Single-phase Pressure Drop Research Articles

Two-phase pressure drop in a helical coil flow boiling system

The objective of the present work is to study the two-phase pressure drop in helical coils. Literature on the two-phase pressure drop in a helical coil suggests the complexity in flow boiling inside a helical coil due to secondary flow. Most of correlations reported in the literature on the two-phase pressure drop in a helical coil are limited to a specific operating range. No general correlation is available for a helical coil which is applicable for all fluids. In the present study, an experimental databank collected containing a total of 832 data points includes the data from the present study and from the literature. The data includes diabatic pressure drop of two fluids namely water and R123. Data covers a range of parameters namely a mass flux of 120–2058 kg/m2 s, a heat flux of 18–2831 kW/m2, an exit quality of 0.03–1, a density ratio of 32–1404 and a coil to tube diameter ratio of 14–58. The databank is compared with eighteen empirical correlations which include well referred correlations of straight tubes and the available correlations of helical coils. The straight tube correlations are not working well for the present data set. The helical coil correlations work reasonably well for the present databank. A correlation is suggested to predict the two-phase pressure drop in helical coils. The present study suggests that the influence of a helical coil is completely included in the single phase pressure drop correlation for helical coils.

Heat transfer and pressure drop of condensation of hydrocarbons in tubes

The heat transfer coefficient and pressure drop are investigated for propane. Two different mild steel plain tubes and saturation pressures are considered for varying mass flux and vapour quality. The pressure drop is compared to the Friedel-Correlation with two different approaches to determine the friction factor. The first is calculation as proposed by Friedel and the second is through single phase pressure drop investigations. For lower vapour qualities the experimental results are in better agreement with the approach of the calculated friction factor. For higher vapour qualities the experimental friction factor is more precise. The pressure drop increases for a decreasing tube diameter and saturation pressure. The circumferential temperature profile and heat transfer coefficients are shown for a constant vapour quality at varying mass fluxes. The subcooling is highest for the bottom of the tube and lowest for the top. The average subcooling as well as the circumferential deviation decreases for rising mass fluxes. The averaged heat transfer coefficients are compared to the model proposed by Thome and Cavallini. The experimental results are in good agreement with both correlations, however the trend is better described with the correlation from Thome. The experimental heat transfer coefficients are under predicted by Thome and over predicted by Cavallini.

Air Water Loop for investigaion of flow dynamics in a steam drum: Steady state two-phase natural circulation experiments and validation

Advanced Heavy Water Reactor (AHWR) is a vertical pressure tube type boiling water reactor that relies on two-phase natural circulation for heat removal from the nuclear core under normal operating as well as accidental conditions. In case of AHWR, the two-phase flow generated in the core is transported by vertical riser pipes to horizontal steam drums at the top. These horizontal steam drums provide sufficient surface area for the separation of steam water mixture purely based on gravity i.e. due to density difference between steam and water. To investigate this gravity separation phenomenon, an experimental facility known as Air-Water Loop has been designed. The facility has a scaled geometry of AHWR steam drum operating with Air-Water mixture as a working fluid. The required flow conditions for the experimental simulations are generated using air-water two-phase natural circulation in this facility. Steady state natural circulation experiments were performed where measurements on recirculation flow rates, two-phase and single phase pressure drop in various sections of the loop have been carried out. The present paper aims to describe the design aspects of the facility, pre-test calculations, steady state two-phase natural circulation experiments and assessment of measured experimental data. The experimental measurements have been predicted using a numerical model that considers various void fraction and pressure drop correlations from the literature for estimation of measured parameters.

Micro-structured heat exchanger for cryogenic mixed refrigerant cycles

Mixed refrigerant cycles (MRCs) offer a cost- and energy-efficient cooling method for the temperature range between 80 and 200 K. The performance of MRCs is strongly influenced by entropy production in the main heat exchanger. High efficiencies thus require small temperature gradients among the fluid streams, as well as limited pressure drop and axial conduction. As temperature gradients scale with heat flux, large heat transfer areas are necessary. This is best achieved with micro-structured heat exchangers, where high volumetric heat transfer areas can be realized. The reliable design of MRC heat exchangers is challenging, since two-phase heat transfer and pressure drop in both fluid streams have to be considered simultaneously. Furthermore, only few data on the convective boiling and condensation kinetics of zeotropic mixtures is available in literature. This paper presents a micro-structured heat exchanger designed with a newly developed numerical model, followed by experimental results on the single-phase pressure drop and their implications on the hydraulic diameter.

Behavior and pressure drop of an upwardly two-phase flow through multi-hole orifices

Experimental results on hydrodynamic behavior and pressure drop of two-phase mixture flowing upwardly in a pipe containing single- and/or multi-hole orifice plate are presented. It was found from the measurement of the void fraction upstream and downstream the orifices that the flow behavior is significantly affected by the layout of the orifice plate used and the flow starts to recover after approximately 7 D downstream the orifice. Furthermore, increasing orifice holes number results in decreasing the slip ratio. The standard deviation of the void fraction was used to identify the flow pattern before and after the orifices and found that the critical threshold transition occurred at a standard deviation of 0.2. The flow homogenization necessitates a minimum value of the liquid superficial velocity to occur, and the position where it takes place depends on this velocity and on the orifice holes number. It was also inferred from the two-phase pressure drop data across the orifices that three different flow regimes, where the transition between bubbly-to-slug and slug-to-churn flow, can be identified. An assessment of the predicted two-phase flow multiplier using some previous models dedicated to single-hole orifice was achieved; and found that the model proposed by Simpson et al. is the most reliable one. Single-phase pressure drop was also measured and compared with correlations from literature.

Measurement of heat transfer coefficient and pressure drop during evaporation of R134a in new type facility with one pass flow through microchannel tube

A new facility has been built for experimental study on microchannel and introduced in this paper. Six heat transfer coefficient and six pressure drop measurements can be conducted simultaneously in one pass from vapor quality of 0 to 1 on the facility. Two water-jacket-design heat exchangers are placed top and bottom on each test section for heating the refrigerant. In each test section, the top and bottom sides are heated and controlled separately to ensure uniform conditions. The environmental heat loss and wall temperature measurements are corrected to increases confidence of results. Port geometry is measured with an optical microscope. Heat transfer coefficient and pressure drop of R134a are measured in a 24-port microchannel tube. The single-phase pressure drop follows the rule of round tube and fRe is 64. The single-phase Nusselt number is more sensitive to Reynolds number, compared to large tubes. As vapor quality increases, two-phase pressure drop increases until quality of 0.9, and then stops increasing or even drops; two-phase heat transfer coefficient increases until quality of 0.5 to 0.6 and then drops. Higher mass flux or lower saturation temperature will increase the pressure drop. Heat flux and mass flux have strong impact on heat transfer coefficient, and the effect of saturation temperature is not clear.

Flow characteristics and heat transfer performance of half-corrugated microchannels

The single-phase pressure drop and heat transfer performance of half-corrugated microchannels under a low Reynolds number (<900) are studied via three-dimensional numerical simulation and experiment. Comparative studies between half-corrugated and flat-bottom copper microchannels are analyzed to access the pressure drop and thermal performance enhancement. Compared with flat bottom microchannels, the half-corrugated mirochannels have a significant pressure drop diminution at a given Reynolds number. The wave length of the half-corrugated microchannels has a strong impact on the pressure drop, and the effect of wave amplitude can be neglected at a Reynolds number of 153–814 (flow speed of 0.2–1.2m/s). In addition, the heat transfer performance for half-corrugated microchannels is enhanced when the effective heat flux is beyond 150kWm−2. The flow behaviors of the microchannels with different half-corrugated structures are obtained from three-dimensional numerical simulations and are applied to explain the enhanced heat transfer and lower pressure drop. Moreover, a new parameter, the relative thermal-hydraulic performance index G, is defined to evaluate the overall performance of the half-corrugated microchannels. Compared with double sinusoidal corrugated microchannels, the half-corrugated microchannels possess excellent overall performance.

An experimental study on single phase convection heat transfer and pressure drop in two brazed plate heat exchangers with different chevron shapes and hydraulic diameters

An experimental study on heat transfer and pressure drop characteristics was performed at single phase flow in two Brazed plate heat exchangers (BPHEs) with different geometries. The corrugation density of one of the BPHE (Type II) was two times as high as that of the other BPHE (Type I). The hydraulic diameter of the type II BPHE was 2.13 mm, which was 38 % smaller than that of the type I BPHE. Also, the cross section shape of the flow channels for the type II BPHE was different from that for conventional BPHEs due to the unusual corrugation patterns and brazing points. The experimental conditions for temperatures were varied from 4.6 °C to 49.1 °C, and for mass flow rates were changed from 0.07 kg/s to 1.24 kg/s. The measured results showed that pressure drop in the type II BPHE was about 110 % higher than that in the type I BPHE. Nu of the type II was higher than that of the type I BPHE and the enhancement became larger with the increase of Re at the ranges above 800. New correlations for f F and Nu were proposed by this study and their prediction accuracy could be improved by considering the surface enlargement factor in the correlations. The performance evaluation of the two BPHEs was performed by (j/f 1/3 ) which represented the ratio of heat transfer and pressure drop performance. Also, a new parameter, the capacity compactness of PHE, was proposed and it presented the PHE capacity per unit volume and unit log mean temperature difference. The comparison showed that the two BPHEs had similar values of the (j/f 1/3 ), whereas they had significantly different values of the capacity compactness. The capacity compactness of the type II BPHE was 1.5 times higher than that for the type I BPHE.

Experimental Investigation of two-phase nitrogen Cryo transfer line

A 6-m long liquid nitrogen based cryo transfer line has been designed, developed and tested at IPR. The test objectives include the thermo-hydraulic characteristics of Cryo transfer line under single phase as well as two phase flow conditions. It is always easy in experimentation to investigate the thermo-hydraulic parameters in case of single phase flow of cryogen but it is real challenge when one deals with the two phase flow of cryogen due to availibity of mass flow measurements (direct) under two phase flow conditions. Established models have been reported in the literature where one of the well-known model of Lockhart-Martenelli relationship has been used to determine the value of quality at the outlet of Cryo transfer line. Under homogenous flow conditions, by taking the ratio of the single-phase pressure drop and the two-phase pressure drop, we estimated the quality at the outlet. Based on these equations, vapor quality at the outlet of the transfer line was predicted at different heat loads. Experimental rresults shown that from inlet to outlet, there is a considerable increment in the pressure drop and vapour quality of the outlet depending upon heat load and mass flow rate of nitrogen flowing through the line.

Experimental Study of Single-phase Pressure Drop Characteristics in Horizontal Internal Helical Finned Tubes

Due to the intense enhancement of the convective heat transfer, internal helical finned tubes are widely applied into the field of HVAC. An experimental setup was built for investigating single-phase flow characteristics of internal helical-rib roughness. The single-phase flow characteristics for water-ethylene glycol mixture in three internal finned tubes and a smooth tube were obtained. The nominal diameter of the two test tubes was 22.48mm and 16.662mm, the number of the fins was 60 and 38, the helix angle was 45 degrees and 60 degrees and the relative roughness was 0.022 and 0.053, respectively. The Prandtl number varied from 10.0 to 177 and the Reynolds number ranged from 185 to 40000. The friction factors were measured under the condition of thermal insulation. Experimental results showed that the smooth-tube results were compared to the Filonenko equation with satisfactory agreement. Transition for internal helical finned tubes occurred at lower Reynolds numbers than that of their smooth tube counterparts. The trend of the friction factor of the internal helical finned tube is remarkably different from that of plain tube in the transition regime. For Tube 2 and Tube 3, the flow turns into the fully turbulent flow at Re=14500, while Tube-4 at Re=9500, which is obviously different from that of the plain tube.

Experimental determination of single-phase pressure drop and heat transfer in a horizontal internal helically-finned tube

The single-phase pressure drop and heat transfer in an internal helically-finned tube and a plain tube are measured for aqueous ethylene glycol. Pressure drop data are collected under isothermal condition and heat transfer experiments are conducted in a flooded evaporator with R134a boiling outside the tube. The tests are performed with Prandtl number from 17 to 29 and Reynolds number from 5000 to 34,000. The main parameters of the internal helically-finned tube are nominal inside diameter (22.48mm), fin height to the tube inside diameter ratio (0.022), number of fins (60), helix angle (45°). It is found that plain tube’s results agree well with Filonenko and Gnielinski correlations. Friction factors of internal helically-finned tube increase with Re below 17,000, reaching a maximum at Recr=17,000 and decrease above 17,000. This indicates that the conventional criterion Re>10,000 for distinguishing turbulent flow isn’t suitable for internal helically-finned tubes. A correlation is developed to predict the experimental heat transfer coefficient within 5%. In evaluation of the thermal performance, the j-factor for internal helically-finned tube is about 3.5 times of that for the plain tube and the efficiency index varies from 1.8 to 1.55. This study offers the reference on engineering design and later study.

Steady state flow analysis of two-phase natural circulation in multiple parallel channel loop

In this work, steady state flow analysis has been carried out experimentally in order to estimate the liquid circulation velocities and two-phase pressure drop in air–water multichannel circulating loop. Experiments were performed in 15 channel circulating loop. Single phase and two-phase pressure drops in the channels have been measured experimentally and have been compared with theoretical model of Joshi et al. (1990). Experimental measurements show good agreement with model.

Pressure drop characteristics of vertically upward flow in inclined rod bundles

An experimental and theoretical research has been carried out for vertically upward two-phase flow of air–water across staggered rod bundles having inclination angles of 0°, 45° and 90°. New correlations for single-phase pressure drops in rod bundles for various inclination angles were developed. The single-phase frictional resistance in the vertical flow was found to have a minimal effect on the total flow resistance in the inclined flow. Based on the single-phase pressure drop data, a new superposition model was proposed and verified to be successful in predicting both the present data and the experimental data in previous experiments of other researchers. The two-phase friction multiplier in the inclined rod bundle, which decreased with increasing mass velocity at a given value of Martinelli parameter, could be fit well in terms of Martinelli parameter and the defined dimensionless mass velocity. In addition, the two-phase friction multiplier first increased and then decreased with increasing Martinelli parameter at a given value of mass velocity for G<200kgm−2s−1. The new correlations developed for two-phase friction multipliers were successful in predicting the two-phase pressure drop data in the inclined rod bundle.

Single phase heat transfer and pressure drop analysis of a dimpled enhanced tube

Thermal-hydraulic performance of an enhanced tube was evaluated using experimental and numerical simulation techniques in a pipe-in-pipe heat exchanger. Steady state single phase (liquid-to-liquid) experiments were performed to determine Nusselt number and friction factor. Experiments with water as working fluid were carried out in the Reynolds number range of (500 < Re < 8000), while for water/glycol solution based experiments the Reynolds number range was kept at (150 < Re < 2000). A non-dimensional performance evaluation criterion (PEC) was used to assess the thermal-hydraulic performance of heat transfer enhancement achieved with the enhanced tube. Based on the experimental data, Nusselt number and friction factor estimation correlations were proposed for the enhanced tube.Simulations were carried out to obtain heat transfer and pressure drop characteristics of smooth and enhanced tubes, using commercial CFD software, Fluent. Realizable k−ε model was employed to assess the influence of dimples on turbulent flow and velocity field. Simulation results showed that dimples disturb and mix boundary layers and generate secondary flows that improve turbulence level. Comparison between experimental and numerical simulation results showed good agreement as the data fell within ±10% error band.

Single-Phase Cryogenic Flow and Heat Transfer Through Microscale Pin Fin Heat Sinks

Single-phase heat transfer and pressure drop of liquid nitrogen in microscale heat sinks are studied experimentally in this paper. Effects of geometrical variations are characterized on the thermofluidic performance of staggered microscale pin fin heat sinks. Pitch-to-diameter ratio and aspect ratio of the micro pin fins are varied. The pin fins have square shape with 200 or 400 μm width and are oriented at 45 degrees to the flow direction. Thermal performance of the heat sinks is evaluated for Reynolds numbers (based on pin fin hydraulic diameter) from 108 to 570. Results are presented in a nondimensional form in terms of friction factor, Nusselt number, and Reynolds number and are compared with the predictions of existing correlations in the literature for micro pin fin heat sinks. Comparison of flow and heat transfer performance of the micro pin fin heat sinks reveals that at a particular critical Reynolds number of ∼250, pin fin heat sinks with the same aspect ratio but larger pitch ratio show a transition in both friction factor and Nusselt number. In order to better characterize this transition, visualization experiments were performed with the Fluorinert PF5060 using an infrared camera. At the critical Reynolds number, for the larger pitch ratio pin fin heat sink, surface thermal intensity profiles suggest periodic flapping of the flow behind the pin fins at a Strouhal number of 0.227.

On the scale-up of micro-reactors for liquid–liquid reactions

The scale-up of a micro-reactor with a mixer designed for liquid–liquid reactions is investigated using a 3/7th approach that scales the hydraulic diameter at increased flow rates and keeps constant the average rate of energy dissipation. Smaller (dh 283µm) and larger-scale (dh 714µm) mixers are compared using single phase pressure drop measurements and a liquid–liquid reactive extraction. The single phase tests demonstrate that the energy dissipation rate of the larger scale mixer is comparable to the smaller scale mixer at flow rates ~8.5 times greater. The overall volumetric mass transfer coefficients of the reactive extraction, Kca, of both scale mixers were also similar at equal energy dissipation rate in the drop flow regime. Finally, the upper limit of the sizing approach is discussed and compared with commercially available static mixers.

Transient pressure drop cross-correlation during flow boiling of R134a in parallel minichannels

This work examines the flow boiling of R134a in 0.54-mm square parallel minichannels with a particular focus on analyzing the transient pressure drop of individual channels in a wide range of heat and mass flux conditions. The flow rates are in the range from 0.1 to 0.51 g/s and heat fluxes are up to 18 kW/m2. Three different types of experiments are conducted, aiming to study the interaction between flow boiling phenomena in parallel minichannels based on the transient pressure drop measurements in each channel independently. Furthermore, cross-correlation analysis is undertaken to quantify the degree of interrelationship between neighboring minichannels. Flow boiling phenomena in a single, diabatic channel influences neighboring adiabatic channels by causing out-of-phase oscillations of single-phase pressure drops. The percentage of single-phase (ΔP) data correlated with two-phase ΔP data increases from 40% to 85% as the flow rate increases from 0.1 g/s to 0.5 g/s. Experiments with nonuniformly heated parallel minichannels show the presence of strong interaction between channels having the highest heat flux difference among a set of channels at a fixed total flow rate. As the flow rate increases and pressure drop across each channel increases, flow boiling behavior in each channel tends to be more independent from other channels. Therefore, less inter-channel interaction indicates better two-phase flow distribution between parallel minichannels, and the cross-correlation coefficient can be used as an indicator of the flow maldistribution.

Numerical Analyses of Single-Phase Pressure Drop and Forced Convective Heat Transfer Coefficient of Water-Ethanol Mixture: An Application in Cooling of HEV Battery Module

The present numerical analyses are related to the cooling of a hybrid electric vehicle (HEV) battery module by water–ethanol mixture. The fluid is passed through a cold plate consisting of two rectangular channels of 0.01 m depth, 0.015 m width, and 0.15 m length. The battery module is represented by a heater placed below the cold plate. The single-phase pressure drop and single-phase heat transfer coefficient for water, water–ethanol mixture of mass fraction of 25%, 50%, and 75%, and ethanol are determined numerically for different heat fluxes of 10, 15, 20, and 25 kW/m2 and different Reynolds numbers 500, 1000, 1500, 2000, and 2500. To solve the Navier–Stokes equation, the pressure correction method was used and to solve the energy equation, the Lax–Wendroff explicit method is used. Numerical results obtained for water are compared with the literature correlations. The friction factor for water deviated by an average of 8.02% from the Lewis and Robertson equation. The Nusselt number for water deviated by 7.35% from the Churchill and Ozoe equation at lower Reynolds number 500 and at higher Reynolds number 2500, Nusselt number deviated by 13.68% from the Stephan equation. The results showed that the heat transfer coefficient increased with an increase in Reynolds number and heat flux. The effect of the increase in Reynolds number is more significant than the increase in heat flux. At higher ethanol mass fraction and higher Reynolds number the heat transfer coefficient increased with heat flux when compared to water. There is no significant decrease in heat transfer coefficient with an increase in ethanol mass fraction. The pressure drop increased and the heat transfer coefficient decreased with an increase in ethanol mass fraction.

Evaluation of horizontal wellbore single-phase pressure drop models based on large-scale experiment

Abstract The prediction accuracy of the five horizontal wellbore single-phase drop models (Siwon, Asheim, Su, Yuan, Ouyang) is evaluated and compared based on the high-quality experimental data measured by a self-developed experimental system with large size horizontal wellbore (ID: 139.7 mm). The results show that the pressure drop prediction accuracy of the five models is, from high to low, Ouyang, Siwon, Asheim, Yuan, and Su. Generally, the Su and Yuan models have high predictions and the Siwon and Asheim model have low predictions. The Ouyang model has good prediction performance, its average relative error is only 5.5%, and the example also proves its good prediction effect, but it can't represent complex mechanisms such as the resistance effect caused by wall perforation. The models for predicting the pressure drop of single-phase flow in a horizontal wellbore need to be further improved to completely represent complex mechanisms of the variable mass flow in the horizontal wellbore, such as the resistance effect caused by wall perforation and lubrication flow drag reduction effect caused by wall influx.

Experimental and numerical study of single-phase pressure drop in downhole shut-in valve

In this work an experimental and numerical analysis of single-phase pressure drop in a downhole shut-in valve is performed. The main goal was to develop a 1D numerical model suitable for both compressible and incompressible flow. For the experimental study a mock-up of the shut-in valve was built and instrumented with pressure sensors and flowmeters. The pressure drop along the different sections of the valve were recorded for various flow rates using water, oil and air as working fluids. For the numerical analysis a two-step approach was used. First a commercial CFD package was used for 3D simulations of the flow, and different turbulence models were compared. Then a 1D model was developed based on a spectral element method, with minor loss factors derived from the CFD simulations. Both the 3D CFD simulations and the 1D model simulations provided a good comparison with the experimental data. The small difference in the simulation results can be attributed to the difference in the frictional coefficient which showed a discrepancy of about 20% compared with the measurements. Minor loss factors derived from CFD simulations of incompressible flow are found to be valid also for 1D simulation of compressible flow of air. The 1D model is developed for future simulation of compressible multiphase flow.