Metal Finishing Guide Book

2012-2013

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Solution Temperature (oF) Nonventilated Losses (BTU/hr/ft2) Ventilated Losses (BTU/hr/ft2) 100 120 140 160 180 170 340 615 900 1,590 290 560 995 1,600 2,750 Table I. Heat losses from Liquid Surfaces ambient temperature from the desired operating temperature (if the shop temperature is kept very cool during winter months, it might be wise to use this temperature as the average ambient temperature). Temperature rise = T operating minus T ambient [To - Ta = T rise] Determine an adequate heat-up time to suit your production requirements. The traditional 2-hour heatup may prove costly and unnecessary since using this value usually provides a heater more than twice the size necessary for heat maintenance. A 4- to 6-hour heatup more closely approximates the heat maintenance value but may impose production constraints deemed impractical. Long heat-up times can be overcome through the use of 24-hr timers; however, unattended heatstarts carry the responsibility of tank liquid level monitoring and approved overtemperature safety shutoffs. With this data, the initial tank heating requirements can be determined. A BTU is the amount of heat required to raise one pound of water one degree Fahrenheit. A BTUH is that amount per hour. Initial BTUH(Q) = Weight �� Trise �� s.h./Heat-up time where s.h. is specific heat. This should be the actual value from the process supplier (water is 1.0). Calculate the approximate heat loss from the tank surface and tank walls. (Use the data shown in Tables I and II.) The losses from the tank surface can represent the most significant loss affecting heater sizing. The addition of even a partial or loose-fitting cover will reduce these losses. The tank surface area is simply the width in feet times the length in feet. You can use inches instead of feet, but then must divide the results by 144 to obtain square feet. If you install partial covers, such as removable covers extending from the tank edge to the anode busing, use the remaining ���open��� dimensions. The covered Solution Temperature (oF) Metal Tank or Thin Plastic (BTU/hr/ft2) Insulated Tank or Heavy Plastic (BTU/hr/ft2) 100 120 140 160 180 170 340 615 900 1,590 290 560 995 1,600 2,750 Table I I. Heat losses from Tank Walls and Bottoms 733

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