Types of Heat Transfer: Convection

len Alfred Ajibola - Thu, 26th December, 2019 @ 5:25 PM

Topics in Physics

Derived Units: Similarities and differences with fundamental units Gravity: Facts on Gravity Relative Density of Substances and Specific Gravity Types of Heat Transfer: Conduction Types of Heat Transfer: Convection Types of Heat Transfer: Radiation Physics Scheme of Work, SS1, First Term Physics Scheme of Work, SS1, Second Term Physics Scheme of Work, SS1, Third Term Velocity and Acceleration Newton's Laws of Motion Importance of Gravity What is Density? Density of various substances Concepts of Force and Motion in Physics Motion and Speed in Physics Concept of Heat Transfer Concepts of Heat and Temperature What is gravity? Concept of gravity on the solar system Zeroth Law of Thermodynamics: Thermal Equilibrium Fundamental Quantities and Units in Physics

Academic Questions in Physics

Please click here to see all Questions and Answers

Which of the following is a fundamental quantity?

  • A. Luminous Intensity

  • B. Area

  • C. Volume

  • D. Velocity

  • E. Concentration

  • F. Acceleration

An object at rest will temporarily stay in its state of rest, and if the object is in uniform motion, it will temporarily move in a straight line, unless an external force acts upon it.

The above statement refers to Sir Isaac Newton's first law of motion.

  • A. True

  • B. False

Which of the following statement is incorrect concerning gravity?

  • A. The force of gravity is generally considered the strongest force among the four forces that govern the universe

  • B. Your weight changes as you travel away from the earth

  • C. If we dig the earth until we get into its center, we will have no weight as a result of lack of gravity

  • D. Gravity prevents us from falling off the constantly rotating earth

  • E. If a hammer and a feather are dropped simultaneously in a vacuum, they will both land at the exact same time as a result of gravity

  • F. Weight is always a function of gravity

Isaac Newton Hit by Apple - Len Academy

Sir Isaac Newton was hit by an apple when he pondered on force, motion and gravity.

  • A. True

  • B. False

The movement of gaseous particles through a tiny hole is termed _____.

  • A. Osmosis

  • B. Diffusion

  • C. Effusion

  • D. Infusion

  • E. Defusion

  • F. Gaslusion

A lighted bulb transfers heat through a process termed _____.

  • A. Conduction

  • B. Convection

  • C. Radiation

  • D. Oxidation

  • E. Reduction

  • F. Electrical Induction

A measurement of how much the velocity of an object changes with time is termed _____.

  • A. Displacement

  • B. Acceleration

  • C. Speed

  • D. Momentum

  • E. Velocity-Time graph

  • F. Average velocity

Which of the following differentiates velocity from speed?

  • A. Distance

  • B. Time

  • C. Momentum

  • D. Inertia

  • E. Direction

  • F. Distance and Time

Heat Transfer: Convection:

Convection is a process of transferring heat from one point to another through the movement of fluids. The points below are noteworthy with regards to heat transfer through convection:

  1. A conductor or metal is usually required to transfer heat into the liquid before the boiling process can proceed through convection.

  2. Convection explains the transfer of heat in liquids and gases.

  3. The boiling process of water occurs through convection.

Please read on the concept of heat transfer here.

Below is an explanation on the processes involved in boiling:

  • The water molecules inside the pot (yet to be boiled) possesses equal kinetic energy.
    Please read on liquids and their characteristics here.
  • When placed on a heat medium, for instance, gas cooker; the water molecules closest to the bottom and margins of the pot will begin to move or rotate as a result of heat transfer by conduction from the metallic pot. This is so because the pot is a metal and a conductor. As a result, the water molecules (closest to the bottom and margins of the pot) becomes hot.
    Please read more on heat transfer by conduction here.
  • Due to the hotness of the water molecules closest to the bottom and margins of the pot, they expand and become lighter, thus gaining an increased ability to move (due to an increase in their average kinetic energy). As a result of their increased kinetic energy, they move to the top and center of the pot, displacing the water molecules that were initially there to the bottom.

The displacement of water molecules in the above paragraph is as a result of the difference in density of water molecules closest to the bottom and margins of the pot versus those at the top/center. Those closer to the bottom/margins of the pot are less dense (or lighter) than those at the top/center. This displacement movement of water molecules is sometimes referred to as the convection current.

You can read on density and specific gravity here.

The image below shows the convection current during the process of boiling:
Heat Transfer by Convection - Len Academy

The water molecules at the top and center of the pot have a higher density since they are farther away from the bottom and margins of the pot. Also, they have a lower kinetic energy when compared to those at the bottom and margins. They are therefore displaced downwards (since they have higher density and lower kinetic energy) by the water molecules at the bottom and margin of the pot which had now moved upwards and inwards.

The above process continues until the entire water molecules attain the same kinetic energy. At this point, thermal equilibrium is said to be achieved.

Please read more on thermal equilibrium and zeroth law of Thermodynamics here.

If the pot (containing the boiling water) remains on the cooking gas, the increased kinetic energy of the water molecules will eventually lead to the escape of water particles into the atmosphere via translational motion. At this point, the water in the pot reduces until nothing is left. This emptiness (of the pot) is a result of an increased kinetic energy of the 'now' gaseous particles. Understand that the water had changed its state from liquid to gas by now.

Please read on gaseous particles, their behavior and characteristics here.

When heating a liquid, the heat energy produced by the particles of higher kinetic energy stimulates the liquid particles of lower kinetic energy (to an increased kinetic energy or rotational motion) until equilibrium is achieved.
Please read on the concept of heat transfer here to better comprehend translational, rotational and vibrational movements in particles).

It is important to understand that convection is the main method of heat transfer in water and air.

Please read on heat transfer through radiation here.

The process of increasing a room's atmospheric (or air) temperature through the use of a radiator occurs via convection. The image below shows this:

Heat Transfer in Air by Convection - Len Academy

With regards to convection in air particles (using the above diagram); When we put on the heater or hot radiator (assuming it’s on the floor), the kinetic energy of the air particles closest to the heater will become increased.

The particles of this 'hot air' move upwards and sideways, mixing with the cooler air in these regions.

The net result of this rising hot air is the transfer of heat energy from a higher region to a lower region.

It is important to state that convection is achieved via the translational and rotational movement of matter. Translational and rotational movements are involved in gases and liquids respectively; and they result in the transfer of heat energy.

Meanwhile, always understand that convection is not achieved through the vibrational movement seen in solids.

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Amazing facts in Physics

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A medium-sized cumulus cloud has a weight of about 80 adult elephants.

You can think of cumulus cloud as a detached, individual, cauliflower-shaped cloud often seen in fair weather conditions

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The Nobel price was named after its founder, Alfred Noble. He is a Swedish, born on October 21, 1833; and was the inventor of dynamite. He was also a a famous scientist and a successful business man.

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Glass balls bounce higher than rubber balls

Every planet has its own unique gravitational force. For instance, Mars has a gravity of 3.711 m/s2 while earth’s gravitational force is 9.807m/s2.

When two metals are put together in space, they will stick together as if they are welded. This phenomenon is called cold welding

The fastest animal on land is cheetah. It can reach a maximum speed of about 113km per hour.

Notable points in Physics

If one covers a distance of 10,000 meters in 50 seconds and another covers the same distance in 5,000 seconds, we can conclude that the first person has a greater speed because he covered the same distance at a lesser time.

  • Speed is defined as distance travelled per unit of time. It can also be defined as the rate of change of distance.

Speed = distance/Time

Speed is a scalar quantity since it has only magnitude. Speed does not have a direction.

In physics, motion is defined as a change in the position of an object with reference to time.

Although we sometimes sit or stand in a fixed position, that doesn’t mean motion isn’t taking place. The fact that the earth is constantly rotating implies that we are indirectly moving along with it. We can thus say that motion can be relative to some frame of reference.

In the above paragraph, the earth (constantly rotating along its axis) is our frame of reference and everything present on earth is in motion (with regard to earth as a frame of reference).

Please read on the concepts of motion and speed here

Heat is a form of energy. It cannot be lost according to the first law of Thermodynamics; rather it will be transferred. The first and second laws of thermodynamics are stated below:

  • Energy can neither be created nor destroyed but can be transformed or converted from one form to another.

    1st law of thermodynamics

  • In the course of energy transfer, some energy is lost in the form of heat to the surroundings.

    2nd law of Thermodynamics

Please read on the concept of heat transfer here

If we have water of 100OC  in an aluminium cup whose temperature is the same as that of its surrounding; let’s say 22OC; We will observe the followings:

  1. The temperature of water inside the aluminum cup will begin to decrease from its initial 100OC.

  2. The temperature of the aluminium cup will increase from its previous 22OC.

  3. After some time, the temperature of the water, aluminium cup and the surrounding will become the same.

From the above instance, it can be deduced that the heat present in the water molecules are first transferred to the aluminium cup and subsequently to the surrounding.

Heat from water >> Aluminium Cup >> Surrounding

Meanwhile, understand that aluminium is a metal; and metals are good conductors of heat.

Eventually, the system (water and aluminum cup) together with the surrounding reaches the same temperature; and the heat transfer ceases. It is at this point that the water, aluminium cup and the surroundings are said to have reached a thermal equilibrium.

Please on the concept of heat and temperature here

Heat is never static. It is always transferred and thus: an object will increase its temperature by gaining heat energy from its surroundings while another object will simultaneously decrease its temperature by losing its heat energy to the surroundings. For this reason, we may also define temperature as:

The measure or ability of an object or substance to transfer heat energy to another object or substance.

The higher the temperature, the greater the ability of an object or substance to transfer heat. Conversely, the lower the temperature, the greater the tendency of an object to receive the transferred heat.

The point is: 'for heat to be transferred, we must have systems or objects or substances with varying temperatures