Heat Transfer Coefficient Of Fluid Research Articles

Saturated nucleate pool boiling of cryogenic fluids: Review of databases, assessment of existing models and correlations, and development of new universal correlation

The absence of a comprehensive and reliable nucleate pool boiling database for heat transfer coefficient (HTC) of cryogenic fluids is the driving force behind this study. Such a database is essential to evaluating the predictive accuracy of existing tools, including both models and correlations, and to pioneering the development of a new, more accurate predictive method. To address this need, a new Consolidated Cryogenic Nucleate Pool Boiling Database (comprised of 2908 data points) was compiled, with emphasis on HTC from flat horizontal and vertical surfaces, drawing from the broad literature resources available from across the globe. The database enabled a comprehensive assessment of prior models and correlations, and careful examination showed most of these tools yield unacceptably large errors in predicting the HTC data, especially for elevated pressures and large heat fluxes. Consequently, a new correlation is proposed for all cryogenic fluids combined, which is fine-tuned to outperform prior predictive tools, particularly for elevated pressures and large heat fluxes. The new correlation has a Mean Absolute Error (MAE) of 25.36 %, with 64.5 % of the predictions falling within ±30 % of the data and 87.2 % within ±50 %. This exceptional predictive capability positions the new correlation as a robust tool for both thermal design and performance assessment of a broad variety of devices and systems.

Thermal Energy Storage Heat Exchanger Design: Overcoming Low Thermal Conductivity Limitations of Phase-Change Materials

Abstract Recently, there has been a renewed interest in solid-to-liquid phase-change materials (PCMs) for thermal energy storage (TES) solutions in response to ambitious decarbonization goals. While PCMs have very high thermal storage capacities, their typically low thermal conductivities impose limitations on energy charging and discharging rates. Extensive research efforts have focused on improving PCM thermal conductivity through the incorporation of additives. However, this approach presents challenges such as achieving uniform mixtures, maintaining high latent heat, and cost. Alternatively, it has been demonstrated that, in this study, reducing the length scale of the PCM-encasement thickness can eliminate the low thermal conductivity effect of PCMs. To illustrate this concept, a one-dimensional PCM slab was numerically simulated. The thickness of the slab was varied to represent dimensions found in flow passages of compact heat exchangers, and the heat transfer coefficient of the heating fluid was varied to represent lower and upper bounds while also including nominal values encountered in air-to-air heat exchangers. The thermal conductivity was parametrically varied from the natural value of the PCM to simulated enhanced values (potentially achieved through additives) of up to 400 times larger. Results show that reducing the PCM-encasement thickness yields substantially better performance than by improving the thermal conductivity, thereby demonstrating the potential for compact heat exchanger design to overcome the PCM thermal conductivity limitations.

Studies on Photovoltaic Thermal System Utilising Titanium Oxide Nano Fluid Experimentally

The present study was designed to experimentally investigate the performance of a solar water heater consisting of a flattened tube absorber with spiral configuration. The analysis is carried out by using water as the working fluid adopting forced circulation for various flow rates of 0.05 kg/s, 0.1 kg/s, 0.15 kg/s, 0.2 kg/s and 0.3 kg/s. The effect of mass flow rate on the flatness of the tube and spiral configuration of the absorber is investigated. The instantaneous efficiency, outlet fluid temperature, Reynolds number, Nusselt number, and heat transfer coefficient, friction factor, and Dean number are investigated. The results presented indicate higher instantaneous efficiency of a flattened tube absorber and a highest outlet temperature was obtained for a mass flow rate of 0.1 kg/s. The removed energy parameter FRUL increases by 3.5% and the absorbed energy parameter FR(τα) increases by 2% for every increase in a flow rate of 0.05 kg/s. The values of the Nusselt number, friction factor and dean number obtained experimentally were compared with numerical correlation and the deviation was found to be. within limits. The Dean number was calculated for different curvature ratio of κ1 ¼ 0:141, κ2 ¼ 0:070and κ3 ¼ 0:047 increase dean number with the increase in curvature ratio was found resulting in an increased Nusselt number better heat transfer was obtained

Numerical Investigation Into Convective Heat Transfer Coefficient of the Grinding Fluid Used in a Deep Grinding Process

Numerical Investigation Into Convective Heat Transfer Coefficient of the Grinding Fluid Used in a Deep Grinding Process

Experimental study on impact patterns and dynamics characteristics of NaCl water droplet with different concentrations on heated surface

This paper reports the experiments for NaCl water droplet with various concentrations impact on heated surface (50 ∼ 400 °C) at Weber numbers from 67 to 101. The impact patterns, spread diameters, residual energy and rebound times were studied in detail. The results show that the patterns can be divided into deposition, partial rebound, rebound, breakup and jet ejection for droplet with different concentrations impact on heated surface, and mapped the distribution of patterns based on the Tw/TsatlgWe and Tw/TsatlgRe parameters. In the deposition region, stable spreading diameter decreases with increasing concentration. At high surface temperatures, high concentration droplets boil more violently due to the intense Marangoni effect and the fluid heat transfer coefficient increases. Moreover, the models of the relationships between the dimensionless maximum spreading factor and Weber number and Reynolds number were established, which optimizes the prediction of spreading of droplets with different concentrations. Based on the energy conservation equation, residual energy was found to decrease with increasing concentration. Rebound time decreases with increasing concentration. Moreover, droplet breakup is resulted from boiling bubbles and lateral splashing of atomized droplets. Besides, the NaCl water droplet is more likely to breakup and jet ejection compared to pure water droplet.

Soft computing approaches for prediction of specific heat capacity of hybrid nanofluids

AbstractNanofluids are thermoelectric substance with a greater thermal transmission effectiveness than traditional thermal fluids. Nanofluid's specific heat capacity (SHC) is a crucial thermophysical parameter since it controls the fluid's heat transfer coefficient. Surprisingly few research investigations have been done on the prognostic modelling of the specific heat capacity of fusion nanofluids, despite the fact that numerous experiments have been conducted on the heat transfer capacitance of blended nanofluids. This study focuses on the use of algorithms based on machine learning procedures (MLP) to estimate the SHC of blended nanofluids. Numerous numbers of hybrid nanofluids are investigated in this investigation. Total of 984 samples of hybrid nanofluids for specific heat capacity has been collected from nine experimental research papers. Various MLP techniques were utilized in this analysis, including extreme boost gradient boost regression (XGB), support vector regression augmented with a genetic algorithm (support vector regression [SVR]‐genetic algorithm [GA]), grid search optimized based gradient boost regression algorithm (GBR) (GBR‐GSO), and voting ensemble procedure (VE). The obtained correlation coefficients of the SVR‐GA, XGB, VE and GBR‐GSO models for the testing dataset are 98.43%, 96.29%, 94.4% and 96.55% respectively. The SVR‐GA model showed a better predictive accuracy relative to other ML models. This SVR‐GA anticipated model could be used for quick and reliable prediction of the SHC of blended nanofluids which reduces the burden associated with experimental measurement possible future work includes applying a machine‐learning strategy to the problem of determining the diffusivity of hybrid nanofluids.

Experimental Investigation to Improve Heat Transfer Rate of Transformer Oil Using Cuo Nanoparticles

In this research, we employed a statistical experimental design approach, specifically the Taguchi method using an L9 orthogonal array robust design, to optimize experimental conditions. Our aim was to maximize the Heat Transfer coefficient of CuO-Transformer oil Nano fluid. We carefully selected three controllable factors with different levels: Concentration of Nanoparticles (0.1, 0.2, and 0.3g/lit), Size of nanoparticles (10, 15, and 20 Nm), and Ratio of Surfactant weight to Nano particles weight (0.1, 0.5, and 1).Our analysis of the results highlighted the significant role played by the Size of nanoparticles in influencing the heat transfer coefficient of the Nano fluid, accounting for approximately 88.852% of the variation. We determined the optimal settings for these three factors to maximize the heat transfer coefficient: Concentration of Nano particlesof0.2g/lit, Size of Nano particles of 10 Nm, and Ratio of Surfactant weight to Nano particles weight of 1. The Heat transfer coefficient predicted by ANOVA under these optimized conditions was 559.443W/m2 K and by regression model was 549.45 W/m2 K.To validate our findings, a confirmation test was conducted at these optimal conditions, and the results demonstrated a high degree of consistency between the experimental and predicted values.

Experimental thermal performance investigation of double pipe heat exchanger using MWCNT/water nanofluid

This paper presents an experimental study investigating the thermal performance of multiwall carbon nanotubes in a twin-pipe heat exchanger using a water-based fluid. The research followed a two-step method, where a concentration of 0.01 weight percent of SDS surfactant was utilized to prepare the carbon nanotubes. The heat transfer coefficient, friction coefficient, and overall heat transfer coefficient of the nanofluid were compared to those of the base fluid. The results revealed that the addition of a small amount of multiwall carbon nanotubes significantly enhanced the thermal conductivity and heat transfer coefficient of the water-based fluid. Moreover, the heat transfer coefficient exhibited an increase with higher Reynolds numbers. When the nanofluid flowed counter currently and was in the outer tube, the highest values for the overall heat transfer coefficient and the heat transfer coefficient were determined as 2864 and 7655.7 W/m2K, respectively. The findings indicate notable improvements in the thermophysical and thermal characteristics of the nanofluid.

Research on one-dimensional digital twin algorithm of plate heat exchanger

Based on the differential idea, this article establishes two segmented algorithms which are the linear equations method and iterative method for solving the one-dimensional digital twin of the temperature field and pressure field of plate heat exchanger (PHE). The segmented algorithms are to consider the change of the physical properties of the fluid along the flow direction, which makes the solution of the temperature field and pressure field more accurate than that without segmentation. It can still get other important parameters besides temperature and is easy to converge with a few iterative steps. When the boundary conditions are known, it can accurately solve the heat transfer, wall temperature, convective heat transfer coefficient, temperature field and pressure field of fluid. Under six groups of test conditions, the heat exchange, temperature and pressure calculated by the two algorithms are compared with the commercial software Flownex, when the number of segments is 100, the average maximum error of each segment is not more than −0.39%, −0.97%, and 0.18%, respectively. To balance accuracy and calculation speed, this article also explores the impact of the number of segments on accuracy. It is found that when the number of segments increases to 10, the impact on the calculation accuracy can be ignored. Compared with Flownex, these two algorithms have smaller errors, and the solution speed of solving linear equations method is faster than that of iteration. It provides application value for emerging digital twin technology, data center chilled water system and other projects and industries that need to accurately control the outlet temperature and wall temperature of PHE.

Study on the heat transfer characteristics of a plate-fin-typed precooler considering cooling fluid phase change

A quasi-two-dimensional calculation method has been proposed to design a plate-fin-typed precooler with high efficiency and low resistance. This method considers the variation of fluid properties during the heat transfer process, particularly for cryogenics with phase change. The precooler heat transfer characteristics are comprehensively investigated based on the proposed method and calculation models. The calculation results demonstrate that the proposed method effectively explores the fluid properties distribution, such as the temperature distribution and steam quality distribution inside the precooler. Besides, the hot fluid temperature drop exceeds 1200 K, while the pressure drop remains below 15% of the inlet pressure above all cases. Moreover, the heat transfer performance between cooling fluid and hot fluid is compared. It is worth noting that the cooling fluid heat transfer coefficient is10∼102 magnitude higher than that of the hot fluid, especially when the cooling fluid steam quality is below 0.60. Therefore, it is critical to improve the heat transfer performance of the hot fluid for the precooler. Additionally, the first heat exchanger inside the precooler plays a more important role in heat transfer than heat exchangers at other locations because the temperature drop and pressure drop inside the precooler account for the largest proportion, with a value up to 50%.

Enhanced heat transfer study of thermoelectric generation system based on bidirectional coupling simulation

ABSTRACT To improve the performance of thermoelectric generator (TEG) for recovering the waste heat of thermaI fluid, a fluid-thermoelectric multiphysics numerical model is developed by using a bidirectional-coupled simulation method. The interaction between the thermal fluid and the TEG system is considered in this method and the numerical model is experimentally validated. Two numerical models of TEG systems with straight fins and corrugated fins are established, respectively. The temperature and potential distributions of the TEG at different inlet velocities and temperatures are analyzed. The results show that the corrugated fins can enhance the convective heat transfer, thereby improving the output characteristics of TEG. The developed model can predict the output characteristics of TEG system accurately. The error between the simulated and experimentally measured open-circuit voltage does not exceed 2.41%. Increasing the inlet air velocity and temperature improves the TEG hot side temperature, thus increasing its output power. Compared with the TEG system with straight fins, the heat transfer coefficient of the thermal fluid in the TEG system with corrugated fins was improved by about 10%. The output power and conversion efficiency were also improved by 18.9% and 0.12%, respectively, at a higher inlet velocity of 5.36 m/s.

Magnetic dipole dynamics on Reiner–Philippoff boundary layer flow

Magneto-thermomechanical applications range from magnetic resonance imaging to electric diodes and the design of dielectric grease. To contribute significantly to the biomedical industry for proper prediction and treatment of diseases such as cancer, stenosis, and technological advancement in the design of electronic tools. This study presents the significance of magneto-thermomechanical modeling of Reiner–Philippoff fluid flow subject to thermal radiation influence. The Reiner–Philippoff fluid encapsulates the properties of shear-thinning, shear-thickening, and Newtonian fluids in different viscosity regimes. The main-stream velocity ue is considered in its generalized form as well as taking into account the influence of thermal radiation and thermal conductivity. To obtain the computational model analysis, a numerical tool via the bivariate spectral collocation method is deployed on the resulting transformed PDEs. Upon validation of the method, the profile distributions of respective boundary layers with respect to the Bingham number, magneto-thermomechanical parameter, and Reiner–Philippoff fluid parameter are analyzed and discussed. The results of the engineering quantities of skin friction and Nusselt number are presented in graphical and tabular form. Among the findings of this study is that the Newtonian fluid is a turning point for skin drag force and heat transfer rate. Besides, the ferrohydrodynamic parameter recedes the velocity of shear-thinning fluid the most, although, boosts its (shear-thinning fluid) heat transfer coefficient.

Heat and mass transfer analysis of constitutive model with autocatalytic chemical reaction within the Jeffery–Hamel flow perspective

This article examines the heat and mass transfer capabilities of a constitutive model in a thermally evolving steady laminar Jeffery–Hamel flow through a convergent-plate channel, including streamwise conduction with step changes in uniform wall temperature. A Jeffery–Hamel problem with a simple shear flow is used to undertake a comparative computational analysis of the thermal behavior of a viscoelastic fluid subjected to autocatalytic processes. The flow is tracked in a purely radial orientation with the deployment of coupled stresses in momentum conservation. The computational solutions for the flow, temperature and concentration distribution, and heat and mass transfer coefficient of a viscoelastic fluid obeying the complex Oldroyd-B constitutive equation in laminar converging channel flows are established. The analysis of the impacts of the thermal radiation, the heat source, and the chemical reaction as an autocatalytic process is included in the model, which is valid for fully developed thermal and hydrodynamic flow conditions with a constant heat and mass flux imposed at the wall. In the diverging part of the channel, where vortex compression is the predominant flow topology, there exist patches of local flow compression. On the flow field, the modified relaxation and retardation parameters show an opposing behavior. An Oldroyd-B fluid exhibits higher interactions with nearby vortices in the divergent channel, allowing a complex flow structure. The viscoelastic characteristics are anticipated to change the homogeneous–heterogeneous reaction transport processes, offering tremendous potential for applications in associated sectors. The deceleration flow in the diverging channel and the acceleration flow in the converging channel augment the average Nusselt numbers.

Experimental and numerical investigation of flow and thermal characteristics of aluminum block exchanger using surface-modified and recycled nanofluids

PurposeThe purpose of this study is to numerically and experimentally survey the thermal efficiency of a block-type heat exchanger operated in different working conditions by using pure water and two nanofluids as heat transfer fluids.Design/methodology/approachAn aluminum block-type heat exchanger integrated with Peltier thermoelectric element was designed and installed to operate in a cycle, and the thermal performance of the heat exchanger, heat transfer rate, Nusselt and heat transfer coefficient variations were examined at different bath water temperatures by using recycled nanofluids. New generation surface-modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol/water nanofluid was used as heat transfer fluid in the cycle. In addition, CFD simulation was performed using ANSYS/Fluent to investigate the temperature distribution and fluid flow structure in the used heat exchanger.FindingsExperiments were carried out by using numerical and experimental methods. In the experiments, the operating conditions such as flow rate, volume fraction of the nanofluid and water bath temperature were changed to find the effect of each parameter on the thermal efficiency. The Reynolds number varied depending on the test conditions, which was calculated in the range of approximately 100 < Re < 350. In addition, Nusselt number and heat transfer coefficient of test fluids were very close to each other. For 0.4% nanofluid, the maximum h value was obtained as 3837.1, when the Reynolds number was measured as 314.4.Originality/valueIn the scientific articles published in the field of heat exchangers operated by nanofluids, little attention has been paid to the stability of the nanofluids and sedimentation of particles in the base fluids. In addition, in most cases, experiments were implemented using an electrical resistance as a heat source. In this research, stable surface-modified nanofluids were used as heat transfer fluids, and it was found that the Peltier thermoelectric can be used as heat sources with acceptable efficiency in flat-type heat exchangers and even non-circular channels.

Detailed Thermal Evaluation of Brazed Plate Heat Exchanger Using Infrared Thermography

AbstractInfrared thermography of brazed plate heat exchangers for evaporators and condensers recently was used to quantify maldistribution. With the knowledge of the secondary fluids heat transfer coefficient and a given secondary fluids distribution, the local heat transfer coefficient of the primary fluid (refrigerant) and its distribution to the channels can be calculated. A sensitivity analysis shows ± 10 % difference of the surface temperature to the wall center temperature at the expected ratios of heat transfer coefficients. The method is presented in this paper using an exemplary infrared picture.

Review on influence of nano bubble technology to enhance nanoboiling heat transfer: Environmental perspective

AbstractThe primary focus of this review article is to investigate the behavior of multi walled carbon nanotubes (MWCNT) suspended in clean water during the boiling heat dispersions (transfer process). With novel nano boiling technique, the convective heat transfer coefficient of nanoparticles in nanofluid, density, viscosity, and thermal conductivity were reviewed. The various research outcomes on MWCNT mixed with water are discussed. Based on various test results, it was evident that adding (MWCNT) raised the boiling heat transfer coefficient of the base fluids.

Artificial Neural Networking Magnification for Heat Transfer Coefficient in Convective Non-Newtonian Fluid with Thermal Radiations and Heat Generation Effects

In this study, the Casson fluid flow through an inclined, stretching cylindrical surface is considered. The flow field is manifested with pertinent physical effects, namely heat generation, viscous dissipation, thermal radiations, stagnation point flow, variable thermal conductivity, a magnetic field, and mixed convection. In addition, the flow field is formulated mathematically. The shooting scheme is used to obtain the numerical data of the heat transfer coefficient at the cylindrical surface. Further, for comparative analysis, three different thermal flow regimes are considered. In order to obtain a better estimation of the heat transfer coefficient, three corresponding artificial neural networks (ANN) models were constructed by utilizing Tan-Sig and Purelin transfer functions. It was observed that the heat transfer rate exhibits an inciting nature for the Eckert and Prandtl numbers, curvature, and heat generation parameters, while the Casson fluid parameter, temperature-dependent thermal conductivity, and radiation parameter behave oppositely. The present ANN estimation will be helpful for studies related to thermal energy storage that have Nusselt number involvements.

Flow and heat transfer characteristics of nano-organic working fluid during evaporation for organic Rankine cycle

Nanoparticle can enhance the heat transfer coefficient of organic working fluids, and thus reduce the heat exchanger area, resulting in the decrease in organic Rankine cycle (ORC) investment. This study presents an experimental investigation on the physical properties and heat transfer characteristics of R123/ZnO with the mass fraction of ZnO of 0.1 %. The stability, viscosity and thermal conductivity of R123/ZnO are analyzed, while the comparison of heat transfer coefficient and pressure drop between nano-organic working fluid and pure R123 are examined. The mass flow rate is in range of 250–500 kg/m2 s. The inlet temperature is in range of 50-70℃, while the inlet pressure is ranging from 0.2 to 0.4 MPa. Results demonstrated that R123/ZnO yields a 111 %-481 % higher thermal conductivity than R123. When the mass flux is 247 kg/m−2·s, the heat transfer coefficients of ZnO/R123 increase from 1274 to 2242 W/m2·K, which is 10.11–27.60 % higher than that of R123 ranging of 1130–2035 W/m2·K with the pipe length, indicating that nano-organic working fluids obtain a relatively higher heat transfer coefficient than the pure working fluids. However, R123/ZnO yields a 1.65 %-79.36 % higher pressure drop than R123. Meanwhile, this study provides a potential of applying nano-organic working fluid on thermodynamic cycle.

Non-invasive thermal energy flow rate sensor for turbulent pipe flows

A non-invasive thermal energy flow rate sensor based on a combination of transient heat flux and temperature measurements has been developed. A heat flux sensor and a thin-film thermocouple are covered by a thin-film electric heater and clamped onto the outer surface of a pipe. 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 and thermal resistance. A parameter estimation code is used to estimate the unknown parameters by using the minimum root mean square error between the analytical and experimental sensor temperature values. The sensor was tested with two different fluids (water and diesel oil) and with two different pipe diameters (d=25.4mm and d=12.7mm). Experiments were completed over a range of Reynolds number from 2000 to 25,000 and a range of fluid temperature from 20 °C to 50 °C. Correlations for the fluid temperature and the fluid velocity were within ±0.13 K and ±5% of the direct measurements. The resulting non-invasive thermal energy flow rate sensor can be used to estimate a fluid velocity and a fluid temperature in heating and cooling pipe applications.

Thermal performance of nanofluids based on tungsten disulphide nanosheets as heat transfer fluids in parabolic trough solar collectors

Nanofluids are considered as a new generation of heat transfer fluids since they exhibit thermophysical properties improvements compared with conventional heat transfer fluids. The high thermal conductivity of nanofluids and even the isobaric specific heat enhancements over conventional liquids make these colloidal suspensions very attractive in many research areas, including solar energy. In this work, nanofluids based on tungsten disulphide (WS 2 ) nanosheets have been prepared from the thermal oil currently used as heat transfer fluid in Concentrating Solar Power (CSP) plants. The high aspect ratio of WS 2 bidimensional nanostructures provides high long-term colloidal stability to the nanofluids and facilitates heat transport. Cetyltrimethylammonium bromide and polyethylene glycol have been used as surfactants to improve the exfoliation process and enhance the colloidal stability of the nanomaterial dispersions. Some properties such as density and viscosity of the base fluid have not been significantly altered by the presence of WS 2 nanosheets in the base fluid. However, studies on the thermal properties of nanofluids have shown promising results with increases in thermal conductivity of up to 33% and heat transfer coefficient by 21% over the base fluid. Furthermore, it has been estimated that the overall efficiency of the CSP system could be improved by 31% by replacing the conventional thermal fluid with 2D-WS 2 -based nanofluids. • The efficiency of PTC solar collectors is increased by 31% by using WS 2 nanofluids. • Nanofluids improved the heat transfer coefficient of the base fluid by 21%. • Thermal conductivity was enhanced by 33% in WS 2 -based nanofluids. • WS 2 nanofluids favours the elimination of selective coatings on the absorber tube.