Boilup heater

The temperature controller in the boil sump should immediately activate the boilup heater, and it should strive to regain the situation whicli was present when the parts entered the vapor degreaser by rapidly adding heat. 

The boilup heater must have a high power capability or rating °. Its duty (job) is nothing like that necessary to compensate for convective and radiative heat losses to the environment so as to maintain the vapor degreaser unit at working temperature. 

The first basis, noted above, for rating the boilup heater is to heat the parts (and metal basket) and the solvent to the normal boiling point of the cleaning solvent (which is different for each solvent). Requirements of the boilup heater to fulfill this task are shown in Table 1.2 ... 

The basis for design included the items noted in Footnote 33 and that the combined weight of parts (and basket) is 50 lbs, and they are made of stainless steel Heat duty is proportional to the mass of metal, and inversely proportional to the required recovery time from when the cold parts and basket disrupt the vapor zone until when the vapor zone has been restored by re-vaporization of solvent. More rapid recovery will require a boilup heater with proportionally more capacity, and the reverse... 

This is an exceptionally large mass of metal to be heated in a small degreaser, but the value was chosen to make a point. The point is that not only is there a volumetric size limitation on parts which can dimensionally fit into a vapor degreaser, but there is a mass limit as well, which can require the boilup heater to have an exceptionally large capacity... 

The second basis, also noted above for rating the boilup heater, is to vaporize solvent to form the vapor zone. 

The boilup heater must independently fulfill both tasks (1) heat the cold parts (and basket) from ambient temperature to the normal boiling point of the solvent (Table 1.2), and (2) replace the vapor zone by providing the latent heat of vaporization (Table 1.3). 

One characteristic which can be used to differentiate among vapor degreasers from different suppliers is the rating of the provided boilup heater. Suppliers may provide a heater with a low rating so they can offer a machine with a lower price (or higher profit), and appear to offer a corollary benefit for the site — a reduced demand on the type and supply of electricity. 

This can be an unwanted bargain. A too-small boilup heater extends the production cycle time because the time to heat the parts (and basket) and establish the vapor zone are lengthened. 

A survey of more than 40 currently produced vapor degreaser models showed a great disparity in the capacity of the provided boilup heater. These details are plotted in Figure 1.27. Only 9 of these 40 machines met the substantial requirement for capacity of their boilup heater for every solvent as noted in Table 1.4. 

A purchaser of a vapor degreaser should either specify the size of the boilup heater using the information above, or specify the required recovery time and solvent, and allow the supplier to provide the specification for the heater. 

In summary, the boilup heater may appear to be a minor appliance in the overall package of components which is a vapor degreaser but it s not. The boilup heater directly controls the cycle time of the process completed in the degreaser. It controls the quality of cleanliness achieved because of the rinsing provided within the vapor zone. And if it s oversized, it can supply hot vapor at a rate faster than the cooling coils can condense it and return it to the liquid sumps. 

This author agrees with Dumey that the cooling coils should be at least 100% oversized (on a rate basis) vs. the instantaneous capability of the boilup heater to produce vapor. Spatially, this places the top of the r por zone in the middle of the cooling coils — leaving the portion of the cooling coils above the vapor zone as an insiuance poUty," and a location where the drying process can be completed (Chapter 1.17). 

Rapidly and effectively dry the parts, while keeping the boilup heater from fiUing the work room with solvent. 

Condensate (hot water produced by the use of steam) or waste steam (steam at a temperature or pressure too low to be useful normally) could be used to provide boilup heat in a way which would not produce sparks when a flammable solvent is used (Ref. 1, Chapter 3.22). Natural gas could be used as a source of boilup heat if there were concerns about hot spots in the heating elements). To avoid hot spots, electric heaters should be rated for no more than 20 to 25 watts/square inch. In this book, electricity is assumed to be the normal source of energy for heating because it is most commonly used, and it allows the degreaser to be mobile. 

---