Two-phase Pressure Drop Correlations Research Articles

Enhanced Subcooled Flow Boiling Heat Transfer in Microchannel With Piranha Pin Fin

An experimental study on subcooled flow boiling with engineering fluid HFE-7000 in a microchannel fitted with piranha pin fins (PPFs) is presented. Heat fluxes of up to 735 W/cm2 were achieved and mass fluxes ranged from 618 kg/m2s to 2569 kg/m2 s. It was found that the flow boiling heat transfer was significantly enhanced with PPFs. The heat transfer coefficient with flow boiling was double the corresponding single-phase flow. Correlations for two-phase heat transfer coefficient and pressure drop in the nucleate flow boiling regime were developed based on the boiling, Weber, and Jakob numbers. The onset of nucleate boiling (ONB) and the critical heat flux (CHF) conditions were determined through visualization and was typically initiated from the last row of fins where temperatures were highest and flow rates lowest.

Comparison and development of new correlation for adiabatic two-phase pressure drop of refrigerant flowing inside a multiport minichannel with and without fins

This study examines the experimental adiabatic two-phase frictional pressure drop of R134a in rectangular multiport minichannel with and without fins having 20 channels with hydraulic diameters of 0.64 mm and 0.81 mm, respectively. The pressure drop measurements were done under mass flux range of 50–200 kg m−2 s−1, saturation temperature range of 20–35 °C, and inlet vapor quality range of 0.1–0.9. The effects of mass flux, saturation temperature, inlet vapor quality and channel geometry on frictional pressure drop were investigated. The results discovered that the mass flux, inlet vapor quality, saturation temperature and channel geometry play an important role in increasing or decreasing the frictional pressure drop. The present experimental data were compared with eleven existing well known frictional pressure drop correlation available in the open literature. In addition, a new two-phase frictional pressure drop correlation is proposed considering the effects of inertia, viscous force, fluid properties, channel geometry and surface tension and also validated the correlation with the available data.

Two-phase flow pressure drop in superhydrophobic channels

Superhydrophobic surfaces have been shown to reduce drag in single-phase channel flow; however, little work has been done to characterize their drag-reducing ability found in two-phase flows. Adiabatic, air-water mixtures were used to explore the influence of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation environments. Pressure drop measurements in a rectangular channel with one superhydrophobic wall (cross-section approximately 0.37×10mm) and three transparent hydrophilic walls were obtained. Data for air/water mixtures with superficial Reynolds numbers ranging from 22–215 and 55–220, respectively, were obtained for superhydrophobic surfaces with three different cavity fractions. Agreement between experimentally obtained two-phase pressure drop data and correlations in the literature for conventional smooth control surfaces was better than 20 percent, which is within the accuracy of the correlations. The data reveal a reduction in the pressure drop for two-phase flow in a channel with a single superhydrophobic wall compared to a control scenario. The observed reduction is approximately 10 percent greater than the reduction that is observed for single-phase flow (relative to a classical channel).

Frictional pressure drop correlation for two-phase flows in mini and micro single-channels

1521 frictional pressure drop data points were collected from 12 literatures. The database included adiabatic and diabatic systems composed of 10 working fluids. The diameter range was from 0.1 to 3mm, and the pressure drop ranged from 1.26kPa/m to 2MPa/m. 17 existing single channel two-phase pressure drop correlations including homogenous flow model and separated flow model were evaluated with the database. The comparison results showed that the correlations of Pamitran et al., Hwang and Kim, Mishima and Hibiki and Zhang et al. gave better predictions than the others. However, the performance evaluation results also showed the mean absolute errors higher than 40%. Based on the relatively large prediction error by the existing correlations, a new correlation was proposed by classifying the flow conditions into four regimes (namely, 1: gas laminar-liquid laminar, 2: gas laminar-liquid turbulent, 3: gas turbulent-liquid laminar, 4: gas turbulent-liquid turbulent). The newly developed correlation is expressed by a function of the two-phase Reynolds number, Retp, the two-phase viscosity number, Nμtp, and the gas quality, x, and was able to predict the two-phase frictional pressure drop with the mean absolute percentage error of 17.4%. The correlation demonstrated an excellent performance for predicting the two-phase frictional pressure drop in mini/micro single channels.

Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps

Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup.Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.

Mathematical Modelling of Silica Scaling Deposition in Geothermal Wells

Silica scaling is widely encountered in geothermal wells in which produce two-phase geothermal fluid. Silica scaling could be formed due to chemical reacting by mixing a geothermal fluid with other geothermal fluid in different compositions, or also can be caused by changes in fluid properties due to changes pressure and temperature. One of method to overcome silica scaling which is occurred around geothermal well is by workover operation. Modelling of silica deposition in porous medium has been modeled in previously. However, the growth of silica scaling deposition in geothermal wells has never been modeled. Modelling of silica deposition through geothermal is important aspects to determine depth of silica scaling growth and best placing for workover device to clean silica scaling. This study is attempted to develop mathematical models for predicting silica scaling through geothermal wells. The mathematical model is developed by integrating the solubility-temperature correlation and two-phase pressure drop coupled wellbore fluid temperature correlation in a production well. The coupled model of two-phase pressure drop and wellbore fluid temperature correlation which is used in this paper is Hasan-Kabir correlation. This modelling is divided into two categories: single and two phase fluid model. Modelling of silica deposition is constrained in temperature distribution effect through geothermal wells by solubility correlation for silica. The results of this study are visualizing the growth of silica scaling thickness through geothermal wells in each segment of depth. Sensitivity analysis is applied in several parameters, such as: bottom-hole pressure, temperature, and silica concentrations. Temperature is most impact factor for silica scaling through geothermal wellbore and depth of flash point. In flash point, silica scaling thickness has reached maximum because reducing of mole in liquid portion.

Experimental study on two-phase flow pressure drop in small diameter bends

Summary Measurement of two-phase flow pressure drop and its prediction across curved tubes and bends is important for the enhancement of the performance and safety of the heat exchangers and flow transmitting devices. The comparative study of some of the available two-phase pressure drop correlations reveals that the predicted values of pressure drops by these leading methods may differ by large. The applicability of these correlations to the small diameter tubes of range 4.0–8.0 mm and different bend angles of the range 90–180° is not fully established. The basic objective of the present experimental investigation is to generate the experimental data to develop the unified correlation applicable for the small diameter tubes of range 4.0–8.0 mm and different bend angles of the range 90–180°. Hence, experimental facility was developed to conduct the experiments to generate the data and to assess the predictive capability of some of the available two-phase pressure drop correlations. It was observed that the correlations considered for comparisons were unable to satisfactorily predict the measured experimental data within the ±50% error bands. A new correlation is developed in terms of curvature multiplier to the straight tube two-phase pressure drop. The correlation is validated with the present measured experimental data. The statistical analysis suggests that correlation shows satisfactory results.

Boiling pressure drop and local heat transfer distribution of water in horizontal straight tubes at low pressure

The objective of the present work is to investigate the heat transfer and pressure drop in flow boiling at low pressure with water as the working medium. The effect of pipe diameter, heat flux and mass flux on boiling pressure drop and local heat transfer coefficient is studied. In the present work, the available correlations are revisited for low pressure flow boiling. Comparison of local heat transfer coefficient with the existing correlation is carried out to identify an appropriate correlation which performs well in complete flow boiling range (subcooled regions and saturated regions) for water at low system pressure.Experiments are performed with eight test sections made of thin walled stainless steel (SS 304) tubes having inner diameters from 5.5 mm to 12 mm and length varying from 550 mm to 1000 mm. The system pressure is varying form 1 bar to 3 bar. No change in slope of heat transfer curve is found for subcooled regions. Heat transfer in all the three regions of subcooled boiling namely partial subcooled boiling, fully developed subcooled and net vapour generation are predicted by a single correlation. Tube diameter has no effect on boiling heat transfer distribution. However, tube diameter affects two phase pressure drop. Increase in mass flux increases the convective heat transfer coefficient. However, mass flux has no influence on subcooled and nucleate boiling heat transfer coefficient. Heat flux increases the boiling heat transfer coefficient. Increase in tube diameter and mass flux decreases the two-phase pressure drop. Most of all the correlations in the subcooled region predict heat transfer coefficient with reasonable accuracy. Kandlikar and Shah correlations perform well in the low pressure saturated boiling i.e. nucleate and convective. None of the available two-phase pressure drop correlations are able to predict the pressure drop in a low pressure system. A correlation is developed to predict two-phase pressure drop in low pressure flow boiling system with a reasonably good accuracy.

Experimental investigation of condensation heat transfer and pressure drop of propane, R1234ze(E) and R22 in minichannels

The paper reports measured heat transfer and pressure drop data for condensation of propane, R1234ze(E) and R22 in circular (dh=1.085mm) and square (dh=0.952mm) horizontal minichannels. The saturation temperatures are 40°C and 50°C with mass fluxes varying from 200 to 800kg/(m2s) and vapor qualities from 0.1 to 0.9. The experiments investigated the effects of mass flux, vapor quality, saturation temperature and channel geometry on the heat transfer coefficients and pressure drops. The results show that the heat transfer coefficients and pressure drops increase with increasing mass flux and vapor quality and decreasing saturation temperature. The heat transfer coefficients in the square minichannel are larger than those in the circular minichannel. The study shows that propane and R1234ze(E) are good substitutes for R22 based on the condensation heat transfer characteristics. The pressure gradients in the circular and square minichannels differ little for propane with mass fluxes of 200, 350 and 500kg/(m2s) and for R1234ze(E) with a mass flux of 500kg/(m2s). The pressure gradients for propane are larger than those of R1234ze(E) which are larger than those of R22. Condensation heat transfer and two-phase pressure drop correlations were evaluated against the experimental data in the square minichannel.

An experimental study of flow boiling frictional pressure drop of R134a and evaluation of existing correlations

A series of experiments on flow boiling frictional pressure drop of R134a in three horizontal circular smooth copper tubes with inner diameters of 1.002, 2.168, and 4.065mm were conducted. A total of 397 experimental data points are obtained for a mass flux range of 185–935kg/m2s, a heat flux range of 18.0–35.5kW/m2, a saturation pressure range of 0.578–0.82MPa, and a vapor quality range of 0.03–1.0. The effects of mass flux, heat flux, vapor quality, saturation pressure, and diameter on the frictional pressure drop are analyzed and the results indicate that the frictional pressure drop increases with increasing mass flux, increases with vapor quality until a peak and then drops, decreases with increasing saturation pressure and hydraulic diameter, and almost keep constant with heat flux. Thirty-two existing correlations of two-phase frictional pressure drop are compared with the experimental data. The best correlation has the mean absolute deviation of 15.0%. Besides, an experimental database of flow boiling frictional pressure drop is complied, which contains 3244 data points, including 397 from the current experiments and 2847 from 27 published papers. The 32 existing correlations are evaluated with the database. The best correlation has the mean absolute deviation of 24.5%. The work provides a guide for selecting a suitable correlation for specific applications of flow boiling frictional pressure drop.

Two-Phase Flow Pressure Drop in Corrugated Tubes Used in an Aero-engine Oil System

In modern aero-engines, the lubrication system holds a key role due to the demand for high reliability standards. An aero-engine bearing chamber contains components like bearings and gears. Oil is used for lubrication and for heat removal. In order to retain the oil in a bearing chamber, pressurized seals are used. These are pressurized using air from the compressor. In order to avoid overpressurization of the bearing chamber, air/oil passages are provided in the bearing chamber. At the top, a vent pipe discharges most of the sealing air and at the bottom, a scavenge pipe is used for discharging the oil by means of a pump (scavenge pump). The scavenge pipe is setup in most cases by tubes of circular or noncircular cross sections. When the scavenge pipe has to be routed in a way that sharp bends or elbows are unavoidable, flexible (corrugated) pipes can be used. Because of the corrugation, considerable flow resistance with high-pressure drop can result. This may cause overpressurization of the bearing compartment with oil loss into the turbomachinery with possibility of ignition, coking (carbon formation), or contamination of the aircraft’s air conditioning system. It is therefore important for the designer to be capable to predict the system’s pressure balance behavior. A real engine bearing chamber sealed by brush seals was used for generating different air/oil mixtures thus corresponding to different engine operating conditions. The mixtures were discharged through a scavenge pipe which was partly setup by corrugated tubes. Instead of a mechanical pump, an ejector was used for evacuating the bearing chamber. An extensive survey covering the existing technical literature on corrugated tube pressure drop was performed and is presented in this paper. The survey has covered both single-phase and multiphase flows. Existing methods were checked against the test results. The method which was most accurately predicting lean air test results from the rig was benchmarked and was used as the basis for extending into a two-phase flow pressure drop correlation by applying two-phase flow multiplier techniques similar to Lockhart and Martinelli. Comparisons of the new two-phase flow pressure drop correlation with an existing correlation by Shannak are presented for mixtures like air/oil, air/water, air/diesel, and air/kerosene. Finally, numerical analysis results using ansys cfx version 15 are presented.

Comparison of Flow Boiling Pressure Drop Correlations for Smooth Macrotubes

This paper investigates two-phase pressure-drop correlations available in the literature and compares them with the experimental data in order to assess their performances in terms of prediction accuracy. Pressure drops for pure refrigerants and mixtures are predicted by comparing 1714 experimental data points with eight two-phase pressure drop correlations. In this context, R22, R407C, R410A, R744, R717, R404A, and R134a are selected as test refrigerants. A flow-pattern-based pressure-drop correlation developed by Moreno Quiben and Thome is also discussed. The Moreno Quiben and Thome model takes the effect of annular to dryout transition, and therefore maximum pressure drop occurs at the end of the annular flow regime. Results refer to experimental works in circular smooth tubes between 3.25 and 14.0 mm, for saturation temperatures between –30.0 and 50.0°C, mass fluxes between 100.0 and 1082.0 kg/m2-s, and heat fluxes from adiabatic to 36.8 kW/m2. The Muller-Steinhagen and Heck correlation shows better performance, predicting 61.7% of experimental data within a ±30.0% error band. It is also seen that the Chawla and Gronnerud correlations agree with experimental results only for R134a and R717.

Pressure drop during near-critical-pressure condensation of refrigerant blends

This paper presents the results of an experimental study on pressure drop during condensation of refrigerant blends R404A and R410A at near-critical pressures inside tubes of 0.76 ≤ D ≤ 9.4 mm. Local frictional pressure gradients were measured at reduced pressures (Pr) of 0.8 and 0.9 for the mass flux range 200 ≤ G ≤ 800 kg m−2 s−1, in small quality increments. The data were compared with adiabatic and diabatic two-phase pressure drop correlations from the literature. These correlations were not able to adequately predict the pressure drop over the range of tube sizes and mass fluxes under consideration here at high reduced pressures. A new correlation for pressure drop is introduced, which accounts for property variations and microchannel effects. The correlation predicts 85% of the data within ±25%, with an average deviation between model predictions and data of ±14%.

Design of a non-intrusive electrical impedance-based void fraction sensor for microchannel two-phase flows

A non-intrusive electrical impedance-based sensor is developed for measurement of local void fraction in air–water adiabatic flow through rectangular microchannels. Measurement of the void fraction in microchannels is essential for the formulation of two-phase flow heat transfer and pressure drop correlations, and may enable real-time flow regime control and performance prediction in the thermal regulation of high-heat-flux devices. The impedance response of the sensor to a range of flow regimes is investigated for a configuration with two aligned electrodes flush-mounted on opposing microchannel walls. Numerical simulations performed on a multi-phase domain constructed from three-dimensional reconstruction of experimentally observed phase boundaries along with the corresponding experimental results serve to establish the relationship between void fraction and dimensionless impedance for this geometric configuration. A reduced-order analytical model developed based on an assumption of stratified gas–liquid flow allows ready extension of these calibration results to different working fluids of interest.

Flow boiling heat transfer and pressure drop of water in a plate heat exchanger with corrugated channels at low mass flux conditions

The plate heat exchanger (PHX) has been widely used as a heat exchanger in fresh water generators (FWGs) at low mass flux conditions. In this study, the flow boiling heat transfer and pressure drop characteristics of water in a PHX for the FWG were measured by varying mass flux from 14.5 to 33.6kgm−2s−1, heat flux from 15.0 to 30.0kWm−2, and mean vapor quality from 0.09 to 0.6 in the pressure range of 112–121kPa. The flow boiling heat transfer of water in the PHX was in the convective boiling region. The flow boiling heat transfer coefficient decreased with increasing mean vapor quality and decreasing mass flux. However, the effect of the heat flux on the flow boiling heat transfer coefficient was almost negligible. In addition, the two-phase frictional pressure drop increased with increasing mean vapor quality and mass flux, but it remained nearly constant according to the heat flux. Two-phase heat transfer and pressure drop correlations for water in PHXs were developed based on the measured data. The proposed heat transfer and pressure drop correlations showed mean absolute deviations of 4.4% and 10.4%, respectively, compared with the measured data.

Experimental sizing and assessment of two-phase pressure drop correlations for a capillary tube with transcritical and subcritical carbon dioxide flow

In the last years, CO2 was proposed as an alternative refrigerant for different refrigeration applications (automotive air conditioning, heat pumps, refrigerant plants, etc.) In the case of low power refrigeration applications, as a household refrigerator, the use of too expensive components is not economically sustainable; therefore, even if the use of CO2 as the refrigerant is desired, it is preferable to use conventional components as much as possible. For these reasons, the capillary tube is frequently proposed as expansion system. Then, it is necessary to characterize the capillary in terms of knowledge of the evolving mass flow rate and the associate pressure drop under all possible operative conditions.For this aim, an experimental campaign has been carried out on the ENEA test loop "CADORE" to measure the performance of three capillary tubes having same inner diameter (0.55 mm) but different lengths (4, 6 and 8 meters). The test range of inlet pressure is between about 60 and 110 bar, whereas external temperatures are between about 20 to 42 °C.The two-phase pressure drop through the capillary tube is detected and experimental values are compared with the predictions obtained with the more widely used correlations available in the literature. Correlations have been tested over a wide range of variation of inlet flow conditions, as a function of different inlet parameters.

A finite volume coaxial heat exchanger model with moving boundaries and modifications to correlations for two-phase flow in fluted annuli

Coaxial Heat Exchangers (CHXs) are now used extensively in heat pump (HP) and refrigeration systems. The design of such systems requires estimation of CHX's thermal and hydraulic performance. This paper presents a generalized finite volume CHX model that is capable of simulating single-phase and two-phase flow with a smooth or fluted inner tube. The concepts of segment insertion and subdivision (moving boundary within the segment) are adopted in this model to track the phase change point along the flow channel. This allows for reliable model accuracy even with a lower number of discretized finite volumes, thereby reducing computation time. For the segment insertion and subdivision functions, four different approaches are provided in order to achieve the best accuracy and least computational effort under various flow configurations and fluid conditions. The simulation model can be applied to straight and helical tubes with choices of smooth, grooved and fluted tube surface. Empirical single-phase and two-phase correlations from the literature are adopted in the proposed model for the applicable surfaces. At present, there are no correlations for two-phase flow in fluted tube annuli, in the open literature. This paper proposes modifications to existing two-phase fluted surface heat transfer and pressure drop correlation formulations by applying empirical two-phase flow multipliers onto existing fluted tube single phase correlations. The solving methodology of this model requires the heat exchanger geometry, flow configuration, inlet states, as well as mass flow rates of the fluids to solve for the outlet conditions, heat load, pressure drop and charge of the CHX. Coupled with non-linear equation solver, the model can also provide the required mass flow rate for a specific superheat/subcooling on either side of the CHX. The model and modified correlations are validated against experimental data of brine-to-refrigerant fluted tube condenser and evaporator used in a heat pump application.

A new correlation of two-phase frictional pressure drop for condensing flow in pipes

The calculation of two-phase frictional pressure drop for condensing flow in pipes is essential in many areas. Although numerous studies concerning this issue have been conducted, an accurate correlation is still required. In this paper, an overall survey of correlations and experimental investigations of two-phase frictional pressure drop is carried out. There 525 experimental data points of 9 refrigerants are gathered from literature, with hydraulic diameter from 0.1 to 10.07mm, mass flux from 20 to 800kg/m2s, and heat flux from 2 to 55.3kW/m2. The 29 existing correlations are evaluated against the experimental database, among which the best one has a mean absolute relative deviation (MARD) of 25.2%. Based on all the experimental data, a new correlation which has an MARD of 19.4% is proposed, improving significantly the prediction of two-phase frictional pressure drop for pipe condensing flow.

A Two-Phase Pressure Drop Model Incorporating Local Water Balance and Reactant Consumption in PEM Fuel Cell Gas Channels

A two-phase 1-D pressure drop modeling scheme that incorporates the effect of local channel saturation on flow regime is introduced. The model provides a basis for extending two-phase pressure drop correlations from fundamental studies to more complex conditions within PEMFC reactant channels. The need for additional studies beyond the fundamental level is highlighted and key factors that separate PEMFC reactant channel conditions are explained. A crucial concern in characterizing two-phase flow within PEMFC reactant channels is the local flow pattern transitions throughout the channel. The application of an elemental step-wise calculation scheme approach for the prediction of localized two-phase conditions allows for a more complete prediction of conditions within the channels. Additionally through the application of a control volume approach, the effect of water addition and mass consumption of reactants on pressure drop within PEMFC flow channels is investigated. The resulting modeling scheme shows the relative effects of relaxing several of the common assumptions made when modeling PEMFC reactant channels.

Correlations for two-phase friction pressure drop under microgravity

The determination of two-phase friction pressure drop (TPFPD) in tubes is required by two-phase systems operating under microgravity. However, there is no proper TPFPD correlation for microgravity or reduced gravity, and thus people have to use a TPFPD correlation for normal gravity to estimate TPFPD under microgravity. This paper proposes a TPFPD correlation for microgravity, for which an up-to-data survey of the TPFPD experimental data under microgravity is carried out and a critical review of the published literature regarding TPFPD methods is conducted. Totally, 593 useful experimental data points under microgravity are obtained from 10 references, including 15 with GN2–water, 256 with air–water, and 322 with R-12. These data are used to evaluate the existing TPFPD correlations and develop the new TPFPD correlation for microgravity. The new TPFPD correlation is the first TPFPD correlation specifically for microgravity with wide application range. The comparison shows that for microgravity applications it is far better than any existing model. It has a mean absolute relative deviation (MARD) of 20.4% with 56.7% of the sample having a relative deviation within±15%, while the best existing model has the MARD of 25.3% with only 33.4% of the sample having the relative deviation within±15%.