4. Results and discussion
This report will show results of the dimensionless parameters
and correlation (see Figs. 3 and 4).
4.1. Effect of dimensionless parameters
The dimensionless parameters, which may have an effect on the
heat flux of VFTs in vertical position, include the aspect ratio (Le/
4Rh), Bond numbers (ratio of buoyancy force to surface tension
force, Bo); Prandtl numbers (ratio of momentum diffusivity to thermal
diffusivity of vapor, Pr); Kutateladze numbers (ratio of heatflux
to critical heat-flux, Ku) and Jacob numbers (ratio of latent
heat to sensible heat of the working fluid, Ja); Bo represents the
state of vapor bubbles which occur in nucleate boiling. If the Bo value
is high, the working fluids boil vigorously. However, if the value
of Bo is lower than 1, the boiling phenomena does not occur. The
change of Bo value depends on two main factors: the types of
working fluid and hydraulic radius (Rh) of the VFT cross section.
Pr represents convection heat transfer phenomenon in the tube
and this may occur when the vapor bubble that moves from the
evaporator to the condenser sections is the medium of convection
heat transfer. Therefore, the size and amount of vapor bubbles
which flow across the condenser section change slightly. Ku explains
the relationship between the input heat to the critical heat
flux of any system which has pool boiling. Ja is the ratio of sensible
heat to latent heat of the working fluid. qv/ql is the ratio of vapor
density to liquid density of the working fluid. This report discusses
the results of a VFT using R123, ethanol and water as the working
fluid. It can be seen from the results that Bo, Ja, Pr and Ku have a