CONVECTION ( Heat Transfer – 2 )

By MacanyTech Editorials
Convection

Through this article, you are able to take a wide knowledge about the following aspects.

  • What is convection, Types of convection, Convection of heat in solids, liquids and in gases,  Examples for convection, Experiments based on convection
  • Laws and theories based on convection

Introduction

Convection is the heat transfer that occurs in moving fluids (liquids and gases), the movement of molecules from one part of a material to another. According to the thermodynamics, convection is the transport of internal energy. It is possible only in a fluid medium.

The convective heat transfer increases as the fluid or gas travels faster. Heat is transferred by the movement of molecules either gas or liquids. For any solid to gain or lose heat by convection, it must be in contact with the fluid. Convection cannot occur in a vacuum. In Maxwell’s point of view, convection is not a purely thermal phenomenon.

There are two types of convection methods.

  • Natural convection: Natural convection is also named as Free Conduction. Gravity is the driving force for natural convection. 

Examples: Rising clouds of cigarette smoke

  • Forced convection: Here, force is given to the fluid by a fan or pump to travel. Forced convection is occurred by either laminar flow or turbulent flow.

Examples:

  1. Air conditioning of the room – Here we force the moisturized air to move around the room.
  2. Hairdryer
Convection

Some other examples for convection:

  • Boiling water
  • Radiator
  • Ice melting
  • Wind is caused by convection

The rate of convective heat transfer depends on the following factors:

  • Type of the fluid
  • Surface temperature
  • Surface area
  • Speed of the flow across the surface

The rate of heat transfer is generally expressed as:

q=hA(Δt)

h – Heat transfer co – efficient (Wm-2K)

????t – Temperature driving force (K)

A – Heat transfer area

Heat transfer co – efficient (h)

The amount of heat transmitted for a unit temperature difference between the fluid and unit area of surface in unit time is known as the heat transfer co – efficient. The value of ‘h’ depends on the following factors:

  • Thermodynamic and transport properties (e.g., viscosity, density, specific heat etc.) 
  • Nature of fluid flow
  • Geometry of the surface 
  • Prevailing thermal conditions

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Here we come to the end of part 2. Stay tuned for the next part. We will publish it here on our website www.macanytech.com. For email notification please subscribe our news alert service.

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