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Ta-Te Lin, Yi-Chung Chang

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1 MODELING AND ANALYSES OF EVAPORATIVE COOLING EFFICIENCY FOR MIST-FOG SYSTEMS
Ta-Te Lin, Yi-Chung Chang Department of Agricultural Machinery Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.

2 INTRODUCTION MODEL DEVELOPMENT SIMULATION AND ANALYSES CONCLUSIONS

3 INTRODUCTION EVAPORATIVE COOLING AND ITS APPLICATIONS
FACTORS AFFECTING EVAPORATIVE COOLING OBJECTIVES

4 EVAPORATIVE COOLING AND ITS APPLICATIONS

5 FACTORS AFFECTING EVAPORATIVE COOLING
RELATIVE HUMIDITY AMBIENT TEMPERATURE DROPLET SIZE VENTILATION RATE DROPLET TRAVEL DISTANCE

6 OBJECTIVES To develop a theoretical model for the calculation of evaporative cooling efficiency base on mass transfer and particle dynamic theories. To validate the model with existing laboratory data. To analyze the influences of selected parameters, such as temperature and relative humidity, on the evaporative cooling efficiency of mist-fog systems.

7 MODEL DEVELOPMENT MASS TRANSFER OF DROPLETS PARTICLE DYNAMICS
CALCULATION OF PSYCHROMETRIC PARAMETERS

8 MASS TRANSFER OF DROPLETS
The Basic Mass Transfer Equation: The Goering Model:

9 MASS TRANSFER OF DROPLETS
Diffusivity Pressure Difference Partial Pressure of Air Pressure Difference

10 PARTICLE DYNAMICS Particle Motion: Drag Force Calculation:

11 PARTICLE DYNAMICS Effect of Wind Direction and Droplet Moving Angle:
Effect of Spray Nozzle Gauge Pressure:

12 Diagram of Particle Dynamics

13 CALCULATION OF PSYCHROMETRIC PARAMETERS
Wet Bulb Saturation Pressure: Dry Bulb Vapor Pressure: Latent Heat of Water:

14 SIMULATION AND ANALYSES
SIMULATION PROCEDURES VALIDATION OF THE MODEL PARTICLE SIZE AND MOVING DISTANCE EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY

15 SIMULATION AND ANALYSES
SIMULATION PROCEDURES VALIDATION OF THE MODEL PARTICLE SIZE AND MOVING DISTANCE EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY

16 SIMULATION AND ANALYSES
SIMULATION PROCEDURES VALIDATION OF THE MODEL PARTICLE SIZE AND MOVING DISTANCE EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY

17 SIMULATION AND ANALYSES
SIMULATION PROCEDURES VALIDATION OF THE MODEL PARTICLE SIZE AND MOVING DISTANCE EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY

18 SIMULATION AND ANALYSES
SIMULATION PROCEDURES VALIDATION OF THE MODEL PARTICLE SIZE AND MOVING DISTANCE EFFECT OF TEMPERATURE AND RELATIVE HUMIDITY

19 Comparisons between predicted and measured evaporation efficiencies.

20 Comparisons between predicted and measured final chamber temperature.

21 Droplet evaporation percentage at various moving distances under different temperatures and relative humidities. Initial droplet size is 45 microns

22 Effect of droplet diameter and psychrometric parameters on the moving distance.

23 Droplet evaporation rate under different relative humidities
Droplet evaporation rate under different relative humidities. Dry bulb temperature is 30℃ and the initial droplet diameter is 65 microns.

24 Droplet evaporation rate under different relative humidities
Droplet evaporation rate under different relative humidities. Dry bulb temperature is 30℃ and the initial droplet diameter is 65 microns.

25 Evaporation rate of droplet with different initial diameter
Evaporation rate of droplet with different initial diameter. Dry bulb temperature is 25℃ and the relative humidity is 90%.

26 Evaporation rate of droplet with different initial diameter
Evaporation rate of droplet with different initial diameter. Dry bulb temperature is 25℃ and the relative humidity is 90%.

27 Evaporation efficiency as affected by droplet diameter and psychrometric parameters. The nozzle height is 1.8m.

28 Evaporation efficiency as affected by droplet diameter and psychrometric parameters. The nozzle height is 3.0m.

29 Droplet evaporation percentage at various moving distances under different temperatures and relative humidities. The nozzle height is 0.9m and the droplet diameter is 65 microns.

30 Droplet evaporation percentage at various moving distances under different temperatures and relative humidities. The nozzle height is 0.9m and the droplet diameter is 105 microns.

31 Droplet evaporation percentage at various moving distances under different temperatures and relative humidities. The nozzle height is 1.2m and the droplet diameter is 65 microns.

32 FITTING WITH SIMPLE FUNCTIONS

33 FITTING WITH SIMPLE FUNCTIONS

34 CONCLUSIONS A theoretical model to predict evaporative cooling efficiency for mist-fog systems was established based on mass transfer theory and particle dynamics. The model was validated with experimental data from existing literature and the predicted evaporation efficiency agreed well with the measured values. The effects of temperature, relative humidity and the size of spray droplet on the cooling efficiency of mist-fog systems were analyzed with the developed model. Useful information can be generated with model simulations as an aid in designing effective mist-fog systems.

35 ISAMA 97 TAIPEI THANK YOU 謝 謝

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