D.C. Groeneveld

A look-up table for fully developed film-boiling heat transfer

Abstract An improved look-up table for film-boiling heat-transfer coefficients has been derived for steam–water flow inside vertical tubes. Compared to earlier versions of the look-up table, the following improvements were made: • The database has been expanded significantly. The present database contains 77,234 film-boiling data points obtained from 36 sources. • The upper limit of the thermodynamic quality range was increased from 1.2 to 2.0. The wider range was needed as non-equilibrium effects at low flows can extend well beyond the point where the thermodynamic quality equals unity. • The surface heat flux has been replaced by the surface temperature as an independent parameter. • The new look-up table is based only on fully developed film-boiling data. • The table entries at flow conditions for which no data are available is based on the best of five different film-boiling prediction methods. The new film-boiling look-up table predicts the database for fully developed film-boiling data with an overall rms error in heat-transfer coefficient of 10.56% and an average error of 1.71%. A comparison of the prediction accuracy of the look-up table with other leading film-boiling prediction methods shows that the look-up table results in a significant improvement in prediction accuracy.

A comparison of predictions of high-temperature steam properties

Abstract Recent literature pertaining to high temperature steam properties has been assessed. After careful assessment of available sets of property tables and equations for high temperature (including dissociated) steam, a set of high temperature steam properties was selected, based heavily on Vargaftik steam tables. A computer code, UODH2O (University of Ottawa Dissociated H 2 O code) is constructed to compute high-temperature steam properties using a lookup table and interpretation technique. The code, which required input values of pressure (0.01–100.0 MPa) and temperature (1000–5726.85°C), can predict four thermodynamic properties - specific volume, entropy, enthalpy and heat capacity, and two transport properties - viscosity and thermal conductivity.

Prediction of CHF enhancement due to flow obstacles

Abstract A semi-theoretical prediction method of CHF enhancement due to flow obstacles inserted in a flow channel was developed in this paper. Compared to the existing CHF enhancement equations, the present prediction model includes the effect of most of the important parameters and correctly represents the observed parametric and asymptotic trends. Good agreement has been found between the model predictions and the existing experimental databases.

Assessment of Selected Two-Phase Friction Multiplier Correlations for Steam-Water Flows in Vertical Heated and Unheated Tubes

In this study, around 10 000 experimental two-phase (2ϕ) flow pressure drop (ΔP) data for steam-water in uniformly heated and adiabatic vertical tubes have been compiled from the literature.The compiled data have been used to assess the prediction accuracy of two-phase friction multiplier (Display Formulaϕlo2) correlations selected from the literature and the homogeneous-flow model for steam-water flow in vertical tubes. The predictions of the Display Formulaϕlo2 correlations have also been compared to the predictions of the homogeneous-flow model. The assessments are based on comparisons of the average and the RMS errors.Additionally, ΔP components (due to gravitation, acceleration and friction) have been examined for a variety of flow conditions in vertical heated and unheated tubes.The results of the assessments show that the predictions of Muller-Steinhagen and Heck (1986) correlation yield the minimum RMS error for flow in heated tubes and the predictions of the Chisholm (1973) correlation yield the minimum RMS error for flow in adiabatic tubes when these predictions are compared with both the data base and the predictions of the homogeneous-flow model.It is concluded from the research and a review of the literature that the current state of the art is such that none of the investigated prediction methods is very good because of their large RMS errors. More work is needed to expand the ΔP data base especially for adiabatic two-phase flow. Also, a systematic experimental study should be performed on the effect of heating on the 2ϕ-flow ΔP.Copyright