Two-phase Pressure Drop Multiplier Research Articles

Pressure drop characteristics in single-side heated circular smooth channel under sub-cooled flow boiling conditions

In this study, the two-phase pressure drop for a one-side heated smooth channel was explored through subcooled flow boiling experiments for divertor applications. When the channel heat load was gradually increased, there was little differential pressure change in the single-phase regime, but when it exceeded the onset of significant void (OSV) heat flux, the differential pressure started to increase. It was found that as the subcooling and flow rate increased, the OSV heat flux increased, and the slope of the two-phase differential pressure decreased, This is because it is possible to condense the generated vapor more quickly under these conditions. Moreover, as the pressure increased, the OSV heat flux increased and the size of the ejected single bubble decreased under high pressure conditions. The prediction performances of existing two-phase pressure drop multiplier correlations were also evaluated. Since most of the existing correlations were developed based on channels of a small diameter, and were not evaluated at a high heat flux, that is, in the order of 10 MW/m2—they exhibited a high average error rate. Therefore, we developed a new two-phase pressure drop multiplier correlation for a smooth channel under one-side high heat load conditions using PYTHON code and artificial intelligence regression method.

Development of a Novel Two-Phase Pressure Drop Multiplier Correlation of Screw Tube for Fusion Reactor Safety

In this study, the two-phase pressure drop in a one-sided high-heat-loaded screw tube was analyzed under subcooled flow boiling conditions. When the loaded heat flux is gradually increased under one-sided heating conditions, although the pressure drop changes slightly in the single phase, it starts to increase when loading above the onset of significant void (OSV) heat flux. The effect of system parameters on the two-phase pressure drop in relation to the change of heat transfer mechanism or fluid properties was analyzed according to each variable change. In addition, this study evaluated the prediction performance of existing two-phase pressure drop multiplier correlations developed under subcooled flow boiling conditions. Because most existing correlations are based on a smooth channel with a small diameter, they tend to overpredict the experimental values. The correlation proposed by Ramesh showed the lowest average error rate (31.94%); however, the results were underpredicted for high-heat-flux conditions. To obtain more accurate results, we developed a Python code using an artificial intelligence regression method to proceed with the optimization process based on the experimental values. Using this code, we developed a novel two-phase pressure drop multiplier correlation for a one-side-heated screw tube that can be used in fusion divertors under high-heat-load conditions.

Two-phase pressure drop analysis of swirl tube in one-side high heat load condition for plasma facing component application

In this study, the two-phase pressure drop of a one-side heated swirl tube (twist ratio = 3, 5) was experimentally studied. If the a heat flux is gradually increased, the vapor blocks the flow path, thus leading to an increase in the differential pressure. As the inset sub-cooling and mass flow rate increase, the vapor is removed by condensation more rapidly, and thus, the rate of increase of differential pressure is reduced. From the evaluation of the prediction performance of the existing two-phase pressure drop correlations, it was found that the mean error rates of all correlations exceeded 50%. This is because most of the existing correlations were not developed based on the microchannel, but they were not focused on the swirl tube. Therefore, the authors developed a new two-phase pressure drop multiplier correlation for a one-side heated swirl tube that reflects the effect of the twist tape by modifying the Manglick single-phase swirl tube pressure drop correlation using the AI regression method.

Development of Empirical Correlation of Two-Phase Pressure Drop in Moisture Separator Based on Separated Flow Model

Pressure drop across the moisture separator installed in the steam generator of a nuclear power plant affects the power generation efficiency, and so accurate pressure drop prediction is important in generator design. In this study, an empirical correlation is proposed for predicting the two-phase pressure drop through a moisture separator. To ensure the applicability of the correlation, a series of two-phase air-water experiments were performed, and the results of the present test and of the benchmark test of high-pressure steam-water were used in developing the correlation. Based on the experimental results, quality, dimensionless superficial velocity, density ratio of the working fluid, and the geometrical factor were considered to be important parameters. The two-phase pressure drop multiplier was expressed in terms of these parameters. The empirical correlation was found to predict the experimental results within a reasonable range.

Modeling of heat transfer coefficient for upward no-phase-change two-phase flow in inclined pipes

This study aims at developing a robust and theoretically-supported correlation of two-phase heat transfer coefficient for upward no-phase-change two-phase flow in inclined pipes based on the concept of extended Chilton-Colburn analogy. Firstly, a comprehensive literature survey was conducted to gather over 1800 experimental data and 12 correlations of two-phase heat transfer coefficient. The comparison results indicated that none of the existing correlations could predict the entire database satisfactorily. Then, the dependence of two-phase heat transfer enhancement ratio (or two-phase heat transfer multiplier) on liquid fraction, two-phase pressure drop multiplier and inclination angle was analysed, and the two-phase heat transfer coefficient correlation was developed. The performance assessment indicated that the newly-developed correlation could predict 95% of the experimental data within ±30% error with the mean absolute relative deviation of 12.9%. The newly-developed semi-theoretical correlation would be useful in designing no-phase-change two-phase heat transfer systems, such as petroleum pipelines and nuclear power plants.

Experimental investigation on non-boiling heat transfer of two-component air-oil and air-water slug flow in horizontal pipes

Gas-liquid slug flow in horizontal pipes occurs frequently in industrial applications and its heat transfer characteristics are very important but complicated due to the intermittent flow structures. This paper aims at investigating the heat transfer mechanism of both air-oil and air-water slug flow in horizontal pipes. An experimental setup was fabricated to investigate the flow and heat transfer characteristics of air-oil and air-water slug flow under cooling conditions in horizontal pipes. The test section was made of a copper pipe with I.D. of 26 mm and a polyvinyl chloride pipe with I.D. of 63 mm using concentric geometry. The effect of flow parameters, such as liquid flow rate, gas flow rate, two-phase pressure drop multiplier, void fraction and slug frequency on heat transfer of gas-liquid slug flow was comprehensively investigated. The heat transfer coefficient of two-phase flow was significantly improved by the introduction of air and the maximum two-phase heat transfer enhancement ratio for air-water and air-oil flow were 150% and 300%, respectively. The circumferential temperature distribution and local heat transfer coefficient were also investigated. The local heat transfer coefficient at the bottom was around 25% higher than that at the top due to the uneven distribution of liquid and gas inside the pipe. Finally, a semi-empirical heat transfer correlation for gas-liquid slug flow was developed based on Reynolds and Chilton–Colburn analogies. The newly developed correlation predicts 96% of the present experimental two-phase heat transfer data within ±20% error and the mean relative deviations of the correlations are estimated to be -2.02% and +2.85% for Ref ≤ 2300 and Ref > 2300, respectively. This research helps researchers and engineers to better understand the heat transfer mechanism of gas-liquid slug flow.

Experimental validation of two-phase pressure drop multiplier as a diagnostic tool for characterizing PEM fuel cell performance

Water management is a key area of interest in improving the performance of Proton Exchange Membrane fuel cells. Cell flooding and membrane dehydration are two extreme conditions arising from poor water management. Pressure drop has been recognized as a good diagnostic tool to determine the presence of liquid water in the reactant channels. Presence of liquid water in the channels increases the mass transport resistances and therefore reduces the cell performance, which is quantified by the cell voltage at a set current density. Since the two-phase pressure drop multiplier is uniquely related to the water content in the channel, it serves as a good diagnostic tool for directly predicting the cell performance. Experiments are carried out to establish the relationship between the pressure drop multiplier and cell voltage at different operating conditions. Cell temperature was varied from 30 °C to 80 °C and the inlet RH was varied from 0 to 95%. At the lower temperatures, a two-phase multiplier below 1.5 reduces flooding in the flow field. However, at the higher temperatures, a two-phase flow multiplier above 1.2 is preferred as it indicates the membrane remains hydrated for improved performance from the cell. The two-phase pressure drop multiplier has been successfully demonstrated as a diagnostic tool to predict cell flooding and membrane dehydration.

Two-phase flow in high-heat-flux micro-channel heat sink for refrigeration cooling applications: Part I––pressure drop characteristics

Two-phase pressure drop was measured across a micro-channel heat sink that served as an evaporator in a refrigeration cycle. The micro-channels were formed by machining 231 μm wide × 713 μm deep grooves into the surface of a copper block. Experiments were performed with refrigerant R134a that spanned the following conditions: inlet pressure of P in = 1.44–6.60 bar, mass velocity of G = 127–654 kg/m 2 s, inlet quality of x e,in = 0.001–0.25, outlet quality of x e,out = 0.49–superheat, and heat flux of q″ = 31.6–93.8 W/cm 2. Predictions of the homogeneous equilibrium flow model and prior separated flow models and correlations yielded relatively poor predictions of pressure drop. A new correlation scheme is suggested that incorporates the effect of liquid viscosity and surface tension in the separated flow model’s two-phase pressure drop multiplier. This scheme shows excellent agreement with the R134a data as well as previous micro-channel water data. An important practical finding from this study is that the throttling valve in a refrigeration cycle offers significant stiffening to the system, suppressing the large pressure oscillations common to micro-channel heat sinks.

Shellside evaporation in a TEMA E-shell: flow patterns and transitions

The paper describes some results from a research programme to study forced flow shellside boiling in a TEMA E-type shell and tube heat exchanger. It focuses on the particular issue of the effect of apparent transitions in the two-phase flow pattern. The results from the programme show a drop in the heat transfer performance at lower mass fluxes and higher vapour qualities. The sudden drop in performance may be caused by a change in the two-phase flow pattern on the shellside from a homogeneous type to a stratified type of flow with separation of the liquid and vapour phases. Support for this conclusion is that the transition in heat transfer performance appears to coincide with a change in the behaviour of the measured two-phase pressure drop multiplier. A model is described which allows for the effects of separated flow and also attempts to predict the apparent transition in the two-phase flow pattern.

A Model for Pressure Drop of Gas-Liquid Bubbly Flow through an Orifice or an Abrupt Pipe Contraction

A new physical model is developed to predict the pressure drop of a steady-state gas-liquid bubbly flow through an orifice or an abrupt pipe contraction. The formulation of the model involves balance equations deduced from the macroscopic mass, momentum, entropy and energy conservation laws as well as a balance of forces exerted on the dispersed bubbles phase. The thermal equilibrium between phases is assumed but the gas-liquid slip motion is taken into account. The gas-liquid interaction and the wall shear stress are evaluated from theoretical considerations. The predictions of pressure drop from the model are found to be in good agreement with several experimental data of the literature obtained for bubbly air-water flows through orifices. In agreement with the experimental observations, the theoretical predictions show that the two-phase pressure drop multiplier is not strongly influenced by the pipe diameter and increases slightly with the cross-sectional area ratio of the orifice. An essential feature of the present model is the absence of adjustable constants.

Two Phase Pressure Drop Multipliers and ICE Technique Applied in a Multibubble Slug Ejection Model

Two-phase flow of coolant is described in subassemblies of liquid metal fast breeder reactors by a one-dimensional two-phase multibubble slug ejection model. Vapor flow of sodium between the slugs is modeled as annular flow with a moving liquid film of variable thickness wetting structural surfaces. The two-phase pressure drop multiplier concept introduced by Lockhart-Martinelli is used in the frame of the slug ejection model with an algorithm that simultaneously computes interfacial friction coefficient and liquid film axial velocity distribution. The implicit continuous Eulerian (ICE) technique developed by Harlow and Amsden for computing pressure distribution in a continuum medium is applied in heterogeneous two-phase flow to the governing equations for the vapor phase. This solution method is more stable than the numerical solution by finite differences of the vapor momentum equation.

Pressure drop and void fraction of two-phase helium flowing in horizontal tubes

The pressure drop and void fraction of two-phase helium in a horizontal flow loop driven by a single stroke bellows pump at mass flow rates ranging from 0.5 to 2.0 g s t-1 and under system pressures between 0.65 and 1.2 atm are reported. The slip ratio (the ratio of the velocity of the gaseous phase over that of the liquid phase) in two-phase helium is deduced from void fraction data obtained with an in-line capacitance probe. The slip ratio is found to be always greater than unity and to decrease towards unity with increasing mass flow rate and increasing system pressure. Results for the twophase pressure drop measurements are analysed in terms of the conventional twophase pressure drop multiplier, which is found to depend on system pressure and vapour quality. The mass flow rate does not appear to have an effect on the two-phase frictional multiplier. A slight tube size effect on the two-phase pressure drop multiplier is found at 1.2 atm; however, this effect quickly diminishes as the system pressure reduces. In general, for the range of parameters studied the homogeneous model gives a much better prediction of the two-phase friction multiplier than does the Lockhart-Martinelli correlation.

Sodium boiling experiments in a seven-pin bundle: Flow patterns and two-phase pressure drop

Two series of quasi-steady state sodium boiling experiments have been carried out in an electrically heated seven-pin bundle. The power levels (130–170 and 30–40 W/cm2) and other test conditions were selected to correspond to the core and radial breeder zones of a typical LMFBR. The test procedure involved the gradual reduction of mass flow rate through the bundle in a simulation of the consequences of a slowly growing blockage in the lower part of a reactor subassembly. By this means it was possible to study the development of quasi-steady state boiling up to the onset of permanent dryout. The results obtained provide information on flow regimes in the two-phase region, vapour qualities and flow rates at which cooling of the bundle can be effectively maintained, and the ultimate incidence of dryout. A relation for the two-phase pressure drop multiplier obtained from adiabatic pressure drop measurements in this geometry is given and compared with earlier results from single-channel geometry tests.