Design Calculation of a Shell-and-Tube Condenser in the ORC Unit Operating on Pentane

Units implementing the organic Rankine cycle (ORC) can utilize dozens of low-boiling substances, also called freons or refrigerants, as the working fluid. However, the classic solution for this cycle is the application of pentane and, therefore, this technology is sometimes called pentanoic. One of the main elements of the ORC unit circuit is the condenser, which is often a shell-and-tube heat exchanger cooled with circulating water. In spite of wide application of such apparatuses in steam turbine units, the elaboration of their design on the basis of the pentane technology is a challenging problem. For a prototype of this apparatuses, the KTR shell-and-tube condenser, which was previously often employed in refrigeration units with R12 refrigerant, is adopted in this work. Since chlorofluorocarbons and hydrochlorofluorocarbons have been phased out, equipment items intended for their application are also no longer manufactured by industry, which resulted in a shortage of information on their design and peculiarities of their design process. Hence, the authors carried out a search for and analysis of information about such apparatuses and developed and verified a procedure of design calculation of this equipment. In addition, models for calculating the heat-transfer coefficient during pentane condensation on tube bundles with rolled fins were reviewed, and these models were verified against experimental data on the condensation of propane, one of the closest homologues of pentane. The model proposed by A. Briggs and J.W. Rose has been found to yield the highest accuracy in engineering calculations of pentane condensers. Other models are also examined, which describe the effects of vapor shear and inundation of the lower tubes in the bundle on the heat-transfer coefficient during pentane condensation. It has been demonstrated that considering these effects during condensation of pentane and its homologues in the examined apparatus is impractical. The results of the design calculation of shell-and-tube condensers of pentane with a capacity of 173- and 2280-kW are presented. Recommendations for further optimization calculations are formulated.