water expansion
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I would like to ask about the water in the steam drum: when it is heated with a large temperature difference, does its expansibility increase? Are water heating expansion and vaporization the same concept? ?
The coefficient of thermal expansion of water should not be high. Heating-induced expansion of water and vaporization are different processes.
The density (or specific volume) of water is a function of pressure and temperature, given by pv=nRt. When the pressure is constant, an increase in temperature leads to an expansion of volume. Generally speaking, the specific volume of liquid water increases as the temperature rises, but compared to steam (with constant pressure and an increase in the same temperature), the change in the specific volume of water is practically negligible. At the molecular level, the expansion of water’s volume when it is heated is essentially similar to its evaporation when heated: the distance between molecules increases, though to different degrees. On a macroscopic level, when water is heated to its saturation temperature at a certain pressure, the temperature stops rising and the water turns into steam (the temperature of the water and the steam is the same); this is the process of vaporization ； Continuing to heat until all the water has turned into steam (at the same temperature and pressure, the specific volume of steam is much larger than that of water), the temperature of the steam rises further.
Oh! I see. So, it’s like when a boiler is first started up, the liquid level in the drum suddenly rises. According to the available information, this is caused by the expansion of water as it heats up. But if we ignore the specific volume of water, then why does the liquid level rise so suddenly?