Heat transfer tubes having dimples arranged between adjacent fins

A construction method for an evaporator of a heat recovery steam generator, the evaporator having at least one tube, the construction method comprising:

• forming a plurality of dimples in an outer surface defining a generally circular cross-section of the at least one tube sufficient to introduce turbulence in a flow of a gas in the heat recovery steam generator around the at least one tube for enhancing heat transfer from the gas to the at least one tube;
• forming one or more fins on the outer surface to further enhance heat transfer from the gas to the at least one tube;
• and
• wherein the plurality of dimples is formed in at least two rings that circumscribe the outer surface between adjacent ones of the one or more fins.

A combined cycle power plant comprising;

• a gas turbine;
• a first generator driven by the gas turbine for generating electricity, wherein during operation of the gas turbine exhaust gas is generated;
• a heat recovery steam generator disposed to receive the exhaust gas from the gas turbine, the heat recovery steam generator including an evaporator having at least one tube receptive to water flow there through, the at least one tube disposed to be exposed to the exhaust gas, wherein a flow of the exhaust gas passes around the at least one tube to transfer heat from the exhaust gas to the at least one tube and thereby the water flowing through the at least one tube sufficient for the water to evaporate into steam, the at least one tube having an outer surface defining a generally circular cross-section with a plurality of dimples formed therein sufficient to introduce turbulence in the flow of the exhaust gas for enhancing heat transfer from the exhaust gas to the at least one tube, the at least one tube including one or more fins projecting outward from the outer surface, the one or more fins being configured and disposed to further enhance heat transfer from the gas to the at least one tube, wherein the plurality of dimples is arranged in at least two rings that circumscribe the outer surface between adjacent ones of the one or more fins;
• a steam turbine receptive to the steam from the heat recovery steam generator for driving the steam turbine;
• and
• a second generator driven by the steam turbine for generating electricity.