Convective Heat Transfer Research Articles

Numerical Analysis of Transient Burn Injury Grading Through Coupled Heat Transfer and Damage Integral Modeling

The accurate assessment of parameters such as burn degree, volume, and depth is a prerequisite for the effective treatment of patients. However, as an unsteady heat transfer process, the temperature of the burn damage volume changes over time, and it is difficult to accurately calculate the integral value of the damage, which is used to assess the burn degree. Therefore, it is impossible to accurately determine the location and volume of damage at all burn degrees. In this study, the C language is used to program a user-defined function of the burn damage integral formula, and the coupled numerical simulation method is used to calculate the heat transfer and damage in a high-temperature water burn process. Then, the temperature and burn damage integral value of each point can be determined to accurately assess and distinguish the burn degree in real time, and estimate the position distribution, volume size, and transient change trend of each burn degree. Under the working conditions selected in this paper, the heat source mainly affects the epidermis and dermis directly below, and has less influence on the area above, which is in convective heat transfer. The damage integral value is very sensitive to temperature, and the highest damage integral value caused by 373 K is two and four orders of magnitude higher than that of 363 K and 353 K, respectively. The increase in the heat source temperature caused the volume of a third-degree burn to increase rapidly in the early stage of injury, but the volume of second-degree and first-degree burns did not change much. After heating at 373 K for 15 s and delaying the action for 45 s, the volume of first-, second-, and third-degree burns accounted for 0.4, 2.9, and 1.9%, respectively, and the total volume of damage accounted for only 5.2% of the total volume.

A computational approach to analyze apple dehydration using hybrid active solar dryer

AbstractIn the present research, the control parameters that is, bed area, water flow rate, and No. of air exchanges of Hybrid Active Solar Dryer integrated with Evacuated Tube Collector located at the solar energy laboratory of Madhav Institute of Technology and Science (MITS) Gwalior (M.P.) India, have been optimized. Moisture removal (mev), convective heat transfer coefficient (hc), evaporative heat transfer coefficient (he) and drying rate (Rd) have been taken as response parameters. Experiments have been conducted in different seasons according to Taguchi's L9 orthogonal array (OA). Response data has been analyzed independently and simultaneously. With the help of signal‐to‐noise (S/N) ratio, optimal parameter setting has been determined for good performance in different seasons. Entropy measuring techniques are used to determine the entropy weightage of each response. Gray relational analysis integrates several responses into a single one, that is, gray relational grade (GRG). The value of predicted S/N ratio for GRG as per optimal parameter setting is −0.04706 which is higher than the experimental S/N ratio which is −0.48614, indicating the successful implementation of this approach.

Flue Gas Recirculation in Steam Boilers: A Comprehensive Assessment Strategy for Energy Optimization and Efficiency Enhancement

In modern steam boilers, flue gas recirculation (FGR) is generally adopted as a temperature control method for reheated steam. Some research suggests that FGR does not affect the thermal performance of steam boilers, while other studies report enhanced thermal performance. This investigation aims to enhance energy efficiency by using an iterative calculation approach to provide a thorough energy evaluation of a steam boiler with an integrated FGR system. The research applies thermodynamic and heat transfer principles to model combustion characteristics, radiative heat transfer in the furnace waterwall, and convective and inter-tube radiative heat transfer in the economizer, superheaters, and reheater. The model is validated using specifications from an existing power plant boiler and a parametric analysis to examine the effects of varying FGR rates on heat distribution and thermal performance at full and partial loads. The results show that radiative heat accounts for an average of 45% of the total heat supplied, with up to 10% in the heat recovery section. As the FGR rate increases, radiative heat in the heat recovery section decreases by 50%, while the convective heat transfer increases then drops. The model shows that the ideal FGR is bounded between 0.3 at 50% boiler load and 0.4 at full load. An analysis of the impact of FGR on the various parts of the boiler reveals that the economizer experiences the most significant net change in heat gain, followed by the reheater. The effect of gas recirculation on the economizer can be nearly twice as great as on the reheater, indicating that FGR has substantial influence on components beyond the reheater. The findings indicate that reducing excessive heat in the economizer and reheater can be accomplished under different load conditions by regulating the fuel consumption rate according to the analysis of the effects of FGR on radiative and convective heat transfer across various components.

Non-intrusive experiments on coupled bubble dynamics and heat transfer during nucleate boiling under varying pressure conditions

The experimental investigation is concerned with the dynamics of single vapor bubble and heat transfer during nucleate boiling under varying pressure conditions, encompassing both atmospheric and sub-atmospheric levels. Utilizing high-speed rainbow schlieren deflectometry, a non-intrusive imaging technique for visualizing and quantifying the flow field variables in the fluid medium, this research examines the influence of operating pressure on some of the important parameters pertaining to boiling phenomenon such as bubble size, shape, and detachment mechanisms. The observations show that a decrease in pressure leads to the formation of larger bubbles, which, in turn, alters their growth mechanism. These changes in bubble behavior have a significant influence on the various forces acting on the growing bubble as well as on the associated heat transfer rates. The analysis provides insights into the complex interplay between buoyancy, surface tension, growth and contact pressure forces. Change in pressure significantly impacts these forces, influencing bubble dynamics. Moreover, the study presents a quantitative analysis of the whole field temperature distribution and heat transfer rates throughout the boiling process. Results reveal a strong dependence of thermal field on the working pressure, with higher pressures leading to more uniform temperature distributions. Evaporative component of heat transfer from the bubble base and convective heat transfer from the superheated layer are identified as the dominant mechanisms. Natural convection initially dominates, decreases post-nucleation, and increases upon bubble departure due to the fluid quenching effects.

On the transitory performance of mixed convective heat and mass transfer around spherical region in the presence of fluctuating streams

On the transitory performance of mixed convective heat and mass transfer around spherical region in the presence of fluctuating streams

Multi-objective geometric optimization of protrusion, droplet ribs, and inclined upper plate of a slit jet impingement heat sink to enhance its thermal performance

To meet the needs of heat transfer and temperature uniformity in the heat dissipation of high-heat-flux electronic devices, a novel slit jet impingement heat sink with a protrusion in the stagnation region, droplet ribs in the wall jet region, and an inclined upper-plate (PDI-SJIHS) is proposed, the coolant is Al2O3-H2O nanofluid. The influences of the structural parameters of the above three components and the Reynolds number on the heat transfer and flow of the PDI-SJIHS are studied numerically. Using the comprehensive heat transfer and temperature standard deviation as objective functions, a multi-objective optimization of PDI-SJIHS is conducted using non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ). The results indicate that the combination of the three components enhances the thermal performance of the PDI-SJIHS, compared with the slit jet impingement heat sink with only one of the above components. Rising the Reynolds number can enhance the thermal characteristics of the PDI-SJIHS. For a Reynolds number of 8000 and nanofluids with a 3% volume fraction, the average convective heat transfer coefficient, friction coefficient, and comprehensive heat transfer coefficient of the optimized PDI-SJIHS are increased by 182%, 153%, and 108%, respectively, and the standard deviation of temperature is 91% less than that of F-SJIHS.

Study on the thermal control performance of lightweight minimal surface lattice structures for aerospace applications

With the rapid evolution of aerospace technology and the increasing complexity of space environments, the demand for lightweight, thermally insulated, and highly efficient heat dissipation materials in aircraft equipment has surged. This study addresses this critical need by investigating Triply Periodic Minimal Surface (TPMS) lattice structures, offering a novel design approach to enhance spacecraft thermal management under extreme temperatures. Our work introduces a methodology to quantitatively assess the thermal insulation and heat dissipation performance of various lightweight lattice sandwich structures. We constructed implicit function models of low volume fractions, including Gyroid, Diamond, Primitive, and IWP, and conducted experiments using an active cooling setup under controlled heating conditions at 300 °C. Key findings reveal that, at flow velocities ranging from 0.25 to 1.5 m/s, the Diamond model exhibited the highest convective heat transfer coefficient, surpassing the Gyroid, Primitive, and IWP models by 6.9 % to 427.3 %, 87.1 % to 485.6 %, and 1.5 % to 98.7 %, respectively. Conversely, at velocities between 1.5 and 3.75 m/s, the Gyroid model demonstrated superior heat exchange performance, improving by 14.6 % to 67.2 %, 73 % to 167.7 %, and 9 % to 64.8 % compared to the Diamond, Primitive, and IWP models. During thermal insulation tests at temperatures from 200 to 400 °C, the Diamond model showed the best insulation effect, while the Primitive model performed poorly. Based on the experimental data, we established empirical relationships between the Nusselt number, friction coefficient, and Geometric Surface Ratio (GS). These findings not only underscore the significant potential of TPMS lattice structures in aerospace applications but also provide a robust theoretical framework and practical guidelines for achieving efficient thermal management in lightweight aerospace manufacturing.

Significance of solar radiation and viscous dissipation on oscillatory and steady convective heat transfer around buoyancy-driven sphere using FDM scheme

Significance of solar radiation and viscous dissipation on oscillatory and steady convective heat transfer around buoyancy-driven sphere using FDM scheme

Local characteristics and predictive models of the natural convective heat transfer coefficient for human body in standing and sitting postures

Local characteristics and predictive models of the natural convective heat transfer coefficient for human body in standing and sitting postures

Experimental study of enhanced convection in mini-tube with jet chamber insert using infrared thermometry

Enhancing single-phase convection in mini-tubes is essential for improving the efficiency and compactness of heat exchangers. Conventional mini-tube inserts, such as twisted tapes and helical screws, suffer from limited fluid mixing and significant pressure drops. These limitations restrict their effectiveness in achieving high heat transfer efficiency, especially in compact systems where space and energy are constrained. To overcome these challenges, this study introduces a novel mini-tube insert design featuring linked jet chambers to promote adequate spatial fluid mixing and significantly boost convective heat transfer. Experimental results demonstrate that at a Reynolds number (Re) of 300, the new insert increases the Nusselt number (Nu) by 67 % over a tube without inserts. Infrared thermometry further reveals that this enhancement leads to a 15.1 °C reduction in average wall temperature. The performance evaluation criterion (PEC) for the jet chamber insert reaches 1.66 at Re = 300, representing an 18.5 % improvement compared to traditional helical screw inserts. Beyond heat transfer, the insert design also improves temperature uniformity along the flow direction and stabilizes the outlet fluid temperature, addressing critical performance metrics for practical applications. The findings highlight its potential to improve energy efficiency and thermal performance in systems where space and thermal management are crucial.

Comparative study for heat transfer characteristics of magnetohydrodynamic viscous fluid in a multilayer flow flanked between nanofluids

This article examines the mixed convection heat transfer analysis of magnetohydrodynamic (MHD) viscous fluid flow over a multilayer channel flanked between nanofluids comprising a porous medium. The research highlights the significance of multilayer nanofluid flow in practical applications such as petroleum filtration process, cooling of electronic systems, nuclear reactors, and solar thermal systems. Ethylene glycol (EG) serves as a coolant due to its excellent miscibility with copper (Cu), enhancing its corrosion resistance properties in the fluid flow system. The purpose of this study is to analyze the impact of magnetic fields on heat transfer in a multilayer flow of Cu-EG-based nanofluids with different nanoparticles. The comparative performance of copper, copper oxide, and silver nanoparticles in enhancing the heat transfer rate is investigated. The non-dimensional equations are highly coupled, and non-linear differential equations are resolved analytically by utilizing regular perturbation approaches to get a closed-form solution. A comparative analysis between analytical results and numerical methods was done, demonstrating excellent agreement for the fluid flow momentum profile. This study reveals the magnetic field reduces heat transfer in the fluid flow system EG as a base fluid, and silver nanoparticles outperform copper, and copper oxide nanoparticles in thermal conductivity. These findings give rise to optimizing nanofluid-based systems in engineering and industrial applications.

Modelling thePerformanceof DoublePassSolar Air Collectors

This study presents a detailed investigation into the thermal performance of double-pass solar air collectors (DPSACs) through a combination of experimental testing and theoretical modelling. DPSACs are widely recognized for their ability to enhance heat transfer and reduce energy losses, making them suitable for applications such as drying and space heating. Experimental measurements were conducted under outdoor conditions focusing on key operational parameters such as mass flow rates (MFR) and solar radiation intensity. A theoretical model was developed and validated against experimental data, achieving high agreement with R2 values of 0.989 for outlet temperature and 0.917 for thermal efficiency. Results indicate that increasing MFRs initially improves thermal efficiency by enhancing convective heat transfer. However, higher MFRs reduce the outlet air temperature, as shorter air residence times limit the transfer of heat to the air. Solar radiation was found to have a pronounced effect at lower MFRs, emphasizing the need for optimal MFR selection to balance efficiency and temperature output. The study highlights a preferred operating range of 0.01–0.025 kg/s for maintaining efficient thermal performance under varying solar intensities. The validated model provides a robust framework for predicting the performance of DPSACs under diverse conditions.

Influence of Boundary Conditions on the Three-Dimensional Temperature Field of a Box Girder in the Natural Environment: A Case Study

The inhomogeneous distribution of temperature in bridges causes stresses and strains inside the structure, thus affecting the safety and durability of bridges. Therefore, the study of temperature action in bridge structures is crucial; boundary conditions of the temperature field are critical to study them. In this study, the calculation method of the boundary conditions for the three-dimensional temperature field of box girders in the natural environment is investigated by taking box girders as the object, which integrates the solar radiation, environmental radiation, structural shading effect, and convective heat transfer between the inner and outer surfaces of box girders. The effects of the atmospheric transparency coefficient and concrete short-wave absorptivity on the temperature field distribution of box girders were also investigated. It is shown that the calculation results obtained by the method in this study are in good agreement with the measured results, and the method can effectively simulate the three-dimensional temperature field of the box girder. The atmospheric transparency coefficient and the short-wave absorptivity of concrete have a significant effect on the temperature field distribution of box girders, and materials with lower short-wave absorptivity can be used in the design of box girders to reduce the structural temperature.

Heat and Mass Transfer in Shrimp Hot-Air Drying: Experimental Evaluation and Numerical Simulation

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0–62.9 W/m2∙K and 0.007–0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10−10–8.5 × 10−10 m2/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data (R2≥ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process.

A Study of Forced Convection in Non-Newtonian Hybrid Nanofluids Embedded in a Heated Cylinder Within a Hexagonal Enclosure by Finite Element Method

Nanofluids have the proven capacity to significantly improve the thermal efficiency of a heat exchanging system due to the presence of conductive nanoparticles. The aim of this study is to simulate the forced convection on a non-Newtonian hybrid with a nanofluid (Al2O3-TiO2-H2O) in a hexagonal enclosure by the Galerkin finite element method (GFEM). The physical model is a hexagonal enclosure in two dimensions, containing a heated cylinder embedded at the center. The bottom, middle left, and right walls of the enclosure are all considered cold (Tc), while the top wall is considered to be moving, and the remaining middle, upper left, and right walls have the adiabatic condition. The Prandtl number (Pr = 6.2), Reynolds number (Re = 50, 100, 300 and 500), power law index (n = 0.6, 0.8, 1.0, 1.2 and 1.4), volume fractions of nanoparticles (ϕ = 0.00, 0.01, 0.02, 0.03 and 0.04), and Hartmann numbers (Ha = 0, 10, 20 and 30) are considered in the model. The findings are explained in terms of sensitivity tests and statistical analysis for various Re numbers, n, and Ha numbers employing streamlines, isotherms, velocity profiles, and average Nusselt numbers. It is observed that the inclusion of ϕ improves the convective heat transfer at the surging values of Re. However, if the augmenting heat transfer requires any control mechanism, integrating a non-zero Ha number is found to stabilize the system for the purpose of thermal efficacy.

Analytical simulation of mixed convective Williamson nanofluid flow above a stretched Riga plate considering viscous dissipation effects

This work examines, accounting for viscous dissipation, an analytical simulation of mixed convection heat transfers in a Williamson blood base nanofluid flow on a stretched Riga plate (RP). The Lorentz force, which influences fluid dynamics, is produced by the alternating magnetic fields that comprise the RP. The flow characteristics are further complicated by the blood base Williamson nanofluid’s (WN) non-Newtonian behavior. The governing partial differential equations (PDEs) for momentum and energy are transformed into a set of nonlinear ordinary differential equations (NODEs) by similarity transformations. We solve these equations analytically using the homotopy analysis method (HAM). We investigate in detail how the temperature and velocity profiles (VPs) are affected by significant parameters as the Williamson parameter (WP), viscous dissipation, volume friction of nanoparticles, modified Hartmann number (MHN), heat generation parameter and Biot number (BN). The findings show that the thermal conductivity (TC) of nanoparticles is increased, improving the efficiency of heat transfer. Moreover, a Lorentz force generated by the RP considerably alters the temperature and flow fields. With regard to the design and optimization of thermal systems utilizing complex boundary conditions (BCs) and non-Newtonian nanofluids, this work offers significant new insights.

Effect of nozzle arrangement on heat dissipation performance and mechanical efficiency loss of bionic texture gear

Abstract Friction and wear are key issues in gear meshing. Lubrication, therefore, is used to reduce heat. The position and direction of the flow of the lubrication determined by the way the nozzles are injecting the fluid and by the texture on the flanks of the teeth, both have an influence on the heat transfer. Furthermore, the geometric characteristics of the tooth texture influences the friction behaviour directly. This article presents investigations on the impact of the tooth texture on wear. A proposal to prepare the tooth flanks with arc shaped grooves is made presenting the manufacturing process. Different measurements to determine the tooth flank texture and the friction are performed. Measurements showed that the arc groove gear had lower friction coefficients, wear depth, surface roughness Ra, and maximum tooth profile peak height Rq compared to conventional gears. The dynamic process of gear meshing is simulated by FEM analysis to understand the physics of heat flow and friction in detail，which revealed that the arc groove gear had reduced sliding distance, contact pressure, and wear depth, along with a higher convective heat transfer coefficient. Based on the measurement results of orthogonal test, two different nozzle arrangements are predicted: one is linear regression prediction (nozzle arrangement A), and the other is nonlinear particle swarm optimization neural network prediction (nozzle arrangement B). By measuring the torque loss value under the two nozzle arrangement conditions, it is found that the nozzle arrangement B is the best arrangement. The specific parameters are: injection distance is 56.0674 mm, injection angle is 8.4527°, nozzle diameter is 3.3955 mm, and pinion speed is 3000r / min. Under this condition, the mechanical efficiency loss is reduced by 94.48 %.

Investigation of convective heat transfer in helically corrugated tubes with inserts using nanofluids

Investigation of convective heat transfer in helically corrugated tubes with inserts using nanofluids

Thermal Diode Films with Liquid Crystal Elastomer Microstructures

Thermal diodes enabling asymmetric heat flow via efficiently conducting heat in one direction while blocking it in the opposite direction have great potential for controlling and managing thermal energy. Here, a thermal diode film with a scalable and thin‐film form factor is presented, which utilizes thermal contact asymmetry that varies with the direction of heat flow. The proposed thermal diode film is fabricated using two liquid crystal elastomer (LCE) layers separated by an air gap: one surface has a pillar structure, and the other has a hexagonal honeycomb structure. In forward mode, heating the LCE layer with the hexagonal honeycomb structure causes the sidewalls to buckle and contact the pillar structure on the opposite side, facilitating efficient conductive heat transfer. In reverse mode, heating the LCE layer with a pillar structure causes it to contract, increasing the gap between the layers with the pillar and hexagonal structures. This increased gap reduces convective heat transfer across the air gap. The thermal contact asymmetry, depending on the direction of heat flow, enables the film to achieve a thermal rectification ratio of ≈2.0 over a wide temperature range of 60–100 °C.

Impact of non-linear motion on convective heat transfer induced by oscillating thermal waves in the presence of heat source and sink

Impact of non-linear motion on convective heat transfer induced by oscillating thermal waves in the presence of heat source and sink