🔥Thermal Thursday
Thursday, August 6, 2026
Three terms every thermo course covers and almost every working engineer still misuses in casual conversation.
Term 1: Entropy
ThermalA measure of disorder in a system. The Second Law of Thermodynamics says entropy in an isolated system never decreases. In an irreversible process, entropy grows. Engineers use it to figure out the theoretical limit on how much useful work an engine can extract from a temperature difference. Nothing real ever beats the second law.
Why it matters: Every Carnot cycle, every refrigeration coefficient of performance, every rocket engine isp limit is a downstream consequence of entropy.
Term 2: Enthalpy
ThermalTotal heat content of a system at constant pressure. Internal energy plus the energy associated with displacing surroundings at the system's pressure and volume. The state variable engineers actually use for flow processes — turbines, compressors, heat exchangers — because mass moves through them at roughly constant pressure.
Why it matters: If you've ever read a steam table or sized a heat exchanger, you've used enthalpy whether you called it that or not.
Term 3: Adiabatic Process
ThermalA thermodynamic process in which no heat crosses the system boundary. All the work goes into changing internal energy. Pressurize a gas adiabatically and it heats up; expand it adiabatically and it cools. Real systems are never perfectly adiabatic, but a fast process in an insulated chamber is close enough.
Why it matters: Adiabatic flame temperature is the upper bound on every combustion chamber design — and it's why turbine inlet temps are limited by metallurgy, not chemistry.
📍 Huntsville Pulse
- •Heat-stress watch: NWS is forecasting a heat index above 105°F through the weekend. Roof and hangar work crews are sliding starts to 5:30 a.m.
- •ASME local section meets next Thursday. Topic: heat-exchanger design for additively-manufactured cold plates.
- •Calhoun Community College's HVAC continuing-ed track is enrolling for fall. ASHRAE-aligned curriculum.
- •Reminder for new transplants from the West Coast: Alabama humidity will recalibrate your HVAC service plan. Get the dehumidifier sized correctly the first time.
“Thermodynamics in three rules: you can't win, you can't break even, and you can't quit the game.”