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CONSOLFOOD2020
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-
SCALE DRYER
• Antonio Lecuona Neumann ([email protected] )
• Eleonora Improta (Master student)
• Sonia López-Larroque (Master student)
• Alfonso Daniel Vega-Palenzuela (Master student)
Grupo ITEA, Universidad Carlos III de Madrid
Leganés; España
Third International Conference CONSOLFOOD2020
Advances in Solar Thermal Food Processing
22-23-24 January 2020
INSTITUTE OF ENGINEERING; UNIVERSITY OF ALGARVE; CAMPUS DA PENHA; FARO-PORTUGAL
Link
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
CONSOLFOOD2020
• According to FAO, 30% of agricultural crops are lost worldwide.
Reasons:
• Cropping season is short.
• Lack of modern transport and/or cold storage.
• Lack of knowledge
• In-situ drying is a good preserving method (less weight, not energy consuming …)
but,
• Needs much heat to evaporate water → same problems as cooking.
• The product can be smoked, reducing quality and potentially toxic
• Solar drying is an option improving open-air drying
INTRODUCTION Food solar drying
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
Advantages of solar drying over open air drying →
• Less space required.
• Faster drying.
• Protects load against: rain, dust and insects as it is enclosed.
Principles of operation and types or dryers:
• Direct: The sun heats the load directly
• Indirect:
• Heats air to increase its moisture capacity (SAHC).
• This air heats and dries the load.
• Air is discarded.
•
INTRODUCTION Food solar drying
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
• Process of indirect solar drying during the day • Air is heated in a SAHC reducing its relative moisture.
• Hot air contacts the food heating it < 70 ℃.
• Superficial humidity evaporates cooling the food.
• Moisture is evacuated by the flowing air (convection).
• Humidity migrates from the inside to the food surface.
• The food reduces in weight and size.
• During off-sun hours. Temperature decreases and air moisture increases.
Mold can grow.
Condensation is possible on the dryer surfaces.
Internal homogenization of humidity contents.
INTRODUCTION Conventional food solar drying
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
• Develop a passive Solar Air Heater Collector (SAHC) of the
cabinet type • Does not need electricity, even no PV as it presents high cost, breakdown
and thieving risk and difficult repairing.
• Incorporating Thermal Energy Storage (TES) to:
• Limit day maximum temperature
• Continue drying during the night and avoid spoilage.
• Low cost.
• Components transportable to remote locations.
• Local construction with common tools.
• Characterize its performances.
INTRODUCTION Objectives
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Main issues. No TES dryer
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
Conventional cabinet type passive solar dryer:
Passive solar dryer with downstream TES.
Link Lecuona, A. Solar convective dryers
for post-collection processing.
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Main issues
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
The low temperatures for drying calls for Thermal Energy Storage (TES):
• Low cost TES is provided by water.
• Water storage is a problem because of: corrosion, vapor pressure and cost of the tank.
• Solution: Soft drinks cans filled with non-caloric tea (99.9% water, non-carbonated):
• Worldwide available.
• Low cost 20 c€/ea. in Spain (cold tea).
• Easily transportable (valid for emergencies).
• Durable (in-house tested up to 80 ºC).
• Can absorb the sun rays when painted black.
• High surface to volume ratio.
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Prototype layout
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
Anti-insects
wire screen, inlet
80 mm thk.
expanded
polystyrene
10 mm thk.
alveolar
Polycarbonate
cover
Hot wire
anemometer+
temperature
Converging
outlet nozzle
° Type K
thermocouples
monitor several
input, output and
half-path air
temperature + can
temperatures
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Some figures
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Instrumentation
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
• TSI and PCE handheld hot wire anemometers in the
center of a 120×120 mm outlet collection section:
• Converging nozzle to reduce boundary layer
thickness.
• It introduced some heat losses. • 8 channel PICOLOG/TC-08 A/D with USB to computer.
• Several handheld thermocouple displays.
• MACSOLAR handheld piranometer.
• 40 deg. fixed tilting angle + azimuth sun tracking.
• Located at UC3M Campus in Leganés,
South of Madrid, Spain.
• The small temperature differences
require a careful thermocouple calibration
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION
Previous experimental studies
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
Low cost pre-heating for cloudy days
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
PRELIMINARY TESTING CAMPAIGN
Parallel plates. No TES. Axial temperature profile
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
20
25
30
35
40
45
50
55
60
65
70
75
Entrada Intermedio Salida
Te
mp
era
tura
(ºC
)
Posición termopar
12:00, 25-03-19
T_Placa_Superior
T_Placa_Inferior
T_Aire_Superior
T_Aire_Inferior
T_Patrón_Superior
T_Patrón_Inferior
T_upper plate
T_lower plate
T upper stream
T_lower stream
T_ upper, reference
T_lower, reference
Inlet (i) Outlet (o)
Thermocouple position
• Inhomogeneity in outlet stream flows were detected, also instabilities
Wind
CONSOLFOOD2020
PRELIMINARY TESTING CAMPAIGN Parallel plates. No TES.
Instantaneous measurements of outlet air temperature and velocity
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
46
47
48
49
50
51
52
53
54
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4 13:3
3:3
6
13:3
3:4
5
13:3
3:5
4
13:3
4:0
3
13:3
4:1
2
13:3
4:2
1
13:3
4:3
0
13:3
4:3
9
13:3
4:4
8
13:3
4:5
7
13:3
5:0
6
13:3
5:1
5
13:3
5:2
4
13:3
5:3
3
13:3
5:4
2
13:3
5:5
1
13:3
6:0
0
13:3
6:0
9
13:3
6:1
8
13:3
6:2
7
13:3
6:3
6
13:3
6:4
5
13:3
6:5
4
13:3
7:0
3
13:3
7:1
2
13:3
7:2
1
13:3
7:3
0
13:3
7:3
9
13:3
7:4
8
13:3
7:5
7
13:3
8:0
6
13:3
8:1
5
13:3
8:2
4
13:3
8:3
3
Te
mp
era
tura
[°C
]
Ve
locity [m
/s]
Time hour each 9 seconds interval
Velocity and upper stream? air outlet temperature vs time hour
velocidad
temperatura
• Low velocity and high wind sensitivity.
CONSOLFOOD2020
0
10
20
30
40
50
60
70
80
90
100
110
120
130
12:2
8:4
8
12:4
0:1
9
12:5
1:5
0
13:0
3:2
2
13:1
4:5
3
13:2
6:2
4
13:3
7:5
5
13:4
9:2
6
14:0
0:5
8
14:1
2:2
9
14:2
4:0
0
14:3
5:3
1
14:4
7:0
2
14:5
8:3
4
15:1
0:0
5
15:2
1:3
6
15:3
3:0
7
15:4
4:3
8
15:5
6:1
0
16:0
7:4
1
16:1
9:1
2
16:3
0:4
3
16:4
2:1
4
16:5
3:4
6
17:0
5:1
7
17:1
6:4
8
17:2
8:1
9
17:3
9:5
0
17:5
1:2
2
18:0
2:5
3
18:1
4:2
4
18:2
5:5
5
18:3
7:2
6
18:4
8:5
8
19:0
0:2
9
19:1
2:0
0
19:2
3:3
1
19:3
5:0
2
19:4
6:3
4
19:5
8:0
5
20:0
9:3
6
20:2
1:0
7
20:3
2:3
8
20:4
4:1
0
20:5
5:4
1
21:0
7:1
2
21:1
8:4
3
A12
A13
A14
9
5
A4
A2
1
PRELIMINARY TESTING CAMPAIGN No TES, empty cans. Instantaneous temperature measurements
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
• Cold gusts perturbate the measurements.
• Temperature differences between the air temperatures at right, center, and left
plate outlets and nozzle exit (possible heat losses or external air contamination).
• Cans temperature differences between plate inlet and outlet.
• Fast cooling after sunset, at 21 h drying stops.
3rd/06/2019→ day
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
DESIGN AND IMPLEMENTATION Natural draft velocity & heat transfer
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
Lower flow neglected
No outlet nozzle
CONSOLFOOD2020
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
Insulation
• TES delivers comparable power after sunset than during the day
0 5 103
1 104
1.5 104
2 104
2.5 104
3 104
10
20
30
40
50
60
70
80
90
1- 103
500-
0
500
1 103
1.5 103
T2 i, /°C
T3 i, /°C
Tatmi/°C
Qni
Qli
Qcolai
i
Sunrise 8 am Noon Sunset 4 pm Afternoon 8 pm Midnight 4 am Sunrise 8 am
1 hypothetical day
Estimated no TES
cooling
CONSOLFOOD2020
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
TESTING CAMPAIGN Instantaneous measurements (smoothed) can TES collector
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
0
10
20
30
40
50
60
70
80
90
100 10:4
8:0
0
11:1
6:4
8
11:4
5:3
6
12:1
4:2
4
12:4
3:1
2
13:1
2:0
0
13:4
0:4
8
14:0
9:3
6
14:3
8:2
4
15:0
7:1
2
15:3
6:0
0
16:0
4:4
8
16:3
3:3
6
17:0
2:2
4
17:3
1:1
2
18:0
0:0
0
18:2
8:4
8
18:5
7:3
6
19:2
6:2
4
19:5
5:1
2
20:2
4:0
0
20:5
2:4
8
21:2
1:3
6
21:5
0:2
4
22:1
9:1
2
22:4
8:0
0
23:1
6:4
8
23:4
5:3
6
00:1
4:2
4
00:4
3:1
2
01:1
2:0
0
01:4
0:4
8
02:0
9:3
6
02:3
8:2
4
03:0
7:1
2
03:3
6:0
0
04:0
4:4
8
04:3
3:3
6
05:0
2:2
4
05:3
1:1
2
06:0
0:0
0
06:2
8:4
8
06:5
7:3
6
07:2
6:2
4
07:5
5:1
2
08:2
4:0
0
08:5
2:4
8
09:2
1:3
6
09:5
0:2
4
Midnight 3rd/07/2019→ day hot, sunny in the morning
Estimated no TES
cooling
CONSOLFOOD2020
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
INTRODUCTION
DESIGN AND IMPLEMENTATION
PRELIMINARY TESTING CAMPAIGN
THEORY OF THE CAN TES COLLECTOR
TESTING CAMPAIGN
CONCLUSIONS AND FURTHER WORK
CONSOLFOOD2020
CONCLUSIONS AND FURTHER WORK
• Indirect passive solar collectors seem possible and convenient for small dryers …
… if pressure losses are limited.
• TES using drinking cans seems successful and of large potential.
• For the can flat absorber and TES there is lack of knowledge on:
Sun collecting capacity.
Pressure loss.
Axial temperature profile
• High wind sensitivity.
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
CONCLUSIONS AND FURTHER WORK
• Fully characterize the collector.
• Characterize the drying performances of sample foods in a cabinet.
• Test low end technologies, such as simple or dual PET film cover.
• Optimize its design (e.g., cross-section for air flow).
• Testing at field conditions, user experience.
• Determine operative life outdoors.
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
CONSOLFOOD2020
Thanks for your attention!
PASSIVE SOLAR COLLECTOR FOR INDIRECT SMALL-SCALE DRYER
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Free pdf in www.marcombo.info
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