Two-phase Flow Heat Transfer Research Articles

Influences of tube pitches on heat transfer and pressure drop characteristics of two-phase propane flow boiling in shell side of LNG spiral wound heat exchanger

For clarifying the influences of tube pitches on heat transfer and pressure drop characteristics of two-phase flow in the shell side of LNG spiral wound heat exchanger, experiments are performed on test samples covering the longitude tube pitch of 2–6 mm and the radial tube pitch of 1–4 mm. Propane is used as the tested fluid. The operational conditions cover the vapor quality of 0.2–0.9, the mass flux of 40–80 kg (m2 s)−1, the heat flux of 4–10 kW m−2, the pressure of 0.25 MPa and the temperature of −19.4 °C. The uncertainties of tested heat transfer coefficients and pressure drops are within 14.4% and 4.0%, respectively. The results indicate that, as the longitude tube pitch increases, both the heat transfer coefficient and pressure drop decrease; while as the radial tube pitch increases, the heat transfer coefficient always decreases for the mass flux of 60 and 80 kg (m2 s)−1, but varies non-monotonously for the mass flux of 40 kg (m2 s)−1; and the pressure drop decreases maximally by 61% with the increasing radial tube pitch. Two-phase heat transfer and pressure drop correlations reflecting the influences of tube pitches are developed, and the deviations of the predicted heat transfer coefficients and pressure drops from the experimental data are within ± 20% and ± 25%, respectively.

Heat transfer and pressure drop characteristics of two-phase propane flow in shell side of LNG spiral wound heat exchanger

For designing LNG spiral wound heat exchangers (SWHE), the boiling heat transfer and pressure drop characteristics of two-phase hydrocarbon refrigerant flowing downward at shell side should be known. In this study, an explosion-proof experimental rig was established for observing flow patterns and measuring heat transfer coefficients and pressure drops. The test section contained three-layer tube bundles to emulate the actual structure and flow conditions of a SWHE. Propane as one main component of shell-side refrigerant was used as the tested fluid. Through the experimental analysis, the influence laws of vapor quality, mass flux on flow pattern, heat transfer and pressure drop of propane are obtained. As the vapour quality increases, the heat transfer coefficient in the shell side of LNG SWHE initially increases and then decreases, representing a maximum at a vapour quality of 0.8~0.9. The flow patterns in the shell side of LNG SWHE present to be the column falling film flow, droplet falling film flow, shear flow, mist flow and gas flow as the vapour quality increases from 0.2 to 1.0.

Newton-Krylov method in solving drift-flux two-phase flow problems for both pre-CHF and post-CHF conditions at steady state

This paper presents numerical simulations of two-phase flow heat transfer for both pre-CHF and post-CHF conditions typical in light water nuclear reactors. The conjugate heat transfer problem is modeled with one-dimensional four-equation drift-flux two-phase flow model for coolant flow and two-dimensional heat conduction equation in solid walls/rods. Fully implicit time integration schemes were employed, and the resulted non-linear equations were solved with a Newton-Krylov method. For the drift-flux two-phase flow model, the EPRI drift-flux closure correlation is used to model the relative motion between the two phases. Additional closure correlations were adopted from REALP5-3D to further improve the model accuracy in complex two-phase flow applications. These correlations are applied to determine two-phase flow regime, wall boiling heat and mass transfer, interfacial heat and mass transfer, and two-phase flow frictional pressure drop. Three sets of experiments were used for code validation, including Bartolomei subcooled flow boiling in vertical pipes, FRIGG boiling tests in vertical bundles, and Bennett heated tube tests. RELAP5-3D simulation results were also provided to perform code-to-code benchmark. Overall, numerical results of this work showed good agreements with both experimental data and RELAP5-3D simulation results. Discrepancy between them were also identified in post-CHF region, which suggests necessary further improvement. This work represents the first successful application of Newton-Krylov method in solving four-equation drift-flux two-phase flow problems with a full realistic boiling curve.

Hydraulic and Heated Equivalent Diameters Used in Heat Transfer Correlations

Hydraulic and heated equivalent diameters are approximations to account for different flow geometries in thermal-hydraulic analyses. Most of the empirical models used in single- and two-phase flow heat transfer are based on experiments in heated tubes and extrapolated to complex geometries by means of the equivalent diameters. For heat transfer calculations, as a general rule, the heated equivalent diameter must be used for bundle geometries and the hydraulic equivalent diameter for annulus geometries. The use of both diameters in different correlations is discussed and clarified in this technical note.

Flow boiling of ethanol/water binary mixture in a square mini-channel

Two-phase flow heat transfer was examined in a single 5mm inner hydraulic diameter square channel in a vertical orientation. The channel uses a resistive coating to allow for transparent heating of the walls. Transparency of the heating enabled high speed visualization of the boiling phenomena at various heat and mass fluxes. The pressure is monitored at the inlet and outlet of the channel. Infra-red thermography is used to map the external wall temperature of the channel and the local heat transfer coefficient is estimated from the local wall temperature and the saturation temperature of the liquid.Ethanol, deionized water and a 5% v/v ethanol/water mixture were used as working fluids. Three mass fluxes (0.33, 0.66 and 1.00kg/m2s) were tested as well as three heat fluxes (2.8, 4.2 and 6.1kW/m2). Experiments were conducted in a controlled temperature environment, where the surrounding air was kept at 40°C. The addition of ethanol into water (5% v/v ethanol/water mixture) was found to enhance heat transfer resulting in higher heat transfer coefficients than for either of its pure components.

Flow visualization and analysis of self-rewetting fluids in a model heat pipe

Experiments are performed to study the fundamental physics and the two-phase flow heat transfer in diluted water/butanol solutions with unusual dependence of the surface tension with temperature (self-rewetting fluids). The heat transfer and the dry-out behaviour are investigated in a grooved heat pipe model, increasing the power supplied at the evaporator section with an electric cartridge heater and cooling the condenser section with a water loop. The experimental configuration includes a top transparent window and a lighting system with diffused light, enabling visualization of the liquid in the groove with a CCD camera. Self-rewetting fluid behaviour is compared with ordinary heat transfer liquids, including an environmentally sustainable engineered liquid, Novec™ 7100 (Methoxy-nonafluorobutane), and bi-distilled water. Experiments with ethanol, butanol and a water/ethanol mixture have been also carried out to compare self-rewetting fluids with ordinary liquids and binary solution having no minimum in surface tension. It is found that the heat pipe filled with Novec™ exhibits good heat transfer performances at relatively low input power and temperatures, before the evaporator begins to dry. Similar behaviour is observed when ethanol is considered. For the heat pipe filled with water the evaporator becomes completely dry at larger power (40W). At the same input power, in the case of the self-rewetting fluid, the liquid is strongly flowing from the cold to the hot region due to the inverse Marangoni effect and this beneficially, rewets the evaporator. This phenomenon is never observed when dry out is established with other working fluids. Numerical simulations are carried out to explain some experimental results in case of pure liquid. A possible explanation of rewetting in the case of water/butanol mixture is given.

Nanolubricants flow boiling heat transfer enhancement in a microfin tube evaporator—IRG0021

The current article experimentally documents the effects of the nanoparticles thermal conductivity and aspect ratio on the two-phase flow heat transfer coefficient and pressure drop of nanolubricants in mixture with refrigerant R410A. Two nanoparticles types were dispersed in the polyolester lubricant: spherical Alumina (γ-Al2O3) nanoparticles with 40 nm nominal particles diameter and ZnO nanoparticles with 20 to 40 nm nominal particles diameter and with an elongated shape. While the two nanolubricants had different nanoparticle aspect ratio, they shared similar thermal conductivity. In refrigerant R410A and polyolester mixtures, they led to measurably different heat transfer coefficient for two-phase flow boiling inside a horizontal 9.5 mm micro-fin evaporator tube. Depending on mass flux, concentration, and heat flux, nanolubricants provided either an enhancement or a degradation, supporting the hypothesis that the nanolubricants thermal conductivity was not the main property responsible for the heat transfer coefficient intensification during flow boiling. The current article presents an analysis of the nanolubricants heat transfer models that adopted homogeneous liquid phase modeling approaches during the two-phase flow process. A sensitivity analysis of the thermodynamic properties highlighted that these type of models were not able to satisfactorily predict the heat transfer coefficient and pressure drop of refrigerant-nanolubricants mixtures.

The effect of red blood cells on blood heat transfer

In an attempt to analyze the effect of red blood cells on heat transfer, a two-phase flow heat transfer model of flowing blood was proposed in this paper. In this model, blood is treated as a two-phase fluid composed of red blood cells as the particle phase and plasma as the carrier fluid. The micro-particle dynamics, including aggregation, deformation, mutual collisions of red blood cells and relative movement of red blood cells to plasma, are considered by some equations or simplified methods. The velocity field, temperature field, fluid viscosity and volume fraction of red blood cells in a two-phase blood flow can be calculated using this model. To verify the accuracy of the simulation results of the model, the velocity distribution and heat transfer efficiency calculated by this model were compared with available experimental data from the literature. Good agreement was obtained between these data; thus, this model can accurately simulate the blood flow and heat transfer in a vessel. Then, the model was used to analyze how the micro-particle red blood cells affect the heat transfer of blood, and red blood cells were found to enhance heat transfer efficiency of blood. The viscosity properties of blood, the solid pressure and the lateral movement of red blood cells are the important determinants of this enhancement. The influence of red blood cells on the heat transfer efficiency of pulsatile blood flow was also calculated using this model.

Analytical solution and heat transfer of two-phase nanofluid flow between non-parallel walls considering Joule heating effect

In this paper, MHD nanofluid flow, heat and mass transfer between non-parallel walls is investigated. Brownian diffusion and thermophoresis effects which are two momentous slip mechanisms in nanofluids have been considered in the nanofluid model. Also, Joule heating effect is taken into account. The governing radial momentum, energy and mass equations are solved by Duan–Rach Approach (DRA). This method allows us to find a solution without using numerical methods to evaluate the undetermined coefficients. This method modifies the standard Adomian Decomposition Method by evaluating the inverse operators at the boundary conditions directly. The effects of active parameters such as the Reynolds number, the opening angle parameter, the Schmidt number, thermophoretic parameter and Brownian parameter are investigated on the velocity, temperature and concentration. Also, the value of the Nusselt number is calculated and presented through figures. The results indicate that the temperature and concentration profiles and Nusselt number increase with the increasing Schmidt number. In addition, the limiting cases are gained and found to be in an excellent agreement with the previous works.

Modeling of subcooled boiling by extending the RPI wall boiling model to ultra-high pressure conditions

Accurate predictions of the two-phase flow pattern and heat transfer inside the high-pressure tubes is of great importance for the safety of steam power equipment. In this paper, subcooled boiling flow was numerically modeled and the RPI (Rensselaer Polytechnic Institute) wall boiling model was extended to ultra-high pressure conditions up to 15MPa. Various combinations of closure models for the key parameters in RPI model, including the nucleation site density (Nw), bubble departure diameter (Dw) and bubble departure frequency (f), were studied in the pressure range of 3–15MPa. The numerical results were carefully validated by comparing the simulations with the experiments of Bartolemei et al. (1967, 1982). A widely applicable combination of closure models for Nw, Dw and f was identified for the pressure range from low to ultra-high levels, with the mass flux range of 503–2123kg/(m2s) and the heat flux range of 0.42–2.21MW/m2. The characteristic parameters of wall subcooled boiling were analyzed and the physical process of subcooled boiling was revealed. Based on the optimized models, the influence of operating parameters including mass flux and heat flux was also studied under the pressures of ∼11MPa and ∼15MPa.

Two-phase flow patterns, heat transfer and pressure drop characteristics of R600a during flow boiling inside a horizontal tube

A detailed experimental study was carried out to investigate the flow boiling heat transfer and pressure drop characteristics of R600a in a smooth horizontal tube with an inner diameter of 6mm. The experiments were performed at conditions covering saturation pressures from 0.215 to 0.415MPa, mass fluxes from 67 to 194kgm−2s−1 and heat fluxes from 10.6 to 75.0kWm−2. Based on an high speed camera, four main flow regimes can be observed: plug flow, stratified-wavy flow, slug flow and annular flow. Intermittent to annular flow transition was detected and plotted on flow pattern maps. Comparisons with available transition lines in the literature have been made. Furthermore, the influences of saturation pressure, mass flux and heat flux on heat transfer coefficient were analyzed. The experimental data was compared with the calculated data of seven well-known correlations. The results indicated that, the correlation of Liu and Winterton showed the best agreement with a mean absolute relative deviation of 11.5%. For two-phase frictional pressure drop, mass flux had obviously positive effect on frictional pressure drop, while negative effect was found for saturation pressure. Eight correlations were evaluated and the correlation of Müller-Steinhagen and Heck gave the best fit to the experimental data with a mean absolute relative deviation of 32.9%. A new correlation of pressure drop which accounted for the influence of surface tension and gravitational force was developed on the basis of Müller-Steinhagen and Heck correlation and its mean absolute relative deviation was about 16.6% for the experimental data.

Computational modelling of flow and conjugate heat transfer of a drop impacting onto a cold wall

Abstract The flow and heat transfer in water drops impinging onto a dry cold surface has been computationally investigated. This situation pertains to aircraft icing or icing of power lines. The computational model solves the hydrodynamics using an algebraic implicit volume-of-fluid-based method for interface capturing with an extension for the simultaneous solution of the heat transfer within the drop and underlying substrate. The numerical solution is validated by computing a series of configurations of two-phase fluid flow and conjugate heat transfer for which experimental and analytical results are available in the literature. In a parametric study, the effect of the impact conditions and initial surface temperatures on the minimum liquid temperature reached and the heat transfer during drop impact are examined, representing the quantities relevant for nucleation and icing modelling. It is shown that these quantities do not depend on the impact conditions. However, the amount of heat transferred between the fluid and the wall is affected by the contact time and area available for heat transfer, which are determined by the impact conditions. Based on the numerical results, a semi-empirical model is developed, which accurately predicts the total heat transferred during a single impact event.

Numerical Study of the CO2 Absorber Performance Subjected to the Varying Amine Solvent and Flue Gas Loads

The paper is devoted to the amine-based post-combustion carbon dioxide capture technology. The aim of the paper was to analyze the effect of varying flow conditions on the CO2 capture efficiency of the absorber column. As a research tool, a numerical model of the chemical absorption with aqueous monoethanolamine solution in a packed bed was employed. A complex physio-chemical process including two-phase flow hydrodynamics, heat transfer, and absorption chemistry was simulated by Ansys Fluent commercial software. The parametric study was focused on CO2 capture efficiency in terms of varying loads of amine solvent (liquid) and flue gas. The corresponding changes of liquid holdup, species concentration, temperature and reaction rate distributions are discussed in detail allowing to better understand the absorption column operation. The simulation results have shown clearly the mutual interactions of partial processes and the sensitivity of the system to varying column loads. They have been found to be useful in defining the optimal ranges of operational parameters.

Heat and mass transfer of two-phase flow with Electric double layer effects induced due to peristaltic propulsion in the presence of transverse magnetic field

Abstract Biologically-inspired propulsion systems are currently receiving significant interest in the engineering applications. Motivated by these developments, in the present article analysed heat and mass transfer with the transverse magnetic field on peristaltic motion of two-phase flow (particle-fluid suspension) through a planar channel have been examined. The flow is observed under the influence of electric field and chemical reaction. The present flow problem is modeled using lubrication theory approximation and also with a combination of long wavelength and creeping flow regime assumptions. Moreover, the problem is further simplified using Debye linearization. Analytical solutions are obtained for the resulting coupled ordinary differential equations. The influence of various emerging parameters is discussed for velocity, temperature and concentration profile. Furthermore, the behavior of pressure rise is also discussed to analyse the pumping characteristics. Trapping mechanism is also presented with the help of streamlines. It is observed that velocity distribution tends to increase significantly due to the greater effect of electric field and electro-osmotic parameter, however, magnetic field and particle volume fraction provides a marked resistance to the flow. The influence of electric field and electro-osmotic parameter depicts converse behavior on temperature and concentration distribution. Furthermore, chemical reaction parameter causes a significant reduction in the concentration distribution. The main motivation of the present study is due to such fact that two-phase flow process is very important to analyse the peristaltic muscular expansion and contraction in propagating various biological fluids that act like a particle-fluid mixture. The present study has a wide range of applications in bio-medical engineering i.e. electromagnetic peristaltic micro pumps.

Selected problems of gas-liquid flow through the channels filled with metal foams

Open-cell metal foams are relatively unknown type of cellular material, which is increasingly being used as structural packing in the industrial equipment. The paper presents an analysis of experimental results on heat transfer and hydrodynamics of gas-liquid two-phase flow through the channels filled with metal foams. The research included the registration of temperature and pressure changes on fluid flow path. Furthermore the phase void fraction was measured and flow patterns in present in the channel were observed. It was found that in two-phase flow, both from heat transfer and hydrodynamics of flow point of view, the liquid plays the dominant role. It was also found a significant influence of flow patterns on frictional pressure loss value and phase void fraction. Whereas the flow patterns and geometry of the foam in much lesser extent influence on the intensity of heat transfer. Type of gas-liquid flow patterns primarily depends on flow conditions, including the velocity and properties of fluids. On the other hand, it wasn’t stated any significant effect of geometrical parameters of foam on the type of flow and the value of phase void fraction. Among many flow patterns observed during the study, there have been identified four basic structures: plug, semi-slug, slug, and stratified.

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.

R32 and R410A condensation heat transfer coefficient and pressure drop within minichannel multiport tube. Experimental technique and measurements

The present paper reports the construction of an experimental installation to measure local condensing two-phase flow heat transfer coefficient and frictional pressure drop within mini-channel tubes, the validation measurements developed with R134a and the experimental measurements of heat transfer coefficient and frictional pressure drop made with R32 and R410A.This experimental work is carried out in a test apparatus which allows determining the local heat flux extracted from the condensing fluid. For this purpose, the wall temperature is measured along the test section in several points.The saturation temperature is determined from the saturation pressure, which is measured at the inlet and the outlet of the test channel.Experimental data of R32 and R410A are also compared with some predicting models widely accepted in the literature.

The effect of drop evaporation on gas turbulence and heat transfer for two-phase flow behind sudden pipe expansion

The effect of drop evaporation on turbulence and heat transfer in a two-phase separated axisymmetric flow was studied numerically. The comparison between the calculation data for evaporating and nonevaporating particles under otherwise identical conditions is given. In the zone adjacent to the wall, drop evaporation was shown to proceed most intensively and almost no suppression of turbulence was observed in this case. The turbulence level is close to that in a single-phase flow regime. In the flow core where virtually no evaporation occurs, there was a decrease in the gas turbulence level (down to 15% compared to singlephase flow).

Modelling of a cross flow evaporator for CSP application: Analysis of the use of different two phase heat transfer and pressure drop correlations

Heat exchangers consisting of bundles of horizontal plain tubes with boiling on the shell side are widely used in industrial and energy systems applications. A recent particular specific interest for the use of this special heat exchanger is in connection with Concentrated Solar Power (CSP) applications. Heat transfer and pressure drop prediction methods are an important tool for design and modelling of diabatic, two-phase, shell-side flow over a horizontal plain tubes bundle for a vertical up-flow evaporator. With the objective of developing a model for a specific type of cross flow evaporator for a coil type steam generator specifically designed for solar applications, this paper analyzes the use of several heat transfer, void fraction and pressure drop correlations for the modelling the operation of such a type of steam generator.The paper after a brief review of the literature about the available correlations for the definition of two-phase flow heat transfer, void fraction and pressure drop in connection with the operation of steam generators, focuses attention on a comparison of the results obtained using several different models resulting by different combination of correlations. The influence on the analysis of the performance of the evaporator, their impact on significant design variables and the effective lifetime of critical components in different operating conditions, simulating the daily start-up procedures of the steam generator is evaluated. The importance of a good calibration of the model based on the comparison with some experimental data is recognised.

An experimental study on two-phase flow patterns and heat transfer characteristics during boiling of R134a flowing through a multi-microchannel heat sink

The present paper presents an experimental study of flow patterns and heat transfer characteristics of flow boiling of R134a in a multi-microchannel heat sink. The copper test section has 27 parallel rectangular channels with a depth of 470μm, a width of 382μm, a length of 40mm, and a fin thickness of 416μm. The experimental results are presented for saturation temperatures of 13, 18, and 23°C, and mass fluxes of 150, 400, and 600kg/m2s. The wall heat flux and inlet vapor quality values were between 3 and 127kW/m2, and 0.05 and 0.92, respectively. The effects of pertinent parameters on the heat and fluid flow characteristics such as saturation temperature, mass flux, heat flux, and inlet vapor quality are studied and discussed. The heat transfer coefficient at high saturation temperatures (i.e. 23°C) is higher than low saturation temperatures (i.e. 13°C) in the heat flux range of 40–120kW/m2. For high heat flux ranges, the heat transfer coefficient increases with increasing mass flux. The convective boiling heat transfer mechanism will play a major role in wavy and annular flow patterns. For wall heat fluxes higher than 80kW/m2, the existence of a partial dry-out phenomenon in the multi-microchannel leads to a decrease in heat transfer coefficient. The results unveil the significant effect of flow patterns on heat transfer characteristics. Based on the experimental data, a correlation is proposed to calculate the heat transfer coefficient for R134a flow in the multi-microchannel heat sink that is useful in electronic cooling applications.