$\begingroup$
I assume you want to keep the beans suspended in the air, like they do with persons at skydive simulators.
In order to do that, you do need a high speed airflow (or CFM). The (static) pressure that the fan can maintain doesn't matter here. The high speed airflow creates dynamic pressure that acts on the beans and keeps them suspended, which is what your looking for if I understand correctly. At terminal velocity, the force that acts on the object due to drag, is equal to the force that pulls it down, which we call gravity.
Consider the following formula for the terminal velocity of an object:
$v=\sqrt(2mg/\rho*C_d*A)$
Where $v$ is the velocity on an object, relative to the medium/stream in metres per second.
$m$ is the mass of the object(beans) in kilogram.
$g$ is the gravitational acceleration, which is about $9.81m/s^2$ everywhere on Earth.
$\rho$ is the density of the medium, which is 1.2kg per cubic metre for air at standard conditions.
$C_d$ is the drag coefficient of the object. This is a factor usually between near 0 and 1. It's defined by the shape and skin texture of the object. A sphere has a $C_d$ of about 0.9, so i'd expect a bean to have a $C_d$ of about 0.85. It depends which orientation the bean has relative to the airflow.
$A$ is the frontal area of the object. This also depends on the orientation of the bean.
Since we can't change the properties of the beans, nor can we significantly change the density of the air, all we're left with is the velocity as tunable parameter.
I can't find the properties of a bean in my physics book, but let's suppose it's as dense as average wood: about 700kg/m3, and that the bean has the shape of a sphere with a diametre of 8mm. (about 1/3rd of an inch) Then the frontal area of the bean will be:
$A=1/4*\pi*D^2=1/4*\pi*8^2=50.3mm^2$ or 5.03e-5 m2.
The volume of the spherical bean will be:
$V=1/6*\pi*D^3=268mm^3$ or 2.68e-7 m3.
Which at a density of 700kg/m3, gives us a mass of the bean of:
$m=\rho*V=700*2.68e-7=0.188grams$ or 1.88e-4 kg.
If we fill in these values in the first formula, it gives us a velocity of:
$\sqrt((2*1.88e-4*9.81)/(1.2*0.85*5.03e-5))=8.5m/s$
That is the needed velocity of the air to keep them suspended. If you multiply it by the surface of your fan, you get the needed airflow. This is assumed the surface of the airduct above the fan is the same surface as the fan. Your 120mm fan has a surface of:
$A=1/4*\pi*D^2=1/4*\pi*0.12^2=0.0113m^2$
Which means that the volume air flow must be:
$Volumeflow=v*A=8.5*0.0113=0.096m^3/s$ or 96L/s or 203CFM.
I'd choose a fan that has a higher CFM rating(300CFM or so), to create a margin to make up for any errors made by assumptions in these calculations. You can always easily throttle down the fan. And also, your mesh, the heater, the beans, and any other construction will restrict the airflow, which makes it impossible for the fan to provide advertised CFM rating. That rating is probably based on an unrestricted fan. That's why you need to aim higher for CFM.
If you want to warm up the beans, i'd recommend to create a construction that makes the fan recirculate the air. So create your airduct like a donut or a square donut. Not only does it allow you to gradually heat up the air and the beans without losing your heat, it also keeps the load of the fan at a minimum.
To select a fan, the required data includes the flow rate (CFM), static pressure (SP), and air/gas density.
You have 3 options to select the right fan or blower for your application:
1
Use ourUse our Quick Selector to narrow your choices and sort by Price or Efficiency.
2
Contact our knowledgeableContact our knowledgeable local sales engineer for application assistance.
3
Follow the steps below to select a fan using catalog data.to select a fan using catalog data.
Flow Rate (CFM)
SCFM stands for Standard Cubic Feet per Minute. It is the CFM at standard density, defined as .075 lb/cubic foot.
ACFM stands for Actual Cubic Feet per Minute. It is the CFM at an identified density other than .075 lb/ft3. It is also the required mass flow rate divided by the density of the gas being handled. Since fans and blowers handle the same volume of air regardless of density, the ACFM value (and corresponding density) is the preferred value to use when selecting a fan or blower. Note that ACFM and SCFM are not interchangeable except at .075 lb/ft3 density.
Airflow is rated in cubic feet per minute (CFM) or the metric equivalent, cubic meters per hour (M3/Hr).
1 CFM = 1.6990 x M3/Hr.
If you will be conveying material, make sure you have enough CFM for the duct, pipe or hose size so the material will maintain the required velocity to carry it completely through the system and not settle in the duct, pipe or hose. See Engineering Data catalog for material conveying velocities.
Static Pressure (SP)
Static Pressure is the resistance to airflow (friction) caused by the air moving through a pipe, duct, hose, filter, hood slots, air control dampers or louvers. Static Pressure is rated in inches water gauge (inWG) or the metric equivalent, millimeters water gauge (mmWG). 1 inWG = 25.4 x mmWG.
Standard air has a density of .075 lb/ft3 and is based on a temperature of 70°F and 29.92" Hg barometric pressure (sea level). Fan performance tables are based on using standard air. Corrections for density changes resulting from temperature and/or barometric pressure variations, such as higher altitudes, must be made to the static pressure before selecting a fan or blower based on standard performance data. The metric equivalent is in kilograms per cubic meter (kg/m3). lb/ft3 = 16.018 x kg/m3.
The temperature of the air going through the fan or blower will affect the density and performance of the fan or blower. Temperature should be shown in degrees Fahrenheit (°F). The metric equivalent is degrees Centigrade (°C).
°F = 1.8 x °C + 32
If the air temperature will vary, what are the minimum and maximum temperatures?
The altitude the fan or blower will be operating at will also affect the density and performance of the fan or blower. The altitude should be given in feet above sea level. The metric equivalent is meters (m). 1 ft = .30480 x m
Air Temperature Altitude Correction
Chart found on Page 5 of Instructions For How to Properly Select a Fan or Blower
Example:
Select a blower for 1500 CFM at 7" WG at 250°F. and at 6500 feet elevation.
NOTE: If the suction pressure on the inlet side of a blower will exceed 15" inWG, a correction for suction pressure (called rarefication) should be made. See chart below.
Chart found on Page 4 of Instructions For How to Properly Select a Fan or Blower
EXAMPLES:
Centrifugal fans or blowers use one of seven types of wheels that are enclosed in a scroll shaped housing. The air enters the fan wheel through the housing inlet, turns 90 degrees and is accelerated radially and exits the fan housing. Centrifugal fans are typically used for lower flows and higher pressures.
Axial fans use a propeller, having two or more blades, to move air in an axial direction through a cylindrical housing or formed orifice panel. Axial fans are typically used for higher flows and lower pressures. Do not use an axial fan to convey material.