الفهرس 
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Abstract
Nanofluid is an advanced kind of fluid, which contains nanometer-sized
(10-9 m) solid particles that are known as nanoparticles. Nanoparticles enhance the
property of normal fluid in particular heat transfer. In the past few years, nano
refrigerant has become the input to many experimental and vapor compression
systems because of shortage of energy and environmental considerations.
This study aims to investigate experimentally the effect of using different types and
concentrations of the nanoparticles including Al2O3, CuO, ZnO with R134a as a base
fluid on the evaporative heat transfer coefficient during the evaporation process of
R134a in vapor compression refrigeration systems. Here, an experimental test rig is
designed and constructed to fulfill this purpose. The test section (evaporator) is a
horizontal tube in tube heat exchanger made from copper, the refrigerant evaporated
inside an inner copper tube and the heating load is provided from hot water which
passes through the annular surrounding the inner tube. Measurements were
performed for heat flux ranged from 40 to 80 kW/m2 using nano fluid with
concentrations ranged from 0.25 % to 1.2 % and spherical particle sizes of 15, 25, 40
nm for Al2O3, and 25 nm for CuO, ZnO. The results indicated that for different nano
fluid concentrations, the evaporative heat transfer coefficient shows a maximum
value at a concentration of 0.5% for all nanofluids used and then decreases. Based
on the experimental results obtained here an empirical correlation equation is
deduced here based on the experimental measurements with ± 10 %, maximum
deviation. The equation is valid for mass flux ranged from 255 to 350 kg/m2
s, heat
flux ranged from 40 to 80 kW/m2
, and Prandtl Number (Pr) for the material types
used as nanoparticles with concentrations ranged from 0.2 to 1.2. The final deduced
empirical equation has the following form:
havg = A(Pr)+B(Pr)(Z) +C(Pr)(Z)
2+D(Pr)(Z)
3+E(Pr)(q).