Issue link: http://metalfinishing.epubxp.com/i/49721
finishing plant engineering IMMERSION HEATER DESIGN BY TOM RICHARDS PROCESS TECHNOLOGY, MENTOR, OHIO; www.process-technology.com The immersion heater represents a sound, economical method of heating process solutions in the finishing industry. Classical heater installations consisted of hanging a steam coil on one tank wall, sized to heat up water to a "rule-of-thumb" temperature in two hours. While this method has proved adequate in providing heat and covering a multitude of oversights, it has also proved unsatisfactory with regard to energy costs and control. As the cost of energy rose, the finisher increased heat-up times in an attempt to conserve energy. Soon, heat losses prevented achieving desired tem- perature levels so tank insulation, covers, and other methods of loss conservation were added. Again, adequate solutions to most of the challenges were found, but the hanging steam coil remained unchanged. Today, we have the knowledge that allows us to adequately plan, design, install, and operate economical, efficient heating systems. Molecular activity, chemical solubility, and surface activity are enhanced through temperature elevation. The reduced solution surface tension, low vapor pressure of some organic addition agents, and heat-sensitive decomposition or crystallization of other additives are major considerations that modify the ben- efits gained as solution temperature rises. To achieve a proper balance of all these factors, while providing economical installation and operation, it is necessary to analyze the individual heating requirements of each process. Your best source of process information is your process chemical supplier, which can tell you: 1. Recommended materials of construction. 2. Maximum (minimum) solution temperature. 3. Maximum heater surface temperature. 4. Specific heat of the process solution. 5. Specific gravity of the process solution. 6. Recommended heel (sludge) allowance. To size the heater, first determine the tank size: space required for the part, parts rack or barrel, space required for busing (anodes), in-tank pumps and filtration, sumps, overflow dams, level controls, air or solution agitation pipes, and any oth- er accessories. From this data, a tank size and configuration can be determined. Calculate the weight of solution to be heated. For rectangular tanks: Weight = L W D S.G. 62.4 lb/ft3 where L, W, and D are length, width, and depth in feet (substitute 0.036 lb/in.3 for dimensions in inches). S.G. is the specific gravity of the solution (water is 1.0). For cylindrical tanks: Weight = R2 D S.G. 62.4 lb/ft3 where R is the radius of the tank. Calculate the temperature rise required by subtracting the average (or lowest) 665