3 1. heat transfer
TRANSCRIPT
3‐1. HEAT TRANSFER3 1. HEAT TRANSFER
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 1
3‐1. HEAT TRANSFER3 1. HEAT TRANSFER
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 2
3‐1. HEAT TRANSFER3 1. HEAT TRANSFER
Q
Heat Transfer per unit mass
(kJ/kg)m
Qq =
t2
∫⋅
Heat Transfer rate is denoted Q
(kJ)dtQQt1
∫=
Heat Transfer rate is denoted Q
(kJ)Q Δ=⋅
tQ
Heat Transfer rate is denoted Q
12ttt
( )Q
−=Δ
Q
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 3
Historical Background on Heatg
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 4
Energy transfer by WorkWork done per unit mass of system,w
W(kJ/kg)
m
Ww =
k d i i i ll dWork done per unit time is called power
kWorkJ/sW.•
kWorkJ/s,W
Path function have inexact differential designated b the s mbol δdesignated by the symbol δ
Exact differential designated by the symbol dsymbol d
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 5
The volume change during a process between states 1 and 2 is
VVVdV Δ=−=∫2
12
between states 1 and 2 is
∫1
12
Total work done during process 1‐2
)( WnotWW Δ=∫2
112δ
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 6
Electrical Work
VNWe =N คือปริมาณไฟฟาที่ผานจุดหนึ่งๆ โดยมีกระแส 1 แอมป แรงเคลือ่น 1 โวลตใน 1 นาที
(W).
VIWe = powerelectricaltheisWe
.
โดยทั่วไปแรงเคลื่อน และกระแสไฟฟาแปรผันตามเวลา
)(kJdtVIWe ∫=2
1
VและI คงที่
)(kJtVIWe Δ=
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 7
MECHANICAL FROMS OF WORK
)(kJFsW =
F is not constant
kJFdW ∫2
)(kJFdsW ∫=1
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 8
Moving Boundary Work
F is not constant
งานทีไ่ดจากการเคลือ่นที่ของขอบเขต
PdVPAdsFdsWb ===δ
F is not constant
(kJ)∫=2
PdVWb ( )∫1
b
The total area A under the processThe total area A under the process curve 1‐2 is obtained by adding these differential area
(kJ)∫∫ ===22
PdVdAAAera
these differential area
9
11
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 10
Moving Boundary Work
(kJ)∫=2
1
dVPW ib
Pi=Pressure is inner face of the pistonW = represent the amount of energy
1
Wb = represent the amount of energy transferred from the system during an expansion process p p
crankatmfrictionb WWWW ++=
dxFAPF crankatmfriction∫ ++=2
1
)(1
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 11
EXAMPLE 3‐5 A rigid tank contains air at 500 kPa and 150 °C . As aresult of heat transfer to the surroundings, the temperature andpressure inside the tank drop to 65 °C and 400 kPa, respectively.Determine the boundary work done during this processDetermine the boundary work done during this process.
Analysis: The boundary work can be determined fromAnalysis: The boundary work can be determined from eq. 3‐11 to be
2
12
0)(dv(kJ),02
1
=== ∫ PdVWb
EXAMPLE 3‐6 A frictionless piston‐cylinder device contains 4.5kg of water vapor at 0.4 MPa and 200 °C. Heat is nowg ptransferred to the steam unit the temperature reaches 250°C. If the piston is not attached to the shaft and its mass ispconstant, determine to work done by the steam during thisprocess.p
)()( 1212
2
0
2
VVmPWorVVPdVPdVPW oboib −=−=== ∫∫
13
11
kJkgmkPakgWb 62.109]/)5342.05951.0)[(400)(5.4( 3 =−=
EXAMPLE 3‐6: Isothermal Compression of an ideal gasA piston‐cylinder device initially contains 0.4 m3 of air at 100p y ykPa and 80 °C. The air is now compressed to 0.1 m3 in such away that the temperature inside the cylinder remainsy p yconstant. Determine the work done during this process.
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EAMPLE 3‐7
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Polytropic ProcessCPV n =
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by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 18
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 19
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 20
by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 21
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by Aj.Sanchai Ramphueiphad ,Program in Air Conditioning & RefrigerationDepartment of Mechanical Engineering
www.arc.rmuti.ac.th;Email:[email protected] 24