04/03000 Local instantaneous temperature and time-averaged heat transfer coefficient in the bottom zone of a circulating fluidized bed

The local instantaneous temperature, heat transfer coefficient, and pressure data, gathered around a horizontal tube in a fluidized bed, have been analyzed using the deterministic chaos theory. A stainless steel heat transfer tube, carrying a hot water flow, was placed in a cold bubbling fluidized bed. The tube was instrumented in the circumferential direction with five fast-responding surface thermocouples and a vertical pressure differential sensor. The local temperature and pressure data were measured simultaneously at a frequency of 120 Hz. Additionally, the local instantaneous heat transfer coefficient was evaluated by solving the transient two-dimensional heat conduction equation across the tube wall numerically. The mutual information function (MIF) has been applied to the signals to observe the relationship between points separated in time. MIF was also used to provide the most appropriate time delay constant τ to reconstruct an m-dimensional phase portrait of the one-dimensional time series. The distinct variation of MIF around the tube indicates the variations of solid-surface contact in the circumferential direction. The correlation coefficient was evaluated to calculate the correlation exponentv, which is closely related to the fractal dimension. The correlation exponent is a measure of the strange attractor. The minimum embedding dimension as well as the degrees of freedom of the system were evaluated via the correlation coefficient. Kolmogorov entropies of the signals were approximated by using the correlation coefficient. Kolmogorov entropy considers the inherent multi-dimensional nature of chaotic data. A positive estimation of Kolmogorov entropy is an indication of the chaotic nature of the signal. The Kolmogorov entropies of the temperature data around the tube were found to be between 10 bits/s and 24 bits/s. A comparison between the signals has shown that the local instantaneous heat transfer coefficient exhibits a higher degree of chaos than the local temperature and pressure signals.

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Mean Heat Transfer Coefficient around a Horizontal Single Pipe in a Fast Circulating Fluidized Bed.

KAGAKU KOGAKU RONBUNSHU ◽

10.1252/kakoronbunshu.23.437 ◽

1997 ◽

Vol 23 (3) ◽

pp. 437-439

Author(s):

Shiro Takashima ◽

Yasuhisa Honda ◽

Jiro Katayama ◽

Eiji Obata ◽

Hiroshi Takahashi

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Single Pipe

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Heat Transfer Performance in a Superheater of an Industrial CFBC Using Fuzzy Logic-Based Methods

Entropy ◽

10.3390/e21100919 ◽

2019 ◽

Vol 21 (10) ◽

pp. 919 ◽

Cited By ~ 6

Author(s):

Krzywanski

Keyword(s):

Heat Transfer ◽

Fuzzy Logic ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Practical Significance ◽

Overall Heat Transfer Coefficient ◽

Bed Temperature ◽

The Heat Transfer Coefficient

The heat transfer coefficient in the combustion chamber of industrial circulating flidized bed (CFB) boilers depends on many parameters as it is a result of multifactorial mechanisms proceeding in the furnace. Therefore, the development of an effective modeling tool, which allows for predicting the heat transfer coefficient is interesting as well as a timely subject, of high practical significance. The present paper deals with an innovative application of fuzzy logic-based (FL) method for the prediction of a heat transfer coefficient for superheaters of fluidized-bed boilers, especially circulating fluidized-bed combustors (CFBC). The approach deals with the modeling of heat transfer for the Omega Superheater, incorporated into the reaction chamber of an industrial 670 t/h CFBC. The height above the grid, bed temperature and voidage and temperature, gas velocity, and the boiler’s load constitute inputs. The developed Fuzzy Logic Heat (FLHeat) model predicts the local overall heat transfer coefficient of the Omega Superheater. The model is in good agreement with the measured data. The highest overall heat transfer coefficient is equal 220 W/(m2K) and can be achieved by the SH I superheater for the following inputs l = 20 m, tb = 900 °C, v = 0.95, u = 7 m/s, M-C-R = 100%. The proposed technique is an effective strategy and an option for other procedures of heat transfer coefficient evaluation.

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