Due to the lack of precise data on the thermal performance of single- and double-flow air solar collectors under the climatic conditions of the Ecuadorian highlands, a comparative analysis based on experimental results was conducted. The measurement system consisted of a data acquisition module connected to twenty thermistors, designed to record the inlet, internal, and outlet temperatures of each collector. A fan was also used to ensure forced air circulation and measure its outlet velocity. The results showed that the double-flow collector reached a maximum outlet temperature of 35.13 °C, higher than the 33.56 °C recorded by the single-flow collector. Similarly, the average thermal efficiency was 51% for the double-flow system and 27% for the single-flow system, under an average solar radiation of 461.76 W/m² and an average ambient temperature of 15.53 °C. These findings confirm the superiority of the dual-flow design in terms of thermal efficiency.
Photovoltaic-thermal (PVT) systems overcome a basic constraint of traditional solar modules by collecting both electricity and usable heat energy from a single integrated collector. In this work, an air-cooled PVT system optimized by coupled thermal-electrical analysis and constrained multi-objective optimization is designed, modeled, and experimentally validated. By prolonging coolant residence time and upsetting thermal boundary layers, the collector's six-baffle flow disruptor shape improves convective heat transfer. The optimized configuration raised electrical efficiency from 12.1% to 15.3% (+26.5%) and stabilized power output at 156.2 W while lowering photovoltaic cell temperature by 8.2°C compared to an uncooled reference under representative operating conditions (623 W/m² solar irradiance, 30°C ambient temperature). At the same time, airflow was used to extract 91.6 W of low-grade thermal energy (0.004167 kg/s), resulting in a system efficiency of 24.6%. A 100 m² array in a Mediterranean climate is expected to generate 12,000 kWh of electricity and 45,000 kWh of thermal energy annually. For residential and light-commercial applications where maintenance simplicity and envelope compatibility are more important than maximum thermal density, the air-cooled architecture offers a practical solution by removing the hydraulic complexity, freeze risk, and scaling management present in liquid-based alternatives. Predictive accuracy within 4% root-mean-square error throughout transient and steady-state regimes was demonstrated by model validation against experimental data. These results show that air-cooled PVT collectors can achieve balanced polygeneration performance with low operational overhead by co-optimizing absorber shape, flow dynamics, and insulation approach.
Degree-days play a crucial role in predicting thermal energy consumption for energy management and forecasting in buildings. Base temperature, commonly used in degree-day calculations, represents the outdoor temperature threshold at which a building’s internal heat balance shifts from passive maintenance to active heating or cooling. This study examines key factors influencing base temperature selection through case studies, refining degree-day calculations for greater accuracy. By utilizing advanced modelling tools such as Degree Days.net and Renewables. ninja. Different countries follow various base temperature conventions, such as 18°C in the USA, 15.5°C in the UK, and 12°C in Switzerland. Unlike a fixed national standard, the true base temperature of a specific building is dynamic, depending on several factors, including the building's thermal properties, the heating system's set temperature, internal heat gains, and solar energy contributions, etc. This work analyses these factors using specific case studies to determine how to calculate the appropriate base temperature for a building. With tools like Degree Days.net, degree-days can be calculated for any desired base temperature. Selecting the most suitable base temperature for each building and heating method ensures more accurate energy predictions.
Microalgae cultivation in horizontal loop tubular photobioreactors (HLTPs) is more efficient for biofuel production than other methods. It is important to inject CO2 into the photobioreactors to ensure microalgal growth. Due to the complex flow path and bubble arising from CO2 penetration in the tube, turbulence may occur in the flow. In this work, a two-phase turbulent flow of CO2 and microalgae suspension is considered for simulating the flow. An HLTP is used here as the computational domain for our simulation. Besides a slow growth in the culture, we have observed that the flow inside the reactor forms a parabolic shape at the straight portion. However, a wavering flow is found around the U-loop portion of the tube. The pressure is gradually dropped along the arc length. The shear rate is somewhat high and fluctuates within the tube. The effect of the nutrient on growth is also found.
In this article we continue our previously conducted research on the construction of a mathematical model for obtaining medicinal nanoforms using cryochemical synthesis methods. In connection with the need to increase their therapeutic effectiveness, it is necessary to take into account the particles size, structure and shape. Thus, to reduce side effects and a toxicity we can reduce the particle size of drugs to nanoscales. It allows us to obtain highly effective drugs and to use its smaller doses. One of the most powerful new methods for obtaining nanoforms of drugs is its cryochemical synthesis. This method is a leading-edge process for producing drugs in nanoparticle form. The procedure involves vaporizing the raw drug material in a vacuum and then channeling this vapor into a stream of gas. The gas stream, now carrying the drug molecules, is directed onto an extremely cold surface where the molecules instantly condense and form nanoscale structures. The first stage of mathematical modeling of cryochemical synthesis processes was the calculation of the temperature field in the carrier gas flow interacting with the cooled surface. At this stage, taking into account the previously obtained results, we study the change in pressure and supersaturation, determining the coordinate of the formation of the first embryo and its critical size, which will allow us to describe the process of embryo growth at the next stage of constructing a mathematical model, and determine their molecular mass as they reach the cooling surface.
A refined thermal model is presented to describe both the early-stage behavior and the dynamic temperature response of cast iron radiators during heating system operation. In the initial phase, the radiator is conceptually subdivided into three thermally distinct subdomains: the region progressively filled with hot water due to fluid motion, the cast iron wall, and a complementary zone where the fluid remains at its initial (ambient) temperature. Once the radiator is filled with hot fluid, this early stage concludes; however, a downstream adiabatic "short volume" is introduced to account for the delay observed in the outlet temperature rise associated with the fluid transit time through the radiator. The proposed modeling framework offers a physically sound and computationally efficient strategy to simulate both start-up transients and the longer-term dynamic thermal response of radiator-based heating systems.
We present a compact semi-analytic framework that couples solid-target energy-deposition physics with two-temperature plasma hydrodynamics to model the earliest stages of a fission-driven fireball. Starting from spherically symmetric conservation laws, the approach replaces cold-matter constitutive closures with a two-temperature equation of state that explicitly includes ionization enthalpy and radiative energy loss, and systematically reduces the full PDE system to a thin-shell ODE model for the shell radius and mean ionization fraction. The manuscript documents the step-by-step asymptotic reduction, derives closed-form limits, and quantifies model uncertainty through analytic sensitivities and example-propagated bounds. A stability study of the reduced dynamics includes analytic results for the ionization subsystem and numerical recipes for instantaneous eigenvalues, finite-time multipliers, and Lyapunov exponents useful for experimental design. Representative parameter sweeps reveal rapid ionization (sub-picosecond) and nanosecond-scale hydrodynamic expansion, characterized by velocities on the order of 106 m·s⁻¹. Comparisons with classical blast scaling solutions and recommended validation pathways (radiation-hydrodynamic benchmarks and targeted laser-plasma experiments) demonstrate the model’s value as a fast, efficient, and physically grounded tool for parametric studies, uncertainty quantification, and experiment planning.
This paper presents a numerical study using CFD to analyze the dynamical and thermal behavior of two turbulent parallel jets of different velocities impinging on a vertical heated plate, to determine the optimal parameters for heat transfer. Two-dimensional unsteady numerical simulations based on the finite volume method are performed. The 2D-URANS equations coupled with the standard k−ε turbulence model is used. The results show a maximum turbulent kinetic energy near the heated plate, due to the strong deflection of the faster jet towards the slower jet, for small velocity ratios. Furthermore, for a velocity ratio of 0.25, local heat transfer is maximal for an impinging distance between 4w and 8w. On the other hand, for velocity ratio λ=0.75 and impinging distances exceeding 8w; a better local cooling is obtained. These results confirm the influence of the velocity ratio on the dynamic and thermal fields. They effectively control the thermal profile.
Various fluids have unique traits that result in different behaviours for varied uses. One of these unique properties of fluids is the couple stress. Couple stress is the result of internal stresses that are contained in the fluid. This work presents a numerical study of convective heat transfer in a couple stress hybrid nanofluid (AA7072-AA7075/CH3OH). The use of similarity transformations ensures that the governing partial differential equations are reduced to a set of ordinary differential equations, which are solved using the bvp4c function in MATLAB. The findings showed the singular and combined impact on the thermal and hydrodynamic behaviour of the fluid. This work attempts to elucidate the optimisation of hybrid nanofluids targeted for cutting-edge engineering uses. It balances the control of parameters and the resultant thermal and flow characteristics to highlight flow and thermal behaviour.
Equations governing the flow of a polar fluid, with pressure-dependent Newtonian viscosity, through a variable-porosity medium are developed. Averaged equations are obtained using intrinsic volume averaging. A drag function is introduced to account for the interactions of the fluid with the porous matrix. Darcy and Forchheimer generalized terms, which utilize friction factor description, are included in the model equations for both granular and consolidated media to account for the effects of the porous microstructure. The developed model equations are important in the study of blood and nutrient flows in body tissues and organs, and in modelling and control of flow through synthetic porous materials that replace human tissues in burn victims. Potential other applications include flow simulation of oil products in ground layers and industrial porous domains.
Forced convection is one of the modes of heat transfer. In the present paper a U-shaped bend tube is considered as a flow domain through which the air is blown for an experimental study. The heat is supplied to the bend pipe with the help of a heater and varying heat rate with voltage and current. The study will predict the heat transfer coefficient (h), temperature profile and Nusselt Number (Nu) on the variation of input heat transfer rate (Q) and the Reynolds Number (Re) of air. After collecting the data experimentally, the Machine learning (ML) based algorithms are used to predict the comparative result data. The ML method applied in the present work is Gradient boosting regression (GBR). The experimental and ML data are compared and predict a correlation. The correlation will be used to design a U-shaped bend tube used in heat exchanger applications.
Under Poiseuelle flow, the effective viscosity associated with Brinkman’s equation is investigated and quantified for a high-porosity porous layer whose geometric factors are given by Ergun’s equation and the Kozney-Carmen equation. An expression for the relative viscosity is derived and expressed in terms of the geometric factors. Viscous and Darcy flow limits are quantified in terms of the relative viscosity and the geometric factors. This work also initiates investigations of the effective viscosity when the Brinkman flow is through a variable permeability porous layer and when the governing equation is the generalized Brinkman equation. When permeability is variable, it is shown that the relative viscosity is always less than unity when the Brinkman pressure gradient is the same as the corresponding Navier-Stokes pressure gradient. A condition on the pressure gradients under which the relative viscosity is greater than unity is derived. When the flow is governed by the generalized Brinkman’s equation, the problem of quantifying the effective viscosity is replaced by that of determining variations in viscosity due to pressure, and variations in pressure due to changes in the porous medium parameters.
A large part of solar irradiation is lost in different forms in the photovoltaic system hybridized with a TEG thermoelectric generator. This is disadvantageous for the best contribution of the TEG generator. The losses occur mainly on the front and rear of the PV-TEG hybrid system. They are usually radiation losses, natural convection losses, and forced convection losses due to the wind. In this paper, we studied the interaction of these different losses in both faces of the hybrid system according to different environmental factors such as solar radiation, ambient temperature, and wind speed. This study concerns two types of PV-TEG hybrid systems, the PV-TEG system with an optical concentrator and the one without an optical concentrator. It aims to determine the influence of environmental factors on these different losses and also to determine the dominant losses in both types of the PV-TEG hybrid system. The determination of the dominant losses and the estimation of their quantity makes it possible to make decisions for the optimization of these two hybrid systems, by adding solutions to reduce these dominant losses and transferring it towards the thermoelectric generator so that it can generate more electric power, and by avoiding that, these solutions strongly influence the performance of these two hybrid systems. For this purpose, an appropriate model is developed which includes all these losses.
Hybrid nanofluids are designed to improve conventional nanofluids' stability and other thermal properties. The present work investigates the flow of combined convective transport and the influence of radiation on the studied flow. A hybrid nanofluid ( Cu Al O 2 3 /water) flows through a vertically inclined stretching/shrinking sheet. To simplify the governing equations, the deterministic two-variable differential equations (PDEs) are systematically transformed into a system of one-variable differential equations by using appropriate similarity transformations. The bvp4c function of the MATLAB program is also used to solve the simplified mathematical model. The present study investigates and presents in tabular and graphical form the effects of stretching/shrinking surfaces, suction, and volume fraction of the nanoparticles on the velocity and temperature profiles as well as on the engineering quantities. The present results are first validated and confirmed as acceptable before the full calculations are performed. Overall, the results of this study show that the investigated parameters influence the flow characteristics, which can serve as a controlling factor for heat transfer.
Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between surface seawater and deep seawater to produce electricity through a heat engine. A major disadvantage of the OTEC systems is that seawater temperature on the surface and on the seabed varies with the geographical location. This difference is also dependent on the depth and the distance from the coastline, where there are cases with the required temperature difference size to be found at a high distance from shore. This study evaluates the heat losses of the cold water pipe, where such long distances occur, and the subsequent effects for such cases. The current investigation is performed computationally and is based on the accurate estimation of the temperature difference between the deep seawater temperature and the inlet to the condenser temperature. Most literature studies do not consider any heat losses due to the transfer of the seawater when evaluating the performance of the CWP; however, in some cases, even a small temperature change can have a major effect on the output of the system.
The problem of unsteady high-speed MHD natural convective flow over an inclined plate in a fluid with variable electrical conductivity, higher-order chemical reaction, thermal radiation, and concentration gradient-dependent heat generation/absorption is investigated. It is assumed that the fluid is chemically reactive, and of the nth-order; electrically and magnetically conducting; viscous, incompressible, and Newtonian; the plate is highly porous, thermally and electrically conductive, and heated to a high-temperature regime to emit thermal rays; the plate is heated at the bottom, and the heat is conducted to the top such that convection currents exist. The equations governing the flow are non-linear and coupled partial differential equations. They are transformed into ordinary differential equations using the time-dependent similarity transformation, and solved by the Modified Homotopy Perturbation approach. Expressions for the concentration, temperature, velocity, rates of heat and mass transfer, and the stress/force on the wall are obtained, computed, and presented graphically and quantitatively for the different parameters. The analysis of results shows among others, that the increase in the: order of chemical reaction parameter causes fluctuation in the fluid concentration structure, but increases the flow velocity; the Forchheimer number decreases the fluid velocity, but increases the force on the surface wall; electrical conductivity causes fluctuation in the temperature structure, increases the rate of heat transfer to the fluid, and decreases the force on the wall; inclined angle decreases the fluid velocity.
Fuel is a major regulator in the current global instability. It is safe to say that energy is the silent hero of the fourth industrial revolution. Because of its environmentally favorable function and cost-effective sustainability, biofuel can be an ideal alternative to fossil fuels. Microalgae-based biofuel is gaining popularity among scientists and entrepreneurs due to its high biomass yield. There are some growth factors like strain properties, light, temperature CO2, PH , nutrients (N, P, Mg, Mn, etc.), culture systems, etc. to increase biomass growth. In this present research, a growth model based on nitrogen intake is considered to investigate the effect on optimal biomass growth. The other kinematic parameters are taken from an experiment for our simulation. The local light intensity is taken into account for a geographical location. Microalgae culture shows a very significant growth in biomass concentration while nitrogen intake gradually decreases. The simulated results were also compared with a reference model and the experimental one and found a good agreement. The rate of biomass concentration within the first 100 hours in our present research work, using 1.575 gL-1 acetate and 0.0735gL-1N, is revealing upper than the compared experimental results. The nitrogen consumption by the culture shows a similar pattern to the reference study.
The present article examines the integrity of the extended Lévêque series solutions of the second Graetz problem engaging uniform wall heat flux that have been published in the heat convection literature over several years. Various flaws have been identified and scrutinized in three extended Lévêque series solutions that are available. To remedy the ongoing anomalies, a comprehensive regression analysis is investigated to search for an empirical correlation equation as a potential replacement to the three extended Lévêque series solutions. Interestingly, a couple of empirical correlation equations have been constructed in this work, which exhibits exceptional quality in the designated sub–domain of operation.
This paper investigates in detail the thermal and chemical effects of an unstable magnetohydrodynamic (MHD) mixed oscillatory flow. The temperature, velocity, and concentration profiles can be investigated in detail by transforming the governing equations into a dimensionless system. These equations are solved using the perturbation method, which reveals details about the significant effects and connections between the variables being examined. The velocity, temperature, and concentration are found to decrease as the magnetic field, heat radiation, and chemical reaction rise. Additionally, artificial neural network (ANN) approaches are applied to these ordinary differential equations (ODEs), and the outcomes are contrasted with numerical simulations. This work illustrates the ANN model's capacity to produce extremely precise heat transfer rate forecasts from an engineering standpoint. This method improves knowledge of complex fluid magnetohydrodynamics and porous medium flows by incorporating artificial intelligence.
The study of the simultaneously developing pipe flow requires facing nonlinear systems of partial differential equations. In this framework, the aim of this paper is to demonstrate that the integral method can be an effective procedure to obtain analytic-approximate solutions that are easy to handle while allowing the recovery of a satisfactory accordance with the exact solution. To prove the above statement this paper will present a comparison between the approximate solution and the corresponding numerical solution in the entrance region of Newtonian pipe flow. Third-kind thermal boundary conditions are included, while velocity and temperature profiles at the inlet are assumed uniform. Numerical results demonstrate that the proposed approximate solution is quite accurate and readily implemented, both in terms of developing velocity and temperature profiles. Moreover, the expected functional dependence on the main parameters of the problem at hand is retained. As a consequence, the developing Fanning friction coefficient and Nusselt curves are satisfactory and accurate for different thermal boundary conditions at the wall.
