Regenerative heating, which involves bleeding steam to reheat feed water in a boiler, has the effect of increasing the thermal efficiency of the cycle. This means that more of the input energy is effectively converted into useful work, resulting in improved overall efficiency.

Here is a detailed explanation of why regenerative heating increases thermal efficiency:

1. Introduction to regenerative heating:
Regenerative heating is a process in which a portion of the steam generated in a power cycle is extracted from the turbine and used to heat the feed water before it enters the boiler. This preheating of the feed water helps to increase the overall temperature of the working fluid entering the boiler, resulting in improved efficiency.

2. Explanation of the impact on thermal efficiency:
a) Preheating of feed water: By bleeding steam to reheat the feed water, the temperature of the water entering the boiler is increased. This reduces the temperature difference between the boiler and the surroundings, resulting in lower heat losses and improved efficiency.

b) Reduced moisture content: When steam is bled off and used to preheat the feed water, it also helps to reduce the moisture content of the steam entering the turbine. This is important because moisture in the steam can cause erosion and damage to the turbine blades. By reducing the moisture content, the efficiency and reliability of the turbine can be improved.

c) Increased mean temperature of heat addition: The process of regenerative heating increases the mean temperature at which heat is added to the working fluid. This is beneficial because the efficiency of a heat engine is directly proportional to the temperature difference between the heat source and the heat sink. By increasing the mean temperature of heat addition, regenerative heating helps to maximize the temperature difference and improve efficiency.

d) Improved utilization of heat: Regenerative heating allows for the effective utilization of waste heat from the turbine. Instead of being wasted, the heat is used to preheat the feed water, which increases the overall heat transfer in the cycle and improves efficiency.

3. Conclusion:
In summary, regenerative heating, which involves bleeding steam to reheat the feed water in a boiler, increases the thermal efficiency of the cycle. This is achieved by preheating the feed water, reducing moisture content, increasing the mean temperature of heat addition, and improving the utilization of waste heat.