Aspects of Two-Phase Flow Boiling Heat Transfer inside Tube of Water Tube Boiler—A Numerical Study

The study of flow boiling heat transfer inside larger diameter tubes, which are used in water tube boilers, is sparse in the literature. Accordingly, the present study explore numerically saturated flow boiling phenomenon of water in a horizontal plain stainless steel tube at atmospheric condition. The effect of mass flux (254.67 kg/m²s–600.00 kg/m²s), heat flux (16.97–135.00 kW/m²), surface roughness (0.15 mm–0.5 mm), inclination angle (0°–60°) and the tube diameter (5 mm–50 mm) on the flow boiling heat transfer coefficient (HTC) and overall vapor volume fraction (VVF) is investigated. A 2D k-\(\varepsilon\) turbulence model of ANSYS-FLUENT platform is used along with the Volume of Fluid (VOF) model to track the interface between the water and vapor. The numerical findings indicate that HTC rises with a rise in mass flux and declines with a rise in heat flux. Furthermore, it is revealed that when heat flux rises, the VVF in the domain increases, corroborating the observation of a drop in HTC. The observed phenomenon is quite true for conventional tubes used in industries. An improvement in flow boiling HTC is also observed for tubes with higher surface roughness. The influence of inclination angle has substantial effect on the HTC, and the HTC rises with rise in inclination angle except for larger mass flux. The HTC of smaller tube diameter is larger compared to larger tube diameter tube, and after certain range of tube diameter (20 mm) the change in HTC is insignificant.