Author: Skip Schaefer
OK, so we want to set up an immersion heater for a DI water tank. Nothing big, by that I mean, not 20 feet long, 5 feet wide and 7 feet, the cleaning tank is just 36” x 30” x 36” deep. This is not a plating tank, so we don’t have to be concerned about the anode/cathode relationship. Simple little deionized cleaner tank and want to heat up to 140ᵒ F. So, we have the total gallons, 168 gallons to the top, but our solution is 5” down. Recalculate… 144 gallons. Because it 140ᵒ F Polyethylene is at the edge (this is from the heater manufacturer) you select a polypro tank. Were good to go.
We want a 3-hour heat up. Again, the quick math: ambient temperature is 70ᵒ -140ᵒ (140ᵒ-70ᵒ) is 70ᵒ Delta T. Weight of the solution 144 gallons x the weight of water we’ll say 9 pounds per gallon is 1296 pounds. Now, times the Delta T of 70ᵒF gives us 90,720 Btu/h, but we said 3 hours. So, divide by 3412 Btu’s per Kwh = 8.8 = round up to 9 kW. With the 8” cold zone on the over-the-side immersion heater, that allows 3” of solution level above the hot zone of the heater. We’re all familiar with that. But at 140ᵒF the heat loss from the top of the tank is 660 Btu’s by evaporation per square ft of surface area. Our tank is 36 x 30 so we have 7.5 sq/ft. 660 Btu/h (loss) x 7.5 is 4950 Btu’s/h.
We all went home for the 4- day Thanksgiving weekend and someone forgot to turn the heater off. Oops, it's a big oops. Let us see what happens… 96 hours * 4950 Btu’s per hour is 475,200 btu losses.
3” x 30 x 36 = 14 gallons. Fourteen gallons is 112 pounds. It takes 1013 Btu’s at 140ᵒ per pound x 112 pounds = 113,456 or 23 hours later.
If you have a Liquid level safety mounted on the lip of the tank to shut the heater off, it would have shut the heater off 3 hours ago.
If you have a thermal cut off device like other brands, you have, maybe, 11 more hours till the thermal cut off is exposed. And exposing the plastic to the radiant heat output at the same time.
Plating and cleaning tank level safety controls come in many types, but we manufacture 3 for the metal finishing industries.
Probe Type - That pass 12 volts AC across a set of probes if there is solution the system it’s activated.
Bottom Up Type - This is a float that works from the bottom up. Works in acids and Di water tanks. Tanks where build-up doesn’t occur. Learn more about our bottom up float switches for tanks.
Air Bubbler Type - This level control works in almost 100% of the chemistries. Especially good in electroless nickel.
Call us for application assistances. Level controls aren’t a “maybe anymore, they are a MUST HAVE”.