VACUUM VAPOR DEGREASING EFFICIENCY
Most industries favor vapor degreasing with chlorinated solvents, primarily because of the Kauri-butanol number as a key indicator. A deeper examination of the cleaning process reveals an even more significant reason for their effectiveness: the Normal Boiling Point (NBP) of chlorinated solvents is considerably higher than that of many alternative solvents. This distinct property is of considerable importance. Vapor degreasing operates by condensing the solvent onto the component, wherein the liquid solvent dissolves the contaminants and subsequently drips away. During condensation, the component’s temperature rises until it reaches the vapor temperature. It is essential to assess whether sufficient liquid solvent is present on the component to dissolve the contaminants effectively.
Three critical factors must be considered: firstly, the NBP; secondly, the size of the component; and thirdly, the latent heat of vaporization, which is the heat energy associated with the volume of liquid condensed. To illustrate, compare trichloroethylene (TCE) with fluorinated blends of trans-dichloroethylene (Trans), which are commonly used as substitutes in vapor degreasers.
The NBP of fluorinated blends varies from 109°F to 118°F, whereas TCE’s NBP is 188°F. The latent heat of vaporization per volume is approximately equivalent—1310 Btu per gallon for TCE and 1255 Btu per gallon for the fluorinated blends. For components introduced into a vapor degreaser at room temperature (70°F), the temperature differential between the vapor temperature and the component ranges from 39°F to 118°F. Consequently, a vapor degreaser utilizing TCE condenses approximately 2.5 to 3 times more liquid on the component (ratio of 118 to 39 or 48). If regulations permit the use of chlorinated solvents, opting for a solvent that supplies more liquid to the component, possibly with a vacuum system, may be advantageous. Transitioning to an unregulated solvent at a later stage remains an option. For optimal vapor degreasing with low-boiling solvents, vacuum vapor degreasers can be designed to meet these requirements.
In conclusion, not all solvents exhibit identical performance characteristics, even when chemically similar. Modifying your cleaning chemistry is more complex than some vendors or regulators may suggest. We recommend you consult with us first—we have over 25 years of experience.