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

Convection is right because conduction is due to molecular vibration not collision but convection is due to molecular collision.

Convection is right.

Convection is the right answer.

It's Convection.

Ref: Khurmi.

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.

No, it is the conduction mode of heat transfer. By collision molecules transfer energy from one to another. In convection mode, molecules themselves carry the heat from one place to another.

In conduction The molecules collide with surrounding molecules, making them vibrate too, resulting in the transportation of thermal energy to neighboring part of the object.

In convection heat transfer, by real movement of matter, that occurs only in fluids. Fluid alludes to any substance, whose molecules move freely from one place to another, such as liquid and gases. It happens naturally or even forcefully.

In radiation, The heat transfer mechanism in which no medium is required is called radiation.

So, I think the given answer is right.

Conduction:- displacement of molecules forming the substance.

Answer [A] is correct. Conduction heat transfer takes place by Molecular collision whereas Convection heat transfer is due to the Bulk motion of the fluid.

Conduction is defined as the heat by the direct collision of molecules.