Heat Transfer Coefficient Of Fluid Research Articles

Development of predictive models for density of hybrid nanofluids using different machine learning techniques

Nanofluids are unique thermal fluids with enhanced heat transfer efficiency relative to conventional thermal fluids. The density of nanofluids is an important thermophysical property that determines the heat transfer coefficient of fluids. Hybrid nanofluids are known to show superior thermal properties compared to normal nanofluids, yet investigation on the predictive modeling of the density of hybrid nanofluids is scarce in the literature. In this report, the application of machine learning (ML) for predicting the density of hybrid nanofluids is examined. The considered hybrid nanofluids consist of Al2O3/SiO2, TiO2-SiO2, Fe3O4-MWCNT, Al2O3-CNT, Al2O3-MWCNT, TiO2-MWCNT, CeO2-MWCNT, ZnO-MWCNT, MgO-MWCNT, CuO-MWCNT, Co3O4/rGO, TiO2-MgO, Ag-GNP, and ND-Fe3O4 nanoparticles suspended in H2O, GB, DW, and W-EG (60:40%). The ML algorithms examined in this report include: support vector regression optimized with genetic algorithm (SVR-GA), Gradient Boost Regression Algorithm (GBR) with Grid Search Optimization (GBR-GSO), Decision Tree (DT), and Voting Ensemble (VE). These models were developed using the following input parameters: temperature, volume concentration, the density of individual nanoparticles, and density of the base fluid. Excellent correlations of 99.81%, 99.76%, 96.36%, and 95.05% were obtained for the SVR-GA, GBR-GSO, VE, and DT, respectively. This result shows that the SVR-GA had the highest correlations with experimental results. The development of a highly accurate predictive model for the density of hybrid nanofluids is essential because it can facilitate the rapid design of heat transfer devices. Developing a diffusivity model for hybrid nanofluids using a machine learning approach is a possible extension of the present study.

Mechanism analysis of the influence of nanoparticles on the convective heat transfer coefficient of traditional fluids

With the continuous progress of science and technology, the heat transfer performance of electronic chips and internal combustion engine pistons is increasingly required by industry. The traditional pure liquid can hardly meet the current heat transfer requirements, and it is known that the heat transfer performance of solids is always better than that of fluids. Therefore, adding solid particles to the fluid has a positive effect on the heat transfer performance of the fluid. In this paper, an experimental system is established to study the heat transfer performance of SiO2-water nanofluids, and the variation of each physical parameter and convective heat transfer coefficient of SiO2-water nanofluids flowing in a circular tube at different volume fractions is measured. The microscopic mechanism of the enhanced heat transfer of nanofluids is also analyzed from the perspective of nanoparticle's micro-motion by numerical simulation. The results show that the convective heat transfer coefficients of nanofluids gradually increase with increasing volume fraction of nanoparticles under the same conditions. The convective heat transfer coefficients of SiO2-water nanofluids with volume fractions of 0.5 %, 1 %, and 2 % increase by 15.1 %, 25.9 %, and 36.8 %, respectively, compared with pure water. Then the extent of the effect of nanofluid physical parameter changes and nanoparticle micro-motion on the improvement of nanofluid heat transfer performance is analyzed. It is found that the micro-motion of nanoparticles has a greater effect on the enhanced heat transfer of nanofluids compared to the variation of physical parameters. It is also found that the conventional convective heat transfer coefficient formulation for single-phase flow is not applicable to calculate the convective heat transfer coefficient of SiO2-water nanofluids. Therefore, the new formulations based on the convective heat transfer coefficient of SiO2-water nanofluids in different flow regimes are established.

Influence of surface roughness on the heat transfer coefficient of fluids in an additively manufactured supercharger

The supercharger is intended for heating a fluid (gaseous helium or gaseous nitrogen) used for the pressurization of fuel tanks of oxidizer and propellant of a rocket engine. The fluid is heated with the generator gas downstream the turbine. A supercharger with increased channel surface roughness was made according to an additive technology. High roughness is one of the features of producing parts by selective laser melting. The article presents a method of calculating the heat transfer of generator gas and nitrogen, as well as the results of heat transfer both with and without account of the surface roughness in the channels of the liquid-propellant engines additively manufactured supercharger. Firing tests were carried out at the research base of NPO Energomash JSC. The calculated and experimental values of the temperature of the working medium at the outlet of the supercharger are compared.

Thermal performance of new type plate heat exchanger with spring turbulence generator using nanofluid flow

ABSTRACT In this study, a new design has been developed to increase the thermal performance of a plate heat exchanger. In the developed design, springs are placed on the heat exchanger plates at an angle of 45°. In this study, which aims to improve heat transfer by increasing turbulence, nanoparticles were also used to increase the heat transfer coefficient of the heat transfer fluid. The nanoparticles used are Al2O3 and CuO in three different densities. The performance factor of the system was calculated experimentally with these fluids entering the heat exchanger at six different speeds. The highest performance factor obtained was 1.33, and it was obtained by using 1% mass ratio Al2O3 nanoparticles. The highest value for CuO, the other nanoparticle used, was determined as 1.27. The highest increases in heat transfer are 60.7% and 56.5% for Al2O3 and CuO, respectively.

Non-uniform heat transfer behavior of wet foam fluid in a narrow fracture channel

The heat transfer characteristic of wet foam fluid in some channels has not been fully understood due to its special evolution characteristic. In this study, we explore distribution laws for the temperature and the heat transfer coefficient of the VES-CO2 foam fluid on the heating surface of a narrow fracture channel. The results show that the heat transfer coefficient of foam fluid on the heating surface is affected by multiple factors, such as the foam quality, foam structure, inclined channel and so on. We find that the temperature on the middle part of the heating surface is higher. Especially, due to the drainage of the flowing wet foam, there are different heat transfer characteristics in the middle and at the side of the heating surface. The heat transfer coefficient displays fluctuation behavior at the side of the heating surface. In the inclined channel, the heat transfer coefficient increases with the inclination angle for the positive inclination, and for the lateral inclination, the average cross-sectional heat transfer coefficient decreases with increasing inclination angle. In the low-permeability oil and gas development, this research has important significance for understanding the heat transfer phenomenon of wet foam fluid in formation fracture. It is also expected that this study could provide a reference for related application of wet foam fluid in some special channels.

THERMAL PERFORMANCE OF SINTERED COPPER WICK HEAT PIPE USING WATER-BASED HYBRID NANOFLUIDS: AN EXPERIMENTAL STUDY

Relatively stable titania and silica-distilled water-based hybrid nano fluid along with surfactant are proved to be more efficient in thermal performance enhancement of heat pipes which are used for efficient cooling in electronic industry. In the current research, sintered copper wick heat pipe is utilized due to its high level of capillary action and low thermal resistance of copper wick. In this article, the vertically mounted copper sintered heat pipe containing hybrid nano fluids is investigated to measure the wall temperature as well as thermal resistance through force convection. The experimentation was carried out at heat loads of 4W, 8W, 12W, 16W and 20W by using water, titania-distilled water nano fluids and titania-silica/distilled water hybrid nano fluid filled in heat pipe in order to compare the results. By increasing the input power, the wall temperature increases from evaporator to condenser section. Maximum reduction in average vapor temperature of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was observed to be 35.74% and 31.10% as compared to water filled heat pipe at 20 W respectively. The maximum decrement in thermal resistance of titania-silica/distilled water hybrid nano fluid filled heat pipe and titania-distilled water nano fluid was observed to be 30.66% and 17.33% in comparison with water based filled heat pipe at 8 W respectively. The highest enhancement in heat transfer coefficient of titania-silica hybrid nano fluid filled heat pipe and titania-distilled water nano fluid filled heat pipe was achieved to be 29.73% and 16.21% compared to water filled heat pipe at 8 W respectively. A vi

Integral identification of fluid specific heat capacity and heat transfer coefficient distribution in heat exchangers based on multiple-case joint analysis

Estimating detailed heat transfer characteristics efficiently is crucial for analysis and optimization of thermal systems. However, there still lacks accurate methods for identifying local parameters in heat exchangers, mainly due to the hindrance of sensor placement. This work proposes a method for identifying fluid specific heat capacity and heat transfer coefficient distribution in heat exchangers from lumped datasets consisting of multiple working cases, which only include mass flow rates of fluids and their inlet and outlet temperatures. Dividing the fluid temperature range in the dataset and combining energy conservation equations of all cases gives a matrix equation. Solving it with the least squares method gives the specific heat capacity distribution. Combining this method and reinforcement learning offers a two-stage strategy for identifying the heat transfer coefficient distribution. The first stage gives an approximation of the distribution, and the second stage refines the approximation by considering secondary effects such as radial property variation. A heat transfer process between supercritical carbon dioxide (sCO2) and water is used to validate the method. Results show that relative identification errors of sCO2 specific heat capacity and heat transfer coefficient distributions are within 3.1% and 6.3%, respectively. The satisfying accuracy proves the proposed method’s efficacy.

Development of a Fast Thermal Model for Calculating the Temperature of the Interior PMSM

A 40 kW–4000 rpm interior permanent magnet synchronous machine (IPMSM) applied to an electric vehicle (EV) is introduced as the study object in this paper. The main work of this paper is theoretical derivation and validation of the first-order and multi-order transient lumped-parameter thermal network (LPTN) for the development of a fast thermal model. Based on the first-order LPTN built, the study finds that the heat transfer coefficient of fluid and thickness of the air gap layer are the main influencing factors for the final temperature and time of reaching the steady state. The larger the heat transfer coefficient of fluid is, the lower the steady node temperature is. The smaller the air layer thickness is, the lower the steady node temperature is. The multi-order LPTN theory is further deduced based on the extension of the first-order LPTN. For the constant load and rectangular periodic load, transient node temperatures of the IPMSM are obtained by modeling and solving the first order inhomogeneous differential equations. Temperature rise curves and efficiency maps of the IPMSM under load conditions are realized on a dynamometer platform. The FLUKE infrared-thermal imager and the thermocouple PTC100 are used to validate the mentioned method. The experiment shows that the LPTN of the IPMSM can accurately predict the node temperature.

Characteristics analysis of an exhaust thermoelectric generator system with heat transfer fluid circulation

Low heat transfer performance in the exhaust channel limits the thermoelectric conversion efficiency of the internal combustion engine exhaust thermoelectric generator. Enhanced heat transfer of exhaust channel improves the thermoelectric performance of the generator, though with an increase in exhaust back pressure. A new type of thermoelectric generator with heat transfer fluid circulation is proposed. A heat transfer fluid replaces the exhaust after heat exchange with the exhaust into the generator. It is possible to improve the thermoelectric performance of the system, counting on the high heat transfer coefficient of the heat transfer fluid in the generator without changing the exhaust channel. A mathematical model of the novel system is constructed, considering the system structure, resistance power consumption, temperature dependence of the physical properties of the module. The influence of structural parameters and heat transfer fluid parameters on thermoelectric performance are analyzed using this model. It is found that the peak net output power of the new generator can be increased by 77.5 % compared with the traditional generator, while the number of modules can be reduced by 83.2%. Therefore, an optimal exhaust heat exchanger configuration is obtained to maximize the net output of the system. In addition, as the heat transfer fluid flow rate increases, the net output power goes up and then down, an optimal heat transfer fluid flow rate can be obtained. The results also give technical guidance on the design and operation criteria of the thermoelectric generator.

CFD study on the effect of nanofluids in natural circulation loop

A vertically placed natural circulation loop consists of a heater in the riser pipe and a heat exchanger at the top end for heating and cooling the working fluid. In this investigation, the heat source is placed in the side pipe of the loop called riser. The performance of natural circulation loop is investigated with water, Alumina nanofluid and Copper Oxide (CuO) nanofluid of 0.5%, 1% and 1.5% (by wt) concentration. The behaviour of the loop for various heat inputs at the heat source is investigated with water and then with Alumina and CuO nanofluids.It is found that the performance of the loop is high when the working fluid used is copper oxide nanofluid compared to alumina nanofluid and water. The mass flow rate is highest for 1.5% CuO nanofluid which is 4.58 g/s. Heat transfer coefficient of the loop fluid at the heat source increases with an increase in the heat input at the heat source. There is also a significant difference for heat transfer coefficients of water and the nanofluids of CuO and alumina in the natural circulation loop for various amounts of heat supplied in the heat source.

Numerical solutions of convective transport on Brinkman-viscoelastic fluid over a bluff body saturated in porous region

Convective is a fundamental mechanism in heat transfer analysis. Convective heat transport refers to the transfer of heat from one stage to another. In order to produce the preferred output, it is critical to understand the properties of fluid flow. In this study, mixed convection flow is considered, which is defined as a situation where the forces of pressure and buoyancy interact. The goal of this endeavor is to scrutinize the numerical solution of Brinkman-viscoelastic fluid for mixed convection transport over a horizontal circular cylinder as one of the bluff body geometry. Using the necessary similarity transformation, the governing equations were converted into a less complicated form and numerically solved using Keller-box procedure. The influence of mixed convection, Brinkman and viscoelastic parameters towards the fluid velocity and temperature together with skin friction and heat transfer coefficient is analyzed and demonstrated in graphs and tables. This study has revealed that the distribution of fluid velocity, skin friction and heat transfer coefficient had strengthened due to rising values of mixed convection parameter and declined by virtue of increasing viscoelastic and Brinkman parameters. The temperature profile, on the other hand, clearly demonstrates the increasing trend as the Brinkman and viscoelastic parameter increase and declines because of mixed convection. The results show that all of the significant parameters in this investigation affluence the fluid flow characteristics. The provided theoretical results will develop a thorough understanding on boundary layer issues and will be used as a reference for future research or validation.

SIMULATION OF WATER DROPLET IMPINGEMENT ON A HEATED SURFACE- SINGLE AND DOUBLE DROPLETS

The present numerical work is concerned with the single drop and double drops impingement on a heated surface. Fluid flow and heat transfer coefficients were modeled using a volume of fluid (VOF) code. The stainless –steel thin plate surface is uniformly heated to reach a constant temperature at (50C°), this was done by using relatively thicker plate underneath the heated plate. The thick plate is made of high conductivity aluminum alloy 2mm thickness. Relatively a lower temperature water drop is used for cooling to ensure that drop temperature remains below the boiling point of water. The drop –plate initial impingement distances were varied in the range (10-60) cm which represent an impact velocity in the range (1.4-3.4) m/s. The single drop fluid flow simulation results are compared with that in the literature, while the heat transfer fluid flow results are represented as instantons heat transfer coefficient variation as alternative to values of heat flux on the surface. Double drops impingement results are then presented and its features are compared to the single drop. Results show that the flow characteristics for the double drops are similar to the single drop at small distances with smaller coverage areas during impingement with lower heat removal rates. As distances increase rebound and splash occurs leading to bigger coverage areas during impingement with relatively smaller heat coefficients compared to the single drop one. The present results shows the same behavior for drop deformation when compared with M.pasandideh-Fard et al. [1] numerical results with an agreement of 90 % and 95 % in calculations the spread factor and impact velocities respectively. The calculated average heat coefficients show acceptable values with that given in literature.

Steady state modeling of steam condensate cooler

Mathematical models for steam condensate cooler were developed. The models were deduced by applying the principle of conservation of energy and yielded an ordinary differential equation, which were solved by using MatLab ODE45 solver and validated using industrial data of a fertilizer company. The result gives minimum percentage absolute error or deviation between model predictions and industrial plant of 0.09% and 0.10% respectively for hot and cold fluid outlet temperature. These shows that the developed model predicted the fluid outlet temperature of the steam condensate cooler closely and the models were used to study the effects of process parameters such as fluid inlet flow rate and heat transfer coefficient on the performance of the steam condensate cooler.

Numerical Simulation of Shell and Tube Heat Exchanger Based on Fluent

In this paper, the classical shell-and-tube heat exchanger is taken as the research object, and the numerical simulation of the heat exchanger is carried out by using Fluent software. The nephogram of temperature field, velocity field and pressure field on the shell side of the fixed tube-and-plate heat exchanger with different baffle spacing is obtained. The variation law of fluid flow and heat transfer coefficient on the shell side of the heat exchanger with different baffle spacing is analyzed. the ratio of convective heat transfer coefficient ᵅ to the third power of pressure drop ∆pis used as the comprehensive performance evaluation index of the heat exchanger, which has a certain reference for evaluating the comprehensive performance of heat exchanger under different baffle spacing.

Efficient Evaluation of Heat Exchangers Behaviour in Nuclear Power Plants

This paper studies the performance of the primary and secondary flow paths of the Heat Exchangers (HEXs) in the Nuclear Power Plants (NPP). Explicit solutions for the wall temperature, primary and secondary wall temperatures of the HEX are presented. Therefore, closed form expressions for wall temperature, primary and secondary wall temperature are proposed. Moreover, performance analysis of HEX is investigated. Curves for the HEX wall temperature are introduced with special emphasis on the initial wall temperature. The various effects of pipe wall heat capacities, perimeter, fluid Heat Transfer (HT) coefficient and wall HT coefficient on the HEX are evaluated. The obtained results confirm that the surface contact between the two fluid passes reduces the temperature to some extent at 5 seconds. Furthermore, it is limited to the pipe length and contact time. As a final point of observation, the distributed temperature through the HEX structure increases with the decrease of perimeter. Since, the wall area decreases with the decrease of perimeter. The proposed work allows more control of the HT process within the HEX. Consequently, the performance of NPPs can be improved.

Noninvasive Method to Measure Thermal Energy Flow Rate in a Pipe

Abstract A noninvasive, thermal energy flowrate sensor based on a combination of heat flux and temperature measurements is developed for measuring the volume flowrate and the fluid temperature in a pipe. The sensor is covered by a thin-film heater and clamped onto the outer surface of the pipe. Two types of thin-film thermocouple elements are compared to minimize the thermal contact resistance R″ between the thermocouple and the surface of the pipe. A thin, flexible thermopile heat flux sensor (PHFS) is mounted over the thermocouples. A one-dimensional transient thermal model is applied before and during activation of the external heater to provide estimates of the fluid heat transfer coefficient h. The results are correlated with the volume flowrate Q and the fluid temperature Twc. Several different parameter estimation codes are used to estimate the optimal parameters by using the minimum root-mean-square (rms) error between the analytical and experimental sensor temperature values. The experiments are completed over a range of volume flowrates—1.3 gallons/min to 14.5 gallons/min. Encouraging measurement results give good correlation, repeatability, and sensitivity between the heat transfer coefficient h and the volume flowrate Q with an accurate estimation of the fluid temperature Twc. The resulting noninvasive thermal energy flowrate sensor can be used to estimate the volume flowrate and the fluid temperature in a variety of applications.

Thermal analysis in swirling flow of titanium dioxide–aluminum oxide water hybrid nanofluid over a rotating cylinder

The purpose of this study is to examine the flow features and heat transfer in the presence of nanoparticles which are used to enhance the thermo-physical properties such as thermal diffusivity, thermal conductivity and heat transfer coefficient of the base fluid. In this work, we analyze thermal features of hybrid nanofluid flow over a stretchable swirling cylinder. Titanium dioxide $$\left( \text {TiO} _{2}\right)$$ , and aluminum oxide $$\left( \text {Al}_{2}\text {O} _{3}\right)$$ are taken as nanoparticles with water as a base fluid. Moreover, the significant characteristics of magnetic flux, thermal radiation and viscous dissipation have been considered to control the flow and thermal mechanisms. The governing system of partial differential equations (PDEs) is transformed into system of ordinary differential equations (ODEs) by mean of similarity transformations. The numerical and graphical results for the flow and heat transfer are obtained by employing a technique, namely bvp4c in MATLAB. The arising parameters which influence the physical problem such as Reynolds number, magnetic field parameter, volume concentration of nanoparticles, radiation parameter, Eckert numbers and Prandtl number are discussed against flow and thermal fields. The analysis eventually proves that nanoparticles are more superior for heat transfer enhancement than usual fluids. An increment in the rate of heat transfer is revealed with an increase in volume fraction of the nanoparticles.

Algorithm Scheme to Simulate the Distortions during Gas Quenching in a Single-Piece Flow Technology

Low-pressure carburizing followed by high-pressure quenching in single-piece flow technology has shown good results in avoiding distortions. For better control of specimen quality in these processes, developing numerical simulations can be beneficial. However, there is no commercial software able to simulate distortion formation during gas quenching that considers the complex fluid flow field and heat transfer coefficient as a function of space and time. For this reason, this paper proposes an algorithm scheme that aims for more refined results. Based on the physical phenomena involved, a numerical scheme was divided into five modules: diffusion module, fluid module, thermal module, phase transformation module, and mechanical module. In order to validate the simulation, the results were compared with the experimental data. The outcomes showed that the average difference between the numerical and experimental data for distortions was 1.7% for the outer diameter and 12% for the inner diameter of the steel element. Numerical simulation also showed the differences between deformations in the inner and outer diameters as they appear in the experimental data. Therefore, a numerical model capable of simulating distortions in the steel elements during high-pressure gas quenching after low-pressure carburizing using a single-piece flow technology was obtained, whereupon the complex fluid flow and variation of the heat transfer coefficient was considered.

Effect of hybrid nanofluids on thermal and hydraulic characteristics of hexagon tube

The commonly determinations of present study are evaluation numerically the thermal transfer and hydraulic distribution inside the turbulent flow pattern for Al2O3-water nanofluids and hybrids fluid of (Al2O3 and CuO) dispersed in pure water concluded a straight hexagon pipe with constant thermal heat flux thermal conditions. 20 nm average diameters of nano particles and 0.1% volume fraction is employed. The numerical analysis includes the numerical simulation of straight tube model by a package ANSYS FLUENT 18 for constant heat flux value of 1 × 104 W/m2 and the Reynolds number had a range of 6 × 103 to 4 × 104. The consequences displayed that heat transfer coefficient of hybrid fluid was better than that of Al2O3-water and pure water by 12% and 23.4% respectively at all Reynolds numbers. The friction factor of hybrid fluid is superior to that of nanofluid and pure water by 4.6% and 11.7% respectively. It found improvement in thermal performance of hybrid fluid compared to that of nanofluids and the pure water. The numerical consequences of Nusselt number values and friction factor magnitudes are validated with the literature consequences obtained and display significant agreement, with a deviation of 7.8 % and 6.4% respectively.

A general heat transfer correlation for flow condensation in single port mini and macro channels using genetic programming

• Evaluated previous flow condensation heat transfer coefficient correlations. • Proposed a new correlation for condensation heat transfer in mini and macro channels. • Verified the model with 6521 data points from 40 published papers. • Discussed the effects of the input parameters on the heat transfer coefficient. A new general explicit correlation is proposed to predict the heat transfer coefficient of fluids condensing in conventional and mini channels. The expression has been developed by correlating the Nu mix number with Re mix , Pr mix , phase density ratio, P res , We GT , and Fr L using genetic programming for the two-phase flow. The model has been validated with a big dataset consisting of 6521 data samples, covering a wide range of fluids used in refrigeration and heat pump industries, cross-sectional geometries (different diameters), mass fluxes, and saturation temperatures. The new generalized correlation fits the wide range of data points used with an average relative error of 17.82 %. The same database has been used to compare predictions of eight correlations available in the literature, but they failed to give a reasonable estimation of the present experimental results.