From f6385564e881e74b25c48f58464d70b30b0021f2 Mon Sep 17 00:00:00 2001 From: Matthis Thorade Date: Fri, 27 Jan 2017 11:55:13 +0100 Subject: [PATCH] Update FAQ.md Extend explanation, mention reference state --- FAQ.md | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/FAQ.md b/FAQ.md index b5d3abe3..6623d443 100644 --- a/FAQ.md +++ b/FAQ.md @@ -7,7 +7,15 @@ Usage 1. My enthalpy and entropy values are not the same as what are used in REFPROP, or EES, or ... - Enthalpy and entropy are only equivalent to within an additive constant, so you should always compare enthalpy and entropy *differences* rather than enthalpy and entropy values + Values for enthalpy, entropy and internal energy are calculated as *difference* + with respect to an arbitrarily chosen reference state. + As a consequence, absolute values may differ hugely between different tools, + but the difference between two states should be equal. + At least the following three states are frequently chosen as reference states: + IIR: saturated liquid (Q=0) at T=273.15 K + ASHRAE: saturated liquid (Q=0) at T=233.15 K + NBP: saturated liquid (Q=0) at p=101325.0 Pa + 2. My calls to REFPROP fail with a mysterious `Segementation Fault`: