## Info

3.27 An elemental solid has a heat capacity of 1 J/mole-K. What is the atomic weight of the element?

Chap. 4 Heat Engines, Power Cycles, and the Thermodynamics of Open Systems

4.1 Heat Engines 1

4.1.1 Single device - sequential states - ideal gas 2

4.1.2 Four devices - circulating fluid - water 4

4.1.3 The First law for heat engines 5

4.2 The Second Law applied to heat-engine cycles 5

4.3 The Carnot Cycle 7

4.4 Thermodynamics of open systems 9

4.4.1 The First law for open (flow) systems 10

4.4.2 The Second Law for open systems 12

4.4.3 Reversible Work of a Flow System 13

4.5 Practical power cycles 13

4.5.1 The Rankine cycle - a steam power plant 14

4.5.2 The Brayton cycle - a gas turbine 20

4.5.3 Refrigeration cycle (heat pump) 21

4.4 Flow Devices Without Shaft Work 23

4.6.1 Orifice or valve - water 24

4.6.2 Nozzle- ideal gas 24

4.7 Summary: properties of flow devices 26

References 26

Problems 27

### 4.1 Heat Engines

In Sect. 1.9, it was noted that the First law regards heat and work as completely interchangeable; if a certain number of Joules of heat added to a system increases the internal energy of a body by, say, AU, the same number of Joules of work performed on the body would produce the same AU. In addition, work can be completely converted to heat, as everyday experience with friction attests. However, the reverse is not true; heat cannot be completely transformed into work. This limitation, which is a consequence of the Second law, is best demonstrated by studying the properties of heat engines.

A heat engine is a system operating in a cycle that receives heat from a high-temperature source (called a reservoir) and produces useful work. However, since the efficiency of conversion must be less than 100%, some of the input heat is rejected to a cold reservoir. Figure 4.1 shows a schematic of a heat engine/heat pump and their associated thermal reservoirs.

Cold reservoir

## Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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