Investigation Of Heat Transfer Research Articles

Dynamic phase change materials with extended surfaces

Phase change materials (PCMs) present opportunities for efficient thermal management due to their high latent heat of melting. However, a fundamental challenge for PCM cooling is the presence of a growing liquid layer of relatively low thermal conductivity melted PCM that limits heat transfer. Dynamic phase change material (dynPCM) uses an applied pressure to pump away the melt layer and achieve a thin liquid layer, ensuring high heat transfer for extended periods. This paper investigates heat transfer during dynPCM cooling when the heated surface has extended features made from high thermal conductivity copper (Cu). Using experiments and finite element simulations, we investigate the heat transfer performance of dynPCM paraffin wax on finned Cu surfaces. A total of 102 transient temperature measurements characterize the performance of dynPCM with extended surfaces and compare the performance with other cooling methods including hybrid PCM and air cooling. The study examines the effects of fin geometry, applied power (20–65 W), and pressure (0.97–12.5 kPa). For dynPCM on a finned surface and a heating power of 65 W, the thermal conductance is 0.45 W/cm2-K, compared to 0.22 W/cm2-K for dynPCM on a flat surface and 0.10 W/cm2-K for hybrid PCM. The heat transfer is highest at the fin tips where the melt layer is thinnest, providing valuable design guidelines for future high performance dynPCM cooling technologies.

Analysis of vapor bubble diameter, departure frequency and dynamics in a single cavity

The ongoing quest for methods that enhance the efficiency of heat transfer processes, particularly those involving phase change, underscores the importance of comprehending the dynamics of vapor bubbles during boiling. This study investigates heat transfer mechanisms and the dynamics of vapor bubbles within the nucleate boiling regime. Experimental tests were conducted on a flat copper surface featuring a single cavity, focusing on analyzing vapor bubble growth and departure stages. The working fluid examined was HFE-7100 under saturated conditions. The formation and growth aspects of vapor bubbles, including their diameter (Dd) and departure frequency (f), were investigated through experimental data obtained by two different techniques: by an optical sensor of variable resistance capable of generating an analog signal from a voltage change and by a high-speed camera that captures images immediately after the instant that the bubble detached from the surface. Both techniques provide visual insights into the boiling phenomenon. An escalation in heat flux and, consequently, wall superheat resulted in an increased bubble departure frequency. Furthermore, the optical flow analysis successfully identified velocity and vorticity fields induced by micro convection, the prevailing heat transfer mode in nucleated boiling. A slight horizontal displacement trend over time was observed, which may be caused by the asymmetry in the velocity profile, confirmed by velocity peaks tending toward one direction. Vortex analysis reveals rotational motion concentrated in specific regions, with noticeable deformation near the bottom of the bubble and asymmetric movement contributing to vorticity. These findings provide insights into the vapor bubble dynamics, which is important for understanding the cavity rewetting phenomena.

Thermal management of a battery pack using fin-embedded phase change material

Abstract The present study focuses on the numerical investigation of heat transfer from a battery cell surrounded by phase change material (PCM) with longitudinal fins embedded in it. Three-dimensional transient heat conduction equation is solved numerically in the battery domain, whereas the solidification-melting model adopting Enthalpy-Porosity approach is solved in PCM to obtain liquid fraction and temperature distribution. PCM with 16 fins was found to be quite effective in reducing the battery surface temperature compared to 12, 8, and 4 fins. However, the effectiveness of 16 fins is observed up to 1500 sec till the PCM completely melts into liquid. A maximum reduction of 25 K has been achieved at 1500 sec by adding 16 fins to PCM. Beyond 1500 sec, the temperature rises sharply, exceeding all other cases at 2200 sec. Fins play an essential role in augmenting heat transfer, which benefits in achieving the phase change process in less time to restrict the temperature rise; however, at the same time, when the phase change process completes, fins become detrimental to the system since the temperature of the battery starts rising sharply.

An investigation of heat transfer and optimization of entropy in bio-convective flow of Eyring-Powell nanomaterial with gyrotactic microorganisms

Entropy generation in nanofluid flows is a critical parameter that influences the performance, efficiency, and sustainability of thermal systems. Understanding and optimizing entropy creation can lead to noteworthy advancements in numerous engineering applications, from renewable energy systems to industrial processes and biomedical equipments. The purpose of this article is to examine the entropy produced in the bioconvection flow of Eyring-Powell nanomaterial with gyrotactic microorganisms. The mathematical equations representing the flow are modeled considering the flow towards a porous surface of a cylinder. Together with the effects of the governing parameters, the mass and heat transfer components of the problem are discussed. The thermal effects of different natures are used in a new way. Overall, entropy creation is designed with regard to the second law of thermodynamics. Activation energy, chemical reaction, thermal radiation, and internal friction force effects are accounted for the development of the mathematical model. Coupled non-linear dimensional equations have been altered into ordinary differential equations (ODEs) and then treated using the MATLAB Finite Difference Method (FDM). Consequence of diverse sundry parameters on entropy production, thermal field, mass concentration profile, Bejan quantity, and motile density of microorganisms is deliberated via plots. Through tables, engineering quantities are analyzed. According to the findings, the velocity profile rises as the curvature and Eyring-Powell fluid parameters rise, while it falls when the magnetic parameter is enhanced. Additionally, it is noted that as the curvature variable enhances, the rate of heat transfer and skin friction coefficient decays.

Numerical Investigation of Mass and Heat Transfer in a New Coaxial with Shell-and-Tube Heat Exchanger

Numerical Investigation of Mass and Heat Transfer in a New Coaxial with Shell-and-Tube Heat Exchanger

Numerical simulation of a partially ionized Oldroyd-B nanofluid flow driven by two homocentric rotating disks with motile microorganisms

Nanofluids are assumed to be an excellent source of enhanced heat transfer with advanced thermophysical characteristics. Nanofluids are the backbone of the heating and cooling in the industrial processes. This research delves into the dynamics of a partially ionized Oldroyd-B nanofluid flowing between stretchable rotating disks. The study investigates heat transfer mechanisms incorporating a modified Fourier law and convective heat conditions. The viscoelastic fluid model presented here allows for the examination of relaxation and retardation times. Furthermore, the heat and mass transport of the Oldroyd-B nanofluid is characterized using a Buongiorno model, which considers thermophoresis and Brownian diffusion effects. Additionally, the study explores the impact of gyrotactic microorganisms in nanofluids, potentially enhancing environmental management strategies. The governing equations transform into dimensionless forms using Von Karman similarity variables. Numerical investigation of the anticipated model is conducted using the bvp4c scheme in MATLAB. The variation of different parameters in the dimensionless equations is illustrated through graphs and in tabulated format. The results indicate that increasing thermophoresis and Lewis numbers lead to a decrease in fluid concentration. Moreover, the temperature of the fluid rises at the lower disk and declines at the upper disk relative to the Biot number. The proposed model is validated through comparison with closely related published work.

Experimental investigation of heat transfer and pressure drop in copper manifold microchannel heat sinks

Over the past decade, various two-phase cooling solutions have been implemented to dissipate power in high heat flux electronic components. The manifold microchannel heat sink is an efficient thermal management solution that reduces heat resistance while also limiting the pumping power. However, there is limited work available on small form factor manifold microchannels with traditional heat sinking materials like copper. In this study, an experimental investigation is conducted to evaluate the heat transfer and pressure drop performance of copper manifold microchannel heat sinks using an environmentally friendly refrigerant, R1233zd(E), as the working fluid. A microchannel plate and a manifold plate, both made of oxygen-free copper, are sandwiched together to form the manifold microchannel test sample assembly. To compare the effects of geometric parameters, a total of six manifold microchannel test samples are investigated, including two types of manifold plates and three types of microchannel plates. The experiments are performed with refrigerant mass flow rates ranging from 5 to 15 g/s and inlet subcooling temperatures ranging from 3 to 10 K. The heat transfer coefficient increases with a decreasing number of manifolds and with an increase in the number and width of the microchannels. The pressure drop decreases in configurations with more microchannels, more manifolds, and larger microchannel widths. Compared to traditional microchannels, manifold microchannels significantly reduce the total pressure drop. However, their heat transfer performance at higher heat flux conditions is limited by the trapped bubbles phenomena. In comparison to traditional microchannels, manifold microchannels demonstrate much higher performance in dissipating the same amount of heat flux while limiting pumping power, as indicated by the COP.

Investigation of Convective Heat Transfer and Stability on a Rotating Disk: A Novel Experimental Method and Thermal Modeling

Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject.

Effects of adding micro/nano-scale surface roughness on upward flow boiling of R-134a through annular tubes

The enhancement of heat transfer efficiency is crucial for development of high-performance thermal systems in various industrial applications. This study investigates heat transfer and pressure drop during upward saturated flow boiling of R-134a in annular tubes featuring smooth and micro/nano-scale roughened copper surfaces achieved through sandblasting and chemical etching. A high-pressure chamber with a glass side is designed to observe surface wettability and measure contact angles of R-134a on both surfaces. The annular tubes, with inner and outer diameters of 28.6 and 42 mm respectively, and a total heated length of 1000 mm, undergo varying mass flux, vapor quality, and saturation pressure within ranges of 6.73–20.19 kg m−2 s−1, 0.14–0.95, and 530–1000 kPa, alongside heat flux variations from 608 to 2432 W m−2. Results indicate that the application of micro/nano-scale roughness to copper surfaces minimally reduces the contact angle of R-134a which slightly improves its wettability. However, this modification significantly increases the heat transfer coefficient by 256 % compared to the smooth tube, albeit with an associated increase in pressure drop. Additionally, increasing mass flux and vapor quality increases both the heat transfer coefficient and pressure drop. Furthermore, higher heat flux results in a higher heat transfer coefficient with a small increase in pressure drop. Also, the experimental results are compared with some of the available correlations in the literature. The novelty and significance of this work advances our understanding of effect of surface roughness on flow boiling characteristics. Understanding these phenomena is crucial for optimizing the design and performance of heat exchangers and other thermal systems used in various industries, including refrigeration, air conditioning, and power generation.

A numerical simulation of heat transfer performance on MHD nanofluids in porous metal for enhancing CPU cooling efficiency

The main goal of this study is to enhance CPU cooling efficiency using nanofluids, and the novelty of the study lies in the investigation of heat transfer and convective flow of MHD nanofluid through porous metal structures and foam heat sink/source to improve CPU cooling efficiency. The governing equations for the flow model are solved using the BVP4C with MATLAB package through shooting techniques. The effects of various parameters on velocity, temperature fields, HT and drag force are discussed through graphical simulations. The results indicate that as the Reynolds and Darcy numbers rise, fluid flow velocity undergoes unique alterations. Higher Reynolds and Darcy numbers result in cooler temperatures, while higher heat generation lead to warmer temperatures.Boosting Prandtl number improves HT by 52% with Cu nanoparticles, whereas elevating heat generation values reduce HT by 6.43% more efficiently with Cu nanoparticles than Al2O3 nanoparticles. Raising the Hartmann number would boost drag force, but the Darcy number opposes it. An increase in Hartmann number leads to a decrease in HT by 30.16% for Al2O3-H2O nanofluids and 47.81% for Cu-H2O nanofluids. The findings contribute to the development of advanced computing devices, paving the way for more efficient and reliable electronic systems in various applications.

Experimental investigation of forced convection heat transfer of heat exchangers with different pin geometries in in-line and staggered design

In this study, the effects of forced convection heat transfer on the surfaces of pin plate heat exchangers with different geometries modified to the heat exchanger form were experimentally investigated. A total of 8 pin fin plate heat exchangers, four of which are staggered and the other four are in-line, were used in the experiments. The heat transfer surface areas of the pin plate heat exchangers are produced equally. The only difference is their geometry, which is produced in four different shapes: triangle, circle, ellipse and square. The experiments were carried out at air velocities of 1 to 6 m/s with 1 m/s increments and at 10 W and 50 W input powers with 10 W increments. The staggered configuration of the pin fin plates demonstrated high performance in heat transfer. The study found that heat exchangers with cornerless pin plates have lower heat transfer compared to those with cornered pin plates. The pressure drops increased as the velocity of the coolant air increased, and the highest-pressure drop was observed in staggered triangular and elliptical pin plate heat exchangers. This research is considered innovative as it involves an experimental comparison between staggered and in-line pin plate heat exchangers in four different geometries, all with equal surface area.

Experimentally validated thermal modeling for temperature prediction of photovoltaic modules under variable environmental conditions

In this work, a detailed analysis and thermal modeling for temperature prediction of a stand-alone photovoltaic module is performed. The study aims to present precise estimation of module temperature, since it is an important parameter for power output calculation. Hence, the required data were collected via experiments. Accounting for all heat transfer mechanisms, and following model validation, a proposed algorithm was implemented to investigate heat transfer from the module to its surrounding and predict different layers’ temperature. Results indicate that accurate energy distribution and temperature prediction was achieved by the adopted thermal model, only about 16% of the received energy is converted to electrical power while the rest is released by heat. Moreover, the proposed simulation algorithm provided one of the best results in comparison to literature models, achieving an R2 of 0.963 and a MAE of 1.883, which is very close to the best overall model by King at R2=0.973 and MAE=1.663. Additionally, two new models for module temperature prediction were proposed. After testing on new data, the explicit model provided a reasonable first approximation attaining an adjusted R2 of 0.97 and a MSE of 3.505, and an accurate implicit model, achieving a MSE of only 1.268.

RETRACTION: Numerical investigation of nanofluid flow and heat transfer in a pillow plate heat exchanger using a two‐phase model: Effects of the shape of the welding points used in the pillow plate

AbstractRETRACTION: Y. A. Al‐Turki, A. Yarmohammadi, A. Alizadeh, D. Toghraie, “Numerical investigation of nanofluid flow and heat transfer in a pillow plate heat exchanger using a two‐phase model: Effects of the shape of the welding points used in the pillow plate,” Zeitschrift für Angewandte Mathematik und Mechanik (Early View): https://doi.org/10.1002/zamm.202000300.The above article, published online on 14 January 2021 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the journal Editor‐in‐Chief, Holm Altenbach; and Wiley‐VCH GmbH. The retraction has been agreed as there is unambiguous evidence that this article was accepted on the basis of a compromised peer review process. Therefore, the review of this article is deemed to be insufficient. The authors disagree with the retraction.

Numerical and Experimental Investigation of Heat Transfer in the Porous Media of an Additively Manufactured Evaporator of a Two-Phase Mechanically Pumped Loop for Space Applications

Two-phase pumped cooling systems are applied when it is required to maintain a very stable temperature for heat dissipation in a system. A novel additively manufactured evaporator for two-phase thermal control was developed at NASA Jet Propulsion Laboratory (JPL). The Two-Phase Mechanically Pumped Loop (2PMPL) allows to manage the heat transfer with much wider breadth of control authority compared to capillary-based systems, while alleviating the system's sensitivity to pressure drops. The focus of this work is the understanding and capturing the micro-scale evaporation occurring in the porous structure of the evaporator. The Boiling and Phase Change Heat Transfer Laboratory at the University of California, Los Angeles (UCLA) developed an all-encompassing numerical simulation tool to predict the operational thermal behavior of the evaporator considering the effect of the liquid-vapor interface at the wick-to-vapor boundary. The numerical model incorporated the behaviour of the liquid-vapor meniscus at particle level located along the evaporative boundary between the wick structure and the vapor chamber. The numerical model allowed to study the effect of different parameters, such as boundary conditions, geometry, wick and fluid properties. An experimental setup was built at UCLA in order to characterize the heat transfer within an additively manufactured porous sample fabricated at JPL and in particular its evaporative heat load under certain heat inputs. The experimental efforts served as validation for the numerical results and aided in the characterization of the transient phenomena, such as dry-out.

Expression of Concern for article entitled “Investigation of heat transfer, melting and solidification of phase change material in battery thermal management system based on blades height”

Expression of Concern for article entitled “Investigation of heat transfer, melting and solidification of phase change material in battery thermal management system based on blades height”

Computational investigation of methanol-based hybrid nanofluid flow over a stretching cylinder with Cattaneo–Christov heat flux

Abstract This study investigates heat transfer rates in (AA7075-AA7072/Methanol) hybrid nanofluid flows, considering non-uniform heat sources and Cattaneo–Christov heat flux, with significant implications for aerospace engineering by enhancing thermal management in aircraft engines. The findings could revolutionize automotive cooling system efficiency, optimize heat dissipation in electronic devices, and advance the design of renewable energy systems such as concentrated solar power plants. The study aims to conduct a comparative analysis of (AA7075/Methanol) nanofluid and (AA7075-AA7072/Methanol) hybrid nanofluid flow, examining heat transfer rates, non-uniform heat sources, and Cattaneo–Christov heat flux theory around a stretching cylinder. Thermal radiation and the Biot number are also evaluated. Two different nanoparticles, AA7072 and AA7075, are used with methanol to create AA7075/Methanol nanofluid and AA7075-AA7072/Methanol hybrid nanofluid. The study compresses the resultant non-linear partial differential equation system and applies suitable similarity transformations to reduce the governing partial differential equations with boundary conditions to dimensionless form. The BVP4C shooting method in MATLAB is employed to numerically and graphically solve these dimensionless ordinary differential equations. The results indicate that higher curvature parameter values correlate with increased velocity and temperature distribution profiles. A rise in nanoparticle volume fraction reduces the radial velocity profile but increases the temperature profile. Temperature distribution profiles increase with higher thermal radiation parameter and Biot number values, while higher thermal relaxation parameter values decrease temperature. Additionally, thermal distribution profiles rise with increasing values of both the time-dependent heat source constant and space-dependent heat source parameter.

Investigation of Convective Heat Transfer of a Multi-Story Building and its Effect to the Comfort of Residents in Metro Manila

Investigation of Convective Heat Transfer of a Multi-Story Building and its Effect to the Comfort of Residents in Metro Manila

Parametric optimization and case study of nanofluid flow between two parallel plates in the presence of Darcy Brinkman Forchheimer: Sensitivity analysis

Due to its vast industrial applications and thermal engineering, the investigation of the inconsistent heat and mass transfer that drives the flow of squeezing viscous nanofluids between two plates is an interesting topic. In this case study, we have investigated the heat transfer analysis of unsteady viscous nanofluid between two parallel plates by using Response Surface Methodology (RSM). The partial differential equations illustrating the flow model are converted to nonlinear ordinary differential equations by suggesting similarity transformations. The resulting dimensionless and nonlinear ODEs of temperature functions and velocity are solved using the well-known numerical technique bvp4c by transforming the problem into initial value problem from boundary value problem. The results found are consistent with this numerical solution. These numerical values are then used to optimize the different input parameters and to design an experimental model. RSM is used to develop an experimental model for skin friction coefficient. ANOVA tables are generated for input parameters and then sensitivity analysis is performed for output response. Further, the impacts of different parameters on temperature profiles and velocity are graphically explored. The results are compared with the results solved by HPM. The results concurred with this numerical solution. These findings considered much be useful in the application of polymer processing, power transmission, compression, temporary loading of mechanical parts, food processing, cooling water, gravity machinery, modeling of plastic transport in vivo, chemical processing instruments, and demolition due to freezing.

Numerical Investigations of Flows and Heat Transfer in Turbine Disk Cavities

Abstract In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier–Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition.

Experimental Investigations of Heat Transfer in Simultaneously Developing Transitional Regime of Mixed Convection Flows in a Vertical Tube

Abstract The study of flow behavior in the simultaneously developing transitional regime of mixed convection flows is rare. It has been believed that the transitional regime will give a good compromise between pressure drop and heat transfer compared to laminar and turbulent flow regime. In this experimental study, the friction factor (f) and Nusselt number (Nu) characteristics for buoyancy-assisted and opposed flows of water in concurrently developing transitional regime of mixed convection through a vertical tube are studied. Experiments were done for Reynolds numbers (Re) varying from 500 to 15,000, Grashof numbers (Gr) from 1.25 × 104 to 5 × 106, Prandtl numbers (Pr) from 3 to 7, and Richardson numbers (Ri) from 0 to 0.1 subjected to uniform heat flux boundary conditions. A flow visualization provision after the test section which confirms an early transition in buoyancy-opposing flow (Rec = 2264) compared to buoyancy-aiding flow (Rec = 2468) at a fixed Ri of 0.1. Further, with the increase in Ri from 0 to 0.1, the average f decreases, and the average Nu increases in both aiding and opposing flows. It confirms that the onset of transition gets delayed with the increase of heat flux supplied in both the flows. Based on the present outcomes, an efficient heat exchanging device can be operated either to delay or advance the transition in a vertical pipe flow for optimum heat transfer.