Does heating rate increase with velocity for sat steam?

[YungPlantEng]

It’s common practice at my plant to bleed condensate manually for under sized steam traps on start up to “heat it more quickly”. Obviously if you have a flooded tube sheet or even overly high tube condensate removing condensate is a good idea but is opening a bypass valve full bore more or less effective than the utilization of a normally sized steam trap in terms of improving rate?

My train of thought is that there would be some upstream loss of pressure if you’re not careful that would move the saturated steam to an unsaturated lower P superheated steam. Don’t really have anything to base that on though

 

[Snickster]

If I understand what you are saying I agree that the pressure upstream of the block valve may lowered so that the steam pressure lowers in the upstream piping and becomes superheated, but it still is at the same temperature and contains the same heat content.

 

[pierreick]

Hi,
Everyone is doing the same at start up to get rid of condensate.
Consider this booklet to support your query.
Pierre

 

[georgeverghese]

The steam side of the HX may have previously accumulated a large amount of condensate during shutdown / cooldown. Made worse if the supply block valves / control valves feeding the steam side are leaking.

 

[TiCl4]

Yung,

Normally, drain valves are opened until steam begins to escape, then closed again. If the steam trap is undersized and operators leave the drain valve cracked open, they normally do it so only wisps of steam come out.

Yes, if you have some cowboys who are blasting out full-pressure steam, your steam pressure in your heat exchanger or jacket may drop P, thus drop T, and lower overall heating rate. However, you'd need to lose a stupidly high amount of steam to accomplish this in most setups (i.e. the drain valve is normally much smaller than the steam supply valve), and most operators don't like turning their workspace into a sauna.

To me, this is a non-concern is a quite normal.