ANS:D - highly turbulent

Convective heat transfer coefficient in the case of fluid flowing in tubes is not affected by the tube length/diameter ratio if the flow is in the laminar zone. In laminar flow, the convective heat transfer coefficient is primarily influenced by properties such as fluid viscosity and velocity, rather than the tube length/diameter ratio. This is because in laminar flow, fluid particles move in parallel layers with minimal mixing, resulting in a predictable flow pattern and heat transfer characteristics. In contrast, in highly turbulent flow, the convective heat transfer coefficient is significantly affected by the tube length/diameter ratio. Turbulent flow promotes better mixing of fluid particles, leading to enhanced heat transfer rates. However, the heat transfer coefficient in turbulent flow can be affected by the length and diameter of the tubes due to changes in flow patterns and frictional losses. Therefore, the statement "Convective heat transfer coefficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the laminar zone." is accurate.