Fluid Pressure Drop Research Articles

Numerical study of the heat transfer and flow stability of water at supercritical pressures in a vertical tube

The subcritical steam generators in the current High-Temperature-Reactor Pebble-Bed Module, HTR-PM, in China can be replaced by supercritical steam generators to better coordinate the reactors and the supercritical steam turbines to improve thermal efficiencies with no phase change at supercritical pressures. This study numerically analyzed the heat transfer and the flow instabilities of supercritical pressure water. Five turbulence models were evaluated to model the heat transfer with a constant wall heat flux for steady-state calculations with the results showing that the RNG k-ε model with the enhanced wall treatment gave the best results. This model was then used in transient calculations with the wall heat flux increasing linearly with time. The flow and heat transfer characteristics and the velocity and turbulence fields at various times were used to analyze the influences of flow rate variations, thermophysical property variations, buoyancy and flow acceleration. The effects of the fluid inlet enthalpy and pressure drop along the tube on the flow instabilities were also studied.

A comprehensive study of the performance of a heat pipe by using of various nanofluids

In this paper, a two-dimensional numerical model is developed to simulate the performance of a heat pipe using various nanofluids. The effect of different nanofluids (prepared using alumina, copper oxide, and silver nanoparticles) at different concentrations and particle diameters on the performance of heat pipe is also studied by through finite volume method. The obtained results show that using a nanofluid instead of water leads to the increased thermal efficiency and reduction in heat at wall of the heat pipe. Also, the temperature difference between the evaporator and the condenser is a function of input power; this means that by an increase in the input capacity, the temperature difference between the evaporator and the condenser increases. It was observed that the use of nanofluid reduces the axial-flow pressure of the fluid inside the wick. As a result, the transmission of fluid flow inside the wick from the condenser to the evaporator is easily done with the cost of using a nanofluid. Moreover, with an increase in thermal capacity, fluid pressure drop becomes maximum and thus temperature difference between the evaporator and the condenser increases.

Constructal design applied to elliptic tubes in convective heat transfer cross-flow of viscoplastic fluids

The objective of this work was to obtain geometries that maximize the heat transfer and minimize pressure drop for viscoplastic fluids in cross flow around elliptical section tubes. The Constructal Design associated with exhaustive search was employed to obtain the ellipse aspect ratios that maximize the Nusselt number and to minimize dimensionless pressure drop, for fixed parameters such as ellipse area, Reynolds (Re=1), Prandtl (Pr=1) and Herschel-Bulkley (HB=1) numbers. The viscoplastic fluid behavior was modeled using the Herschel-Bulkley constitutive equation. The power-law index, n, was a parameter to predict fluid shear thinning. The system of differential equations for flow and heat transfer was solved numerically by the finite volume method. The aspect ratio to maximize Nu‾, rq,opt, and the one to minimize Δp̃, rp,opt, were searched for different values of n, ranging from 0.4 to 1. The rq,opt was found to be very close to 1 for all n’s, which corresponds to the tube of circular cross section. Low aspect ratio tubes lead to the formation of greater unyielded zones as compared to high aspect ratio tubes. This may be a key to understand the increase in heat transfer from the tube as the aspect ratio increases to one. The aspect ratio that led to the lowest pressure drop was not the same for all fluids, contrarily to the behavior noticed for thermal purpose. It was noticed that as n decreases, the rp,opt, also decreases, meaning that to reduce pressure drop for more shear thinning fluids the tube must be slender. This may lead to the conclusion that elliptic tubes might be a good alternative in applications of heat transfer with mild viscoplastic fluids (low HB) only when there is the need to reduce pressure drop or pumping power.

Exergy Analysis of a Parallel-Plate Active Magnetic Regenerator with Nanofluids

This paper analyzes the energetic and exergy performance of an active magnetic regenerative refrigerator using water-based Al2O3 nanofluids as heat transfer fluids. A 1D numerical model has been extensively used to quantify the exergy performance of a system composed of a parallel-plate regenerator, magnetic source, pump, heat exchangers and control valves. Al2O3-water based nanofluids are tested thanks to CoolProp library, accounting for temperature-dependent properties, and appropriate correlations. The results are discussed in terms of the coefficient of performance, the exergy efficiency, and the cooling power as a function of the nanoparticle volume fraction and blowing time for a given geometrical configuration. It is shown that while the heat transfer between the fluid and solid is enhanced, it is accompanied by smaller temperature gradients within the fluid and larger pressure drops when increasing the nanoparticle concentration. It leads in all configurations to lower performance compared to the base case with pure liquid water.

Analysis by the Dissipation Theorem of Turbulent Flow in a Pipe

More than a year ago, I proposed analyzing turbulent flow and predicting friction and mass transfer by relating one statistical quantity for the flow to other statistical quantities on a local basis. This is what we do with laminar flow, where the stress is related to the viscosity and the velocity gradient. Excellent data could be found on turbulent mass transfer in the system where one cylinder rotates within a larger stationary cylinder. Excellent data on fluid friction and pressure drop are found for turbulent pipe flow. The dissipation theorem has been applied to this system. In the course of doing this, several aspects of the earlier work have been refined. Furthermore, one can make predictions of the eddy viscosity and the dissipation that accord with old measurements. Of course, some empiricism is required, but one strives to keep this on a local level where the volumetric dissipation is related to the eddy viscosity. The behavior of the system is surprising, and the literature data are quite different from what one might have expected.

A Study About Performance Evaluation Criteria of Tube Banks With Various Shapes and Arrangements Using Numerical Simulation

Tube bank heat exchangers are designed to efficiently transfer heat between two fluids. Shapes and arrangements of tubes in heat exchangers have significant effects in heat transfer and pressure drop of fluid. In this study, the three-dimensional (3D) numerical investigation is performed to determine heat transfer coefficients, friction factor, and performance evaluation criteria (PEC) of cam-shaped tube banks in aerodynamic and inverse aerodynamic directions in the cross flow air and compared with those of elliptical tube banks in heat exchanger. The arrangements of tubes are aligned and staggered with longitudinal pitch of 44.88 mm and transverse pitch of 28.05 mm. Reynolds number in the range of 11,500–18,500 was used, and the tube surface temperature was fixed and considered 352 K. Results indicate the superior heat transfer of elliptical tube bank over the cam-shaped tube banks in inverse aerodynamic and aerodynamic directions in both arrangements. Moreover, the PEC of the cam-shaped tube banks with inverse aerodynamic and aerodynamic directions and elliptical tube bank in aligned arrangement are approximately 1.4, 1.1, and 1.6, respectively. The obtained results for staggered arrangements are also 1.5, 1.3, and 1.8, respectively.

Multi-Objective Optimization of Force Convective Heat Transfer in a Stack of Horizontal Channels Using CFD and Genetic Algorithms: a Comparison with Asymptotic Method Results

In this paper, by combining the computational fluid dynamics (CFD) and NSGA II algorithm, the forced convective heat transfer flow in a stack of horizontal parallel plates has been multi-objectively optimized. In the optimization process, the distance between the plates in the set of parallel channels has been changed so as to simultaneously optimize the amount of heat transfer between the plates and fluid and the pressure drop of the fluid (maximization of heat transfer and minimization of pressure drop). The Pareto front, which illustrate the changes of the heat transfer from the plates and the pressure drop of fluid simultaneously, have been presented in the results section. This result contains important information regarding the thermal designing of stack of channels subjected to forced convective heat transfer. The Pareto front have been obtained for four different fluids that have different Prandtl (Pr) numbers (mercury, air, water and oil), and the results related to each fluid have been discussed. Finally, the multi-objective optimization results obtained in this paper have been compared with the results of the asymptotic analysis method (which is a single-objective method aimed at increasing the amount of heat transfer from plates) for internal fluid flows; and useful information has been obtained.

NUMERICAL INVESTIGATION OF HEAT TRANSFER AND FLOW CHARACTERISTICS IN SHELL-AND U-TUBE HEAT EXCHANGER WITH BAFFLES

In this paper the numerical model of cylindrical coordinates, three dimensional of a laminar heat transfer and fluid flow inside shell and tube heat exchanger is examined. The thermo-hydraulic performance of heat exchangers is predicted with finite volume method by CFD simulations using ANSYS 15.0 code. Shell-and-tube heat exchanger is consisted of one pass of warm water laminar flow at the shell side and two passes single tube of laminar cold water. The annular baffles are inserted on shell side, and on the facing distances of the length of tube from the outer surface. Baffles are inserted with staggered position on the shell and tube to achieve good fluid circulation. Also baffles on the tube side are varied with angle inclination, number and diameter while only number and length on the shell side. The tube baffles angle inclination as (45o, 0o and -45 o) and without baffles and the range of Reynolds number from 100 to 2000. The results show high effect of baffles angles on the heat exchanger performance at high Reynolds number. Maximum heat transfer from hot fluid occurs at baffle with angle 0o and high 30mm. Also baffles number increases Nusselt number at high fluid flow rate while a little effect of baffle height and number on the fluid pressure drop is absorbed as obtained by Mica et.al [1].

Heat Transfer Enhancement and Optimization of Lean/Rich Solvent Cross Exchanger for Amine Scrubbing

The lean/rich amine cross exchanger is one of the cost centers in the amine scrubbing process, and accounts for 20–30% of the capital cost. To minimize the cross exchanger cost, shortcut methods that determine optimum LMTD and fluid velocity were developed. The optimum LMTD is a function of heat transfer coefficient, temperature change and the capital cost of heat exchanger. A greater LMTD should be used to prevent excessive capital cost when the number of heat transfer units (NTU) is large and the heat transfer coefficient is small. The heat transfer performance can be enhanced by increasing pressure drop and reducing solvent viscosity. The corrugation angle is the primary design geometry for plate-and-frame exchanger (PHE). Based on the empirical correlations for PHE, the heat transfer coefficient at 60° is almost double that at 30°; however, the pressure drop at a large corrugation angle is also greater. The dependence of the pressure drop per unit length on the heat transfer coefficient is 0.35–0.40, which implies that the heat transfer coefficient will increase 30% by doubling the pressure drop per unit length. The cost associated with the optimization of the cross exchanger has been developed as a function of the fluid velocity, the physical properties, the exponents of the empirical correlations and the pricing parameters. The optimum velocity is independent of the solvent rate, the temperature change of the cross exchanger, and the cross exchanger LMTD. To stay at optimum fluid velocity, the plate number needs to increase as the solvent rate increases while the plate length will increase as the NTU increases. Viscous solvent will result in a lower optimum velocity since it causes higher pressure drop. Typical optimum fluid velocity is at 0.32–0.42 m/s for 8 m PZ. It is worthwhile to utilize higher fluid velocity and pressure drop when the heat transfer can be effectively enhanced by turbulence.

Numerical study of pulsatile MHD counter-current nanofluid flows through two elastic coaxial pipes containing porous blocks

We investigate the MHD convective pulsatile flow through a counter-current two-nanofluid (Cu-water and CuO-water) system. This system consists of two elastic coaxial pipes, with porous blocks mounted on the walls of each channel. Hot CuO-water nanofluid flows upwards in the inner channel, while cold Cu-water nanofluid flows downwards in the outer channel. A two-phase model that considers the effects of thermophoresis and brownian motion on the concentration of nanoparticles within the fluid is used to describe heat and mass transfer within the system. The governing equations with the associated initial and boundary conditions are solved using the mixed finite element method with P2-P1 Taylor-Hood elements. The influence of time, pulsation frequencies and amplitudes of the inner and outer fluids, elastic modulus, Reynolds number, solid volume fractions of the inner and outer nanofluids, and the diameters of the Cu and CuO nanoparticles on fluid flow, heat transfer, nanoparticle concentration and pressure drop is studied. We found that heat transfer may be enhanced by increasing parameters such as the elastic modulus of the pipes, Reynolds number, solid volume fraction of nanoparticles in the inner fluid and nanoparticle size in the outer fluid. Similarly, heat transfer is enhanced by reducing the solid volume fraction of nanoparticles in the outer fluid and nanoparticle size in the inner fluid. In most cases, the heat transfer enhancement observed in the study is accompanied by increases in pressure drop.

Influences of Hydraulic Fracturing on Fluid Flow and Mineralization at the Vein-Type Tungsten Deposits in Southern China

Wolframite is the main ore mineral at the vein-type tungsten deposits in the Nanling Range, which is a world-class tungsten province. It is disputed how wolframite is precipitated at these deposits and no one has yet studied the links of the mechanical processes to fluid flow and mineralization. Finite element-based numerical experiments are used to investigate the influences of a hydraulic fracturing process on fluid flow and solubility of CO2and quartz. The fluids are aqueous NaCl solutions and fluid pressure is the only variable controlling solubility of CO2and quartz in the numerical experiments. Significant fluctuations of fluid pressure and high-velocity hydrothermal pulse are found once rock is fractured by high-pressure fluids. The fluid pressure drop induced by hydraulic fracturing could cause a 9% decrease of quartz solubility. This amount of quartz deposition may not cause a significant decrease in rock permeability. The fluid pressure decrease after hydraulic fracturing also reduces solubility of CO2by 36% and increases pH. Because an increase in pH would cause a major decrease in solubility of tungsten, the fluid pressure drop accompanying a hydraulic fracturing process facilitates wolframite precipitation. Our numerical experiments provide insight into the mechanisms precipitating wolframite at the tungsten deposits in the Nanling Range as well as other metals whose solubility is strongly dependent on pH.

Influence of fully miscible lubricating oil on the pressure drop during flow boiling of CO2 inside an enhanced tube

The total static pressure drop in both adiabatic and diabatic two-phase flow conditions during flow boiling of CO2-oil mixtures inside a horizontal enhanced tube of 8.62mm inner diameter were investigated, yielding interesting insights and supporting the design process of evaporators. The nominal mass fraction of fully miscible POE lubricating oil (1.3–3%), saturation pressure (10–39bar), mass flux (75–500kgm−2s−1), inlet vapor quality (0.1–0.9), and heat flux (0–120kWm−2) were varied over a wide range of parameters. An isothermal peripheral boundary condition was realized for the electrically heated tube. Experimentally determined pressure drops are discussed with respect to operating conditions as well as observed flow patterns. The findings are compared to experimental results for pure CO2 obtained in the same test facility under similar conditions. The pressure drop of both pure fluid and a mixture with an oil mass fraction of 1.3% can be predicted satisfactorily by using established correlations including the hydraulic diameter of the enhanced tube. A significant influence of oil on the pressure drop is observed especially for high oil mass fractions, high vapor qualities, and high heat fluxes.

Comparison of three types of swirling generators in coarse particle pneumatic conveying using CFD-DEM simulation

The present investigation aims at developing a gas and particle flow model based on CFD-DEM coupling for three types of swirling generators. Grid and time size dependence tests were performed to validate the numerical model; the prediction ability of the model was confirmed through comparison with experimental data. Detailed studies of certain parameters (including the fluid pattern, swirling number and pressure drop) were based on the CFD method for the three-lobed, rifle and internal spiral vanes swirling generator pipelines. These studies were performed using dimensionless forms and numerical simulations. The peak regions of the axial velocity for the three-lobed and internal spiral vanes pipes have obvious asymmetrical patterns that rotate quasi-periodically downstream; the three-lobed pipe generates the largest swirl number and decays the fastest. In addition, quantitative calculations using the CFD-DEM coupling model, which include the particle distribution and the pneumatic conveying efficiency, suggest that the three-lobed swirling generator is suitable for the preliminary conveying stage and that the internal spiral structure in this work is a favorable option for swirling pneumatic conveying systems for coarse particles.

A three-dimensional analysis of simultaneous and sequential fracturing of horizontal wells

Horizontal well fracturing is most commonly used to improve well productivity from the lower quality formations that could not have been economically developed using the conventional hydraulic fracturing approach. These horizontal wells can be stimulated to increase reservoir permeability via multiple hydraulic fractures using different design concepts. In this paper, we present a 3D fully coupled numerical model with capabilities to simulate multiple fracture clusters propagation from horizontal wells. The numerical model is developed using a combination of the boundary element method, the finite element method, and the linear elastic fracture mechanics for the fracture propagation. The fluid flow inside the fracture is assumed to be laminar flow and the fluid follows Newtonian behavior. The Galerkin’s finite element approach is used for fluid flow modeling, the rock mass deformation is simulated using elastic displacement discontinuity method, and crack tip displacement approach is used for the mixed-mode fracture propagation. The brief descriptions of the governing equations and their numerical implementation are presented first. Then, the fracture propagation model is verified using semi-analytical solution from the Khristianovic-Geertsma-de Klerk (KGD) model for a circular planar fracture. A sensitivity analysis of various parameters effecting the mechanical interaction among multiple propagating fractures is conducted. Finally, numerical examples of multiple fracture propagation for sequential and simultaneous fracturing procedures from a single horizontal well and multiple horizontal wells are presented. In simultaneous fracturing case, the fluid injection rate is dynamically partitioned among the fractures depending upon wellbore frictional losses, perforation frictional losses, and fluid pressure drop in the fractures. Results of a sensitivity analysis demonstrate the effects of the in-situ stresses, rock and fluid properties, and “stress shadowing”. The simultaneous and sequential fracturing results show that the generated fracture network geometries are strongly influenced by the mechanical interactions among the fractures or fracturing stages. The conventional zipper fracturing tends to generate nearly straight fractures with potential for tip coalescence and thus wellbore communications. The modified zipper fracturing tends to yield potentially more complex fracture geometries due to fracture turning.

Modelling soot deposition and monolith regeneration for optimal design of automotive DPFs

Diesel particulate filters (DPFs) are extruded monoliths comprising many square channels. The material of the monolith, and the size and shape of channels require optimization to guarantee best performances. In this work, we develop an original semi-analytical model to analyze filter behavior during both loading and regeneration operations. Fluid flow and pressure drop along/across monolith channels are calculated based on lubrication theory and Darcy sub-model. Time evolution of filter properties induced by soot deposition and cake formation is modelled using a unit collector sub-model. Cake burn-out and the thermal response of the monolith during the regeneration stage is modelled using a simplified soot combustion and heat transfer sub-model. The impact of channel number and size, filter hydraulic permeability and thermal capacity on back-pressure build-up, regeneration efficiency and risk of thermal failure are discussed to improve the design of automotive DPFs.

Deposition conditions and distribution features of native gold individuals in the veins of the Tokur mesothermal deposit, Russia

The paper discusses factors in the deposition and concentration of native gold and the spatial distribution of its individuals within the sufide-poor gold–quartz veins at the mesoabyssal Tokur deposit. The major factors in deposition of gold were sealing of the hydrothermal system, a sudden drop in fluid pressure, and repeated immiscibility in the fluid. Native gold was deposited in relation to initial acts of prolonged and discrete opening and preopening of cavities in three mineral assemblages of the productive association II. Most native gold individuals with a visible size of 0.1–1.5 mm were together with the early generation of quartz 2 on cavity walls adjacent to altered rocks. This is caused by the high content of Au complexes in initial hydrothermal solutions favoring rapid oversaturation during cavity formation. Gold fills interstices between grains of quartz 2 throughout the deposit and mineral assemblages. The vertical-flow distribution of gold has been established in economic veins; the upper and middle levels are enriched in gold, and samples with the greatest gold grade of 100–500 g/t or higher are concentrated there. This is caused both by the predominance of mineral association II at these levels and probable natural flotation of gold grains contained in the gold–gas associate for immiscibility of the hydrothermal fluid at the second stage of the ore-forming process.

Pressure drop of HFE7000 and HFE7100 during flow condensation in minichannels

Attention is focused on the issues of flow resistance and pressure drop of perspective refrigeration fluids during condensation in the two-phase flow in minichannels. The case of the flow through a cylindrical single channel of 2.3 mm inner diameter was carefully analyzed. Pressure drop tests have been performed in diabatic flow conditions. The effect of heat flux, mass flux, vapour quality and saturation temperature on the two-phase pressure drop have been scrutinised. In the course of investigations, the new fluids, namely HFE 7100 and HFE 7000, have been tested. Calibration of the measurement system for the case of single phase flow and comparison of the results with the Blasius friction correlation show the accuracy of ±15%. Additionally, the data were compared with some well established correlations for two-phase flow exhibiting that the correlation due to Fronk and Garimella (2010) and the in-house model are found in best agreement with the experimental data.

Pressure Drop Calculation Models of Wellbore Fluid in Perforated Completion Horizontal Wells

Perforated completion is a main method of horizontal well completion. Based on the mass conservation equation, the momentum conservation equation and the variable mass flow in the horizontal wellbore, pressure drop calculation models of the wellbore fluid are established in perforated completion of horizontal wells. The results of calculation and analysis show that the frictional pressure drop, acceleration pressure drop and mixing pressure drop have different effects on total pressure drop of the wellbore fluid, and the frictional pressure drop plays a major role while the acceleration pressure drop and mixing pressure drop have little influence. The liquid viscosity, production and horizontal wellbore length also have different effects on various kinds of pressure drop. When liquid viscosity is smaller and the length of the horizontal wellbore is shorter, the effects of the acceleration pressure drop and mixing pressure drop cannot be neglected. The theoretical basis and the calculation model of the variable mass flow pressure drop of horizontal wellbore are provided.

The preliminary thermal–hydraulic analysis of a water cooled blanket concept design based on RELAP5 code

Water cooled blanket (WCB) is very important in the conceptual design and energy transfer in future fusion power plant. One conceptual design of WCB is under computational testing. RELAP5 code, which is mature and often used in transient analysis in Pressurizer water reactor (PWR), is selected as the simulation tool. The complex inner flow channels and heat sources are simplified according to its thermal–hydraulic characteristics. Then the nodal model for REALP5 is built for approximating the conceptual design. Two typical operating plans, superheated steam scheme and PWR scheme, are analyzed. After some adjustments of the inlet flow resistance coefficients of some flow channels, the reasonable stable conditions of both operation plans can be obtained. The stable fluid and wall temperature distributions and pressure drops are studied. At last, a supposed slow flow decreasing is discussed under two operating conditions separately. According to present results, the superheated steam scheme still needs to be further optimized. The PWR scheme shows a very good safety feature.

Numerical simulation of fracture network generation in naturally fractured reservoirs

In this study, numerical modeling of hydraulic fractures propagation is performed to analyze the forming mechanism of complex fracture network during the process of hydraulic fracturing in naturally fractured reservoirs. The model couples fracture deformation with fluid flow in the fracture network and horizontal wellbore. The enhanced 2D displacement discontinuity method is used to capture fracture deformation. When fracturing fluid fills the natural fracture before crossing happens, the interaction criterion between hydraulic fracture and natural fracture developed by Gu et al. (2012) is modified to incorporate fluid pressure in natural fracture. The implicit level set schemes based on tip asymptotical solution is presented to locate the fracture tips. Simulation results indicate that fracture spacing and stress anisotropy have significant influence on the propagation path and geometry of multiple fractures. Accounting fluid pressure drop in the wellbore will lead to asymmetrical geometry and stress shadowing effect of side fractures on the middle fracture when three-cluster fractures propagate simultaneously. Multiple fractures will be directed back to the maximum stress direction after long propagation length. Results show that stress shadowing effect and natural fractures are key controlling factors of complex fracture networks in unconventional reservoirs.