Increased Heat Dissipation Research Articles

EXPLORING ELECTROMECHANICAL SYSTEMS IN THE DEVELOPMENT OF NEXT-GENERATION ELECTRIC POWERTRAINS

In the rapidly evolving electric vehicle industry, the study of electromechanical systems in next-generation electric powertrains is of particular relevance. This is driven by the need to enhance energy efficiency, reduce costs, and improve the reliability of vehicles. The article examines the role of innovative materials, advanced design methods, and control algorithms in creating high-efficiency and reliable electric powertrains. Specifically, the impact of nanomaterials such as graphene and carbon nanotubes on reducing motor weight and increasing heat dissipation is analyzed, contributing to improved efficiency and extended driving range. The adoption of additive manufacturing (3D printing) and digital twins accelerates prototyping and component optimization in electric powertrains. Adaptive control algorithms ensure optimal system performance in real-time, enhancing overall efficiency and reliability. Research methods included the analysis of modern materials and technologies, prototyping using additive manufacturing, and the implementation of predictive and adaptive control algorithms. The results demonstrate significant improvements in the performance of electric powertrains due to the use of innovative materials and cutting-edge design technologies. Conclusions confirm that the application of advanced materials and adaptive control algorithms is critical for ensuring the sustainable development of the electric vehicle industry. Future research prospects focus on further refining materials and technologies to enhance scalability and reduce production costs, making electric powertrains more accessible and efficient.

Dynamic blade tip clearance control of aero-engine by the integration of cooling air with fuel thermal management system

In advanced aero-engines, the precise control of tip clearance and thermal management of the fuel system are two important measures to improve the transient performance of the aero-engine. In order to optimize the overall performance of an aero-engine during a full-flight mission, this paper proposed a novel architecture integrating active clearance control system and aero-engine fuel thermal management system, which utilizes fuel heat sink to achieve indirect regulation of the tip clearance. Furthermore, a set of critical optimization criteria for the new architecture was derived to achieve dynamic heat distribution in the fuel thermal management system. Subsequently, the transient performance was tested under a complete flight mission with a duration of 10,000 s. The calculation results indicate that the new architecture effectively raises the fuel temperature to its maximum allowable value during low thermal load phases, which increases heat dissipation capability of the system. The new architecture exhibits a significant effect on the control of the tip clearance during the ground idle, cruise, and engagement phases, resulting in a maximum increase of 1.86% in the relative efficiency of the high-pressure turbine. The new architecture also prevents the engine from experiencing excessively narrow tip clearance during acceleration. Ultimately, the new architecture achieves a 2.59% reduction in total fuel consumption compared to the original design. The new architecture has significant potential to improve engine efficiency and increase operational safety.

Transcriptional profiling of the M. complexus in naked neck chickens suggest a direct pleiotropic effect of GDF7 on feathering and reduced hatchability

BackgroundThe locus for naked neck (Na) in chickens reduces feather coverage and leads to increased heat dissipation from the body surface resulting in better adaptability to hot conditions. However, the Na gene is linked to significantly lower hatchability due to an increased late embryonic mortality. It has been argued that the causative gene GDF7 may have a direct pleiotropic effect on hatchability via its effect on muscle development. Thus, the study presented here analyses the transcriptome of the hatching muscle (M. complexus) and shows how GDF7 impacts development leading to reduced hatching rates in Na chickens.ResultsUsing 12 chicken embryos (6 x wildtype (Wt) and 6 x Na) RNA was extracted from the M. complexus of each embryo and sequenced. The resulting differential expression analyses led to the discovery of 461 differentially expressed (DE) genes in the M. complexus of the experimental group. Among those, 77 genes were of uncertain function (LOC symbols), with 31 were classified as uncharacterised. The regulation of a number of pathways involved in normal embryonic development, were found to be negatively influenced by the Na genotype. Further pathways involved in cell-cell adhesion, cell signalling pathways, and amino acid (AA) metabolism/transport were also observed. GDF7 (alias BMP12), whose localised overexpression in the neck skin causes the Na/Na phenotype, was significantly overexpressed in the M. complexus of Na/Na embryos, and shows a significant increase in the number of binding sites for the transcription factor PITX2 was also observed.ConclusionIn Na chickens, GDF7 is under the control of a mutated cis-regulatory element, whose actions are known to suppress the development and distribution of feathers through the sensitizing action of retinoic acid. In this study, a number of DE genes with over 10 retinoic acid response elements (RAREs) in close proximity were observed, indicating changes to the retinol metabolism. With the understanding that the Na/Na mutation leads to increased retinoic acid activity, this indicates a high likelihood of GDF7 excerpting a direct pleiotropic effect, not just in the observed reduction in feather patterning, but also impacting the development of the M.complexus, and consequently leading to the reduced hatchability observed in birds with the Na/Na genotype.Furthermore, the enrichment of PITX2 binding sites in proximity to DE genes in the M. complexus, also indicates that muscle development is still ongoing in Na embryos. This suggests that the M. complexus is not yet fully developed, further increasing the potential for late embryonic mortality in Na chicks at hatching.

Chronic heat stress upregulates pyruvate metabolic process and gluconeogenesis but downregulates immune responses in Sahiwal cattle.

Climate change and growing population and their strain on animal production are the impending challenges that the developing countries, like India, need to tackle in the coming days. This study aimed to detect and analyze the uncharacterized variation in the gene expression patterns with the change of condition, from thermoneutral to chronic hot-humid, in the Sahiwal cattle, one of the best breeds of milk-producing cattle in India, known for being heat-tolerant. Using RNA-Seq analysis on peripheral blood mononuclear cells (PBMCs), 4021 differentially expressed mRNAs (2772 upregulated, 1249 downregulated) and 1303 differentially expressed long non-coding RNAs (769 upregulated, 534 downregulated) were identified, with the thresholds of false discovery rate < 0.05 and|log2(fold change)| > 2. Significantly (p-adjusted < 0.05) overrepresented Gene Ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome pathways were analyzed, revealing upregulation of processes like pyruvate metabolic process, gluconeogenesis, ion transmembrane transport, neuropeptide signaling pathway, and animal organ development, with genes like SHH, GRK1, CHRM3, CAMK2A, and HSPB7 were upregulated, while translation and immune responses, with genes like RPS3, EEF1A1, TNF, BoLA-DRB3, and UBB were downregulated. Analysis of cis-mRNAs of DE-lncRNAs showed presence of both up- and down-regulated cis-mRNAs for both up- and down-regulated lncRNAs indicating existence of positive and negative regulation of mRNA expression by lncRNAs. Managemental nudges that decrease metabolic heat generation, like betaine and chromium supplementation, and increase heat dissipation, like microenvironment cooling, should be utilized. This study highlights the role of pyruvate metabolism and gluconeogenesis in coping up with heat stress and offers an improved understanding of the heat stress response of Sahiwal cattle along with the genes and pathways responsible for it.

Superconducting Qubits above 20 GHz Operating over 200 mK

Current state-of-the-art superconducting microwave qubits are cooled to extremely low temperatures to avoid sources of decoherence. Higher qubit operating temperatures would significantly increase the cooling power available, which is desirable for scaling up the number of qubits in quantum computing architectures and integrating qubits in experiments requiring increased heat dissipation. To operate superconducting qubits at higher temperatures, it is necessary to address both quasiparticle decoherence (which becomes significant for aluminum junctions above 160 mK) and dephasing from thermal microwave photons (which are problematic above 50 mK). Using low-loss niobium-trilayer junctions, which have reduced sensitivity to quasiparticles due to the higher superconducting transition temperature of niobium, we fabricate transmons with higher frequencies than previously studied, up to 24 GHz. We measure decoherence and dephasing times of about 1μs, corresponding to average qubit quality factors of approximately 105, and find that decoherence is unaffected by quasiparticles up to 1K. Without relaxation from quasiparticles, we are able to explore dephasing from purely thermal sources, finding that our qubits can operate up to approximately 250mK while maintaining similar performance. The thermal resilience of these qubits creates new options for scaling up quantum processors, enables hybrid quantum experiments with high heat-dissipation budgets, and introduces a material platform for even-higher-frequency qubits. Published by the American Physical Society 2024

Feasibility study on the heat transfer enhancement of gap flow induced by wasted vibration of linear compressor body

Refrigerators account for 20–30 % of household electricity consumption, with the compressor contributing to 80 % of the total consumption. Therefore, it is essential to increase the compressor efficiency. One approach to enhance compressor performance involves increasing heat dissipation to lower the temperature of the suction system and boost the refrigerant density entering the suction chamber. To achieve that innovatively, we harnessed the waste vibration of the linear compressor body to create a gap flow between the body and the housing, enhancing compressor performance by augmenting heat dissipation. Measurements of gap flow temperature, cylinder surface temperature, and heat flux on the cylinder surface were conducted, varying the RPM, gap size, and the shape of the gap flow path. We also observed variations in the gap flow rate with RPM and stroke. The results revealed that gap temperature and heat flux increased with higher RPM and smaller gap size, and the application of ribs to the gap flow path proved to be more effective in enhancing temperature and heat flux. Additionally, it is anticipated that heat flux will further increase with a longer stroke as the flow rate increases. Therefore, to optimize heat dissipation through gap flow using the waste vibration of the compressor body, it is advantageous to employ a smaller gap size, higher RPM, longer stroke, and apply ribs to the gap flow path. Future research should focus on verifying the effectiveness of increased heat dissipation and improved Energy Efficiency Ratio (EER) through actual compressor experiments.

Enhancing reliability in laser powder bed fusion through substrate modification: microstructure, mechanical properties and residual stress

Laser additive manufacturing (LAM) is prone to excessive tensile residual stresses, leading to cracking or even failure, seriously hindering its wide application. Therefore, controlling residual stress to avoid crack formation and improve forming quality is crucial for reliable LAM. Most of the past research controls the residual stresses by modifying the process during the forming process, which is a very complicated method. In this study, through alterations in the form of a substrate to modify its restraint effect on the resulting structure and heat dissipation channels, the impact of them on the microstructure, defects, residual stress, and fracture characteristics to mitigate the likelihood of cracking in laser powder bed fusion (LPBF) was systematically studied. The results showed that the microstructure of all the specimens consists of fine dendritic, cytosolic, and columnar. Specimens with un-grooved substrates exhibited more holes and cracks, and solidification cracks were predominant. The crack density in specimens with grooved substrates was reduced by 71 %, reaching a relative density of 98.94 %. Tensile test results showed that the mechanical properties of the grooved specimens were excellent, with the tensile strength and yield strength higher than the un-grooved samples by 29 MPa and 11.7 MPa, respectively. And the results of the residual stresses indicated significantly lower tensile residual stresses in specimens with grooves, due to reduced restraint stresses and increased heat dissipation, mitigating the extent of crack propagation. These findings provided a simpler new approach to LPBF of crack-free components with excellent mechanical properties.

Assessment of the Thermomechanical Behavior and Microstructure of AA 7075-T6 Aluminum Alloy Lap Joints at Optimal Predicted FSW Process Parameters

The lap joints of AA 7075-T6 aluminum alloy were assembled using the friction stir welding (FSW) technique. Experimental studies were performed to characterize the thermomechanical properties of these welds. The main goal of this research was to comprehensively assess the thermomechanical behavior of AA 7075-T6 aluminum alloy under FSW conditions. Tests were carried out at a tool rotational speed of 1320 rpm and at two advancing speeds of 70 mm/min and 120 mm/min, selected based on a previous study aiming to optimize the heat input during the FSW process. The experimental investigations involved the characterization of temperature profiles during welding, mechanical properties such as microhardness and tensile strength, and microstructure examination at the two advancing speed conditions. This study revealed that the welding speed has an obvious influence on the material thermal behavior during the FSW process. Indeed, the peak temperature obtained with a lower welding speed (70 mm/min) was higher by almost 10% compared to that obtained with a higher speed (120 mm/min). Moreover, by increasing the welding speed, the mechanical characteristics, such as microhardness and tensile strength, were increased by almost 5% for the mean microhardness and 6% for the ultimate tensile strength. Additionally, the microstructure examination demonstrated that, by decreasing the welding speed, more interaction between the tool and the material is observed, resulting in a deeper stir zone due to increased heat dissipation downwards into the material, affecting the thermal profile and influencing the resulting mechanical properties of the welded joint.

The physiochemical characteristics and glycerolipid profile of Cycas panzhihuaensis in response to individual and combined drought and freezing temperature stress

The frequency and intensity of the occurrence of drought (D) events during winter are increasing in most areas of China. To explore the interactive effects of D and freezing temperature (F) on plants of endangered Cycas panzhihuaensis, some physiochemical characteristics and the lipid profile were determined. Drought and F stress had no or little impact on the traits of leaves, which, however, bleached following a combination of D and F treatment (DF). Drought treatment did not affect the chlorophyll fluorescence parameters and the flavonoid content of C. panzhihuaensis. Besides the increase in flavonoid content, a decrease of photochemical efficiency and an increase of heat dissipation were induced by both F and DF treatment, with the effects being greater in the latter treatment. The malondialdehyde content decreased significantly and the total antioxidant capacity increased significantly in the plants exposed to both D and DF treatments. The D treatment did not impact the amount of phospholipids but led to an accumulation of saccharolipids. Additionally, the amount of both phospholipids and saccharolipids remained unchanged following F treatment but decreased significantly following DF treatment compared with those of the control. The unsaturation level did not change significantly in most lipid classes of membrane glycerolipids following various stresses but increased significantly in phosphatidylserine, monogalactosylmonoacylglycerol, digalactosyldiacylglycerol and sulphoquinovosyldiacylglycerol following D or both D and F treatments. Generally, plants of C. panzhihuaensis showed relatively strong tolerance to individual D stress, while D aggravated the F-induced damage, which was likely caused by the degradation of the membrane glycerolipids.

Cyclic Electron Flow Alleviates the Stress of Light Fluctuation on Soybean Photosynthesis

Crops often face light intensity fluctuations in natural settings. Intercropping is widely used to improve crop yield and resource utilization worldwide, but crops suffer from high-frequency and high-intensity light fluctuations due to mutual crop influence. Soybean is an important legume crop and is often intercropped with other crops, but little is known about soybean’s response to light fluctuation environments. Herein, three fluctuation frequencies (1, 10, and 20 min/cycle) were used to analyze soybean photosynthesis responses by measuring leaf growth, chlorophyll content, gas exchange, and electron transfer. Our data revealed that faster fluctuation frequencies led to the stronger suppression of soybean morphology and photosynthesis, with significant reductions of 31.31% and 21.58%, respectively. Damage to photosystems II (PSII) and I (PSI) also intensified, with significant decreases of 18.52% and 18.38% in their effective quantum yields Y(II) and Y(I). Additionally, increased fluctuation frequency exacerbated the consumption of the plastoquinone pool and linear electron flow but enhanced the cyclic electron flow across the thylakoid membrane and, thus, increased heat dissipation in PSII. Our findings indicate that an increased fluctuation frequency inflicted more severe damage on the soybean photosynthesis system. However, PSI-enhanced CEF improved NPQ and coordinated photoprotection to some extent.

Hypothalamic Neuromodulation and Control of the Dermal Surface Temperature of Livestock during Hyperthermia.

Hyperthermia elicits several physiological and behavioral responses in livestock to restore thermal neutrality. Among these responses, vasodilation and sweating help to reduce core body temperature by increasing heat dissipation by radiation and evaporation. Thermoregulatory behaviors such as increasing standing time, reducing feed intake, shade-seeking, and limiting locomotor activity also increase heat loss. These mechanisms are elicited by the connection between peripheral thermoreceptors and cerebral centers, such as the preoptic area of the hypothalamus. Considering the importance of this thermoregulatory pathway, this review aims to discuss the hypothalamic control of hyperthermia in livestock, including the main physiological and behavioral changes that animals adopt to maintain their thermal stability.

Analyzing Tribological and Mechanical Properties of Polymer Nanocomposite for Brake Pad Applications - A Critical Review

A brake pad is an integral component of a vehicle's braking system, designed to impart controlled friction and, ultimately, assist in slowing or stopping a vehicle. Their constituents include binder, filler, abrasive, lubricant, and reinforcing fiber. Materials for brake pads must have excellent wear resistance, increased heat dissipation, a consistent coefficient of friction, low noise and vibration, durability, compatibility, minimal environmental impact, and cost-effectiveness. This paper aims to examine the various materials used in brake pad applications. They are composed of matrix, ceramic, and polymer composites, and are manufactured using various processes. In addition to mechanical and tribological testing, there are various methods for testing the mechanical and tribological properties of brake pads. Various instruments, such as SEM, TEM, AFM, and XRD, were surveyed in order to analyse the morphology and crystal structure of nanoscale brake pads. Various applications such as automobiles, railroads, and aerospace utilise brake pads. The study reveals that integrating nano-fillers into polymer composites significantly enhances the mechanical and tribological properties of automotive brake pads, offering a promising route toward more durable, efficient, and safer braking systems. Through this analysis, researchers will gain a deeper understanding of the materials used in brake pads and their adaptability for various applications.

Three-dimensional simulation and artificial neural network optimization of a flat plate heat pipe for the cooling of telecommunication equipment

To address the significantly increased heat dissipation requirements of 5G base stations, a flat plate heat pipe (FPHP) of 500 × 200 × 3 mm3 comprising of 19 independent channels was developed. To solve the problem of simulation distortion due to the high superheat of the initial boiling of the working fluid in the ultra-long channel of 490 × 5 × 1.5 mm3, this paper adopts the Lee model considering the superheat, and simulates based on the Volume of fluid method, and the simulation results are compared with the experiments, and the average relative error is less than 5 %. The FPHP was explored at 100–500 W heat power and filling ratio of 30 %-70 %, depending on the application scenarios of the base station. By partitioning the 19 channels and calculating the thermal resistance of the FPHP based, an Artificial neural network (ANN) model with 10 hidden layer nodes is established based on 675 data sets. The results showed that the mean square error and correlation coefficient were 1.30 × 10-5 and 0.9990. The ANN prediction results are validated, the mean relative error is 5.4 %, demonstrating that the ANN model can be an effective tool to optimize the FPHP for the telecommunication equipment.

Boiling heat transfer enhancement by a pair of elastic plates

Boiling heat transfer enhancement is essential for energy utilization. Traditional passive boiling enhancement methods aiming at bubble departure promotion usually depend on the modulation of surface tension force by surface modification. However, the limited driven force which benefits bubble departure cannot help the further improvement of heat transfer performance facing the increased heat dissipation amounts. In this paper, a novel boiling enhancement method using a pair of elastic plates (i.e., flexible parallel plates made of stainless steel) which promotes bubble departure by its swing effect for boiling on Pt wire in confined space is proposed and investigated. Compared to boiling with a pair of rigid plates (the thickness of 0.5 mm and the length of 12 mm), the heat transfer coefficient (HTC) is improved by 55.8% of those with elastic plates (the thickness of 0.01 mm and the length of 12 mm).Periodic expansion and recovery process of plates coupling bubble dynamics is observed and studied. Experimental results indicate that elastic plates enhance boiling heat transfer performance significantly by smaller bubble departure diameter and lower wall superheat at the same wall heat flux. A correlation for bubble departure diameter prediction in elastic channel is proposed which matches well with experimental results. It is found that the stronger pumping effect induced by higher swing rate of plates enhance HTC significantly. The mechanism where expansion process of plates promotes bubble departure while its subsequent recovery process benefits the supply of the cold liquid is verified by simulation. This study proposes a new approach for boiling heat transfer enhancement by inducing the energy exchange between bubbles and elastic plates, and provides theoretical and technical support for boiling study based on flexible materials.

Design Procedure of Cascaded Multilevel Inverter for High-Power Amplifier in SONAR System

In recent years, there has been a trend toward expanding the operating frequency range and increasing the output power of Sound Navigation and Ranging (SONAR) systems to enhance their acoustic detection capabilities. However, due to this increase in operational power, the electrical capacity of amplifiers for SONAR system operation also increases, necessitating High-Power Amplifiers. When configured with a single amplifier, as in conventional methods, the volume of amplifiers increases due to volumetric increases in heat dissipation, components, and windings. These issues are detrimental to SONAR amplifier installation, mobility, maintenance, and equipment lifespan due to stress on individual components. Additionally, amplifiers for SONAR systems are comprised of power conversion devices, transformers for LC filters and matching, necessitating consideration of LC filters and matching transformers for enhancing voltage quality and efficiency to improve amplifier performance transmitted to SONAR transducers. However, previous research has focused on single-amplifier design methods, neglecting such considerations. Therefore, this paper proposes a design technique that overcomes the drawbacks of using the conventional design method by configuring multiple H-bridge inverters in a cascade format and utilizes one of the optimization algorithms, Particle Swarm Optimization (PSO), to derive amplifier design techniques that optimize component parameters for enhancing high-capacity amplifier performance. Subsequently, theoretical analysis, simulations, and experimental results comparing the proposed high-power amplifier design method with conventional single-amplifier design methods demonstrate similar error rates in operational frequency bands.

Analysis of Thermal Management Strategies for 21700 Lithium-Ion Batteries Incorporating Phase Change Materials and Porous Copper Foam with Different Battery Orientations

The significant amount of heat generated during the discharge process of a lithium-ion battery can lead to battery overheat, potential damage, and even fire hazards. The optimal operating temperature of a battery ranges from 25 °C to 45 °C. Hence, battery thermal management cooling techniques are crucial for controlling battery temperature. In this work, the cooling of 21700 lithium-ion batteries during their discharging processes using phase-change materials (PCMs) and porous pure copper foams were simulated. The effects of discharge intensities, battery orientations, and battery arrangements were investigated by observing the changes in temperature distributions. Based on current simulations for a 2C discharge, air-cooled vertical batteries arranged in unidirectional configuration exhibit an increase in heat dissipation by 44% in comparison to the horizontal batteries. This leads to a decrease in the maximum battery temperature by about 10 °C. The use of either PCMs or copper foams can effectively cool the batteries. Regardless of the battery orientation, the maximum battery temperature during a 2C discharge drops dramatically from approximately 90 °C when air-cooled to roughly 40 °C when the air is replaced by PCM cooling or when inserted with a copper foam of 0.9 porosity. If the PCM/copper foam approach is implemented, this maximum temperature further decreases to slightly above 30 °C. Although not very significant, it has been discovered that crossover arrangement slightly reduces the maximum temperature by no more than 1 °C. When a pure copper foam with a porosity ranging from 0.90 to 0.97 is saturated with a PCM, the excellent thermal conductivity of pure copper, combined with the PCM latent heat absorption, can best help maintain the battery pack within its range of optimal operating temperatures. If the porosity of the copper foam decreases from 0.95 to 0.5, the volumetric average temperature of the batteries may increase from 30 °C to 31 °C.

A comprehensive investigation of thermal management strategies in dissimilar micro-friction stir welding (dissimilar µFSW): Insights from numerical simulation and experimental observations

The increased heat dissipation rate from thin sheets and differences in material properties lead to difficulties in controlling the heat input in dissimilar micro-friction stir welding (dissimilar µFSW). As a result, improper material mixing and defect formation significantly increase, which deteriorates weld performance and escalates its rejection rate. This issue of thermal mismanagement is mitigated in the present work by utilizing suitable material positioning and tool offset strategies during the dissimilar µFSW of 0.5 mm thick AA 2024-T3 and AA 6061-T6. To date, post-weld analysis was predominantly utilized to derive the physics for explaining these strategies in dissimilar µFSW. However, for proper utilization of these strategies, it is important to comprehend the underlying process physics by investigating the parameters that evolved during the process, such as temperature distribution, material flow velocity, and material intermixing. The literature currently available lacks a systematic investigation in this direction. For this purpose, a 3-D thermo-mechanical model based on coupled Eulerian-Lagrangian formulation was employed in this study. The numerical results showed that an optimal temperature difference between the advancing and retreating sides facilitates achieving a higher degree of velocity symmetry with a uniform higher magnitude of velocity vectors. Importantly, this degree of velocity symmetry showed a good agreement with experimentally determined weld characteristics, namely macro and microstructures, and mechanical performance. By appropriate thermal management, a joint efficiency of 77.3 % (weld strength = 243.58 MPa) was obtained upon tensile loading, and the weld fractured from the heat-affected zone of the AA 6061-T6 side, exhibiting characteristics of ductile failure.

Optimization of Exergy Efficiency in a Walking Beam Reheating Furnace Based on Numerical Simulation and Entropy Generation Analysis

An analysis of entropy generation and exergy efficiency can effectively explore the energy-saving potential of reheating furnaces. This paper simulated the combustion, flow, and heat transfer in a walking beam reheating furnace by establishing a half-furnace model. The entropy generation rate distribution of different thermal processes was numerically calculated. The effect of slab residence time and fuel distribution in the furnace was studied to optimize exergy efficiency. The results indicated that combustion and radiative heat transfer are the primary sources of entropy generation. Irreversible losses accounted for 26.39% of the total input exergy, in which the combustion process accounted for 16.43%, and radiative heat transfer accounted for 8.47%. Reducing the residence time by 60 min decreased irreversible exergy loss by about 2.5% but increased heat dissipation and exhaust exergy loss by 5.8%. Energy saving can only be achieved when the heat exchanger’s exergy recovery efficiency exceeds 36% under different fuel supplies. Keeping the total fuel supply unchanged, increasing the fuel mass flow rate in heating-I zone while decreasing it in heating-II zone resulted in a 1.5% decrease in exergy efficiency. This study provides new insights into the energy-saving potential of reheating furnaces.

Limits to sustained energy intake. XXXIV. Can the heat dissipation limit (HDL) theory explain reproductive aging?

According to the heat dissipation limit (HDL) theory, reproductive performance is limited by the capacity to dissipate excess heat. We tested the novel hypotheses that (1) the age-related decline in reproductive performance is due to an age-related decrease of heat dissipation capacity and (2) the limiting mechanism is more severe in animals with high metabolic rates. We used bank voles (Myodes glareolus) from lines selected for high swim-induced aerobic metabolic rate, which have also increased basal metabolic rate, and unselected control lines. Adult females from three age classes - young (4 months), middle-aged (9 months) and old (16 months) - were maintained at room temperature (20°C), and half of the lactating females were shaved to increase heat dissipation capacity. Old females from both selection lines had a decreased litter size, mass and growth rate. The peak-lactation average daily metabolic rate was higher in shaved than in unshaved mothers, and this difference was more profound among old than young and middle-aged voles (P=0.02). In females with large litters, milk production tended to be higher in shaved (least squares mean, LSM±s.e.: 73.0±4.74 kJ day-1) than in unshaved voles (61.8±4.78 kJ day-1; P=0.05), but there was no significan"t effect of fur removal on the growth rate [4.47±2.29 g (4 days-1); P=0.45]. The results provide mixed support of the HDL theory and no support for the hypotheses linking the differences in reproductive aging with either a deterioration in thermoregulatory capability or genetically based differences in metabolic rate.

Performance analysis of single cylinder engines with enhanced heat dissipation fins using computational fluid dynamics

Engine cooling plays a major role in engine performance. The expanded surfaces that aids to dissipate the engine’s heat are called fins, but their length is limited, which constrains the heat dissipation rate. The automotive industry as a whole works to increase the rate of heat dissipation so that engine efficiency may be increased. Current work aims to increase heat dissipation rate through these extended surfaces by varying the shape of the fins. Here, four different fins are considered, namely circular fins, rectangular fins, aerodynamic fins and curved fins for the analysis. Firstly, finite volume method (FVM) analysis was carried to obtain convective heat transfer coefficient “h” value for each fin shape in FLUENT software. These “h” values are imported for FEA thermal analysis and the result of temperature distribution across the engine cylinder fins and heat flux values at three different vehicle speeds are examined. The heat dissipation rates were observed low for circular fins at all speeds.