Two-Phase Flow

Aiming at developing a more common method for predicting two-phase flow pressure drop for small channels, experiments on frictional pressure drop of air-water flow in a vertical narrow rectangular duct with a cross-section of 40 mm by 1.6 mm were conducted at atmospheric pressure. The mass flow rates of air and water covered the ranges from 0.03 to 12.5 kg/h and from 19 to 903 kg/h, respectively. It was found that the two-phase flow can be divided into three regions according to the liquid only Reynolds number, by which a modified Chisholm two-phase multiplier was proposed for predicting frictional pressure drop. Some leading correlations for predicting two-phase flow pressure drop were compared with the new correlation against current experimental data, the latter had and a mean deviation of 7.2%, showing a better agreement with the experimental results.

Commonly used methods for injection moulding simulation involve a considerable number of simplifications, leading to a significant reduction of the computational effort but, in some cases also to limitations. In this work, Reaction Injection Moulding (RIM) simulations are performed with a minimum of simplifications, by using the general purpose CFD software package Ansys CFX, designed for numerical simulation of fluid flow and heat and mass transfer.

The Ansys CFX’s homogeneous multiphase flow model, which is generally considered to be the appropriate choice for modelling free surface flows where the phases are completely stratified and the interface is well defined, is shown to be unable to model the filling process correctly. This problem is overcome through the implementation of the inhomogeneous model in combination with the free-slip boundary condition for the air phase.

The cure reaction is implemented in the code as a transport equation for an additional scalar variable, with a source term. Various transient and advection schemes are tested to determine which ones produce the most accurate results.

Finally, the mass conservation, momentum, cure and energy equations are implemented all together to simulate the simultaneous filling and curing processes present in the RIM process. The obtained numerical results show a good global accuracy when compared with other available numerical and experimental results, though considerably long computation times are required to perform the simulations.

Purpose-The purpose of this study is three-dimensional flow and heat transfer investigation of water/ Al 2 O 3 nanofluid inside a microchannel with different cross-sections in two-phase mode. Design/methodology/approach-The effect of microchannel walls geometry (trapezoidal, sinusoidal and stepped microchannels) on flow characteristics and also changing circular cross section to trapezoidal cross section in laminar flow at Reynolds numbers of 50, 100, 300 and 600 were investigated. In this study, two-phase water/Al 2 O 3 nanofluid is simulated by the mixture model, and the effect of volume fraction of nanoparticles on performance evaluation criterion (PEC) is studied. The accuracy of obtained results was compared with the experimental and numerical results of other similar papers. Findings-Results show that in flow at lower Reynolds numbers, sinusoidal walls create a pressure drop in pure water flow which improves heat transfer to obtain PEC < 1. However, in sinusoidal and stepped microchannel with higher Reynolds numbers, PEC > 1. Results showed that the stepped microchannel had higher pressure drop, better thermal performance and higher PEC than other microchannels. Originality/value-Review of previous studies showed that existing papers have not compared and investigated nanofluid in a two-phase mode in inhomogeneous circular, stepped and sinusoidal cross and trapezoidal cross-sections by considering the effect of changing channel shape, which is the aim of the present paper. Nomenclature A = Amplitude, mm; C p = Heat capacity, J/kg.K; k = Thermal conductivity coefficient, W/m-K; L = Microchannel length, m; Nu = Nusselt number; P = Fluid pressure, Pa; S = Space of steps, mm; q" = Constant heat flux, W/m 2 ; R = Thermal resistance, m.K/W; Re = Reynolds number; T = Temperature, K; u, v,w = Velocity components in x, y and z directions, m/s; and u c (m/s) = Inlet velocity in x directions, m/s. Greek symbols w = Nanoparticles volume fraction; m = Dynamic viscosity, Pa.s; r = Density, kg/m 3 ; and l = Wave length. Super-and subscripts Eff = Effective; f = Base fluid (pure water); In = Inlet; nf = Nanofluid; and Out = Outlet.

There is a strong tendency for two immiscible fluids to arrange themselves so that the low viscosity constituent is
in the region of high share. Therefore, it may be possible to introduce a beneficial effect in any flow of a very viscous liquid by
introducing amount of a fluid lubricated as liquid-liquid oil-water flow. Two main classes of flows are seen, annular and small
bubble in all experimental results. The pressure drop and mean heat-transfer coefficients were observed to depend strongly on
the flow patterns. A correlation of the two-phase mean heat-transfer coefficients, based on a simple model of liquid flow, with a
Reynolds number based on the actual mean velocity of the liquid mixture two-phase flow, were developed. An experimental
rig facility has been designed and constructed, to enable measurements of local parameters in oil-water flow in the developing
region of the flow in a 32 mm ID 6 m long pipe. The large discrepancies between model predictions and experimental data are
reported in the literature review that the physics of oil-water flow is complex and not yet fully understood. The flow patterns
that appear are classified in flow pattern maps as functions of either mixture velocity and water cut or superficial velocities.
From these experiments a smaller number of annular flows are selected for studies of velocity and turbulence. The theoretical
study was executed using software Fluent program, a modified turbulent diffusion model is presented. Simulation results
carried out with the model show more physical predictions with respect to the particle deposition process and concentration
profile. The theoretical results represent the pressure gradient distribution, velocity and mean heat transfer coefficient, pressure
contours, velocity vectors, streamlines, and also velocity profiles. It was found that the methods with more restrictions (in
terms of the applicable range of void fraction, liquid superficial Reynolds number) give better predictions.

Turbulent solid-liquid slurry flows in pipes are encountered in many engineering fields, such as mining. In particular, the distribution of the solids is a serious concern to engineers, but its determination involves considerable technical and economic difficulties. A two-fluid model for the numerical prediction of this parameter is presented. The model is robust and numerically stable, and requires relatively short computer time to provide a converged steady-state solution. The novelty of the proposed model and its better performance compared to similar ones reside in the method of accounting for some key physical mechanisms governing these flows, namely turbulent dispersion, interphase friction, and viscous and mechanical contributions to friction. The model is first validated by comparison with many experimental data available in literature regarding the horizontal pipe case over a wide range of operating conditions: delivered solid volume fraction between 9 and 40%; slurry velocity between 1 m/s and 5.5 m/s; and pipe diameter between 50 and 160 mm. A further comparison was performed with respect to recent experiments concerning a horizontal 90 degrees bend.

Author Keywords:two-fluid model; numerical analysis; slurries; two-phase flow; horizontal pipes; pipe bends

The objective of the present work is to investigate numerically the 3D flow within diesel injector-like geometries using a cavitation model implemented in a commercial CFD code. A comprehensive study of various numerical parameters is performed which can subsequently be used to simulate cavitation under realistic diesel engine conditions. Numerical predictions were performed on a throttle channel at different operating conditions, with and without cavitation, and compared to available experimental measurements. Overall, it was found that the cavitation model was able to predict the onset of cavitation. Satisfactory agreement was found in both the injection rate and the occurrence of choked flow conditions when compared with experiments.

Keywords: cavitation; injection nozzle; modelling; choked flow; two-phase flow

Undesired entrainment of air in a bottom spillway often leads to problems in both safety and operational functions. A numerical analysis of a transient process of air entrainment into bottom spillway flows when a spillway gate is opened was conducted in this study. The Volume of Fluid (VOF) model was used. The 3D computational domain consisted of a spillway conduit, a moving bulkhead gate, a gate shaft, an upstream reservoir and a downstream outlet. The large number of cells, together with the dynamic mesh modelling of the moving gate, required substantial computational resources, which necessitated parallel computing on a mainframe computer. The simulations captured the changes in the flow patterns and predicted the amount of air entrainment in the gate shaft and the detrainment downstream, which help in the understanding of the system behaviour during opening of the spillway gate. The initial conduit water level and the gate opening procedure affect the degree of air entrainment in the gate shaft. To release the undesired air, a de-aeration chamber with a tube leading to the atmosphere was added to the conduit. Despite the incomplete air release, the de-aeration chamber was found to be effective in reducing water surface fluctuations in the downstream outlet.

Keywords: bottom spillway, moving gate, air entrainment, two-phase flow, CFD

This research work presents a detailed description of the flow patterns maps generated in a horizontal pipe of the collector/evaporator of a direct-expansion solar-assisted heat pump, using R600a refrigerant as working fluid. The study was performed in a pipe with an internal diameter of 3.8 mm and a length of 1000 mm, mass velocities varying between 197.59 and 267.26 kg•m −2 •s −1 and heat flux between 72.83 and 488.27 W•m −2 ; during the experimental tests, an incident solar radiation between 0 and 652.9 W•m −2 was present. The Wojtan, Ursenbacher and Thome correlation was considered for the analysis and the model used does not require iterative calculations;

Time delay estimation is an important research question having many applications in a range of technologies. Measurement of a two-phase flow in a pipeline or an open channel using radioisotopes is an example of such application. For instance, the determination of velocity of dispersed phase in that case is based on estimation of the time delay between two stochastic signals provided by scintillation probes. The proper analysis of such signals, usually in presence of noise, requires the use of advanced statistical signal processing. In this paper, the simulation studies of time delay estimation were carried out with the use of the following differential methods: average magnitude difference function, and average square difference function and proposed combined methods comprising the above-mentioned differential and cross-correlation functions are presented. Attached simulations have been carried out for models of stochastic signals corresponding to the signals obtained in gamma-ray absorption measurements of gas-liquid flow in a horizontal pipeline. The standard uncertainties of time delay estimations have been determined for each of the methods. Improved metrological properties have been stated in the combined methods in comparison with the classical cross-correlation procedure.

The paper reports a study of the water surface profile of an entrapped air cavity while emptying water in an initially filled inclined duct. A one-dimensional (1D) model, which consists of the continuity and momentum equations applicable for open channel flow, pipe flow and air–water interface flow, is developed based on the finite volume method. A pressure drop model is proposed to reproduce a better profile around the cavity front, with a particular focus on air pressure changes inside the confined cavity to simulate a kind of transient flow with an entrapped air cavity. In contrast to the previous studies, the application of the model shows that when the pressure drop is not considered and the air pressure is not changed, the confined cavity soon vanishes. A comparison between the simulated and experimental results shows that the model is able to accurately reproduce the water surface profile of an entrapped air cavity while emptying inclined ducts.

The two-phase flow through vertical transparent pipe is investigated
experimentally. The experimental rig designed to achieve the measurements of
pressure drop for various combinations of phases, flow pattern regimes such as
bubbly, slug and annular, with various range of water and air volumetric high speed
camera . The air volumetric ranged from 8.3334 L/min to 25 l/min, while the water
volumetric ranged from 5 l/min to 20 l/min and of 50 mm internal diameter along 1 m
length. The measured of the pressure will be done using four pressure sensors along
test pipe. The measured pressure values were used for different air volumetric and
different water volumetric. It has been found that the measuring of pressure gradient
through the distance of rig pipe are inversely changed with air volumetric. In
addition, it has been analyzed the flow pattern through obstruction, it has showed one
phase flow, bubbly and slug flow.

The two-phase flow through vertical transparent pipe is investigated
experimentally. The experimental rig designed to achieve the measurements of
pressure drop for various combinations of phases, flow pattern regimes such as
bubbly, slug and annular, with various range of water and air volumetric high speed
camera . The air volumetric ranged from 8.3334 L/min to 25 l/min, while the water
volumetric ranged from 5 l/min to 20 l/min and of 50 mm internal diameter along 1 m
length. The measured of the pressure will be done using four pressure sensors along
test pipe. The measured pressure values were used for different air volumetric and
different water volumetric. It has been found that the measuring of pressure gradient
through the distance of rig pipe are inversely changed with air volumetric. In
addition, it has been analyzed the flow pattern through obstruction, it has showed one
phase flow, bubbly and slug flow.

In this paper we have developed a robust WAF-HLL scheme for the compressible two-pressure two-velocity six-equation two-fluid model by improving the earlier WAF-HLL scheme (Yeom and Chang, 2010b) that was also proposed by the authors. The earlier scheme has, however, shown spurious oscillations and instabilities across the shock wave for some severe two-phase flow problems because the WAF (Weighted Average Flux) procedure was applied to the single numerical flux that consists of the gas and the liquid phases. The main idea of the new WAF-HLL scheme is to split the numerical flux of the overall two-phase flow into two phasic components for the gas phase and the liquid phase before we apply the WAF procedure to each of the two phasic numerical fluxes. The present scheme has become numerically very robust as we have removed the oscillations. Furthermore, it makes use of the quadrilateral unstructured grid for more flexibility to deal with complex flow geometry. We demonstrate by solving several two-phase benchmark problems that the new WAF-HLL scheme is significantly more robust than the earlier WAF-HLL scheme, while having accuracy comparable to the earlier one.

Keywords: WAF scheme; HLL scheme; WAF-HLL scheme; two-fluid model; two-phase flow; unstructured grid

We study a high-viscosity two-phase flow through an analysis of the corresponding pressure signals. In particular, we investigate the flow of a glycerin-air mixture moving through a horizontal pipeline with a U-section installed midway along the pipe. Different combinations of liquid and air mass flow rates are experimentally tested. Then, we examine the moments of the statistical distributions obtained from the resulting pressure time series, in order to highlight the significant dynamical traits of the flow. Finally, we propose a novel correlation with two dimensionless parameters: the Euler number and a mass-flow-rate ratio to predict the pressure gradient in high-viscosity two-phase flow. Distinctive variations of the pressure gradients are observed in each section of the pipeline, which suggest that the local flow dynamics must not be disregarded in favor of global considerations.

The objective of the study is to investigate bubble motion and local variables for two-phase flow in reducer pipelines. A three-dimensional computational fluid dynamics (CFD) model using volume of fluid (VOF) method is presented for predicting the development of phase distribution, velocity profiles as well as local and average friction factor using a commercial CFD package FLUENT. Model predictions agree with data reported in the literature. The results reveal that the air and water interface tends to become concave and wavy while fluid travels through the junction of the reducer. The length to achieve fully developed flow increases with increasing pipe contraction. The velocity profiles appear to be prominent in the center of the pipe ahead of the junction. Axial velocity profiles in the horizontal centerline remain symmetrical, but velocity profiles in vertical centerline have velocity peaks near the top of the pipe, where the gas phase exists. Reduction of pipe diameter causes unbalanced increase of gas and liquid velocities, leading to significant non-uniform increase in wall shear stress.

Keywords: reducer pipe; two-phase flow; bubble motion; VOF method; CFD modeling

The aim of this work is to enhance the permeation flux and rejection during the
reverse osmosis (RO) filtration process of simulated seawater, using gas-liquid
two-phase flow to reduce the concentration polarization layer by injecting air. The
effect of various operating conditions (feed concentration, flow rate, temperature,
operating pressure, and gas flow rate) on RO performance was evaluated and optimized.
The central composite design (CCD) technique was used to find the optimal
operating conditions. The objective function (Response) was the flux of permeate
and salt rejection. The coefficients of the proposed model were found, and the significant
and nonsignificant parameters for the proposed model were checked by the
F-test method. In order to ensure a good model the test for significance of the
regression model (F-test) was performed by applying the analysis of variance
(ANOVA). It was found that the flux and the rejection of NaCl solution throughout
the RO are dependent on the operating conditions in the following sequence: concentration>
pressure>temperature>flow rate. In addition, the results showed that the
experimental data have good agreement with the values predicted by the response
model for permeation flux and salt rejection. The results showed a positive effect
of constant gas-liquid two-phase flow on permeate flux and salt rejection. At low
liquid flow rates, better improvement was achieved with a horizontally installed
membrane. Using the gas-liquid two-phase flow technique with an injection factor
of 0.878, slug flow pattern, superficial air velocity of 1.5923m=s, and superficial
liquid velocity of 0.221m=s, the permeate flux increased from 3.406 to 5.676 kg=
m2.h and salt rejection increased from 85% to 91%.

Acoustic Doppler Velocimeter(ADV) has been successfully utilized to capture the flow pattern in neutral and particleladen flow and mainly to investigate the effect of a baffle on the flow structure in a rectangular sedimentation open channel. In particleladen flow a substantial deviation of flow pattern from uniformity was observed. The existence of densitycurrent flow in the presence of particles was confirmed. At higher inlet concentrations the bottom current was observed to be stronger. Also in the presence of the baffle fully developed flow has been noticed in its upstream. In addition, the existence of strong degree of spatiality and high levels of turbulent intensities was identified in downstream of the baffle. Importantly, by using a smoothing method a peak structure has been found in the space averaged power spectra of streamwise and vertical velocities. It was found that baffle causes the peak structure to be alleviated downstream the baffle for the streamwise component and not for the vertical one. As a result the baffle affects on the streamwise energy dissipation and not on the vertical energy dissipation.

The objective of this work is to gain insight into liquid-liquid annular flow, two-component Iraqi gasoil-water flow lengths in horizontal circular transparent pipe of 32mm inner diameter and 6m length, experiments done at atmospheric condition with oil and water as the working fluids. The flow patterns that appear are classified in flow pattern maps as functions of either mixture velocity and water cut or superficial velocities. The superficial water velocity ranged from 1.69 m/s to 3.38 m/s with superficial oil velocity around 0.39 m/s to 1.58 m/s. The effects of superficial water velocity, superficial oil velocity on annular flow lengths were taken into account. However, the essentials of the problem involve the determination of the pressure gradient. In this experimental work a video camera "high speed camera" system with image processing technique by MATLAB were used to extract the hold up for the fluid that being the annular flow. The theoretical study was executed using fluent program, a modified turbulent diffusion model is adopted. Simulation results show more physical predictions with respect to the particle deposition process and concentration profile. New data for hold up lengths were found which achieved good agreements with the previous works. ‫ﺍﻻﻓﻘﻴﺔ‬ ‫ﺍﻟﺤﻠﻘﻴﺔ‬ ‫ﺍﻻﻧﺎﺑﻴﺐ‬ ‫ﺧﻼﻝ‬ (‫)ﺯﻳﺖ-ﻣﺎء‬ ‫ﺍﻟﻄﻮﺭ‬ ‫ﺛﻨﺎﺋﻲ‬ ‫ﺍﻟﺠﺮﻳﺎﻥ‬ ‫ﻋﺒد‬ ‫ﻋﺎﻤر‬ ‫اء‬ ‫زﻫر‬ ‫ﻋﺒد‬ ‫ﻤﺤﻤد‬ ‫ﻋﺼﺎم‬ ‫اﻟﺨﻼﺼﺔ‬ : ‫ﺴﺎﺌﻝ-ﺴﺎﺌﻝ‬ ‫ﻟﻤﺎﺌﻌﻴن‬ ‫ﺤﻠﻘﻲ‬ ‫ﻴﺎن‬ ‫ﻟﺠر‬ ‫اﻟطور‬ ‫ﺜﻨﺎﺌﻲ‬ ‫ﻴﺎن‬ ‫ﺠر‬ ‫اﺴﺔ‬ ‫در‬ ‫ﻋﻠﻰ‬ ‫اﻟﻀوء‬ ‫ﺘﺴﻠﻴط‬ ‫ﻫو‬ ‫اﻟﺤﺎﻟﻲ‬ ‫اﻟﻌﻤﻝ‬ ‫ﻤن‬ ‫اﻟﻬدف‬ ‫داﺨﻠﻲ‬ ‫ﺒﻘطر‬ ‫ﺸﻔﺎف‬ ‫أﻓﻘﻲ‬ ‫اﻨﺒوب‬ ‫ﻓﻲ‬ 32 ‫وطوﻝ‬ ‫ﻤﻠم‬ 6 ‫م‬ , ‫اﻟﻤﺨﺘﺒر‬ ‫ﻓﻲ‬ ‫اﻟطﺒﻴﻌﻴﻪ‬ ‫اﻟﺒﻴﺌﻴﻪ‬ ‫اﻟظروف‬ ‫ﺘﺤت‬ ‫اﻟﺘﺠﺎرب‬ ‫ﻴت‬ ‫أﺠر‬ ‫ﻟﻘد‬ ‫ﺴﺎﺌﻠﻴن‬ ‫ﻴن‬ ‫ﻛطور‬ ‫اﻟﻤﺎﺌﻌﻴن‬ ‫ﻛﻼ‬ ‫ﺒﺎﺴﺘﺨدام‬. ‫ﻛﻤﻌﺎدﻟﻪ‬ ‫وﺘﻛون‬ ‫ﻴﺎن‬ ‫اﻟﺠر‬ ‫اع‬ ‫أﻨو‬ ‫ﺘوﻀﻴﺢ‬ ‫ﻴطﺔ‬ ‫ﻛﺨر‬ ‫ﻤﺼﻨﻔﻪ‬ ‫ﺘظﻬر‬ ‫ﻴﺎن‬ ‫اﻟﺠر‬ ‫ﻨﻤﺎذج‬ ‫اﻟﺨﻠﻴط‬ ‫ﻟﺴرﻋﺔ‬. ‫ﻤن‬ ‫اوح‬ ‫ﻴﺘر‬ ‫اﻟﻤﺎء‬ ‫ﺴرﻋﺔ‬ ‫ﻤﻌدﻝ‬ 1.69 ‫اﻟﻰ‬ ‫م/ﺜﺎﻨﻴﻪ‬ 3.38 ‫ﻤن‬ ‫اوح‬ ‫ﻴﺘر‬ ‫اﻟﻨﻔط‬ ‫ﺴرﻋﺔ‬ ‫وﻤﻌدﻝ‬ ‫م/ﺜﺎﻨﻴﻪ‬ 0.39 ‫اﻟﻰ‬ ‫م/ﺜﺎﻨﻴﻪ‬ 1.58 ‫م/ﺜﺎﻨﻴﻪ‬. ‫اﻟدﻗﻪ‬ ‫ﻋﺎﻟﻴﻪ‬ ‫ﻴﺔ‬ ‫ﺘﺼوﻴر‬ ‫اﺼﻔﺎت‬ ‫ﻤو‬ ‫وذات‬ ‫اﻟﺴرﻋﺔ‬ ‫ﻋﺎﻟﻴﻪ‬ ‫ا‬ ‫ﻛﺎﻤﻴر‬ ‫ﺒﺎﺴﺘﺨدام‬ ‫ﺘﺼوﻴري‬ ‫ﻨظﺎم‬ ‫اﺴﺘﺨدام‬ ‫ﺘم‬ ‫اﺴطﺔ‬ ‫ﺒو‬ ‫اﻟﺼور‬ ‫ﻤﻌﺎﻟﺠﺔ‬ ‫ﺘﻘﻨﻴﺔ‬ ‫ﻤﻊ‬ MATLAP ‫ﺘﻨﻔﻴذ‬ ‫ﺘم‬ .‫أﻟﺤﻠﻘﻲ‬ ‫ﺘدﻓق‬ ‫اﻟﺴﺎﺌﻝ-اﻟﺴﺎﺌﻝ‬ ‫ﺜﺎﻗﺒﺔ‬ ‫ة‬ ‫ﻨظر‬ ‫ﻋﻠﻰ‬ ‫اﻟﺤﺼوﻝ‬ ‫ﻫو‬ ‫اﻟﻬدف‬ ‫و‬ ‫ﻓﻠوﻨت‬ ‫ﻨﺎﻤﺞ‬ ‫ﺒر‬ ‫ﺒﺎﺴﺘﺨدام‬ ‫ﻴﺔ‬ ‫اﻟﻨظر‬ ‫اﺴﺔ‬ ‫اﻟدر‬ CFD ‫ﺘظﻬر‬ ‫اﻟﻤﺤﺎﻛﺎة‬ ‫ﻨﺘﺎﺌﺞ‬ .‫اﻟﻤﺤﺴن‬ ‫اﻟﻤﻀطرب‬ ‫اﻻﻨﺘﺸﺎر‬ ‫ﻨﻤوذج‬ ‫اﻋﺘﻤﺎد‬ ‫و‬ ، ‫أوﺠدﻩ‬ ‫ﻤﺎ‬ ‫ﻤﻊ‬ ‫اﻓق‬ ‫ﺘﺘو‬ ‫ﺠدﻴدة‬ ‫ﺒﻴﺎﻨﺎت‬ ‫ﻋﻠﻰ‬ ‫اﻟﻌﺜور‬ ‫ﺘم‬ .‫اﻟﺘرﻛﻴز‬ ‫و‬ ‫اﻟﺠﺴﻴﻤﺎت‬ ‫ﺘرﺴب‬ ‫ﻋﻤﻠﻴﺔ‬ ‫ﻴﺨص‬ ‫ﻓﻴﻤﺎ‬ ‫أﻛﺜر‬ ‫اﻟﻔﻌﻠﻴﺔ‬ ‫اﻟﺘوﻗﻌﺎت‬ .‫ﺴﺎﺒﻘﺎ‬ ‫اﻟﺒﺎﺤﺜون‬

Most work in literature on condensation in tubes has been done for smooth tubes in the horizontal and vertical configurations. Recent experimental works with condensation at different inclination angles showed that the heat transfer characteristics were a function of inclination angle. These works were limited to heat transfer and pressure drop measurements with visual observations. However, no work has been done on measuring the void fractions during condensation at different inclination angles. The purpose of this study was to measure void fractions and heat transfer coefficients during condensation for tube inclinations ranging from vertical downwards (−90 °) to vertical upwards (90 °) at a saturation temperature of 40 °C. Measurements were taken in an experimental setup in which condensation occurred on the inside of a test section. The test section was a circular tube with an inner diameter of 8.38 mm and a heat transfer length of 1.488. The refrigerant used was R134a, and the void fractions were measured using two capacitive void fraction sensors. Mass fluxes ranging from 100 to 400 kg/m 2 s and vapour qualities ranging from 10–90% were considered. Heat transfer coefficients were also compared with void fractions. It was found that at combinations of low mass fluxes and vapour qualities, void fraction and heat transfer were significantly affected by changes in inclination angle. Generally, void fractions and heat transfer coefficients increased with downward inclination angles with an optimum angle between −10 ° and −30 ° (downward flow). At some intermediate mass flux and vapour quality conditions, the void fraction and heat transfer coefficients were observed to be independent of the inclination angle despite changes in the prevailing flow patterns.