Heat pipes working fluids

An example of a heat pipe s construction is shown in Figure 3.17 [28]. It can be round or rectangular in shape. After the interior atmosphere has been evacuated, a working fluid is placed inside the heat pipe. This fluid can be water, ammonia, acetone, me anol, Dow-A, Dow-E, Freon-ll M, or Freon-113 (a registered trademark of E.I. duPont de Nemours Co.). The heat pipe vessel must be compatible with the fluid. Vessel materials used include copper, stainless steel, aluminum, nickel, and refrasil. The wick can be made from felt, a fine-screen mesh material, sintered material, or just grooves in the wall of the heat-pipe vessel. 

The vessel, as weU as the wick, must be compatible with the working fluid. Where possible, the wick and vessel are made of the same material to avoid the formation of galvanic corrosion ceUs in which the working fluid can serve as the electrolyte. In addition to its role within the heat pipe, the vessel also serves as the interface with the heat source and the heat sink. 

Working capital estimates, 9 530-531 Working electrodes, 9 568-571, 585 Working fluids, heat pipe, 13 230-233 Working Party of Experts on the Official Control of Pesticides, 18 541 Working solution, 14 43, 44 composition of, 14 46-47 hydrogen peroxide recovery from,... 

OCEAN THERMAL ENERGY CONVERSION (OTEC). Utilization of ocean temperature differentials between solar-heated surface water and cold deep water as a source of electric power. In tropical areas such differences amount to 35-40°F. A pilot installation now operating near Hawaii utilizes a closed ammonia cycle as a working fluid, highly efficient titanium heat exchangers, and a polyethylene pipe 2000 feet long and 22 inches inside diameter to handle the huge volume of cold water required. Alternate uses for such a system, such as electrolysis of water,... 

In our experiments as an experimental set-up an aluminium multi-channel panel was chosen. The main parameters of flat aluminium heat pipe panel, developed in the Luikov Institute are HPP width -70mm, HPP height - 7 mm, HPP length - 700 mm, evaporator length - 98 mm, condenser length - 500 mm, mass- 0, 43 kg. Propane was applied to fill the HPP and it is interesting as a working fluid with the point of view of its compatibility with all heat pipe envelopes and wick materials (aluminium, steel, stainless steel, copper, AL2 O3, etc). 

Compare the axial heat flux in a heat pipe using water as the working fluid at 200°C with that in a solid copper rod 8 cm long with a temperature differential of 100°C. 

Experimental results confirmed that propane (R290) is beneficial as a working fluid for low temperature heat pipes, thermosyphons, sorbers of chemical heat pumps, chillers of electronic components and for other evaporative heat transfer devices. The experimental data at the saturated condition Ts = 20°C (ps=8.4 bar, pr = p/pcr=0.197) are obtained in this series of experiments. 

Following this analysis Q depends on two eapillary structure parameters - the mean hydraulic pore diameter and the inner diameter of the porous wick. To find the Qmax we need equation (3.9) analyze for the extreme function finding. Due to the temperature dependenee of the thermo-physical properties of the working fluid the maximum heat flow Q ,ax will be different for different saturated vapor temperatures Tsat in the heat pipe transport zone. Figure 8. For different angles of heat pipe inelination to the horizon we need to determine Qmax at the worst situation with the point of view of the heat transfer, when the heat pipe evaporator is above the heat pipe eondenser, vertieal (inverted) heat pipe disposition. 

Badran B., Gerner F., Ramada R, Henderson T., Baker K., (1997), Experimental results for low - temperature silicon micromashined micro heat pipe arrays using water and methanol as working fluids, Experimental Heat Transfer, 10,253 - 272... 

Figure F. Sorption heat pipe. 1 — vapor channel 2 - porous sorption structure 3 - finned surface of heat pipe evaporator/condenser 4 - porous wick inside heat pipe 5- porous valve 6 - heat pipe low temperature evaporator with porous wick 7- working fluid accumulated inside the evaporator 8 - cold box.

The considered experimented set - up can be applied in two different ways. The first one is to use is as a semiconductor sensor cooler with low heat dissipation to cool the sensor down to the ambient temperature. It is interesting to be applied in cryogenic range of temperatures. The second option is related with the cooler for high energy dissipation devices (for example laser diode cooler). The first set of experiments was performed with sorption heat pipe and ammonia as a working fluid to demonstrate the basic possibility to decrease the temperature of the heat loaded wall to compare with the temperature of this wall in the phase of loop heat pipe cooling mode. 

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