Condensation heat transfer and convective heat transfer -2
The following is specific example of how the heat is transferred.
First of all, heat transfer during indirect heating using highly-heated oil or heated water will be explained. There is no phase transition in these heating mediums. They are heating by sensible heat. They give their heat energy to the heated materials as lowering their temperature. This heat transfer can be said as convective heat transfer.
The indirect heating with steam, on the other hand, occurs with phase transition. Phase transition, which suggests change from saturated steam to saturated water here, is took place for an instant when steam hits objects and the steam release its latent heat in a moment. By releasing latent heat at once, the objects are heated. This is called condensation heat transfer.
Addition to the latent heat, one example of making use of it is dry mist spray cooling in which cooling effect of sprinkle water is applied. Micronized mist of water evaporates for an instant when it is sprinkled. This phase transition during the evaporation takes heat around. The heat used here is latent heat. Heat of evaporation, latent heat in other words, is taken from the heat around and atmosphere is cooled down. Steam releases only latent heat during its condensation.
The liquified water generated after releasing the latent heat during phase transition is called condensed water or drain and it is discharged from steam trap in case of steam dryers, and sensible heat is released during the discharging process. Therefore, indirect heating with steam is took place only by latent heat and sensible heat is released by steam trap.
Please see the details of steam drying in this page.
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Latent heat utilization
The heat capacity of the latent heat of the steam is about 2-5 times as large as that one of oil or hot water.
Closed drain recovery
Temperature is adjusted to the desired level by changing pressure.
Temperature of the dryer can be adjusted to the desired level by changing steam pressure.
Comparison with hot air drying
There is less damage on the dryer body because of the low temperature.
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