Sensible heat and latent heat

Sensible heat: When a solid, liquid, or gas is heated, as long as its state remains unchanged, the addition of heat causes its temperature to rise. The amount of heat added can be reflected in the increase in temperature; heat that causes a change in temperature without altering the substance’s state is known as sensible heat. Latent heat: For example, when liquid water is heated, its temperature rises. When it reaches the boiling point, even though heat continues to be added, the temperature of the water does not increase any further and remains at the boiling point. The heat added is used solely to convert the water into steam, that is, from a liquid state to a gaseous state. The heat that causes a change in the state of matter (also known as a phase change) without altering the temperature of the substance is called latent heat. The heat absorbed when 1 kg of liquid completely turns into saturated vapor at the same temperature is called the latent heat of vaporization at that temperature; it is denoted by the symbol r, with units of kJ/kg.

The last edit to this post was made by ylb913 on 2016-11-20 at 06:52. The saturation temperature of steam at 1000 kPa (absolute pressure) is 179.9°C, while the saturation temperature of steam at 1000 kPa (gauge pressure) is 184.0°C. At constant pressure, steam with a higher temperature is called superheated steam. Assuming that 1000 kPa is the absolute pressure, steam at 300°C remains steam until its temperature drops to 179.9°C; the heat released during this period is sensible heat. It is only when the temperature reaches 179.9°C that condensation begins, and latent heat is then released. To heat something else, the steam’s temperature is reduced by only 30°C, resulting in an ultimate temperature of 270°C. This temperature is far above the saturation temperature of steam at the same pressure; it remains superheated steam, and only part of the sensible heat is released throughout this process. ——At the same time, if you use steam to heat another medium in the distillation tower, there are specific requirements regarding the final temperature of that heated medium. In such cases, only a small amount of the sensible heat of the steam can be utilized, and it is also necessary to control the temperature at the steam outlet; this is quite difficult to achieve. It’s not merely a matter of control, but rather an issue related to the design of the heat exchanger.

Thank you for the explanation, but in practical operations I have indeed encountered such problems: when the temperature drops, people think it’s necessary to increase the steam supply, yet the temperature of the entire tower rises rapidly; ultimately, it is by reducing the steam supply that the temperature can be stabilized

It seems that this is done by supplying a large amount of steam to prevent it from condensing and releasing latent heat.