Thermodynamics

Chapter 2ENERGY, ENERGY TRANSFER, ANDGENERAL ENERGY ANALYSISWhether we realize it or not, energy is an importantpart of most aspects of daily life. The quality of life,and even its sustenance, depends on the availabilityof energy. Therefore, it is important to have a good understandingof the sources of energy, the conversion of energyfrom one form to another, and the ramifications of these conversions.Energy exists in numerous forms such as thermal,mechanical, electric, chemical, and nuclear. Even mass canbe considered a form of energy. Energy can be transferred toor from a closed system (a fixed mass) in two distinct forms:heat and work. For control volumes, energy can also betransferred by mass flow. An energy transfer to or from aclosed system is heat if it is caused by a temperature difference.Otherwise it is work, and it is caused by a force actingthrough a distance.We start this chapter with a discussion of various forms ofenergy and energy transfer by heat. We then introduce variousforms of work and discuss energy transfer by work. Wecontinue with developing a general intuitive expression for thefirst law of thermodynamics, also known as the conservationof energy principle, which is one of the most fundamentalprinciples in nature, and we then demonstrate its use. Finally,we discuss the efficiencies of some familiar energy conversionprocesses, and examine the impact on energy conversionon the environment. Detailed treatments of the first lawof thermodynamics for closed systems and control volumesare given in Chaps. 4 and 5, respectively.ObjectivesThe objectives of Chapter 2 are to:• Introduce the concept of energy and define its variousforms.• Discuss the nature of internal energy.• Define the concept of heat and the terminology associatedwith energy transfer by heat.• Discuss the three mechanisms of heat transfer: conduction,convection, and radiation.• Define the concept of work, including electrical work andseveral forms of mechanical work.• Introduce the first law of thermodynamics, energy balances,and mechanisms of energy transfer to or from a system.• Determine that a fluid flowing across a control surface of acontrol volume carries energy across the control surface inaddition to any energy transfer across the control surfacethat may be in the form of heat and/or work.• Define energy conversion efficiencies.• Discuss the implications of energy conversion on theenvironment.| 51