Fog Density Meter<

Project Description<

Motivations<

My ongoing PhD thesis is about understanding fog droplets motion around obstacles and more specifically trying to use these understandings to improve fog harvester. To conduct these research, our team is using a test bench that was built in the lab allowing one to simulate real conditions and test their prototypes.

It is composed of a fog generator, a laminar air flow generator, two concentric plastic cylinders and two weighing scales. The fog created by the generator is carried away by the laminar air flow and passes around a hanging obstacle. The top weighing scale measures the mass of the fog water deposited on the obstacle while the bottom one measures the mass of the water drained and hence harvested.

A fog harvester efficiency is computed as the ratio between the incoming fog water mass rate and the harvested water mass rate. We easily measure the harvested water mass rate with a scale under the harvester however we can not yet measure the incoming fog water mass rate, at least not directly. For now we simply estimate it by measuring the water tank mass before and after our measurements and averaging the mass rate.

This measurement method is an issue for two main reasons. First, the efficiency of the nebulizer that creates fog depends on the water level and the fog generation process obviously uses water and make the water level decrease. The incoming water mass rate is hence not constant and the method we use to estimate its value is not accurate for large duration measurements. Second, the water mass rate leaving the tank is not the incoming fog water mass rate. Indeed there is loss on the way hence we overestimate it.

My Fab Academy final project goal is to solve at least one of these problem :

Make the incoming water mass rate more constant
Have a direct measurement of the incoming fog water mass rate

At first I started working on the water level control part with a water level sensor and a pump. However, at the beginning of the Week 9 I realised it would way simpler to use a purely mechanical system which would not work for a Fab Academy final project. I then started to work on the fog density measurement.

Sketches<

Side View

Project SketchActual Setup

Front View

Project SketchActual Setup

System Diagram<

Current State<

Masterpiece Plan<

What will it do ?<

My final project will be a device measuring the liquid water content (g/m³) of the fog generated by our lab's test bench. This measurement will allow us to characterize more precisely the collect efficiencies of our net prototypes. Indeed, the latter are defined as a ratio of the collected water mass rate and the incoming water mass rate. Until now, we estimated the incoming water mass rate by looking at the mass difference of the water tank between the beginning and the end of the experiment.

Who's done what beforehand ?<

One should be carefull when talking nd searching about fog density because the tools and techniques to be used completely depends on the scale of the phenomenon one is studying.

For 10 meters to kilometer scale, visibility measurment can be used :

Narendra Nelli, Diana Francis, Rachid Abida, Ricardo Fonseca, Olivier Masson, Emmanuel Bosc, In-situ measurements of fog microphysics: Visibility parameterization and estimation of fog droplet sedimentation velocity, Atmospheric Research, Volume 309, 2024, 107570, ISSN 0169-8095

At a few centimeter scale like ours, the following article makes a comparative overview of the existing techniques :

Kos, Gerard, and Kevin Noone. “Comparison of Techniques for Measurements of Fog Liquid Water Content.” Tellus B, 1992.

The reviewed techniques can be shortly identified as :

Average scattered laser flux
Single particle counter (using light scattering)
Wire resistance influenced by droplets impaction
UV absorbtion
Fog Collection

Visibility is never mentionned and the mainly used techniques are based on light scattering.

A frequently used device in researches is the FM-120 by Droplet Measurement Technologies, Envea Group as mentionned by :

However, in the next research was developed a "homemade" fog liquid water content meter that also relies on light scattering :

Ovsenik, Lubos & Turán, Ján & Mišenčík, Pavol & Bito, Janos & Csurgai-Horváth, László. (2012). Fog density measuring system. Acta Electrotechnica et Informatica. 12. 10.2478/v10198-012-0021-7.

What sources will you use ?<

Scientific papers :

Research Center Documentation :

L'Observatoire de Recherche Atmosphérique SIRTA

ScienceDirect :

Liquid Water Content

Wikipedia :

Liquid Water Content

AI chatbots :

What Will You Design ?<

Printed Circuit Board

PCB DESIGN PICTURE
PCB Container

PCB CONTAINER PICTURE
Adapted UC2 Containers

UC2 CONTAINERS PICTURE
Adapted UC2 Supports

UC2 SUPPORT PICTURE
Calibration Board

CALIBRATION BOARD PICTURE
System Integration

SYSTEM INTEGRATION SKETCH PICTURE

Bill of Materials<

Parts	Materials and Components	Quantity	Origin	Cost
Electronics	Copper Plate
	AtTiny412
	Resistor
	Capacitor
	Transistor
	6-Pin Headers
	4-pin Headers
	2-pin Headers
	Laser
	LED
	Phototransistor
PCB Container	PLA
	Screws
UC2 Containers	PLA
	Magnets
	Screws
System Integration	Wires
	FTDI Cable
	Extrusion Bar
	PLA Corner Brackets
	Screws
Calibration Board	Wood
	Screws
	Humidifier