Search

During solar cell operation, most light energy converts to heat, raising the battery temperature and reducing photoelectric conversion efficiency. Thus, lowering the temperature of solar cells is essential. Nanofluids, with their superior heat transfer capabilities, present a potential solution to this issue. This study investigates the mechanism of enhanced heat transfer by nanofluids in two-dimensional rectangular microchannels using the two-phase lattice Boltzmann method. The results indicate a 3.53% to 22.40% increase in nanofluid heat transfer, with 0.67% to 6.24% attributed to nanoparticle–fluid interactions. As volume fraction (φ) increases and particle radius (R) decreases, the heat transfer capability of the nanofluid improves, while the frictional resistance is almost unaffected. Therefore, the performance evaluation criterion (PEC) of the nanofluid increases, reaching a maximum value of 1.225 at φ = 3% and R = 10 nm. This paper quantitatively analyzes the interaction forces and thermal physical parameters of nanofluids, providing insights into their heat transfer mechanisms. Additionally, the economic feasibility of nanofluids is examined, facilitating their practical application, particularly in solar cell cooling. [ABSTRACT FROM AUTHOR]

The paper presents a method for improving the lime production process by increasing the efficiency of the lime slurry transport that occurs in it. The aim of the study was to reduce the energy demand of the pump installed in the discharge line. The presented solution consists of applying an additive called deflocculant to the transported slurry in order to reduce its viscosity while increasing the concentration of solids content. The deflocculant applied to the slurry is composed of waste material from the lime slaking process and an environmentally neutral chemical substance in the form of sodium-water glass. The rheological studies conducted confirm the positive effect of the selected deflocculant on the properties of the slurry tested. As a result of the analysis, it has been shown that the proposed solution has a substantial effect on reducing the friction factor of the transported slurry, thus reducing the energy consumption in the investigated process. [ABSTRACT FROM AUTHOR]

This paper theoretically studied pressure drop variation in microchannels having different cross sections (circular, rectangular, square, trapezoidal, triangular, elliptical, parallel plate, co-centric circles, hexagonal, wavy, smoothed or rounded corners cross sections, and rhombus) for single phase Newtonian fluid (gas and liquid) flow. Based on 41 years (approximately) prior literature (1981–till now), 249 articles were studied and number of correlations of pressure drop calculation in microchannels with or without friction factor equation for four cross sections i.e., rectangular, square, circular, trapezoidal, wavy and triangular is collected and also mentioned their limitations at one place. Other than these four cross sections, there is very few experimental/numerical works was present in the literature. A comparable study was performed for laminar as well as turbulent friction factor to calculate the pressure drop with the help of classical theory for gas and liquid flow in microchannels with circular and rectangular cross sections. Results show wonderful outcomes i.e., correlations of laminar pressure drop study can be extendable for transition and turbulent regime in both types (circular and rectangular) of cross sections of microchannels. In different types of flow regime, it is suggested that for each type of cross section (circular and rectangular) we can go for single correlation for gas/liquid system. It is also investigated that the macro channels pressure drop equations can be used for microchannels up to the certain values of Reynolds number. Basically, this paper provides all possible equations of friction factor related to the microchannels that helps to calculate the pressure drop, is collected at one platform also compared their deviation with conventional channels. [ABSTRACT FROM AUTHOR]

The paper chronologically describes the results of research on the flow of micro-encapsulated PCM (mPCM) and nano-encapsulated PCM (nPCM) slurry in heat-transfer systems. The focus is on three thematic groups: mPCM (nPCM) slurry flow pressure drop; the friction factor in the laminar, transient, and turbulent flow of slurry in the channels; and the assessment of the effectiveness of using the mPCM (nPCM) slurry in the context of improving heat-transfer coefficients but with increased pumping power. It was found that the number of publications devoted to the above-mentioned topics is very limited compared to the research on the thermal and rheological properties of the mPCM (nPCM) slurry, which has resulted in the lack of systematized knowledge about the influence of slurry concentration, particle size, materials, etc., for example, on the friction factor. It was found that the use of the mPCM (nPCM) slurry in heat-transfer systems may be proper, provided that an appropriate and sufficiently high flow rate is ensured. [ABSTRACT FROM AUTHOR]

A hydro-dynamic thermal fully developed forced convective heat transfer analysis of magneto-hydrodynamics fluid flow through an annular sector duct is presented in this paper. Two types of thermal boundary conditions i.e., axially uniform heat flux along with peripherally uniform temperature (known as H1-condition) and, axially and peripherally uniform temperature (known as T condition), have been considered to carry out the thermal analysis of fluid. The velocity components along r and θ direction are transformed into algebraic form by using power law discretized scheme, whereas cross-sectional pressure P (r , θ) is estimated with the help of well know technique S I M P L E R. The governing partial differential equations are solved by numerically with the help of M A T L A B code. Furthermore, simulated results have been compared with the existing results of literature to validate the results. From the results, it is noted that hydro-dynamically and thermally impacts relate directly by increasing the Hartman number, (M). It is further reported that the effect of magnetic field becomes insignificant for the higher number of fins, N. The findings of the present analysis will be applicable in various types of thermal systems. [ABSTRACT FROM AUTHOR]

Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes. [ABSTRACT FROM AUTHOR]

Microchannels are small-scale channels with unique properties that make them useful in various fields, such as electronics, biomedical engineering, and chemical engineering. This research paper investigates the effect of microchannel geometry on fluid flow behavior at different values of the Reynolds number. A rectangular microchannel with a pattern of obstructions and water as the working fluid was used in this study. Computational fluid dynamics (CFD) simulations were used to investigate the impact of different channel geometrical configurations and different values of the Reynolds number on fluid flow behavior. The results showed that the channel geometrical configuration and the Reynolds number significantly affect fluid flow behavior. A geometry with increasing obstruction heights led to higher values of pressure drop than the geometry with decreasing obstruction heights. This study provides valuable insights into microchannel flow behavior and can be used for the development of optimized microchannel designs for diverse applications. [ABSTRACT FROM AUTHOR]

The appropriate estimation of frictional losses in a pipeline system is essential. So far, little attention has been paid to determining the friction factors with non-Newtonian fluids, especially in rough pipes. This study aims at calculating the friction factor using validated three-dimensional Computational Fluid Dynamics models in Ansys CFX. Steady-state computations are performed with three different incompressible Herschel-Bulkley fluids in rough pipes with relative roughness of the inner pipe surface ε = 0.0005 - 0.01. A power-law type bath gel as a test fluid is used for experiments to validate our numerical model. The numerical results are compared with the measured values and also with numerous existing friction factor estimation models with the help of generalization of the Reynolds number in the relevant engineering range of Regen = 100 - 40,000. This paper shows that the existing approximations can not accurately describe the friction factor with pseudoplastic fluids in rough pipes. On the contrary, in the case of Bingham plastic fluid, a new, explicit calculation relation is found in a unified form accepted by the literature. [ABSTRACT FROM AUTHOR]

This paper presents experimental investigation of flow configurations and pressure drop of single-phase water flow and two-phase air-water flow in a vertical annulus. The annular test section had a concentric geometry with a casing and tubing diameter of 50 and 33.7 mm, respectively. The superficial velocity conditions of the liquid and gas were ranged 0.08–1.56 and 0–3.56 m/s, respectively. The combination of these superficial velocities produces the bubbly, slug and churn flow regimes. The identification of the flow patterns shows that the Mishima and Ishii model is the most relevant to highlight the flow transition. The measured friction factors were compared to prediction models from the literature. It was deduced that the model proposed by Gunn and Darling underestimates the liquid friction factor in the annulus. The measured pressure drops and the dimensionless pressure gradient evolution exhibits different slopes that characterize each flow pattern. The standard deviation and structure frequency describe specific ranges for each flow pattern. These two parameters can also be used for the prediction of flow patterns. [ABSTRACT FROM AUTHOR]

Phase-change materials (PCMs) are attractive materials for storing thermal energy thanks to the energy supplied/returned during the change in matter state. The encapsulation of PCMs prevent them from connecting into large clusters, prevents the chemical interaction of the PCM with the walls of the tank and the exchanger material, and allows the phase change to be initiated in parallel in each capsule. The microencapsulation of PCMs (mPCMs) and the nanoencapsulation of PCMs (nPCMs) entail that these particles added to the base liquid can act as a slurry used in heat exchange systems. PCM micro-/nanocapsules or mPCM (nPCM) slurry are subjected to numerous physical, mechanical, and rheological tests. However, flow tests of mPCM (nPCM) slurries are significantly limited. This paper describes the results of detailed adiabatic flow tests of mPCM slurry in a tube with an internal diameter of d = 4 mm and a length of L = 400 mm. The tests were conducted during laminar, transient, and turbulent flows (Re < 11,250) of mPCM aqueous slurries with concentrations of 4.30%, 6.45%, 8.60%, 10.75%, 12.90%, 15.05%, and 17.20%. The mPCM slurry had a temperature of T = 7 °C (the microcapsule PCM was a solid), T = 24 °C (the microcapsule PCM was undergoing a phase change), and T = 44 °C (the microcapsule PCM was a liquid). This work aims to fill the research gap on the effect of the mPCM slurry concentration on the critical Reynolds number. It was found that the concentration of the mPCM has a significant effect on the critical Reynolds number, and the higher the concentration of mPCM in the base liquid, the more difficult it was to keep the laminar flow. Additionally, it was observed that, as yet unknown in the literature, the temperature of the slurry (and perhaps the physical state of the PCM in the microcapsule) may affect the critical Reynolds number. [ABSTRACT FROM AUTHOR]

This paper offers an experimental investigation of the effect of metal foam on the thermal and hydrodynamic performance of a parabolic trough collector (PTC). Metal foams play a crucial role in heat transfer improvement due to their high thermal conductivity. Three different arrangements of metal foams are applied inside the absorber tube of the PTC. The flow regime in the absorber tube is laminar at different Reynolds numbers of 422, 844, 1267, and 1689. Experimental tests are designed with Design-Expert software in which the response surface method is utilized. Experimental results revealed that maximum enhancement in thermal efficiency is related to the periodic array arrangement of the metal foam inside the tube. This arrangement leads to a 14% increase in thermal efficiency. However, in this arrangement, the friction factor increases considerably compared to a plain receiver tube. [ABSTRACT FROM AUTHOR]

This paper examines the turbulent hydrothermal performance of boehmite/water–ethylene glycol (γ - AlO (OH) / H 2 O - EG) nanofluid flowing through a square duct fitted with various coiled-wire inserts (CWIs) using the finite volume method. The turbulent flow of γ - AlO (OH) / H 2 O - EG nanofluid is modeled using single-phase and k - ε model. A parametric study is carried out on the effect of Reynolds number ( 5.0 × 10 3 ≤ Re ≤ 4.0 × 10 4 ), the geometry of wire (circular, triangular, square, square-diamond, hexagon, octagon, and decagon), nanoparticle volume ratio ( 0 ≤ φ ≤ 4 % ), and nanoparticle shapes (blade, brick, cylinder, platelet, and oblate-spheroid) on hydrodynamic and convective heat transfer performance (CHTP). The results showed that the combination between CWI and nanofluid enhances hydrothermal performance. For instance, among the geometries of CWI considered at Re = 5.0 × 10 3 , the square CWI has the highest normalized Nu G (referencing empty channel) of 2.58, while the decagon has the lowest value of 1.78. Furthermore, regarding the nanoparticle shapes, the platelet shape has a maximum normalized Nu N (referencing base fluid) of 1.53, while the oblate-spheroid has a minimum value of 0.93. Lastly, in terms of application, square and octagon wire-fitted channels are better than empty channel at low Re , as the values of their hydrothermal performance evaluation criteria are greater than unity. [ABSTRACT FROM AUTHOR]

Solar air heater (SAH) is simple and the greatest effective approach to utilize and convert solar energy into thermal energy for heating utilizations. The employment of artificial roughness under side of the observer surface is the key technique for augmenting heat transfer with minimal friction factor penalty. Current paper summarized different kinds of artificial roughness used in SAH, which augments its performance. In this review article, 96 research papers are cited, which provide detailed information about the effect of different geometrical parameters on heat transfer and friction factor. This paper also brings the information about the optimum roughness parameters and heat transfer and friction factor correlation developed by different investigators in tabular form. Optimum roughness parameters and empirical correlations are used for comparative analysis of heat transfer, friction factor, and thermo-hydraulic performance parameter (THPP) of different roughness geometries. The best performing roughness geometry is reported on the basis of comparative analysis. Mathematical model is developed for predicting the thermal efficiency (ηth) of roughened SAH duct. [ABSTRACT FROM AUTHOR]

The aim of this study is to utilize waste thermal energy from industries into useful heat for water and air heating. In this paper, the thermal modeling and performance of three fluid heat exchangers (TFHE) have been experimentally investigated. The TFHE considered here is an enhanced version of the double‐pipe heat exchanger. A novel TFHE having fin (1 mm thin copper wire of 10 mm pitch) acts as a roughness element, which is wrapped on the helical coil's outer surface for increasing heat transfer (HT) rate and the turbulence effect for normal water, and this outer surface finned helical coil is inserted between two concentric straight tubes. The innermost tube carries atmospheric air, the finned helical coil tube carries waste hot fluid while normal water flows in the inner annulus of the outermost tube. The coiled‐side Reynolds number is varied in the range of 7000–30,000, while the curvature ratio of 0.1315, pitch‐to‐inside diameter ratio of 2.88 and wire‐to‐tube diameter e/d=0.182 $e/d=0.182$ of the helical tube is kept constant. A counterflow arrangement has been made for experimentation. Nusselt number is calculated using the traditional Wilson plot method that is compared and validated with results available in the literature. The overall HT coefficient is found to increase by increasing the volume flow rate of fluids, while effectiveness decreases or increases depending on residence time and capacity ratio. The percentage increment in the Nusselt number, maximum friction factor, overall HT coefficient between waste hot fluid to normal water, effectiveness is found to be 21.10%–23.88%, 90.91%, 3.40%–29.45%, 3.40%–25.33%, respectively, for the coil side. TFHE is thus proposed for heating water and space simultaneously. [ABSTRACT FROM AUTHOR]

Evaluation of flow resistance is necessary for the computation of conveyance capacity in open channels. The significance of the friction factor in channels with bedload conditions is paramount. The response of flow resistance in gravel-bed channels in bedload transport conditions is distinct from that of a fixed bed. The paper studies the different empirical approaches in the literature to determine the friction factor under bedload transport conditions and proposes an expression by genetic programming for the same. Various hydraulic and geometric parameters affect flow resistance in the bedload transport condition. The present study includes bed slope, relative submergence depth, aspect ratio, Reynolds number, and Froude number as influencing factors for such flow conditions. A wide range of experimental datasets is employed to determine the effect of these influencing parameters and develop a customised single expression for the friction factor. The experimental data set has also been moderated for sidewall corrections. The predictability of the proposed model is compared to various empirical equations from the literature. Unlike the existing models, the proposed model provides a more extensive expression for effectively predicting the friction factor for a wide range of datasets. The conveyance capacity of a river is validated from the estimated value of friction factor, as compared to other standard models. The developed Multi-Gene Genetic Programming (MGGP) model reasonably predicts discharge in the rivers, signifying that the model can competently be applied to field study within the specified range of parameters. [ABSTRACT FROM AUTHOR]

A microchannel heat exchanger effectively evacuates heat from a confined space. This paper attempts to gain insight into the combinatorial repercussions of simultaneously coupling two factors that affect a microchannel's performance, of which channel size and micro-insert complexity are the two main contributors. With water as the working fluid, an ANSYS-based numerical analysis was carried out for two distinct channel sizes, 1 and 2 mm, both with and without micro-inserts. The Reynolds numbers varied between 125 and 4992 and between 250 and 9985 for the 1 and 2 mm channels, respectively. For the 2 mm diameter channel, adding micro-inserts raised the overall pressure drop with increased Reynolds number. The inclusion of micro-inserts increased the pressure drop in the 1 mm channel at first, and thereafter the pressure drop decreased. Incorporating micro-inserts into the channel resulted in enhanced heat transfer. The trade-off between enhanced heat transfer performance and a larger pressure drop was calculated by evaluating the channel's overall performance using the thermal performance factor. Micro-inserts were found to be most useful for improving overall performance in the low-to-moderate Reynolds number range, and their effectiveness increased with decreasing channel size. Changing the channel diameter and structure of the design can improve heat transmission through microchannels. [ABSTRACT FROM AUTHOR]

This paper proposes correlation equations of heat transfer and pressure drop for the design and operation of tunnel kilns loaded with lattice brick settings of different geometrical parameters in the form of Nusselt number and friction factor. The developed correlation equations considered parameters that were not investigated in previous studies, such as the relative roughness of the bricks and the stack channels, and they also extended the Reynolds numbers to a practical range that was not covered before in a simple, practical form. The correlation equations are valid for Reynolds number between 125 and 10,200, Prandtl number between 0.68 and 0.73, brick's relative roughness between 0.23 and 0.93, voidage fraction between 0.48 and 0.653, and the geometrical parameters of the tested lattice brick settings. The achieved correlations of the Nusselt number and the friction factor are well compared with the available correlations in the literature in their valid range of parameters. It is found that Nusselt numbers and the friction factors for low-density are higher than those of high-density settings for all considered parameters except the voidage fraction. The effect of the considered parameters confirms that Nusselt numbers increase and the friction factors decrease substantially with the Reynolds number and slightly with the Prandtl number. At a constant Reynolds number, both the Nusselt number and the friction factor increase as the brick's relative roughness is increased. Moreover, as the stack channel spacing is increased, the Nusselt number decreases, and the friction factor increases. The voidage fraction of the setting has a monotonic effect on both Nusselt numbers and friction factors. Nusselt numbers for high-density are higher than those for low-density settings as the voidage fraction varies. [ABSTRACT FROM AUTHOR]

Plate heat exchangers (PHEs) are widely used in multiple industries and applications ranging from refrigeration to paper, oil and gas, chemical and power industries. In the current study, a novel wavy pattern design is introduced for chevron-type PHEs in order to improve the overall performance of the heat exchanger. The new plate design is manufactured and tested within an experimental test rig. A numerical heat transfer model is also developed to analyze variations of the heat exchanger pressure drop and heat transfer coefficient. Hydraulic and thermal performance of the new plate pattern is investigated using the numerical model and experimental test rig. The effects of the proposed plate pattern on the thermal efficiency and pressure drop of the PHE are compared with those of a conventional plate pattern. Experimental and numerical results confirm that the heat transfer rate is virtually constant in the new designed PHE, while the pressure drop decreases remarkably. Consequently, the performance of the developed wavy chevron pattern is increased by about 10–15% in comparison with conventional chevron patterns. [ABSTRACT FROM AUTHOR]

This article presents an in-depth analysis of internally finned tube heat exchangers, which are used in a broad variety of condensers and evaporators for air conditioners, as well as radiators for vehicles and solar air heaters, amongst other places. The growing need for cooling systems that are more efficient and heat exchangers that take up less space has inspired many studies in this area of expertise. This research uses both experimental and computational analysis to compare and contrast the efficacy of various heat transfer enhancement processes in internally finned tube heat exchangers concerning the impacts they each have and the operating parameters they each need. This study aims to investigate how altering the fins' design affects heat transfer and pressure drop under varying operational situations. This paper examines the ranges in which these correlations have been verified, as several correlations have been created to assist in estimating heat transfer and pressure drop characteristics on internally finned tube heat exchangers. This study extensively delves into various analytical approaches such as Log Mean Temperature Difference (LMTD), Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and other methodologies specifically tailored to address the unique goals of the particular problem. To derive a conclusion with practical significance, we categorize these relationships into multiple groups and conduct a comparative analysis. [ABSTRACT FROM AUTHOR]

The influence of heat transfer and frictional characteristics of air that is turbulent and transitting rectangular channel textured by novel hybrid roughness (multi-V shaped ribs combined with hemispherical protrusion in V-fashion) has been studied experimentally. A uniform solar intensity of 1000 W/m2 is incident over the opposite side of the roughened plate. The relative roughness pitch, angle of attack, Reynolds number, hydraulic diameter, relative protrusion pitch, and relative gap width majorly influence the thermal and frictional characteristics of solar air heater. In this research paper, the effect of Reynolds number from 4281 to 18,250, relative protrusion pitch from 0.375 to 0.625 and relative gap width from 2 to 4 on heat transfer and friction factor on hybrid roughness geometry have been studied. The highest value of Nusselt number is 4.15 obtained at a relative protrusion pitch of 0.5, relative gap width of 2 compared to smooth duct and Reynolds number value of 18,250. By increasing the Reynolds number, the value of friction factor keeps on decreasing and highest value of friction factor of about 3.8 is obtained at a relative protrusion pitch of 0.375, Reynolds number value of 4,281 and relative gap width of 4 as compared to smooth duct. The results of the experiment shows that hybrid roughness performs thermally better than their solitary roughness geometries. Further, Nusselt number and friction factor correlations were also developed and show a very good match with the experimental results. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement is an essential parameter of heat exchangers, that can increase by increasing the value of heat transfer coefficient. So, researchers used different types of inserts, in which, single strip helical screw tape showed excellent enhancement in heat transfer, due to the formation of high-intensity swirl flow. However, to increase more intensity of swirl flow, Double strip helical screw tape inserts (DS-HST) used in present work. An experimental analysis is carried out to analyze thermal and friction factor characteristics of fluid flow in heat exchanger tube, with DS-HST, at twist ratio of 1.5, 2.5, and 3, in the range of Reynolds number from 4000 to 16000, at constant heat flux condition. Experimental results showed that Nusselt number and friction factor achieved excellent enhancement with double strip helical screw tape insert than single strip helical screw tape insert (SS-HST) with decreasing value of twist ratio. The correlation developed for Nusselt number at a range of Reynolds number, twist ratio and a number of strips. Moreover, Thermal performance factor achieved maximum value at twist ratio of 2.5 and 3 for DS-HST, than SS-HST inserts in the higher values of Reynolds number, at constant pumping power. So this range of turbulent flow showed the suitability of DS-HST inserts, which can reduce the size of heat exchangers or thermal applications, utilize energy resources, and decrease pollution in the environment. [ABSTRACT FROM AUTHOR]

This paper focuses on augmentation of heat transfer and thermal performance factor of tubular heat exchanger by using a novel Perforated Rectangular Cut Twisted Tape (PRCTT) and comparison was made with Plain Tube (PT), Simple Twisted Tape (STT) and Rectangular Cut Twisted Tape (RCTT). Analysis of Nusselt number and friction factor for the twisted tape insert having twist ratio (TR) of 3, rectangular cuts of 2 mm width and 1 mm depth is done. Rectangular cuts of different pitch, that is, 3 mm, 5 mm and 7 mm is used for the analysis. To reduce the friction factor, further analysis has been done with perforation of circular hole in the same RCTT with perforation ratio (d/w) of 0.55 in the core of insert. Numerical analysis shows that in turbulent zone (4000 16000), highest enhancement in Nusselt number is 2.3 times and highest enhancement of friction factor by 3.2 times with comparison to plain tube when reducing the pitch of rectangular cuts. Perforation further decreases the friction factor by 20%. Highest thermal performance factor is observed 1.48 with the use of Perforated Rectangular Twisted Tape (PRCTT) at Re = 4000. [ABSTRACT FROM AUTHOR]

This paper will validate two basic concepts of numerical models for prediction of pressure change along the transport pipeline in the case of long distance and high capacity lignite ash pneumatic conveying. Application of various friction factor correlations and variation of given parameter, led to the total of fourteen different numerical models and program codes in FORTRAN. The input data for numerical models are based on comprehensive experimental research of high capacity and long distance Kolubara lignite fly ash pneumatic conveying system within 620 MWe thermal power plant unit under operating conditions. Numerical simulation results are validated against experimental data and subjected to statistical analysis methods. The functional dependence obtained by the least squares method was evaluated using mean squared deviation and correlation ratio. The predicted pressure changes show the best agreement, with the measured decrease of pressure amplitudes along the transport pipelines, for the model based on the momentum balance of air-ash mixture flow and friction factor correlation given by Dogin and Lebedev for the parameter A = 1.4∙10-6. This model achieved the best correlation ratio of 93.99% for Pipeline 1 and 91.33% for Pipeline 2, as well as the best mean squared deviation of 9.58% for Pipeline 1 and 13.66% for Pipeline 2. Also, the fanning friction factor values are fully consistent with previously examined cases available in the literature. Numerical simulation model can be used for prediction of the ash pneumatic conveying capacity and pressure drop for the specified transport pipeline. [ABSTRACT FROM AUTHOR]

The present paper deals with the thermal and hydraulic performance of engine radiator with Al2O3, CuO, and TiO2 nanoparticles distributed at an equal volume fraction of (0.06–0.12%) called THNF (Ternary Hybrid Nanofluid), into the base fluid water, operated under 3–8lpm CFR (Coolant Flow Rate), and fan velocity varied 0.25–1.25 m s–1 at 50% load on the engine. Preparation, detailed thermophysical properties evaluation, and characterization (Scanning Electron Microscopy, Zeta potential), justifying nanofluid durability for the long run. Radiator performance parameter, PEC (Performance Evaluation Criteria), and friction factors are investigated to evaluate the penalty in pressure drop for the heat transfer enhancement. Also, the effects of fuel preheating on engine parameters (BTE and BSFC) using 0.12% THNF coolant on the engine performance at part loads with variable radiator parameters are investigated. The experimental analysis revealed a maximum heat transfer enhancement of 17.6% at a 6lpm coolant flow rate operated under a 0.12% volume fraction of THNF and requiring a 20.6% higher friction factor than water. The PEC value is obtained within the limit of 1.0045–1.098, which indicates a remarkable heat transfer enhancement on nanoparticle addition. Concurrently fuel elevated temperature resulted in in 13.06% higher brake thermal efficiency, 16.6% lower BSFC, and corresponding 13.54% fuel consumption saving obtained at 0.25 m s–1 of frontal air velocity, 6lpm of 0.12% THNF coolant flow rate at 50% load condition on engine and radiator. Therefore, preheating fuel through the radiator waste heat successfully improves the thermal efficiency, lowers the BSFC, and saves fuel consumption. [ABSTRACT FROM AUTHOR]

• The influence of geometric parameters including twist pitch and cross section sizes on friction factor and heat transfer coefficient is studied in the helical cruciform single rod. • Geometric dimensionless numbers are proposed to fit the friction factor and heat transfer coefficient of helical cruciform. • The proposed empirical correlations of frction factor and heat transfer coefficient are validated respectively based on numerical simulation. Helical cruciform fuel is a novel type of nuclear reactor fuel with self-supporting and large surface-volume ratio features, potential to increase the reactor power density. However, the shape of the fuel is so complicated that influence of geometric parameters on thermal hydraulic characteristics was not clearly researched. In this paper, geometric dimensionless numbers are proposed and validated based on the numerical simulation to modify friction factor and heat transfer coefficient correlations proposed through experiments of helical cruciform fuels. Twist pitch of the fuel has a great impact on flow resistance and heat transfer, resulting in the modified coefficient ranging from 0.94 to 1.04 for friction factor and from 0.022 to 0.024 for heat transfer coefficient respectively. Change in cross-section parameters has little influence on the fuel performance, leading to the unit cross-section modified factor for both friction factor and heat transfer coefficient. After fitting the correlations with the dimensionless number, several cases are established to validate the empirical correlations, with a maximum error below 10.0 % for friction factor equation and 8.5 % for heat transfer coefficient correlation when Reynolds number is between 2.7 × 104 and 2.7 × 105. This paper provides a guide for study of heat transfer and fluid flow in helical structures, and a reference for establishment of reactor system model using helical cruciform fuels. [ABSTRACT FROM AUTHOR]

Purpose |!|#8211; The Colebrook equation for determination of hydraulic resistances is implicit in fluid flow friction factor and hence it has to be approximately solved using iterative procedure or using some of the approximate explicit formulas developed by many authors. The purpose of this paper is to compare different Lambert W based solutions of the Colebrook equation and to make comparisons among them and identify some constraints in applicability of certain solutions. Design/methodology/approach |!|#8211; Alternate mathematically equivalents to the implicit Colebrook equation in explicit form with no approximation involved actually exist. Findings |!|#8211; These alternate equations were developed using Lambert W-function. The paper compares various implementations of the Lambert W methodology and shows that some of these are less able than others to yield solutions using modern computer hardware. This is because the functions require the evaluation of terms with numerical values outside the ranges that can be expressed on most computers. Research limitations/implications |!|#8211; Some of existed transformations cannot be applied for high values of relative roughness of inner pipe surface and the Reynolds number. This limitation applied only for computer computations. Other presented transformations do not sufferer of this limitation. Practical implications |!|#8211; Presented procedures can be easily implemented in a computer code. Recommended solution can be used in all cases that can occur in engineering practice. Originality/value |!|#8211; The paper shows some possible practical procedures for solution of the transformed Colebrook equation. Accuracy analysis and comparisons of presented formulas are also performed and recommendation for use is shown. [ABSTRACT FROM AUTHOR]

This paper aims to experimentally investigate pressure drop and water holdup in vertical upward oil-in-water emulsions. As a key factor to extract water holdup with differential pressure method, friction factor is complicatedly associated with the Reynolds number of mixed fluid. However, due to the fact that oil and water phase cannot be easily separated in emulsions, the traditional quick-closing valve (QCV) method is incapable of determining water holdup, which is imperative to determine the Reynolds number of mixed fluid. In this paper, regarded as an auxiliary measurement method, an arc type conductivity probe (ATCP) is utilized to derive water holdup parameter. Combining water holdup and differential pressure information, we extract friction factor and analyze its relationship with the Reynolds number of mixed fluid. Besides, drag reduction phenomena in surfactant aqueous solution and oil-in-water emulsions are discussed as well. Finally, water holdup is predicted using differential pressure information and experimental expression of friction factor, the result of which proves the effectiveness of differential pressure method for the measurement of water holdup in oil-in-water emulsions. [ABSTRACT FROM PUBLISHER]

Flow through packed beds of spheres is a complex phenomenon and it has been extensively studied. Although, there is many different correlations there is still no reliable universal equation for prediction of pressure drop. The paper presents the results of experimental research of pressure drop in packed bed of monosized spheres of three different diameters, 8, 11, and 13 mm set within cylindrical vessel of diameter dk = 74 mm, and two different heights of packed bed, hs = 300 and 400 mm. It has been proposed modification of widely used Ergun's equation in the form of fp = [150 + 1.3(Rep/(1 - ε))](1 - ε)2/(ε3Rep) and new correlation fp = 1/[(27.4 - 25700dh)/Rep + 0.545 + 6.85dh] for pressure drop calculation in simple and convenient form for hand and computer calculations. For total number of 362 experimental runs the correlation ratio of the modified Ergun's relation was CR = 99.3%, and standard deviation SD = 12.2%, while novel relation has CR = 93.7% and SD = 5.4%. [ABSTRACT FROM AUTHOR]

Determining the pipe diameter is one of the principal problems encountered in designing and analyzing pipe flow lines. However, the direct determination of a pipe's diameter is not possible because of the implicit form of the Colebrook resistance flow formula through commercial pipes. Traditionally, the pipe diameter is determined using a trial procedure. In this paper, the pipe diameter problem was solved using explicit equations in terms of the Lambert W-function. The maximum relative errors of the developed solutions are less than 0.013% for the rough and smooth flow regimes and less than 0.8% and 0.6% for the transition flow region between them. In addition, a method for determining pipe diameter under uncertainty, including design graphs, is presented. It is hoped that the developed solution for predicting pipe diameter will be helpful in the analysis of pipe flow and the design of pipelines and water distribution networks. [ABSTRACT FROM AUTHOR]

This paper communicates the enhancement of heat transfer, friction characteristics and thermal performance of micro finned tube fitted with Left/Right and regular insert tape inserts using CNT and CNT/Al2O3 nanofluid. Two different concentrations of nanoparticles were used in the present investigation. In contrast, the CNT/Al2O3 nanoparticles are mixed in a weight ratio (50:50) and sonicated for about 2 hours using a bath type sonicator. The prepared nanofluids are stable for almost 48 hours without any sedimentation. Results show that the increase in nanoparticle concentration in the base fluid increases the performance index under turbulence flow regime while the Reynolds number in the range of 2000< Re<5500. Similarly, the Nusselt number and friction increase by 250% and 400%, respectively, with the maximum concentration of nanoparticle and minimum twist ratio. Results also reveal that the use of alternate arrangement increases the turbulence for maximum friction gain and improvement in the convective heat transfer coefficient. [ABSTRACT FROM AUTHOR]

In this paper, numerical analyses on a concentrated solar receiver pipes have been performed. The fluid is considered to be superheated steam phase. The pressure drops and temperature distribution in the absorber tubes of the parabolic trough solar collector (PTSC) have been explored in detail. In the numerical studies, the experimental data received from the solar test facility located at the Plataforma Solar de Almeria, Spain has been used for the real world application in order to shed a light on the superheated phase of the plant. The RNG k-ε turbulence model is considered for the Computational Fluid Dynamics analyses. In the explorations, especially the fluid behavior at different mass flows has been taken into account. The process has been evaluated for different temperate T and pressure P cases such as Case 1: p = 3.21 MPa, T = 240.4°C and Case 2: p = 10 MPa, T = 500°C. According to the results, the numerical results have been in good agreement within the error rate of 0.79% for the experimental temperature measurements. Therefore, the proposed numerical technique can be generalized for different steam parameters of PTSC in order to estimate the steam characterization for the experimental facility. [ABSTRACT FROM AUTHOR]

Flow and heat transfer analysis of an electrically conducting MHD power law nano fluid is carried out through annular sector duct, under the influence of constant pressure gradient. Two types of nano particles (i.e. Cu and TiO2) are used in power law nano fluid. Strongly implicit procedure, (SIP) is used to simulate the discretized coupled algebraic equations. It has been observed that volume fraction of nano particles, ϕ and magnetic field parameter, Ha are favourable for the heat transfer rate, however, both resist the fluid flow. Impact of applied uniform transverse magnetic field exceeds in the case of shear thickening fluids (i.e. n>1) by increasing the value of Ha as compared to that in shear thinning fluids (i.e. n<1). Therefore, enhancement in heat transfer rate is comparably more in shear thickening fluid. Furthermore, comparable limiting case study with published result is also carried out in this research paper. [ABSTRACT FROM AUTHOR]

The baffling technique is well-known for its efficiency in terms of enhancement of heat transfer rates throught channels. However, the baffles insert is accompanied by an increase in the friction factor. This issue remains a great challenge for the designers of heat exchangers. To overcome this issue, we suggest in the present paper a new design of baffles which is here called graded baffle-design. The baffles have an up- or down-graded height along the channel length. This geometry is characterized by two ratios: up-graded baffle ratio and down-graded baffle ratio which are varied from 0-0.08. For a range of Reynolds number varying from 104 to 2 x 104, the turbulent flow and heat transfer characteristics of a heat exchanger channel are numerically studied by the computer code FLUENT. The obtained results revealed an enhancement in the thermohydraulic performance offered by the new suggested design. For the channel with a down-graded baffle ratio equal to 0.08, the friction factors decreased by 4-8%. [ABSTRACT FROM AUTHOR]

Numerous questions and problems on Earth and questions with respect to other planets arise from morphodynamic processes caused by sediment movements driven by flows of fluids, such as water, air and other gases. A sediment surface opposes the current with a resistance that is determined by its skin or grain roughness. As soon as sand waves, such as ripples and/or dunes, are formed, these bedforms cause a further resistance to the flow, the so-called form roughness. Dependent on the dimensions of the ripples and dunes, the form roughness can be much more pronounced than the skin roughness. The relevant literature provides a large number of solution approaches based on different basic ideas and different result quality. The aim of this paper is a comparative analysis of solution approaches from the literature. For this purpose, 14 approaches to bedform-related friction in the subaqueous case are evaluated using 637 measurements from laboratory and natural settings. We found that all approaches were significantly more accurate for ripples than for dunes. Since this was equally the case for all approaches tested, it is reasonable to assume that this is caused by measurement inaccuracies for dunes in the natural case rather than due to the approaches themselves. The approach of Engelund 1977 proved to be most accurate among all approaches investigated here. It is based on the Borda–Carnot formulation and an additional empirical term. An analytical derivation and justification is provided for this additional term. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study carried out to investigate the influence of different performance parameters on heat transfer and fluid flow characteristics of a roughened double pass duct provided with combination of discrete multi V and staggered shaped ribs. The investigation has covered the range of operating parameter, i.e. Reynolds number (Re) from 3000 to 21000, and roughness parameters, i.e. relative inclined gap distance (Ig/Lv) from 0.4 to 0.8, and angle of attack (α) from 30° to 75° while the other roughness parameters are kept as constant. The Nusselt number, friction factor, and thermohydraulic performance for the artificially roughened double pass duct have been investigated. The results of the study have been compared with that of double-pass channel without roughness and considerable enhancement in the performance of the duct has been achieved. Based on the experimental results, the optimum values of roughness and operating parameters have also been identified. Further, the pumping power reduction to circulate the air has also been investigated. [ABSTRACT FROM AUTHOR]

Among the heat exchangers (HE), the shell and tube type is being widely used in different applications like oil, chemical, and power plant Industries. The incorporation of segmental baffles (SB) improves the HE capacity from higher temperature fluid to lower temperature fluid. Nanofluids can be effectively used to enhance the heat transfer rate. In this study, numerical simulations have been carried out in a shell and tube heat exchanger (STHX). Among HE design methods, Tubular Exchanger Manufacturers Association (TEMA) standard is being used for better design by many researchers. In this paper, the computational fluid dynamics analysis was carried out with Al2O3, CuO, and SiO2 nanofluids amid 1, 3, and 5 vol. % with water emulsion to enhance the heat transfer coefficient of STHX. The nanofluid has been used in the cold fluid of the HE and on the other side hot water is used. From the results, it is noticed that with the increase of Nanofluids, the value of heat transfer coefficients is found to be increasing. The overall heat transfer coefficient has been enhanced for Al2O3, CuO, and SiO2 about 10.41%, 12.27%, and 9.56%, respectively, at 0.22 kg/s for the 5 vol. % addition. It is also depicted that the pressure drop is increasing with the incorporation of nanofluids. [ABSTRACT FROM AUTHOR]

The heat transport and friction factor in a three‐dimensional horizontal concentric annular duct filled with nanofluids comprising clove‐treated multiwalled carbon nanotubes are investigated numerically in this paper. The cylinder's outer surface is thermally insulated, while uniform heat flux is imposed on the cylinder's inner surface. The problem is formulated in dimensionless cylindrical coordinates. The numerical solutions were obtained based on the finite volume technique with second‐order precision, and cover a range of the Reynolds number 1000 ≤ Re ≤ 2000 and nanoparticle weight fractions 0.075, 0.125, and 0.175 wt%. To describe the results for both heat exchange and fluid flow performance, the temperature profile, Nusselt number, heat transfer coefficient, and friction factor are represented. The findings state that heat transport increases as Reynolds is increased and nanoparticles are introduced. The friction factor was also observed to improve as the concentration of nanoparticles increased. In addition, two new Nusselt number and friction factor correlations were established. [ABSTRACT FROM AUTHOR]

The paper presents some modification of the previously published model of thixotropic fluids for the case of fluids with irreversible destruction of the structure. In the second part of the paper the laminar flow of this kind of fluids in pipes is discussed. A simple method of determining the initial value of the structural parameter at the inlet to the pipe is proposed. [ABSTRACT FROM AUTHOR]

The effects of surface roughness and material properties of the planetary roller screw mechanism (PRSM) on the axial stiffness and load distribution are rarely studied. In this paper, the load distribution model is presented by incorporating into friction factor and surface microtopography. The microcontact model is built by considering elastic and plastic regimes to calculate the total actual contact area. Moreover, the load distribution model is modified by introducing surface microcontact coefficient. Then, the influences of the nut position, fractal dimension, fractal roughness, friction factor, axial load, and material yield strength on the axial stiffness and load distribution are studied in detail. The numerical results show that the axial stiffness rises with the increment of the nut position, axial load, fractal dimension, and yield strength, and reduces with the fractal roughness and friction factor increasing. In addition, the uniformity of the load distribution increases with the increment of the fractal roughness, and drops with the increase of the fractal dimension and material yield strength. This investigation lays the foundation for the design, manufacturing, and use of the PRSM. [ABSTRACT FROM AUTHOR]