Final answer:
The correct option is d. The factors on which natural convective heat transfer depends are variation of temperature on the surface, orientation of the surface, and geometry of the surface.
Step-by-step explanation:
The factors on which the natural convective heat transfer on a surface depends are:
- Variation of temperature on the surface: The greater the temperature difference between the surface and its surroundings, the higher the rate of convective heat transfer. This is because a larger temperature difference leads to a stronger buoyancy force, which drives fluid motion and convective heat transfer.
- Orientation of the surface: The orientation of the surface affects the rate of convective heat transfer. For example, a vertical surface will have higher convective heat transfer compared to a horizontal surface due to natural convection caused by density differences in the fluid.
- Geometry of the surface: The geometry of the surface also affects convective heat transfer. Different geometries can create different flow patterns and affect the heat transfer rate. For example, fins or protrusions on a surface can enhance convective heat transfer by increasing the surface area and promoting fluid mixing.
Therefore, the correct option is d. geometry of the surface as well as its orientation.