You can prevent boiling using a mixture of water and propylene glycol. In the following link you can find the variation of the boiling point of the mixture as a function of the percentage of glycol:

http://www.lyondellbasell.com/techlit/techlit/2519.pdf

I hope this information can help you.

Thermodynamically speaking, adding pressure will increase boiling point.

Not sure what kind of device you are talking about. Adding pressure requires good seal

and can be quite expensive. Thus I am not sure I have answered your question.

BTW: adding salt can also raise boiling point some what. Again, I have no idea

about what your device is.

If you work with microchannels, and that their inner surface is clean and smooth (no nucleation sites) then you can have superheated water quite easily (up to 10`s of Kelvins above the saturation temperature). From an engineering point of view, it might not be safe though. Better use both answers hereabove. 

"The required temperature is above 100°C ..."

Well: How much above 100°C?

You can easily check the required pressure by this table: (in german) 

http://www.wissenschaft-technik-ethik.de/wasser_dampfdruck.html 

Temp.(°C) Dampfdruck(mbar)  [vaporAE pressure [phys.]]

===========================

(sub zero deleted here)

--------------------------

0               6,10 Wasser

5               8,7

10           12,3

15           17,0

20           23,4

25           31,7

30           42,4

35           56,2

40           73,7

50          123

60          199

70          311

80          473

90          701

97,9       940

98,2       950

98,5       960

98,7       970

99,0       980

99,3       990

99,6     1000

99,9     1010

100      1013

100,2   1020

100,7   1040

101,2   1060

110       1433

120       1985 (1,985 bar)

130         2,70 bar

150         4,76 bar

200       15,54 bar

250         39,7 bar

300         85,8 bar

350          165 bar

374,12     221,2 bar (kritischer Punkt)

(critical point, no difference between water and vapour)

Mit zunehmender Temperatur nähern sich die Eigenschaften von flüssigem und gasförmigem Wasser immer mehr aneinander an. Bei 374,12 °C ("kritische Temperatur") haben sich die Eigenschaften vollkommen aneinander angeglichen, so dass es keinerlei Unterschied mehr zwischen flüssigem und gasförmigem Wasser gibt. Folglich kann oberhalb dieser Temperatur weder ein Sieden noch ein Kondensieren stattfinden.

Aus den Dampfdruckdaten ist ersichtlich, wieviel Druck mindestens erforderlich ist, um Wasserdampf bei einer gegebenen Temperatur zu verflüssigen (zu kondensieren) oder umgekehrt, bei welcher Temperatur Wasser bei einem gegebenen Druck siedet.

As you can see: 5 bar is enough for 150°C, 16 bar is enough for 200°C.

Boiling Point of Propylene Glycol/Water Mixtures 60/100 can raise boiling point by 10 degree C, . This is what ocean water will do. PG is better than ocean water because

it is purposely design for that purpose. I don't believe it will has erosion problem.

But ocean water is definitely cheaper. For very high boiling point, one needs to increase pressure which can be quite expensive. (this answer was posted 6 hours ago, but for some reason, it did not show, so, I post it again.

Boling point of water is a function of pressure. Based on this principle, steam jet refrigeration system is developed. 

Thank you everyone.. I got a lot of options from you.

As mentioned above using some additives to the water increases the boiling temperature. But what I suggest (as I have in my system) is using higher pressures for preventing water boiling. For example, at 5bar, the boiling temp is more than 150C.

Best wishes

When using TRNSYS, the easiest is to use diathermic oil instead of increasing pressure (no pressure in TRNSYS). You need to adjust the cp and implement the effect of higher viscosity on pumping power uptake.

Please bear in mind the difference between simulation and reality. In reality, an oil based system does not need high pressure components/seals/welding, which can add up to very high investment. But there are some drawbacks:

- High price per litre

- Higher viscosity at low temperatures and lower cp (compared to water)

- Safety regulations like fire prevention (which might revoke the monetary savings from low pressure installation)

- Your components need to be fit for use with oil

Hope that helps.

J