Very small work of pump

Hi Ludwig,

First of all thank you very much for building this model!

I think i get a wrong value when runnning the base_model_LiBr. I use the following values as input;

`if not external_input:

working_fluid = "LiBr_H2O"  # Choose the working fluid ("NH3_H2O" or "LiBr_H2O")

cycle_model = "base"        # Choose the cycle_model ("base", "DE" or "DL")

save_as_csv = "False"        # Save the results as .csv? ("True" or "False")

#THESE VALUES CAN AND SHOULD BE CHANGED DEPENDING ON INPUT AND OUTPUT REQUIREMENTS
# External temperature boundary conditions
# Heat source temperature
T.ext_des_in = 51 + 273.15
# Cold output temperature
T.ext_evap_out = 5 + 273.15
# Heat sink temperature
T.ext_abs_in = 20 + 273.15
T.ext_cond_in = 20 + 273.15

# WE SET THESE VALUES TO DEFAULT VALUE
# Heat exchanger PP temperature differences
HX.T_PP_evap = 3
HX.T_PP_abs = 5
HX.T_PP_des = 5
HX.T_PP_cond = 5
HX.SC_cond = 0          # Defines subcooling at condenser
HX.T_PP_SHEX = 5
HX.T_PP_RHEX = 100
HX.T_PP_SHEXI = 5       # Only necessary for DE and DL
HX.T_PP_cond_int = 5    # Only necessary for DE
HX.dT_ref_des = 5       # Defines superheating of refrigerant after desorber
HX.dT_ref_desI = 5      # Defines superheating of refrigerant after desorber I

# Defining which heat flow will be provided. Q_evap or Q_des?
s.requirement = "Q_des"

# Value of heat flow
Q.dec = 10000

# Efficiency of the pump
eta.pump = 0.85`

OUTPUT: ----Q:---- 0 propertie dec 10000.000000 Q SHEX 1746.455428 Q cond -8886.868568 Q evap 8629.744195 Q abs -9742.918718 Q des 10000.000000 Q RHEX 0.000000 Q ----Q:---- 0 propertie W_pump 4.309051e-02 PP COP 8.629707e-01 PP COP_rev 1.597025e+00 PP zeta_thermodynamic 5.403613e-01 PP my_throttle 2.186934e-02 PP f 1.615597e+01 PP energyBalance -1.818989e-12 PP massBalance -1.387779e-17 PP

What i find curious is that the work of the pump is so small compared to the evap capacity Q_evap = 8629.7 and W_pump = 4.3E-2. I looked at other papers on the internet and found that a ratio of evap_cap/W_pump = 20-50. Do you know what could be the cause, have you ever experienced such values?

Thank you

Hi Melbatoastje,

I apreciate your interest for the models and am looking forward to help you with any questions regarding the modelling.

The small pump work is an issue which I experienced myseld. The pump efficiency can be varied to get an more realistic value. With the way the pump power consumption is calculated (volumetric efficiency) only very small pump efficiencies lead to realistic values. Alternative ways for pump power consumption could be implemented.

Generally I think the models are not able to predict pump power consumption very well and you are best advised to use evap_cap/W_pump ratios from the literature and experimental inverstigations.

If you have ideas or implement an alternative power consumption calculation, let me know.

BR, Ludwig

LudwigIrrgang / SorpPump

Very small work of pump #1