The importance of steam dryness
We know that the steam produced by the boiler is not 100% saturated. When the steam boiler heats the water, the foam on the surface of the water will mix some small water droplets into the steam when it is broken, otherwise the steam mixed with water droplets will make it wet, which is what we call wet steam. Steam dryness measures the amount of water in the steam. If the steam contains 10% water, it means that the steam dryness is 90%, or the dryness is 0.9.
Effect of steam dryness on steam system
Steam dryness is very important because in the steam system we usually use the latent heat of steam. If the steam contains misty water, the steam latent heat utilization rate will be reduced.
For example: saturated steam (100% dry) contains 100% latent heat at the current pressure. Saturated water, which has no latent heat, has a dryness of 0 and contains only sensible heat.
Steam dryness calculation
The actual evaporation enthalpy of wet steam is the product of the dryness (x) of the wet steam and the enthalpy of evaporation (hfg).
Actual 焓÷ evaporation 焓 = dryness
Note: If the steam dryness exceeds 100%, heating or decompression will form superheated steam.
The temperature of this steam exceeds the temperature of the saturated water helium. We can get its temperature by measurement.
Calculation of the devaluation of wet steam
In the steam meter, we only need to know the steam temperature to find the steam temperature, sensible heat, latent heat, specific volume and total heat according to the steam meter. However, steam meters are not suitable for wet steam.
The enthalpy of the wet steam in the steam system can be calculated by calculation. We only need to know the dryness (x) of the steam, the enthalpy of evaporation (h(fg)) and the arrival of liquid helium (h(f)). The calculation formula is as follows
h = hf + X • hfg
Effect of steam drying degree on heat transfer efficiency
Steam dryness is an influential parameter for 100% operation of the equipment, because the more humid the steam, the lower its specific volume, specific heat and specific entropy. Therefore, when the steam dryness is relatively low, the heat exchange efficiency is relatively low. When the dryness of the steam is high, the heat exchange efficiency is relatively increased. Of course, if the steam is superheated steam, the heat exchange efficiency of the steam is also obtained. Therefore, steam is close to or equal to 100%, which is very important for the improvement of heat transfer efficiency.
Dryness in transport steam will decrease
During the transportation process, the heat radiation loss of the pipeline will cause some of the steam to lose latent heat to become condensed water, which will reduce the steam dryness. Wet steam not only affects heat transfer efficiency, but also causes erosion of important equipment such as pipes and turbine blades.
How to increase dryness
Steam dryness affects heat transfer efficiency, so we should deal with steam lines with a lot of wet steam, such as installing a steam separator to remove the condensed water from the steam.
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