The Graetz number is used to determine the thermal entry length for developing flow in pipes. The Graetz number for flow in a circular pipe is defined as,

where D is the inside diameter of the pipe, L is the length from the pipe entrance, Re is the Reynolds number of the flowing fluid, and Pr is the Prandtl number of the fluid. The Reynolds number and Prandtl number are defined as, In these equations, the fluid properties are ρ (density), cp (specific heat), μ (dynamic viscosity), and k (thermal conductivity). V is the fluid’s velocity in the pipe and D is the inside diameter of the pipe. Determine the Graetz number for liquid dodecane flowing at 20°C, with a velocity of 0.05 m/s in a pipe with an inside diameter of 5.25 cm at a location that is 0.5 m from the entrance of the pipe.

Transcribed Image Text:

GZL D Re Pr L