Water Temperature Limitations

Direct contact water heaters are incapable of producing usable steam and have difficulty in achieving outlet water temperatures higher than 188°F. Direct contact water heaters can achieve water temperatures up to 193°F. However, the efficiency of the heater drops dramatically even with cold water entering the upper portion of the heating tower as large amounts of water are vaporized carrying heat energy away from the heater.

Direct contact water heaters operate with a system pressure just a couple of inches water column above atmospheric pressure. In theory it should be possible under these condition to heat water up to 200°F or even higher in a direct contact water heater. The limiting factor is presented by when the water is heated. The water is heated as the droplet falls through open air in the heat transfer section of the direct contact. Because the heating occurs while the water is moving through the air there are wind aerodynamics that drop the localized pressure around the water droplets to a point that is lower than the available atmospheric pressure. This in turn lowers the temperature at which the liquid water phase changes to a gaseous form. Because if this effect attempting to achieve exit water temperatures higher than 188°F becomes inefficient and unstable. The altitude at which a heater is operating will affect the maximum temperature output capability of the direct contact heater because of the reduction in available atmospheric pressure.

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