ISSN:0145-7632    

DOI:10.1080/01457630050144442

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/01457630050194753

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

In conventional and high-efficiency boilers it is important to understand where water from the products of combustion may condense onto the heat exchanger surface. The usual fin modeling approach is inadequate because it predicts no circumferential preference for condensation, whereas spatial effects have been observed. Two alternative approaches for modeling fin heat transfer are explored: one method is based on a generalization of observed trends in local convective heat transfer coefficients, and the other on a semiempirically motivated variation in convective flow temperature. Temperature distribution and fin efficiency predictions are compared to the conventional fin modeling approach. The alternative fin heat transfer models described in this study both predict more extensive condensation on the portion of the fin within the wake of the tube. Furthermore, both models predict fin efficiencies below those obtained using an assumption of constant heat transfer coefficient and convective temperature.

ISSN:0145-7632    

DOI:10.1080/01457630050194762

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

A mathematical model is developed to study the performance of a parallel-flow heat exchanger in which both fluid streams are interacting thermally with the surroundings. The fluid temperatures are found to be dependent on the magnitude of the ambient temperature relative to fluid inlet temperatures, the ratios of conductances between the fluids and the ambient and the interfluid conductance, the ratio of minimum to maximum fluid capacities, and the number of transfer units, NTU, for the heat exchanger. Two heat exchanger effectiveness criteria, one each for the hot and cold fluids, are used to study performance. The effectiveness is found to be adversely affected by increasing conductance ratios, increasing NTU, and increasing temperature difference between the ambient and the fluid of interest. For very high values of the conductance ratios, the heat exchanger will not perform as expected and both fluid temperatures will approach that of the ambient. The parallel-flow arrangement is compared to counterflow and is found to be less effective under the external heat transfer condition.

ISSN:0145-7632    

DOI:10.1080/01457630050194771

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/01457630050194780

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

An improved analysis model is presented for predicting the local heat transfer coefficient of forced condensation in the annular flow region inside smooth horizontal tubes. Heat transfer experiments for R-12 and R-134a are conducted inside a condensing tube with an inner diameter of 11 mm and a length of 13 m. The mass flux ranged from 200 to 510 kg/m2s, and the vapor qualities varied from 1.0 to 0.0. Compared with the experimental data, the numerical results have a deviation of not more than 20% and 25% for 80% of the total 47 points of R-12 and 88% of the total 226 points of R-134a, respectively.

ISSN:0145-7632    

DOI:10.1080/01457630050194799

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

In the present work, noncondensable contaminant accumulation in tubes of single-pass, multiple-row, cross-flow condensers is investigated. A mathematical model of condensation in such heat exchangers is proposed, which considers changes along the tubes in the saturation temperature, coolant velocity, and heat transfer effectiveness. The model equations are solved with an original algorithm. The vapor distribution, the global effectiveness of the condenser, and the pressure drop between the inlet and outlet plena are determined under different working conditions.

ISSN:0145-7632    

DOI:10.1080/01457630050194807

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Wall-to-bed heat transfer coefficients to pulp mill Kraft black liquor in a nominal 25-mm tubular, liquid?solid fluidized bed have been determined. The fluidizing particles were stainless steel balls of 4.0, 4.76, and 6.35 mm diameter. The heat transfer coefficients were determined for conditions where porosity, bulk temperature, and liquor concentration were varied. The best correlation was obtained when the data were split into two groups of low and high liquor concentrations, i.e., 30?40% and 50?65% total dissolved solids. The data were also compared with the predictions obtained from 26 published correlations, of which the best 10 are presented and discussed in this article. The results of this investigation are relevant to other fluidized bed systems with high liquid viscosity, such as sugar concentrations, hydrocarbons, and polymers.

ISSN:0145-7632    

DOI:10.1080/01457630050194816

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/01457630050194825

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/01457630050127973

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor