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:10.1080/01457630050144451

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Since 1974, Siemens' Power Generation Group (KWU) has been operating a high-pressure two-phase flow test loop-called the Benson test rig-which offers a range of operating conditions that is unique in the world (1 to 330 bar, 20 to 600°C, and 0 to 2 MW electric heating power). The 25th anniversary of the first tests performed at this test rig presents a good occasion not only for reviewing the past, but also for contemplating the future of two-phase flow experiments. The past was characterized by integral and separate effect tests for power generation using nuclear, fossil, and renewable energy sources as well as for process industries. This article will present examples demonstrating the flexible and broad range of applications for the Benson test rig. The results of the tests have been used to develop algorithms for implementation in computer programs and also for validating such programs. Usually these computer programs-so-called analysis tools-are used for analyzing systems or components. From an analyst's point of view, two-phase flow experiments serve either to verify global flow conditions or to supply inputs such as boundary conditions and material laws and/or initial conditions for the analysis tools. An advanced way of making sure that all available knowledge can be input into the analysis tools is to collect and store it in a program system from which it can be called up, whenever required, according to the task in hand. Siemens' KWU Group has started developing such a system. Apart from integral tests conducted for new power plants, future two-phase flow experiments will probably focus on expanding this program system's database.

ISSN:0145-7632    

DOI:10.1080/01457630050144460

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

A general correlation for heat transfer during film boiling in tubes is presented. It is based on the two-step model. It has been verified with data for nine fluids flowing up in tubes. The fluids include water, cryogens, refrigerants, and chemicals. The range of data includes pressures from 1 to 215 bar, reduced pressures from 0.0046 to 0.97, mass velocities from 4 to 5,176 kg/m² s, tube diameters from 1.1 to 24.3 mm, and qualities from 0.1 to 2.4. The 546 data points are predicted with a mean deviation of 15.2%. Deviation is defined as the difference between the measured and predicted heat transfer coefficients divided by the measured heat transfer coefficient, the heat transfer coefficients being based on the saturation temperature. Three other well-known correlations are also compared to the same data and found to have much larger deviations. The correlation is also compared with a limited amount of data from horizontal tubes; the results are encouraging.

ISSN:0145-7632    

DOI:10.1080/01457630050144479

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

The effect of a D.C. electric field on nucleate boiling heat transfer for refrigerants, R11, R113, and FC72, was investigated experimentally in a single-tube shell/tube heat exchanger by using the temperature control method of wall superheat. Also the behavior of bubble under nonuniform electric field produced by wire electrodes was studied by numerical calculation. For R11, the electrohydrodynamic (EHD) enhancement for boiling heat transfer was observed for all ranges of wall superheat tested. However, the enhancement in boiling heat transfer disappeared if the wall superheat exceeded 13°C for R113, and no electric field effect on the boiling heat transfer was observed for FC72. An application of approximately 5 kV was enough to eliminate the boiling hysteresis for R11 and R113. Numerical study of the electric field in a single medium has hinted that the bubbles are forced away from the heating surface and toward the electrostatic stagnation point by the dielectrophoretic force. Such modified bubble motion turns out to promote the boiling heat transfer if one uses proper electrode configuration.

ISSN:0145-7632    

DOI:10.1080/01457630050144488

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

The article is a presentation of a new method for enhancement of filmwise condensation heat transfer on a vertical tube. The method is that a tube is fluted on its outer surface and coated with metallic powder on the crest, which is called a fluted tube with coatings. The experimental results show that the enhancement of condensation is more notable because of the dual function of Gregorig effect and the thin porous coatings.

ISSN:0145-7632    

DOI:10.1080/01457630050144497

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

The present article reports on the results of experimental research carried out on compact plate heat exchangers, currently used as evaporators and condensers in refrigeration loops. The research was aimed at getting information on the thermal efficiency of the heat exchangers, under reference commercial conditions, when using new ozone-friendly refrigerants to replace CFCs and HCFCs. Specifically, the influence of some thermal-hydraulic parameters on the heat flux and the overall heat transfer coefficient are investigated for evaporators, using R134a, R407C, and R410A, three fluids proposed to replace R22, and HCFC, currently the most common refrigerant used in residential and commercial air conditioning equipment. Moreover, in this article a new thermodynamic method has been applied with the purpose of defining the saturation temperature and investigating the other main parameters for mixtures in the two-phase region for the fluids R407C and R410A, which are blends of, respectively, three and two pure refrigerants.

ISSN:0145-7632    

DOI:10.1080/01457630050144505

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

Thermal insulation economic analysis for a system of pipelines insulated by different materials composite layers is studied. The analysis is based on an explicit nonlinear cost function that includes the annual energy losses and the insulation initial costs. Practical ranges of different insulation thicknesses are included as a set of inequality constraints. Furthermore, the analysis accounts for the safety limits required for the temperature of the outer surface of the insulation. A search procedure, modified Hook and Jeeves, is employed to find the optimum thickness for the least annual cost within the domain bounded by the constraints. The procedure has been verified against the analytical solution for a single pipeline with a single insulation layer. The analysis is employed for a system of pipelines (4-10" nominal size) [1] with flow of superheated steam. Furfural, crude oil, and 300-distillate. The results show significant cost saving with optimal insulation compared to the dimensions of engineering practice. Detailed data for these cases are presented and discussed.

ISSN:0145-7632    

DOI:10.1080/01457630050144514

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

摘要:

The unknown boundary surface heat flux in workpieces during grinding is estimated by the application of inverse heat transfer analysis. The conjugate gradient method of function estimation is used for the minimization procedure. Simulated temperature measurements are used in the inverse analysis for typical practical cases, in order to show that results more accurate than those available in the literature are obtained with the present solution approach. Actual experimental data are also used in the computations to estimate the surface heat flux.

ISSN:0145-7632    

DOI:10.1080/01457630050144523

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor

ISSN:0145-7632    

DOI:10.1080/01457630050144532

出版商:Informa UK Ltd    

年代:2000

数据来源: Taylor