Why Don't Glassblowing Pipes Get Too Hot to Hold?

[waltl]

Hi. Often, when I am a tour guide at the Museum of Glass, Tacoma,WA. glassblowing shop. I get a question for which I don't have a definitive answer. I thought someone might know.
The question is "why don't the glassblowing pipes(steel tubes, 4.5 feet long, .75" wide) get too hot to hold"
Some of the tour guides say that it is the stainless steel which has a relatively low thermal conductivity(which it does), but that can't be the whole story since stainless pipes are relatively new and that doesn't account for at least 1900 years of glassblowing.
I tell them it is a combination of two things. One the shape of the pipe which has a high surface area to mass ratio so it radiates heat efficiently, the other is that once a pipe head is covered in glass it is to some extent insulated from the heat of the gloryhole.
Which is a bigger factor in the cooling of the handle end of the pipe? Conduction or convection from the surface?

What's your take??

PS. Do you know of anyone who has addressed this question experimentally?

Thanks for your help.

 

[AlephZero]

Glass is a very poor conductor of heat. The thermal conductivity of glass is about 10% of stainless steel, and only about 1% to 2% of iron and most steels.

So if you have a layer of molten glass at say 1500C around the end of the pipe, about 90% of the temperature gradient will be inside the glass. In other words the hot end of the pipe will be at about 150C, and you then have the length of the pipe to dissipate that heat by convection and radiation to the air.

It is counter-intuitive, but if you used an iron or non-stainless steel pipe which has an even higher thermal conductivity, the pipe would be even cooler, because the rate of heat flow is limited by what can conduct through the glass not what can conduct along the pipe, and the temperature gradient along the pipe would be smaller.

 

[waltl]

Thanks for your help, AlephZero.
I am not a scientist, so I am still a little unclear about the last paragraph.
Do you mean that the pipe with higher thermal conductivity is better able dissipate the heat before it reaches the handle?
Or perhaps something else?

Glass is a very poor conductor of heat. The thermal conductivity of glass is about 10% of stainless steel, and only about 1% to 2% of iron and most steels.

So if you have a layer of molten glass at say 1500C around the end of the pipe, about 90% of the temperature gradient will be inside the glass. In other words the hot end of the pipe will be at about 150C, and you then have the length of the pipe to dissipate that heat by convection and radiation to the air.

It is counter-intuitive, but if you used an iron or non-stainless steel pipe which has an even higher thermal conductivity, the pipe would be even cooler, because the rate of heat flow is limited by what can conduct through the glass not what can conduct along the pipe, and the temperature gradient along the pipe would be smaller.

 

[NobodySpecial]

Do you mean that the pipe with higher thermal conductivity is better able dissipate the heat before it reaches the handle?

No it means the higher conductivity metal is colder at the glass end - because it is connected to a cold thing = you.
The biggest temperature difference will then be between the glass end of the pipe and the molten glass - since this temperature difference is across low conductivity glass there is less overall heat flow.

A good way of thinking about it is the traffic jams that would be caused if an 8 lane highway went down to 1 lane - compared to it being 4 lanes all the way

 

[alphy]

I can provide some insight into this question. First, it is important to understand the process of glassblowing and the materials involved. The pipes used by glassblowers are typically made of stainless steel, which has a low thermal conductivity. This means that it does not transfer heat easily.

However, as you mentioned, stainless steel pipes are a relatively recent development in the history of glassblowing. So, what has allowed glassblowers to hold and use these pipes for centuries without getting burned?

One possible explanation is the shape of the pipe. As you mentioned, the long, thin shape of the pipe allows for a high surface area to mass ratio. This means that there is a large surface area for heat to escape from, compared to the amount of material in the pipe. This allows for efficient heat dissipation and helps to prevent the pipe from getting too hot to hold.

Another factor to consider is the process of glassblowing itself. When the pipe is used to gather molten glass from the furnace, the glass forms a layer on the end of the pipe. This layer acts as an insulator, preventing the heat from transferring directly to the handle end of the pipe.

In terms of which factor is more important in cooling the handle end of the pipe, it is likely a combination of both conduction and convection. The shape of the pipe allows for efficient heat dissipation through convection, while the layer of glass on the end of the pipe acts as an insulator, reducing the transfer of heat through conduction.

As far as experimental evidence, I was unable to find any studies specifically addressing this question. However, there are many studies on the thermal properties of materials and heat transfer, which could provide further insight into this topic.

In conclusion, the combination of the shape of the pipe and the insulating layer of glass on the end are likely the main factors that prevent glassblowing pipes from getting too hot to hold. Further research could be done to better understand the specific mechanisms at play in this process.