Mixed convection in horizontal channels heated below with external heat losses on upper plate and partially filled with aluminum foam

In this paper an experimental investigation on mixed convection in air in a heated channel partially filled with an aluminum foam is carried out. The aluminum foam layer is sets on the lower heated wall of the channel. The channel upper plate has a heat transfer toward the external ambient. The investigation allows to evaluate the effect of the aluminum foam on the mixed convection in the heated channel by wall temperature measurements and flow visualization. Results are given for heated channel without and with foam in terms of wall temperature profiles for different Reynolds number value, form 10 to 300, wall heat flux and for aluminum foam with 10 and 20 pore per inch. Lower wall temperature values are detected for the channel with foam with respect to the channel clean without foam. Foams with higher pore per inch shows lower average wall temperature values whereas the local wall temperatures showed different behaviors for the different pore per inch values. The presence of foam in heated channel determined weaker secondary motions with respect to the clean cases. The effect of the foams seems more significant for the high Reynolds number values and average Nusselt number increases with the foam presence in the heated channel

Local Thermal Non-Equilibrium Investigation on Natural Convection in Horizontal Channel Heated from Above and Partially Filled with Aluminum Foam

Abstract The configuration of two horizontal parallel walls, with heated upper plate and open cavities, gets considerable attention in many thermal engineering applications. In this work, a numerical investigation on steady state natural convection in a horizontal channel partially filled with a porous medium and heated at uniform heat flux from above is carried out. The local thermal non-equilibrium (LTNE) hypothesis is invoked. A three-dimensional model is realized and solved by means of the ANSYS-FLUENT code. Results are presented in terms of velocity and temperature fields and profiles, and they show that the use of porous medium improves the heat transfer in the channel due to the aluminum foam high conductivity

An experimental investigation on effect of pores per inch in compact heat exchanger with aluminum foam

Metal foams are a new class of materials with low densities and novel thermal and mechanical properties. Aluminum foams combine low weight with good rigidity, strength, damping of vibrations and noise, shock resistance and low thermal conductivity [1]. An experimental investigation on a single row of aluminum tubes, covered with layers of aluminum foams, was carried out by T’joen et al. [2]. A range of foam layer thickness, Reynolds number tube spacing and different type of foam were considered and compared with compact helically finned tube heat exchangers. An experimental investigation was carried out by Sertkaya et al. [3] to compare three metal foam heat exchangers (10, 20 and 30 PPI) to three finned heat exchangers with the same tube layout and overall dimensions. Please download the full abstract below

Numerical simulation of thermal energy storage with phase change material and aluminum foam

A Latent Heat thermal energy storage system (LHTESS) is employed as a thermal buffer, since it avoids the intermittent supply of thermal energy due to the behaviour of the thermal source, in particular the renewable thermal source like the solar radiation. Therefore a LHTESS allows supplying the thermal energy in continuous way. The principal material of a LHTESS is the phase change material (PCM) given that it storages a high quantity of thermal energy during its phase change process thanks to the high value of latent heat. Moreover the thermal energy is stored at quasi-constant temperature because during the phase change process the heat is engaged to change phase and not to raise the temperature. Please download the full abstract below

Heat transfer of chemically reacting mixed convection fluid using convective surface condition: Non-Darcy model

This work reports the study of mixed convection of permeable fluid with Robin conditions in the vertical channel including the effects of chemical reactions. The fluid transport is designed by the Darcy-Forchheimer-Brinkman model. The series method is adopted for approximate solutions for governing equations considering the Brinkman number as the perturbation characteristic whose outcomes correspond to magnitudes of Brinkman number less than one. Adopting a numerical scheme followed by fourth order Runge–Kutta algorithm with shooting method, the solutions for bigger magnitudes of the Brinkman number are obtained. The present results for limiting cases are compared with the literature and good agreement is seen. For various values of thermal and mass Grashof numbers, porous parameter, inertial parameter, Darcy number and first order chemical reaction the problem is resolved for the same and distant Biot numbers reflecting the border temperatures symmetric and asymmetric. Finally, the outcomes are tabulated for wall friction parameters, Nusselt and Sherwood numbers for innovated parameters. It is noticed that enhancing buoyancy and dissipations, thermal Grashof number helps to improve the flow rate for all values of Biot number. The Schmidt and Soret parameters can improve concentration patterns. Nusselt number can be improved with thermal Grashof number and Brinkman number and it is dropped with inertia and porous parameters. The solutions have a very good agreement with Zanchini data without mass Grashof number

Double diffusion in a rectangular duct using metals or oxides suspended in a viscous fluid

In this study, double diffusive free convection of nanofluid within a confined rectangular duct is investigated numerically. The momentum and energy equations are placed in the form of difference equations and solved numerically. The left wall conditions for the concentration and temperature are lesser than those of the right wall and the upper and lower walls are insulated. Different nanofluids are considered such as mixtures with copper, diamond, silicon oxide and titanium oxide, suspended in water. Brinkman and Maxwell models are used to characterize the nanofluid. Tiwari and Das model is opted to define the nanofluid behavior. The simulations are conducted using different nanoparticles, thermal Grashof number 1 ≤ GrT ≤ 20, solute Grashof number 1 ≤ GrC ≤ 15, solid volume fraction 0 ≤ Φ ≤ 0.05, Dufour number 0 ≤ Df ≤ 1, Brinkman number 0 ≤ Br ≤ 2, and Soret number 0 ≤ Sr ≤ 5. Additionally, behavior of volumetric flow strength, skin friction, heat transport intensity and Sherwood number is also examined. The thermal Grashof number, Brinkman number, Dufour, Soret and Schmidt parameters accelerate the velocity and temperature and dwindle the concentration whereas the reversal effect was obtained for the solid volume fraction. The concentration Grashof number diminishes the velocity and temperature and intensifies the concentration. The silver nanoparticles produce the highest velocity whereas diamond nanoparticles cause the lowest velocity and temperature. The maximum temperature is attained with silicon oxide

Experimental Investigation on Fluid Dynamic and Thermal Behavior in Confined Impinging Round Jets in Aluminum Foam

In this paper an experimental investigation is carried out on impinging jets in porous media with the wall heated from below with a uniform heat flux. The fluid is air. The experimental apparatus is made up of a fun systems, a test section, a tube, to reduce the section in a circular section. The tube is long 1.0 m and diameter of 0.012 m. The test section has a diameter of 0.10 m and it has the thickness of 10, 20 and 40 mm. In the test section the lower plate is in aluminum and is heated by an electrical resistances whereas the upper plate is in Plexiglas. The experiments are carried out employing aluminum foams with 5, 10 and 40 PPI and three thickness over the heated circular plate. Results are obtained in a Reynolds number range from 500 to 1500 and wall heat flux from 500 W/m2 to 1400 W/m2. Results are given in terms of wall temperature profiles, local and average Nusselt numbers, pressure drops, friction factor and Richardson number. Moreover, to evaluate the improvement due to the presence of the metal foam, it is necessary a quantitative methodology. In this work an energy performance ratio is employed to compare the performances of surface with and without foams in terms of heat transfer coefficients and pressure drops. Preliminarily experimental results has confirmed that the use of the porous medium improves the heat transfer promoting the heat dissipation of the surface with high efficacy but determines an increase in pressure drops

Lumped Capacitance Thermal Modelling Approaches for Different Cylindrical Batteries

Received: 3 November 2023. Revised: 15 November 2023. Accepted: 8 December 2023. Available online: 29 December 2023.In the pursuit of optimal energy storage solutions, rechargeable batteries have gained significant attention for their applications in electric vehicles, aircraft, and satellites. This research focuses on the thermal management of lithium manganese dioxide and nickelcadmium batteries, utilizing the lumped capacitance thermal modelling technique in the preliminary stage of analysis. The study focuses on the general lumped capacitance thermal equation to estimate battery temperature through analytical and numerical methods. The numerical approach employs the fourth order Runge-Kutta's method, which involved less computational cost, relatively stable and accurate to estimate the temperature with a variable internal resistance, a crucial factor in thermal behaviour analysis. In contrast, the analytical approach assumes a uniform temperature distribution across the battery's surface, simplifying the gradual variance between internal conductive and external convective thermal resistances. A comparative analysis against experimental data using error criterion techniques reveals that the numerical model, considering dynamic changes in internal resistance, aligns more closely with experimental findings and offers a statistically superior fit compared to the analytical model assuming constant internal resistance. This study underscores the effectiveness of the lumped capacitance thermal modelling technique in battery thermal management, emphasizing the importance for dynamic internal resistance for analysis of thermal behaviour

Diversity and ethics in trauma and acute care surgery teams: results from an international survey

Background Investigating the context of trauma and acute care surgery, the article aims at understanding the factors that can enhance some ethical aspects, namely the importance of patient consent, the perceptiveness of the ethical role of the trauma leader, and the perceived importance of ethics as an educational subject. Methods The article employs an international questionnaire promoted by the World Society of Emergency Surgery. Results Through the analysis of 402 fully filled questionnaires by surgeons from 72 different countries, the three main ethical topics are investigated through the lens of gender, membership of an academic or non-academic institution, an official trauma team, and a diverse group. In general terms, results highlight greater attention paid by surgeons belonging to academic institutions, official trauma teams, and diverse groups. Conclusions Our results underline that some organizational factors (e.g., the fact that the team belongs to a university context or is more diverse) might lead to the development of a higher sensibility on ethical matters. Embracing cultural diversity forces trauma teams to deal with different mindsets. Organizations should, therefore, consider those elements in defining their organizational procedures. Level of evidence Trauma and acute care teams work under tremendous pressure and complex circumstances, with their members needing to make ethical decisions quickly. The international survey allowed to shed light on how team assembly decisions might represent an opportunity to coordinate team member actions and increase performance

Global disparities in surgeons’ workloads, academic engagement and rest periods: the on-calL shIft fOr geNEral SurgeonS (LIONESS) study

: The workload of general surgeons is multifaceted, encompassing not only surgical procedures but also a myriad of other responsibilities. From April to May 2023, we conducted a CHERRIES-compliant internet-based survey analyzing clinical practice, academic engagement, and post-on-call rest. The questionnaire featured six sections with 35 questions. Statistical analysis used Chi-square tests, ANOVA, and logistic regression (SPSS® v. 28). The survey received a total of 1.046 responses (65.4%). Over 78.0% of responders came from Europe, 65.1% came from a general surgery unit; 92.8% of European and 87.5% of North American respondents were involved in research, compared to 71.7% in Africa. Europe led in publishing research studies (6.6 ± 8.6 yearly). Teaching involvement was high in North America (100%) and Africa (91.7%). Surgeons reported an average of 6.7 ± 4.9 on-call shifts per month, with European and North American surgeons experiencing 6.5 ± 4.9 and 7.8 ± 4.1 on-calls monthly, respectively. African surgeons had the highest on-call frequency (8.7 ± 6.1). Post-on-call, only 35.1% of respondents received a day off. Europeans were most likely (40%) to have a day off, while African surgeons were least likely (6.7%). On the adjusted multivariable analysis HDI (Human Development Index) (aOR 1.993) hospital capacity > 400 beds (aOR 2.423), working in a specialty surgery unit (aOR 2.087), and making the on-call in-house (aOR 5.446), significantly predicted the likelihood of having a day off after an on-call shift. Our study revealed critical insights into the disparities in workload, access to research, and professional opportunities for surgeons across different continents, underscored by the HDI