An experimental investigation of the effect of longitudinal fin orientation on heat transfer in membrane water wall tubes in a circulating fluidized bed (original) (raw)
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Effect of Fins on Heat Transfer of Horizontal Immersed Tube in Bubbling Fluidized Beds
2009
— Steady state time averaged local heat transfer coefficient measurements were made by the local thermal simulation technique in a cold bubbling fluidized bed with horizontally immersed tube initially with no fin and then with three fixed annular fins of constant thickness. Silica sand of mean particle diameter 307 μm and 200 μm were used as the bed materials. The results indicate that although the heat transfer coefficient falls with the use of fins, the total heat transfer rises as the result of the greater surface area. Increasing the particle diameter reduces the heat transfer coefficient not only for unfinned horizontal tube but also for annular finned horizontal tube at the same conditions of fluidized bed. Based on the experimental data, correlations are proposed for predicting heat transfer coefficient from fluidized bed to horizontally immersed tubes with and without fins. Index Terms — Annular fin, Bubbling fluidized bed, Heat transfer.
Heat transfer in a membrane assisted fluidized bed with immersed horizontal tubes
The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity. In the d...
International journal of …, 1995
Measurements of local solids concentration, heat transfer and erosion were obtained in a 152 mm diameter x 9.3 m tall circulating fluidized bed operated at room temperature with 200 /zm sand particles al: a superficial gas velocity of 7.0 m s-l with different solids circulation rates. Local solids concentrations were found to be higher in the fin region than on the crests of membrane tubes. For the small heat transfer surfaces investigated, this led to higher local heat transfer coefficients in the fin region, a trend which is the reverse of that for long heat transfer surfaces. Erosion rates were higher on the tube crests than on the fins.
Effect of annular fins on heat transfer of a horizontal immersed tube in bubbling fluidized beds
Powder Technology, 2005
Experiments were conducted in a bubbling air-fluidized bed to investigate the effect of annular fins of constant thickness on heat transfer. Steady state time averaged local heat transfer coefficient measurements were made by the local thermal simulation technique in a cold bubbling fluidized bed (90 mm ID, 260 mm tall) with horizontally immersed tube initially with no fin and then
Heat transfer between a fluidized bed and a horizontal tube
Chemical Engineering Science, 1958
Measurements of coefficients of heat transfer from fluidized beds to horizontal watercooled tubes are discussed. The bed diameter was 0.565 m. The following quantitities were varied : (1) bed temperature ; (2) mass velocity of the fluidizing air ; (3) mean particle diameter ; (4) particle shape; (5) particle density; (6) water-tube diameter. The second, third and fifth quantities were varied down to much lower values than before [l] ; the sixth quantity had not previously been varied.
Heat transfer from a circulating fluidized bed to membrane waterwall surfaces
AIChE Journal, 1987
Average and local heat transfer coefficients were measured for transfer from circulating fluidized beds of sand particles (mean size 188 and 356 pm) to two water-cooled membrane wall surfaces located on one face of a 152 mm square by 7.3 m tall column. The measurements cover a range of superficial gas velocities from about 4 to 7 m/s, suspension densities from about 8 to 130 kg/m3, suspension temperatures from 150 to 400"C, and secondary-to-primary air ratios of 0 to 1.5. Heat transfer coefficients, averaged over a 1.53 m length of the membrane waterwall surfaces, depend strongly on suspension density, but show almost no separate dependence on gas velocity, bed temperature, or secondary-to-primary air ratio for the conditions studied. For the surface nearest the top of the unit, the coefficient decreases with distance measured downward from the top, suggesting that particles travel downward along the surface. As a result, averaged coefficients are lower and the influence of particle size is less than for previously reported circulating fluidized bed heat transfer measurements where miniature heat transfer surfaces were employed.
A study of heat transfer in a circulating fluidized bed
International Journal of Energy Research, 1993
An experimental investigation was carried out to study the effects of operating parameters on the local bed-to-wall heat transfer coefficient in a 4.5 m tall, 0.150 m diameter circulating fluidized bed with a bed temperature in the range of 65°C to 80°C, riser flow rate varying from 1400 litres/min to 2000 litres/min, bed inventory in the range of 15 kg to 25 kg of sand, and average sand sizes of 200 pm, 400 pm and 500 pm. A heat flux probe was attached to the riser wall at five different vertical locations for measuring the heat flux from the bed to the wall surface. From the present work, the heat transfer coefficient in the dilute phase was found to be in the range of 62 to 83 W/m2 K, 51 to 74 W/mZ K, and 50 to 59 W/mZ K for sand sizes of 200 pm, 400 pm and 500 pm, respectively. Relevant mathematical correlations were developed to predict local heat transfer coefficient based on the results of the practical work.
2013
The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity. In the design of membrane assisted fluidized beds care must be taken to include the effect of gas addition or withdrawal through the membranes on the required heat transfer surface area.
Experimental Analysis of Fin and Tube Heat Exchanger in Heating and Cooling Mode
2017
The paper provides the results of experimental tests of a wavy fin and tube heat exchanger used to heat (cool) air in a ventilation system when the finned plate of the heat exchanger is dry and wet. The experimental tests, performed in the range of 1000<Re<4500 of the Reynolds number, determined the dependency of the heat transfer coefficient on the amount of supplied air with the varying geometry of the heat exchanger (the number of tube rows, the distance between fins, the thickness of the fin and the diameter of the tube). The experimental tests were performed on 9 heat exchangers in heating mode (dry fin) and 6 heat exchangers in cooling mode (wet fin). The ratio of heat transfer coefficient values when the fin is dry and wet varies from 0.79 to 1.12. After processing the results of the experimental tests, equations defining the dependency of the heat transfer coefficient on the amount of air and varying geometric parameters of the heat exchanger were derived, based on whi...
Heat transfer in a membrane assisted bubbling fluidized bed with immersed horizontal tubes
International Journal of …, 2005
The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity.