Non-uniform Heat Research Articles

A comparative study of purge slot exit shape on the film cooling effectiveness of a gas turbine shroud

To achieve higher efficiency and performance, a modern gas turbine withstands the extremely high thermal environment. In the turbine endwall passage, a high and non-uniform heat transfer appears due to various secondary flow. The purge flow injected through the upstream slot between the stationary and rotating pars can thermally protect the endwall surface by forming air film layer on it. However, since an excessive amount of purge flow reduce the system efficiency, it is needed to effectively inject the purge flow with a limited amount. Accordingly, in the present study, the effect of purge slot exit shape on the film cooling effectiveness (hereby FCE) of a shroud surface was discussed. As nondimensional design parameters of the purge slot, L/Ws, RW/Ws, and RL/Ws were defined, representing the geometric features: the slot width (Ws), the fillet radius at the windward side (RW) and fillet radius at the leeward side (RL) of slot exit, respectively. The measurement of the FCE was performed in a five-blade linear cascade rig using the PSP (Pressure sensitive paint) technique. The results showed that the FCE increased for wider slot width at a given blowing ratio condition. In addition, the fillet radius at the windward side (RW) has a negative effect on the FCE regardless of blowing ratio condition since the purge flow was easily disturbed by the accelerated mainstream injection. On the other hand, the Case 7 with the RW/Ws = 0.9 showed 5.1 % of the improvement of FCE at a higher blowing ratio M = 0.25 compared with the Case 2 with RW/Ws = 0, which represents the sharp edge at the windward side of the slot exit.

Subchannel thermal–hydraulic analysis of a wire-wrapped 19-pin rod bundle in the NACIE-UP facility

Based on the experimental campaign performed on the NACIE-UP (NAtural Circulation Experiment-Upgraded) facility, the benchmark activity was proposed by ENEA to qualify and validate the numerical tools for the Heavy Liquid Metal (HLM) system. Xi’an Jiaotong University participated in the benchmark exercise of subchannel validation and the self-developed subchannel code YAOGUANG was applied to the thermal hydraulic analysis. The performed two tests with different power distributions on the Fuel Pin bundle Simulator (FPS) were simulated, characterized by transition from forced to natural circulation. The applicability of this code to the stable state and mass flow rate transient was evaluated by comparing the numerical outcomes with the experimental results. Then the effect of the non-uniform heating on the thermal field was analyzed. The results indicate that this subchannel code has good accuracy in simulating both steady state and transient conditions with uniform power distribution. For the non-uniform case, the subchannel calculations can capture the general trend of temperature distributions, with a larger simulation deviation observed. This discrepancy is mainly due to the limitations of existing models adopted because they didn’t consider the impacts of non-uniform conditions on the flow and heat transfer in rod bundles. Finally, the influence of non-uniform heating is mainly manifested as the increase of axial and radial temperature gradients and it helps to flatten the radial thermal field to some degree.

Thermal-mechanical coupling analysis of the ribbed channels in regenerative cooling

Regenerative cooling plays a critical role in the thermal management for scramjet combustors, and the design of cooling channels is of utmost importance. To comprehensively analyze the performance of cooling channels, a validated thermal-mechanical coupling model was utilized in this study. The thermal and mechanical performance of both smooth and ribbed channels in regenerative cooling was investigated using Finite Volume Method and Finite Element Method. The findings indicate that the ribbed wall has a notable effect on enhancing the overall thermal performance of the channel. Moreover, the presence of ribs weakens the influence of buoyancy in the flow field, which can be one of the contributing factors in inhibiting heat transfer deterioration. Additionally, the design of ribs significantly reduces the average thermal stress experienced by the channel. However, it should be noted that the non-uniform heat transfer in the axial direction leads to a significant increase in local thermal stress. The triangular ribbed channel proves to be an effective approach in reducing thermal stress. Compared to rectangular ribbed ribs, the utilization of triangular ribs can result in a reduction of thermal stress by up to 30%. This observation highlights the advantage of triangular ribs in enhancing system life and safety by minimizing thermal stress.

Thermal and aging performance characteristics of pouch-type lithium-ion battery using heat pipes under nonuniform heating conditions

Lithium-ion (Li-ion) batteries are excellent energy storage technologies for electric vehicles. However, the performance and life cycle of a battery can be degraded by extremely high temperatures under nonuniform heating conditions. This study aims to investigate the performance improvement of a battery thermal management system (BTMS) using heat pipes (HP) under various heat generation conditions. The cooling performances of the BTMS using aluminum plates (AP) and HP were compared by analyzing battery temperature and life cycle while varying the discharge rate (C-rate) from 1C to 5C and the ambient and liquid temperatures from 25 °C to 40 °C. Furthermore, the nonuniform heat ratio, defined as the heat ratio between the tab and bottom of the battery, was introduced to emulate the uneven temperature distribution, ranging from 1 to 3. The average temperature (Tavg) increases of AP and HP decreased by 22.7 % and 32 %, respectively, compared with that using natural convection (NC). HP showed a much lower maximum temperature (Tmax) and temperature difference (ΔT) of the battery than AP, owing to the effective heat transfer using the heat pipe. During cyclic operation, HP maintained stable Tmax and ΔT within 34.3 °C and 4 °C, respectively. As the nonuniform heat ratio increased, Tmax increased significantly, which was more severe in AP than in HP. HP exhibited up to a 41 % higher normalized performance index of Tmax than AP. Additionally, with the nonuniform heat ratio increasing from 1 to 3 at a C-rate of 5C, the ΔT of AP and HP increased by 7.6 °C and 4.4 °C, respectively. Finally, the normalized equivalent full cycles of AP and HP at a nonuniform heat ratio of 3 and a C-rate of 5C decreased by 4.3 % and 1.6 %, respectively, compared to their performance under uniform heat.

Experimental study on heat transfer performance of high temperature heat pipe under axial non-uniform heat flux

Non-uniform high-temperature large heat flux is commonly encountered in engineering applications, posing challenges to heat transfer processes and affecting system performance. High temperature heat pipes offer an effective solution to mitigate the adverse effects of non-uniform heat flux by leveraging the unique characteristics of their inner alkali metal (or alloy) working fluid, such as high latent heat of vaporization, strong heat flux density, and ability to operate at elevated temperatures. These features enable high temperature heat pipes to achieve excellent isothermal and uniform heat transfer performance, thereby improving overall thermal management in heat transfer systems. Building upon the investigation of the original high temperature heat pipe, this study designed and fabricated a specially shaped high temperature heat pipe with a spherical crown surface as the evaporator. Experimental research was conducted to assess its frozen start-up performance and heat transfer characteristics under the influence of axial non-uniform heat flux. The results were also analyzed theoretically, providing valuable insights into the frozen start-up performance and heat transfer performance of the high temperature heat pipe in the presence of non-uniform heat flux conditions. The analysis results reveal several important findings: (1)The high temperature heat pipe demonstrates its capability to convert axial non-uniform high-temperature large heat flux into a uniform heat flux, thus achieving excellent uniform heat transfer performance. (2)The theoretical solution obtained through the lumped heat capacity analysis method shows satisfactory agreement with the actual frozen start-up process of the high temperature heat pipe. This theoretical reference can aid in the transient analysis of the frozen start-up process under the influence of axial non-uniform high-temperature large heat flux. (3)The experiment investigated the influence of heating power on heat transfer performance and temperature uniformity. The results indicate that the temperature uniformity of the high temperature heat pipe exhibits a trend of initially increasing and then decreasing. Specifically, the best temperature uniformity is achieved when the heating power is 1084.7 W. Moreover, when the heating power is 1197.9 W, the high temperature heat pipe exhibits the lowest equivalent thermal resistance of 0.0265 K/W, indicating the best heat transfer performance. (4) The variable power heating approach demonstrates that increasing the heating power leads to an extension of the effective length of the heat pipe. The most favorable heat transfer performance and temperature uniformity are observed when the heating power is set to 1133.7 W, allowing the full length of the condenser of the high temperature heat pipe to participate actively in the heat transfer process. These results can provide quantitative experimental data and theoretical references for improving the thermal shock of non-uniform high-temperature large heat flux.

Impact of Arrhenius energy and irregular heat absorption on generalized second grade fluid MHD flow over nonlinear elongating surface with thermal radiation and Cattaneo–Christov heat flux theory

In this paper, the free convection flow phenomenon on magnetized second-grade nanofluid over a nonlinear elongating surface has been modeled under the assumptions of generalized Fick’s and Cattaneo–Christov heat flux relations. The non-uniform heat source and sink and thermal radiation effects are used in the energy equation with the Buongiorno nanofluid model. The effect on activation energy and chemical processes is also examined, making the current numerical scrutinization innovative. The current mathematical model begins with partial derivative equations (PDEs), which are then transformed into ordinary derivative equations (ODEs) using similarity transformations. The outcomes are obtained using a combination of the finite-difference scheme with the collocation method, approximated up to desirable accuracy, and the effects of various parameters on the modified second-grade nanofluid are discussed using tables and graphs. The temperature distribution for the thermal boundary layer is raised with nonlinear thermal radiation and Brownian motion parameters. The present thorough analysis identified several technical and industrial applications, including Biomedical applications in cancer treatment, electrical wire manufacturing, oil friction control in pipelines, manufacturing processes, and aerodynamic expulsion utilizations.

Thermal performance research on a novel coupled heating system combined solar air heater with ventilation PCM wall

Solar heating technology is increasingly recognized as a prominent option for clean building heating. However, challenges such as intermittent thermal energy supply and supply–demand mismatch hinder its widespread adoption. To address this issue, this paper introduces a novel coupled heating system that combines a solar air heater with a ventilation Phase Change Material (PCM) wall. A rural residential house in Tianjin was chosen as an experimental platform and comparative experiments was conducted to compare the advantages of the ventilation PCM wall with the conventional wall. Additionally, numerical simulations were utilized to address the non-uniform heat transfer in the direction of the Heat Transfer Fluid (HTF) flow by employing cascaded PCM. The experimental results demonstrated that the coupled heating system exhibited high thermal storage and release efficiency, significantly improving indoor thermal comfort. Under optimal operating conditions (air supply temperature: 35-45℃, air supply speed: 3–4 m/s), the system achieved rapid thermal storage within 4 h, reaching a maximum thermal storage efficiency of up to 87.6 %. The test room maintained a nighttime temperature of 15.7 °C, exhibiting temperatures 6.3–10 °C higher than the control room. Numerical results revealed that the cascaded PCM enhanced the thermal storage rate, particularly at the first 2.8 h of the thermal storage period, contributing to the overall efficiency and flexibility of the system. This research provides theoretical guidance for the optimal design and practical application of the ventilation PCM wall.

Experimental studies of effects of temperature gradients on performance of pouch type large format NMC/C lithium-ion battery

Cell to pack design concept for energy storage in automotive applications leads to a substantially increased cell size that results in temperature gradients over the surface induced by non-uniform heat transfer linked to the cooling system design, which influences the cell performance. In this paper, temperature gradient effects on life performance of a large-format cell are experimentally investigated, using a developed device that can actively control appropriate gradients in the longitudinal direction and simultaneously measure the heat generation rate (HGR). Performances under uniform and non-uniform temperature conditions (MMM: uniform temperature, LMH: low-mean-high, HLH: high-low-high) are compared and quantified. At beginning of life (BOL), the low-temperature regions in the HLH and LMH conditions dominantly limit the cell capacity, and the HLH condition suppresses the HGR at high C-rates. During aging, the cell experiences a larger capacity fade and HGR increase under the HLH than MMM condition. The analyses of half coin cell, differential capacity (dQdV), dynamic resistance and impedance reveal that the attributing mechanisms are mainly the loss of Cathode active material, potentially the loss of lithium inventory, and the increase of impedances, indicating the electrochemically promoted side reactions and corrosions in the high-temperature regions of the HLH condition.

Numerical study on the heat transfer characteristics of hydrocarbon fuel in the cooling channel filled with porous media

Regenerative cooling channel is only heated by a single wall in practical applications, resulting in serious thermal stratification. Under the action of porous media, the wall temperature decreases, which avoids the heat transfer deterioration caused by velocity distortion near the high temperature wall. Compared with the cooling channel without porous media, the porous media improves the homogeneity of the coolant heat sink, and the physical and chemical heat sink non-uniformity coefficient at the outlet is close to 0 with the change of aspect ratio. The increase of the height of the cooling channel increases the heat transfer distance in the height direction, which increases the heat transfer resistance of the heat flux and makes the uniformity of the heat sink worse. The positive feedback between the coolant flow rate and the non-uniform heat flux on the parallel filled channel wall can be effectively suppressed. The porous media greatly reduces the radial transfer shortens the axial distance between the upper and lower walls maximum temperature difference, and reduces the thermal stress of channel during the cooling process.

Impact of Linear Heating Profiles on Nanofluidic Convection in Enclosure

The present study demonstrates the influence of non-uniform heating on the nanofluidic thermal convection in an enclosure by keeping the mean temperature of heating constant. The non-uniform heating is applied by varying the slope of the linear temperature profile from 0° to 60° at an interval of 15°. The investigation is executed numerically following the finite volume discretization technique. Two different cases are taken into consideration: Case A for linearly increasing temperatures and Case B for linearly decreasing temperatures. The flow structures and heat transfer characteristics are studied for the Rayleigh number from 103 to 106 and the copper-water nanoparticle concentrations from 0 to 0.04, utilizing the streamlines, isotherms, and heatlines. The results reveal that the mean Nusselt number monotonically increases with a rise in slope for all linearly increasing temperature profiles. For the decreasing profiles (Case B), the Nusselt number decreases with a rise in the temperature slope for the lower Rayleigh number (103 and 104); however, a marginal increment is observed at the maximum profile angle for the higher Rayleigh number (105 and 106). This study provides findings helpful for designing thermal devices with the efficient utilization of heating sources.

Computational Study of MHD Nanofluid Flow with Effects of Variable Viscosity and Non-uniform Heat Generation

Computational Study of MHD Nanofluid Flow with Effects of Variable Viscosity and Non-uniform Heat Generation

Publisher Correction: Significance of nanoparticle radius on EMHD Casson blood-gold nanomaterial flow with non-uniform heat source and Arrhenius kinetics

Publisher Correction: Significance of nanoparticle radius on EMHD Casson blood-gold nanomaterial flow with non-uniform heat source and Arrhenius kinetics

A review on active heating for high performance cold-proof clothing

PurposeThe present study provides a comprehensive review of the advancements in five active heating modes for cold-proof clothing as of 2021. It aims to evaluate the current state of research for each heating mode and identify their limitations. Further, the study provides insights into the optimization of intelligent temperature control algorithms and design considerations for intelligent cold-proof clothing.Design/methodology/approachThis article presents a classification of active heating systems based on five different heating principles: electric heating system, solar heating system, phase-change material (PCM) heating system, chemical heating system and fluid/air heating system. The systems are analyzed and evaluated in terms of heating principle, research advancement, scientific challenges and application potential in the field of cold-proof clothing.FindingsThe rational utilization of active heating modes enhances the thermal efficiency of cold-proof clothing, resulting in enhanced cold-resistance and reduced volume and weight. Despite progress in the development of the five prevalent heating modes, particularly with regard to the improvement and advancement of heating materials, the current integration of heating systems with cold-proof clothing is limited to the torso and limbs, lacking consideration of the thermal physiological requirements of the human body. Additionally, the heating modes of each system tend to be uniform and lack differentiation to meet the varying cold protection needs of various body parts.Research limitations/implicationsThe effective application of multiple heating modes helps the human body to maintain a constant body temperature and thermal equilibrium in a cold environment. The research of heating mode is the basis for realizing the temperature control of cold-proof clothing and provides an effective guarantee for the future development of the intelligent algorithms for temperature control of non-uniform heating of body segments.Practical implicationsThe integration of multiple heating modes ensures the maintenance of a constant body temperature and thermal balance for the wearer in cold environments. The research of heating modes forms the foundation for the temperature regulation of cold-proof clothing and lays the groundwork for the development of intelligent algorithms for non-uniform heating control of different body segments.Originality/valueThe present article systematically reviews five active heating modes suitable for use in cold-proof clothing and offers guidance for the selection of heating systems in future smart cold-proof clothing. Furthermore, the findings of this research provide a basis for future research on non-uniform heating modes that are aligned with the thermal physiological needs of the human body, thus contributing to the development of cold-proof clothing that is better suited to meet the thermal needs of the human body.

Effect of Magnetic field on Unsteady Mixed convection Micropolar Nanofluid flow in the Presence of Non-Uniform Heat Source/Sink.

: The idea of the current investigation is to study the two-dimensional unsteady mixed convection MHD flow of a micro-polar nanofluid with non-uniform heat source/sink. Effects of radiation, reaction, thermo-diffusion, and viscous dissipation are considerednanoparticles are suspended in water base fluid. The governing non-linear system of PDEs is transformed into a system of ODEs using the similarity transformation and HAM is employed for obtaining solutions. Effects of different physical parameter on momentum, microrotation, energy, and concentration profiles are discussed through graphs. From graphical results, it is concluded that the unsteady parameter and magnetic parameter tend to improve the motion of the fluid. It is also seen that microrotation is raised in the shrinking sheet and reduced in the stretching sheet with the increase in the unsteady parameter. The mass transfer process improved with thermal diffusion parameter while delayed with chemical reaction.

The apparent effusivity method for normalized thermal contrast evaluation in infrared thermographic testing

Thermographic nondestructive testing is used for the detection of near-surface discontinuities in materials, where indications of potential defects or discontinuities are detected and evaluated by their thermal contrast. The key requirements for successful thermographic data processing include managing non-uniform heating and identifying nominal areas. Advanced methods often rely on numerical simulation, which can be challenging and time-consuming. This study suggests a new simple method of thermal contrast calculation for flash-pulse thermography. It is based on the analysis of the inverse apparent effusivity. It includes an automated indication of the sound (defect-free) area and the creation of an artificial reference sequence, which is based on a temperature profile of the sound area and the non-uniform heating map. Derivative analysis of the smoothed contrast data is applied to improve detectability and Contrast/Noise Ratio (CNR). An experimental comparison of the proposed method with other known methods is presented. In the presented example, it allowed detection of 23 defects with an average CNR of 6.13 dB, against the traditional differential absolute contrast method, which detected only 13 defects with an average CNR of 0.53 dB. Thus, high detectability and high CNR values provided by the proposed method are demonstrated.

Analysis of Entropy Generation on MHD Radiative Viscous-Ohmic Dissipative Heat Transfer Over a Stretching Sheet in a Chemically Reactive Jeffrey Nanofluid with Non-Uniform Heat Source/Sink Based on SQLM

We have examined the effect of entropy generation and nonlinear thermal radiation on magnetohydrodynamic (MHD) in Jeffrey nanofluid over a permeable stretching sheet with viscous-Ohmic dissipation and non-uniform heat source/sink. Brownian motion and thermophoresis effects have also been taken into account. The basic governing equations of the boundary layer flow are then solved numerically by the Spectral Quasilinearization method (SQLM). Various controlling physical parameters effects on velocity, temperature, concentration, entropy generation and Bejan number profiles are presented graphically. Results show that increasing the magnetic parameter, Brownian motion parameter, and thermophoresis parameter enhance the temperature profiles. Furthermore, the entropy generation profiles increase with space-dependent and temperature-dependent parameters, wall mass flux parameter, and chemical reaction parameter near to the sheet. In contrast, reverse trends are observed away from the sheet. Novelty of entropy generation is also provided to reflect the effects of several relevant physical parameters on the entropy generation rate and Bejan number.

Simulation and optimization of square fin concentric tube heat storage exchanger

The square fin was used to improve the heat transfer rate of the concentric tube phase change heat exchanger. The effects of fin spacing, fin arrangement, and fin length on the melting process of phase change material (PCM) were studied. The influence and mechanism of non-uniform fin arrangement were discussed in detail. The liquid phase distribution and temperature distribution of PCM with time were analyzed. The results indicated that the heat exchanger with square fins can significantly improve the heat storage rate and shortened the complete melting time of PCM. Compared with heat exchangers without fins, the melting time of PCM in a 40 mm equidistant fin heat exchanger was shortened by 15.85%, and that in a 70 mm, non-uniformly spaced fin heat exchanger was shortened by 36.79%. Due to the different distances between the square fins and the outer boundary of the concentric tube, the temperature distribution near the square fin showed anisotropy, which enhanced the melting rate of PCM. The sensitivity order was fin arrangement > fin length > fin spacing. The research results can provide a reference for the design of phase change heat exchangers.

Fuzzy fault tree analysis of EVAC system based on improved SAM- FFTA with butterfly optimization algorithm

At this stage, 3D elliptical vibration-assisted cutting(3D-EVAC) systems have proven to be a highly promising method of machining for a wide range of new materials, which can meet the requirements of ultra-precision machining. In practice, however, there are still various problems that affect its ability to achieve the desired accuracy. The functional reliability of the system should therefore be improved. Considering that the failure probability of 3D-EVAC system components cannot be obtained accurately, this paper proposes an improved similarity aggregation method (SAM) based on the butterfly optimization algorithm (BOA), called BOA -SAM. In the experiment, thirty-six events are selected and these events are aggregated by BOA-SAM. The experimental results show that BOA-SAM not only avoids the variability of the aggregation results with the relaxation factor (β) but also improves the accuracy of the aggregation results compared with SAM. BOA-SAM and FTA are connected by the center-of-mass method to form BOA-SAM-FFTA. Finally, a fuzzy fault tree analysis of the 3D-EVAC system was carried out using the BOA-SAM-FFTA method to calculate the probability of failure for each bottom event and to analyze its importance. It was found that non-uniform heating of the tool was the event that had the greatest impact on the functional reliability of the system, which offered a theoretical basis for improving the functional reliability of the system. The probability of failure of other bottom events during the experiment also can provide some theoretical guidance for the system maintenance plan .

Radio frequency heating of granular and powdered foods in aluminum, polypropylene and glass container: Heating rate and uniformity

Non-uniform heating is the primary challenge during large-scale radio frequency (RF) disinfestation and pasteurization applications. Packaging materials can absorb, transmit or reflect RF energy and can be used to overcome high-temperature differences throughout the product caused by overheating at the edges and corners. In this study, effects of three container materials (aluminum-AL, polypropylene-PP, and glass-GL), electrode gap, end-point temperature, and processing time on heating uniformity were investigated by determining the temperature distribution, heating uniformity index (λ), and heating rate (v) profile in the upper, middle, and bottom layers of RF (6 kW, 27.12 MHz) treated corn kernels associated with different sizes (d) and moisture content (MC). Results showed that corn kernels (d = 6 mm), powders (d = 2 mm) and flours (d = 0.2 mm) in the AL container (200 × 120 × 40 mm3) indicated a lower v (AL: 3.73 ± 0.21, 4.21 ± 0.21, and 6.17 ± 0.31, PP: 7.77 ± 0.14, 7.97 ± 0.40, and 8.98 ± 0.32, GL: 6.24 ± 0.19, 6.55 ± 0.19 and 7.16 ± 0.10 °C/min), but better heating uniformity, λ (AL: 0.101 ± 0.005, 0.090 ± 0.004, and 0.082 ± 0.004, PP: 0.214 ± 0.010, 0.187 ± 0.009, and 0.172 ± 0.009). The shielding effect of AL container on RF wave was stronger than that of PP and GL. The corner overheating problem in the AL container was greatly improved, and the hot spot was shifted from the corner of the sample to the center. Meanwhile, the λ of corn kernels with different sizes in AL container first decreased and then increased with the increase of MC (from 10 to 16%, w.b.). When the λ reached a minimum value, in order to further increase the v of food in the AL container, the relationship between d, MC and v was finally established. The results can provide valuable information for improving the heating uniformity of food particles/powders and optimizing the shielding structure and performance of metallized RF packaging.

Pulsed microwave radiation for extraction of betalains from red beetroot: Engineering and technological aspects

Betalains are water-soluble plant-derived red pigments with high red color intensity besides functional properties. Extraction is a critical step in isolating these bioactive compounds from natural sources. In this study, microwave treatments with different powers, duty cycles, and process times were applied to extract betalains, from red beet. Results revealed that increments in power, extraction time, and duty cycle led to a steep temperature increase in all samples. However, the severity of temperature rise declined at higher power, time, and duty cycle. The minimum non-uniform heating was obtained at power 450 W, duty cycle 0.17, and process time 0.5 min. The minimum energy consumption was observed at the lowest power, time, and duty cycle. The highest betacyanin content (about 175–200 mg/L) was shown at higher microwave powers. Increment in all extraction parameters, namely process time, power, and duty cycle, improved the total phenolic content. Maximum antioxidant capacity, 73 %, was obtained at 1.5 % citric acid, 0.17 duty cycle, 230 W microwave power, and 4 min extraction time. Overall, microwave with pulsed radiation is a powerful and advanced technique for efficiently extracting betalains from red beetroot for usage in the food industries.