Hot Source Research Articles

FINITE DIFFERENCE METHOD BASED-NUMERICAL SIMULATIONS AND CAVITY TILTING ANALYSIS ON MAGNETOCONVECTION IN AN INCLINED PARALLELOGRAMMIC POROUS ENCLOSURE

This article numerically investigates the buoyancy-assisted convective flow and associated thermal characteristics in an inclined parallelogram-shaped porous geometry containing heat source and sink of different lengths placed at various locations. The left tilted wall has a hot source, and right tilted wall contains a cold sink, while the remaining regions of the inclined sidewalls are thermally insulated. The geometry is filled with fluid-saturated porous material and, in addition, an externally applied magnetic field (MF) has been supplied in lateral direction. The model equations governing the physical processes involve Darcy's law for the momentum equations and energy equations to account thermal variations. Using a stable and implicit finite difference methodology, these set of coupled and nonlinear partial differential equations are solved by reducing them to a system of linear algebraic equations. A wide range of numerical experiments are performed to determine the influence of various physical and geometrical parameters on the flow and thermal structure as well as thermal dissipation rate inside the geometry. Further, a suitable pair of inclination angles is found, at which maximum heat transport could be produced as compared to other combination of angles. Furthermore, an optimum size and location for the source-sink combination has been predicted which induces higher heat transport rates.

Effects of magnetism on porous rectangular fins with convection and radiation

A fin is an extended surface used to enhance the surface area of a heat transfer surface between a hot source and the outside environment. To maximise the rate of heat transportation, the exterior surface of heated equipment is equipped with fins of various geometries. Heat is exchanged using fins in radiators, refrigeration systems, superheaters, combustion engines, electrical equipment, electric transformers, space vehicles, and aircraft engines. Reflecting these applications, we analyse the effect of a magnetic field on the thermal properties of radiating porous rectangular fins. The proposed model is numerically analysed using the shooting method under the influence of radiation and convection, then compared with the DTM solution and both the solution found closer to each other. The effect of various dimensionless parameters on temperature transmission in magnetized rectangular-shaped porous fins is revealed using numerical results. It is revealed that, when the Raleigh, Hartmann, Peclet numbers, convective and radiative parameters increase, the fin?s thermal profile decreases, whereas the thermal profile increases with an increase in surface temperature, porosity, and ambient temperature. It is observed that the magnetic effect increases the heat transfer rate from porous rectangular fin surfaces. Accordingly, efficiency increases as Hartmann number, Raleigh number, and radiative parameter rise. Increasing Peclet number, surface temperature, and ambient temperature leads to a reduction in efficiency.

Experimental study of single-phase change material thermal diode based on calcium chloride hexahydrate

Phase change material thermal diodes designed on the basis of different heat transfer forms and coefficients caused by different phase transition degrees in opposite heat transfer directions are considered as potential thermal management devices. However, the use of a variety of materials or only relying on numerical simulation research makes its structure complex or idealized, which reduces the possibility of practical application. Therefore, in this work, a simple thermal diode structure containing only CaCl<sub>2</sub>·6H<sub>2</sub>O single-phase variable material is proposed in combination with changes in heat transfer form and heat transfer coefficient in solid-liquid phase change and natural convection process. The corresponding device is prepared, and a steady-state heat flux test system is set up for experimental study, the measured results are close to those recorded in the literature with good accuracy. The influence of the temperature difference between hot end and cold end and the direction of positive heat transfer and negative heat transfer on the thermal rectification effect of the thermal diode are studied experimentally. The results show that the heat flux of the thermal diode decreases with the decrease of the difference in temperature between the cold source and hot source, and the thermal rectification ratio reaches to 1.58 when the forward and reverse along the antigravity direction and gravity direction, respectively. The optimal cold source temperature range is 20–25 ℃, which is close to room temperature. The proposed phase change material thermal diode structure has a certain application potential in energy saving and thermal management of building.

Inexpensive Fabrication of Sn-Ag- Cu/Cu:ZnO/Al/PET Memristive Devices through Unconventional Synthesis Techniques

In the last few decades there has been rapidly growing research interest in resistive switching devices which led to tremendous technological advancements. In this work, copper (Cu) doped zinc oxide (ZnO) thin film was deposited on Aluminum coated PET conductive sheets having a sheet resistance of 20 Ω. Soldering balls of 2 mm diameter consisting of 96.5% Sn, 3% Ag and 0.5% Cu alloy were dropped into this thin film to form the Sn-Ag- Cu/Cu:ZnO/Al/PET memristive devices. No additional annealing temperature was required as the heat transfer from 350 C hot soldering ball onto the Cu:ZnO thin film was sufficient to anneal the thin film. The electronic characteristics of the device were obtained by employing a function generator and an oscilloscope instead of an expensive source meter. The elimination of redundant hot furnace (for annealing) and source meter (for I-V characterization) resulted in the improvement of total equipment expenses by ~96%.

THERMAL SOURCE EFFECT ON THE NATURAL CONVECTION OF A NANOFLUID WITHIN A TRIANGULAR CAVITY

Natural convection is numerically studied in a triangular cavity whose inclined walls that is isothermal at temperature TC, while its base is thermally insulated. The cavity contains a hot isothermal cylindrical heat source TH of diameter D. In this study, we used the nanofluid (water + TiO2). The nanoparticle volume fraction is varied within the range 0.01 ≤ ϕ ≤ 0.05, and the Rayleigh number is set between 103 and 106. The main objective of this study is to explore the impact of nanoparticle concentration, Rayleigh number (Ra), and heat source position (h) on the enhancement of convective thermal transfer. The simulation results show that thermal exchange improves with increasing Ra, heat source diameter, and nanoparticle volume fraction (ϕ).

Characterization of blast waves induced by femtosecond laser irradiation in solid targets

Abstract Blast waves have been produced in solid target by irradiation with short-pulse high-intensity lasers. The mechanism of production relies on energy deposition from the hot electrons produced by laser–matter interaction, producing a steep temperature gradient inside the target. Hot electrons also produce preheating of the material ahead of the blast wave and expansion of the target rear side, which results in a complex blast wave propagation dynamic. Several diagnostics have been used to characterize the hot electron source, the induced preheating and the velocity of the blast wave. Results are compared to numerical simulations. These show how blast wave pressure is initially very large (more than 100 Mbar), but it decreases very rapidly during propagation.

Identification and Study of Thermophilic Bacteria Found in the Sulfur-Infused Hot Springs of South Lampung

Thermophilic bacteria are microorganisms with the capability to produce a specific enzyme known as amylase, which exhibits resistance to heat and is referred to as thermostable. This study aims to isolate, characterize, and assess the enzyme-producing activity of bacteria from the hot springs of Way Belerang, Lampung, specifically amylase. The research procedures encompassed sample collection, isolation of thermophilic bacteria incubated in NA media for 48 hours, amylum testing with iodine after a 24-hour incubation in NA media containing starch/amylose, biochemical tests including TSIA, SIM, SC, urea test, sugar fermentation test, and catalase test. The results of the study yielded two isolates successfully isolated from the hot spring source, and Gram staining indicated that both isolates were Gram-negative bacteria. The assessment of bacterial activity in producing amylase was demonstrated by the presence of clear zones, with the largest bacterial diameter measuring 1.04 mm as measured using a vernier caliper. Characterization of the bacteria identified them as belonging to the Pseudomonas genus for isolates AB2 and AB3. Thus, the bacteria obtained in this study produce amylase enzymes that can be utilized in various industrial applications, including the food, beverage, textile, detergent, paper, pharmaceutical, and other sectors.

The combined application technology of solar heat utilization and ground source heat pump

Energy issues play an increasingly important role in national security and economic development. The country has put forward the policy of building energy-saving and land-saving buildings. The application of the comprehensive utilization of renewable energy in the construction field has gradually become a need for technical progress and industry development. With the official promulgation and implementation of the Renewable Energy Law in 2006, the application of solar energy, geothermal energy, and other related renewable energy in the construction industry has attracted more and more attention. However, the scope of practical application is currently limited to solar energy alone to supply domestic hot water, power generation, or ground source heat pump system heating and cooling. The actual engineering cases of the combined operation of the two are relatively few, and the unreasonable joint operation mode leads to low system efficiency. In this paper, the combined application system of solar heat utilization and ground source heat pump is elaborated and analyzed in detail, from the technical feasibility, system efficiency, and other aspects of the analysis. It emphasizes the necessity and development prospect of the comprehensive utilization of renewable energy.

Towards absolutely calibrated ECE Michelson measurements in EC heated plasmas at W7-X

A Michelson Interferometer is in use at Wendelstein 7-X (W7-X) to probe the Electron Cyclotron Emission (ECE) spectrum [1], [2], [3]. During the past operational campaign (OP2.1), 2nd and 3rd harmonic ECE power density spectra have been routinely recorded in the presence of X2and O2-mode Electron Cyclotron Resonance Heating (ECRH). However, combination of the particular notch filter arrangement and high transmission line losses have thus far prevented overall calibration using a hot source cold source exposure at the input antenna. As an alternative, the response of the individual components is measured and summed. While reasonable numbers on electron temperature are obtained in X2-mode polarisation, interaction between front-end components is neglected and large error bars must be assumed. But the information on the individual components, together with synthetic modelling and data from experiment (OP2.1), has been used to design a new front-end with improved S/N. This optimisation is discussed in this paper with focus on notch filter selection, a new transmission line (Tx-line) and a novel combined quasi-optical taper / polarizer tuner.

The dynamic behaviour of ORC-based power units fed by exhaust gases of internal combustion engines in mobile applications

Exhaust gases Waste Heat Recovery (WHR) in Internal Combustion Engines (ICEs) performed through ORC-based Power Units (ORC-bPU) ensures a reduction of fuel consumption and consequently CO2 emissions. Nevertheless, high fluctuations of hot source push the ORC-bPU to work frequently in severe off-design conditions. Hence, a deep knowledge of the unit dynamic behaviour is fundamental to develop control and operating strategies allowing to achieve a successful recovery. Dynamic response assessment of ORC-bPUs has been treated in literature but making mainly reference to theoretical approaches or to variations of input variables without considering the matching to the engine and the necessary constraints which are present in a real mobile application. Moreover, Moving Boundary (MB) models are generally used as theoretical tools to support the dynamic analysis focusing the attention on Heat Recovery Vapor Generator (HRVG) which rules the plant dynamic response. In MB models, boundary conditions at the HRVG exit are mainly fixed by the expander and by the remaining circuit. To date, the attention was focused on the presence as expander of dynamic machines (turbine), deserving an evident lower attention to volumetric expanders nonetheless their higher suitability for low-medium scale ORC applications (few kWs). To fill these knowledge gaps, a novel approach is pursued in the present paper. The dynamic response of an ORC-bPU was experimentally observed for a step change of torque and revolution speed of an ICE directly connected to the recovery unit. The variation of engine operating conditions produced an unsteady variation of the temperature and flow rate of the exhaust gas feeding the unit. The dynamics of the engine and the connecting pipes is considered as well as all the typical constraints of a real situation. Results show HRVG and exhaust pipe ruling the dynamic behaviour of the unit, leading to long time constant and raising time of gas temperature of 150 s and 300 s respectively. These results show that the unit almost always works in transient conditions being engine torque and speed variations very fast. Nevertheless, thanks to the self-regulation capacity and the robustness of the scroll expander, the unit reacts in a satisfactory way. A further novelty of the present study concerns the integration of the widely used Moving Boundary (MB) approach with Permeability theory which considers the presence of a volumetric expander and all the ither downstream components, finding a match not available in literature between the HRVG and a volumetric expander and pump. The results of the new Permeability-Moving Boundary model (P-MB) was compared with those of a more comprehensive mathematical model. The comparisons show a comparable accuracy and a significantly lower computational time achieved with P-MB. Hence, P-MB could be implemented on board to set up control strategies enhancing the recovery tuned by a model-based approach.

Real-time temperature field reconstruction using a few measurement points and RPIM-AGQ6 interpolation

In thermal management systems, temperature field monitoring is vital for the structural safety of electronic equipment. However, there are practical challenges when it comes to installing temperature sensors on some monitoring points directly. To solve this problem, a novel temperature field reconstruction method is proposed. This strategy offers the advantage of using only a limited number of discrete values to predict temperature fields across an entire plane. Initially, the approach constructs a composite interpolation function, named RPIM-AGQ6, by coupling the mesh-free radial point interpolation method (RPIM) with the quadrilateral area coordinate method (AGQ6) The temperature field is discretized and represented as the product of the nodal temperatures and the RPIM-AGQ6. Next, ill-posed equations are established and solved using Bayesian Multivariate Linear Regression (BMLR) to obtain the temperature in the key points. Subsequently, a novel optimization strategy is proposed to achieve the cooperative optimization of the number of sensors and reconstruction accuracy. Finally, the simulated calculation and experimental tests are used to demonstrate the effectiveness and accuracy of the proposed approach. The results show that the proposed methodology can accurately reconstruct the plane temperature field of plate structure with one and two hot sources and the relative percentage error is within 2.6 %. Therefore, it can be utilized as an effective tool to real-time monitor structural surface temperature.

Investigation of the Stretching/Shrinking of a Convective-Radiative Radial Fin

Fins are extended surfaces that increase the surface area for heat transfer between a hot source and an ambient fluid. Heat transfer is increased by adding radial or concentric annular fins to the outside surface of a circular conduit. The fins are used in devices that exchange heat such as car radiators, electrical equipment, and heat exchangers. Based on these applications, the current article examines a stretching/shrinking convective-radiative radial fin. Additionally, parameters such as the Peclet number, surface temperature, and ambient temperature are taken into account. The shooting technique is used to investigate the thermal profile, fin’s tip temperature, and efficiency of the radial fin. It is revealed that the thermal profile enhances with stretching, the Peclet number, surface temperature, and ambient temperature, while declining with radiative and convective parameters. It is observed that the radial fin’s tip temperature versus stretching/shrinking increases with increasing values of the Peclet number and ambient and surface temperatures, but the fin’s tip temperature diminishes with increasing convective and radiative parameters. Additionally, when the radiative and convective parameters increase, efficiency also increases. However, when the Peclet number, surface temperature, and ambient temperature increase, the efficiency decreases. As a result of increasing the convection parameter N c from 0.1 to 0.3, the temperature distribution increases about 7%, and an increase of 5% in temperature distribution is achieved by increasing the radiation parameter N r from 0.1 to 0.3, and when the peclet number P e is increased from 0.3 to 0.8, the temperature distribution decreases by approximately 0.5%. It is also revealed that when the shrinking effect is exposed to a stretching/shrinking moving fin along with the radiative parameter, the thermal performance of the radial fin improves. From the results, it is concluded that stretching/shrinking radial fins improves efficiency and performance. Finally, a comparative study has also been made between the present and published results, and for every case study, superiority of results obtained from the present model is noticed and the degree of supremacy increases with the increase in condensation rate of vapor on fin surfaces.

Experimental investigation on the performance of a micro-ORC system for different operating conditions

The micro-ORC systems are widely considered a reliable solution for domestic power production from renewable sources. The investigation of the optimal operating conditions to maximize system efficiency is an interesting challenge. In this study, a preliminary experimental campaign has been carried out on a biomass-fired micro-ORC system. The system is designed for stationary applications for domestic users, with a gear pump, a scroll expander and R245fa as the working fluid. The performance characterization of the micro-ORC under steady-state conditions has been obtained varying the water flow rate in the condenser at constant pump and expander speeds. The temperature of the hot source (thermal oil) is the maximum achievable in each operating condition. The temperature at the expander inlet and the condenser and evaporator pressure strongly influence the system performance. The increase in water flow leads to a decrease in the condenser pressure and a reduction of the superheating degree of the organic fluid. The system reaches the maximum electric power output of approximately 2565 W with a water flow rate of about 20 l/min. The highest electrical efficiency increases as the refrigerant flow rate decreases and reaches the highest value of 8.1% for the minimum investigated water flow rate.

Solar-driven chemisorption cogeneration system integrated with thermal energy storage

In this study, a power and cooling cogeneration system is introduced, consisting of a chemisorption cycle, a latent heat thermal energy storage (TES) system employing phase change materials (PCM), and a solar system employing compound parabolic collectors (CPC). The system is targeted at being employed in a residential area in Shiraz City and TRNSYS and MATLAB software environments are utilized to simulate and assess the system. In the system, power is generated by a turbine with the pressure difference elicited through the chemical reaction in the chemisorption cycle. Also, the cooling is produced via the evaporation of ammonia in the evaporator. The effect of the supplied hot source temperature for the reaction in the adsorbent bed was investigated. It was observed that in the 100–200 °C heat source temperature range, the total energy efficiency increased from 0.313 to 0.467 and the COP for the refrigeration process reduced from 0.71 to 0.53. Also, the maximum overall energy and exergy efficiency in this temperature range were 0.46 and 0.405, respectively. Also, at the heat source temperature of 200 °C, the average maximum electrical power and cooling capacity were gauged at 2.7 kW and 14.5 kW, respectively. In the TES system with a volume of 1.5 m3, the maximum achievable capacity was 250 kWh and the solar system showed its highest temperature in July and August. It was observed that heat source temperature augments the production capacity of the system while it reduced the coefficient of performance (COP) of the system. Sustainable development goals (SDG) impact [Display omitted]

Development of a Machine Learning Framework Based on Occupant-Related Parameters to Predict Residential Electricity Consumption in the Hot and Humid Climate

Occupant-related variables constitute one of the most significant groups of factors influencing residential building energy consumption. However, prediction methods often oversimplify these parameters, leading to substantial discrepancies between predicted and actual consumption. To address this issue, the present study aims to develop a machine learning framework for predicting electricity consumption in residential buildings based on occupant-related factors. The study incorporates twenty-six inputs, including occupant characteristics such as demographics, occupancy, behavior, and behavioral efficiency, two time-related factors, and three extra parameters related to equipment (refrigerator age, hot water source, and type of electricity meter) for training and testing the Random Forest (RF) algorithm in both regression and classification forms. The results indicate that the trained RF regressor exhibits well performance (R2Train = 0.989, R2Test = 0.916, MAETrain = 0.81, MAETest = 2.21, RMSETrain = 1.27, and RMSETest = 3.45). Furthermore, feature importance analysis reveals that the most significant parameter is the time of year, representing weather conditions, followed by the number of occupants, neighborhood, indoor set-point range, mean age of occupants, window opening, and cooling system mode. Even after removing the least impactful factors, the model maintains strong performance with the 16 most important variables (R2Train = 0.986, R2Test = 0.910, MAETrain = 0.83, MAETest = 2.25, RMSETrain = 1.31, and RMSETest = 3.49). Additionally, the RF classifier is designed for problems with 2, 4, 6, and 8 classes based on energy consumption ranges. The results of this model demonstrate that the 2-class model achieves the highest performance (AccuracyTest = 0.963, MAETest = 0.04, and RMSETest = 0.19). However, it lacks detailed categorization of homes based on electricity consumption. On the other hand, the 4-class and 6-class models strike a good balance between prediction performance and the level of detail. In conclusion, the proposed method can accurately predict residential electricity consumption and can serve as a valuable reference for researchers and utility managers when formulating energy reduction policies and comparing the effectiveness of different strategies.

Simulation investigation of the oscillatory motion of two elliptic obstacles located within a quarter-circle cavity filled with Cu-Al2O3/water hybrid nanofluid

This study investigates the consequences of introducing a pair of oscillating elliptical obstacles on the natural convection and entropy generation within a quarter-circle cavity that is filled with a water-based hybrid nanofluid. The Galerkin Finite Element Method was utilized to perform numerical simulations on a 2-dimensional cavity, where the outer wall was set to a low temperature and the inner wall was kept at a high temperature, while the other walls were adiabatic. The hybrid nanofluid containing Cu-Al2O3 nanoparticles was used. The impact of changes in the values of dimensionless parameters, such as the Rayleigh number, heated wall length, oscillation frequency, oscillation amplitude, and oscillation period, on the flow and heat transfer within the cavity was examined. Results showed that an increase in the length of the hot source resulted in a decrease in heat transfer rate and that increasing the Rayleigh number led to a significant increase in total entropy generation and heat transfer irreversibility. A drop in the average Bejan number was noted as the Rayleigh number increased, demonstrating the prevalence of entropy caused by fluid friction. The effect of changing the amplitude had a higher impact on the average Nusselt number compared to the frequency value. At low Rayleigh numbers, the average Nusselt number was higher when the elliptical obstacles oscillated in the same direction, while the opposite trend was observed at higher Rayleigh numbers.

Numerical study on thermal resistance of PCMs incorporated in novel roof structures against energy loss

Incorporating Phase Change Materials (PCM) into building enclosures is one of the passive techniques to improve thermal comfort and reduce energy costs. The present study is dedicated to the assessment of various configurations of PCM incorporation in a roof structure in order to evaluate their impact on thermal resistance and consequent reduction in energy losses. Several arrangements of the PCM and brick are tested: small PCM blocks distributed through the structure, multiple long PCM blocks distributed horizontally or vertically, single PCM block occupying either the right half or the left half, and single PCM block occupying the top half or bottom half. The equations governing the flow and thermal transfer in the PCM, as well as heat transfer in the plaster and brick, are defined and derived in the non-dimensional form. The hydro-thermal behavior of the melting PCM is assessed in the different configurations and for two values of Rayleigh number. The results indicate that for low Ra, the highest thermal resistance is obtained when a single PCM block is located at the top of the cavity and separated from the hot source by brick. For high Ra, the maximum resistance is found when the PCM is placed in multiple vertical blocks. Putting the PCM in multiple horizontal blocks or in small blocks does not change the PCM melting when Ra is varied. In all cases, the fastest PCM melting is obtained when the PCM block is close to the hot source and is either in one single block or in multiple vertical blocks.

Study of the absorption refrigerating cycle, NH3-H2O coupled with the solar absorption heat transformer, H2O-LiBr by solar data from the City of Oujda (Morocco)

A solar refrigerator is made of a solar collector and a refrigeration system. This paper concerns the study of a two-stage vapour absorption cycle (heat transformer and refrigerating cycle) employing the refrigerant absorbent combinations of H2O-LiBr and NH3-H2O successively. The system consists of coupling the previous absorption cycle so that the first-stage absorber produces heating water to circulate in the generator of the second stage. It is found that the system can be operated at lower hot source temperatures and, thus, it can be supplied either from flat plate collectors.

Numerical simulation and optimization of heat pipes using nanoparticles: a feasibility study

This study investigated the effect of different particle sizes on the thermal effectiveness of a cylindrical screen mesh heat pipe using silver nanoparticles as the test substance. The study compared the effects of three different particle sizes (30, 50, and 80 nm) on heat transmission characteristics of the heat pipe. The results showed that the heat pipe’s thermal conductivity increases as the particle size decreases. The thermal conductivity measurements revealed 250 W/mK, 200 W/mK, and 150 W/mK for particles of 30, 50, and 80 nm sizes. Furthermore, the study analyzed thermal resistance of heat pipe for each particle size and found that as particle size decreases, thermal resistance decreases as well. The heat transfer coefficient values for particle sizes of 30, 50, and 80 nm were found to be 5500 W/m2K, 4500 W/m2K, and 3500 W/m2K, respectively. The ANOVA method was used to analyze the results statistically. The 30 nm particle size was found to have significantly higher thermal conductivity, lower thermal resistance, and a higher heat transfer coefficient than other particle sizes. Additionally, simulations were conducted to analyze the temperature variation of the hot source as a function of power dissipation for design and optimization.

Heat pump efficiency with energy geostructure: Numerical long term modelling

Heat pump efficiency with energy geostructure: Numerical long term modelling