Heat and cold storage with PCM An up to date introduction into basic
Latent heat storage with phase change materials (PCM) has the potential to improve significantly the efficiency of heat and cold storages and to reduce their size considerably. The book is an introduction into the field for researchers and students. It su
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Other common units units
A
m2
area
C
J/kg⋅K, J/m3⋅K, J/mole⋅K
heat capacity
c
C/mass, …
specific heat capacity per mass, per volume, or per amount
CR
mg/m2yr
corrosion rate
d
m
thickness
H
J
enthalpy
h
J/kg, J/m3, J/mol
specific enthalpy per mass, per volume, or per amount
k
W/m2K
overall heat transfer coefficient
m
kg
mass
mol
mol
f
fraction of mass, volume, or amount
amount of matter / number of molecules
n
integer number
P
J/s = W
kW
p
Pa
bar (=105 Pa) pressure
Q
J
kWh
dQ/dt W (=J/s) dV/dt m3/s
power heat heat flux
liters/s
volume flow rate
dq/dt
W/m2
heat flux density
r, R
m
radius
Rth
K/W
thermal resistance
S
J/K
entropy
s
m
location of the phase front
T
°C
temperature
ΔT
K
temperature difference
+
dimensionless ratio of radiuses
s
t
s
U
J
min, hour
time
u
m/s
V
m3
x,y,z
m
Cartesian space coordinates
α
W/m2K
convective heat transfer coefficient
internal energy flow speed liter (=10-3 m3) volume
(Continued)
298
10 Appendix
Table 10.1. (Continued) Si-units
α
m2/s
β
K/s
Other common units units thermal diffusivity K/min
heating rate
β
dimensionless ratio of thermal resistances
η
N⋅s/m2
λ
W/mK
thermal conductivity
ρ
kg/m3
density
viscosity
Because of the frequent use of h as enthalpy, it would be confusing using also h as convective heat transfer coefficient. To avoid confusion, a different notation described in the following table is used throughout the book to describe heat transfer. Generally, the heat flux dQ/dt and the heat flux density dq/dt are related by dQ/dt = A ⋅ dq/dt. Table 10.2. Notation for heat transfer. effect
sketch
Heat transT fer dQ/dt through an area A by conduction ΔT
Notation often used
Notation here
dQ / dt = Q&
dQ / dt = Q&
= A⋅ k ⋅
ΔT Δx
= A⋅λ ⋅
ΔT Δx
k = thermal conductivity
λ = thermal conductivity
dQ / dt = Q&
dQ / dt = Q&
x Δx Heat transfer dQ/dt from an area A by convection
T
= A ⋅ hconv ⋅ ΔT
= A ⋅ α ⋅ ΔT
hconv = convection heat transfer α = convection heat transfer coefficient coefficient
ΔT x
10 Appendix
effect
Notation often used
sketch
Overall T heat transfer dQ/dt through an area A, for ΔT example by convection on the surface and conduction inside
dQ / dt = Q&
299
Notation here
dQ / dt = Q&
= A ⋅ U ⋅ ΔT = A ⋅ k ⋅ ΔT 1 / U = 1 / hcond + Δx / λ 1 / k = 1 / α + Δx / λ + 1/ α + 1 / hcond x
U = overall heat transfer coef- k = overall heat transfer coefficient ficient, or just U-factor R = 1/U overall thermal resistance, or just R-value with
dQ / dt = Q& = A ⋅ 1 / R ⋅ ΔT
300
10 Appendix
Table 10.3. Subscripts a, amb ambient air
air
bp
boiling point
eff
effective
el
electric
f
fusion
i, j
integral numbers
in
ingoing
lm
logarithmic mean
max
maximum value
min
minimum value
mol
molar
mp
melting point
obj
object
out
outgoing
p
at constant pressure
pc
phase change
r
reference
s
sample
st
standard
th
thermal
V
at constant volume
wall
wall
water water Table 10.4. Superscripts. a
air
amb ambient CV
con
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