1. **Reynolds number** (**Re**) Reynolds number, which relates inertial forces to viscous forces and thereby characterizes the type of flow regime

2. **Prandtl number (Pr)**, which relates the thermal properties of the fluid to the conductivity of the pipe.

3. **Nusselt number (Nu) **, a dimensionless group defining the relative significance of the film heat transfer coefficient to the conductivity of the pipe wall

where:

Dh is the hydraulic diameter of the pipe; its characteristic travelled length, , (m).

Q is the volumetric flow rate (m3/s).

A is the pipe cross-sectional area (m²).

v is the mean velocity of the object relative to the fluid (SI units: m/s).

mu is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/(m·s)).

nue is the kinematic viscosity ( (m²/s).

rho is the density of the fluid (kg/m³).

Calculation of Prandtle number :

Where

Based on these parameter, we can now calculated Heat transfer co-efficient on either side.

Where kw is thermal conductivity of the bulk fluid.

With this you are now equipped to calculate over all heat transfer.

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## Himesh