Lesson 5 - Convection SAQ
This lesson allows you to test yourself on the material covered in the lesson on Convection, and to determine the level to which you have met the learning outcomes.
Self-Assessment Questions
1. * The film heat transfer coefficient is dependent on which of the following parameters?
a) The material of the heat transfer surface
b) The temperature of the heat transfer surface
c) The surface area of heat transfer
d) The viscosity of the fluid
2. * Provide short answers to the following:
a) Compare and contrast natural and forced convection.
b) Explain the difference between film boiling and nucleate boiling. Which is more desirable?
c) Why is it important that utility steam remains free from air?
d) Explain why turbulent flow in a heat exchanger is more desirable than laminar flow.
3. * Calculate the heat transfer rate due to convection in a pipe between water flowing within it at 90°C and the inside of the pipe wall at 10°C. The length of the pipe is 6.5 m with an inner diameter of 0.5 m. The film heat transfer coefficient is 1,020 W m-2 K-1.
4. ** The use of steam is the most common method for heating process fluids, usually indirectly via a heat exchanger or a jacket around the pipe or vessel. Describe the mechanisms by which steam can condense on cooler surfaces. What influences the mechanism that takes place? What are the relative film heat transfer coefficients that can be expected for each of these mechanisms? Explain why this is important for efficient heating.