Principles of naval engineering - Historic Naval Ships Association

Chapter 8-INTRODUCTION TO THERMODYNAMICSWORK OUT; THERMALENERGY OF STEAMCONVERTED TO MECHANICALENERGY IN TURBINESCONDENSATEPUMPTHERMAL ENERGY OFAUXILIARY STEAMCONVERTED TOMECHANICAL ENERGYTHERMAL ENERGY OFAUXILIARY EXHAUST STEAMUSED HERE TO HEAT ANDDEAERATE FEED WATER:FEEDmT6ipipspiiipp?S^i^Figure 8-18.— Energy relationships in the basic propulsion cycle of conventional steam-driven ship.38.2propulsion cycle of a conventional steam-drivenship with geared turbine drive and shows someof the major energy transformations that takeplace.The first energy transformation occurs whenfuel oil is burned in the boiler furnace. By theprocess of combustion, the chemical energystored in the fuel oil is transformed into thermalenergy. Thermal energy flows from the hot combustiongases to the water in the boiler. Whilethe boiler stop valves are still closed, steambegins to form in the boiler; the volume of thesteam remains constant but the pressure andtemper atuire increase, indicating a storage ofinternal energy. When operating pressure isreached and the steam stop valves are opened,the high pressure of the steam causes it to flowto the turbines. The pressure of the steam thusprovides the potential for doing work; the actualconversion of heat to work takes place in theturbines. The changes in internal energy betweenthe boiler and the condenser (as evidencedby changes in pressure and temperature) indicatetliat heat has been converted to work in the turbines.The work output of the turbines turns theshaft and so drives the ship.Two main energy transformations are involvedin converting thermal energy to work inthe turbines. First, the thermal energy of thesteam is transformed into mechanical kineticenergy as the steam flows through one or morenozzles. And second, the mechanical kinetic189