Abstract

DOBSON, R.T.  and  KROGER, D.G.. Thermal characterisation of an ammonia-charged two-phase closed thermosyphon. R&D j. (Matieland, Online) [online]. 2000, vol.16, pp.33-40. ISSN 2309-8988.

The thermal performance characteristics including the evaporator and condenser heat transfer coefficients and the maximum heat transfer rate for an ammonia charged two-phase closed thermosyphon have been experimentally determined for vertical and inclined orientations. The thermosyphon tested is 6.2 m long and has an internal diameter of 31.9 mm and is made of grade 304 stainless steel. Hot water of up to 80° C and cooling water of between 10 and 20°C, inclination angles of 30, 45, 60, 75 and 90° to the horizontal, evaporator to total length ratios of 0.06 to 0.33 and liquid charge fill ratios (Le/L_e) of between 20 and 100 % were considered. The correlations of the experimental data for the heat transfer coefficients are given in terms of the wall heat flux, internal pressure, liquid charge fill ratio and angle of inclination. The correlation for the superficial velocity at which the heat transfer rate could not be increased further by increasing the temperature difference between the evaporator and the condenser was determined in terms of internal temperature, liquid charge fill ratio and inclination angle. The experimentally determined values of the heat transfer coefficients did not correspond well with existing correlations. This is attributed to the limited availability of ammonia as working fluid and inclined thermosyphon orientations in the data sets upon which these existing correlations 'were based, as well as the generally complex nature of the various heat transfer mechanisms that occur in a thermosyphon.

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