Well, it is here. The middle of summer cannot be denied in Cincinnati this week. We have had a high temperature of at least ninety degrees the last five days with near 100% humidity. These are the days when you have to either work very earlier in the morning or very late at night to get any yard work done. You’ll notice that the most of our blogs the last couple weeks have been about keeping things cool, like Cabinet Cooler systems, or High Temperature Cabinet Coolers. I’m not one to buck a trend, so I’m going to talk about cooling as well, but I will talk about cooling a manufactured product.
A customer this week was designing a new plastic extrusion system and he needs to quickly cool four plastic extrusions strands from 400 degrees Fahrenheit to 120 degrees at a fairly high feed rate. In the past the customer had used an immersion bath followed by a blow off station using EXAIR’s Air Knives, Air Wipes, or Super Air Nozzles depending on the plastic extrusions geometry. The immersion bath would use the specific heat of the water to quickly take away the heat from the extruded plastic. This process had worked well for him in the past, but the immersion bath was expensive to build and maintain. For these reasons, he was looking for an alternative.
What is going to cool better than water? The water in the immersion bath has a very high specific heat, which is what makes it such a good material for cooling large amounts of heat very quickly. Specific heat is the amount of energy it takes to raise 1 pound of mass 1 degree Fahrenheit. One British Thermal Unit (BTU) is the amount of energy it takes to heat or cool one pound of water one degree. A BTU is 1,055 Joules, which is a very high specific heat compared most other common materials. So we can’t change the immersion liquid, but could we come up with a better process?
Well of course we can. We can use both the specific heat of water and the latent heat of water. The latent heat is the amount of energy water takes to evaporate. The latent heat of water is 970.4 BTU per pound. If we can use both the specific heat of water and the latent heat of water, we can increase our cooling and not need a large, expensive immersion bath. The customer came up with the idea of using Atomizing Spray Nozzles and a blow off station to get the same amount of cooling but without needing a water bath. By spraying a fine mist of water onto the extrusions, we create almost the same amount of conduction with the water and the plastic. The water takes out the energy of rising from room temperature to its boiling point, then takes out the energy of evaporating, and then the air dries the remaining water and takes away any more heat that may be remaining.
Dave Woerner
Application Engineer
davewoerner@exair.com
@EXAIR_DW
