When incorporating a sub cooling zone in a high pressure heater, what is the intended purpose?

The intended purpose of incorporating a sub cooling zone in a high-pressure heater is to cool the condensate below the saturation temperature of the steam. This process is crucial in maximizing the efficiency of the heat exchange and ensuring that the condensate reaches a lower temperature before entering the feedwater system. By reducing the temperature of the condensate, it can absorb more heat from the steam, improving overall system thermal efficiency.

When the condensate is cooled to a temperature lower than the saturation point, this allows for optimal heat recovery from the steam in the heater. The result is a reduction in the energy required to bring the feedwater to the required temperature, resulting in fuel savings and more effective use of resources.

The other options do not accurately reflect the function of the sub cooling zone. For example, cooling feedwater above saturation temperature, warming up condensate above saturation temperature, or preventing overheating of the heater do not capture the main goal of enhancing heat recovery and improving efficiency through the cooling of the condensate.