Page 50 - Winter Issue 2018
P. 50

Advancements in The:-mnphanes : :
bustion explosions, none of which held up successfully to I I
scrutiny. It was not until after experiments were performed ‘ I
by Sondhauss (1850) and Rijke (1859) that an adequate the- : :
ory was developed by Lord Rayleigh (1878). com ‘-1 L HOT
Experiments were performed by Sondhauss and Rijke be- i l
tween 1850 and 1860 resulting in the setups that bear their
names. A Sondhauss tube is a thermoacoustic device with B ‘\ /’ e°"VE‘-"'VE F‘-°W
a long cylindrical neck that is closed off at one end, some-
times in a bulbous structure (Figure 1A). W'hen the bulb or
closed end is heated, sound may emit from the opening in
the neck, with a frequency dependent on the resonant struc-
ture created by the bulb and neck. This effect had long been
known by glassblowers who, at times, noticed a sound pro- HEATED
duced as blown glass bulbs began to cool. In the Sondhauss Wm‘ "'55"
tube, a parcel of cool air enters the heated bulb and heats up
as it is compressed further into the bulb. The heated parcel
subsequently expands and further cools as it comes in con-
tact with the colder tube. The rarefied region then collapses j K CONVECHVE new
again toward the bulb as it heats, completing a cycle. Ray- _,
leigh posed that the condition that enables the amplification c
of sound (which occasionally needs a small “kick” to jump C 1
start) is that the parcel is heated during compression and '13?
cooled during rarefaction by displacing to the hot and cold 1
regions of the tube, respectively. l /:3)‘ l 
A Rijke tube is a simple vertical cylinder open on both ends, ,t:l  
with a heat source, often a heated wire mesh or gauze, in- ,_9_!,.‘ ‘F,% _._,
serted in the bottom half of the tube (Figure 1B). Here, “F?” 4 J“-W‘ 
convective flow rises through the bottom of the tube and is  3.
heated as it passes through the mesh. The gas first expands ‘AL,,.,;,.;-:z~--<@y‘) ' ' I
and then contracts as it interacts with the sidewalls of the A  ‘S "  til
tube. Eventually, a standing wave is created (which can be 1 ’ 3 mt 
mathematically represented as a combination of traveling E‘  ~:.-_—‘..':.‘.’.  :__Vk
waves moving up and down the tube, being partially reflect- “"“itW[" -l 5*
ed at the openings) superimposed on the convective flow.  
Early embodiments of both devices by Herschel (1874) can 4 e
be seen in Figure 1C.
The Source ofheat for «Singing flames» was originally through Figure 1: A: a simple bulb—end Sondhauss tube. Typically, a flame is
the Combustion ofhydmgen gas although the ability to Pro_ used to heat the bulb externally. B: a Rljke tube with open ends and
’ ’ a heated wire mesh inserted in the bottom half of the tube. A and B:
dhee an aeohstle leSP°n5e ls largely lndependent Of how the heuristic representations of the hot (red) and cold (blue) regions and
heat iS generated. Instead. What matters most is how heat i5 are not accurate representations of the temperature profiles. See text
distributed and how it propagates throughout the system_ for details. C: various embodiments of Rijke and Sondhauss tubes, al-
some R1}-ke tubes’ even early on’ used batterY_Powered re_ though not referred to as such, by Herschel (1874). 1 and 4: Bunsen
sistive heating (]oule heating) of coiled wires. Furthermore, burner?’ elfigatzmfgtfe gas thatltlm mm: 5:0” (,1) at l°"gl(3 an:
if the heating element is fine enough, sound can be produced 4) vemm 1] B m 8" 6 gm mm um at t B of Wm gnu.“ mate
partway up from the bottom of the tube. Even after the gas is shut ofif
Wlthoht the lesonatlng tube by Oselllatlng the telhpelathle 0t a loud sound can be heard that fades as the gauze cools. 2 and 4: Two
the element at acoustic frequencies. Such a device is called short bulbous Sondhauss tube;
a thermophone, a term coined by Weisendanger (1878a,b).  
43 | Acnuaeica Thday | Winter 2018

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