Jökull - 01.12.1984, Page 43

we have obtained new information that allows a
more detailed description of the heat flow from
the geothermal system. The separation of the
geothermal component from the total mass as
expressed by the geothermal mass fraction k has
now added the third equation (Eq.(2) above).
The flow of mass to the Grímsvötn lake is the
sum of four components:
Mt = Mj + Mgw + Mgv + Ma (3)
where
M; is the mass flow of ice that is melted by
geothermal heat in the lake.
Mgw is the mass flow of geothermal water.
Mgv is the flow of mass in the form of vapour into
the lake.
Ma is the flow of water that is melted on the
surface of the glacier.
Heat is brought into the lake by the mass flow
of geothermal water (Mgw) and vapour (Mgv) and
some heat is conducted through the lake floor.
This heat melts a certain mass of ice (Mj) and
warms up this mass inside the lake together with
water that drains into the lake as surface ablation
(Ma). If we neglect the heat flow by conduction,
the energy equation can be written
Mgw c2(T3—T2)+MgV(Lv+C2(T3—T2)) =
MjtLj+cCTz—Tj))+ Ma C|(T2—Tj) (4)
where
Tt is the melting point of ice.
T2 is the temperature of the lake.
T3 is the temperature of the geothermal fluid
when it flows into the lake.
Cj and c2 represent the specific heat of water in
the respective temperature intervals.
L; is the Ltent heat of fusion for water.
L„ is the latent heat of vaporization of water.
We include the equation (2) from the discus-
sion of the chemical analyses.
Mgw + Mgv = k (Ma+Mj+Mr+Mgw+Mgv) (2)
in which k is the geothermal fraction and Mr is
the normal mass flow in the river Skeidará that
does not originate from Grímsvötn.
As we know Mt and Ma and Mr these three
equations can be used to estimate the mass of ice,
Fig. 9. Thermal power and steam ratio as
functions of the geothermal mass fraction. Res-
ults of calculations.
9. mynd. Reiknað varmaafl jarðhitasvœðisins í
Grímsvötnum (lóðréttur ás) miðað við hlut jarð-
hitavökva í heildarmassa vatns í Grímsvötnum
(láréttur ás). Aðskilinn er varmi frá vatni og gufu.
Efsti hluti myndarinnar sýnir hvernig gufuhluti í
jarðhitavökvanum breytist eftir því sem heildar-
massi jarðhitavökva vex.
geothermal water and vapour. The solution is
M; = (1—k)Mt - kMr - Ma (5)
JÖKULL 34. ÁR 41