Heat Exchanger World Magazine October 2024 | Page 33

Pillow Plate

Cooling / evaporation plates are used with : - Ice water 0.5 ° C - Glycol - Freon , R12 , R22 , R143a , R404a , etc . - Ammonia R717 - CO2

Pillow plate heat transfer calculations The heat transfer K-value from pillow plates is based on experience values . The K-value can differ from 5 W / m 2 with natural flow of gasses up to 1400 W / m 2 for a forced steam application . Over the last 20 years , there have been calculations developed for dimensioning the heat transfer area for tanks , bulk solid heat exchangers , falling films and ice banks . These calculations are available at Keppels Laser Welding . The calculations are from simple heat transfer equation with the K-value , calculations with Reynold values , calculations with ice growth rates and differential equations for heat transfer in solid applications . The simple calculation is used for cooling or heating tanks , whereas the more complex calculations are used for the double embossed plates , submerged in liquids or solids .

What we also see is that companies with pillow plate products develop their own calculations for their specific pillow plate applications , for example in the condensing , chemical and pulp & paper industry . Over the course of our twenty-four-year pillow plate business venture , we have seen that , in order to ensure the application ’ s functionality , an additional reserve heat transfer area is included after the heat transfer calculation . A classic failure in dimensioning is a different K-value in heating or cooling of oils , leading to an under dimensioned heat exchanger .

The future of pillow plates In 2024 , 99 % of the pillow plates are made of stainless steel , grade 304 to SMO254 , duplex and exotic stainless steel version . The rest is made of titanium or carbon steel . The stainless steel grades are welded perfectly with the fiber laser and the materials that can handle thermal changes in the applications . With the relatively bad heat transfer from stainless steel , we are looking for other materials to produce pillow plates . Until 2024 , we have never seen a pillow plate in copper or aluminum because they are difficult to weld and process afterwards to a pillow plate . This year , Keppels Laser Welding has achieved laser welded pillow plates from copper and aluminum . We advise to do a welding and inflation test on the type of material for your application with possible following top plate thicknesses :

- Copper : from 0.1 to 1.5 mm thickness ; - Aluminum : from 1 – 3 mm thickness .