Talk:Vapor-compression evaporation

Comments

I am reshaping this article. It will maybe be necessary to separate the MVR and thermocompression items, but for the time being this seem premature - at least until the page reaches a decent length and completeness. I will probably be obliged to amend some points, which are clearly referred only to MVR.--UbUb (talk) 20:56, 20 April 2008 (UTC)

Well, it's done, at least as a first phase. The name should probably be changed to V. C. evaporator rather than evaporation; I will leave that to the next contributor.--UbUb (talk) 22:07, 20 April 2008 (UTC)

-Good and clear article. One point though: Under the headline "MVR Process" energy is given in power units, which is misleading. "...the compression energy is between 35 and 45 kW per metric ton of compressed vapors." Do you mean kWh? Haukun (talk) 08:43, 23 March 2010 (UTC)

-There is a unit incompatibility error in this article. It is impossible for a device to consume 35-40kW per ton of vapor compressed. A power (kW) must corespond to a mass flow rate, not a stand alone mass. So either the 35-40kW should be in kWh or kJ or the ton of compressed vapor must be in ton/s or ton/hr. kW is incompatible with ton. — Preceding unsigned comment added by 41.190.172.67 (talk) 06:18, 8 July 2014 (UTC)

I agree and I have added a clarify tag. Biscuittin (talk) 15:05, 15 January 2015 (UTC)

A diagram would help

Can a simply schematic diagram be added to this article? I am having trouble following the interactions of the liquid, vapor, and compressor units. Also, perhaps the diagram can be labled with the variables used in the equations. Thanks! --Lbeaumont (talk) 17:56, 4 March 2012 (UTC)

Agreed, this article is a mess of technobabble with no clear indication of what is going on. Whatever is happening is only halfway described, partial, and incomplete. (Arriving looking for more info, via TED / Slingshot (water vapor distillation system) ).

So it's basically.. a heat-pump condenser system, using steam from the source liquid as the pumped working fluid for adding heat back to the source liquid? Is a thermal energy source involved anywhere for also heating the source liquid? After all, first you need steam for the heat pump system to do anything... DMahalko (talk) 00:14, 7 March 2012 (UTC)

Usage

These were used in fleet-type submarine boats for producing fresh water? Jack Waugh (talk) 16:49, 29 July 2012 (UTC)

See Evaporator (marine) Andy Dingley (talk) 17:20, 29 July 2012 (UTC)

Error

Quote: "The compression ratio in a MVR unit does not usually exceed 1.8. This means that, if evaporating at atmospheric pressure (0.101 MPa and 100 °C), the condensation pressure at the heat exchanger will be 116.9 °C". Comment: 116.9 °C is a temperature, not a pressure, and how is the figure calculated? It would be sensible to use absolute temperatures, rather then Celsius temperatures. Biscuittin (talk) 18:23, 14 January 2015 (UTC)

When dealing with saturated vapor, the pressure defines the saturation temperature (and vice versa). Thus while the above statement is technically incorrect, it's not completely inaccurate. I clarified that list item and showed how the 2nd temperature is calculated. Since we're dealing with water vapor, Celsius is more correct to use here than Kelvin. You'll notice that standard SI steam tables and charts are always given in C, not K. --84.94.83.131 (talk) 18:32, 9 June 2017 (UTC)

Energy input

Quote: "This theoretical value shall be increased by the efficiency, usually in the order of 30 to 60%". Comment: Suppose the theoretical energy input is 300 kJ and the efficiency is 30%. The actual energy input would be 300 x 100/30 = 1,000 kJ. However, the sentence is unclear and might be interpreted as 300 + 30% = 390 kJ. This needs clarification. Biscuittin (talk) 10:22, 15 January 2015 (UTC)

I have re-written the sentence to clarify it. Biscuittin (talk) 10:35, 15 January 2015 (UTC)

Comments 2

Much of the article is badly written and I have added some comments. I also suspect it may have been copied and pasted from somewhere but I have not been able to verify this. Biscuittin (talk) 11:07, 15 January 2015 (UTC)

At least part of it seems to have been copied from [4]. I have added a copyvio tag. Biscuittin (talk) 16:52, 15 January 2015 (UTC)

That would be the intro of a, then tiny, WP page in 2006, also appearing as the intro of a web page with a 2007 copyright date, that doesn't appear in any web archives I can see until 2007.

Mind, at least that web page (and the initial WP stub, until 2008) does get the purpose of vapour compression right and states that it's done to increase the temperature of the liqour, rather than the pressure. Andy Dingley (talk) 18:25, 15 January 2015 (UTC)

Sorry, I can't restore the blanked content until the issue is resolved by an administrator. Biscuittin (talk) 23:31, 15 January 2015 (UTC)

Efficiency

I can't see any reason for using Vapor-compression evaporation. Surely, it would always be more efficient to use direct heating? Biscuittin (talk) 15:13, 15 January 2015 (UTC)

Heat transfer efficiency may well be higher, but total system efficiency will be lower. Direct heating requires an external heat source (fuel). The higher the energy input to the drying system, the lower the system efficiency. Vapor-compression evaporation uses the latent heat of the evaporated water as a 'free' heat source. By investing energy in vapor compression, we create a temperature difference that lets heat flow back in to the evaporation chamber, and allows us to reuse most of the energy we invested in evaporation in the first place. (Cost-effectiveness is a different question... that typically depends on the scale of the system.) --84.94.83.131 (talk) 18:42, 9 June 2017 (UTC)