Page 130 - Mechanical Engineers' Handbook (Volume 4)

1 Introduction 119

k thermal conductivity, W/(m K)
L length, m
m mass, kg
˙ m mass flow rate, kg/s
M mass, kg
N mole number, kmol
N ˙ molal flow rate, kmol/s
entropy generation number, S /S
N S
gen gen,min
Nu Nusselt number
number of heat transfer units
N tu
P pressure, N/m 2
Pr Prandtl number
q heat transfer rate per unit length, W/m
Q heat transfer, J
˙
Q heat transfer rate, W
r dimensionless insulation resistance
R ratio of thermal conductances
Reynolds number
Re D
s specific entropy, J/(kg K)
S entropy, J/K
entropy generation, J/K
S gen
S ˙ gen entropy generation rate, W/K
˙
S gen entropy generation rate per unit length, W/(m K)
˙
3
S entropy generation rate per unit volume, W/(m K)
gen
t time, s
time constraint, s
t c
T temperature, K
U overall heat transfer coefficient, W/(m K)
2
free stream velocity, m/s
U
3
v specific volume, m /kg
V volume, m 3
V velocity, m/s
˙
W power, W
x longitudinal coordinate, m
z elevation, m
P pressure drop, N/m 2
T temperature difference, K
first law efficiency
II second law efficiency
dimensionless time
viscosity, kg/(s m)
* chemical potentials at the restricted dead state, J/kmol
i
0,i chemical potentials at the dead state, J/kmol
2
kinematic viscosity, m /s
specific nonflow exergy, J/kg

nonflow exergy, J

nonflow chemical exergy, J
ch

t nonflow total exergy, J
density, kg/m 3