Heat Transfer Effects Research Articles

A Simplified Approach for Calculating Heat Transfer Coefficients for Fluid Guiding Elements with Alternating Redirections of Flow

AbstractFluid guiding elements (FGEs), additive manufactured inserts that enhance heat transfer, have shown the potential to reduce the size of pipe‐in‐pipe heat exchangers up to a factor of 20. Due to their unique design, the calculation of the geometrical parameters for a specific application remains challenging and was initially solved by computationally expensive computational fluid dynamics simulations. This work presents a simplified approach, which treats the fluid and the FGE as pseudo‐homogeneous to enable the fast calculation of effective heat transfer coefficients. The approach is developed based on water in laminar flow state and subsequently tested with different fluids.

Thermodynamic analysis of two-fluid, two-phase immersion cooling system for cooling of electronic components

Two-phase immersion cooling system is a specialized and increasingly popular method for cooling high-power density electronic components, such as CPUs, GPUs, and other server equipments. In a typical two-phase immersion cooling system, a dielectric fluid is employed for immersing electronic components. The challenge lies in the fact that the fluid chosen often has limited thermal conductivity, hindering effective heat transfer. In a two-fluid immersion cooling system, electronic components are submerged in a dielectric fluid known as the boiling fluid. Within the same tank, a separate condensing fluid is introduced, which is immiscible with the boiling fluid. The condensing fluid, characterized by its lower density and higher thermal conductivity compared to the boiling fluid, enhances heat transfer within the system. In the current study, Novec 7100 serves as the boiling fluid, while deionized water is employed as the condensing fluid. In this work, exergy analysis is conducted to assess and compare the efficiency of a two-fluid, two-phase immersion cooling system in contrast to a single-fluid, two-phase immersion cooling system. Additionally, a comparison is carried out to evaluate how the performance of the system varies under diverse operating conditions. The study is conducted for a maximum heat flux of 12.3 W/cm2 and performance of the system is evaluated at condenser inlet temperatures spanning from 5 to 25 °C. From the investigations carried out, it is seen that the exergy efficiency of the two-fluid system surpasses that of the single-fluid system by approximately 70% under same heat flux and condenser inlet temperature conditions.

Effects of temperature and nanoparticle mixing ratio on the thermophysical properties of GNP–Fe2O3 hybrid nanofluids: an experimental study with RSM and ANN modeling

This study investigated the impact of temperature and nanoparticle mixing ratio on the thermophysical properties of hybrid nanofluids (HNFs) made with graphene nanoplatelets (GNP) and iron oxide nanoparticles (Fe2O3). The results showed that increased temperature led to higher thermal conductivity (TC) and electrical conductivity (EC), and lower viscosity in HNFs. Higher GNP content relative to Fe2O3 also resulted in higher TC but lower EC and viscosity. Artificial neural network (ANN) and response surface methodology (RSM) were used to model and correlate the thermophysical properties of HNFs. The ANN models showed a high degree of correlation between predicted and actual values for all three properties (TC, EC, and viscosity). The optimal number of neurons varied for each property. For TC, the model with six neurons performed the best, while for viscosity, the model with ten neurons was optimal. The best ANN model for EC contained 18 neurons. The RSM results indicated that the 2-factor interaction term was the most significant factor for optimizing TC and EC; while, the linear term was most important for optimizing viscosity. The ANN models performed better than the RSM models for all properties. The findings provide insights into factors affecting the thermophysical properties of HNFs and can inform the development of more effective heat transfer fluids for industrial applications.

Numerical study of heat transfer characteristics of intermittent flow cold storage surface heat exchanger

The intermittent flow cold storage surface heat exchanger is a key component of the new pulse tube expansion cryogenic refrigerator, which is responsible for the periodic heat transfer of cold and hot helium, and its heat exchange efficiency directly affects the thermodynamic efficiency of the whole machine. In this study, a three-dimensional model of the heat exchanger unit is established, and numerical simulation is employed to investigate its heat exchange characteristics. The analysis focuses on understanding the internal temperature distribution patterns within the heat exchanger and explores the influence of wall materials on its heat transfer characteristics. Results show that the existence of the temperature lag loop minimizes the effective heat transfer temperature difference, consequently decreasing the heat exchanger’s efficiency. Moreover, the choice of wall material significantly affects the performance of the heat exchanger, with optimal thermal conductivity and volumetric specific heat enhancing its efficiency. This research provides valuable insights for future design and improvement of similar heat exchangers.

Heat transfer during droplet impact on a cold superhydrophobic surface via interfacial thermal mapping

AbstractUndesired heat transfer during droplet impact on cold surfaces can lead to ice formation and damage to renewable infrastructure, among others. To address this, superhydrophobic surfaces aim to minimize the droplet surface interaction thereby, holding promise to greatly limit heat transfer. However, the droplet impact on such surfaces spans only a few milliseconds making it difficult to quantify the heat exchange at the droplet–solid interface. Here, we employ high‐speed infrared thermography and a three‐dimensional transient heat conduction COMSOL model to map the dynamic heat flux distribution during droplet impact on a cold superhydrophobic surface. The comprehensive droplet impact experiments for varying surface temperature, droplet size, and impacting height reveal that the heat transfer effectiveness () scales with the dimensionless maximum spreading radius as , deviating from previous semi‐infinite scaling. Interestingly, despite shorter contact times, droplets impacting from higher heights demonstrate increased heat transfer effectiveness due to expanded contact area. The results suggest that reducing droplet spreading time, as opposed to contact time alone, can be a more effective strategy for minimizing heat transfer. The results presented here highlight the importance of both contact area and contact time on the heat exchange between a droplet and a cold superhydrophobic surface.

Designing & Developing a Porous based Box-Type Heat Exchanger for Enhanced Heat Transfer Rate

Abstract: The shell-and-tube heat exchanger's geometric configuration is optimized during the design development phase by taking into account various aspects like baffle spacing, tube arrangement, and overall system integration. Incorporating a blower into the system results in improved air circulation and effective heat transfer. By placing the band heater in a strategic location, air is heated precisely and locally, which helps to create a more responsive and controlled heating process. One essential tool for assessing the system's thermal and fluid dynamics is CFD analysis. The heat exchanger, blower, and band heater components' fluid flow patterns, temperature distributions, and pressure gradients are investigated through simulations. The CFD analysis provides valuable insights that guide design modifications aimed at optimizing heat transfer rates, minimizing pressure drops, and improving the integrated system's overall performance

Magnetic field impact on ferronanofluid laminar flow

A comprehensive understanding of the magnetic field interaction with the flow of ferronanofluids is essential to determine the heat transfer effect and the potential for use in industrial applications. The purpose of this work is to determine the effects of magnetic field orientation and intensity, as well as inertia forces, on heat transfer in the laminar flow of a ferronanofluid. The experiment involved the use of five permanent magnets positioned both below and above the flowing magnetite-based ferronanofluid. The analysis of the effect on heat transfer is carried out using the similarity numbers, Reynolds number (ratio of inertia and viscous forces), magnetic number (ratio of magnetic and inertia forces) and product of the two (ratio of magnetic and viscous forces).The findings indicate that the orientation of the magnetic field relative to temperature gradient-induced secondary motions plays a crucial role in either enhancing or inhibiting heat transfer. The magnet positioned below the flow leads to improved heat transfer, while placement above hinders it. To determine the magnetic field effect on heat transfer, the ratio of magnetic to viscous force introduced as MnRe is used. Taking the 5 % Nusselt number change as the threshold, the critical value for the orientation of magnet above the tube is MnRe = 24,000, while for the configuration with the magnet below, MnRe = 32,000 for Re = 109 and MnRe = 88,000 for Re = 150 and 163. The magnetic field effect is local and diminishes as the fluid flows, ultimately causing the heat transfer parameters to revert to their reference state. However, an increase in the ratio of inertia and viscosity forces enables the magnetic field interaction effect to propagate over a longer distance.

Effective Heat Transfer Between a Porous Medium and a Fluid Layer: Homogenization and Simulation

Effective Heat Transfer Between a Porous Medium and a Fluid Layer: Homogenization and Simulation

Computational Fluid Dynamics Process for Front Windshield Mist Deposition and Its Subsequent Demisting

<div>A vehicle’s heating, ventilation, and air-conditioning system plays a dual role in passenger thermal comfort and safety. The functional aspects of safety include the front windshield demist and deicing feature of the system. The thin-film mist is a result of condensation of water vapor on the inner side of the windshield, which occurs at low ambient temperatures or high humidity. This mist deposition depends on the air saturation pressure at the front windshield. Indian regulation AIS-084 defines the experimental setup for testing, which encompasses both the mist deposition and its subsequent demist process. This regulation mandates testing, which occurs at a later stage of product development. This performance validation can be performed using a three-dimensional computational fluid dynamics approach.</div> <div>Current work summarizes the simulation process for both the mist deposition and the subsequent demisting phenomenon. The complexity of the flow physics is captured via the transient multiphase fluid flow phenomenon subjected to buoyancy effects. This phenomenon is simulated using the Eulerian wall film approach. The wall film deposition of the mist is modeled via species transport. Further, the near-wall thermal effects of surface conduction and heat transfer are simulated by modeling shell conduction layers. Vapor diffusion and relative humidity inside the cabin are modeled using a user-defined function. The process correlation is achieved for two categories of vehicles to establish the process efficacy and robustness. Moving ahead, a design of experiments (DOE) is planned to mitigate the need to simulate mist deposition. The DOE is planning to incorporate deviations in both the input airflow conditions and the imposed ambient conditions. The results from DOE point toward factors that might cause deviations in simulation results with respect to the test. Importantly, the study concludes that the uniform initial thickness assumption of the mist layer can be used for subsequent demist analysis.</div>

Direct numerical simulations of first-mode oblique breakdown in a supersonic boundary layer under wall transpiration

Complete first-mode oblique breakdowns under wall transpirations in a Mach 2 flat-plate boundary layer are investigated by direct numerical simulations. The parameters of oblique waves are determined by linear stability analysis, while air transpiration is modeled by a wall-injection boundary condition. Wall transpiration with various blowing ratios is imposed at two distinct streamwise regions to assess its effects. When wall transpiration is located in the linear and early nonlinear region, the transition shifts upstream with increasing blowing ratios. This promotion effect arises from the destabilization of the oblique mode, steady vortex mode and higher-harmonic modes. Wall transpiration also leads to reduced skin friction and heat transfer in the transpiration and downstream turbulent regions. Through integral analysis, the impacts of transpiration on the generation mechanisms of skin friction and heat transfer are gained. The reduced skin friction and heat transfer in the transpiration region are mainly attributed to the amplified negative contributions from mean convection. In the turbulent region, the reduction of skin friction can be attributed to the heightened negative contributions from mean convection and the diminished positive contributions from turbulent convection. Concurrently, heat transfer experiences a decrease as a consequence of reduced positive contributions from spatial development and augmented negative contributions from mean convection. When wall transpiration is located in the late nonlinear region, its impacts resemble those observed when transpiration is located in the linear and early nonlinear region. However, the transition-promoting effect weakens, and the heat-transfer reduction effect becomes more pronounced.

Experimental study of heat transfer performance in rectangular microchannels enhanced by ultrasound

Ultrasound is recognized as an effective technology to enhance heat transfer, which is widely used in industrial fields such as microelectronics and heat storage. However, the heat transfer characteristics in rectangular microchannels assisted with ultrasound has little revealed in present research. In this work, the external ultrasonic was added in a rectangular microchannel to reveal the influence of ultrasound on the heat transfer characteristics of micro-channels. Hence, the comparative experiments were completed to explore the heat transfer performance with and without ultrasonic. Moreover, a large number of experiments were carried out within rectangular microchannels by varying the velocity of the working fluid and the heat flux at the bottom of the microchannels. The results indicate that the heat transfer performance of rectangular microchannels can be enhanced by ultrasound. But the enhanced heat transfer effect could be limited with the increase of the flow velocity and heat flux in microchannel correspondingly. For rectangular microchannels with adding ultrasound, the lower the flow rate and heat flow density are, the better the enhancement effect will be. During the measurement, when the fluid flow velocity is 0.2 m/s and the heat flux is 408.2 kW/m2, the heat transfer performance of the ultrasound-enhanced microchannel can be improved by a maximum of 12.9 %. Additionally, the tests indicate that the pressure drop mainly comes from the viscous loss along rectangular channel, yet the ultrasound has no negative impact on pressure drop in microchannel. This work could be beneficial to the further application of ultrasonic enhancement technology.

Experimental investigation on the heat transfer performance of pulsating heat pipe with self-rewetting Fe3O4-nanofluid

This paper conducted an experimental study on the heat transfer performance of pulsating heat pipe (PHP) under three different working fluids: ultrapure water, n-butanol self-rewetting fluid (SRWF), and self-rewetting Fe3O4-nanofluid (SRNF). The effects of filling ratio (FR), heating power, and magnetic field are studied. The results mainly show that the PHP with SRNF under a magnetic field, the start-up time increases, the evaporation section operating temperature increases, and the thermal performance decreases as the filling ratio increases. Increasing the FR, applying SRWF and SRNF can effectively increase the dry-out limit of PHP. At FR = 50 %, the overall thermal performance of PHP is best. In 10–130W, the thermal resistance of the SRWF and the SRNF with/without magnetic field is reduced by 14.5 %–27.8 %, 27.6 %–47.9 %, and 4.2 %–24.8 %, respectively, compared with that of ultrapure water. Similarly, compared without a magnetic field, the thermal resistance of SRNF with a magnetic field is reduced by 14.0 %–35.1 %. At FR = 50 %, the heat transfer performance of SRNF-PHP is best with a magnetic field. When the input power is 130W, the effective heat transfer coefficient keff is 5967.6 W/m∙ K, approximately 13.92 times greater than copper.

Soret Effect on Magneto Hydrodynamic Free Convective Heat and Mass Transfer Effects Flow over an Inclined Plate Embedded in a Porous Medium

Soret Effect on Magneto Hydrodynamic Free Convective Heat and Mass Transfer Effects Flow over an Inclined Plate Embedded in a Porous Medium

Study of ultrasonic influence on heat transfer and resistance performance of round tube with twisted belt

Abstract In this study, ultrasonic technology is combined with twisted belts to explore the comprehensive performance, and this study also investigated the effect of different Reynolds numbers, ultrasonic frequencies, and number of transducers on the performance of circular and twisted band tubes. It was found that ultrasonic waves applied on the tube plate enhanced the heat transfer performance of the heat exchanger tubes, reduced the flow resistance, and improved the overall performance, and the lower the ultrasonic frequency, the better the heat transfer and resistance reduction ability, and at the experimental condition frequency of 21 kHz, the maximum increase of Nu is 19.06%. With the increase of Reynolds number, the better the ultrasonic enhancement heat transfer performance, but the worse the resistance reduction performance. For different heat exchanger tube structures, the synergistic enhanced heat transfer effect of ultrasonic waves with the twisted belt is better than round tubes, and the synergistic drag reduction effect with the round tube is better than the twisted tape round tube. When the installed ultrasonic transducers are two, the heat transfer performance of the heat exchanger tube is the best, and the maximum increase in the value of Nu was 28.06%.

AFSD-Nets: A Physics-Informed Machine Learning Model for Predicting the Temperature Evolution During Additive Friction Stir Deposition

Abstract This study models the temperature evolution during additive friction stir deposition (AFSD) using machine learning. AFSD is a solid-state additive manufacturing technology that deposits metal using plastic flow without melting. However, the ability to predict its performance using the underlying physics is in the early stage. A physics-informed machine learning approach, AFSD-Nets, is presented here to predict temperature profiles based on the combined effects of heat generation and heat transfer. The proposed AFSD-Nets includes a set of customized neural network approximators, which are used to model the coupled temperature evolution for the tool and build during multi-layer material deposition. Experiments are designed and performed using 7075 aluminum feedstock deposited on a substrate of the same material for 30 layers. A comparison of predictions and measurements shows that the proposed AFSD-Nets approach can accurately describe and predict the temperature evolution during the AFSD process.

Numerical study on cooling characteristics of turbine blade based on laminated cooling configuration with clapboards

The double-wall configuration, characterized by its notable overall cooling effectiveness, serves as a pivotal reference configuration in the design of next-generation turbine blades. In this study, a laminated cooling configuration with clapboards is developed, based on insights derived from both double-wall cooling configuration and laminated cooling configuration. Through a comparative analysis, with the double-wall cooling configuration and laminated cooling configuration as benchmarks, the newly constructed configuration is capable of enhancing overall cooling effectiveness while maintaining control over total pressure loss in the study. Specifically, in the context of external film cooling with an adiabatic condition, the laminated cooling configuration with clapboards attains the highest value at low blowing ratios, while the laminated cooling configuration excels in average adiabatic film cooling effectiveness at high blowing ratios. Importantly, the inclusion of clapboards significantly improves the internal heat transfer area, resulting in a greater internal total heat exchange in the laminated cooling configuration with clapboards. Consequently, this proposed configuration achieves the highest overall cooling effectiveness, achieving increases of 9.02%–14.08 % and 2.77 %–3.54 % relative to the double-wall cooling configuration and laminated cooling configuration, respectively. A comprehensive performance evaluation criterion is applied to assess cooling effectiveness and pressure loss. The results indicate that the laminated cooling configuration with clapboards enhances heat transfer effectiveness while effectively controlling pressure drop, with an evaluation value of over 1.0. Furthermore, the overall cooling effectiveness of the three cooling configurations is compared at two Reynolds numbers. It is found that the proposed configuration exhibits the best cooling performance, especially at the high Reynolds number.

Prediction of burden distribution and electrical resistance in submerged arc furnaces using discrete element method modelling

A computational model of a submerged arc furnace (SAF) used in the production of ferrochrome is presented. The model's intended use is to investigate the extent to which intrinsic and extrinsic properties of the raw materials affect burden distribution and electrical resistance within the furnace. The model is built on the discrete element method and calculates the mechanical interactions of particle distributions resulting from the flow motion of typical raw materials used in the smelting of chromium ore. This model excludes the effects of thermodynamics, furnace chemistry, and heat transfer. It illustrates how the consumption of materials (chromite pellets, flux, and reductant) is affected by changes in electrode length, reductant fractions, and reductant sizing and density during the formation of a reductant bed. The resistance calculation algorithm developed by Mintek was applied to construct networks developed from particle contacts, which can quantitatively generate estimates of the electrode-to-electrode and electrode-to-bath electrical conduction conditions.

Thermo-hydraulic performance of metal oxide nanofluid flow through the helical coil tube of a three-fluid heat exchanger: an experimental and optimization study

ABSTRACT The thermo-hydraulic performance of a three-fluid heat exchanger (TFHE) to concurrently transfer heat from a heated nanofluid to ordinary water and air is the subject of investigation in this paper. The fluid flow and heat transfer abilities of the TFHE concerning changes in nanofluid (Al2O3-water, CuO-water, Fe2O3-water) are used to quantify effectiveness and pressure drop. Parametric studies having nanofluid volume fraction (1%, 5%, and 10%), flow rate (100LPH, 150LPH, and 200LPH), and inlet temperature (80°C, 120°C, and 160°C) respectively are considered in the present experimentation. The results of the experiment demonstrate that the use of CuO-water nanofluid at an intake temperature of 160°C and 5% volume percentage led to a considerable improvement in heat transfer effectiveness, with a maximum value of 0.884. At a flow rate of 100 LPH, a volume percentage of 1%, and an inlet temperature of 160°C, the Al2O3-water nanofluid exhibits the least amount of pressure loss. Nine test runs with four control factors are conducted using Taguchi’s experiment design. From Taguchi analysis, it is observed that the nanofluid volume flow rate and nanofluid inlet temperature have the largest and lowest contributions of 68.83%, 3.76%, and 72.05%, 2.03% respectively on heat transfer effectiveness and pressure drop of the TFHE. A multi-response optimization is carried out using the Taguchi-Gray Analysis to determine the least pressure drop and the highest possible heat transfer effectiveness. At 1% volume fraction, 100 LPH volume flow rate, and 160°C intake temperature, Al2O3-water nanofluids show an increase in the total performance of the TFHE of 10.39%.

Study on magnetohydrodynamic internal cooling mechanism within an aluminium oxide cutting tool

One of the challenges in the transfer of heat during the mechanical machining process is the coolant substance used in the internal cooling method which is generally liquid water or a water-based coolant. This limits the heat transfer capacity insofar as the thermal conductivity of liquid water is concerned. The other difficulty is the requirement for an external mechanical system to pump the coolant around the internal channel, providing efficient transfer of the accumulated thermal energy. This study proposes a novel method to address this issue by using liquid gallium which provides the means to transfer the excess heat generated during the cutting process by integrating the design into an aluminium oxide insert. Combining this with a magnetohydrodynamic drive, the coolant system operates without the need for mechanical input. Liquid gallium is nontoxic and has a much higher thermal conductivity over liquid water. Investigations of the novel cooling system is performance compared against liquid water through numerical modelling, followed by an experimental machining test to ascertain the difference in heat transfer effectiveness, tool wear rates and workpiece surface finish when compared to dry machining and external cooling conditions on stainless steel 316L. Without cooling, experimental machining tests employing a cutting speed of Vc = 250 m min−1 resulted in a corner wear VBc rate of 75 μm, and with the magnetohydrodynamic-based coolant on, produced a VBc rate of 48 μm, indicating a difference of 36% in relative tool wear under the same cutting conditions. Increasing the cutting speed Vc to 900 m min−1, produced a corner wear VBc rate of 357 μm without the active coolant and a VBc rate of 246 μm with the magnetohydrodynamic-based coolant on, representing a decrease of 31% in relative tool wear. Further tests comparing external liquid water cooling against the liquid gallium coolant showed at Vc = 250 m min−1, a difference of 29% in relative tool wear rate reduction was obtained with the internal liquid gallium coolant. Increasing the cutting speed to Vc = 900 m min−1, the data indicated a difference of 16% relative tool wear reduction with the internal liquid gallium. The results support the feasibility of using liquid gallium as an internal coolant in cutting inserts to effectively remove thermal energy.

Study of the characteristics of the separated gravity heat pipe of a self-activated PCM wall system

Self-activated phase change material (PCM) wall integrated with radiative sky cooling (RSC) is a novel wall system that uses natural energy directly for low-energy buildings to support carbon peaking and neutrality goals. A separated gravity heat pipe (SGHP) is an effective heat transfer component for heat transport from the wall body to the radiative cooler without using mechanical energy. Its heat transfer characteristics affect the thermal performance of the wall system. In this study, a numerical Volume of Fluid (VOF) model of the SGHP is established. The thermal and flow characteristics under the small temperature difference boundary of building scenarios are simulated and analyzed. Results show that the average temperature of the working fluid inside the SGHP in the “steady stage” is about 26.3 °C when the boundary temperature of the evaporation and condensation sections are respectively 28 °C and 20 °C. The heat exchange can reach 356 W/m2 and the flow velocity of the working fluid is about 0.1 m/s. Influences of different evaporation/condensation boundary temperatures on the heat transfer effect are further studied. Compared to increasing the evaporation section temperature, decreasing the condensation section temperature is a better strategy for improving the heat exchange capacity of the SGHP.