Hot soot particles trace paths in turbulent buoyant plume above a fire

Hot soot particles trace paths in turbulent buoyant plume above a fire

By Marco Gardi for Get Wet 2016

Hot ashes in the column of rising gases above a fire.

Report:

I came up with the idea for this image somewhat by accident while I was talking to some friends by my newly made fire pit one night. The shots I took of the fire that night contained the hot ash tracers that inspired me but I didn’t have my tripod with me so I couldn’t properly frame the whole fire pit. For the final image I planned to move the camera about five feet away in order to capture the entire flame and the column of rising air above it.

The apparatus producing the flow is a wood fueled fire inside a backyard fire pit. The logs were burning for about 30 minutes before the shot and were completely charred on the outside. By disturbing the logs with an iron poker, some of the hot ashes on the surface of the logs detached. The rising hot gases propelled the ashes vertically. The particles of ash are visible because of the energy they are dissipating. The streaks of hot ash form a compact column where the flames stop; as they’re carried away from the flames and their velocity decreases it looks like they diverge from the center of the column, falling back towards the ground. The ashes that depart closer to the edge of the main flames seem to travel shorter, more turbulent paths while the ashes that start at the center of the fire leave longer and smoother vertical paths suggesting the velocity of the gases is highest in this region due to higher temperatures. Overall the flow appears to be turbulent suggesting the Reynolds number is greater than 4000. I estimate that the speed of the particles at the center of column is about 3 m/s based off a light trail 5 feet in length captured in half a second.

The camera I shoot with is a Nikon D3100. As for the technique, the shutter speed was set to a half second which was slow enough to capture the light trails of the hot ashes. The aperture was f/7.1 and I set the ISO to the minimum level of 100 to compensate for the long exposure. Even though I took the image outside at 10 pm, no external light sources were necessary to achieve this image leaving the background completely unexposed and adding most of the contrast to the image. I placed the camera on a tripod six feet away from the fire and two feet off the ground. I set the focus manually. In photoshop I increased the contrast just a little using a curves layer. I also increased the clarity in the raw editor and applied a high contrast filter with the radius set to 5 pixels and the blending mode set to overlay.

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29 Comments. Leave new

  • This is a gorgeous image using some great photography skills. The focus on the flame and sparks is spot on along with the contrast. The sparks dying off up top are very well captured with the long exposure. I’m sitting here wishing I had some marshmallows!

    Reply
  • Sierra Castillo
    September 20, 2016 7:57 pm

    I love these types of images. The contrast is great between the flames and the black background. The rocks from the pit really add a physical presence in the image that makes it feel real.

    Reply
  • Schuyler Vandersluis
    September 19, 2016 12:46 pm

    The contrast in this image is awesome. The flow is represented and understandable, and the focus is also good.

    Reply
  • I like the color and length of the exposure to show enough trails but not too many. Making the background black but keeping some foreground also helps add to the artistic value. I found the few ashes on the edge interesting that are rising then begin to fall as their weight counteracts the thermal lifting forces closer to the center of the fire. It helps depict where the natural flume of smoke rises in thermally.

    Reply
  • I really like the contrast and long exposure in this photo. A very different take on a photo of a campfire. Great work!

    Reply
  • Art: Fire is one of the most common elements in artistry. It gives people a sense of tranquility.
    Flow: Clearly illustrates the locomotion of the flame above the burning wood.
    Photography: The shutter speed control was a perfect maneuver. Fantastic!

    Reply
  • Well done getting the ember trails on the fire with the long exposure. Focusing is superb, quite a crisp image. In the future might want to try and crop a little more off the bottom, the fire pit itself distracts away a little from the fire.

    Reply
  • Preston Marcoux
    September 15, 2016 2:34 pm

    The focus makes this image, nice use of longer exposure to capture tips of the fire.

    Reply
  • I like the artistic aspects of this photo. I like the illumination of the ground in a circle. The particle tracks are nice to see the flow of the air rising above the fire. Nice technique, with the open shutter time.

    Reply
  • Joseph Straccia
    September 14, 2016 7:23 pm

    The long exposure on this image really reveals the complexity of turbulent mixing in natural convective plumes. The warm colors are appealing and the subject speaks to that primal human instinct that draws people to sit around a fire and stare into the flames in quiet reflection. If you ever get the chance to play with software that has an HDR (High Dynamic Range) function you may be able to recover some detail in the hottest parts of the flame. The one risk is that the software will probably try to bring out details in your background that you’d rather leave on the black end. I use Photomatix and I think for a student it’s ~$30.

    Reply
  • Katherine Yarnell
    September 14, 2016 7:17 pm

    This photo had very good focus. This was a very interesting photograph and had really great contrast. You are able to see the particle tracking very well.

    Reply
  • Alexander Thompson
    September 14, 2016 4:03 pm

    Fantastic job capturing the intent of the image, which was to track the embers released by the fire while being disturbed (poked with a stick). Great idea! And great photographic techniques adjusting the exposure and shutter speed to capture particles’ movements.

    Reply
  • 1. Love this image!
    2. The tight focus is really well done
    3. The contras is beautiful

    Reply
  • Art: Aesthetically astounding. Framed perfectly as the fire elements captures the majority of the image.

    Flow: The flow is understandable and is of high quality.

    Photographic: Wonderful employment of technique! Captures the image perfectly!

    Reply
  • 1. The image is dramatic and pleasing.
    2. The flow physics of the image are less apparent.
    3. The photographic technique is good with excellent focus showing the fire.

    Reply
  • Maxfield Scrimgeour
    September 14, 2016 12:46 pm

    The focus of the photo and the long shutter speed of the image really provides a dynamic visualization of the flow. The contrast of the photo is very nice and has a whole range of color included.

    Reply
  • Michael Waterhouse
    September 14, 2016 12:43 pm

    Art: Very effective contrast of colors. Flow: Interesting flow. It was nice to see how much detail you were able to get. Photographic technique: Good distance to the firepit. Flow is captured all over the image.

    Reply
  • This image is great because it shows the life of the fire. Your contrast and focus is great.

    Reply
  • Art: Dramatic image of fire being extended up in the air.
    Flow: Really cool to see ember tracks as they rise up.
    Photo: Looks really good with black background, helps to clearly see embers.

    Reply
  • The quality of this image is awesome. The particle tracks are my favorite, looks beautiful from an artistic standpoint. Simple technique that produced a really clear, beautiful image.

    Reply
  • The intent was to be able to capture the streaks of amber rising up above the fire pit. The flow is controlled using a poker which allowed for easy amber production. The focus is perfect.

    Reply
  • A. Beautiful contrast between the red hot fire/sparks and the blackness in the background
    B. Very creative flow
    C. Great focus on the fire with no distractions

    Reply
  • CRISP. Really like it. The shutter speed was really cool. The framing is really cool.

    Reply
  • Art: I love the streams of the flames. Amazing work on the framing.
    Flow: It was a great decision on poking the fire before the picture. It clearly shows how dynamic fire can be.
    Photographic technique: Possibly more contrast but do love the difference between the black and red.

    Reply
  • Alexander Rosenberry
    September 14, 2016 12:41 pm

    Sharp focus and good detail lends a dramatic feel to this image. The slightly longer exposure that reveals the paths of the sparks makes this image striking.

    Reply
  • Art: The color contrast between the fire and the background is very dramatic, the colors that are in the fire gives it a look like it is alive.
    Flow: The flow is understandable and easily recognized.
    Photographic technique: The detail of the embers is very nice, the trailing of each ember is fantastic.

    Reply
  • – Intent is realized.
    – Great use of particle tracking and use of exposure, no distracting outside elements.

    Reply
  • The focus in your image is very crisp and the contrast is very clean as well. it enhances the “alive’ feeling of the flames as the ash. The speeds should be easy to calculate as long as you have the shutter speed documented.

    Reply
  • Branden Goldenberg
    September 14, 2016 12:41 pm

    Love the extended shutter speed to see the flow of the embers. leaving the fire pit in the image is an effective way of giving the photo depth. Very creative spin on a common visual.

    Reply

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