|
|
Post by anounaki on Jul 27, 2021 20:51:08 GMT -8
Greedings
I would like to ask the proffesionals here what is the average air input of common batchrocket stove? I need this value for a flow simulation.
Regards
|
|
|
|
Post by peterberg on Jul 28, 2021 1:25:20 GMT -8
I don't know what the air input is, in whatever value. The flow isn't a fixed value though, since it's tied to the underpressure generated by the chimney. The hotter the chimney, the greater the temperature difference between inside and outside the stack. And the greater the temperature difference, expressed as delta T. Hotter chimney, faster flow and higher volume of air through the system. Every atmospheric driven combustion appliance equipped with a chimney stack shows this behaviour.
Having said all this, the air feed opening in a batch box rocket heater is around a quarter of the riser's cross section area. And the under pressure in the chimney should be at least 6 hPa (same as millibar) for a cold heater to start with. Otherwise, the thing will belch smoke into the house. During the burn, the temperature of the chimney should be at least 60 ºC within 20 minutes of the starting point. If not, there's a good chance the thing will belch smoke again where you don't want it.
The temperature in (the center of) the chimney at the end of the burn could be as much as 120 ºC with a corresponding under pressure of about 25 hPa. A good average chimney draw is 12 hPa, so this would be a good value for the chimney.
As it happens, a European certification test should be done with this 12 hPa as the chimney's draw.
|
|
|
|
Post by fiedia on Jul 28, 2021 12:49:54 GMT -8
I am very interested by your simulation project. Please tell us more about what you want to compute and what tools you are using. I put an anemometer in the air inlet of a 125mm batch box. As Peterberg said, air flow is very dependent on a large number of parameters as flue temp, length... It can double within few seconds, especially by windy weather. Air speed is roughly between 2 and 4 m/s. Here is an example of temp and air speed measurements : Air speed goes to zero when I open the door (no air is flowing through the sensor then). The anemometer was calibrated by the supplier ( here). I did not calibrate it again. I put it in the middle of a small tunnel (160mm long, CS 145x30 mm²), expecting the flow to be laminar there. Air in temp comes from the anemometer NTC which I did not calibrate. Measurements are not that accurate. Tell me what kind of data would be useful.
More information about the set up here |
|
|
|
Post by anounaki on Jul 28, 2021 21:01:10 GMT -8
Very useful information. However, what I need right now is an average flow rate of the air that a common batchrocket stove consumes.
I cannot make complicated calculations now; I lack some scientific knowledge and software (Solidworks CFD) I use has some restrictions.
For the flow simulation I can set some boundary conditions an input value of flow rate and an outer value of environmental pressure.
I have researched that a commercial wood stove consumes about 20-50 CFM. Probably batchrocket stoves consume more but I can’t measure exactly. I have a hot wire anemometer but it is very sensitive to heat and I am afraid I will damage it.
|
|
|
|
Post by fiedia on Jul 29, 2021 12:49:24 GMT -8
You can get some conversion hints between CFM and m3/s here.
Multiply Inlet CS (m²) by air speed (m/s) then you get the air flow (m3/s).
looking at the curves, you notice the air input can vary from 0 to 4m/s in my setup. the "average" you are seeking depends on time interval you take, i.e. what are you willing to simulate and for what purpose. Is it a 24h run ? what happens during the 30mn burning phase ?...
I wish I could help you but it requires you to explain what you want to get from your simulations.
|
|
