This paper aims to study the effect of the addition of Al2O3, CuO and ZnO nano particles to R134a on the 
evaporative heat transfer coefficient. A horizontal copper tube in a tube heat exchanger is designed and constructed here as a part of the experimental test rig. The heating load is provided by hot water passing through an annulus surrounding the inner copper tube. Measurements were carried out using heat flux ranged from 40 to 80 kW/m2 and nano fluid concentrations ranged from 0.25 % to 1.2 % and nano particle size 25 of nm for all material samples. It is worth mentioning that the evaporative heat transfer coefficient increases and reaches its maximum value at 0.5 % of 
nanoparticles concentration and then decreases for all nano particles sample this is due to the high thermal conductivity 
of the material used here.