Heat Transfer Correlations For Two-phase Flow Research Articles

Condensing two-phase pressure drop and heat transfer coefficient of propane in a horizontal multiport mini-channel tube: Experimental measurements

This article reports the condensing flow heat transfer coefficient and pressure drop results of propane (R290) flowing through a square section horizontal multiport mini-channel tube made of aluminium having an internal diameter of 1.16 mm and a condensing length of 259 mm. Pressure drop and two phase flow experiments were performed at saturation temperatures of 30, 40 and 50 °C. Heat flux was varied from 15.76 to 32.25 kWm−2 and mass velocity varied from 175 to 350 kg m−2 s−1. The results show that the two-phase friction pressure gradient increases with the increase of mass velocity and vapour quality and with the decrease of saturation temperature. The heat transfer coefficients showed to increase with increases of vapour quality and mass velocity while increases of saturation temperature were observed to reduce heat transfer coefficient. The two phase frictional pressure drop correlations of Sun and Mishima and Agarwal and Garimella, and the two-phase flow heat transfer correlations of Koyama et al. and Wang et al. predicted well the experimental results.

Shell-and-tube evaporator model performance with different two-phase flow heat transfer correlations. Experimental analysis using R134a and R1234yf

This work presents a model of a shell-and-tube evaporator using R1234yf and R134a as working fluids. The model uses the effectiveness-NTU method to predict the evaporation pressure and the refrigerant and secondary fluid temperatures at the evaporator outlet, using as inputs the geometry of the evaporator, the refrigerant mass flow rate and evaporator inlet enthalpy, and the secondary fluid volumetric flow rate and evaporator inlet temperature. The model performance is evaluated using different two-phase flow heat transfer correlations through model outputs, comparing predicted and experimental data. The output parameter with maximum deviations between the predicted and experimental data is the evaporating pressure, being the deviations in outlet temperatures less than 3%. The evaporator model using Kandlikar's correlation obtains the highest precision and the lowest absolute mean error, with 4.87% in the evaporating pressure, 0.45% in the refrigerant outlet temperature and 0.03% in the secondary fluid outlet temperature.

Assessment of Two-Phase Flow Heat Transfer Correlations for Molten Core-Concrete Interaction Study

In case of a pressurized water reactor’s severe accident with core meltdown and vessel failure, corium would spread on the concrete basemat of the plant. The high temperature of the corium pool maintained by the residual power would lead to the erosion of the concrete walls and potentially to the bypass of the containment. The ablation velocity of concrete is governed by the heat flux between the corium pool and the concrete wall, and its calculation is of particular significance to predict whether and when the basemat would fail in such a situation. From a hydrodynamic point of view, this issue is related to heat transfer between a volumetric heated bubbling pool and a porous wall with gas injection. Several experimental studies have been performed in the past, and many correlations have been proposed to address this issue. The main purpose of this paper is to assess these correlations from comparisons against the available experimental data. After a review of these data, the different correlations are presented. Attention focuses here on the correlations generally used in molten core-concrete interaction study: The Kutateladze-Malenkov, Konsetov, and BALI correlations. Deckwer’s correlation is also included in this review. The comparisons between the results of these correlations and the experimental data are then discussed.

00/02925 Two-phase flow heat transfer correlations for refrigerant—oil mixture flows inside augmented tubes

In this study, the two-phase heat transfer coefficient characteristics of HFC-134a evaporating under forced flow conditions inside a smooth horizontal tube are experimentally investigated. Different from most previous studies, the present experiments have been performed with lubricating oil in the refrigerant loop at high flow rate and high heat flux conditions. The test section is a 1.8 m long counterflow double tube heat exchanger with refrigerant flowing in the inner tube and heating water flowing in the annulus. The inner tube is made from smooth horizontal copper tubing of 9.52 mm. outer diameter and 7.2 mm. inner diameter. The test runs were done at average saturated evaporating temperatures ranging between 4 and 25 °C. The inlet dryness fractions were between 0.1 and 0.25. The mass fluxes were between 160 and 470 kg/m2s. and the heat fluxes were between 8 and 55 kW/m2. The inlet dryness fraction of the refrigerant in the test section was calculated using the temperature and pressure obtained from the experiment. The exit dryness fraction and heat transfer coefficient of the refrigerant were determined by applying an energy balance based on knowledge of the energy going into the test section. The effects of heat flux, mass flux, evaporation pressure and lubricating oil on the convection heat transfer coefficient are also discussed. The results from the experiment are compared with those calculated from correlations reported in the literature. Moreover, new correlations for the convection heat transfer coefficient are proposed for practical applications. The results of this study are of technological importance for the efficient design of evaporators when systems are assigned to utilize HFC-134a.

Two-phase Flow Heat Transfer Correlations for Refrigerant - Oil Mixture Flows Inside Augmented Tubes

Two-phase Flow Heat Transfer Correlations for Refrigerant - Oil Mixture Flows Inside Augmented Tubes