Page 370 - Mechanical Engineers' Handbook (Volume 4)

Nomenclature 359

heat pipes. The capillary limit, sonic limit, entrainment limit, or boiling limit governs the
heat transport limitation. Of those operating limits, the capillary limit from the low surface
tension is the primary factor affecting the heat-transfer performance in the cryogenic heat
pipes. For this reason, considerable effort has been conducted to develop wicking structures
that further increase the capillary limitation.

NOMENCLATURE
A cross-sectional area, m 2
C constant
c specific heat, J/kg-K
d diameter, m
ƒ friction factor
F correction factor
g gravitational acceleration, m/s 2
h ƒg latent heat, J/kg
k thermal conductivity, W/m-K
1
K curvature, m ; permeability, m 2
L length, m
Ma Mach number
˙ m mass flow rate, kg/s
N mesh number
r radius, m
R universal constant, J/kg-K
p pressure, N/m 2
P perimeter, m
q heat transfer, W
q heat flux, W/m 2
Re Reynolds number
s coordinate, m
S crimping factor
T temperature, C
u vertical velocity, m/s
u average velocity, m/s
We Weber number
x coordinate, m
y coordinate, m
z coordinate, m

Greek Symbols
contact angle, degree
film thickness, m
porosity
ratio of specific heats
tilt angle, degree
dynamic viscosity, N-s/m 2
mass density, kg/m 3
surface tension, N/m
shear stress, N/m 2