NCI Tank heating eductors provide a direct contact of the steam into the liquid. This assures complete transfer of the energy in the steam into the liquid being heated. Other types of heating lose efficiency as the interior of the heat exchanger builds up a scale. With eductors, the velocity of the steam being injected into the vessel also causes the liquid contents of the vessel to be agitated while heating occurs, without the need for other types of mixers in the vessel. This provides for more even heating of the vessel contents. They also permit the steam to be dispersed over more of the liquid volume, resulting in a more homogenous heating than with other methods of injecting steam.
These designs of eductors allow steam to be used from 10 to 140 PSIG for heating. Because of the nature of direct steam injection, heating vessels at atmospheric pressure beyond 140° F should not be attempted. Exceeding this temperature could result in uncondensed steam evolving from the liquid.
Tank Eductor Sizing Request Form (We’ll reply with the recommended size along with price & availability)
*** To help eliminate steam hammer, ensure that the minimum absolute pressure of the eductor is at least twice the absolute pressure inside the tank, at eductor depth.
TLM PERFORMANCE CHARTGallons Heated Per Minute - (GHPM)
Operating Steam Pressure (hm)
|20 PSIG||40 PSIG||60 PSIG||80 PSIG||100 PSIG||120 PSIG||140 PSIG|
|Size||Temp Rise °F||TLM||TLM||TLM||TLM||TLM||TLM||TLM|
Heating with Steam
Steam is supplied in a gaseous state. Heat transfer with saturated steam utilizes the latent heat of steam, releasing a large amount of energy as it condenses (changes to the liquid state). The amount of energy released per unit of steam is high (up to 539 kcal/kg, or 970 Btu/lb, and higher with vacuum steam).
Summary of Benefits
Utilizing latent heat (steam heating) for heat transfer is far more effective than utilizing sensible heat (hot water or oil heating), as a much higher amount of energy is released in a shorter period of time.
This offers the following benefits:
|Rapid even heating through latent heat transfer||Improved product quality and productivity|
|Pressure can control temperature||Temperature can be quickly and precisely established|
|High heat transfer coefficient||Smaller required heat transfer surface area, enabling reduced initial equipment outlay|
How Does Steam Provide Stable, Even Heating?
Unlike heat transfer by convection (e.g. hot water), heat transfer by condensation (e.g. steam) does not involve a temperature change. When steam condenses on the heat transfer surface, it passes on its latent heat to the product. The condensate then formed still contains its sensible heat, so it is of the same temperature as the steam from which it was produced. This enables even heating across the whole heat transfer surface.
If the pressure at the heat transfer surface of the equipment is held constant, continuous heating at a constant temperature can take place throughout every part of the heat transfer surface.
On the other hand, with hot water or oil heating, the temperature of the heating medium is reduced as sensible heat is transferred from the heating medium to the product. The temperature gradient is therefore constantly dropping because each unit of heat transferred will also lower the heating medium’s temperature. This can result in uneven heating, which may adversely affect the product being heated.
How Does Steam Provide Rapid Heating?
Heat Transfer from Condensation (Steam)
The secret is in the transfer of heat resulting from the process of condensation.
The latent heat contained in steam is released the instant steam condenses into the liquid state. The amount of latent heat released is 2 to 5 times greater than the amount of sensible heat available from hot water (saturated water) after condensation. This latent heat is released instantaneously and is transferred through the heat transfer surface to the product being heated.
Through condensation, steam naturally flows against the heat transfer surface. This helps speed the heating process.
Heat Transfer by Convection (Hot Water and Oil)
In contrast, hot water and oil transfer heat by convective heating, which does not involve a change of state. If left to natural convection, heat transfer is extremely slow. Thus, a pump is typically used to create flow against the heat transfer surface to increase the rate of heat transfer. This is known as forced convection heating.