Explore the vast range of titles available.

Flat plate solar water heaters (SWHs) are well‐known thermal systems for their simplicity and efficiency in heating water. Enhancing their functionality, dual‐purpose solar air‐water heaters (SAWHs) integrate both water and space heating, thereby reducing energy costs while maintaining minimal installation complexity. These systems harness solar energy to efficiently transfer heat to both air and water, presenting a versatile solution for sustainable energy applications. This research investigates the thermal performance of a new design of dual‐purpose SAWH under solar irradiation of 1100 W/m. In this innovative design, the water tubes feature a semi‐circular cross‐section to maximize contact area with the absorber. The study examines the effect of varying inlet water temperatures (32, 37, and 42°C) on heat transfer, temperature distribution, and thermal efficiency. Additionally, the effects of different air mass flow rates have been investigated. Results indicate that as the inlet water temperature increases, the heat transfer rate on the waterside decreases from 788 to 695 W due to the reduced temperature difference between the water tubes and the absorber. Conversely, the air‐side heat transfer rate increases from 120 to 157.6 W, benefiting from enhanced heat transfer facilitated by higher temperature difference. Thermal efficiency shows a slight decline, dropping from 82.5% to 77.5% with higher inlet water temperatures. The effect of air mass flow rates (0.01–0.026 kg/s) and water mass flow rates (0.015–0.06 kg/s) on thermal efficiency were investigated, showing a 1.77% improvement in efficiency for air and a 5.13% increase in water flow rates. These findings emphasize the advantages of dual‐purpose solar air water heater systems, achieving an average thermal efficiency of about 80%, which is significantly higher than the 77.6% and 27.8% efficiency of a comparable single‐purpose solar air heater (SAH) and solar water heart, respectively.

This paper presents a numerical analysis of interaction between non-gray radiation and laminar forced convection flow in a duct with an expansion. Distributions of absorption coefficients across the spectrum (50 cm −1 < η < 20000 cm −1 ) are obtained from the HITRAN2008 database. The full spectrum k-distribution method (FSK) is used to deal with the non-gray part of the problem, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. In addition, the results of non-gray medium are compared with the gray results in order to judge if the differences between these two approaches are significant enough to justify the usage of non-gray models. Results show that for air mixtures with different mole fractions of CO 2 and H 2 O, use of gray model for the radiative properties may leads to considerable errors and should be eschewed.

A numerical investigation of entropy generation in laminar forced convection of gas flow over a recess including two inclined backward and forward facing steps in a horizontal duct under bleeding condition is presented. For calculation of entropy generation from the second law of thermodynamics in a forced convection flow, the velocity and temperature distributions are primary needed. For this purpose, the two-dimensional Cartesian coordinate system is used to solve the governing equations which are conservations of mass, momentum and energy. These equations are solved numerically using the computational fluid dynamic techniques to obtain the temperature and velocity fields, while the blocked region method is employed to simulate the inclined surface. Discretized forms of these equations are obtained by the finite volume method and solved using the SIMPLE algorithm. The numerical results are presented graphically and the effects of bleeding coefficient and recess length as the main parameters on the distributions of entropy generation number and Bejan number are investigated. Also, the effect of Reynolds number and bleeding coefficient on total entropy generation which shows the amount of flow irreversibilities is presented for two recess length. The use of present results in the design process of such thermal system would help the system attain the high performance during exploitation. Comparison of numerical results with the available data published in open literature shows a good consistency. nema

This research work presents a numerical investigation of three-dimensional combined convection-radiation heat transfer over a recess including two inclined steps in a horizontal duct. To simulate the inclined surface boundaries, the blocked off method is employed for both fluid mechanic and radiation problems. The fluid is treated as a gray, absorbing, emitting and scattering medium. In numerical solution of the governing equations including conservation of mass, momentum and energy, the three-dimensional Cartesian coordinate system is used. These equations are solved numerically using the CFD techniques to obtain the temperature and velocity fields. Discretized forms of the governing equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, all of the convection, conduction and radiation terms are presented in the energy equation. For computation of radiative term in energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution inside the radiating medium. The effects of radiation-conduction parameter, optical thickness and albedo coefficient on heat transfer behavior of the system are presented. Comparison of numerical results with the available data published in open literature shows a good agreement.

In this research, the coupling between non-gray radiation and separation convection flow in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to deal with the non-gray part of the problem, while the gray radiation calculations are performed using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). The effects of radiation-conduction parameter, scattering coefficient and wall emissivity on thermal behaviors are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results as a real case. The results show that in many cases, use of gray simulations is not acceptable and leads to significant errors, especially in non-scattering medium with high values of radiation-conduction parameter and wall emissivity.

The present work investigates the laminar forced convection flow of a radiating gas over an inclined backward facing step (BFS) in a horizontal duct. The momentum and energy equations are solved numerically by the CFD techniques to obtain the velocity and temperature fields. Since, the twodimensional Cartesian coordinate system is used to solve the governing equations; the flow over inclined surface is simulated by considering the blocked-off region in regular grid. Discretized forms of the governing equations in the (x,y) plane are obtained by the control volume method and solved using the SIMPLE algorithm. The fluid is treated as a gray, absorbing, emitting and scattering medium. Therefore, all of the convection, conduction and radiation heat transfer mechanisms take place simultaneously in the gas flow. For computation of the radiative term in the gas energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the radiative heat flux distribution inside the radiating medium. In the numerical results, effects of inclination angle, optical thickness, scattering albedo and the radiation-conduction parameter on the heat transfer behavior of the convection flow are investigated. This research work is a new one in which a combined convection-radiation thermal system with a complex flow geometry is simulate by efficient numerical techniques. nema

Radiation is a major component of heat transfer in the modeling of furnaces. In this study, coupled radiative and conductive heat transfer problems are analyzed in complex geometries with inhomogeneous and anisotropic scattering participating media. A 3-D model is developed using combination of the discrete ordinates method and blocked-off-region procedure. The finite volume method has been adopted to solve the energy equation and the radiative source term in the energy equation is computed from intensities field. The accuracy of radiative conductive model is verified by comparison with benchmark solutions from the literature. As an example of engineering problems, radiative-conductive heat transfer in a furnace model with gray, inhomogeneous, and anisotropic scattering media is numerically studied. The distributions of temperature and heat flux in the furnace are analyzed for different thermoradiative parameters such as conduction-radiation parameter, scattering albedo, and anisotropic scattering coefficient. The numerical algorithm described is found to be fast and reliable for studying combined conductive and radiative heat transfer in 3-D irregular geometries.

This paper presents a numerical study about lubricant inertia effect on thermohydrodynamic (THD) characteristics of Rayleigh step bearings running under steady, incompressible and laminar condition. To reach this goal, the set of governing equations is solved numerically with and without considering the inertia terms. The discretized forms of the momentum and energy equations are obtained by the finite volume method and solved using the Computational Fluid Dynamic (CFD) technique. These equations are solved simultaneously because the dependency of lubricant viscosity with temperature. The hydrodynamic and thermal behaviors of the slider step bearings are demonstrated by presenting several figures including the lubricant pressure and temperature distributions with and without considering the fluid inertia effect. Numerical results show that inertia term has considerable effect on THD characteristics of step bearings, especially when they run with high velocity of runner surface.

Radiation is a major component of heat transfer in the modeling of furnaces. In this study, coupled radiative and conductive heat transfer problems are analyzed in complex geometries with inhomogeneous and anisotropic scattering participating media. A three-dimensional model is developed using combination of the discrete ordinates method and blocked-off-region procedure. The finite volume method has been adopted to solve the energy equation and the radiative source term in the energy equation is computed from intensities field. The accuracy of radiative conductive model is verified by comparison with benchmark solutions from the literature. As an example of engineering problems, radiative-conductive heat transfer in a furnace model with gray, inhomogeneous and anisotropic scattering media is numerically studied. The distributions of temperature and heat flux in the furnace are analyzed for different thermoradiative parameters such as conduction-radiation parameter, scattering albedo and anisotropic scattering coefficient. The numerical algorithm described is found to be fast and reliable for studying combined conductive and radiative heat transfer in three-dimensional irregular geometries.