The Equivalent Diameter for Pressure Drop is Smaller than that for Heat Transfer

Explanation:
The equivalent diameter is a concept used in fluid mechanics to simplify the analysis of flow in non-circular ducts or pipes. It is defined as the diameter of a circular pipe that would have the same pressure drop or heat transfer characteristics as the non-circular duct or pipe under consideration.

Pressure Drop:
Pressure drop refers to the decrease in pressure that occurs as a fluid flows through a pipe or duct. It is influenced by factors such as fluid velocity, pipe geometry, and fluid properties. In non-circular ducts or pipes, the flow is generally more complex compared to circular pipes, which makes the analysis and calculation of pressure drop more challenging.

When determining the equivalent diameter for pressure drop, the aim is to find a circular pipe that would have the same pressure drop as the non-circular duct or pipe. Since non-circular ducts or pipes typically have more surface area compared to circular pipes, the equivalent diameter for pressure drop is usually smaller than the actual hydraulic diameter of the non-circular duct or pipe. This is because the flow in non-circular ducts or pipes experiences more frictional losses due to the increased surface area, resulting in a higher pressure drop.

Heat Transfer:
Heat transfer refers to the transfer of thermal energy between two bodies or systems. In non-circular ducts or pipes, heat transfer is influenced by factors such as fluid velocity, pipe geometry, and thermal properties of the fluid. The heat transfer characteristics in non-circular ducts or pipes can be more complex compared to circular pipes due to the irregular flow patterns.

Similar to pressure drop, the equivalent diameter for heat transfer aims to find a circular pipe that would have the same heat transfer characteristics as the non-circular duct or pipe. However, in heat transfer, the surface area plays a crucial role. Non-circular ducts or pipes generally have a larger surface area compared to circular pipes, which allows for more heat transfer. Therefore, the equivalent diameter for heat transfer is usually larger than the actual hydraulic diameter of the non-circular duct or pipe.

Conclusion:
In conclusion, the equivalent diameter for pressure drop is smaller than that for heat transfer. This is because the increased surface area in non-circular ducts or pipes leads to higher frictional losses and a higher pressure drop. On the other hand, the larger surface area allows for more heat transfer, resulting in a larger equivalent diameter for heat transfer.