American Journal of Mathematical and Computational Sciences 2016; 1(1): 18-28 http://www.aascit.org/journal/ajmcs Keywords Condensation, Heat Exchangers, Air Cooled, Modeling, Refrigeration, Numerical Received: March 8, 2016 Accepted: March 21, 2016 Published: May 13, 2016 A Numerical Rating Model for Thermal Design of Air Cooled Condensers in the Industrial Applications Ali Hussain Tarrad 1, * , Ali F. Altameemi 2 , Deyaa M. Mahmood 3 1 Private Consultant, Thermal Engineering Specialist, Copenhagen, Denmark 2 Mechanical Engineering, Adhwa Alshamal Contracting and General Trading, Baghdad, Iraq 3 Technical Training Department, Technical Institute, the Foundation of Technical Institutes, Baghdad, Iraq Email address [email protected] (A. H. Tarrad), [email protected] (A. F. Altameemi), [email protected] (D. M. Mahmood) * Corresponding Author Citation Ali Hussain Tarrad, Ali F. Altameemi, Deyaa M. Mahmood. A Numerical Rating Model for Thermal Design of Air Cooled Condensers in the Industrial Applications. American Journal of Mathematical and Computational Sciences. Vol. 1, No. 1, 2016, pp. 18-28. Abstract The thermal assessment of a water chiller air cooled condenser is outlined in the present work. The steady state experimental data of a water chiller unit was implemented to build a tube by tube model to investigate the louvered finned tube air cooled condenser performance. The refrigerants selected for this object were R-22, R-134a, R-404A and R- 407C for the ambient dry bulb temperature range of (24 – 46)°C. The validation of the present numerical model for pure and zeotropic mixtures showed a reasonable agreement between experimental and those predicted values. The maximum scatter between experimental and predicted condenser duty was within (±8)% for R-22, R-134a and R- 407C refrigerants. The predicted condenser exit air temperature showed a lower scatter for these refrigerants to be within (±4)%. The model prediction for R-404A refrigerant underestimated the heat duty and exit air dry bulb temperature by (30)% and (15)% respectively. 1. Introduction Fischer and Rice (1981) [1] developed a model for a heat pump system including condenser and evaporator finned tube heat exchanger. The condenser was divided into three regions; superheated, two-phase (condensation) and sub-cooled. Each region was analyzed separately using effectiveness NTU method. Domanski and Didion (1983) [2] presented a model of evaporator and condenser finned tube heat exchanger in a heat pump systems. The model based on tube-by-tube approach. The model assumes a uniform air distribution and assigns the same air mass flow rate for each tube. Domanski (1989) [3] developed a computer simulation program of modeling evaporator finned tube heat exchanger for air conditioning system. The model has one dimension air distribution, each tube was assumed to have uniform air distribution over its entire length. The percentage of discrepancy between the experimental and predicted total cooling capacity was (-6%). Zietlow et al. (1992) [4] developed a scheme model of condenser finned tube heat exchanger for mobile air conditioning unit. In this model the total length of the condenser was divided into few segments which are further divided into several models,
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American Journal of Mathematical and Computational Sciences
2016; 1(1): 18-28
http://www.aascit.org/journal/ajmcs
Keywords Condensation,
Heat Exchangers,
Air Cooled,
Modeling,
Refrigeration,
Numerical
Received: March 8, 2016
Accepted: March 21, 2016
Published: May 13, 2016
A Numerical Rating Model for Thermal Design of Air Cooled Condensers in the Industrial Applications
Ali Hussain Tarrad1, *
, Ali F. Altameemi2, Deyaa M. Mahmood
3
1Private Consultant, Thermal Engineering Specialist, Copenhagen, Denmark 2Mechanical Engineering, Adhwa Alshamal Contracting and General Trading, Baghdad, Iraq 3Technical Training Department, Technical Institute, the Foundation of Technical Institutes,
1. A simple and detailed air cooled condenser model has
been developed for pure and mixture refrigerants R-22,
R-134a, R-407C and R-404A.
2. The present model provided detailed information for the
condenser design and performance characteristic. It
offers a practical tool for the rating process of an
existing water chiller for refrigerant alternatives.
3. The model showed excellent agreement for the load
capacity and exit air temperature for the simulation of
R-22, R-134a and R-407C to be within (±8)% and
(±4)% respectively. The model underestimated the heat
load and exit air temperature for R-404A by (30)% and
(15)% respectively.
4. The model revealed its ability to predict the same trend
of the condenser heat duty in a similar fashion as that of
the refrigeration load of the water chiller measured
during the experiments.
American Journal of Mathematical and Computational Sciences 2016; 1(1): 18-28 27
Nomenclature
Symbol Description Units
A Area m2
Ac Cross sectional area m2
Af Fin area m2
Amin Minimum flow area m2
Ao Total heat transfer area on the air side m2
At Surface area of the tubes m2
ast Kays & London coefficient ---
bst Kays & London power coefficient ---
C Heat capacity W/K
cp Specific heat at constant pressure kJ/kg.K
Cr Heat capacity ratio ---
Dc Collar diameter m
Ddep Depth of heat exchanger m
DH Hydraulic diameter m
D Diameter m
Fj Lanced fin enhancement multiplier ---
G Mass flux kg/m2.s
g Gravitational acceleration m/s2
hfg Latent heat J/kg
j Colburn j-factor ---
j4 j-factor for four rows ---
k Thermal conductivity W/m.°C
L Length of tube m
ls Width of a stripe m
m˙ Mass flow rate kg/s
mes Extended surface parameter ---
N Number of rows ---
Nf Number of fins ---
Nt Number of tubes ---
Nu Nusselt number ---
ns Number of strips ---
P Pressure Pa
Pr Reduced pressure ---
Pr Prandtle number ---
Q Heat transfer W
Re Reynolds number ---
Re Fin equivalent radius m
Rf Fouling factor m2.°C/W
Rw Tube resistance m2.°C/W
ro Outside tube radius m
St Stanton number ---
S Fin spacing m
ss Length of a strip m
T Temperature °C
Tdew Dew point temperature °C
tf Fin thickness m
U Over all heat transfer coefficient W/m2.°C
V Velocity m/s
XL Longitudinal tube spacing m
XT Transverse tube spacing m
X Vapor quality ---
Zg
Ratio of the sensible cooling of the
vapor to the total cooling rate ---
Greek Symbols:
α Heat transfer coefficient W/m2.°C
αeff Effective heat transfer coefficient W/m2.°C
ε Effectiveness ---
ζ Tube per row ---
η Efficiency ---
ηf Fin efficiency ---
ηs Surface efficiency ---
λ Parameters m
µ Viscosity Pa.s
ρ Density kg/m3
τ Life time year
φ Fin efficiency parameter ---
Subscripts:
a Air
act Actual
g Vapor
in Inlet
l Liquid
max Maximum
meas Measured value
min Minimum
out Outlet
r Refrigerant
simu Simulated value
tp Two phase
References
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Condensers in the Industrial Applications
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