To determine the value of the overall heat transfer coefficient for ammonia condensers, we need to consider various factors that affect heat transfer during condensation. The overall heat transfer coefficient (U) represents the combined effect of the resistance to heat transfer on both the coolant side and the process side of the condenser.

Factors affecting the overall heat transfer coefficient:
1. Heat transfer on the process side: The process side involves the condensation of ammonia vapor. The heat transfer coefficient on this side depends on several factors such as the physical properties of the ammonia, the surface area available for heat transfer, the condensation temperature, and the presence of any fouling or scaling on the heat transfer surface.

2. Heat transfer on the coolant side: The coolant side involves the flow of a cooling medium, such as water or air, that removes heat from the condenser. The heat transfer coefficient on this side depends on factors such as the flow rate, temperature difference between the coolant and the condenser, and the type of coolant used.

3. Overall design and configuration: The overall heat transfer coefficient can also be influenced by the design and configuration of the condenser, including the geometry of the heat transfer surface, the use of fins or tubes, and the presence of any additional heat transfer enhancement devices.

Explanation of the correct answer:
Option A states that the value of the overall heat transfer coefficient for ammonia condensers is in the range of 800-1400 W/m2K. This range is a reasonable estimate based on typical values for ammonia condensers. The actual value of the overall heat transfer coefficient will depend on the specific operating conditions and design parameters of the condenser.

Conclusion:
The overall heat transfer coefficient for ammonia condensers can vary depending on several factors. The correct answer, option A, provides a reasonable range of 800-1400 W/m2K for the value of the overall heat transfer coefficient.