Air Coolers in the Organic Rankine Cycle ORC System

Air Coolers in the Organic Rankine Cycle ORC System

The air cooler in an Organic Rankine Cycle (ORC) is one of the key components of the system responsible for cooling and condensing the circulating working fluid.ORC systems are typically used to convert low-grade heat sources (e.g., waste heat, geothermal heat, solar energy, etc.) into electricity, where the role of the air cooler is to cool the working fluid back to the liquid state during the heat exchange process so that it can re-enter the cycle.

Main functions and design features of ORC air coolers:

Cooling Medium:

Air coolers use air as the cooling medium. The air is forced through the cooling fin tube bundle via a fan and exchanges heat with the working fluid therein.

This design allows ORC systems to be deployed in areas where water resources are scarce, as water cooling is not required.

Principle of operation:

The hot organic work fluid enters the air cooler from the evaporator or turbine outlet of the ORC system, where the work fluid flows inside the tubes of the air cooler and the air flows on the outside of the tubes.

Through the walls of the tubes, the heat from the work mass is transferred to the air, causing the work mass to cool and condense into a liquid state, ready to be returned to be pumped to the evaporator for reheating.

Design Requirements:

Air coolers typically need to be designed as very large finned structures to compensate for the low specific heat capacity of air and its relatively low heat dissipation efficiency.

Air coolers are designed to maximise air flow, often with multiple large fans to enhance air convection and thus improve cooling efficiency.

Air coolers are often modularised to meet the needs of different sized ORC systems.

Environmental Impact:

Air cooler performance is significantly affected by ambient air temperature. In high ambient temperatures, where the air temperature is close to the condensing temperature of the mass, the cooling efficiency may be reduced.

To improve performance in hot climates, the air cooler may be designed with a larger area, or a more efficient fan system may be used to increase air flow.

Application Scenarios:

Air coolers are widely used in remote areas and where water resources are scarce, such as solar farms in deserts or geothermal farms where no water resources are available.