Page 362 - Mechanical Engineers' Handbook (Volume 4)

4 Heat-Pipe Fabrication Processes 351

Table 4 Working Fluids and Temperature Ranges 9
Melting Point, K Boiling Point, K Useful Range,
Working Fluids at 1 atm at 1 atm K
Helium 1.0 4.21 2–4
Hydrogen 13.8 20.38 14–31
Neon 24.4 27.09 27–37
Nitrogen 63.1 77.35 70–103
Argon 83.9 87.29 84–116
Oxygen 54.7 90.18 73–119
Methane 90.6 111.4 91–150
Krypton 115.8 119.7 116–160
Ethane 89.9 184.6 150–240
Freon 22 113.1 232.2 193–297
Ammonia 195.5 239.9 213–373
Freon 21 138.1 282.0 233–360
Freon 11 162.1 296.8 233–393
Pentane 143.1 309.2 253–393
Freon 113 236.5 320.8 263–373
Acetone 180.0 329.4 273–393
Methanol 175.1 337.8 283–403
Flutec PP2 223.1 349.1 283–433
Ethanol 158.7 351.5 273–403
Heptane 182.5 371.5 273–423
Water 273.1 373.1 303–473
Toluene 178.1 383.7 323–473
Flutec PP9 203.1 433.1 273–498
Naphthalene 353.4 490 408–478
Dowtherm 285.1 527 423–668
Mercury 234.2 630.1 523–923
Sulphur 385.9 717.8 530–947
Cesium 301.6 943.0 723–1173
Rubidium 312.7 959.2 800–1275
Potassium 336.4 1032 773–1273
Sodium 371 1151 873–1473
Lithium 453.7 1615 1273–2073
Calcium 1112 1762 1400–2100
Lead 600.6 2013 1670–2200
Indium 429.7 2353 2000–3000
silver 1234 2485 2073–2573

4.3 Cleaning and Charging

All of the materials used in a heat pipe must be clean. Cleanliness achieves two important
objectives: it ensures that the working fluid will wet the materials, and that no foreign matter
is present that could hinder capillary action or create incompatibilities. The presence of
contaminants either in solid, liquid, or gaseous state may be detrimental to heat-pipe per-
formance. If the interior of a heat pipe is not clean, degradation of the performance can
result over time. Solid particles can physically block the wick structure, decreasing the liquid
flow rate and increasing the likelihood of encountering the capillary limit. Oils from ma-
chining or from the human hand can decrease the wettability of the wick. Oxides formed
on the wall and wick can also decrease the ability for the liquid to wet the surface. Therefore,
proper cleaning of all of the parts in contact with the interior of the heat pipe (pipe, end