Combined cycle power plant

A combined cycle power plant (10) includes at least one gas turbine (12), at least one steam turbine (14) and a heat recovery boiler (24) in combination to produce electricity and/or process steam. The heat recovery boiler (24) has a duct (28) for receiving and confining gas turbine exhaust gas (30) from the gas turbine (12). Heat transfer tubes (32) for heating water and steam (35) for use in the bottoming steam cycle (steam turbine and/or process steam) are disposed within the heat recovery boiler (24) and have exterior surfaces in fluid communication with the gas turbine exhaust gas (30) and interior surfaces in circulatory fluid communication with water and/or steam (35). A cellular material (40) is attached to the exterior surfaces of the heat transfer tubes (32) and operates to enhance heat transfer from the gas turbine exhaust gas (30) to the water and/or steam (35).