DEVELOP TEST RIG TO INVESTIGATE THE EFFECTS OF TEMPERATURE ON JET NEBULISER DROPLET SIZE

Richard Conlon

DT022/4 - Mechanical Engineering

15th April 2015

Supervisor: Peter McCluskey

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Background

• Nebulisers produce an aerosol mist of medication containing droplets of a particular size

• How Nebulisers Work– Compressed air is forced through small orifice– Increase in velocity causes local pressure drop– Medication drawn upwards forming droplets

• Aerosol Therapy• Asthma, COPD → Relieve inflamed airways• Cystic Fibrosis → Loosen mucus and combat infection

Air Tubing

Nebuliser Chamber & Mouthpiece

Air Tubing

Orifice

Fig. 1 – Jet Nebuliser

Fig. 2 – Separated Nebuliser Chamber

Compressor

Importance of Droplet Size• Effective treatment relies on drug reaching target area

– Aerosol Therapy → lower respiratory system

• Size of droplets determines deposition region in respiratory system

• Nebulisers produce heterodisperse aerosols– Aerosol made up of droplets of many different sizes– Only droplets between 0.5 – 5 μm deposit successfully

Optimum Range

< 0.5µm > 5µm

Droplets too small to deposit and are

exhaled

Droplets too large to reach smaller airways

Fig. 3 – Droplet Size and Deposition Region

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Importance of Droplet Size• Correct droplet size is critical for effective aerosol therapy

Droplet Size

Temperature

Humidity

Static ChargeDrug Viscosity

Flow Rate

Nebuliser are used in domestic and care settings:‘Develop a test rig to investigate the effects of temperature on droplet size’

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• Innovative medical device and drug delivery company• Specialising in aerosol drug delivery systems• Located in IDA Business Park, Galway

Senior Scientist Dr Ronan Mac Loughlin

Laboratory Technician Andrew O’Sullivan

Fig. 4 – Aerogen Facility, Galway

Laser Diffraction Analysis• Laser beam is passed through aerosol cloud• Droplets diffract the light at angles inversely related to their diameter

Malvern Spraytec • He-Ne Laser• Wavelength: 632.8 nm

Laser Diffraction Analyser

Nebuliser

Fig. 5 – Malvern Spraytec Laser Diffraction Analyser

Laser Emitter

Aerosol Cloud

Detector Rings

Test RigControl Volume

Temp. & Humidity

Sensor

Nebuliser

Insulated Air Tubing

Power Supply

Microcontroller & Circuit

Power Inverter

Heater & Mixing Fan

Fig. 6 – Completed Test Rig

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Test Rig• Control Volume

– 2.8x10-2m3

– IP66 Rating– 20mm insulation on sides

• Heater– 20 W Cirrus 25– Activated by solid state relay

• Heater-Fan– 12V DC motor– Forces air over heater

Enclosure

Heater-Fan

Heater

Nebuliser Hose Access

Nebuliser ON/OFF

Solid State Relay

20mm Insulation

Fig. 7 – Control Volume

Fig. 8 – Control Volume Components

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Test Rig• SHT15 Sensor

– Positioned at nebuliser air inlet– Arduino serial monitor– Feedback to other components

• Mixing-Fan– Positioned in upper portion of control volume– 5V DC motor– Proportional Control

• Fan output proportional to error

Heater & Heater-Fan

Mixing-Fan

SHT15 Temp & Humidity

Sensor

Fig. 9 – SHT15 Sensor & Jet Nebuliser

Fig. 10 – Mixing-Fan

Jet Nebuliser

Air Inlet

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DemonstrationStep 1: Specify desired temperature in software

Step 2: Select frequency on Inverter

Step 3: Monitoring temperature change– Seen in Arduino serial monitor

Step 4: Switch on nebuliser– Relocated outside of control volume

Step 5: Measure droplet size produced– Laser Diffraction Analyser

Fig. 11 – Arduino Main Loop

Fig. 12 – Arduino Serial Monitor

Fig. 13 – Test Rig Side View

Nebuliser Switch

Inverter

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Testing with Rig• Initial Testing

– Measured droplet size produced over a range of flow rates

• Final Testing– Control temperature of air entering nebuliser– Measure droplet size produced over a range of flow rates

• Data– Temperature range: 22 – 34°C– Flow rate range: 7.5 – 9.5 L/min

Fig. 15 – Test Rig & Laser Diffraction Analyser

Laser Diffraction Analyser

Test Rig

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Results

22°C 25°C 28°C 31°C 34°C0

1

2

3

4

5

6

7

7.48 L/min8.82 L/min9.54 L/min

Control Volume Temperature[°C]

Med

ian

Drop

let S

ize[µ

m]

Initial TestingIncreasing flow rate produced smaller

droplets

42% increase in droplet size

Observations• As temperature was increased, droplet sizes measured increased

• Aerosol output from nebuliser decreased noticeably as temperature and flow rate increased

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Analysis of Results

Fig. 17 – Nebuliser & Face Mask

Fig. 16 – Nebuliser & 90° Fitting

• Aerosol encountered 90° turn before measurement

• Smaller droplets were generated

• Droplets gained kinetic energy from carrier gas– Droplets with less mass would have higher velocity

• Droplets crashed into wall of fitting• Rebounded and collided with oncoming aerosol

• Accumulated and flowed back down into nebuliser

Why did the median droplet size increase and aerosol output decrease?

Conclusion• Temperature is a factor that effects droplet size

• Temperature may not be independent of the patient interface

• Results also highlight need for regular sterilisation of equipment– Accumulated droplets could wash bacteria into medication

Further Research• Repeats test for correlation

• Investigate impact of humidity on droplet size– Ice bath in control volume

• Carry out comparison between other brands and models of nebuliser

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Any Questions?