Heat Transfer Lab. Experiment 3

EXPERIMENT NO.3

OBJECT: To calculate the value of heat transfer coefficient from the fin and to determine efficiency, effectiveness of pin-fin in Forced Convection.

INTRODUCTION: Extended surfaces of fins are used to increase the heat transfer rate from a surface to a fluid wherever it is not possible to increase the value of the surface heat transfer coefficient or the temperature difference between the surface and the fluid. Circumferential fins around the cylinder of a motor cycle engine and fins attached to condenser tubes of a refrigerator are a few familiar examples.

It is obvious that a fin surface sticks out from the primary heat transfer surface. The temperature difference with surrounding fluid will steadily diminish as one move out along the fin. The design of the fins therefore required knowledge of the temperature distribution in the fin. The main objective of this experimental set up is to study temperature distribution in a simple pin fin.

APPARATUS: A brass fin of circular cross section in fitted across a long rectangular duct. The other end of the duct is connected to the suction side of a blower and the air flows past the fin perpendicular to the axis. One end of the fin projects outside the duct and is heated by a heater. Temperature is measured at five points along the length of the fin. The air flow rate is measured by an orifice meter fitted on the delivery side of the blower.

SPECIFICATIONS:
Diameter of fin (D) = 12 mm
Length of fin (L) = 150 mm
Width of duct (b) = 150 mm
Height of duct (w) = 100 mm
Orifice Diameter (d) = 20 mm
Orifice discharge Coefficient (Cd) = 0.6
Thermal conductivity of fin material (k) = 109 W/mK
Perimeter of fin = 0.0377 m
Cross section area of fin = 0.000113 m2
Orifice Area, Aorf = 0.00031416 m2
Duct Area, Ad = 0.015 m2
Heater: 250W, 220V.

FORMULAS:

If h is average heat transfer coefficient from fin surface to surrounding, general equation of one dimensional heat flow for uniform k and h is given by

Boundary conditions:

a) At x=L, dT/dx=0 (Insulated)

b) At x=0, T = Ts

The heat loss by the fin is then given by

Fin Performance Parameters:
Two basic measures of fin performances are particularly useful in fin designing

OBSERVATIONS: 

Voltage reading, V =   (Volts)

Ammeter reading,I =    (Amperes)

Orifice Pressure drop h_water =   (mm)        Thermal Conductivity of air at film temperature T_f, k_air =      W/mK    

Density of air at film temperature T_f, ρ_air = kg/m³

Dynamic viscosity of air at film temperature T_f, =     kg/ms

Prandtl No. of air, Pr = 0.712

T_air = T₆ =        ºC

CALCULATION:
Average surface temperature of the fin

The fluid properties are evaluated at the film temperature given by

Reynold Number 

Where V is average velocity of air in the duct, given by V=Volume Flow rate (Discharge)/Duct Area

H_w = Difference of water levels in U-tube manometer

Re =

 Efficiency =

Effectiveness =

PRECAUTIONS: 

1. Operate the changeover switch of temperature indicator, gently.
2. Make sure that the steady state is reached before taking the final reading.
3. See that throughout the experiment, the blower is ON

 RESULT: 

 DISCUSSION: 

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