Heat Transfer Lab Lab Experiments

Determination of Heat Transfer Coefficient Through Forced Convection

Nov 25 2023

Aim

To determine the heat transfer coefficient of a steel pipe in a forced convection environment.

Apparatus required:

Forced convection experimental setup
Stabilized power supply
Stop Clock

Procedure:

Switch on the heater and set an input voltage (50V) using the regulator
After a short interval of time, Switch on the blower to establish a forced convection environment.
Set the blower speed regulator to a desired flow rate of air.
The heating coil transfers heat to the surface of the steel pipe through conduction. As the blower blows air inside the pipe, the inner surface of the pipe loses heat through convection.
Allowing the heater to continuously heat the pipe and also the blower to convect the heat, observe the temperatures at specific locations at equal internals of time until the system reaches steady state and tabulate them.
Observe the pressure load readings on the u - Tube manometer to calculate the flow rate of air.
Using heat and mass transfer data book choose formula for forced convection internal flow heat transfer and calculate the heat transfer co- efficient for the surface.

Observations:

S. No.	Voltage (V) Volts	Current (I) Amps	Temperature (°C)/T1/T2/T3/T4/T5/T6	Manometer head(Cm)/h1/h2/h1-h2
1	Forced convection
2
3
4
5

Formula Used

Heat input (q) V*I Watts

Average air temperature (T_a) = (T₁+T₆) /2 (°C)

Average surface temperature (T_s) = (T₂+T₃+T₄+T₅) /4 (°C)

Volume of air flow (Q_B) = C_d (μd²/4) (ν2g h_w) (P_w/P_a) m³

Where

Cd - Co-efficient of discharge = 0.64

hw - Difference of water level in manometer in meter

d - Diameter of orifice = 0.0.14 m

Velocity of air in Pipe (V) = Q_B/ cross section of pipe in m/sec

Reynolds number = VD /γ

Where,

γ= Kinematic viscosity of air from HMT DATA BOOK

Nusselt Number (Nu) = 0.023 (Re)^0.8(Pr) ^0.4

Prandtl no from HMT Data Book of (T_a)

Heat transfer co-efficient = Nu K /D Wm ²/K

Result:

The convective heat transfer coefficient is (ha) _____ _______ Wm ²/K
Temperature distribution
Fin efficiency

Viva-Voce Questions

What is Orifice - meter?

Orifice- meter is used to measure discharge.

What is the function of blower?

Blower is an external mechanical device which is essential for forced convection process

What is Newton's law of cooling?

The rate equations for convective heat transfer between a surface and an adjacent fluid is prescribed by Newtons law of cooling.

What is meant by free or natural convection?

It is fluid motion is produced due to change in density resulting from temperature gradients, the mode ofheat transfer is said to be free or natural convection.

Define Grashof number [Gr].

It is defined as the ratio of product of inertia force and buoyancy force to the square of viscous force. Gr =Inertia force x Buoyancy force / [Viscous force]