ISSN:0145-7632    

DOI:10.1080/01457639608939864

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical investigation has been carried out to determine the effects of condensation inundation, noncondensable gases, and cooling water velocity upon the local and overall condensation heat transfer in horizontal tube bundles. Five inundation correction factors are tested against the experimental data. Comparisons between the predicted results and the experimental data are made in terms of total condensation rates and local heat flux distributions. The effects of noncondensable gases and cooling water velocity arc assessed by comparing local heat flux distributions, total condensation rates, and average steam-side and average overall heat transfer coefficients under different inlet air mass fraction and inlet cooling water velocity conditions.

ISSN:0145-7632    

DOI:10.1080/01457639608939865

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A numerical analysis of forced-convection heat transfer from a horizontal stationary circular cylinder dissipating a uniform heat flux in a crossflow of air is conducted by solving the full two-dimensional steady-state Navier-Stokes and energy equations in the range of the Reynolds numbers from 100 to 500 (based on diameter). A numerical study by this author for Reynolds numbers less than 100 was previously conducted and therefore is not repeated here. Dependence on the Reynolds number of the flow and thermal fields, vorticity and pressure distributions, separation angle, drag coefficient, and local and average Nusselt number around the cylinder are shown. Correlations for the separation angle and drag coefficient as functions of Reynolds number are suggested. Quantities such as vorticity, pressure, and Nusselt number at the forward and rear (base) stagnation points are also calculated and correlated as functions of Reynolds number. The local and average values of the Nusselt numbers are shown to be in good agreement with available correlations and experiments. The average forced-convection Nusselt number is correlated. A new correlation for the mean value of forced-convection Nusselt number based on 27 previous studies, including the present results, is proposed. Theoretical predictions and available experimental data are found to be in agreement. Theoretical prediction of the thermal field has no precedence. Flow control methods (which may be possible when turbulence is understood) to stabilize unstable solutions may lead to significant new classes of flows, which at first may be studied numerically more easily and cheaply. The extensive comparison and literature survey given in this article have shown that this fundamental problem is one of such continuing interest, at least from the perspective of fluid flow studies.

ISSN:0145-7632    

DOI:10.1080/01457639608939866

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effect of nonuniform (or maldistributed) inlet airflow and temperature on the thermal performance of cross-flow air-cooled heat exchangers, with both fluids unmixed, and taking into consideration differences in performance characteristics of individual tube rows, is addressed in this article. The latter may be due to different fin pitches or other geometric variations or row effects due to changes in air turbulence. Downstream tube rows in such a multirow tube bundle experience higher performance reductions than the tube row at the air inlet. A nonuniform air velocity distribution to a tube row leaves the row with a distorted temperature profile. This temperature nonuniformity increases as the air passes through subsequent tube rows, and causes the downstream rows to be progressively less effective. The present analysis is used to evaluate the performance of the individual tube rows and ultimately the entire bundle. Velocity distributions which have been measured on air-cooled heat exchanger models are employed in the analysis in order to determine to what extent airflow maldistribution reduces exchanger performance. It is found that maldistribution occurring in well-designed air-cooled heat exchangers reduces the thermal performance by only a few percent.

ISSN:0145-7632    

DOI:10.1080/01457639608939867

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Performance of heat exchangers with helical baffles, or helixchangers, is discussed using the results of tests conducted on units with uarious baffle geometries. An optimum helix angle is identified at which the conversion efficiency for converting pressure drop to heat transfer on the shell side of helixchangers is maximized. Designs for standard industry applications are optimized using the analysis of test results.

ISSN:0145-7632    

DOI:10.1080/01457639608939868

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor