Unit 61: Engineering Thermodynamics Unit code: D/601/1410 QCF level: 5 Credit value: 15 Aim This unit will extend learners knowledge of heat and work transfer. It will develop learners understanding of the principles and laws of thermodynamics and their application to engineering thermodynamic systems. Unit abstract This unit will build on learners understanding of polytropic expansion/compression processes, the first law of thermodynamics and the concepts of closed and open thermodynamic systems. Learners are then introduced to the second law of thermodynamics and its application in the measurement and evaluation of internal combustion engine performance. This is followed by measurement and evaluation of air compressor performance. Finally, learners will develop an understanding of the layout and operation of steam and gas turbine power plants. Learning outcomes On successful completion of this unit a learner will: 1 Understand the parameters and characteristics of thermodynamic systems 2 Be able to evaluate the performance of internal combustion engines 3 Be able to evaluate the performance of reciprocating air compressors 4 Understand the operation of steam and gas turbine power plant. BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010 281
Unit content 1 Understand the parameters and characteristics of thermodynamic systems Polytropic processes: general equation pv n = c, relationships between index n and heat transfer during a process; constant pressure and reversible isothermal and adiabatic processes; expressions for work flow Thermodynamic systems and their properties: closed systems; open systems; application of first law to derive system energy equations; properties; intensive; extensive; two-property rule Relationships: R = c p c v and γ = c p /c v 2 Be able to evaluate the performance of internal combustion engines Second law of thermodynamics: statement of law; schematic representation of a heat engine to show heat and work flow Heat engine cycles: Carnot cycle; Otto cycle; Diesel cycle; dual combustion cycle; Joule cycle; property diagrams; Carnot efficiency; air-standard efficiency Performance characteristics: engine trials; indicated and brake mean effective pressure; indicated and brake power; indicated and brake thermal efficiency; mechanical efficiency; relative efficiency; specific fuel consumption; heat balance Improvements: turbocharging; turbocharging and intercooling; cooling system and exhaust gas heat recovery systems 3 Be able to evaluate the performance of reciprocating air compressors Property diagrams: theoretical pressure-volume diagrams for single and multi-stage compressors; actual indicator diagrams; actual, isothermal and adiabatic compression curves; induction and delivery lines; effects of clearance volume Performance characteristics: free air delivery; volumetric efficiency; actual and isothermal work done per cycle; isothermal efficiency First law of thermodynamics: input power; air power; heat transfer to intercooler and aftercooler; energy balance Faults and hazards: effects of water in compressed air; causes of compressor fires and explosions 282 BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010
4 Understand the operation of steam and gas turbine power plant Principles of operation: impulse and reaction turbines; condensing; pass-out and back pressure steam turbines; single and double shaft gas turbines; regeneration and re-heat in gas turbines; combined heat and power plants Circuit and property diagrams: circuit diagrams to show boiler/heat exchanger; superheater; turbine; condenser; condenser cooling water circuit; hot well; economiser/feedwater heater; condensate extraction and boiler feed pumps; temperature-entropy diagram of Rankine cycle Performance characteristics: Carnot, Rankine and actual cycle efficiencies; turbine isentropic efficiency; power output; use of property tables and enthalpy-entropy diagram for steam BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010 283
Learning outcomes and assessment criteria Learning outcomes On successful completion of this unit a learner will: LO1 Understand the parameters and characteristics of thermodynamic systems Assessment criteria for pass The learner can: 1.1 evaluate polytropic process parameters 1.2 explain the operation thermodynamic systems and their properties 1.3 apply the first law of thermodynamics to thermodynamic systems 1.4 determine the relationships between system constants for an ideal gas LO2 Be able to evaluate the performance of internal combustion engines 2.1 apply the second law of thermodynamics to the operation of heat engines 2.2 evaluate theoretical heat engine cycles 2.3 evaluate the performance characteristics of spark ignition and compression ignition internal combustion engines 2.4 discuss methods used to improve the efficiency of internal combustion engines LO3 Be able to evaluate the performance of reciprocating air compressors 3.1 evaluate property diagrams for compressor cycles 3.2 determine the performance characteristics of compressors 3.3 apply the first law of thermodynamics to compressors 3.4 identify compressor faults and hazards LO4 Understand the operation of steam and gas turbine power plant 4.1 explain the principles of operation of steam and gas turbines 4.2 illustrate the functioning of steam power plant by means of circuit and property diagrams 4.3 determine the performance characteristics of steam power plant. 284 BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010
Guidance Links This unit has links with Unit 1: Analytical Methods for Engineers, Unit 2: Engineering Science and Unit 41: Fluid Mechanics. Essential requirements Laboratory facilities will need to be available for the investigation of the properties of working fluids, internal combustion engines and compressor performance. Employer engagement and vocational contexts Liaison with industry can help centres provide access to relevant industrial laboratory facilities, engines, compressors and related plant. Where possible, work-based experience should be used to provide practical examples of the characteristics of thermodynamic systems. A visit to a power station will be of value to support delivery of learning outcome 4. BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010 285
286 BH023332 Edexcel BTEC Levels 4 and 5 Higher Nationals specification in Engineering Issue 1 May 2010 Edexcel Limited 2010