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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.

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l INTRODUCTION l MODEL DEVELOPMENT l SIMULATION AND ANALYSES l CONCLUSIONS

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

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EVAPORATIVE COOLING AND ITS APPLICATIONS

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

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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.

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

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

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

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PARTICLE DYNAMICS Particle Motion: Drag Force Calculation:

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

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Diagram of Particle Dynamics

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

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

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

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

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

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

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Comparisons between predicted and measured evaporation efficiencies.

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Comparisons between predicted and measured final chamber temperature.

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

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

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

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

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

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

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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.

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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.

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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.

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FITTING WITH SIMPLE FUNCTIONS

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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.

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THANK YOU 謝 謝 ISAMA 97 TAIPEI

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