Question

Saturdated water vapor (steam) is commonly used as a heat source in heat exchanger applications. Why saturated vapor? Why saturated water vapor? In a plant of any reasonable size, several varieties of saturated steam are commonly available; for example, saturated steam at 4.5,9,17, and 33 bar. But the higher the pressure the lower the useful energy content (why?), and the greater the unit cost. Why then is higher-pressure steam used?

Answer 1

The water goes from a liquid state to a vapour state and it receives energy in the form of “latent heat of vaporization”. Until there’s some liquid water left, the steam’s temperature is the same as the liquid water’s. Steam is then called saturated steam.

Saturdated water vapor (steam) is commonly used as a heat source in heat exchanger applications. e.g.cooking,drying,heating etc.Because

1-Energy transfer capacity, e.i, the heat transfer coefficient (U)for saturated steam is 1600W/m^2K which is very high. The value of U is determined by the number of watts that goes through per surface unit and per degree of temperature difference. The greater this value, the greater the heat transfer for a given situation.

2-heat transfer by saturated steam is uniform & no temp.profile is appear.

3-saturated steam is not in direct contact with the heating surface

4-safe ,clean & low cost

Higher-pressure steam used because pressure can control temperature & Temperature can be quickly and precisely established.