Thread by @BreizhLondon

Pushed beyond my rusty boundaries by @paulportesi and @edw_perry
When I was younger (some time ago), in thermodynamics was mostly using U = internal energy and H = Enthalpy both state function (not depending on path), Energy say E way too imprecise.
en.wikipedia.org/wiki/Enthalpy

Now you'd say for practical purposes, who cares ?
If you want to assess how much weight you will lose through say exercise from energy content of food tables/chemical reactions (usually stated as H), there won't be much difference E/H/U due to the already significant imprecision

Quick shortcut : climb 1000m, lose 125 g fat (for say a 80kg dude with friction).

But where U/H precision matters A LOT in practical purposes is e.g. efficiency of Combined Cycle Gas Turbines (CCGT) especially when considering Low Heating and High Heating Values (LHV, HHV)

lpelc.org/what-is-the-di…

A manufacturer will state for instance 57% efficiency, when considered from HIS point of view, but the owner will only see 52% from gas he buys in the market. Both are right, but very confusing. You have no idea how many energy analysts have told me :

Look, this CCGT MUST be extremely profitable, I calculated with gas prices, different taxes, with this high efficiency of 57% they make a killing !
Hmmmmm, pb is my friend, genuine efficiency only 52% when new under normal circumstances and btw during a heat wave drops to 45%.

(a mixture of Carnot cycle and gas intake in hot humid air).

So in normal unlevered life H, U, G, E ..... no BIG difference (pun intended).

But in levered energy projects, be careful what form of energy U R tawking about