Further design improvements to return loops have been added to the Aspen stainless steel heat exchangers. The new loops are orbital welded to improve the unit's cleanliness, appearance and pressure drop. The series was engineered for ultra-clean operation, making it suitable for laser applications that require extremely high purity water or for applications that use corrosive liquids. The new design allows for reduced weight, lower air and liquid side pressure drop and improved internal cleanliness. The redesigned liquid side returns eliminate trapped particles, which can contaminate the cooling fluid.