functionality for subcooling and superheating

[fwitte]

Add functionality for setting subcooling oder superheating temperature. With this feature you are able to specify the temperature difference to boiling point (Td_bp). I have added an example code:

nw = nwk.network(['water', 'air'], T_unit='C', p_unit='bar', h_unit='kJ / kg')

so = cmp.source('so')
si = cmp.sink('si')

c = con.connection(so, 'out1', si, 'in1')

nw.add_conns(c)

c.set_attr(p=1, fluid={'water': 1, 'air': 0}, m=5, Td_bp=-5) # temperature is 5 K below boiling point

nw.solve('design')
nw.print_results()

c.set_attr(p=1, fluid={'water': 1, 'air': 0}, m=5, Td_bp=5) # temperature is 5 K above boiling point

nw.solve('design')
nw.print_results()

resolve #65

[fwitte]

I will add the option the predefine the state of pure fluids for connections using the keyword state. The convergence check manipulates enthalpy values for convergence stability, if the keyword state is passed.

Usage:

from tespy import cmp, con, nwk
import numpy as np

nw = nwk.network(['water'], T_unit='C', p_unit='bar', h_unit='kJ / kg')

so = cmp.source('so')
he = cmp.heat_exchanger_simple('he')
si = cmp.sink('si')

c1 = con.connection(so, 'out1', he, 'in1')
c2 = con.connection(he, 'out1', si, 'in1')

nw.add_conns(c1, c2)

he.set_attr(pr=0.99, Q=-10e3)

c1.set_attr(p=1, fluid={'water': 1}, T=120)
# the state is just above boiling point, an error in jacobian matrix is very likely
c2.set_attr(T=99.5)

nw.solve('design')

# using state='g' the convergence_check will keep the enthalpy values for
# this connection just above the wet steam area
c2.set_attr(state='g')
nw.solve('design')

[fwitte]

Merged.