الفهرس 
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Abstract
In the present work the effect of heating surface material on pool boiling heat transfer coefficient of refrigerant R-12 from horizontal tubes is investigated.
A test apparatus was designed and constructed to achieve heat transfer measurements from three horizontal tubes. The tubes were made from copper, brass and stainless steel with different surfaces finish. The boiling medium was refrigerant R-12 at saturation pressures between 11 to 46 percent of the original pressure, and at heat flux up to 34 kw/m2.
from a detailed analysis of the experimental results of the whole range of pressure investigated, it was found of that the influence of the different surface conditions, achieved mechanically by different grained emery papers, on the absolute value of the heat transfer coefficient cannot be correlated by one of the roughness parameters used in literature. Also, the relative pressure dependence of the heat transfer coefficient is similar for the tubes with different surface finish. A three parameteric distribution function N(r) for the size of stable vapour buble in nucleation sites is obtained for each of the tested tubes using the heat transfer measurements.
New correlations have been done to find the relationship between the constants of the distribution function, the thermophysical properties of the heating tube material (pyc) and the surface roughness parameter (Rp) measured directly by a profilometer.
from the experimental results, it was concludes :
(1)It is not the absolute value of the heat transfer of surface roughness on the absolute value of the heat transfer coefficient ( oc) in a wide range of pressure by a single roughness parameter in the form ( oc~ROp.133) or ( oc~Roz.2).
(2)It should be possible to deduce the distribution function of the size of stable bubbles in avtive nucleation sites of the heated surface from pool boiling heat transfer data.
(3)The three-parameteric constants for each tube surface (Nmax /A,rst,m ) show a certain trend with the functions F1,F2 relating the thermophysical properties of the heating tube material and the surface roughness parameter (Rp)The exponent (m) increases with (Rp ), (Nmax/A ) decreases with the parameter (Rp/F2 ) and decreases with the parameter (Rp.F1).
(4)New correlations are obtained relating the surface roughness parameter (Rp), the thermophysical properties of the heating tube material and the distribution function constants (Nmax/A,rst,m). from these correlations the oc (q) relation of any heating surface material could be predicted from the knowledge of (Rp) measured directly by a profilmeter and functions (F1) and (F2) including the thermal properties of the surface material.