What is Convection Heat Transfer?

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Convection Heat Transfer requires a solid-fluid interface, a temperature difference between the solid surface and the surrounding fluid, and a motion of the fluid. We all see heat transfer in our daily lives. Thermal energy (heat) is exchanged between physical systems in the heat transfer process. Conduction heat transfer, convection heat transfer, radiation heat transfer, and energy transfer via phase changes are all examples of heat transfer mechanisms. When the bulk flow of a fluid (gas or liquid) transfers its heat through the fluid, it is called convection heat transfer.

Diffusion is used in part by all convective processes to transfer heat. External processes can push fluid flow, or buoyancy forces can influence fluid flow (for example, in gravitational fields) when heat energy expands the fluid (for example, in a fire plume). “Natural convection” is a term used to describe the latter process. The former is commonly referred to as “forced convection.” A pump, fan, or other mechanical device is used to force the fluid to flow in this scenario. Let’s take a closer look at convection heat transfer, including the concepts behind it and some real-life examples.

Download Formulas for GATE Mechanical Engineering- Heat Transfer

What is Convection Heat Transfer?

The process of heat transfer through the bulk movement of molecules inside fluids such as gases and liquids is known as convection heat transfer. The initial heat transfer between the body and the fluid occurs by conduction, but the bulk of the heat transfer occurs owing to fluid motion.

The process of heat transfer in fluids through the actual motion of materials is known as convection heat transfer.

  • It occurs in both liquids and gases.
  • It could be natural or forced.
  • It involves the mass transfer of fluid portions.

Thermal expansion occurs when a fluid is heated from below. The fluid’s density decreases as it cools in the lower layers, which are hotter. Colder fluid is denser, as we all know. The less-dense, hotter section of the fluid rises due to buoyancy. It is replaced by a colder, denser fluid. When this component heats up and rises to be replaced by the colder upper layer, the process is repeated. Convection is used to transfer heat in this way.

Download Formulas for GATE Mechanical Engineering – Refrigerating and Air Conditioning

Types of Convection Heat Transfer

Convection heat transfer occurs when the fluid is heated at a lower level. As a result of the buoyancy mechanism, the fluid below becomes less dense and the hotter component rises. The heated fluid takes the place of the denser, cooler fluid. When that section heats up and rises, the process repeats. As a result, it shifts back to the colder upper layer. Heat is transferred through convection in this manner. Convection can be divided into two types:

  • Natural or free convection
  • Forced convection

Natural or Free Convection

when the fluid moves due to buoyancy forces induced by density fluctuations caused by temperature variations in the fluid When a fluid comes into touch with a heated surface in the absence of an internal source, its molecules separate and scatter, making the fluid less dense. As a result, the fluid is displaced, and the cooler fluid becomes denser, sinking the fluid. As a result, the hotter volume of the fluid transfers heat to the cooler volume. The upward flow of air caused by a fire or a hot object, as well as the circulation of water in a heated pot from below, are both well-known instances.

Download Formulas for GATE Mechanical Engineering – Thermodynamics

Forced Convection

Convection is created by external systems such as pumps and fans, and this is referred to as forced convection. Forced convection can be seen in the use of a geyser or water heater to heat water, as well as the use of a fan in the summer.

Newton’s Law of Cooling

Newton’s law of cooling defines the rate equation for convective heat transfer between a surface and an adjacent fluid. Mathematically,

Convection Heat Transfer Formula

dQ/dt = hA(ts-tf)


  • dQ/dt = Heat transfer rate
  • A = Area exposed to heat transfer
  • ts= Surface temperature
  • tf= Fluid temperature
  • h = Coefficient of convective heat transfer or convection heat transfer coefficient

Convection Heat TransferCoefficient

The value of the coefficient of convective heat transfer or convection heat transfer coefficient ‘h’ depends on the following factors

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

Convection Heat Transfer Example

We can see the various example of heat transfer by convection in our day-to-day life. A few common convective heat transfer examples are given below:

  • Boiling Water
  • Radiator
  • Hot Air Popper
  • Refrigerator
  • Breeze
  • Blood Circulation in Warm-Blooded Mammals
  • Air-Conditioner
  • Hot Air Balloon
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