Fluid In Pipe Research Articles

Experimental and numerical study on thermal performances of a modular hydronic thermal barrier wall with heat injection system in filler cavities

The hydronic thermal barriers with dynamically adjustable thermal performance have become one of the highly anticipated solutions for opaque envelope insulation while improving the efficiency of the use of low-grade energy. In response to the technical constraints encountered by conventional hydronic thermal barrier walls (i.e., CHTBs) when it comes to enhancing heat transfer, the concept of modular hydronic thermal barrier walls (i.e., MHTBs) was introduced. The MHTB incorporates a heat injection system within its filler cavities, a feature designed to promote the overall thermal performance of the opaque enclosure structure. The performance enhancement described is mainly achieved through active management of the thermal conductivity of the filling material within the vicinity of fluid pipes. In this study, field thermal performance assessments were carried out during winter conditions in three reduced-scale experimental rooms. The southern boundary of these test rooms adopts walls with different configurations, i.e., MHTB, CHTB, and traditional thermal insulation wall. Subsequently, a comprehensive investigation regarding the impacts of filling materials on the energy performances of MHTB was conducted through numerical simulations. The outcomes demonstrated a substantial reduction in heat loss through the south wall by using MHTB, leading to reduced room thermal discomfort. In particular, with a charging temperature set at 35.0 °C, the inner surface temperature of MHTB displayed a noteworthy increase of 10.3 °C compared to that of the traditional thermal insulation wall, resulting in a significant reduction in heat load by a factor of 7.4. Additionally, it was observed that the filler material within the pipe cavity played a vital role in shaping MHTB's thermal performance. For instance, considering the case with a heat injection temperature of 25.0 °C, a doubling of thermal conductivity resulted in an enhancement of 0.24 W/m2 in heat gain on the outer surface and an overall increase of 0.04 MJ in total injected heat. This study demonstrated the positive effect of MHTB on optimizing the efficiency of hydronic thermal barriers and guided their further application and research.

Effect of the heat flow distribution and thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble

A novel non-intrusive thermal diffusion measurement (TDM) method has been proposed for measuring the phase flowrates of gas–liquid slug flows in our previous research. Since the structure of TDM was arbitrarily designed and needed to be optimized for accurate measurement, the effect of the heat flow distribution and the thermophysical properties of the pipe wall and fluid on the wall temperature response to a rising Taylor bubble (TB) is further investigated by using the CFD tool in this paper. The wall temperature and temperature rise are used to describe the wall temperature response, and their variation rules with heat flow distribution and the thermophysical properties of the pipe wall and fluid are presented and analyzed based on heat transfer. The simulation results indicate that the optimal heating length for a large wall temperature rise and small power consumption is 0.6D, and the optimal pipe material should be with small density and specific heat and a suitable thermal conductivity of about 15 W/(m·K). Moreover, the wall temperature response is obvious, especially for TBs moving in the liquid with large fluid thermal conductivity, density, and specific heat, and small viscosity. The paper can clarify the wall temperature response mechanism of the heated pipe wall and provide a theoretical basis for the development of the TDM method.

Fast Meshless Solution With Lumped Friction for Laminar Fluid Transients

Abstract Fluid transients without friction in pipelines can be solved by a time-domain exact solution, using a simple recursive process without computational grid. However, the calculation time cost of this approach is very high because of the recursion algorithm. Its improved method, named as the fast meshless solution (FMS), was developed to speed up the computation by introducing time-line interpolation. However, when the friction is considered, the conventional distributed friction model cannot be employed directly for the FMS is meshless. To address this problem, the fluid friction is lumped at pipe ends, and both steady and unsteady laminar flow are investigated. Three kinds of lumped models are proposed here, and compared with a numerical case of the water hammer. The laminar fluid transients can be calculated quickly by the present method, with a little reduced accuracy. This method may be of interest in a quick assessment of the piping fluid transients.

Real Time Measurement of Multiphase Flow Velocity using Electrical Capacitance Tomography

Accurate and real-time measurement of fluid flow velocity is crucial in various industrial processes, especially when dealing with multiple phase fluids. Traditional flow measurement methods often struggle to accurately quantify the velocity of complex multiphase flows within pipes. This challenge necessitates the exploration of innovative techniques capable of providing reliable measurements. This paper proposes the utilization of Electrical Capacitance Tomography (ECT) as a promising approach for measuring the velocity of multiple phase fluids in pipes. The ECT technique involves the non-intrusive imaging of the electrical capacitance distribution within the pipe. By utilizing an array of electrodes placed around the pipe circumference, the capacitance distribution can be reconstructed, offering insight into the fluid flow patterns. By analyzing the temporal changes in the capacitance distribution, the velocity of different phases within the pipe can be estimated. To achieve accurate velocity measurements, an ECT system needs to account for the complexities introduced by multiphase flows. Various image reconstruction algorithms, such as linear back-projection and iterative algorithms like Gauss-Newton and Levenberg-Marquardt, are employed to reconstruct the capacitance distribution. Additionally, advanced signal processing techniques, such as cross-correlation analysis and time-difference methods, are used to extract velocity information from the reconstructed images. This paper presents an experimental investigation of measuring the velocity of multiple-phase fluids in pipes using the ECT technique. The study aims to address the challenges associated with different flow regimes, fluid properties, and pipe geometries by exploring advancements in electrode design, system calibration, and data processing techniques to enhance the accuracy and robustness of ECT-based velocity measurements.

The role of Cheeger sets in the steady flows of viscoplastic fluids in pipes: A survey

Given a convex or a Jordan domain Ω, let Ω′ be a subset of this domain, with P(Ω′) denoting its perimeter and A(Ω′) its area. If a subset Ωc exists such that h=P(Ωc)/A(Ωc) is a minimum, the subset Ωc is called the Cheeger set of Ω and h, the Cheeger constant of the given domain. If one considers the reciprocal of this minimum or the maximum ratio of the area of the subset to its perimeter, t∗=1/h. It follows from the work of Mosolov and Miasnikov that the minimum pressure gradient G to sustain the steady flow of a viscoplastic fluid in a pipe, with a cross section defined by Ω, is given by G>τy/t∗, where τy is the constant yield stress of the fluid. In this survey, we summarize several results to determine the constant h when the given domain is self-Cheeger or a Cheeger-regular set that touches each boundary of a convex polygon and when the Cheeger-irregular set does not do so. The determination of the constant h for an arbitrary ellipse, a strip, and a region with no necks is also mentioned.

Use of geothermal energy to prevent road pavement icing and damage in cold climate areas

In cold climate or alpine regions, freezing temperatures and snow can result into road icing, with consequent threat of the circulation security (Figure 1(a)). When the road surface temperature goes below zero, not only the road surface ices, but also the soil below the pavement can undergo freezing. The phenomenon of soil freezing is complex due to the multi-phase and porous nature of the soil itself. Generally speaking, as ice expands in the soil pores, the soil volume increases (of about 9%, depending on the soil porosity and water saturation). This can induce frost heaving, with consequent damage of the road pavement. In this framework, the possibility to use geothermal energy systems embedded in tunnel linings for road pavement de-icing has rarely been investigated. In such systems, the concrete tunnel lining is equipped with a circuit of pipes, in which a heat carrier fluid circulates and exchanges heat with the ground. As the rock or soil around the tunnel is generally hotter than the external air temperature, heat is extracted from the rock or soil to the fluid, transported through the pipes circuit outside the tunnel, and used to de-ice the pavement road.
 The objective of this study is to go a step forward in the investigation of this innovative application, for both road de-icing and prevention of frost heave. A portion of a geothermally activated tunnel and its connection to a road pipe circuit was simulated numerically (Figure 1 (b)). Appropriate climatic conditions were considered as boundary conditions at the surface level and inside the tunnel, according to available data. The efficiency of the technology was investigated under different climatic and exploitation scenarios. Figure 1 (c) shows as an example the thermal field obtained after the activation of the geothermal plant. The evolution of temperature on the road pavement surface and at the road pipes depth (30 cm from the road pavement surface) are presented on Figure 2 (a), together with the evolution of the external air and tunnel temperature, imposed as boundary conditions according to the monitored climatic conditions in the city of Oslo [1].
 The geothermal system was activated after two years of simulation, by changing the fluid pipes velocity from 0 (non active system) to 0.9 m/s (purple curve on the right axis on Figure 2 (a)). The results show that the road temperature increases thanks to the activation of the system (i.e. when the fluid pipes velocity is imposed to 0.9 m/s).
 Furthermore, a recently developed thermo-hydro-mechanical constitutive model for frozen soils [2] was used to quantify the soil heave due to freezing, with and without the activation of the geothermal system. For this purpose, a similar numerical model has been developped where a column of saturated soil below the road and the tunnel were modelled. The phreatic water table is at the ground surface level and gravity as well as the geostatic stress conditions are considered. The soil is a clay with a low hydraulic conductivity of Kw=4.1×10-10 m/s and a thermal conductivity of Γ=2.35 W/m/K. The other soil properties are: soil stiffness E=100 MPa, Poisson’s ratio ν=0.3, porosity n=0.25, solid grain thermal volumetric expansion coefficient αs=3.4×10-4 K-1. The same soil surface climatic conditions used in the first part were applied. The temperature evolution obtained in the road from the previously mentioned analyses (Figure 2 (a)) was imposed to reproduce the effect of the geothermal activation on the road behaviour. Furthermore, the soil surface is free of stress to study the soil swelling and settlement. The bottom limit of the soil column is hydraulically drained and allows heat flux (at constant liquid pressure and temperature). The lateral far field boundaries are thermally adiabatic, hydraulically impervious, and with oedometric conditions. The results were firstly compared with the case without geothermal activation to quantify the effects in terms of road heave and settlement (Figure 2 (b)). Swelling and settlement are due to thermal expansion and compression of the soil under positive temperature (T>0°C) and to frost heave and thaw settlement under negative temperature (T<0°C). The liquid pressure at the road surface is also depicted (Figure 2 (b)). These results and comparisions allowed understanding the performance of the technology in reducing road mechanical damage induced by freezing.

Comparative study of the accuracy of friction factor correlations developed for flow of inelastic yield power-law fluids in pipes

An extensive review of the friction factor correlations used for pressure loss prediction of yield power-law (YPL) fluid flow in pipes has been conducted, and the results are summarized in this paper.A comparative study was also conducted to determine the predictive performances of various laminar and turbulent friction factor models developed for YPL fluid flow in pipes. Model predictions of frictional pressure losses were validated by comparing them with the experimentally measured pressure drop data obtained from the flow of several YPL fluids in pipes.Investigations were further extended to determine the impact of the variation of YPL fluid rheological characteristics (resulting from using different rheological characterization methods) on the pressure drop predictions.A wide range of generalized Reynolds numbers (i.e., 20 to 9000, as defined by the API-RP:13D) in a pipe flow configuration was considered in the analyses. The yield stress of the test fluids (determined by using the nonlinear curve fitting technique recommended by the API RP:13D) varied from 0.10 to 0.95 Pa.The results indicated that Hanks and Ricks' model predicted the pressure drop of YPL fluid flow in pipes better than any other models, both in laminar and turbulent flow regimes, matching the experimental data within a ±10% error range.Variations of the YPL model parameters (resulting from using different rheological characterization methods) significantly impacted the pressure drop predictions. Using YPL model parameters obtained from the non-iterative dual power law (DPL) approximation method (as recommended by API-RP:13D) and Hanks and Ricks' model yielded the most accurate pressure drop predictions for the pipe flow of YPL fluids.

Local instantaneous heat transfer characteristics around a rising single Taylor bubble and the temperature response of relatively thick pipe wall under local constant heat flux

A novel non-intrusive thermal diffusion measurement (TDM) method is proposed to measure the flow rate of gas–liquid two-phase flows under the slug flow state in our previous research. To improve the measurement accuracy of TDM by clarifying the real-time correspondence between wall temperature change and Taylor bubble (TB) location, the local instantaneous heat transfer characteristics around a rising single TB and the corresponding temperature response of the pipe wall are further investigated in detail by using the CFD tool in this paper. During the passage of TB, the local heat transfer between the pipe wall and fluid was analyzed based on the dynamic velocity field and temperature boundary layer, and the temperature on the fluid–solid interface presents the opposite trend with the heat transfer coefficient. For the zone upstream of the heat flux center, the lag time and increase of the wall temperature become large and weak along the radial direction, respectively, whereas the lag time is independent of the axial location, TB velocity, and TB length. Meanwhile, the increase in wall temperature shows an upward trend with the TB length for short TBs but is the same for long TBs.

(Invited) The Evolution of Membrane Electrochemical Cell Stacks and Balance of Plant Integration with Increasing Product Scale and Manufacturing Volume Ramp up

As PEM and similar electrochemical devices get further scaled to meet the growing demand for renewable hydrogen solutions, the real-world design elements of electrochemical cell to balance of plant integration are key factors in the timeline for product development and manufacturing volume increases, for the system performance, and for the overall cost of hydrogen. The optimization of both cell components such as porous transport layers and bipolar plates, as well as system components such as AC-DC rectifiers for real devices need to consider and incorporate the existing volume and size constraints within the supply chain. Form factors of cells, number of cells per stack, number of stacks per plant and the corresponding layout of rectifiers, fluid pipes, and phase separators are considerations for optimization in product stack and system design. As the scale of product manufacturing and the scale of individual building blocks increases, the balance of these trades will evolve over time, requiring flexibility in design approaches to meet near term plants in the 10-MW class and medium-term plants in the 100-MW class. The discussion of these inter-relationships will explain how this evolution has proceeded to date and evaluate the impact of decisions made today on future product roll-out.

On Exact Solutions to Problems of Steady Flow of Incompressible Viscous Fluid in a Channel and in a Circular Pipe

Turning to the well-known Couette flow, we again, but now in a new formulation, consider the steady motion of an incompressible viscous fluid in a channel with two parallel flat walls, one of which is stationary while the other moves at a constant speed in its plane. In the classical formulation of this problem on a layered (laminar) fluid flow in a channel, the wall velocity and the constant pressure drop along the channel are independent quantities and are considered predetermined. However, when a solid body moves along the fluid surface, the fluid particles are set in motion. This occurs due to the arising pressure generated in the fluid caused by the movement of the solid body. Therefore, here the pressure or pressure drop is not predetermined but is determined as a result of solving the corresponding two-dimensional boundary value problem of a steady flow of a viscous fluid in a channel. For this, the corresponding boundary value problem of a fluid flow in the channel is formulated based on the linearized Navier-Stokes equations obtained from the general nonlinear Navier-Stokes equations for a steady flow of a viscous fluid neglecting the convective terms, which is true for small Reynolds numbers. Using the Fourier integral transform method, an exact (closed) solution to this boundary value problem is constructed; the velocity and pressure components are determined. Then it is shown that the resulting solution, different from the known Couette flow solution, also satisfies the original nonlinear Navier-Stokes equations, the continuity equation, and boundary conditions. A comparative analysis of the new solution with the Couette flow solution is carried out. The well-known Hagen-Poiseuille problem is also discussed from the point of view of establishing the conditions for the laminar axisymmetric and steady flow of an incompressible viscous fluid in a straight circular pipe According to the study's results, to implement laminar flow under the indicated conditions, the pressure drop along the pipe must be constant. The study demonstrates that this condition is simultaneously sufficient, and therefore, the necessary and sufficient condition is established for a laminar flow in a straight circular pipe.

Heat transfer and entropy optimization for unsteady MHD Casson fluid flow through a porous cylinder: Applications in nuclear reactors

Heat transfer and entropy generation are crucial considerations in the nuclear industry, where the safe and efficient transfer of heat is essential for the operation of nuclear reactors and other nuclear systems. Casson fluid is a useful tool in the nuclear industry for simulating the flow behavior of nuclear fuels and coolants, and for optimizing the design and operation of nuclear reactors. In view of this, the current investigation deals with the heat and fluid flow of unsteady Casson fluid in a circular pipe under the influence of magnetic field, internal heat generation, entropy generation and porous media. The governing equations have been simplified under suitable assumptions and nondimensional quantities. The simplified dimensionless governing equations have been solved using the method of separation of variables along with Bessel functions. It is concluded from the investigation that the temperature increases with time. The Casson fluid parameter raises the temperature and entropy generation. The temperature, entropy generation and Bejan number are the decreasing functions of the Prandtl number.

The simulation of non-stationary gas pressure in a pipeline with pumping and injection

In this work, based on the fundamental research of I. A. Charny on the unsteady movement of a real fluid in pipes, an equation that describes the pressure dynamics in a complex section of a gas pipeline was compiled. The use of the Dirac impulse function made it possible to describe the dynamics of unsteady pressure in a single equation in the case of point pumping and injection at given points. Linearization of the model by averaging the velocity of the gas made it possible to bring the equation to a hyperbolic form. If we neglect the forces of inertia compared to the forces of resistance, then the mathematical model will represent a partial differential equation of the second order parabolic type. The dynamics of pressure at specific points of pumping and injection under boundary conditions of the second kind (rates are given) was obtained using the finite cosine Fourier transform. The working formula that allows you to determine the pressure at any point at a given point in time is a trigonometric series. The series are rapidly convergent, so there is no difficulty in working with them. Particular cases are considered (without pumping and injection). The fulfillment of the boundary conditions is checked. It is easy to rebuild the working formula for pumping and / or injection at several points in a given area. Calculations of the mass flow and average velocity are made. In practice, the pressure is usually set at the start and end points of the area under study. In this case, it becomes possible to go to the costs (to derivatives) at the ends of the section under consideration.

Entrance length estimates for flows of power-law fluids in pipes and channels

Entrance length estimates for flows of power-law fluids in pipes and channels

EXPERIMENTAL AND NUMERICAL RESEARCH IN THE FLEXIBLE PIPES OF COIL TUBING INSTALLATIONS TAKING INTO ACCOUNT THE RHEOLOGY OF THE TECHNOLOGICAL FLUID

The current direction of the country's economic development is an intensive increase in hydrocarbon production on the territory of Ukraine, the introduction of new modern technologies and an increase in the efficiency of power equipment. One of the modern directions used in the oil and gas industry is the use of specialized equipment for coiled tubing units. Also, with the development of well drilling and oil production intensification technologies, modern multicomponent flushing (process) waters appear. The need for polymers is based on their ability to influence the properties of aqueous and hydrocarbon systems and form gels of different density, viscosity and rheology. Polymer systems are widely used due to their high cleaning, transporting and holding properties. Widely known polymer systems of technological solutions based on Xanthan Gum. Generalized information about the rheological parameters of fluids used to intensify the work of oil and gas wells is considered. The main rheological indicators of the studied liquid are the shear stress and the strain rate of the medium. These indicators are determined using an OFITE 900 rotational viscometer. The results of experimental studies of the properties of an aqueous solution with different concentrations of Xanthan gum from 0.6 to 8 g/l are presented. The study showed that an aqueous solution of gum creates a non-Newtonian behavior of the liquid. The coefficients of the rheological model of the solution were obtained by approximation of laboratory data. To simulate the hydrodynamic characteristics of a polymer system, a nonlinear viscous fluid model and a model with the introduction of effective viscosity are used. The results of studies of rheology indicators are used to determine the fluid flow regime, predict the hydraulic resistance coefficients in pipes and the energy characteristics of pumping equipment for supplying process fluid to the well. Experimental and calculated dependences of the influence of polymer additives on the resistance to the movement of liquids in coiled tubing of a coiled tubing unit are presented. The analysis of experimental and numerous hydrodynamic studies has been carried out. For numerical simulation of the hydrodynamics of non-Newtonian behavior of fluid in pipes, the open integrated platform OpenFOAM is used.

Operating flow rate prediction of H4 condition in NPP

In this study, we present a method to predict the working volume flow rate of H4 conditions in nuclear power plants. The working flow rate can be predicted using the intersection points of the two curves on a hydraulic characteristic diagram using the quantitative relationship between fluid flow and pipe resistance under the turbulence model and the hydraulic performance characteristics of the hydraulic equipment. The H4 condition volume flow rate of a power plant is predicted in this research using this method. The findings demonstrate that the method can substitute the actual H4 working condition test to lower operating costs while having high accuracy and little deviation. This approach can be usefully expanded to cover more comparable circumstances.

Evolution of microstructure, microhardness and surface roughness of Al alloy thin-walled tube during flaring process

Flaring forming has been widely utilized in connecting tubes, fluid pipe circuit components and flight fairings. Surface quality of the flared inner wall significantly affects the connection properties and service reliability. However, the surface microstructure, hardness and roughness of flared thin-walled tubes have long lacked corresponding characterization and correlation analysis. In the present study, wear mechanism of a 5052 Al alloy flared tube is analyzed based on multi-scale characterization. Furthermore, the impact of flaring process parameters including spindle speed, feed rate and holding time on the surface roughness is investigated by considering the evolution of microstructure and microhardness. The results reveal that adhesive wear is the main wear mechanism in the flared tube, accompanied by a small amount of abrasive wear. The effect of process parameters on dynamic recrystallization (DRX) and grain orientation are also analyzed in detail. Based on ANOVA analysis, the spindle speed is found as the most crucial controllable parameter affecting the surface roughness. The feed rate is the second important parameter, while the holding time is found to be insignificant. Simulation and experimental results indicate that with the increase of strain, surface roughness first increases and then decreases. This non-monotonic trend is associated with the evolution of strain (strain rate, strain path, etc.) and microstructure (DRX, texture, hardening, etc.).

A critical review on renewable battery thermal management system using heat pipes.

The critical review presented here exclusively covers the studies on battery thermal management systems (BTMSs), which utilize heat pipes of different structural designs and operating parameters as a cooling medium. The review paper is divided into five major parts, and each part addresses the role of heat pipes in BTMS categorically. Experimental studies, numerical analyses, combined experimental and numerical investigations, optimum utilization of a phase-change material (PCM) with a heat pipe (HP), oscillating heat pipe (OHP), and micro heat pipes combined with PCM for Li-ion BTMS using heat pipes are presented. The usage of HP's and PCM can keep the temperature of the battery system in the desirable limit for a longer duration compared to other traditional and passive methods. More emphasis is made on how one can achieve a suitable cooling system design and structure, which may tend to enhance the energy density of the batteries, improve thermal performance at maximum and minimum temperature range. Arrangement of battery cells in a pack or module, type of cooling fluid used, heat pipe configuration, type of PCM used, working fluid in a heat pipe, and surrounding environmental conditions are reviewed. According to the study, the battery's effectiveness is significantly influenced by temperature. The usage of flat HPs and heat sink proves to be the best cooling method for keeping the battery working temperature below 50°C and reduces the heat sink thermal resistance by 30%. With an intake temperature of 25°C and a discharge rate of 1 L per minute, an HP that uses water as a coolant is also effective at regulating battery cell temperature and maintaining it below the permissible 55°C range. Using beeswax as a PCM in HPs reduces the temperature of BTMS by up to 26.62°C, while the usage of RT44 in HPs reduces the temperature of BTMS by 33.42°C. The use of fins along with copper spreaders drastically decreases the temperature capability of HPTMS by 11°C. MHPA shows excellent performance in controlling the battery temperature within 40°C. The effective thermal management can be done by incorporating heat pipe alone or by coupling with liquid cooling or metal plate. However, extensive and extended research is required to improve thermal management to safely and effectively use the battery for day-to-day applications.

Study on Heat Transfer Design of Green Energy-saving Heating Pipe

To design a green energy-saving heating pipe, this paper studied the structural transformation of the heating pipe and carried out the effect simulation analysis. The key is to add an impeller device inside the ordinary heating pipe to convert part of the kinetic energy of the fluid in the heating pipe into the mechanical energy of the impeller. The energy generated by the rotation of the impeller can be transferred through gears, connecting rods, and other components and converted into heat energy for recovery in the boiler room to achieve the reheating effect. This design model is mainly used by Solid works and then imported into ANSYSF Fluent for numerical simulation to analyze and study the fluid around the impeller. The result showed that the flow velocity of the fluid around the impeller was reduced, and the local resistance loss was negligible. Meanwhile, part of the kinetic energy of the fluid has been converted into the mechanical energy of the impeller, effectively realizing energy saving.

Experimentation on Fabrication of Double Pipe Heat Exchanger

Abstract: A heat exchanger is a piece of equipment designed to transfer heat from one medium to another efficiently. It relies on the conduction, convection, and radiation principles with fluids flowing against one another. There are many other forms of heat exchange, but we choose the double pipe heat exchanger since it has two pipes (outer pipe with cold fluid and inner pipe with hot fluid). The goal is to maximize the rate of heat transfer while monitoring the mass flow rates of the two fluids. In order to achieve this, we placed washers between the outer and inner pipes at a certain distance, which would lower the speed of the cold fluid and increase the efficiency of the heat transfer rate. They are extensively utilized in power plants, chemical and petrochemical facilities, oil refineries, sewage treatment facilities, air conditioning, refrigeration, and space heating systems. A heat exchanger is most commonly seen in internal combustion engines, where engine coolant circulates through radiator coils as air passes by, cooling the coolant and heating the incoming air.

Slug flows of gas and shear-thinning fluids in horizontal pipes

Experiments on slug flow are carried out with air and three solutions of carboxymethylcellulose (CMC)(0.05, 0.1 and 0.2% w/w) in a 44.2 mm ID horizontal pipe. The lengths, velocities and frequency of passage of the large bubbles are obtained through a high-speed digital camera. The gas fraction and length of liquid slugs are also estimated. Pressure changes along the pipe are measured with a differential pressure transducer. Particle Image Velocimetry is used to obtain the mean velocity of the continuous liquid field in the film and slug regions. The combination of tested gas and liquid superficial velocities and of distinct fluid rheology results in 48 different experimental conditions. The flow behavior is found to be strongly dependent on the rheological properties of the continuous phase. In particular, the gas volume fraction within the liquid slug (α=1−Rs), the passage frequency of the large bubbles (νt) and the pressure changes are increased. New expressions are proposed for α and νt to account for the rheology of the liquid phase. Predictions of the flow parameters obtained through two modified mechanistic models are compared with the experimental data. The friction coefficient expression proposed by Anbarlooei et al. (Phys. Rev. E, 92(6), 5–9, 2015) is also tested. The impact of the proposed modifications on the calculated properties of slug flow is assessed; typical RMS-errors of less than 15% are obtained for parameter predictions.