Explanation:

Journal bearings are used to support rotating machinery such as turbines, pumps, and engines. They are designed to reduce friction and wear between the journal (rotating component) and the bearing (stationary component). The friction circle is a graphical representation of the contact area between the journal and the bearing. It is a circle that is tangent to the maximum and minimum bearing oil film thicknesses.

Effect of Journal radius on Friction Circle:

The radius of the friction circle is directly proportional to the radius of the journal. This means that as the radius of the journal increases, the radius of the friction circle also increases. The reason for this is that the contact area between the journal and the bearing increases with the increase in journal radius. This leads to an increase in the maximum and minimum oil film thicknesses, which in turn increases the radius of the friction circle.

Effect of Load on Friction Circle:

The load on the bearing also affects the friction circle. When the load increases, the oil film thickness decreases, which leads to a decrease in the radius of the friction circle. This can cause the journal to come in contact with the bearing, leading to wear and damage.

Effect of Speed on Friction Circle:

The speed of the journal has a significant effect on the friction circle. At high speeds, the oil film thickness decreases due to the shearing action of the oil, which leads to a decrease in the radius of the friction circle. This can cause the journal to come in contact with the bearing, leading to wear and damage.

Effect of Viscosity of Lubricant on Friction Circle:

The viscosity of the lubricant affects the oil film thickness, which in turn affects the friction circle. A higher viscosity lubricant will have a thicker oil film, which leads to a larger radius of the friction circle. On the other hand, a lower viscosity lubricant will have a thinner oil film, which leads to a smaller radius of the friction circle.

Conclusion:

In the given options, the correct answer is option A, i.e., the radius of the friction circle increases with the increase in radius of the journal. This is because the contact area between the journal and the bearing increases with the increase in journal radius, which leads to an increase in the maximum and minimum oil film thicknesses, and ultimately an increase in the radius of the friction circle.