Geothermal Rankine-cycle condensers

A major study of condensing on the outside of vertical enhanced tubes has been carried out at Oak Ridge National Laboratory in connection with geothermal Rankine cycle condensers. About 12 tubes were tested with ammonia, isobutane, and various fluorocarbons. The report by Domingo [163] on R-ll concluded that the best surface was the axially fluted tube, followed, in order, by the deep spirally fluted tube, spiral tubes, and roped tubes. The composite (vapor and tube wall) heat transfer coefficient was as much as 5.5 times the smooth-tube value. This high performance was further improved to a factor of 7.2 by using skirts to periodically drain off the condensate. 

A power plant operating on heat from a geothermal source uses isobutane as the wor medium in a Rankine cycle. Isobutane is heated at 3,400 kPa (a pressure just a little below its cri pressure) to a temperature of I40°C, at which conditions it enters the turbine. Isentropic expan- in the turbine produces superheated vapor at 450 kPa, which is cooled and condensed at cons pressure. The resulting saturated liquid enters the pump for return to the heater/boiler. If the rate of isobutane is 75kgs-1, what is the power output of the Rankine cycle and what are heat-transfer rates in the heater/boiler and condenser What is the thermal efficiency of the cy... 

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