# Liquid-Phase Speed of Sound Measurements of Octafluorocyclobutane (RC-318) and Hexafluoroethane (R-116)

## TL;DR

This study measures sound speed in two fluorinated compounds under various temperatures and pressures to evaluate their equations of state.

## Contribution

New high-precision sound speed data for RC-318 and R-116 liquids are presented, showing the need for updated equations of state.

## Key findings

- RC-318 sound speed data show an average deviation of 0.56% from the reference equation of state.
- R-116 data show a larger average deviation of 4.85%, indicating a need for refitting.
- Both equations of state require refinement to accurately model liquid-phase sound speeds.

## Abstract

Sound speed data measured using a dual-path pulse-echo
instrument
are reported for octafluorocyclobutane (RC-318) at temperatures ranging
from 240 to 390 K and at pressures up to 49.01 MPa, and for hexafluoroethane
(R-116) at temperatures ranging from 230 to 320 K and at pressures
up to 50.27 MPa. The combined expanded uncertainty in the speed of
sound varies from 0.035% to 0.102% for RC-318 and 0.039% to 0.097%
for R-116 of the measured speed of sound value. The data reported
in the present study and those available in the literature are compared
to reference equations of state (EOS) for RC-318 and R-116 included
in REFPROP version 10.0. The overall performance of both EOS is characterized
by an average absolute relative deviation and the maximum deviation.
The RC-318 EOS compared to the reported sound speed data with an absolute
average relative deviation of 0.56% and a maximum deviation of 1.62%.
The R-116 EOS compared to the reported sound speed data with an absolute
average relative deviation of 4.85% and a maximum deviation of 6.35%.
In both cases, these comparisons show that a refitting of both EOS
is required to accurately reproduce the liquid-phase speed of sound
for RC-318 and R-116.