Why is saturated stream is the most commonly used as heat transfer fluid in chemical plants?

Question

I am doing on a project on heat transfer fluid. Then i realise stream is commonly used for heat transfer fluid. Why is this so? is it becos it cheap or any other purposes? Guys out there if u have any website strongly link to stream to let me know. Would like to research on it more? any comment on stream is very much appricepated. Thanks,

Answer 1

This is used because of the low price involved. Water is readily available, and it vaporizes at a relatively low point (100 degrees C). The heat energy required to vaporize the water is low compared to other means of transferring heat. When the steam transfers its heat to the surroundings (thermal exchange) it becomes liquid water which is also easy to work with and cheap.

Answer 2

There are two considerations here. If you wished to transfer much heat energy say from building to building, hot water (or better yet pressurized hot water) will transfer more energy per unit time through a pipe of a given diameter than steam of the same temperature because the hot water will have a much higher mass flow rate. The pressurized hot water of course can be flashed to steam resulting in a mix of hot water and saturated steam. A steam kettle on a stove produces saturated steam at atmospheric pressure while a pressure cooker on a stove produces saturated steam at an elevated pressure and temperature (controlled by the weight at the discharge connection that limits pressure buildup). Steam (void of air) will be saturated unless a second heat source is used to heat the steam (superheated) to a higher temperature than it would normally exist at the given pressure. For example in a power plant, a boiler may produce saturated steam and the steam may be passed again through separate tubes in the furnace to produce superheated steam that is hotter and more energetic. When I visited a huge power plant near Boston (Boston Edison), an operator there told me that superheated steampipe leaks were invisible. The steam could cross the entire building before hitting a wall and condensing into visible steam. The men tried to trace the steam leak backwards by walking along catwalks waving a broom until the steam cut the broom whiskers. The steam leak could cut a man in half if not detected. Use of saturated steam would require less expensive heating equipment and would also be safer to use. The temperature of saturated steam can also be easily controlled by controlling steam pressure.

Answer 3

Saturated steam is a good heat transfer agent, because you can transfer a lot of thermal energy at constant temperature.

The latent heat of vaporization of water is 540 cal/gm. In other words, transfering 540 cal of energy requires condensing 1 gm of saturated steam at 100 oC (1 atm pressure).

It also greatly helps that water is non-toxic, abundantly available and non-corrosive (no exotic materials of construction needed).