Batch box dimensional limits

Dear Rocketeers...

I have a couple of questions for the experts amongst us relating to a rather esoteric design requirement for a rocket mass heater.

The premise is that I would like to try and fit a batch box into the geometry of a hanging fire shown in Figure 1, with the thermal mass located above the fire, hidden out of the way. This means I would like to reduce the aspect ratio of the batch box.

A standard batch box is shown to the right of the hanging fire with a "cinemascope" version with reduced H/W to the right of this.

The three questions are:
• By how much can I reduce the height/width aspect ratio of the batch box without significant impact on the ability of the fire to burn properly?
• How much could I Iower the height of shoebox (H_shoebox) without damaging the vortex flame?
• What is the minimum thickness (T_flue) required for the flue between the burn chamber and the shoe box. In the design that I downloaded, T_flue is 40mm.

In Figure 1 :
• The normal design has H/W= 300/300, ,  H_shoebox =110mm, T_flue=40mm
• The “cinemascope” design has H/W = 300/500, H_shoebox= 80mm, T_flue =40mm

If anyone has tested any of these parameters ie H/W ratio,  H_shoebox , T_flue , I would love to hear what observations you made.

Thank you in advance

Stephen

Hi Stephen;
It appears that you're looking at a Double Shoebox batch, not a standard batch.
There are three variations of the shoebox design.
Only Peter could tell you for sure if you can change the shape or not.
I highly suspect that it would not function properly with the different dimensions.
No harm in asking perhaps it can be done.

stephen wilson wrote:A standard batch box is shown to the right of the hanging fire with a "cinemascope" version with reduced H/W to the right of this.

What you are calling a "standard batch box" is probably a Vortex core or a Double Shoebox Rocket, DSR1 for short. The DSR1 is discontinued as a proper core because of its very temperamental behaviour. The Vortex core is still being worked on, mostly by its designer and Fox James, who's posting here regularly.
But let's see what I could make of your design deviations.

stephen wilson wrote:The three questions are:
• By how much can I reduce the height/width aspect ratio of the batch box without significant impact on the ability of the fire to burn properly?

All batchrocket designs are very tight, changing the ratios mean it would be turned in a very different core altogether. I have tested a lot of variations in the past 12 years, anything that is being done differently to date will turn the thing into a badly smoking mini dragon.

stephen wilson wrote:• How much could I Iower the height of shoebox (H_shoebox) without damaging the vortex flame?

Simply: in my honest opinion you can't, see above.

stephen wilson wrote:• What is the minimum thickness (T_flue) required for the flue between the burn chamber and the shoe box. In the design that I downloaded, T_flue is 40mm.

Most of these designs (the recent Shorty being the exception) tolerate a port (or gate) that's as deep as wide. With a general tolerance of +/- 25%.
You downloaded this design, from where? Who's the author?

stephen wilson wrote:In Figure 1 :
• The normal design has H/W= 300/300, ,  H_shoebox =110mm, T_flue=40mm
• The “cinemascope” design has H/W = 300/500, H_shoebox= 80mm, T_flue =40mm

If anyone has tested any of these parameters ie H/W ratio,  H_shoebox , T_flue , I would love to hear what observations you made.

I'm inclined to think you downloaded a design sketch of Trevor's. He's the guy who built a succesful mass heater/cooker with it. Have a look at https://donkey32.proboards.com/thread/703/vortex-stove, best to contact him. Warning! Very long thread!

Hi Peter,

thank you for the response. I will take on board your comment about the tolerances of the DSRx cores being very tight. Perhaps my only route for making the hanging fire is to keep to the parameters for the Vortex core that you mention and either size it to fit in the design aesthetic that I have ... or change the aesthetic.

As regards DSR design that I showed ... I can't recall where that one came from ... I just downloaded a bunch in the past. It's good to know that the DSR1 is now considered obselete/temperamental. Sounds like I need to do some revision on the development history of the batch rocket.

Regards

Stephen
FYI - I finally finished off my batch rocket pizza oven/parrilla a few weeks ago. She's working a treat. So many thanks for all your work on the sketchup designs and proper empirical observations.  https://permies.com/t/223663/Casting-batch-rocket-heat-source