With a coefficient of determination (R2) of 0.84. Fig. 4 shows a comparison
of heat-flux from the experiment to heat-flux predictions
from Eq. (5). The standard deviation (STD) of experimental heat
fluxes from the predictions of Eq. (5) is ±25%. Thus Eq. (5) can be
used to predict the heat-flux of a VTF in its vertical position. However,
in literature review [2], it is clear that the filling ratios do have
a significant influence on the heat flux of the VFT, and this paper as
well. A correlation of the dimensionless parameters for predicting
VFT heat-transfer rate can be used in range filling ratios of 20–
80%. Furthermore, the correlation of the VFT and the CT of [3] from
literature review was compared. It can be clearly seen that the heat
flux of the VFT is higher than that of the CT. Because it is known
from Payakaruk et al. [3] that there is no mechanism of convection
(Pr) and condensation of working fluids (Ja).