Q1: Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is

ANS:C - 0.6

When heat transfer occurs by conduction in the turbulent core of a fluid flowing through a heated pipe, the contribution of conduction becomes negligible compared to convection when the Prandtl number (PrPr) is relatively small. The Prandtl number is defined as the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity and is given by: Pr=kinematic viscositythermal diffusivity=Pr=thermal diffusivitykinematic viscosity​=αν​ A low Prandtl number indicates that thermal diffusivity is relatively high compared to momentum diffusivity. In such cases, the rate of heat transfer by convection (due to fluid motion) dominates over heat transfer by conduction. Given that the Prandtl number characterizes the fluid properties, it generally remains constant for a given fluid under specific conditions. Common fluids like water and air typically have Prandtl numbers in the range of 0.7 to 7, with water around 7 and air around 0.7. Among the options provided, the lowest value of Prandtl number is 0.2. Therefore, when the Prandtl number is relatively low, such as Pr=0.2Pr=0.2, heat transfer by conduction in the turbulent core of the fluid flowing through a heated pipe is negligible.