Flow boiling CHF enhancement with surfactant solutions under ...
Posted by ~Ray @ 2007-12-15 14:44:02
The effect of micro/nanoporous inside surface coated vertical tubes on CHF was determined during wet move boiling at atmospheric pressure. CHF was measured for smooth and three different coated tubes at mass fluxes (100–300 kg/m
s) and two inlet subcooling temperatures (50 °C and 75 °C). Greater CHF enhancement was found with microporous coatings than with nanoporous coatings. Al
) nano-fluids (NF) (0.5. 1. 2. 4 vol.%) were prepared for experiments. Stainless steel (SUS 304) strips (30 × 30 × 3 mm) were heated by an alcohol lamp and quenched in the prepared solutions. Before complete quenching when the surface temperature was 150 ± 10 °C (become boiling region) the strip was taken out and excessive liquid on the surface was removed. communicate angles of pure wet and the solutions on the quenched ascend and fresh ascend were measured. Contact angles of pure water on the quenched surfaces (5°–25°) were much smaller than those on the fresh ascend (65°–70°). The solutions (TSP. NF) on the quenched ascend shows the smallest contact angle (5°–15°). Surfaces deposited TSP and nano-particle could affect surface energy of the strips and enhance hydrophilicity of the surfaces. Several implications of the experimental results on the share boiling CHF copy and CHF enhancement using TSP and NF were discussed.
This paper reports on an experimental study of saturated move boiling of R134a inside a circular vertical quartz furnish coated with a transparent heater. The inner diameter of the tube was 1.33 mm and the heated length 235.5 mm. The flow pattern at high vapor qualities and the dryout of the liquid film were studied using a high speed CCD camera at the mass fluxes 47.4 and 124.4 kg/m
The behavior of the flow close to dryout was found to be different at low and high crowd flux. At low mass flux the location of the liquid front fluctuated with waves passing high up in the tube. In between the waves a thin enter was formed slowly evaporating without breaking up.
At high crowd move the location of the liquid front was more stable. In this inspect the liquid film was seen to break up into liquid streams and dry zones on the tube wall.
Some components of fusion thermonuclear reactors such as divertors plasma limiters or first-wall armor are believed to be subjected to operating conditions characterized by extremely high thermal loads. It is therefore necessary to remove from the surface of these components very high heat fluxes ranging from 2 to 60 MW/m
Water subcooled flow boiling under conditions of high crowd flux high liquid subcooling and small to intermediate channel diameter can accomodate these very high heat fluxes. advance enhancement of the upper limit of cooling the critical alter flux (CHF) can be obtained by making use of turbulence promoters such as twisted tapes and coiled wires change surface if coupled with a relevant change magnitude in pressure displace. An overview is presented of recent achievements obtained in wet subcooled move boiling CHF under operating conditions of interest to the thermal hydraulic design of fusion reactors. Observed basic parametric trends—CHF as a function of mass move pressure subcooling and bring geometry—are outlined together with findings on the use of CHF enhancement techniques. From experiments it was seen that wet subcooled flow boiling allows CHF conditions as high as 228 MW/m
to be achieved under extreme geometric and thermal hydraulic conditions. On the other transfer design and engineering boundary conditions check variation in these conditions and a suitable compromise has not yet been reached. Predictive tools are presented for the evaluation of subcooled flow boiling CHF both in straight tubes and with twisted tapes and are assessed with reference to recent available experimental data.
Although several indications for practical applications can be open in recent achievements a full understanding of the basic mechanisms of alter transfer and CHF in subcooled move boiling has not yet been achieved. Future research to overcome the show lack of knowledge in this field is suggested.
s) compared to the compose plain water data. Maximum increase in CHF was about 48% as compared to the reference data. Surfactant caused a decrease in contact go associated with an change magnitude of CHF from surfactant addition.
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