Mechanical Engineering - Heat Transfer, Refrigeration and Air Conditioning - Discussion

Convection is right answer. As they said molecular collision in the question so that it's mean that the movement of particle so that actual migration of particles are only seen in convection. Therefore the answer is convection.

It should be Conduction.

Conduction : molecular vibration.

Convection : molecular collision.

I think it's conduction.

Conduction is the right answer.

It must be conduction. Because in conduction molecules are closely packed. When one molecule is heated it vibrates higher than lower energised molecules or lower temperature molecules and collide with and finally transfer some energy to them. In this way heat transfer in solid by conduction.

The answer will be CONDUCTION.

Why is it convection and not conduction?

Conduction is the transfer of the heat through a solid object, liquid or gas. In order for the heat to be conducted, there should be physical contact between particles and some temperature difference. When one part of an object is heated, the molecules within it vibrate against one another, begin to move faster and more vigorously, when these molecules hit other molecules within the object they cause heat to be transferred through the entire object. Substances that conduct heat readily are called conductors, while substances that don't conduct heat readily are called insulators. Metal (e.g. copper, platinum, gold iron, etc) is a good conductor of thermal energy, aluminum is a good insulator. Wood falls somewhere in between. Conduction is greater in solids, where molecules are in constant contact.

As density decreases so does conduction. Therefore, fluids (and especially gases) are less conductive. This is due to the large distance between atoms in a gas, fewer collision between atoms means less conduction. Conductivity of gases increases with temperature. Conductivity increases with increasing pressure from vacuum up to a critical point that the density of the gas is such that molecules of the gas may be expected to collide with each other before they transfer heat from one surface to another. After this point density, conductivity increases only slightly with increasing pressure and density. In liquids (except liquid metals) and gases, the molecules are further apart, giving lower chance of molecules colliding and passing on the thermal energy.