الفهرس 
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Abstract
The thesis is concerned with experimental study of the natural convection heat transfer from the inside surface of the equilateral triangular tubes at different positions (horizontal, vertical and inclined positions with different inclination angles). This experimental study was done on two open ended equilateral triangular tubes, one has smooth inner surfaces and the other has rough inner surfaces of 0.02mm roughness. The equilateral triangular tube is uniformly heated by electric heater with a constant heat flux. Effect of different inclination angles, θ, (varied from 0o to 90o) were taken into account. The setting condition of triangular tube is classified according to the flow of air due to buoyancy force inside the tube in each case. The experiments covered a range of Rayleigh number, Ra, from 6.45 × 105 to 4.78 × 106. The local and average heat transfer coefficients and Nusselt numbers were obtained for Smooth and rough triangular tubes at different heat flux values (q), different inclination angles (θ) and different Rayleigh numbers (Ra). The experimental results showed that there is an enhancement of heat transfer coefficient with rough surface and inclination angles (θ) at the same heat flux (q). The average heat transfer coefficient (hm) of rough tube is higher than hm of smooth tube by about 7% in horizontal case, 8.1% in inclined case at θ = 45o and 10% in vertical case. The heat transfer coefficient for vertical triangular tubes (smooth and rough tubes) is greater than that of inclined triangular tubes and than that of horizontal triangular tubes. The values of temperature difference between the inside surface and ambient air increase with increase of axial distance from both ends of the horizontal triangular tube until a maximum value at the middle of the tube. The results obtained are correlated using dimensionless groups for both rough and smooth surfaces of the equilateral triangular tubes. The horizontal and vertical triangular tubes correlations configure the mean Nusslet number as a function of Rayleigh number. The inclined triangular tubes correlation configures mean Nusslet number as a function of Rayleigh number and sin θ.