ou are designing an electric air heater for large conference rooms. A 75mm OD, 4mm wall thickness intake pipe sucks air into the unit at 2 m/s. The air passes over a 3m long heater coil and is exhausted at a temperature of 38degC. What is the average heat rate of the heater coil into the air?

ou are designing an electric air heater for large conference rooms. A 75mm OD, 4mm wall thickness intake pipe sucks air into the unit at 2 m/s. The air passes over a 3m long heater coil and is exhausted at a temperature of 38degC. What is the average heat rate of the heater coil into the air?

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.53P

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Question

You are designing an electric air heater for large conference rooms. A 75mm OD, 4mm wall thickness intake pipe sucks air into the unit at 2 m/s. The air passes over a 3m long heater coil and is exhausted at a temperature of 38degC. What is the average heat rate of the heater coil into the air?

Expert Solution

Step 1

Given Data:

The outer diameter of the pipe is D = 75 mm.
The wall thickness of the pipe is t= 4 mm.
The velocity of air is V = 2 m/s.
The exhaust temperature is $T_{e} = 38 ° C .$

The area of cross-section of pipe can be determined as,

$\begin{array}{rcl} A & = & \frac{π}{4} {(D - 2 t)}^{2} \\ = & \frac{π}{4} {(75 mm - 2 \times 4 mm)}^{2} \\ = & \frac{π}{4} {(68 mm)}^{2} \\ = & 3631.68 {mm}^{2} \end{array}$

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