passive solar collector for indirect small- scale dryer › ... › 2020 › 02 ›...

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

mailto:[email protected]

http://www.irandriedfruits.ir/en/

CONSOLFOOD2020

INTRODUCTION

DESIGN AND IMPLEMENTATION

PRELIMINARY TESTING CAMPAIGN

THEORY OF THE CAN TES COLLECTOR

TESTING CAMPAIGN

CONCLUSIONS

CONSOLFOOD2020

INTRODUCTION




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


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


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


CONSOLFOOD2020

INTRODUCTION




TESTING CAMPAIGN



CONSOLFOOD2020


Main issues. No TES dryer


Conventional cabinet type passive solar dryer:

Passive solar dryer with downstream TES.

Link Lecuona, A. Solar convective dryers

for post-collection processing.

http://www.marcombo.info/

CONSOLFOOD2020


Main issues


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


Prototype layout


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


Some figures


CONSOLFOOD2020


Instrumentation


• 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


Previous experimental studies


Low cost pre-heating for cloudy days

CONSOLFOOD2020

INTRODUCTION




TESTING CAMPAIGN



CONSOLFOOD2020


Parallel plates. No TES. Axial temperature profile


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


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


• 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




TESTING CAMPAIGN



CONSOLFOOD2020

DESIGN AND IMPLEMENTATION Natural draft velocity & heat transfer


Lower flow neglected

No outlet nozzle

CONSOLFOOD2020


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




TESTING CAMPAIGN



CONSOLFOOD2020

TESTING CAMPAIGN Instantaneous measurements (smoothed) can TES collector


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


INTRODUCTION




TESTING CAMPAIGN


CONSOLFOOD2020


• 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.


CONSOLFOOD2020


• 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.


CONSOLFOOD2020

Thanks for your attention!


On the front desk you have samples of these books. They are not for sale. A free

pdf file can be obtained thanks to the fellowship of the thematic network

CYTED/AESCA “ALMACENAMIENTO DE ENERGÍA SOLAR PARA COMUNIDADES AISLADAS”

Free pdf in www.marcombo.info

password cocinas1

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passive solar collector for indirect small- scale dryer › ... › 2020 › 02 ›...

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