Which is better saturated or superheated steam for heat exchanger?

Super heated steam is not easy to control required set point, that's why desuperheater required for controlling the temperature of the steam to required set point.

Superheated steam keeps condensate out of the steam pipework over longer distances. Less effort is required to eliminate condensate and return it along the way.

Using superheated steam in heat exchangers can, if the temperature is too high, give rise to quality problems with whatever is being (over)heated on the other side of the exchanger. Other than that, it's "horses for courses", really.

<>I'm not educated enough in science to disagree with you, so please don't think that I am; rather, I am trying to understand this stuff. I wholeheatedly agree that if steam on the inside of the heat exchanger is, let's say, 250F, then the surface area on the other side of the heat exchanger is going to try to be at 250F -- but it is presumeably being cooled by whatever is heating on the other side. So it seems to me that it then becomes a matter of how much heat energy can be applied on the steam side in order to maintain the same temp on the surface of the other side of the exchanger. But my impression up to this point is that steam has a very low energy density -- except for the latent heat released during phase change from steam to water which can't happen unless it drops below 212F. So I'm wondering how high of a temperature would actually be maintained on the other side, as you've suggested, and whether in reality what happens is that the superheated steam just very quickly drops below 212F and condenses to do the major portion of heating? If the latter, then the surface temp on the steam side obviously must be below 212F to allow condensation, and that should mean that the temp on the other side of the heat exchanger couldn't possibly be any higher than that. So my suspicions is that steam would be superheated merely to a minimize condensation while in transit. I mean, you certainly wouldn't want to be using steam if it is NOT condensing, right? If I'm wrong, I hope someone will explain this to me.

<>Thanks.

<>Bill Velek

About 1/3 of the way into this page will help you:

http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/superheated-steam.asp

Thanks a lot for your input... It really helped me in clearing my various doubts regading this.

You only care about the heat of vaporization when using steam as a heating utility.

saturated steam is preferred because latent heat >> sensible heat. When comparing the capital cost ($$$) for having a much higher design temperature and poor heat transfer medium for superheated steam it's a no brainer.

The phase change from saturated steam to saturated liquid occurs isothermally, so a steam pressure is chosen which fixes the saturation temperature approximately 45 °F greater than the process stream outlet temperature.

The 45 °F is a common heuristic which minimizes film boiling and also maximizing the rate of heat transfer.

-David

Hi, Dave. Thanks for the post. Can you give an example so that I can get a better grasp of what you are saying? Also, the application that I am studying will involve bubbling steam up through a liquid to heat it; dilution of the liquid with condensation doesn't matter. I would assume that, in order to maximize condensation and release of latent heat, the steam should be as close to 212F as possible, i.e., that for my type of process your suggested 45 degrees above process temp would not apply.

Thanks for any further help.

Bill Velek

Dear Friend,

Super Heated Steam is having poor HEAT TRANSFER CO-EFFICIENT and LOW SPECIFIC HEAT where as Saturated Steam is having a better HEAT TRANSFER CO-EFFICIENT.

While SATURATED STEAM is used as HEATING MEDIUM in a Heat Exchanger, while Heat Transfer takes place, the entire Latent Heat is RELEASED by Saturated Steam and transferred to the heaer and in turn to the Heated Medium.

As regards, Super heated Steam it has to loose its Super Heat and reach Saturated level and the tranfer the Latent hheat. The time taken to reach the Saturation level is high on account of Low Heat Transfer Co-efficient.

Hence Super Heated Steam is NOT DESIRABLE or NOT TO BE PREFERRED for Heat Exchanger.

DHAYANANDHAN.S