Convective heat transfer refers to the transfer of heat between a solid surface and a fluid medium through the combined mechanisms of conduction and fluid motion (convection). The direction of heat transfer, as well as the rate at which it occurs, can be influenced by the properties of the fluid and the surface involved.
When considering convective heat transfer between water and air, there are some key differences to take into account:
Heat transfer coefficient: The convective heat transfer coefficient, often denoted as "h," represents the rate of heat transfer per unit area. In general, the convective heat transfer coefficient for air is lower than that for water. This is primarily due to the lower thermal conductivity and specific heat capacity of air compared to water. Consequently, when heat is transferred from water to air, the convective heat transfer coefficient will be higher on the water side.
Density and viscosity: Water is denser and has a higher viscosity than air. This has an impact on the convective heat transfer process. The higher density and viscosity of water result in slower fluid motion and more resistance to flow compared to air. Consequently, convective heat transfer from water to air tends to be less efficient and slower than from air to water.
Heat capacity: Water has a higher specific heat capacity than air, meaning it can absorb and retain more heat energy per unit mass. As a result, water is generally more effective at carrying and transferring heat compared to air. Therefore, when heat is transferred from water to air, it takes more energy to raise the air temperature by a given amount compared to transferring the same amount of heat from air to water.
Temperature differences: Temperature differences between the solid surface and the fluid medium also play a role in convective heat transfer. Typically, when transferring heat from water to air, there is a larger temperature difference between the two media. This temperature difference promotes a higher rate of heat transfer according to Newton's law of cooling.
Overall, the differences in convective heat transfer between water and air stem from variations in their thermal properties, such as heat transfer coefficients, density, viscosity, specific heat capacity, and temperature differences. These differences influence the efficiency and rate at which heat is transferred between the two media.