I have a Sunbeam home espresso machine with a steam wand. The steam roars out straight from the end of the wand. When it's first placed in the cold milk it really screams! Once the milk has a bit of a whirlpool action going it's much quieter, so I guess that the noise is because of fast-moving steam hitting stationary cold milk. Something something fluid dynamics?
[Physics] Why does the milk frother on the coffee machine make so much noise
everyday-lifefluid dynamicshome-experiment
Related Solutions
What you need to apply is the engineering equations for a heat exchanger. In the below equation, $\dot{Q}$ is the heat transfer rate, $UA$ is the heat transfer coefficient times the area and $\Delta T_m$ is the log mean temperature difference (LMTD).
$$\dot{Q}=U A \Delta T_m$$
For this problem there are 3 barriers to the heat transfer in series. You have the convective heat transfer coefficient of the syrup $h_c$, the convective heat transfer of the steam $h_s$, and that of the pipe metal $h_R$. Take $n$ to be the number of pipes, $r_i$ to be the inner radius of the pipe, and $r_0$ to be the outer radius of the pipe, and $R$ the heat transfer coefficient of the Copper.
$$UA = \frac{2\pi n}{\frac{1}{h_s r_i}+\frac{1}{R L} ln \frac{r_o}{r_i} +\frac{1}{h_c r_0} }$$
The LMTD is the average temperature difference, but for the specific case where one part of the heat exchanger is saturated, and thus constant temperature, just know that it is the following, where $T_{s}$ is the saturation temperature of the steam, or 100 degrees C. Then $T_h$ and $T_c$ are the temperatures after and before preheating respectively.
$$\Delta T_m = \frac{T_h-T_c}{ln\frac{T_h-T_s}{T_h-T_s} }$$
The hard part of the above equations is the $h_c$ and the $h_s$. You will probably use things like the Dittus-Boelter correlation. But it's more important that for the moment we address $\dot{Q}$ itself. For the described hood, I see two possibilities.
- The steam is being provided at a faster rate than it is being condensed
- The steam is being provided at a slower rate that it is being condensed
In the first case, you will see steam leaking out of the hood. In this case, the equilibrium operation see the air mostly evacuated because it is pushed out. In the other case, steam is present with air and the air reduces the heat transfer. In case #2 the given is the rate of steam condensation, which directly determines $\dot{Q}$ and $h_c$ adjusts to compensate. In case #1 $h_c$ is a given based on the assumption of your geometry and the atmospheric steam heat transfer properties.
For $h_s$ use Wikipedia:
$$h_s={{k_w}\over{D_H}}Nu$$ where
$k_w$ - thermal conductivity of the liquid
$D_H$ - $D_i$ - Hydraulic diameter (inner), Nu - Nusselt number $Nu = {0.023} \cdot Re^{0.8} \cdot Pr^{n}$ (Dittus-Boelter correlation)
Pr - Prandtl number, Re - Reynolds number, n = 0.4 for heating (wall hotter than the bulk fluid) and 0.33 for cooling (wall cooler than the bulk fluid).
What I don't have right now are the numbers for applying the above for Maple Syrup and the approach for the steam side of the tubes. This is all I have time for right now, but I think this amount will still be helpful. I can try to look up these things later, maybe you can specify what you understand the least first.
Yes, it's the cooling down. This happens mostly with CRT monitors (I've own a lot) and could still happen with LCD monitors (rarely, mostly occurs in cold temperature). Electronic components wouldn't be the source at all.
Capacitors don't make a noise when it discharges gradually which is assumed. If it does then the world would be a bad place to live (too much dB).
Things I can say to be NOT the source of sound are:
electrical components: The only electrical components that makes a noise are speakers and relays. Both are eliminated as a source since a speaker probably don't exist in a typical CRT and, though a relay may, a relay only makes a single tick sound - a quiet one.
static: it can't be static, a crack and static sound barely have similarities.
To be concise, the sound is simply the case. That's why this seems to happen more often in colder weather is because when the monitor is turned on it heats up (especially CRTs) expanding the case a bit, and during cool down, the manufactured plastic will start to change shape in edges causing the sound, and in colder environments this will tend to be more pronounced because the collapse in a greater magnitude is like to occur more.
Best Answer
There is a lot of protein in milk, so when it is heated with steam, the water evoporates and protein start to foam around the steam wand. Due to tiny holes on the steam wand, the velocity of the jet will be high(high velocity) and the moment it reaches out of the wand, it heats the milk producing protein foam making it thick blocking the orifice creating a whistling noise. If you notice the steam wand, however smooth surface it has got, you can see a layer of milk protein stuck to it. This thick layer of milk moves/provides steam to expand away if you give the cup a worlpool action.
To understand this, just leave some steam without placing cup. It makes a noise. Steam tries to expand the moment it comes in contact with cold air absorbing water content from surrounding.