Multi-Circuited Evaporator¶

In an evaporator, there is always the possibility that the distribution of refrigerant or air may be unequal between the circuits, which usually results in lower evaporator performance. In the case of equal distribution between circuits, the analysis of the Evaporator can be used, otherwise the multi-circuited evaporator is needed. The multi-circuited evaporator (MCE) analyzed as being a set of evaporators, each comprising one circuit, that are then each fed fed some (not necessarily even) distribution of refrigerant and air.

Mathematical Description¶

The MCE model is capable of handling the following types of maldistribution:

Volumetric air flow mal-distribution
Air-side inlet condition mal-distribution
Refrigerant mass-flow-per-circuit mal-distribution
Refrigerant quality-per-circuit mal-distribution

For the MCE, there are $N_{circuits}$ circuits, and each circuit is treated as an individual evaporator, since then the analysis for each circuit can be provided by the analysis for the conventional evaporator with one circuit.

For the MCE, the total refrigerant mass flow rate $\dot m_r$ is known as an input (which arises from the compressor map). The total refrigerant mass flow rate per circuit can be given by

$\dot m_{r,i} = \gamma _i \dot m_r$

where $\gamma_i$ is the mass flow distribution factor for the i-th circuit of the evaporator. The sum of the indices is given by

$\sum_{i=0}^{N_{circuits}-1}[\gamma_i]=1$

and if the flow is equally distributed, all the terms $\gamma_i$ are equal.

If the inlet refrigerant quality is not balanced between circuits, the refrigerant vapor mal-distribution can be given by a set of weighting parameters that distribute refrigerant vapor among the circuits. The total amount of vapor entering the evaporator can be given by

$\dot m_v=x\dot m_r$

and the amount of vapor entering the i-th circuit can be given by

$\dot m_{v,i}=\xi_i \dot m_v$

where the factors $\xi_i$ also must sum to unity. The inlet quality for each circuit is then equal to

$x_i=\frac{\dot m_{v,i}}{\dot m_{r,i}}$

where all the $x_i$ values must be greater than zero. The evaporator component model takes enthalpy as the inlet, which can be calculated from

$h_i=h(p_{evap},x_i)$

using the CoolProp property routines.

MCE Sample Code¶

Minimal Component Test:

from FinCorrelations import FinInputs
from Evaporator import EvaporatorClass
from MultiCircuitEvaporator import MultiCircuitEvaporatorClass
from CoolProp.CoolProp import Props

FinsTubes=FinInputs()

FinsTubes.Tubes.NTubes_per_bank=32
FinsTubes.Tubes.Ncircuits=5
FinsTubes.Tubes.Nbank=3
FinsTubes.Tubes.Ltube=0.452
FinsTubes.Tubes.OD=0.009525
FinsTubes.Tubes.ID=0.0089154
FinsTubes.Tubes.Pl=0.0254
FinsTubes.Tubes.Pt=0.0219964

FinsTubes.Fins.FPI=14.5
FinsTubes.Fins.Pd=0.001
FinsTubes.Fins.xf=0.001
FinsTubes.Fins.t=0.00011
FinsTubes.Fins.k_fin=237

FinsTubes.Air.Vdot_ha=0.5663
FinsTubes.Air.Tmean=299.8
FinsTubes.Air.Tdb=299.8
FinsTubes.Air.p=101.325
FinsTubes.Air.RH=0.51
FinsTubes.Air.RHmean=0.51
FinsTubes.Air.FanPower=438
    
#This uses the normal baseline evaporator model
kwargs={'Ref': 'R410A',
        'mdot_r':  0.0708,
        'psat_r':  Props('P','T',282.0,'Q',1.0,'R410A'),
        'Fins': FinsTubes,
        'hin_r':Props('H','T',282.0,'Q',0.15,'R410A')*1000,
        'Verbosity':0
        }
Evap=EvaporatorClass(**kwargs)
Evap.Calculate()
print 'Evap Q=' + str(Evap.Q) + ' W'
    
#This uses the multi-circuited evaporator model but with no mal-distribution
kwargs={'Ref': 'R410A',
        'mdot_r':  0.0708,
        'psat_r':  Props('P','T',282.0,'Q',1.0,'R410A'),
        'Fins': FinsTubes,
        'hin_r':Props('H','T',282.0,'Q',0.15,'R410A')*1000,
        'Verbosity':0
        }
MCE=MultiCircuitEvaporatorClass(**kwargs)
MCE.Calculate()
print 'MCE Q='+str(MCE.Q)+' W w/o mal-distribution'
#Not exactly the same since 

# This uses the multi-circuited evaporator model with mal-distribution of 
# refrigerant, refrigerant quality, and air volumetric flow rate
kwargs={'Ref': 'R410A',
        'mdot_r':  0.0708,
        'psat_r':  Props('P','T',282.0,'Q',1.0,'R410A'),
        'mdot_r_coeffs': [0.3,0.2,0.1,0.2,0.2],
        'mdot_r_coeffs': [0.4,0.2,0.1,0.2,0.1],
        'Vdot_ha_coeffs': [0.3,0.2,0.2,0.2,0.1],
        'Fins': FinsTubes,
        'hin_r':Props('H','T',282.0,'Q',0.15,'R410A')*1000,
        'Verbosity':0
        }
MCE=MultiCircuitEvaporatorClass(**kwargs)
MCE.Calculate()
print 'MCE Q='+str(MCE.Q)+' W w/ mal-distribution'

If you open an IPython(x,y) shell in the root of the documentation (folder Documentation/Web relative to the main trunk), and run the commands below, you should get

In [6]: execfile('ACHPComponents/ComponentTests/MCETest.py')
Evap Q=13222.5359037 W
MCE Q=13199.5742675 W w/o mal-distribution
MCE Q=12126.0551536 W w/ mal-distribution

If not, first stop should be the Frequently Asked Questions

Component Class Documentation¶

class MultiCircuitEvaporator.MultiCircuitEvaporatorClass(**kwargs)[source]¶

Calculate()[source]¶

OutputList()[source]¶

Return a list of parameters for this component for further output

It is a list of tuples, and each tuple is formed of items:: [0] Description of value [1] Units of value [2] The value itself

Update(**kwargs)[source]¶

Multi-Circuited Evaporator¶

Mathematical Description¶

MCE Sample Code¶

Component Class Documentation¶

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Multi-Circuited Evaporator¶

Mathematical Description¶

MCE Sample Code¶

Component Class Documentation¶

Table Of Contents

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Next topic

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