Thermodynamics

Heat Transfer Convection

You must have observed that a hot glass of water will get cold at some time. It happens as the heat gets lost to the environment. Hence, we can say that heat transfer is the transferring of thermal energy between two physical systems.  In case of temperature difference, the heat gets transferred from a hot system to a colder one. However, there are three types of heat transfer- convection, conduction, and radiation. In this blog, you will find details about heat transfer convection.

heat transfer convection

Introduction to Heat Transfer convection

According to the Principle of heat transfer, the exact definition of Convection is “The procedure of heat transfer with the motion of molecules in fluids like liquids and gases. In the starting, the heat transfer between fluid and object takes place via conduction. However, bulk heat transfer occurs with the movement of fluid.”

Important points to remember

  • Liquids and gases are bad conductors of heat in normal situations. Although, they transfer heat with ease.
  • The heat transfer in this method takes place via advection, diffusion, or both.
  • Convection does not occur in solids as there is no movement of particles. In solids, the heat gets transferred through diffusion, known as thermal conduction.

How does Heat transfer Through the Process of Convection?

The thermal expansion occurs on the heating of the fluid at the lower level. Thus, the fluid below becomes less dense and the hotter portion rises due to the process of buoyancy. The hot fluid replaces denser and colder fluid. The process repeats itself when that portion gets heated and rises. Therefore, it changes again by the colder upper layer. In this way, heat transfers via convection.

heat transfer convection

The Kinds of Convection Heat

Mainly, there are two kinds of heat transfer convection that are seen during the energy release.

These are:

a) Forced Convection b) Natural convection.

heat transfer convection

                                                             Types of Convection

Natural convection- The convection occurring due to buoyant force with the distinction in densities caused by the distinction in temperature is called natural convection. The oceanic wind is an example of natural convection.

Forced convection- The external systems like pumps and fans create convection and is called forced convection. The geyser or water heater for heating of water and use of a fan in summer are some examples of forced convection.

The link between the forced convection with Newton’s law of cooling

P= dq/dt= hA (T-T0)

Where,

P= dq/dt is the rate at which heat gets transferred.

H is the coefficient of convection heat transfer

A is exposed surface area

T is immersed object temperature

T0 is the fluid temperature under convection

  • Value of h is based on viscosity, density, thermal conductivity, and specific heat capacity

Ideal Examples of Heat Transfer Convection

The easiest and most common examples of natural convection are land and sea breeze.

Sea breeze- It occurs in the day time. The sun heats both land and sea. Moreover, the sea with greater heating capacity absorbs more Sun energy but warms up slower than the land surface. Hence, the temperature above land increases and heats the air. Moreover, warm air expands as it is less dense and creates low pressure over the land near shore. The air pressure difference leads the air to flow from sea to land. Finally, we refer to the sudden wind as a sea breeze.

Land breeze- The process happens at night. The sea and land get cool. Thus, the land loses heat rapidly than water due to heat capacity difference. The sea temperature is higher that results in low air pressure. A cool breeze is known as the land breeze.

FAQ on Heat Transfer Convection

Question 1: What is the reason for the occurrence of Heat Transfer?

Answer 1: When heated particles move and replace the cooler particles, the process of Heat transfer begins. Thus, the heated particles emit energy that gradually transfers into the cooler particles through convection current. Thus, it results in the heating of the particles. We refer to this as Heat Transfer mechanism.

Question 2: What are the types of heat transfers?

Answer 2: The three types of heat transfer are:

  1. Radiation
  2. Conduction
  3. Convection

Question 3: Why is Convection faster than Conduction?

Answer 3: Conduction is a static process where heat is transferred from one medium to the other. However, in the case of Convection, the heat is transferred via the motion of the air. As a result of the individual working principle, convection is a faster way of heat transfer than conduction.

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