IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C2-A, November 9, 2009
Proceeding from the sumps to the tube bundles, the mass flow balance yields
Generator: m & − m&
− m&
0
(19)
sol, wA,
i−c2
vG,
i sol,
tb,
G,
i
=
Absorber: m & + m&
− m&
0
(20)
sol, sG,
i−c1
vA,
i sol,
tb,
A,
i
=
The salt flow balances of the tube bundles read
Generator: m & ⋅ x − m&
⋅ x 0
(21)
sol, wA,
i−c2
wG , i−c2
sol,
tb,
G,
i sG,
i
=
Absorber: m & ⋅ x − m&
⋅ x 0
(22)
sol, sG,
i−c1
sA,
i−c1
sol,
tb,
A,
i wA,
i
=
Pressure drop
The strong solution flow from generator to absorber is driven by gravity and a pressure
difference. The pressure loss of the solution heat exchanger and its adjacent piping is
assumed constant which is a good approximation as long as the flow variations are not too
large; hence the mass flow of the strong solution depends only on the pressure difference
between generator/absorber and the liquid solution column at heat exchanger inlet. This
assumption, of course, can be refined in future works. During operation, the static pressure
of the liquid column has to equal the dynamic pressure loss caused by flow restrictions
through piping and solution heat exchanger. The mass flow of the strong solution can
therefore be calculated as
( p − p + ρ ⋅ g ⋅ ( h + z ))
2 ⋅ ρsol,
s
⋅
G,
i A,
i sol,
s
i
m& sol,
s,
i
= At
⋅
, (23)
ς
where generator/condenser and evaporator/absorber pressure are calculated using the
equation of Clausius-Clapeyron as shown in equation (24). There, the pressure and
temperature values of solution interval (i-1) are being used to calculate the values of
simulation interval i. This is a valid approximation as long as the time between two simulation
intervals,
∆ t , is not too long.
⎛ p
X , i
⎞ r ⎛
⎞
⎜ ⎟
0
= ⋅⎜
1 1
ln ⎟
−
(24)
⎝ p
X , i−1
⎠ R ⎝ TX
, i−1
TX
, i ⎠
Thermal storage
page 69