Towards Prediction of Artificial Monolayer Performance for Water Conservation

1
Towards Prediction of Artificial Monolayer
Performance for Water Conservation

• Pam Pittaway Nigel Hancock
• National Centre for Engineering in Agriculture
• University of Southern Queensland, Toowoomba.

2
ARTIFICIAL MONOLAYER TECHNOLOGY

• Potential for cost-effective water saving BUT
• Averaged daily data indicates highly variable
  performance.

THIS PRESENTATION

• Understand the cause of highly variable
  performance to predict optimal conditions for
  cost-effective monolayer application.

3
ARTIFICIAL MONOLAYER TECHNOLOGY IN PRACTICE
4
VARIATION IN MONOLAYER FIELD TRIAL PERFORMANCE
(Craig et al 2005)
Location Storage size (km2) Trial monitoring period (days) Evaporation Reduction ()
University of Southern Queensland, Toowoomba, Qld 0.0001 1- 6 days 2- 8 days 3- 6 days 4- 7 days 5- 7 days 38 17 10 38 40
Capella Qld 0.042 1- 9 days 2- 8 days 3- 7 days 4- 8 days 0 0 0 0
Cubby Station, Dirranbandi, Qld 1.2 1- 5 days 2- 10 days 3- 8 days 31 27 0
5
ARTIFICIAL MONOLAYERS FOR EVAPORATION REDUCTION

• Monomolecular fatty alcohol films compressing at
  water surface to retard evaporative loss
• Long-chain, saturated fatty alcohols form
  continuous condensed film
• Condensed film retards molecular transfer across
  liquid thermal and gaseous boundary layers
• Wind speeds gt6 m sec-1 disrupt films

6
(No Transcript)
7
(No Transcript)
8

1. IMPACT OF ARTIFICIAL MONOLAYER AT MONO-MOLECULAR
   SCALE

(Figure 7.1 Davies and Rideal 1963)
GAS PHASE
Liquid thermal boundary layer (LTBL)

• Damping capillary waves reduces wind shear RG
  reduced and eddies (Rayleigh-Benard convection)
  RL reduced.

A condensed monolayer increases RG , RI RL
9

1. IMPACT OF MICROMETEOROLOGY ON RESISTANCE TO
   EVAPORATIVE LOSS

(Figure 7.1 Davies and Rideal 1963)
GAS PHASE
Liquid thermal boundary layer (LTBL)

• Cold surface film thermally unstable, strong
  eddies reduce RL.
• Warm surface film thermally stable, no eddies
  increase RL.

10
(No Transcript)
11

1. METEOROLOGICAL DRIVERS AT THE MICRO SCALE

If ?a ?wgt 0 induces a cold surface film
(?0?wlt0), small RL induces evap
loss. Increasing wind speed to 1.5 m sec-1
increases the cold surface film, reducing RG
RL, increasing evap loss.
Fig 2.5, Gladyshev (2002)
12
METEOROLOGICAL DRIVERS AT THE MICRO SCALE
concluded

• Airsubsurface water (?a ?w) is a surrogate of
  QH
• Surfacesubsurface water (?0 ?w) is a surrogate
  of Liquid Thermal Boundary Layer resistance
• (?0 ?w) lt0 cold surface film (thin LTBL, lt
  RL)
• (?0 ?w) gt0 warm surface film (thick LTBL, gt
  RL)

13
TRIALS IMPACT OF PHYSICAL COVERS ON
MICROMETEOROLOGY RESISTANCE TO EVAPORATIVE LOSS
Trial 1 black Atarsan cover on x2 tanks,
monolayer on x1 tank
Trial 2 white shade cloth cover on x2 tanks,
monolayer on x1 tank
14
INSTRUMENTATION ABOVE AND UNDER PHYSICAL COVERS
NOT TO SCALE
15
(No Transcript)
16
DIURNAL ENERGY BALANCE FOR SHALLOW WATER (Fig
3.15 Oke 1987)
Shallow water Japan (QG is soil heat flux)
17
(No Transcript)
18
(?0 ?w)
(?0 ?w)
(?a ?w)
19
(No Transcript)
20
(No Transcript)
21
CONCLUSIONS

• Monomolecular films increase R in liquid thermal
  (RL) gaseous (RG) boundary layers
• Calm conditions with thermally stable LTBL (warm
  surface film),
• RL gt Rmonolayer (no effect)
• Light wind, thermally unstable LTBL,
• RL lt Rmonolayer (water savings)
• Hourly analysis is ESSENTIAL to interpret R and
  drivers of evaporation (QH, QE, Q)

22
THANK YOU