Vol.1, No 6 1998 pp. 703 - 710
UDC 563.255
THE INFLUENCE OF FLUIDIZATION VELOCITY
ON HEAT TRANSFER BETWEEN FLUIDIZED BED
AND INCLINED HEAT TRANSFER SURFACES
Branislav Stojanović, Mladen Stojiljković
Faculty of Mechanical Engineering, Niš
Abstract. The paper presents an experimental investigation of the influence of fluidization velocity on heat transfer coefficient between fluidized bed and inclined heat transfer surfaces.
The investigation was conducted on laboratory scaled apparatus, of the square cross section 160x160 cm. Bed material was quartz sand, with equivalent diameter of 0,3 mm. Heat transfer surface - electrical heater is made of copper tube with inner diameter of 16 mm and 100 mm long. Investigation was conducted so that, for defined fluidization velocity, temperature measurement on front, lateral and back side of the heater, relating to the fluidization air flowing direction, was done for different angles of inclination.
Based on obtained heat transfer coefficient values it can be concluded that tendency of change of heat transfer coefficient with increasing fluidization velocity is similar for all heater inclination angles. With increasing angle of inclination, i.e. heater position from vertical to horizontal, heat transfer coefficient values decrease almost uniformly in the whole range of fluidization velocity.
The biggest change of heat transfer coefficient was obtained for fluidization rate of 1,25, slightly over the minimum fluidization velocity.
At fluidization rate over 2,5 heat transfer coefficient's change insignificantly depends on fluidization rate and maximum appears at the angle of inclination 10 to 150.
UTICAJ BRZINE FLUIDIZACIJE NA RAZMENU TOPLOTE
IZMEĐU FLUIDIZOVANOG SLOJA I NAGNUTIH RAZMENJIVAČKIH POVRŠINA
U ovom radu je dat prikaz eksperimentalnog istraživanja uticaja brzine fluidizacije na promenu koeficijenta prelaza toplote između fluidizovanog sloja i nagnutih razmenjivačkih površina. Ispitivanje je sprovedeno na laboratorijskoj aparaturi dimenzija 160x160 mm, a kao materijal sloja korišćen je kvarcni pesak srednjeg prečnika čestica 0,3 mm. Sloj je zagrevan električnim grejačem prečnika 16 mm i dužine 100 mm. Ispitivanja su obavljena tako da je za za određenu brzinu fluidizacije izvršeno merenje temperature površine grejača na čenoj, bočnoj i gornjoj strani u odnosu na smer strujanja vazduha za fluidizaciju za različite uglove nagiba grejača.
Na osnovu dobijenih vrednosti koeficijenta prelaza toplote može se zaključiti da je tok promene koeficijenta prelaza toplote sa porastom brzine fluidizacije sličan za sve uglove nagiba grejača. Pri tom, sa porastom ugla nagiba, tj. pri promeni položaja grejača od vertikalnog ka horizontalnom položaju vrednosti koeficijenta prelaza toplote se smanjuju skoro podjednako u celom dijapazonu promene brzine fluidizacije. Najveća proemna koeficijenta prelaza toplote dobijena je za stepen fluidizacije 1,25. Pri stepenima fluidizacije većim od 2,5 promena koeficijenta prelaza toplote veoma malo zavisi od stepena fluidizacije i pri tom se uočava pojava maksimuma za uglove nagiba 10-150.