Bài giảng Chapter 3: Compressor

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Nội dung Text: Bài giảng Chapter 3: Compressor

CHAPTER 3: COMPRESSOR Lecturer : ThS.Nguyễn g y Duyy Tuệ ệ 12/2015 Chapter 3 : Compressor 1
OBJECTIVES Student can: - Understand components and operation principles of some kinds of refrigerant compressor -UUnderstand de s a d thee e effect ec oof working o g co conditions d o s oon compressor’s efficiency 12/2015 Chapter 3 : Compressor 2
REFRERENCE [1]. Trane document - Compressor [1] [2]. Industrial refrigeration handbook – McGraw- Hill ( Chapter 4,5 45) 12/2015 Chapter 3 : Compressor 3
CONTENTS COMPRESSORS TYPES RECIPROCATING COMPRESSOR SREW COMPRESSOR SCROLL COMPRESSOR CENTRIFUGAL COMPRESSOR 12/2015 Chapter 3 : Compressor 4
COMPRESSOR TYPES Reference :(Page ( g 1,[1]) ,[ ]) The purpose of the compressor in a refrigeration y system is: 1/ to raise the p pressure of the refrigerant g vapor from evaporator pressure to condensing pressure. 2/ to remain the p p pressure in evaporator p 12/2015 Chapter 3 : Compressor 5
COMPRESSOR TYPES A review of the refrigeration g cycle, y , using g the pressure–enthalpy chart, will help to illustrate this p point. 12/2015 Chapter 3 : Compressor 6
COMPRESSOR TYPES There are p primarily y four types yp of compressors p used in the air-conditioning industry: reciprocating, scroll,, helical-rotaryy ((or screw), ), and centrifugal. g 12/2015 Chapter 3 : Compressor 7
COMPRESSOR TYPES We also classifyy to three types yp of compressor: p + Hermetic type compressor : 12/2015 Chapter 3 : Compressor 8
COMPRESSOR TYPES + Open p type yp compressor p : 12/2015 Chapter 3 : Compressor 9
COMPRESSOR TYPES + Semi-Hermetic type yp compressor p : 12/2015 Chapter 3 : Compressor 10
RECIPROCATING COMPRESSOR 1. Construction : Reference (p(page g 4,, [[1]) ]) The refrigerant vapor is compressed by a piston y , similar to the engine that is located inside a cylinder, g in an automobile. A fine layer of oil prevents the g refrigerant vapor p from escaping p g through g the mating g surfaces. 12/2015 Chapter 3 : Compressor 11
RECIPROCATING COMPRESSOR The ppiston is connected to the crankshaft byy a rod. As the crankshaft rotates, it causes the piston to y travel back and forth inside the cylinder. This motion is used to draw refrigerant vapor into the cylinder, p compress it,, and discharge g it from the cylinder. y 12/2015 Chapter 3 : Compressor 12
RECIPROCATING COMPRESSOR Crankshaft,, connecting g rod and oil ring g: 12/2015 Chapter 3 : Compressor 13
RECIPROCATING COMPRESSOR A ppair of valves,, the suction valve and the discharge valve, are used to trap the refrigerant p within the cylinder vapor y during g this p process. 12/2015 Chapter 3 : Compressor 14
RECIPROCATING COMPRESSOR Cylindrical valve 12/2015 Chapter 3 : Compressor 15
RECIPROCATING COMPRESSOR During g the intake stroke of the compressor, p , the piston travels away from the discharge valve and creates a vacuum effect,, reducing g the ppressure within the cylinder to below suction pressure. 12/2015 Chapter 3 : Compressor 16
RECIPROCATING COMPRESSOR Duringg the compression p stroke,, the ppiston reverses its direction and travels toward the g valve,, compressing discharge p g the refrigerant g vapor p and increasing the pressure within the cylinder. When the p pressure inside the cylinder y exceeds the suction pressure, the suction valve is forced closed, pp g the refrigerant trapping g vapor p inside the cylinder. y 12/2015 Chapter 3 : Compressor 17
RECIPROCATING COMPRESSOR - The compressor p possesses a certain p refrigerating capacity in kW (tons of refrigeration) p means that the compressor is capable p of p pumping p g the flow rate of refrigerant that will provide the g stated refrigeration capacity p y at the evaporator. p - The influences of evaporating and condensing p temperatures on the refrigerating g g capacity p y and power requirement of the compressor must be understood 12/2015 Chapter 3 : Compressor 18
RECIPROCATING COMPRESSOR 2. Effect of the evaporating p g temperature p on volumetric efficiency: (page 97, [2]) The volumetric efficiencyy of a compressor, p , ην in percent, is defined by the equation: The displacement rate is the volume rate swept g byy the p through pistons during g their suction strokes. 12/2015 Chapter 3 : Compressor 19
RECIPROCATING COMPRESSOR The volumetric efficiencyy is less than 100% because of such factors: - Leakage g ppast the p piston rings g - Pressure drop through the suction and g valves discharge - Heating of the suction gas when it enters the y cylinder byy the warm cylinder y walls - The reexpansion of gas remaining in the y cylinder following g discharge g 12/2015 Chapter 3 : Compressor 20