Pressure Drop Coefficient Research Articles

Two-phase flow, pressure drop, and Joule-Thomson effect in a micro-orifice with trans critical carbon dioxide flow

Two-phase flow, pressure drop, and Joule-Thomson coefficient (JTh) of sub- and super- critical carbon dioxide expanding through a 81 µm orifice embedded inside a 300 µm microchannel was experimentally studied. It was demonstrated and validated that a flow of CO2 in a micro-orifice can support the thermodynamic conditions that are ripe for the JTh effect to be significant. The inlet pressure, temperature, and mass flux were independently varied between 5.6 MPa and 10.2 MPa, 293 K and 314 K, and 47,277 kg/m2s and 162,101 kg/m2s, respectively. The measured pressure drop and Joule-Thomson coefficient ranged from 0.1 MPa to 5 MPa and from 0 K/MPa to 10 K/MPa, respectively. Pressure drop results were compared with the homogenous two-phase flow model, the separated two-phase flow model, the capillary tube model, and an empirical fit equation that resulted in mean average errors of 0.84 MPa, 1.4 MPa, 0.7 MPa, and 0.75 MPa, respectively.

Experimental investigation of critical heat flux, pressure drop and heat transfer coefficient for the flow boiling in a horizontal lobed channel with R-123

ABSTRACT The current study investigates the distribution of local heat transfer coefficient, measurement of pressure loss and CHF in a lobed horizontal channel for flow boiling. Lobed channels with different lobed depths of 2.3, 2.0 and 1.25 mm, each having three different channel lengths (400, 600, and 1000 mm), are used for the experiments. The working substance used is R-123 with different mass flux. The heat flux range used is from 14 to 375 kW/m2. Pressure drop, critical heat flux, and local heat transfer coefficients of the lobed channel are compared with corresponding smooth horizontal tubes.

CFD analysis andheat transfer characteristics of printed circuit heat exchanger

This paper aims to investigate the cubical fins and the thermal-hydraulic characteristics in a Printed Circuit Heat Exchanger (PCHE). The working fluid is considered a supercritical LNG. The outcomes show that the thermal-hydraulic performance is enhanced using the cubical fins comparing it to the straight channel. The maximum and minimum difference of N_u/E_u between the cubical fins channel and the straight channel were 71.7 % and 64.8 % respectively. It is noticed that the pressure drop and Heat Transfer coefficient are increasedsimultaneously with increasing the mass flux.Using Ansys Fluent 15.0, numerical optimization isperformed to examine and analyzethe influence of the sparser staggered arrangement. The computed results show that this type of arrangement improves the thermal-hydraulic efficiency of the cubical fins in a PCHE. A comparison between the straight fins arrangement and the staggered fins arrangement is reported.It has been noticed that the velocity of the LNG flow in the cubical fins channel is increased along the length of the PCHE,and decreased byincreasing the vertical separationL_V. The side effect of the vertical separation L_V on the PCHE’s efficiency was more evident than that of the staggered arrangementL_S. Finally, afeasibility study is performed to inspect the power consumption of the new design.

Study on the flow and heat transfer characteristics of liquid sodium in a hexagonal 7-rod bundle

The flow and heat transfer characteristics of liquid metal sodium are different from the ordinary fluids, which brings great challenges to the CFD simulation in the sodium-cooled fast reactor (SFR). Therefore, the accurate flow and heat transfer models are particularly significant in the high fidelity three dimensional analysis of liquid metal reactors. In this paper, the OpenFOAM solver implemented with k – ε – kθ – εθ turbulent heat transfer model was developed and used to study the flow and heat transfer characteristics of liquid metal sodium. Firstly, the proposed thermal hydraulic models were validated against the thermal hydraulic experiment of single-phase liquid sodium in a 7-rod bundle. The key thermal hydraulic parameters, such as the Nusselt number, pressure drop and frictional coefficient, were compared with the experimental data. Results show that the developed OpenFOAM solver with new implemented model performs well and the simulated results were in good agreement with the experimental data. Then the thermal–hydraulic characteristics of liquid sodium in the bend rod bundle were investigated. The effects of bending angle, Reynolds number on peak wall temperature and Nusselt number were investigated. CFD results suggest that the heat transfer in the bend rod bundle is highly sensitive to the bending angle but not to Reynolds number. Two opposite-direction cross flows were formed in the sections before and after the maximum bend position, which reveals the formation and disappearance of hot spot in the narrow gap.

Experimental and Numerical Study on the Hydraulic Characteristics of an S-Type Bidirectional Shaft Tubular Pump

In order to study the characteristics of a bidirectional shaft tubular pump with S-type symmetric airfoil blades, a prototype model was designed, manufactured, and tested. The energy characteristics, cavitation characteristics, and runaway characteristics of the pump were obtained under forward and reverse operating conditions for five different blade angles. Based on the basic equations of the pump and the inlet and outlet velocity triangles, combined with model tests and numerical simulations, the hydraulic performance of the pump was extensively analyzed and evaluated. In addition, semi-empirical equations for reverse efficiency and runaway characteristics were proposed. The dynamic pressure-drop coefficients were introduced to compare the cavitation performance under different flow rates in forward and reverse operations. The results reveal that the efficiency of the pump in reverse operation is greater than that of forward operation only under a very small flow rate. While the cavitation performance of the bidirectional pump in the two operating modes is almost the same, the runaway speed and backflow rate in forward operation are considerably greater than those of reverse operation. The results provide an important reference for the safe and stable operation of bidirectional shaft tubular pumps.

Performance analysis of double-stage perforated plate flowmeter for cryogenic fluids

In this paper, a novel flowmeter with a double-stage perforated plate structure is proposed, and its pressure drop and flow coefficient are numerically compared with the commonly used single-stage perforated plate structure for the cryogenic fluid measurement. The numerical calculations are based on the Realizable k-ε turbulence model and consider the influence of cavitation with thermal effects, which is validated by modeling the cavitating flow of liquid nitrogen over the hydrofoil in the publications. The influence characteristics of the thickness of the single-stage perforated plate on the performance are firstly clarified. Then the emphases are focused on the analysis of the effects of the gap of the double-stage perforated plates on the discharge coefficient, the pressure loss coefficient and the deviation coefficient. The results reveal that compared with the single-stage perforated plate, the double-stage one with the optimized gap has a smaller pressure drop and more horizontal flow coefficient profile with the Re number. The reason for the performance improvement is primarily ascribed to the “thickness effect”, which is explained in detail. While, the increase in the number of stages makes the cavitation more likely to occur, which leads to a smaller Re range of the horizontal flow coefficient profile. The results can be used as a useful reference for the design of the cryogenic differential pressure flowmeter.

Three-dimensional tunnel face stability considering slurry pressure transfer mechanisms

In slurry-shield tunneling, the bentonite slurry tends to infiltrate into the soil skeleton ahead of the tunnel face, causing a forward seepage flow associated with excess pore pressures in the ground. Both the slurry infiltration and the forward seepage flow significantly impact the tunnel face stability. In the present paper, a kinematic approach of limit analysis with the classical three-dimensional discretized rotational failure mechanism is employed to assess the face stability of a slurry-shield-driven tunnel. Three situations of slurry infiltrations that influence the face pressure transfer mechanisms were considered: a full filter cake, a penetration zone, and pure groundwater flow without a filter cake or a penetration zone. The pore pressure distributions surrounding the tunnel face were firstly obtained using numerical calculations. Afterward, the incorporation of numerically obtained pore pressure distributions into the work rate calculations allows considering a three-dimensional forward seepage flow ahead of the tunnel face, which provides a rigorous upper-bound estimation to the tunnel face safety factor determined by the strength reduction technique. The proposed method is validated by comparing the calculated results with those provided by previously published literature. The effects of excess slurry pressures, hydraulic conditions, pressure drop coefficients, and soil shear strength were investigated. Several design charts are given for practical application.

Numerical simulation of two-phase flow in a multi-gas channel of a proton exchange membrane fuel cell

Understanding the two-phase distribution characteristics within the multi-gas channel of a fuel cell is important for improving fuel cell performance. In the paper, the volume of fluid model is used to predict the dynamic behaviour of water in the multi-gas channel, analyze the pressure drop, velocity distribution, and flow resistance coefficient between different channels, and investigate the influence of operating conditions, surface wettability and channel structure on the two-phase distribution characteristics in the channel. The results show that water undergoes the processes of growth, separation, single droplet transport, wall impact, droplet collision, liquid film formation, and liquid film transport in the multi-gas channel. Inlet velocity and surface wettability significantly affect the pressure drop, water saturation, and surface water coverage. As the inlet velocity and gas diffusion layer surface wettability increase, the flow resistance coefficient and unevenness of the distribution decrease, indicating that the in-channel flow distribution homogeneity is enhanced. The rectangular channel has better water removal and flow distribution uniformity than the tapered channel, and the unevenness of distribution decreases significantly with decreasing rectangular width, from 0.15715 to 0.00315. The research work is a guide to understanding water transport in multi-gas channels, accelerating water removal, and improving inter-channel flow distribution uniformity.

Open-cell aluminum foams with bimodal pore size distributions for emerging thermal management applications

Recent advances in cellular materials for active thermal management applications involve the integral design of their porous structure. In this work, open-cell aluminum foams with porosities in the range of 0.60–0.76 are developed, containing pores with spherical geometry and a bimodal pore size distribution. The fabrication strategy involves the use of the replication method by infiltration with liquid aluminum of porous preforms formed by packing NaCl spheres of two largely different sizes (7 mm and 1 mm average diameter), which are then removed by water dissolution. The paper describes cellular materials with different proportions of coarse and fine pores. Their detailed characterization by pore volume fraction, pressure drop, permeability, thermal conductivity and heat transfer coefficient is supported by analytical schemes. In addition, these materials were characterized under realistic operating conditions using computational fluid dynamics simulations. The material with 67 percent coarse pores and 33 percent fine pores, which has the highest porosity (and thus permeability), has the most appealing heat dissipation properties with the lowest pressure drops, making it an excellent candidate for emerging thermal management applications in electronic systems.

Numerical analysis and artificial neural network-based prediction of two-phase flow pressure drop of refrigerants in T-junction

The two-phase flow behaviors in T-junction are quite complex in energy transport systems. In this paper, the two-phase flow pressure drop of refrigerants in a horizontal branching T-junction was analyzed numerically and predicted using artificial neural network. Firstly, the distribution of static and total pressure was obtained based on Eulerian method, and the parametric studies on the local pressure drop were conducted. It is observed that the vortexes in the entrance of branch pipe lead to the pressure fluctuation and irreversible pressure losses, and the “descend-ascend” of static and total pressure happens under high mass flow split ratio in run pipe. Then, the ANN predicting model of local pressure drop coefficients was established. It shows that GA-BPNN and PSO-BPNN has the best predicting ability for K12J and K13J respectively, and the relative errors are within 10% for most cases. Finally, the sensitivity analysis was conducted, indicating that the effect of mass flow split ratio (F) and inlet quality (x1) is the most significant for K12J and K13J respectively.

RETRACTED: Utilization of a solar system to charge lithium-ion batteries and using the heat generated in an in-line lithium-ion battery to heat a guard room

In this research, three packs of cylindrical li-ion batteries inside the air duct used to heat a guard room are simulated numerically. Heat is generated inside lithium batteries due to the electrochemical process. To enhance the performance of the battery, the heat must be rejected; but the generated heat is used as a heating source in this study. The airflow passes through three battery packs and exits. The airflow exits from several outlets. The number of outlets varies from one to five, and their effect is examined. The room is studied in a cold environment and has dimensions of 2×3m. Carrier software is employed to estimate the room heat transfer and COMSOL software is used to simulate the battery. The results of this study show that an increment in the velocity increases the pressure drop and heat transfer coefficient (HTRC) in the system, but reduces the outlet temperature (Toutlet) and the maximum temperature (Tmaximum) of the battery. The model with 1 outlet has the lowest Tmaximum of battery cells and the lowest temperature of air outlet, while the model with 3 outlets has the highest Tmaximum of the battery cell and air outlet. Using this system is useful to provide heating energy for the guard room in the not-so-cold months and can provide up to 86.95% of the total energy required. But, in the very cold months, the system has a minor effect on the total heat required and provides less than 20% of the total energy needed.

Heat transfer enhancement in double-pipe heat exchanger: A review

Due to the wide need for heat transfer improvement in heat exchangers, it always stands a challenging field to grow effective and efficient heat transfer equipment with qualities of cost-effectiveness, reduced size, and maximum usage in a wide variety of applications under several operating conditions. The heat exchangers are mostly used to fulfil the requirements of high heat dissipation in industries. In this review article, a focused analysis is done on heat transfer improvement in double-pipe heat exchangers using different geometries in the flow, and heat transfer characteristics are also taken into consideration for the analysis. Many researchers have already analyzed a double-pipe heat exchanger as an experimental unit and with the help of simulation. Several past studies are examined and concluded to build an effective system using a heat exchanger. The significance of Prandtl number, Reynolds number, Nusselt number, and pressure drop coefficient quantities are shown in the studies. A close concern on nanoparticles in inside pipe is also studied for heat transfer improvisation using a double-pipe heat exchanger. New outcomes are perfectly verified and assist in the investigation of various other studies.

Particle resolved numerical modeling of unsteady forced convection of nanofluid around a porous cuboid with sinusoidal inlet velocity

Abstract In this research, the laminar, incompressible, unsteady oscillatory flow and convective heat transfer of nanofluid around a porous cuboid were studied two-dimensionally using particle resolved calculations. Several cuboids of different sizes and porosities and with a constant temperature were subjected to a nanofluid flow with a sinusoidal velocity profile. The effects of the Reynolds number (Re = 100–900), the volume fraction of nanoparticles, the aspect ratio of the porous cuboid, the Darcy number and the amplitude and frequency of the inlet velocity on the flow field and heat transfer were investigated. To evaluate the system’s optimal performance, performance evaluation criteria (PEC) were also investigated. The results showed that increasing the Reynolds number improved thermal performance. Increasing the volume fraction of nanoparticles increased the Nusselt number; however, the pressure drop coefficient increased more strongly. The heat transfer and pressure drop coefficient increased in line with the growth of the porous cuboid aspect ratio. When the Darcy number was increased, the Nusselt number first increased and then decreased and the pressure drop coefficient continuously decreased. A higher amplitude of the inlet velocity profile augmented the heat transfer and pressure drop coefficient. An increase in the amplitude and frequency of the inlet velocity profile widened the range of drag and lift coefficients. Furthermore, flow at different inlet velocity frequencies (f * = 0–10) behaved differently; as a result, the maximum rate of heat transfer and pressure drop was obtained at f *=5. However, considering the ratio of the Nusselt number to the pressure drop coefficient and PEC parameter, the optimum frequency was f *=9.

Numerical investigation of turbulent forced convection flow in a two-dimensional curved surface cavity

A numerical study was carried out to investigate the thermal and flow fields of a two-dimensional vented cavity subjected to forced convection turbulent flow. The cavity with three distinct configurations of inlet and outlet ports having three different cases of top surfaces, i.e. flat, semi-elliptical and semi-circular was studied numerically for a range of Reynolds numbers. The objective of the study is to investigate the effect of the top curved wall surface on heat transfer in different configurations of inlet and outlet ports. The various results were presented for streamlines and thermal fields. The variations in the pressure-drop coefficient, local Nusselt number and average Nusselt number were also evaluated. The results show the significant dependence of heat exchange and pressure drop on Reynolds number, location of ports, and the height of the top curved wall surface. The rate of heat transfer was enhanced by increasing the height of the curved surface, but relatively high-pressure drop was observed in top curved surface cavity for the given Reynolds number. On the contrary, the semi-elliptical top surface cavity with inlet and outlet ports positioned on the same axis, displayed an improved performance in terms of maximum average Nusselt number and minimum pressure drop.

Computational Analysis of Fluid Forces on an Obstacle in a Channel Driven Cavity: Viscoplastic Material Based Characteristics.

In the current work, an investigation has been carried out for the Bingham fluid flow in a channel-driven cavity with a square obstacle installed near the inlet. A square cavity is placed in a channel to accomplish the desired results. The flow has been induced using a fully developed parabolic velocity at the inlet and Neumann condition at the outlet, with zero no-slip conditions given to the other boundaries. Three computational grids, C1, C2, and C3, are created by altering the position of an obstacle of square shape in the channel. Fundamental conservation and rheological law for viscoplastic Bingham fluids are enforced in mathematical modeling. Due to the complexity of the representative equations, an effective computing strategy based on the finite element approach is used. At an extra-fine level, a hybrid computational grid is created; a very refined level is used to obtain results with higher accuracy. The solution has been approximated using P2 − P1 elements based on the shape functions of the second and first-order polynomial polynomials. The parametric variables are ornamented against graphical trends. In addition, velocity, pressure plots, and line graphs have been provided for a better physical understanding of the situation Furthermore, the hydrodynamic benchmark quantities such as pressure drop, drag, and lift coefficients are assessed in a tabular manner around the external surface of the obstacle. The research predicts the effects of Bingham number (Bn) on the drag and lift coefficients on all three grids C1, C2, and C3, showing that the drag has lower values on the obstacle in the C2 grid compared with C1 and C3 for all values of Bn. Plug zone dominates in the channel downstream of the obstacle with augmentation in Bn, limiting the shear zone in the vicinity of the obstacle.

Design and thermal-hydraulic optimization of a shell and tube heat exchanger using bees algorithm

The present study modifies the structural design of a shell-and-tube heat exchanger by considering two key parameters such as the maximization of the overall heat transfer coefficient and minimization of the total pressure drop. Five geometric design variables which include the tube inside diameter, tube outside diameter, pitch size, baffle spacing, and the tube length are investigated for optimization. The governing equations for design and optimization of the shell-and-tube heat exchanger are evaluated and the optimum design parameters are obtained by bees algorithm. The selection of the important design parameters to achieve the proper design is evaluated by fixing each of these parameters, while the other the design parameters are selected as variable to optimize the effectiveness. Compared with the original shell-and-tube heat exchanger, the overall heat transfer coefficient is increased by 22.78% with the minimum increase in the total pressure drop by 1.8%.

Mechanistic modeling of flow and heat transfer in vertical upward two-phase slug flows

Two-phase slug flow exhibits intrinsically stochastic and statistically periodic flow behaviors. Understanding the mechanisms of flow and heat transfer of upward two-phase slug flow is important. This paper develops a mechanistic model of flow and heat transfer for upward two-phase slug flow in vertical pipes. First, a hydrodynamic model of two-phase slug flow in regular-sized channels is developed based on the hypothesis of the slug unit cell. Each slug unit cell is hypothesized to be composed of a liquid slug and a Taylor bubble region. Second, a mechanistic heat transfer model is derived based on the hydrodynamic model. The overall heat transfer coefficient is integrated by using the local heat transfer coefficients of liquid slug and the Taylor bubble region. Third, the proposed mechanistic model is validated by the experimental void fraction, pressure drop, and two-phase heat transfer coefficient from different sources. Finally, the effect of flow geometry and parameters—such as superficial gas and liquid velocities, void fraction, slug frequency, pressure drop, and the ratio of slug length to unit cell length—on heat transfer in two-phase slug flow is comprehensively investigated. The enhancement in heat transfer in two-phase slug flow compared with that of single-phase flow can be attributed to an increase in the turbulence of the liquid due to the injection of air and a reduction in the thermal boundary layer owing to the frequent alternation between liquid slug and the Taylor bubble.

Forced convective heat transfer in optimized kelvin cells to enhance overall performance

The optimization of pore structure for metal foam is considered a feasible approach for improving the overall heat transfer performance. Thus, we numerically investigated Kelvin cells with different throat areas and structures (elliptical Kelvin cell (EKC)) to characterize the influence on pressure drop and heat transfer coefficient using FLUENT 18.0. The standard k–ε model exhibited a better agreement with experimental data and required less time to achieve convergence. The results revealed that the throat area could not feasibly optimize the overall heat transfer performance. Moreover, the area goodness factor j/f that considered the influences of both heat transfer coefficient and pressure drop on the overall heat transfer performance of EKC with the higher than conventional Kelvin cell. Based on comparative analysis between pressure, velocity, turbulence kinetic energy, and temperature distribution, increasing the space and decreasing the angle between the skeleton and flow direction caused a significant pressure drop in the EKC samples. Owing to the existence of a lower temperature area at the leeward of skeletons and a small difference of impingement cooling on windward skeletons, the reduction of HTC was acceptable. Therefore, the EKC exhibited immense potential for enhancing the design of heat transfer devices.

Effect of inlet and outlet size, battery distance, and air inlet and outlet position on the cooling of a lithium-ion battery pack and utilizing outlet air of cooling system to heat an air handling unit

This paper evaluated the cooling of a plate li-ion pack of batteries (LIPB) with 12 battery cells using airflow. The LIPB is placed in a cooling chamber that is cooled by a forced flow of air passing through the battery cells. The impact of using the outlet air from 5 LIPBs of this type of battery for heating an air handling unit (AHU) is assessed. The variables include the input distance from the lower wall and the output distance from the upper wall, the input and output dimensions, as well as the distance between the battery packs, which are in the range of 0 to 1 meter, 0 to 0.8 m and 0 to 0.1 m, respectively. The amount of energy required for the residential unit in different months of the year for a cold and dry environment is estimated using the Carrier software. COMSOL Multiphysics software is also employed to simulate LIPB cooling. The heat transfer coefficient, the temperature of the batteries, the outlet temperature, and the pressure drop in the cooling system are determined by changing the size of the inlet and outlet of the airflow, the distance of the batteries from each other, and the change of the inlet and outlet location. The results reveal that an increment in the inlet airflow enhances the amount of pressure drop and heat transfer coefficient and reduces the value of battery cell temperature and outlet air temperature. As the distance between the batteries is enhanced, the pressure drop and air outlet temperature are intensified and the temperature of the battery cells is reduced. Also, it is observed that 10.3 kWh of the required heating energy of the building can be achieved from the outlet air from the cooling system of the batteries. Therefore, this system provides a maximum of 100% of heating energy in June and October and a minimum of 15% of the energy required for the house in October.

ANSYS-CFX simulation of the SRBTL test loop core with nanofluid coolant

AbstractIn the present study, CFD calculations are presented for the three types of water-based nanofluids Al2O3/water, CuO/water and TiO2/water with 0.1% volume fraction. These calculations are done with ANSYS-CFX and as geometry the SRBTL test loop as scaled down test loop for a VVER-1000 reactor core design is used. The goal of this study is to evaluate the CFD program against the SRBTL test loop core as a scaled core for applying water-based nanofluids as coolant. ANSYS-CFX simulation data are validated against the RELAP5/MOD3.2 simulation data for pure water. This comparison shows a good agreement. The simulation results for the nanofluids and water including Re number, temperature, viscosity, pressure drop and heat transfer coefficient through the SRBTL test loop core are compared. The results of the comparisons show that the SRBTL test loop core is suitable to extract experimental data of water-based nanofluids for using them as coolant in the VVER-1000 reactor.