tailieunhanh - Ebook Fundamentals of engineering thermodynamics (4th edition): Part 2

(BQ) Part 2 book "Fundamentals of engineering thermodynamics" has contents: Refrigeration and heat pump systems; thermodynamic relations; ideal gas mixtures and psychrometrics applications; reacting mixtures and combustion; chemical and phase equilibrium. | C H A P 10 chapter objective ᭤ T E R Refrigeration and Heat Pump Systems E N G I N E E R I N G C O N T E X T Refrigeration systems for food preservation and air conditioning play prominent roles in our everyday lives. Heat pumps also are used for heating buildings and for producing industrial process heat. There are many other examples of commercial and industrial uses of refrigeration, including air separation to obtain liquid oxygen and liquid nitrogen, liquefaction of natural gas, and production of ice. The objective of this chapter is to describe some of the common types of refrigeration and heat pump systems presently in use and to illustrate how such systems can be modeled thermodynamically. The three principal types described are the vapor-compression, absorption, and reversed Brayton cycles. As for the power systems studied in Chaps. 8 and 9, both vapor and gas systems are considered. In vapor systems, the refrigerant is alternately vaporized and condensed. In gas refrigeration systems, the refrigerant remains a gas. ᭢ Vapor Refrigeration Systems The purpose of a refrigeration system is to maintain a cold region at a temperature below the temperature of its surroundings. This is commonly achieved using the vapor refrigeration systems that are the subject of the present section. CARNOT REFRIGERATION CYCLE To introduce some important aspects of vapor refrigeration, let us begin by considering a Carnot vapor refrigeration cycle. This cycle is obtained by reversing the Carnot vapor power cycle introduced in Sec. . Figure shows the schematic and accompanying T–s diagram of a Carnot refrigeration cycle operating between a region at temperature TC and another region at a higher temperature TH. The cycle is executed by a refrigerant circulating steadily through a series of components. All processes are internally reversible. Also, since heat transfers between the refrigerant and each region occur with no temperature differences, there are no .