Why Not? It’s Cheap & Easy
In-line heaters are generally the lowest cost solution, and often the easiest to implement, so that makes them a natural choice for the uninitiated. Unfortunately, as with most things in life, the easiest solution is usually not the right one.
Because they are so easy, it is equally easy to jump right to this solution rather than to properly analyze the problem and determine that this is really the best solution.
Is Heating Really the Right Answer?
It is common to automatically think of heating as “temperature control.” But if you stop to think about it for just a moment, heating is only half the story. The logic goes something like this:
“If I heat my (coating, ink, paint, etc.) the viscosity will go down and I won’t have to add as much solvent to get it to my target viscosity. And if heating it a little is good, and requires less solvent, then heating it more is better and maybe I can get to a point where I don’t have to add any solvent!”
And some even take it one step further:
“If I choose a temperature that is above my highest ambient temperature, I will eliminate seasonal variations because I will always be in the heating mode!”
But one simple question puts all this logic squarely in perspective:
“Is this elevated temperature the temperature that will get the best performance out of my (coating, ink, paint, etc.)?”
Yes, it really is that simple!
What Do You Do When Cooling is Required?
Most paints, coatings, inks, and other process fluids work best when they are at “room temperature” – a temperature that is comfortable for you and me. But ambient fluctuates more than that. Just like in our homes and businesses, we need heating in the winter and cooling in the summer. Sometimes we even need heating in the morning and cooling in the afternoon!
But if you go with an in-line heater, what do you do when you need cooling?
The reality is you can’t do anything, temperature-wise. You must make other adjustments to compensate for the changes in viscosity caused by temperature variations. Just like you did when you didn’t have any kind of temperature control.
It’s Almost Like No Control at All
It primarily boils down to the fact that, when you try to operate at an elevated fluid temperature in a normal ambient environment, losses in the system fight against you. Once your material leaves the heater, it is exposed to ambient surfaces that begin to pull down its temperature. The rate of loss is dependent on three things:
- The surface area exposed to ambient between your heater and your point of dispense.
- The temperature differential between your material and ambient.
- The exposure time.
And this is where it all begins to spin out of control. This is where you begin to address other issues instead of focusing on what’s important – the temperature of the material you are dispensing.
You need to place the in-line heater as close to the point of dispense as possible. But what if the fluid you are dispensing is solvent-based and therefore creates an explosive environment? In this case, you either must take extraordinary measures to prevent detonation, or you must place the heater outside of the explosion-proof area, well away from the actual point of dispense.
Of course, now there is more surface area exposed to ambient, so the longer the material sits in the system after the heater, the more it changes temperature.
The solution? Insulation!
Of course, insulation only slows the temperature change, it does not stop it, so you’re right back where you started!
But Worst of All, In-Line Heaters Can Damage Your Delicate Fluids!
…and destroy themselves in the process!
The drawback with in-line heaters is that they are small, and therefore have limited available surface area through which to transfer the required heat. Without getting too deep into the physics involved, when there is limited thermal transfer area, there must be a corresponding increase in temperature differential (ΔT) between the heater surface and the fluid being heated.
Unfortunately, the high surface temperature can damage the delicate (coating, ink, paint, etc.) fluid that you are applying. This can cause it to behave poorly in your process and even create unacceptable results.
This phenomenon can also lead to premature failure of the heater itself. When exposed to the hot surface inside the in-line heater, the (coating, ink, paint, etc.) “bakes” onto the surface. This creates a layer of insulation between the fluid and the heater surface, so to get the outlet to the proper temperature, the heater applies more heat. This bakes another layer onto the surface. This process repeats itself until the baked fluid completely plugs the heater passages. The only solution would be to replace the heater.