Hasil untuk "Heat"

S. Perkins, L. Alexander

Jae‐Hyun Lee, Jung-tak Jang, Jin-sil Choi et al.

A. Grigor’yan

C. Christov

S. Kotak, J. Larkindale, Ung Lee et al.

H. Pollack, S. Hurter, Jeffrey R. Johnson

H. Taha

Xuezhi Liu, Jianzhong Wu, Nicholas Jenkins et al.

Energy supply systems are usually considered as individual sub-systems with separate energy vectors. However, the use of Combined Heat and Power (CHP) units, heat pumps and electric boilers creates linkages between electricity and heat networks. Two combined analysis methods were developed to investigate the performance of electricity and heat networks as an integrated whole. These two methods were the decomposed and integrated electrical-hydraulic-thermal calculation techniques in the forms of power flow and simple optimal dispatch. Both methods were based on models of the electrical network, hydraulic and thermal circuits, and the coupling components, focusing on CHP units and circulation pumps. A case study of Barry Island electricity and district heating networks was conducted, showing how both electrical and heat demand in a self-sufficient system (no interconnection with external systems) were met using CHP units. The comparison showed that the integrated method requires less iteration than the decomposed method.

Subhalaxmi Dey, Surender Ontela, P.K. Pattnaik et al.

In recent trends science and technology is developed due to the utilization of modern devices of high quality and their longevity with potential efficiency. The implementation of nanoparticles now characterizes the effectiveness and efficiency. Specifically, in biomedical research drug delivery into the target, hyperthermia treatment for cancer, etc. the use of nanofluid is vital. The present article brings the characteristic of the blood-based tri-hybrid nanofluid through a porous channel embedding within a porous matrix with the interaction of magnetization and Darcy-Forchheimer inertial drag in the flow behavior. Further, the inclusion of thermal radiation, and heat source energies the heat transport properties. The formulated model for the interaction of alloy nanoparticles AA7072 and AA7075 with Zirconium oxide ZrO2 in the base liquid blood is characterized by their physical properties. The designed model is transformed into a non-dimensional form with the utilization of similarity rules. Further, a semi-analytical approach Adomian Decomposition Method (ADM) is proposed for the solution of the model. The validation with the existing article shows the convergence properties of the current methodology and the significant behavior of the factors involved in the flow phenomena are presented through graphs. Finally, the important findings are reported as; The enhanced Reynolds number decelerates the inertia force and a velocity profile shows a dual characteristic for the increasing deformation factor. Further, in comparison to the single and hybrid nanofluid, the tri-hybrid nanofluid encourages the fluid temperature due to the increasing thermal conductivity.

Yuto Takada, Hiroshi Doi, Yuko Kinoshita et al.

A case of a patient who developed a radiation recall reaction (RRR) triggered by coronavirus disease 2019 (COVID-19) infection following surgery and chemoradiotherapy for carcinoma of the buccal mucosa is reported. A 75-year-old woman presented in October 2023 with pyrexia and erythema extending from the left cheek to the anterior chest area. In December 2021, she had undergone surgery to remove a carcinoma of the left buccal mucosa (pT2N0M0), followed by left comprehensive neck dissection for delayed cervical lymph node metastasis in June 2022, with subsequent adjuvant chemoradiotherapy. Her course was uneventful until September 2023, when she developed COVID-19. Twenty-three days after COVID-19 infection had been confirmed, she developed systemic pyrexia with erythema and a heat sensation from her left cheek to the left anterior chest. On presentation, her temperature was 39 ºC, and she had a mild sore throat. Erythema and a heat sensation were apparent from the left cheek to the neck and anterior chest, corresponding to the previously irradiated area. Laboratory tests showed a white blood cell count of 11,760/μl, and C-reactive protein of 16.0 mg/dl. Computed tomography did not show any obvious abscess formation or infection source. An RRR was diagnosed, and she was admitted for treatment with intravenous sulbactam/ampicillin and intravenous hydrocortisone sodium succinate. Five days after admission, the inflammatory reaction had improved, and she was discharged. Her subsequent course has been uneventful, with no flareup of the RRR. This case is presented along with a review of relevant literature.

Majkić Mira, Spasojević Jovan, Nikolić Sandra et al.

Heat stress has a significant impact on the health and productivity of dairy cows, making early and accurate detection essential for effective welfare management. The aim of this study was to determine cut-off values of body surface temperature across different anatomical regions, measured by infrared thermography (IRT), to distinguish cows under heat stress from those in thermoneutral conditions. The research was conducted on a Holstein-Friesian farm in the Vojvodina region, with 200 total measurements collected during spring and summer. The identified cut-off values were as follows: 36.06 °C for the eye, 32.2 °C for the ear, 33.6 °C for the nose, 37.3 °C for the forehead, 35.8 °C for the whole head, 35.1 °C for the abdomen, 36.6 °C for the udder, 32.3 °C for the front limb, 33.5 °C for the hind limb, and 35.95 °C for the whole body. All values demonstrated satisfactory to high discriminative power (AUC = 0.71-0.95) for identifying cows under heat stress. These thresholds enable early identification of thermal load and timely interventions. Although body surface temperature is a sensitive and non-invasive indicator, its application requires contextual interpretation and integration with other physiological parameters. The results support the development of automated systems for continuous monitoring and prevention of heat stress, contributing to more sustainable dairy farming practices under changing climatic conditions.

Lihui ZHANG, Shuo XIE, Mingfa LUO et al.

Objectives: Bone tissue grinding is one of the common and basic applications in orthopedic surgery clinics. The grinding process is energy-intensive and generates a lot of grinding heat. The accumulation of this heat may cause thermal damage to biological tissues. This paper presents experimental research to investigate the bone-grinding heat and the cooling method. Methods: The combined influence of nozzle position and feed direction on the cooling effect of bone grinding under cryogenic spray cooling conditions is experimentally investigated. A bone grinding platform with three-dimensional motion, as well as a cryogenic spray generation device, is designed and constructed. A spherical diamond grinding head with a diameter of 4 mm and a grit size of #150 is utilized. Fresh bovine cortical bone is used as the processing sample. The temperature at the nozzle outlet is 13 ℃, and the flow rate valve regulates the coolant flow rate to 400 mL/h. A three-dimensional force transducer (DJSW-40, China) is connected to a data acquisition system, which captures the forces applied to the bone sample along the X, Y, and Z directions at a frequency of 100 Hz. Simultaneously, a 0.1 mm diameter type K thermocouple (Omega Inc., TT-K-36) is embedded inside the bone sample to measure the grinding temperature in real-time. Three different nozzle arrangements were designed: above, in front of, and to the side of the abrasive tool, with the nozzles 10 mm away from the spray surface. Six sets of experiments (3×2) were designed using three nozzle orientations and two feeding directions. Each set of experiments was repeated three times to study the cooling effect of the spray under the combined influence of nozzle orientation and feed direction. Results: (1) During bone grinding, the abrasive tool is subjected to three orthogonal directional forces, namely FX (the tangential grinding force used for removing material), FY (the axial grinding force, representing the resistance of the abrasive tool during its feed), and FZ (the normal grinding force, which serves as the support force of the workpiece on the abrasive tool). For forward feed, the average values of the individual forces are: FX = 0.37 N, FY = -0.72 N, FZ = 1.38 N. For backward feed, FX = 0.46 N, FY = 0.78 N, FZ = 1.67 N. Since the grinding tool remains in the same rotational direction, the tangential force FX is consistently positive. For forward/backward feed, the axial force FY is in the -Y and +Y directions respectively, thus the sign of the FY value changes. When feeding forward/backward, the tangential force (FX) is 0.37 N and 0.46 N, respectively, which are relatively similar to each other, in accordance with the grinding theory. The power consumed for grinding is approximately 1.6 W and 1.9 W for forward and backward feed, respectively. (2) The nerve tissue is more heat-sensitive than bone tissue. Taking the human body's 37 ℃ as the base temperature, the threshold for the occurrence of thermal injury is 43 ℃, so the temperature rise threshold for thermal injury of nerve tissue is 6 ℃. In our experiment, the maximum temperature rise of bone under low-temperature spray cooling was lower than 4 ℃, indicating that the cooling method is effective. The effect of the nozzle arrangement was investigated under a fixed forward or backward feeding direction. When the abrasive tool is fed forward, the cooling of the thermocouple under the front nozzle is obvious. This is because, in addition to the contact arc area between the abrasive tool and the bone sample, a portion of the coolant from the front nozzle is sprayed onto the bone sample surface, resulting in a pre-cooling effect within the bone. When the abrasive tool is fed backward, the grinding temperature is lowest when the nozzle is placed above. For the different nozzle orientations, the side nozzles are in a perpendicular plane to the feed direction (Y-direction) of the grinding tool, so the feed direction has the least influence on the grinding temperature. The upper and front nozzles are in the same plane as the feed direction of the abrasive tool, so the influence of the feed direction is more significant. Conclusions: (1) The average tangential grinding force is 0.42 N, axial grinding force is 0.75 N, normal grinding force is 1.53 N, and the average power consumed by grinding is approximately 1.75 W when bone grinding is performed at a depth of 0.5 mm using a spherical diamond abrasive tool with a diameter of 4 mm. (2) Under the cooling effect of the cryogenic spray, the maximum temperature rise of grinding is less than 4 ℃, which can effectively prevent the occurrence of thermal damage in biological tissues. The temperatures of the two thermocouples in the same set of experiments were more consistent when the nozzle was placed above or side, while there was a significant difference in the temperatures of the two thermocouples when the nozzle was placed in front. This indicates that the cooling effect is more uniform when the nozzle is placed above and to the side. (3) The coupling of the nozzle arrangement and the feeding mode has a greater impact on the grinding temperature. When the nozzle is placed on top, it is favorable to backward feeding; when the nozzle is placed in front, it is conducive to forward feeding; and when the nozzle is placed on the side, there is no significant difference in the temperature between forward and backward feeding.

Maha Rahman Rahi, Saba Ostadi, Amin Rahmani et al.

This study delves into the integration of phase change materials (PCM) in solar thermal collector systems to address this challenge. By incorporating nano encapsulated PCMs, researchers have mitigated concerns surrounding PCM leakage, revolutionizing the potential of solar collector systems to elevate energy efficiency, diminish carbon emissions, and yield manifold benefits. This article comprehensively investigates the design and utilization of solar phase change energy storage devices and examines the transformative impact of employing nano-coated phase change materials (Nano capsules) to augment solar collector performance. The integration of paraffin-based PCM and the insulation of the collector system have been crucial in optimizing heat retention and operational efficacy. The composition of the PCM involves a balanced blend of octadecane phase-change particles and water as the base fluid, designed to maximize thermal performance. Analysis of the experimental findings demonstrates the dynamic thermal behavior of the nano encapsulated phase change material, revealing distinctive temperature profiles about fluid dynamics and absorbent characteristics. Notably, the study emphasizes the nuanced trade-offs associated with the conductivity and melting temperature of the Nano encapsulated PCM, yielding valuable insights into energy storage capacity limitations and thermal performance variations throughout diurnal cycles. Central to the investigation, the optimal nanoparticle proportion is elucidated, shedding light on its pivotal role in modulating PCM performance. Furthermore, findings underscore the complex interplay between nanoparticle volume fraction and thermal fluid temperature, providing critical perspectives on optimizing PCM-enhanced solar collector systems.

M.M.E. Barakat, T.A. Abdel-Baset, M. Belhaj et al.

In the phase diagram of iron pnictides, superconductivity arises at the border of antiferromagnetism, which raises the question of the role of symmetry of the gap and quantum criticality. Although more than 15-years of extensive research, the microscopic origin of the pairing symmetry inside the superconducting (SC) dome and its link to quantum criticality still remains elusive. Here, we report two new findings on BaFe2−xNixAs2: (1) A sharp peak in the x-dependence of the lower and upper critical fields, the SC critical current density Jc, the size of the jump in the specific heat ΔCel/T and the Sommerfeld coefficient (γ) at the optimum composition x = 0.10, where the SC transition temperature Tc reaches a maximum. Our obtained reliable values as a function of doping of the normal-state Sommerfeld coefficient increase with doping, illustrating the strong competition between magnetism and superconductivity and attributed to closing of spin density wave gap with Ni doping. (2) We show that doping induced a sudden change of the gap structure from nodeless to nodal. Our results imply that the superconductivity in BaFe2−xNixAs2 is closely linked to the quantum criticality and is characterized by a complex order parameter.

Sameh Alsaqoor, Ahmad Alqatamin, Ali Alahmer et al.

This study examines the impact of incorporating phase change material (PCM) in photovoltaic thermal (PVT) systems on their electrical and thermal performance. Although PVT systems have shown effectiveness in converting solar energy into both electricity and heat, there is a necessity for studies to investigate how integrating PCMs can further enhance performance. The study also aims to explore the effect of solar irradiation and coolant mass flow rate on the electrical and thermal output of both PVT and PVT-PCM systems. A graphical user interface was developed within the MATLAB Simulink under the weather conditions of Amman, Jordan. The results show that the incorporation of PCM in PVT systems significantly reduces solar cell temperature and increases electrical efficiency. The highest electrical efficiency of a PVT system with PCM was found to be 14%, compared to 13.75% in a PVT system without PCM. Furthermore, the maximum achievable electrical power in a PVT system with PCM was 21 kW, while in the PVT system without PCM it was 18 kW. The study also found that increasing the coolant mass flow rate in a PVT system with PCM further reduced PV cell temperature and increased electrical efficiency, while the electrical efficiency of both the PVT and PVT-PCM systems decreases as solar incident radiation flux increases, resulting in a significant rise in cell temperature. At an increased solar radiation level from 500 W/m2 to 1000 W/m2, the electrical efficiency of the PVT configuration decreases from 13.75% to 11.1%, while the electrical efficiency of the PVT-PCM configuration falls from 14% to 12%. The findings of this study indicate that the use of PCM in PVT systems can lead to significant improvements in energy production and cooling processes. The results provide valuable information for designing and optimizing PVT-PCM systems.

Kevin P. Drummond, Doosan Back, M. Sinanis et al.

Abstract A hierarchical manifold microchannel heat sink array is fabricated and experimentally characterized for uniform heat flux dissipation over a footprint area of 5 mm × 5 mm. A 3 × 3 array of heat sinks is fabricated into the silicon substrate containing the heaters for direct intrachip cooling, eliminating the thermal resistances typically associated with the attachment of a separate heat sink. The heat sinks are fed in parallel using a hierarchical manifold distributor that delivers flow to each of the heat sinks. Each heat sink contains a bank of high-aspect-ratio microchannels; five different channel geometries with nominal widths of 15 μm and 33 μm and nominal depths between 150 μm and 470 μm are tested. The thermal and hydraulic performance of each heat sink array geometry is evaluated using HFE-7100 as the working fluid, for mass fluxes ranging from 600 kg/m2 s to 2100 kg/m2 s at a constant inlet temperature of 59 °C. To simulate heat generation from electronics devices, a uniform background heat flux is generated with thin-film serpentine heaters fabricated on the silicon substrate opposite the channels; temperature sensors placed across the substrate provide spatially resolved surface temperature measurements. Experiments are also conducted with simultaneous background and hotspot heat generation; the hotspot heat flux is produced by a discrete 200 μm × 200 μm hotspot heater. Heat fluxes up to 1020 W/cm2 are dissipated under uniform heating conditions at chip temperatures less than 69 °C above the fluid inlet and at pressure drops less than 120 kPa. Heat sinks with wider channels yield higher wetted-area heat transfer coefficients, but not necessarily the lowest thermal resistance; for a fixed channel depth, samples with narrower channels have increased total wetted areas owing to the smaller fin pitches. During simultaneous background and hotspot heating conditions, background heat fluxes up to 900 W/cm2 and hotspot fluxes up to 2700 W/cm2 are dissipated. The hotspot temperature increases linearly with hotspot heat flux; at hotspot heat fluxes of 2700 W/cm2, the hotspot experiences a temperature rise of 16 °C above the average chip temperature.

T. Ambreen, Man-Hoe Kim

Abstract The study presents the combined effects of using nanofluid and varying fin cross-sectional shape on the heat transfer characteristics of a micro pin-fin heat sink by employing discrete phase model (DPM). Three fins configurations of the square, circular and hexagon cross-section with constant fin diameter and height have been analyzed for the inline arrangement of 17 × 34 fins. Aqueous nanofluid containing spherical shaped particle dispersions of TiO 2 has been simulated for the particle concentration and size of 4.31 vol% and 30 nm respectively. Constant heat flux (192 W) boundary condition at the base of heat sink has been considered for the range of Reynolds number 250 ≤ Re ≤ 550. The influence of fin shape on the thermal efficiency of the heat sink has been analyzed by evaluating heat sink base temperature, Nusselt number, convective heat transfer coefficient distribution and temperature contours along the surface of the heat sink. Additionally the velocity streamlines and contours have also displayed to elaborate the fluid flow attributes. Results demonstrate that under identical flow conditions, the nanofluid cooled circular fins displayed most efficient thermal performance followed by the hexagon and square fins. While the water cooled square fins depicted lowest heat transfers characteristics. The best thermal performance of the circular fins is the response of the delayed flow separation along the smooth surface of fins and the subsequent uniform flow distribution along the whole sink. For all the cases, upstream fin rows played a primary contribution in flow distribution and hence thermal characteristics of the heat sink.

M. Pizzarelli

Abstract Nowadays, both experimental and computational research on the turbulent convective heat transfer to supercritical fluids is particularly active, especially because the actual poor comprehension and prediction of the possible heat transfer deterioration is limiting the design of new promising engineering applications. In this review, such applications, among which supercritical water-cooled nuclear reactors, supercritical CO2 power generation cycles, and oxygen/methane-fuel rocket engines, are firstly introduced. Then, after a phenomenological description of the heat transfer deterioration, the status of the research is analysed in details, highlighting the major advantages and limitations of both experimental and computational studies performed so far. The review demonstrates that experimental research is mostly focused on finding simple heat transfer correlations rather than detailed models. Also detailed numerical insight of the problem is still almost unexplored. The main conclusion is that new approaches, possibly integrating extensive experiments and computations, are needed to shed new light on the problem of heat transfer to supercritical fluids.

Qinlong Ren, F. Meng, Penghua Guo

Abstract Latent heat thermal energy storage (LHTES) has attracted lots of attention due to its nearly constant working temperature and large thermal energy storage density. However, the thermal conductivity of phase change materials (PCMs) is usually low which impedes the heat transfer efficiency in the LHTES system. Adding high thermal conductivity nanoparticles or metal foams are the two common approaches to enhance the thermal performance of the PCMs. In the current work, the PCM melting performance in a heat pipe-assisted LHTES unit enhanced by nanoparticle-metal foam combination is numerically investigated by immersed boundary-lattice Boltzmann method (IB-LBM) at pore scale. The microstructure of metal foam is reconstructed using the quartet structure generation set (QSGS). The PCM melting performance in LHTES is studied in terms of porosity and pore size of metal foams, volume fraction of nanoparticles, and radius of heat pipe. A comparative study is carried out to illustrate the effectiveness of enhancing PCM melting performance with different combinations of nanoparticles and metal foams. The results indicate that there exist the optimum metal foam porosity and heat pipe radius for the energy storage efficiency in the LHTES unit. Besides, it is found that using metal foams is more effective than adding nanoparticles for the improvement of PCM heat transfer capability.

Yuji YAHAGI

Vortex structures behind two highly heated cylinders of equal diameter in tandem arrangements have been investigated experimentally. The experiments were performed under the following conditions: cylinders diameter, D = 4 mm; mean flow velocity of air, U∞ = 1.0 m/s; Reynolds number, Re = 250; cylinders spacing ratio, S/D = 1.0~10.0; and cylinder heat flux, q = 0~72.6 kW/m2. Two distinct flow structures are formed in the region of the cylinder clearance which depends on the S/D and the cylinder surface temperature, Tw. One is a quasi-stationary twin vortex at the small S/D condition (S/D<3.0~5.0) and the other is a shedding Karman vortex for large S/D condition (S/D>3.0~5.0). Behind the downstream cylinder, the Karman vortex street is formed in all conditions. The critical S/D changing to the Karman vortex increases with increasing the temperature of the upstream cylinder. The Strouhal number St under the twin vortex forming is in the range of 0.150 to 0.155 regardless of the S/D and heating conditions, while the St of the Karman vortex formed behind the downstream cylinder is decreased significantly as the S/D increases. For the large S/D, the Karman vortex is formed behind both of the cylinders then the upstream St agreed with the downstream St. St of the Karman vortex coincides with St in the single-cylinder condition taken into account of the cylinder heating conditions. For the small S/D and the upstream cylinder in a highly heated condition, the twin vortex structure behind the upstream cylinder plays a key role in the downstream shedding Karman vortex structure.