: The evaporative cooler equation is defined in terms of air temperatures; the cooling tower equation is defined in terms of water temperatures. They have the same mathematical form but different physical variables — the leaving air temperature from an evaporative cooler is not the same as the leaving water temperature from a cooling tower. Pay close attention to what each variable represents and which fluid each equation is tracking.