Add new feature: Implementation of incompressible binary mixtures

[fwitte]

This PR prepares the fluid property back-end for the usage of binary mixtures of incompressible fluids with fixed fractions. These are, for example, aqueous mixtures for freezing protection as used in ground source heat pumps. Furthermore, starting value generation requires an update/fix to enable usage of many incompressibles.

ToDo:

• [ ] Add method to specify mass fractions
• [ ] Add method to update fluid property value range according to mass fraction (i.e. CP.iT_freeze for lower temperature limit)
• [ ] Fix starting value generation
• [ ] Add tests
• [ ] Add documentation/example of usage

Variable fractions are not intended at the moment as this would require a lot of work on additional components and/or additional routines on existing components.

[fwitte]

Here is an example which works for the simulation, if you check out this PR. The print_results() method does not work!

# -*- coding: utf-8 -*-

from tespy.components import Compressor
from tespy.components import Condenser
from tespy.components import CycleCloser
from tespy.components import HeatExchanger
from tespy.components import Sink
from tespy.components import Source
from tespy.components import Valve
from tespy.components import Pump
from tespy.connections import Connection
from tespy.connections import Bus
from tespy.networks import Network
from tespy.tools.characteristics import CharLine
from tespy.tools.characteristics import load_default_char as ldc
from tespy.tools import document_model
from tespy.tools import ExergyAnalysis
from tespy.tools.fluid_properties import Memorise
import numpy as np
from CoolProp.CoolProp import PropsSI

# %% network
pamb = 1.013    # ambient pressure
Tamb = 2.8      # ambient temperature

Tgeo = 9.5      # mean geothermal temperature (mean value
                # of ground feed and return flow)

nw = Network(fluids=['water', 'NH3', 'INCOMP::MPG'], T_unit='C', p_unit='bar',
             h_unit='kJ / kg', m_unit='kg / s')

# Der erste Befehl setzt die Mischungsanteile
# Der zweite Befehl verändert die Temperaturgrenzen für das physikalische Modell (hängen von den Mischungsanteilen ab)
Memorise.state['MPG'].set_mass_fractions([0.2])
Memorise.value_range['MPG'][2] = PropsSI('T_freeze', 'INCOMP::MPG[0.2]')

# %% components

cc = CycleCloser('cycle closer')

# heat pump system
cd = Condenser('condenser')
va = Valve('valve')
ev = HeatExchanger('evaporator')
cp = Compressor('compressor')

# geothermal heat collector
gh_in = Source('ground heat feed flow')
gh_out = Sink('ground heat return flow')
ghp = Pump('ground heat loop pump')

# heating system
hs_feed = Sink('heating system feed flow')
hs_ret = Source('heating system return flow')
hsp = Pump('heating system pump')

# %% connections

# heat pump system
cc_cd = Connection(cc, 'out1', cd, 'in1')
cd_va = Connection(cd, 'out1', va, 'in1')
va_ev = Connection(va, 'out1', ev, 'in2')
ev_cp = Connection(ev, 'out2', cp, 'in1')
cp_cc = Connection(cp, 'out1', cc, 'in1')
nw.add_conns(cc_cd, cd_va, va_ev, ev_cp, cp_cc)

# geothermal heat collector
gh_in_ghp = Connection(gh_in, 'out1', ghp, 'in1')
ghp_ev = Connection(ghp, 'out1', ev, 'in1')
ev_gh_out = Connection(ev, 'out1', gh_out, 'in1')
nw.add_conns(gh_in_ghp, ghp_ev, ev_gh_out)

# heating system
hs_ret_hsp = Connection(hs_ret, 'out1', hsp, 'in1')
hsp_cd = Connection(hsp, 'out1', cd, 'in2')
cd_hs_feed = Connection(cd, 'out2', hs_feed, 'in1')
nw.add_conns(hs_ret_hsp, hsp_cd, cd_hs_feed)

# %% component parametrization

# condenser
cd.set_attr(pr1=0.99, pr2=0.99, ttd_u=5, design=['pr2', 'ttd_u'],
            offdesign=['zeta2', 'kA_char'])
# evaporator
kA_char1 = ldc('heat exchanger', 'kA_char1', 'DEFAULT', CharLine)
kA_char2 = ldc('heat exchanger', 'kA_char2', 'EVAPORATING FLUID', CharLine)
ev.set_attr(pr1=0.99, pr2=0.99, ttd_l=5,
            kA_char1=kA_char1, kA_char2=kA_char2,
            design=['pr1', 'ttd_l'], offdesign=['zeta1', 'kA_char'])
# compressor
cp.set_attr(eta_s=0.8, design=['eta_s'], offdesign=['eta_s_char'])
# heating system pump
hsp.set_attr(eta_s=0.75, design=['eta_s'], offdesign=['eta_s_char'])
# ground heat loop pump
ghp.set_attr(eta_s=0.75, design=['eta_s'], offdesign=['eta_s_char'])

# %% connection parametrization

# heat pump system
cc_cd.set_attr(fluid={'water': 0, 'NH3': 1, 'MPG': 0})
ev_cp.set_attr(Td_bp=3)

# geothermal heat collector
gh_in_ghp.set_attr(T=Tgeo+1.5, p=1.5, fluid={'water': 0, 'NH3': 0, 'MPG': 1},
                   offdesign=['v'], h0=22)
ev_gh_out.set_attr(T=Tgeo-1.5, p=1.5, design=['T'], h0=20)

# heating system
cd_hs_feed.set_attr(T=40, p=2, fluid={'water': 1, 'NH3': 0, 'MPG': 0})
hs_ret_hsp.set_attr(T=35, p=2)

# starting values
ev_cp.set_attr(p0=5)
cc_cd.set_attr(p0=18)

# %% power bus

# characteristic function for motor efficiency
x = np.array([0, 0.2, 0.4, 0.6, 0.8, 1, 1.2])
y = np.array([0, 0.86, 0.9, 0.93, 0.95, 0.96, 0.95])

char = CharLine(x=x, y=y)
power = Bus('power input')
power.add_comps({'comp': cp, 'char': char, 'base': 'bus'},
                {'comp': ghp, 'char': char, 'base': 'bus'},
                {'comp': hsp, 'char': char, 'base': 'bus'})

# %% key paramter

cd.set_attr(Q=-4e3)

# %% design calculation

path = 'NH3'
nw.solve('design')
# alternatively use:
# nw.solve('design', init_path = path)
print("\n##### DESIGN CALCULATION #####\n")
nw.print_results()
nw.save(path)

[jelic1marko]

Note to anyone interested in this issue, #294 has been proposed to implement changes in the backend as mentioned above by @fwitte and support the integration of incompressible binary mixtures.

[fwitte]

Close in favour of #294