B M Burnside

A comparison between HIGHFLUX and plain tubes, boiling pentane in a horizontal kettle reboiler

Abstract An experimental study has been undertaken into the enhancement obtained in the heat-transfer coefficients when HIGHFLUX tubes are used in preference to plain tubes while boiling pentane. The study involved two experimental facilities, a single-tube pool boiler and a 241 tube, 17 row by 17 column, thin slice kettle reboiler. The pool boiling results show that the HIGHFLUX tubes produce heat-transfer coefficients that are up to five times larger than their plain tube counterparts. In flow boiling the enhancement is 3–6 times. In both cases, HIGHFLUX tube performance is shown to deteriorate when small degrees of subcooling are present in the liquid. The deterioration still leaves the HIGHFLUX tubes with a significantly higher heat-transfer coefficient than the plain tubes. Existing flow boiling design methodologies are shown to produce performance characteristics that HIGHFLUX tubes do not follow.

Dropwise condensation of steam on a small tube bundle at turbine condenser conditions

Application of dropwise condensation to utility turbine condensers is investigated by comparing the thermal performance of dropwise and filmwise bundles at industrially relevant conditions. Steam and steam-air mixtures were condensed on bundles of in-line, titanium tubes. The row-by-row heat transfer coefficients are presented against bundle position. They show the expected behavior for filmwise condensation but demonstrate a different one for dropwise. In air-free steam, the dropwise heat transfer coefficients are much larger and do not vary significantly with bundle position. In air-steam mixtures the dropwise values decrease similarly to their filmwise equivalents. The findings are in accord with those found for other geometries. The findings indicate that significant reductions in condenser size can be obtained if permanent dropwise condensation can be produced at industrially relevant conditions.Application of dropwise condensation to utility turbine condensers is investigated by comparing the thermal performance of dropwise and filmwise bundles at industrially relevant conditions. Steam and steam-air mixtures were condensed on bundles of in-line, titanium tubes. The row-by-row heat transfer coefficients are presented against bundle position. They show the expected behavior for filmwise condensation but demonstrate a different one for dropwise. In air-free steam, the dropwise heat transfer coefficients are much larger and do not vary significantly with bundle position. In air-steam mixtures the dropwise values decrease similarly to their filmwise equivalents. The findings are in accord with those found for other geometries. The findings indicate that significant reductions in condenser size can be obtained if permanent dropwise condensation can be produced at industrially relevant conditions.

Boiling the immiscible water/n-nonane system from a tube bundle

Abstract A series of experiments is described in which water and the C 9 alkane n -nonane (b.p. 150.5°C, s.g. 0.72) was boiled in a short electrically heated shell and tube arrangement at heat fluxes up to 110 k W m −2 . Vapour composition, temperatures of vapour and liquid and the boiling curves were measured over the whole range of boiler liquid compositions. Systematic variations are discussed. The nature of the boiling process is described. Provided that at least the bottom row of tubes is immersed in water the boiling heat transfer coefficient based on the temperature difference between tube wall and t sat water was very close to that for boiling pure water. The paper concludes with recommendations for design.

Pressure drop measurements in condensing steam over a horizontal bundle of staggered tubes

Pressure drop measurements in a 15 row staggered configuration condenser, p/D=1.33, are described. Heat flux densities of up to 90 kW·m−2 were used. The results are compared with the those of another investigation using a condenser with much less closely packed tubes. At relatively low suction, pressure drop in the closely packed condenser could be predicted by conventional single phase correlations. At higher values of suction the condensing pressure loss was considerably lower in this condenser than the single phase value. In the more loosely packed condenser this difference occurred at all values of suction. It is concluded that more experimental and theoretical work is required to explain these effects in view of their importance in turbine condenser design.

A comparison between a small in-line and a staggered tube bank condensing steam filmwise at low-pressures

Abstract Data have been produced for filmwise condensation of steam, and steam–air mixtures, flowing downwards across two tube bank, a 15 row, in-line bank containing 75 tubes and a 15 row staggered bank containing 82 tubes. Both banks were tested at conditions typical of those found in the UK electricity generating industry. Steam was supplied at pressures of 50, 75 and 100 mbar, at velocities of 10, 20 and 33 m/s and with air concentrations of 0 and 10,000 ppm. Steam to cooling water temperature differences of 5, 10 and 15 K were used to generate heat fluxes of up to 90 kW / m 2 . The data and a mathematical model were used to investigate the effect of geometry difference on the heat transfer and pressure difference characteristics. For this particular configuration, the staggered and the in-line tube banks gave the same performance. This is not consistent with similar studies done by other researchers and indicates that tube spacing is important.

PRESSURE DROP IN DOWNWARD FLOW OF CONDENSING STEAM OVER A HORIZONTAL BUNDLE OF SQUARE PITCHED TUBES

Pressure drop measurements in a 15-row steam condenser configured with in-line tubes, p/D < 1.33, are described. Pressures from 50 to 100 mb and Remax in the range 1,000-18,000 were imposed. It is shown that pressure loss coefficients for the bundle and for two-row pairs were lower than predictions for equivalent single-phase tests except near the bottom of the bundle. There was some evidence that increase in suction parameter increased this effect in the top rows. Taken together with previous investigations [3, 4], a falling trend of suction effect is evident the more closely packed the tubes are. The discrepancy between these findings and the results of simulation experiments [7] is noted.Pressure drop measurements in a 15-row steam condenser configured with in-line tubes, p/D < 1.33, are described. Pressures from 50 to 100 mb and Remax in the range 1,000-18,000 were imposed. It is shown that pressure loss coefficients for the bundle and for two-row pairs were lower than predictions for equivalent single-phase tests except near the bottom of the bundle. There was some evidence that increase in suction parameter increased this effect in the top rows. Taken together with previous investigations [3, 4], a falling trend of suction effect is evident the more closely packed the tubes are. The discrepancy between these findings and the results of simulation experiments [7] is noted.

Instability in pool boiling of a wide boiling mixture on a horizontal tube

Abstract Events occurring during pool boiling of the wide boiling range equimolar pentane/tetradecene mixture on a horizontal tube are described. Due to preferential evaporation of pentane, a film of liquid rich in tetradecene builds up on the lower part of the surface and breaks away from time to time causing fluctuation in the liquid temperature near the boiling surface. The effect of this phenomenon on heat transfer coefficients over a range of heat fluxes is discussed. It is shown that the measured heat transfer coefficients follow the same trend of variation with heat flux as that predicted by Schlunder. However, it is argued that this agreement is fortuitous and that no current prediction method may be used with confidence to estimate heat transfer coefficients of wide boiling range mixtures.