Question

Consider two fluids, one with a large coefficient of volume expansion and the other with a small one. In what fluid will a hot surface initiate stronger natural convection currents? Why? Assume the viscosity of the fluids to be the same.

Short answer

Answer: The fluid with the larger coefficient of volume expansion would initiate stronger natural convection currents upon contact with a hot surface. This is because the larger expansion leads to a greater density difference in the fluid, which in turn creates stronger buoyancy forces driving the convection currents.

Step-by-step solution

Understanding Coefficient of Volume Expansion

The coefficient of volume expansion is a parameter that measures how much a fluid expands when its temperature increases. A larger coefficient of volume expansion means that the fluid will expand more when heated. In this exercise, we are comparing two fluids, one with a large coefficient of volume expansion and the other with a small one.

Understanding Natural Convection

Natural convection is the process of heat transfer in a fluid due to the differences in temperature within the fluid itself. When a fluid is heated, it expands, causing it to become less dense. This less dense fluid then rises since it is lighter than the surrounding fluid, while the cooler, denser fluid sinks. This circulation creates convection currents that help to transfer heat from the hot surface to the fluid.

Comparing the Fluids

Since both fluids have the same viscosity, we need to focus on how their coefficients of volume expansion affect the strength of natural convection currents. As a fluid with a larger coefficient of volume expansion is heated, it will expand more than a fluid with a smaller coefficient of volume expansion. This increased expansion will cause a larger density difference between the hot and cold regions of the fluid, leading to stronger buoyancy forces that drive the convection currents.

Conclusion

The fluid with the larger coefficient of volume expansion will initiate stronger natural convection currents when in contact with a hot surface. This is because the larger expansion leads to a greater density difference in the fluid, which in turn creates stronger buoyancy forces driving the convection currents.