If low-temperature steam has a high latent heat, then why use high-temperature steam for heating?
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If low-temperature steam has a high latent heat, then why use high-temperature steam for heating? For example, steam at 70 degrees has a higher latent heat than steam at 120 degrees, but factories mostly use steam at 120 degrees or higher for heating.
On the one hand, it is a matter of temperature; if the material to be heated reaches 150 degrees, then high-pressure and high-temperature steam is definitely required
I agree with the view above: if it is necessary to heat the fluid to a temperature above 70 degrees, high-temperature steam is required. The latent heat is more or less the same, but there is also an issue related to the level of energy involved. Heat can only be transferred from a higher temperature to a lower one; if the quality of the heat source is poor, no amount of heat will be useful.
The question is very interesting; the previous answers were correct, so I’ll summarize them. 1. A high saturated steam pressure corresponds to a high temperature; therefore, a higher pressure is required when high-temperature heating is needed ； 2. From the formula Q=KAΔt, it can be seen that when the steam temperature is low, Δt is small; as the area A increases, the cost of the equipment rises ； 3. When the steam pressure is low, its density is low and its volume is large; to meet a certain heat load, larger steam pipes are required, which increases the investment in pipelines ； The opposite is true when the pressure is high.
The specific heat value cannot be equated with temperature; it’s not the case that a higher latent heat means a higher temperature. How can heating take place without a temperature difference?
There are mainly two points: The first is the temperature requirement (the outlet temperature of the material that needs to be heated is relatively high)； Additionally, if the steam temperature is low, the heat transfer temperature difference is small, requiring a larger heat exchange area). Secondly, the steam transmission process involves pressure losses; low pressure not only makes transmission difficult but also requires thicker pipes due to the low density of the steam. (The utilization of low-pressure steam is also a common challenge worldwide nowadays.) This post was last edited by lucky1909 on 2009-4-17 at 14:09.]
A large temperature difference facilitates heat transfer, thus saving on equipment investment. :)
The main reason is that when heated by high-temperature steam, the logarithmic mean temperature difference is much larger; as a result, the heat exchange area required is smaller, which in turn leads to lower investment costs and less floor space needed for the heat exchanger. This makes it more suitable compared to using latent heat.