Industrial CO2 laser temperature management

[theycallmevirgo]

TL;DR Summary

How do I evaluate operating temp for co2 laser cutter?

Here it is specified that optimum operating temp for industrial C02 laser is within the range 59 °F to 77 °F. This is what is generally specified online, but it leads to a number of questions;

• How is this measured? Does it refer to the whole unit, or the point of emission of the beam, or some other part? Most sources seem to imply that coolant temp===unit temp. Is this accurate? If so, why? More importantly, how can it be accurate given an unknown circulation rate?
• If measuring temperature of the unit as opposed to coolant, what sensor can be used, and how should it be positioned? I'm guessing infrared just won't do it.
• One of the implications is that if you cool below 59F you might be able to overpower. Is this accurate? Does anyone know of any experimental data or calculations to support this?

Thanks so much in advance for any help

Joe

 

[DaveE]

Summary:: How do I evaluate operating temp for CO2 laser cutter?

Here it is specified that optimum operating temp for industrial C02 laser is within the range 59 °F to 77 °F. This is what is generally specified online, but it leads to a number of questions;

• How is this measured? Does it refer to the whole unit, or the point of emission of the beam, or some other part? Most sources seem to imply that coolant temp===unit temp. Is this accurate? If so, why? More importantly, how can it be accurate given an unknown circulation rate?
• If measuring temperature of the unit as opposed to coolant, what sensor can be used, and how should it be positioned? I'm guessing infrared just won't do it.
• One of the implications is that if you cool below 59F you might be able to overpower. Is this accurate? Does anyone know of any experimental data or calculations to support this?

Thanks so much in advance for any help

Joe

Don't overthink this. While I haven't seen the installation manual for your laser, I saw a lot of them when I worked for a big laser manufacturer (wrote several of them too). So here's my guess:

- It refers to everything unless they say otherwise. Definitely not at the beam aperture only. Also, temperature of what? The air? the coolant? That should be clear in the manuals. Read the manuals very carefully, even the footnotes.

- I'd use a thermocouple sensor myself. However, there are a lot of different ways of measuring temperature.

- No one will tell you that you can get more power reliably at lower temperatures, even if you can. Only the manufacturer has the data to support this, and you already have their conclusion in the specifications. Manufacturers want specifications that are attractive to their customers. If they say 58F is too cold, they had a reason, otherwise they would have set the limit lower. Almost anything you do to try to get more power will have a significant effect on lifetime and reliability. Trust me, the manufacturer has already carefully considered those tradeoffs and designed accordingly.

Time to call the manufacturer for customer support. As an aside, one of the reasons the company I worked for got big was because of the effort that went into customer support, things like good designs, good clear manuals, customer support in sales, field service, applications engineering. But, you get what you pay for, especially in the laser business. Use the customer support, if they have it, you'll get better answers from them than us. Social media (even PF) isn't the place to get information about redesigning lasers or the consequences of exceeding their specifications.

In general, this question falls into the most difficult category for any engineer: "If I do something wrong, how bad is it?"

PS: Also, why do you link to a chiller manufacturer and not the laser manufacturer? They don't know either. This is what a typical laser installation manual looks like, and yes, you have to read the whole thing if this was your laser.

 

[theycallmevirgo]

Thanks so much for this. For reference, I didn't start with laser manuals because I'm building a system for personal use with off the shelf parts, and the kind of thing that shows up on Amazon tends to have some shortcomings when it comes to manufacturer documentation. I spoke with the people behind that website on the phone, and they made it very clear that they only measure the water temp. Frankly, I find this extremely confusing. I realize that maintaining a constant water temperature will dissipate a large maximum laser unit body heat, but how is it possible to design the cooling unit unless you know how hot the laser will get?

 

[Tom.G]

but how is it possible to design the cooling unit unless you know how hot the laser will get?

By knowing how much energy (in this case, electrical energy, Watts) is supplied TO the Laser. That is the amount of energy the cooling system must REMOVE.

You will also need to know the Maximum allowable temperature of the Laser, the coolant temperature must be below this value upon exiting the Laser. How far below is determined by the thermal transfer characteristics between the Laser itself and the coolant.

Now you can adjust the coolant flow rate to carry the required energy from the Laser to the Cooler.

Keep in mind that there is likely a Minimum temperature for the coolant entering the Laser.

Are you sure you want this as a DIY project?

Cheers,
Tom

 

[theycallmevirgo]

By knowing how much energy (in this case, electrical energy, Watts) is supplied TO the Laser. That is the amount of energy the cooling system must REMOVE.

Surely not all the supplied energy is converted to heat? Surely some does the work of laser emission?
You will also need to know the Maximum allowable temperature of the Laser...determined by the thermal transfer characteristics between the Laser itself and the coolant.

This makes much more sense. How can you calculate/evaluate thermal transfer?

Are you sure you want this as a DIY project?

People have been building diy systems with Chinese parts for years. If you Google k40 laser I'm sure you'll see things that will make you cry.

Frankly, what they generally do is fill a 5 gal bucket with water, throw in a few frozen water bottles, hook up an aquarium pump and call it a day. Even if I didn't consider this super ignorant, I just don't have the freezer space :).

Even given that simple setup, how many frozen water bottles do I need? What volume? If there is no answer more specific than "some", why not zero? What is the minimum volume of ice?

My general approach to diy projects is a desire to learn something. Of course I could blindly follow some online instructions. They would probably even work. But I have this amazing resource here, so why not make full use of it?

 

[Tom.G]

How can you calculate/evaluate thermal transfer?

Essentially you don't!
You get the tube manufacturers specs for maximum coolant outlet temperature, or maximum inlet temperature, and minimum coolant flow rate. There is probably a maximum coolant pressure too, but I didn't find any mention of it.

I checked the specs of a few K40 laser tubes online. They range in power input from 225W to over 400W.
(here is one reference I found:
http://donsthings.blogspot.com/2017/05/k40-laser-tube-specifications.html)

how many frozen water bottles do I need? What volume?

That you will have to calculate. You need to look up the 'heat of fusion' between water and ice. This will be either BTU per pound, or Joules per gram or kilogram, depending on whether you use English or Metric units. (on Google, search for heat of fusion of ice)

Then you need to know the power input to the K40 Laser tube.

From those two pieces of information you can determine the operating time until you melt most of the ice.
(note: conversion between BTU and Watts: 1 Watt = 3.41 BTU)

Cheers,
Tom