Values Of Temperature Difference Research Articles

Rapid tooling: investigation of soft-tooled micro-injection moulding process characteristics using in-line measurements and surface metrology

PurposeThe purpose of this study is to demonstrate and characterise a soft-tooled micro-injection moulding process through in-line measurements and surface metrology using a data-intensive approach.Design/methodology/approachA soft tool for a demonstrator product that mimics the main features of miniature components in medical devices and microsystem components has been designed and fabricated using material jetting technique. The soft tool was then integrated into a mould assembly on the micro-injection moulding machine, and mouldings were made. Sensor and data acquisition devices including thermal imaging and injection pressure sensing have been set up to collect data for each of the prototypes. Off-line dimensional characterisation of the parts and the soft tool have also been carried out to quantify the prototype quality and dimensional changes on the soft tool after the manufacturing cycles.FindingsThe data collection and analysis methods presented here enable the evaluation of the quality of the moulded parts in real-time from in-line measurements. Importantly, it is demonstrated that soft-tool surface temperature difference values can be used as reliable indicators for moulding quality. Reduction in the total volume of the soft-tool moulding cavity was detected and quantified up to 100 cycles. Data collected from in-line monitoring was also used for filling assessment of the soft-tool moulding cavity, providing about 90% accuracy in filling prediction with relatively modest sensors and monitoring technologies.Originality/valueThis work presents a data-intensive approach for the characterisation of soft-tooled micro-injection moulding processes for the first time. The overall results of this study show that the product-focussed data-rich approach presented here proved to be an essential and useful way of exploiting additive manufacturing technologies for soft-tooled rapid prototyping and new product introduction.

The Temperature Field Effect on Dynamic Stability Response of Three-layered Annular Plates for Different Ratios of Imperfection

Abstract The paper presents the temperature field effect on the dynamic stability problem of plates with imperfection. The main objective is to conduct numerical investigations which show the relations between the imperfection ratio and plate dynamic response in a thermal environment. The plate is composed of three layers: thin facings and a thicker core. The plate can be loaded mechanically and thermally or only thermally. The facings are mechanically compressed with the forces acting in a plane. The temperature field model is defined by the temperature difference, which occurs between the plate edges. Two plate models are examined as follows: built using the approximation methods – orthogonalization and finite differences – and composed of finite elements. The analytical and numerical solution procedure is the main one, which is the proposal to perform the problem analysis. The plate reaction is described by the obtained values of the critical temperature differences for plates loaded only thermally and by the critical mechanical loads and the corresponding temperature differences for plates loaded mechanically and subjected to the uncoupled temperature field. The effect of the plate imperfection ratio under time-dependent loads is shown by numerous observations and results, which are shown graphically. The importance of the imperfection ratio on the plate's dynamic stability response in complex loading conditions is studied.

Shape and size design, preparation and test evaluation of color unit in visible light and infrared camouflage

This study presents a novel method for designing and preparing a visible light-infrared-compatible camouflage sample based on the shape, size of the visible band’s color unit and the infrared band’s material coatings. The coatings were prepared by using the cold spray method on 1 m × 1 m aluminum substrates with a color unit of the regular hexagonal sample (M1) and regular quadrilateral sample (M2). Then the color difference, the temperature difference and image salience value methods were used to analyze the effectiveness of camouflage samples through the real-scene tests. The results indicate that designed and prepared compatible camouflage samples are effective in their surrounding environment. Meanwhile, it can be concluded that M1 has high fusion with a background in visible and infrared bands compared to M2, M1 has 90.6% color similarity and only 0.8% temperature difference, the M2 has 85.4% color similarity and 1.6% temperature difference with the green background. These findings indicate that the cold spray method could compensate for conventional visible light camouflage design limitations. The combination of camouflage color unit design and visible/infrared material coating could be helpful in optical camouflage research. Furthermore, to improve the military equipment’s survival time on the battlefield.

Novel approach for the performance augmentation of phase change material integrated battery thermal management system for number of charging/discharging cycles

AbstractWith the development of fast charging unit for electric vehicles (EVs) battery, it is required to develop a battery pack that can maintain the temperature in the desired range. Hence, some thermal management system is required to enhance performance and safety issues. The objective of the present work is to enhance the performance of phase change material (PCM)‐based battery thermal management system (BTMS) for continuous charging/discharging cycles. The cycle is considered as 3C‐1C as charging‐discharging rates. The PCM‐in‐pack BTMS is effective only for one cycle, and after that, the value of maximum battery temperature (Tmax) and maximum battery temperature difference (ΔTmax) reaches above 60°C and 5°C, respectively. The PCM‐around‐cell BTMS (PCM layer around battery cells) is found effective in maintaining ΔTmax below 5°C for three consecutive cycles but found effective in maintaining Tmax below 60°C for the first cycle only. For further improvement, fins are utilized, and found that fin and PCM‐around‐cell BTMS can effectively maintain Tmax below 60°C for two cycles. Even the addition of fins is found effective after the second cycle; therefore, rest time between charging and discharging is explored for further improvement. With a 10‐min rest time, both Tmax and ΔTmax are found under 60°C and 5°C for four consecutive cycles. However, the value of Tmax increases around 4°C to 5°C after each cycle. This problem of increment in Tmax after each cycle is eliminated by 20‐min rest time and found almost similar Tmax for four consecutive cycles. For 20 min of rest time between charging and discharging, Tmax is found with PCM‐around‐cell with fin based BTMS as 44.98°C, 45.98°C, 46.49°C, and 46.82°C during four consecutive cycles. Hence, PCM‐around‐cell arrangement, fins, and rest time of 20 min can provide desirable results for a large number of consecutive cycles.

Thermal performance of a hybrid thermal management system based on the half helical coil coupled with air jet cooling for cylindrical Lithium-ion battery

The Battery Thermal Management System (BTMS) is crucial for the efficient and safe operation of Lithium-ion batteries (LIBs). It is challenging for liquid cooling to apply to areas of battery modules with complex surface forms, such as the positive and negative cell terminals, cell holders, etc. Herein, the thermal management scheme integrated with the half helical coil and air jet impingement is proposed for cylindrical LIBs. Heat is transferred from the LIBs' sides by helical flow and dissipated from the LIBs' ends by air jet impingement. The three-dimensional computational fluid dynamics model of battery modules with cell holders is developed. The thermal performance of the LIBs at various BTMS strategies, the number of turns of the helical coil, airflow inlet velocity, inlet temperature, and contact resistance are investigated. When the impinging air jets are arranged on both ends of the cylindrical form, the maximum values of temperature difference (ΔT) of the LIBs fall from 5.7°C to 4.0°C compared with that of liquid-based BTMS. The arrangement of the half helical duct divided into two separate sections reduces the coolant flow path length, which decreases the maximum temperature (Tmax) and ΔT to 28.9°C and 3.6°C. The proposed BTMS exhibits an enhanced heat dissipation performance and provides a design guideline for developing the hybrid BTMS.

Simulated Trends in Land Surface Sensible Heat Flux on the Tibetan Plateau in Recent Decades

The spatial distribution and temporal variation of land surface sensible heat (SH) flux on the Tibetan Plateau (TP) for the period of 1981–2018 were studied using the simulation results from the Noah-MP land surface model. The simulated SH fluxes were also compared with the simulation results from the SEBS model and the results derived from 80 meteorological stations. It is found that, much larger annual mean SH fluxes occurred on the western and central TP compared with the eastern TP. Meanwhile, the inter-annual variations of SH fluxes on the central and western TP were larger than that on the eastern TP. The SEBS simulation showed much larger inter-annual variations than did the Noah-MP simulation across most of the TP. There was a trend of decrease in SH flux from the mid-1980s to the beginning of the 21st century in the Noah-MP simulations. Both Noah-MP and SEBS showed an increasing SH flux trend after this period of decrease. The increasing trend appeared on the eastern TP later than on the western and central TP. In the Noah-MP simulation, the western and central TP showed larger values of temperature difference between the ground surface and air (Ts–Ta) than did the eastern TP. Both mean Ts–Ta and wind speed decreased from the mid-1980s to approximately 2000, and then increased slightly. However, the Ts–Ta transition occurred later than that of wind speed. Changes in mean ground surface temperature (Ts) were the main cause of the decreasing and increasing trends in SH flux on the TP. Meanwhile, changes in wind speed contributed substantially to the decreasing trend in SH flux before 1998.

Analysis on construction technology of large steel structure building thermal insulation engineering

In order to solve the need of maintaining temperature in large steel structure buildings, the author proposes a method of applying new materials, this method is used to analyze the properties of exterior insulation materials for steel structure buildings. Combining with the need of heat preservation in large steel structure cold storage, the author puts forward a new construction technology and applies it into practice by combining autoclaved gas technology, the advantages and disadvantages of organic and inorganic materials on heat preservation effect are analyzed, through the value engineering formula of maximum efficiency analysis, the minimum life cycle cost, in the ideal place, time to play the necessary function of the product. Finally, the experimental samples adopted the author?s method are compared with the ordinary samples. The experimental results show that the absolute value of indoor and outdoor temperature difference under the construction process is significantly greater than that under the current construction process, the highest temperature reached 29.2? and the lowest was 25.6?. In conclusion, the method adopted by the author can greatly help the current construction technology and reduce the loss of enterprises.

PERFORMANCE SIMULATION ON THE SHELL AND TUBE OF HEAT EXCHANGER BY ASPEN HYSYS V.10

Heat exchanger type shell and tube, which is the most commonly used heat exchanger in various industries. The efficiency of heat exchangers can be seen from their performance to affect its economy from a process. The purpose is to determine the influence of the hot fluid flow rate and the cold fluid on the overall heat transfer coefficient (U) and log mean temperature difference (ΔTLMTD) values. This simulation is done using Aspen HYSYS V.10 applications and obtained data of the total heat transfer coefficient (U) and ΔTLMTD values. The heat exchanger shell and tube used type 1-2 with single segment type 4 baffle, triangular tube layout, and shell length 1000mm. This simulation results in a hot fluid flow rate compared to reverse with the overall heat transfer coefficient and a cold fluid relative to the overall heat transfer coefficient, with the two best fluid flow rates at 2100 kg/h hot fluid and 1800 kg/h cold fluid at 10400 Kj/oC.h. The influence of the hot fluid flow rate on ΔTLMTD is relative to the straight, while the cold fluid flow rate is relative to the reverse, with the value of the second-best fluid flow rate at the 2100 kg/h hot fluid and the 1800 kg/h cold fluid at 26.25oC

Numerical analysis of the thermal-elastic-plastic state of electrical contact gasket made from dispersion-reinforced composite materials using the fusioned deposition modeling method

The article presents the results of a theoretical study on determining the suitability of using electrical contact gaskets (ECG) in industrial conditions (Castner direct graphitization furnaces), made of coke-pitch composite using additive technologies based on the Fused Deposition Modeling (FDM) method.
 Numerical analysis of the physical state of ECG under the conditions of industrial application was performed on the basis of the mathematical statement of the thermo-elastic-plasticity problem and the algorithm of implicit inverse mapping of its solution based on the finite element method in the Mathcad programming environment. To construct the geometry and tetraid mesh of the ECG model, a freely open program code was used - the Gmsh CAD system for grid generation, and for the visualization of the results of physical field calculations, the free open program code ParaView was used.
 The study of the thermo-elastic-plastic state of ECG under the conditions of the graphitization process in Castner furnaces was carried out in the temperature range up to 900 °С, at which the thermoplastic properties of the material are manifested. At the same time, such physical fields of ECG were analyzed as temperature distribution, resulting displacements, equivalent elastic stresses according to Mises, equivalent total, elastic and plastic deformations according to Mises, and the volume fraction of ECG material in a plastic state, depending on the temperature level and radial gradient temperatures (radial temperature difference) of electrical contact gaskets.
 Numerical simulation of the thermo-elastic-plastic state of the ECG was carried out under the conditions of force loading by external pressure on the lateral surface of the gasket of 2.5 MPa and different values ​​of the radial temperature difference in the range of 15–90 °C in the temperature range up to 900 °C. It was established that: at the stages of formation of semi-coke and coke in the material of the coke-pitch composite ECG under the thermomechanical conditions of operation of the Kastner furnace, a margin of strength of not less than unity was obtained; with the subsequent increase in the temperature level in the Castner furnace to 3000 °C and above, the raw material of ECG, as a result of thermal destruction, has already turned into coke and, therefore, its mechanical properties have become close to the mechanical properties of electrode blanks in columns that are subjected to graphitization. This gives reason to assert that the ECGs will not be mechanically destroyed during the entire graphitization campaign of the Castner furnace.
 On the basis of the analysis of the results of numerical simulation, the possibility of using ECGs made from dispersion-reinforced composite materials (coke-pitch mixtures) by the FDM method in the technology of graphitizing electrode products according to the Сastner method is substantiated.

Climate Behaviour and Plant Heat Activity of a Citrus Tunnel Greenhouse: A Computational Fluid Dynamic Study

Response to the expanding demand for high-quality citrus saplings plants requires optimisation and a deep understanding of production climate behaviour. In this context, greenhouse production is the most used technique because it allows farmers to effectively monitor plant growth through production condition control, especially climatic parameters. The current work presents an analysis of climate behaviour and plant heat activity of a citrus sapling tunnel greenhouse in the middle region of Morocco. In this regard, a computational fluid dynamic (CFD) model was developed and validated with respect to temperature and relative humidity measured values. The specificity of this model is the inclusion of a new non-grey radiative and heat transfers physical sub-models to couple the convective and radiative exchanges at the plastic roof cover and crop level. The findings showed that using a green shade net increased the greenhouse shadow, and the layering of plastic and shade net significantly reduced solar radiation inside the greenhouse by 50%. Also, the greenhouse airflow speed was deficient; it cannot exceed 0.3 ms−1, hence the dominance of the chimney effect in heat transfer. Despite the previous results, analyses of greenhouse temperature and relative humidity fields clearly showed the greenhouse climate behaviour heterogeneity, where spatial greenhouse air temperature and relative humidity difference values reached a maximum of 29.7 °C and 23%, respectively. For citrus plants, heat activity results showed that a weak fraction (1.44%) of the short wavelength radiation is converted to latent heat, which explains the low plant transpiration under these conditions. While the convective currents are the primary source of temperature and relative humidity heterogeneity inside the greenhouse, the presence of crop rows tends to homogenise the climate inside the greenhouse. We also concluded the necessity of proper condensation modelling near ground surfaces and inside the crop, and the water vapour effect on climate determination.

CMOS SPAD Imager Array for Wide Radiation Temperature Sensing and Thermal Imaging

We have demonstrated a wide radiation temperature measurement by using a single-photon avalanche diode (SPAD) image array that is analogous to a silicon photomultiplier with a time-gating technique and an adjustable summed output. The detection temperature window ranging from 280 °C to 1050 °C can be achieved with a noise equivalent temperature difference (NETD) value of below 1 °C. The thermal image with a high detection rate up to 1680 Hz is obtained at the same detection temperature as a commercial CMOS thermal camera. We further demonstrate a thermal image with a spatial resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu \text{m}$ </tex-math></inline-formula> .

Comparative Analysis of PID and Fuzzy Temperature Control System on Infant Warmer

Infant Warmer is a life support equipment that is used to provide heat relief for normal and premature babies who are unable to maintain their own body temperature when in a new environment. The purpose of this research is to design an infant warmer using the DS18B20 sensor to analyze the efficiency and effectiveness between PID and fuzzy temperature control. This study used temperature settings of 34 °C, 35 °C, and 36 °C. The tool used for reference from standard measurements uses a standard infant warmer. When using the PID control used in the microcontroller detects the set temperature difference value with the actual temperature, the difference in value will be input to the PID control. The error value becomes PWM input on the PID control, the PID control will process the error value and determine the output value for the heater, the temperature sensor will read the actual temperature value which will be compared again with the temperature setting, the PID control will continue to process the error value and determine the PWM output value. until the actual temperature is equal to the setting temperature or the error value is zero

An infrared thermographic analysis of the sensitization acupoints of women with primary dysmenorrhea.

To explore the sensitization acupoints of women with primary dysmenorrhea (PD) by comparing infrared radiation temperatures between acupoints and non-acupoints. We tested 10 acupoints of every woman with PD and healthy subjects on premenstrual, menstrual, and postmenstrual days using an infrared imaging device. The primary outcome was the absolute value of body surface temperature difference (AVTD) between the left and right sides of the same testing point. A total of 58 PD patients and 57 healthy volunteers completed the test from May 2016 to May 2017. Compared with the healthy group, we observed a significant reduction and increase in the AVTD in Taichong (LR3) and Sanyinjiao (SP6), respectively, during menstrual days in the PD group (= 0.01; = 0.04); while during postmenstrual days, all AVTDs of Shuiquan (KI5), Diji (SP8), and Xuehai (SP10) were diminished in the PD group (= 0.01; = 0.03; = 0.01, respectively). No significant differences in AVTD were detected at any other points or testing times. Compared with the healthy group, the AVTDs of Taichong (LR3), Sanyinjiao (SP6), Shuiquan (KI5), Diji (SP8), and Xuehai (SP10) at menstruation-relevant points of PD patients were sensitized, providing a reference for the selection of acupoints in the treatment of PD.

Thermal performance evaluation of boiling cooling system for the high-rate large-format lithium-ion battery under coolant starvations

The boiling cooling system exhibits superior cooling capacity and temperature homogenization ability, which has great potential in managing the undesirable temperature spike and temperature gradient of the large-format lithium-ion batteries. However, in-depth experimental investigation to reveal the effects of harsh operation conditions and parameters on the cooling characteristics are still lacking. In this study, thermal control ability of the boiling cooling system using Novec 7000 as coolant is evaluated for a large-format 20-Ah lithium-ion battery, with special attentions to the cooling performance under harsh operation conditions such as high-rate cyclic and coolant starvation. The experimental results show that the boiling-cooling system with uninterrupted/small coolant flow exhibits superior cooling capacity and the battery temperature can be controlled around 35 ± 2 °C over the high-rate cycles. However, when the coolant starvation issue occurs in the static mode, the maximum temperature and temperature difference rise drastically up to 53.45 °C and 18.56 °C in the fourth discharge process, which are abnormally higher than the system without injecting liquid coolant. The incorporation of 20PPI copper foam filler can alleviate the coolant starvation issue to some extent, which reduces the peak values of battery temperature and temperature difference by 13.28 % and 39.33 % under the same condition.

Field test study on early strain development law of mass concrete in cold weather

The early cracking of mass concrete in low temperature environment has always been a hot issue in the industry. The exploration of the development law of temperature and strain of mass concrete in low temperature environment is conducive to prevent its early cracking. Strain gauges are embedded in the upper, middle, and lower layers of the four measuring points of mass concrete on site to obtain the development data of early temperature and strain. Then analyze these data and reveal their internal laws. The following conclusions are drawn: (1) During the 0–30 h of concrete curing monitoring, the temperature in the middle layer of concrete is the highest, followed by the temperature in the upper layer, while in the subsequent monitoring period, a cooling gradient is formed from the lower layer to the upper layer. (2) The maximum compressive strain of concrete mainly occurs in the middle layer, and the maximum temperature and maximum compressive strain of concrete are positively correlated with its thickness. The ratio value of temperature difference between inside and outside of concrete and its thickness is the key factor affecting its external tensile strain. The strain of concrete decreases with the decrease of temperature and the development of strength, and finally tends to be stable. (3) The thickness of concrete has a significant effect on the complexity of the early strain development curve, but it does not affect the time when the strain development tends to be stable. (4) The decisive factor affecting the spatial correlation of concrete strain development is not its thickness and temperature, but the specific factors need to be further discussed.

Proposal and application of comprehensive thermal comfort evaluation model in heating seasons for buildings with solar Trombe wall

The accurate prediction of thermal comfort in indoor environment is an important precondition for energy-saving in buildings. In this study, a thermal comfort evaluation model for buildings with solar Trombe wall, by incorporating multiple thermal comfort indicators, i.e. the average values of temperature difference in the air near the head and feet (Δt), predicted mean vote (PMV), predicted percentage of dissatisfied (PPD) and standard effective temperature (SET), was proposed and validated. As the application of this proposed model, the indoor thermal comfort of a single room with two Trombe walls was evaluated and compared. Also, the indoor thermal comfort under different ambient conditions was discussed. The results show that the proposed model can efficiently realize the management of indoor thermal comfort, and is meaningful for energy-saving design of modern buildings and promoting the application of Trombe wall. There exist differences in the time periods occupied by different thermal comfort states for different evaluation indicators, which will lead to different building energy-saving effects under the condition of maintaining comfortable indoor environment. The SET indicator has stricter requirements for comfort state, and is more suitable for changeable indoor environment of the room with solar Trombe wall. Ambient conditions have significant effects on the indoor thermal comfort. Solar Trombe wall can create a very comfortable indoor environment for warmer regions in heating seasons, and provide a cool and uncomfortable environment when the ambient temperature is lower than 9 ℃ and the global solar radiation intensity is smaller than 200 W/m2.

PINCH-INTEGRATIONAL OPTIMIZATION OF HEAT EXCHANGE NETWORK OF THE HYDROLYTIC SULFURIC ACID CONCENTRATION PROCESS

The paper considers the question of the possibility of thermal energy saving at an industrial enterprise. As a means of optimizing energy consumption, one of the methods for integrating chemical-technological processes, pinch analysis, was used. It has been established that the problems of significant energy consumption are relevant for researchers and industrialists around the world, and scientists see their solution primarily in the development of alternative energy sources and modern methods of energy saving with well-predictable results. It is indicated that the target functions in this case can be combined: financial-energy and energy-environmental, since exactly these kinds of results are provided by the very essence of energy-and-resources saving applied to the industrial process.&#x0D; At the initial stage of the study, an analysis of thermal energy consumption structure provided by apparatuses in hydrolytic sulfuric acid concentration process was made. Based on its results, it was found that the existing minimum temperature difference in the system is far from the optimal and technically achievable value. Taking into account the confirmed energy-saving potential, its value was estimated. For this, the value of the present heat recovery in the system is established through calculation, and the volume of energy coming from external heat carriers and refrigerants is determined. Based on the calculation results, a Grid diagram and Composite curves of the specified technological process were constructed.&#x0D; At the second stage, optimization measures, which began with the choice of a new, lower value of the minimum temperature difference for the entire heat exchange network of this industrial plant, were carried out. For this value, shifted composite curves were constructed and an updated grid diagram was developed. In the integrated heat exchange network, there is three additional recuperative heat exchanger and were revised the operating modes of devices that it was decided to save. Based on the optimization results, a technological scheme of the hydrolytic sulfuric acid concentration process was designed while maintaining the key elements of the production technology.&#x0D; The result of the work is an optimized heat exchange network of the industrial enterprise section, which makes it possible to increase the thermal energy recuperation by 32,7 %, while reducing the consumption of external heat carriers by 30,3 %, as well as external refrigerants – by 50,1 %. The results obtained indicate a very high economic efficiency and a prospects of implementation the project into production.

Influence of confined optical phonons on the Photo-stimulated thermo-magnetoelectric effect in cylindrical quantum wires

The Photo-stimulated thermo-magnetoelectric effect in cylindrical quantum wires (CQW) under the effect of confined optical phonons (OP) is investigated. Analytical expressions of the Ettingshausen coefficient (EC), the Peltier coefficient (PC) and the temperature difference are obtained. The limitation for unconfined OP case and bulk semiconductor case could be achieved. Numerical evaluation for GaAs CQW with an infinite potential reveals that confined OP increase the EC about 2.5 times and decrease the PC about 1.01 times compared with the unconfined OP case. The appearance of an EMW with amplitude 107 V m−1 could rise the EC about 3.35 times and reduce the PC about 1.02 times. The EC and the PC start changing rapidly as the CQW radius is smaller than 20nm. The values of temperature difference are the same order as that measured for pure bismuth crystal and its changing sign is connected to previous experimental result.

Natural convection of Boussinesq and non-Boussinesq airflows simulated in a tall annular cavity

Natural convection of air in a tall annular cavity is explored by numerical solutions of the fully compressible Navier­Stokes equations in transient, axisymmetric (two-dimensional) form. A temperature difference is imposed on the two vertical walls, each isothermal, with the two horizontal boundaries adiabatic; the outer cylindrical surface is heated and the inner cylindrical surface cooled. Thermophysical properties of air, including density, viscosity, thermal conductivity, and specific heat are all variable with temperature. Laminar flow inside a tall annular cavity is prone to an instability which takes the form of a multicellular cat’s eye pattern drifting downward in the cavity. In this study, non-Boussinesq effects on the cat’s eye instability are explored by simulating flows in an annular cavity of aspect ratio A = 40 and diameter ratio η = 0.8, for Rayleigh numbers less than 14,000. A range of dimensionless wall temperature differences are investigated, 0 < ε ≤ 0.2, where ε is the temperature difference between the two vertical walls, Th – Tc , divided by the sum of the absolute temperatures, Th + Tc . The dimensionless wall temperature difference is shown to have pronounced effects on: the onset of the cat’s eye instability, subsequent flow bifurcations, wave speeds, oscillation time-periods as well as local heat transfer rates. The critical Rayleigh number, Rac , signifies a transition from steady unicellular flow to transient multicellular flow; Rac is found to increase with ε. At higher values of dimensionless wall temperature difference ε, mono-periodic oscillatory flows are predicted to occur over a smaller range of Rayleigh numbers, prior to the onset of quasiperiodic flow.

Analysis of cavitation artifacts in Magnetic Resonance Imaging Thermometry during laser ablation monitoring.

Magnetic Resonance Thermometry Imaging (MRTI) holds great potential in laser ablation (LA) monitoring. It provides the real-time multidimensional visualization of the treatment effect inside the body, thus enabling accurate intraoperative prediction of the thermal damage induced. Despite its great potential., thermal maps obtained with MRTI may be affected by numerous artifacts. Among the sources of error producing artifacts in the images., the cavitation phenomena which could occur in the tissue during LA induces dipole-structured artifacts. In this work., an analysis of the cavitation artifacts occurring during LA in a gelatin phantom in terms of symmetry in space and symmetry of temperature values was performed. Results of 2 Wand 4 W laser power were compared finding higher symmetry for the 2 W case in terms of both dimensions of artifact-lobes and difference in temperature values extracted in specular pixels in the image. This preliminary investigation of artifact features may provide a step forward in the identification of the best strategy to correct and avoid artifact occurrence during thermal therapy monitoring. Clinical Relevance- This work presents an analysis of cavitation artifacts in MRTI from LA which must be corrected to avoid error in the prediction of thermal damage during LA monitoring.