الفهرس 
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Abstract
The main objective of the present study is to investigate experimentally the
pool boiling heat transfer characteristics of nanofluids during nucleate pool boiling
on a horizontal circular flat plate made from aluminum. The target is studying the
effect of the concentration of nanoparticles on the heat transfer coefficient in the
refrigeration and air conditioning equipment for the energy saving during pool
boiling in these systems. The experiments were carried out on a horizontal circular
flat plate made from aluminum with mirror surface roughness value of (Ra =0.09
μm) at different values of heat flux (q) ranged from 20 to 105 kW/m2, saturation
pressure 4.4, 6.4, 8.6, 10.7 bar corresponding to saturation temperature 12,24, 34,
42 oC respectively. The nanofluids have been prepared by suspending Al2O3
nanoparticles with diameters 20 to 55 nm in R134a as abase fluid with
concentrations of 0.01, 0.03, 0.05, 0.07 and 0.10 % by vol. respectively. An
experimental test rig equipped with the necessary measuring devices is designed
and constructed to achieve this purpose.
The results based on the experimental measurements show that the nucleate
pool boiling heat transfer coefficient increases with increasing the heat flux,
pressure and Al2O3 nanoparticles concentration in refrigerant R134a for all
concentrations of the nanoparticles used here.Large enhancement up to 16.8 % is
observed at high values of heat flux 105 kW/m2 and pressure of 10.7 bar compared
to the results obtained using pure refrigerant R134a only. This is because the
addition of nanoparticles increases the effective thermal conductivity of the mixture
of nanoparticles of Al2O3 and refrigerant R134a; hence the boiling heat transfer
characteristics are improved. The effect of influence the boiling pressure is small
on the enhancement of the pool boiling heat transfer coefficient. The present results
based on the experimental measurements are compared with the corresponding
available published data Favorable agreement is noticed between the present results
and the published ones.
Finally as a conclusion for the experimental measurements and the
corresponding results presented here a correlated equation is extracted based on the
different operating conditions and the surface roughness of the flat plate used. The
heat transfer coefficient during pool boiling can be calculated from the following
derived correlation:
The present experimental measurements fit the correlation equation with
maximum deviation of ± 9%.