liquid-air transpired solar collector (latsc): model development, validation and optimization-thesis...
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Liquid-Air Transpired Solar Collector(LATSC): Model Development,Validation and Optimization
By: Abdul Qadir
Advisor: Dr Peter ArmstrongRSC members: Dr Tariq Shamim, Dr Afshin Afshari
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OutlineMotivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
LATSC -Liquid Air TranspiredSolar Collector
LDR - LiquidDesiccantRegenerator
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MotivationIncreased use of solar thermal collectors forcooling and desalinationConventional flat plate collectors have a high
capital costUnglazed collectors have high convection lossesUse of polymer materials in glazed collectors
causes degradation of material at stagnation A supply temperature between 50-70 oC required
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Liquid Desiccant Cooling
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Humidification-Dehumidification(HDH) Desalination
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Research objectivesDevelop through first principles, amathematical/numerical model of the LATSCExperimentally validate the LATSC model
Build a numerical model of a liquid desiccantregenerator(LDR) and couple the model with theLATSC
Optimize the combined system for typical AbuDhabi conditions.
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Concept
Flat platecollector
TranspiredCollector
LATSC
Water heating
Efficient atdesired heating
temperature
Air heating Convectionsuppression
Low cost9
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The DifferenceFlat Plate w/o suction Flat Plate with suction
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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AssumptionsUniform flow of water in the tubesUniform flow of air through perforationsUniform distribution of perforationsNegligible starting length of boundary layerFlat plateNo leakage
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Heat flows from absorber plate
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Energy balance on differentialelement
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Coupling of heat transfer at the back of the plate
Air is also heated inthe back channel
Results in coupledheating throughholes and at theback of upper plateand lower plate.
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Change in ODE for air heating
Efficiency:
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Constant Parameters for First andSecond Analysis
Property Value Solar radiation (S) 800W/m 2
Wind speed(V w) 3 m/s
Air temperature(T amb ) 25 oC
Air density( a) 1.184kg/m 3
Air Viscosity ( a) 1.849*10 -5 Ns/m 2
Air C p (c pa ) 1.007kJ/kgK
Water C p 4.183kJ/kgK
Water Density 997 kg/m 3
Length of collector (L) 2m
Width of collector (W) 1m
Plenum depth (D) 0.1m Perimeter of plenum cross
section 2.2m
Plate absorptivity 0.9
Hole pitch (triangular pattern) 0.025m
Plate emissivity 0.9
Hole diameter 0.00159m
Property Value
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Total thermal capacitance rate:
Air capacitance rate fraction:
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Effect of varying ( c p)total and R c p
Uncoupled Model Coupled Model
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1
E f f i c i e n c y ,
(
- )
Air capacitance rate fraction ,Rmcp (-)
mdotcptot=25W/m2K mdotcptot=20W/m2K mdotcptot=15W/m2K
mdotcptot=10W/m2K mdotcptot=5W/m2K
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1
E f f i c
i e n c y ,
( - )
Air capacitance rate fraction ,Rmcp (-)
mdotcptot=25W/m2K mdotcptot=20W/m2K mdotcptot=15W/m2K
mdotcptot=10W/m2K mdotcptot=5W/m2K
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Effect of varying ( c p)total and R c p
Uncoupled Model Coupled Model
0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1
T w o u
t ( o C )
Air capacitance rate fraction ,Rmcp (-)
mdotcptot=25W/m2K mdotcptot=20W/m2K mdotcptot=15W/m2K
mdotcptot=10W/m2K mdotcptot=5W/m2K
0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1
T w o u
t ( o C )
Air capacitance rate fraction ,Rmcp (-)
mdotcptot=25W/m2K mdotcptot=20W/m2K mdotcptot=15W/m2K
mdotcptot=10W/m2K mdotcptot=5W/m2K
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Effect of varying T in at Rc p =0.1,mCp(tot)=15W/m 2K
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 0.02 0.04 0.06 0.08 0.1 0.12 E
f f i c i e
n c y
,
( -
)
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
e=0.1(C) e=0.5(C) e=0.9(C) e=0.1(UC) e=0.5(UC) e=0.9(UC)
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Effect of varying T in at Rc p =0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.02 0.04 0.06 0.08 0.1 0.12
E f f
i c i e n c y
, (
- )
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
e=0.1(C) e=0.5(C) e=0.9(C) e=0.1(UC) e=0.5(UC) e=0.9(UC)
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Effect of varying T in at Rc p =0.9
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.02 0.04 0.06 0.08 0.1 0.12
E f f
i c i e n c y
,
( - )
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
e=0.1(C) e=0.5(C) e=0.9(C) e=0.1(UC) e=0.5(UC) e=0.9(UC)
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Parameters Varied for Third AnalysisParameter Values
Air temperature(T amb ) 25,35,45(oC)
Water inlet temperature(T wi) 25-115 (
oC) with 10
oC
intervals Air to total thermal capacitance
fraction( Rc p) 0.1, 0.5
Solar radiation (G) 300, 500, 800 (W/m2)
Wind speed(V w) 0, 3, 5 (m/s)
Plate emissivity ( ) 0.9
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Rc p =0.1, (c p)total =15W/m 2K
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
E f f
i c i e n c y
,
( -
)
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
Vw=5m/s Vw=3m/s Vw=0m/s
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At ASHRAE 93 standard test flow rate
Wind Speed (m/s) Optimum air thermalcapacitance rate (W/m 2K) Rmcp
1 2.5 0.029
3 5 0.0565 6.5 0.072
Parameter Value
Water flow rate 0.02kg/s-m 2= 83.66W/m 2K
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Wind Speed=3m/s
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 0.02 0.04 0.06 0.08 0.1 0.12 E f f i c i e n c y
,
( -
)
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
e=0.1(C) e=0.5(C) e=0.9(C)
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-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 0.02 0.04 0.06 0.08 0.1 0.12 E f f i c i e n c y
,
( -
)
Collector Loss Potential, (Tin-Tamb)/G, (K-m 2/W)
e=0.1(C) e=0.5(C) e=0.9(C) Flat Plate Collector
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Experimental Setup
Flowmeter
Pumpvalve
Wateroutlet
collector
Outletwatertank
Inlet watertank
Waterinlet 31
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y = -7.126x + 0.6491
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-0.01 0.01 0.03 0.05 0.07 0.09
E f f i c i e n c y
(Ti-Ta)/G
Flat Plate Collector Testing
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Calibration of flow meter
Flowmeter
Inletwatersupply
Outlet pipewithinserted TC
WatercollectingBucket
Precisionweighingscale
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Side View
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Front View
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Flowmeter Pump
Collectoroutlet
Collector
Water tank
Collectorinlet
LoggerBox
Flange Assembly
Air outlet
Pyranometer
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Same Wind Speed (3-4m/s)
y = xR = 1
y = 1.039x - 0.191R = 0.972
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.2 0.3 0.4 0.5 0.6 0.7 0.8
E x p e r i m e n t a
l E f f i c i e n c y
Predicted Efficiency
Predicted vs. Experimental Results
Model
Experiment
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Same Air Flow Rate
y = xR = 1 y = 1.1295x - 0.2298
R = 0.9792
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.2 0.3 0.4 0.5 0.6 0.7 0.8
E x p e r i m e n t a
l E f f i c i e n c y
Predicted Efficiency
Predicted vs. Experimental Results
Model
Experiment
Lower windspeed
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Model Actual Steady State Transience mainly due to erratic wind speed
Uniform distribution of holes Slightly non-uniform hole distribution with largegaps in between patches near tubes
Flat plate Plate has waviness near top due to soldering
faults
Negligible starting length forboundary layer
Large starting length depending on the windspeed and air suction velocity. For some casesup to full collector length in starting region.
Uniform parallel flow of air
behind absorber plate
Non uniform flow with streamlines crossing due
to pressure drop in across plenum
No leakage in collector shell Finite leakage in setup
Uniform absorptivity of collectorplate surface across the solarspectrum.
Non uniform deposition of paint on the absorberplate and specular reflectance of absorber plate.
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Liquid Desiccant Regenerator (LDR)Falling film typeCounter flow configurationMany parallel plates
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Mass and Energy Balance
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Solving Method
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Combined Model
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Solution Procedure
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Regenerator Efficiency =
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
R e g e n e r a t i o n E f
f i c i e n c y
R cp
Regeneration Efficiency vs. Rmcp
( cp)total=5 W/m2K
( cp)total=10 W/m2K
( cp)total=15 W/m2K
( cp)total=20 W/m2K
( cp)total=25 W/m2K
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Overall Efficiency=
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
O v e r a
l l E f
f i c i e n c y
R cp
Overall Efficiency vs. Rmcp
( cp)total=5 W/m2K
( cp)total=10 W/m2K
( cp)total=15 W/m2K
( cp)total=20 W/m2K
( cp)total=25 W/m2K
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Motivation
ResearchObjectives
LATSC
Experimental Numerical
Sensitivity Analysis
LDR
Numerical
CombinedLATSC-LDR
Model
Sensitivity Analysis Optimization
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Optimization Air flow rate, water flow rate and desiccant flowrate required for optimum performance ofcombined LATSC-LDR system
Typical Abu Dhabi conditions to be modeled.
Parameter Value
Solar Radiation 850 W/m 2
Wind Speed 4 m/sHumidity 0.02 kg w/kg daTemperature 27.5 oC
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Objective FunctionMaximize desiccant flow rateDesiccant outlet concentration =0.4 kg d/kg w
Genetic Algorithm used to minimize function
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Results
Parameter Value
Water thermal capacitance rate 176.0257 W/m 2K
Air thermal capacitance rate 22.7955 W/m 2K
Desiccant flow rate 0.0001172 kg/s
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Parameter Value
Water thermal capacitance rate 123.0850 W/m 2K
Air thermal capacitance rate 51.7855 W/m 2K
Desiccant flow rate 0.00013771 kg/s
Plate Width =0.5m
Plate Width =1m
Increase in Efficiency= 17.5%
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Conclusion
LATSC Numerical model Sensitivity Analysis shows that optimum R mcp
decreases with increasing mc p(tot) Decreasing emissivity and wind speed increasesefficiency Increasing temperature and solar radiation increases
efficiency
LATSC model partly verified Large discrepancies between model and experiment Experimental conditions deviate from assumptions
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Conclusion
Combined LATSC-LDR model Optimum Rmcp decreases with increased
mc p(tot) Regenerator prefers hot water over hot air Role of air to suppress convection
Combined system optimization System optimized for typical Abu Dhabi
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Further Work
Retesting of collector with area at least 5m 2
Wind tunnel testing for heat exchange effectiveness of plate in starting region AND/OR CFD Analysis
Changes in numerical model to account for starting region
Optimize the height, width and number of plates in the regenerator
Experimental validation of LATSC-LDR combined system
Numerical model and experimental validation of LATSC-HDH Desalinationsystem
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AchievementsInvention DisclosureJournal Publication:
Qadir, A. and P. Armstrong. Liquid-Air Transpired Solar Collector: ModelDevelopment and Sensitivity Analysis . ASME Journal of Solar Energy
Engineering. Under second review
Conference Paper:Qadir, A. and P. Armstrong. Hybrid Liquid-Air Transpired Solar Collector: ModelDevelopment and Sensitivity Analysis in ASME 2010 International MechanicalEngineering Congress & Exposition . 2010. Vancouver, Canada: ASME.
Potential/Upcoming Publications:Experimental validation of LATSCLATSC-LDR modeling and optimization for hot humid climatesLATSC-HDH Desalination modeling and optimization
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AcknowledgementsDr Peter ArmstrongRSC membersDr Matteo ChiesaLENS group:
Steven MeyersMarwan MokhtarMuhammad Tauha Ali
Irene RubalcabaDr Pawan Singh
All my kith and kin for providing moral and physicalsupport
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THANK YOU!