1,721,012 research outputs found
Effects of viscous dissipation on laminar forced convection with axially periodic wall heat flux
No full textThe laminar forced convection in a circular duct is investigated in the case of a sinusoidal axial variation of the wall heat flux. The axial heat conduction in the fluid is neglected, while the effect of viscous dissipation is taken into account. The heat transfer in the thermally developed region, where the temperature is the sum of a linear function and a periodic function of the axial coordinate, is analyzed. Both the temperature field and the local Nusselt number are evaluated analytically. Comparisons with the solution in the absence of viscous heating are performed. It is shown that the effect of viscous dissipation on the temperature field may be relevant especially in the case of a sinusoidal wall heat flux distribution with a vanishing mean value
Effect of viscous dissipation on mixed convection heat transfer in a vertical tube with uniform wall heat flux
No full textThe laminar and parallel flow of a Newtonian fluid in a vertical cylindrical duct with circular cross section has been analysed. Both the viscous dissipation effect and the buoyancy effect have been taken into account. The momentum balance equation and the energy balance equation have been solved by means of a perturbation method, in the case of a uniform heat flux prescribed at the wall of the duct. The velocity distribution, the temperature distribution, the Nusselt number and the Fanning friction factor have been evaluated analytically. Moreover, the velocity and temperature of the fluid have been compared with those obtained in two special cases: forced convection with viscous dissipation (i.e. negligible buoyancy effect); mixed convection with negligible effects of viscous dissipation
Forced convection in a circular duct with periodic boundary conditions and axial heat conduction
No full textAn investigation of the effect of axial heat conduction in the fluid on laminar forced convection is performed in a cylindrical duct with circular cross section. Two different kinds of boundary conditions are analyzed: (a) a wall temperature distribution which undergoes a sinusoidal axial variation; (b) a wall heat flux distribution which undergoes a sinusoidal axial variation and such that its mean value is equal to the modulus of the amplitude. Reference is made to the hydrodynamically and thermally developed region, where the temperature distribution is given in case (a) by an axially periodic function and in case (b) by the sum of an axially periodic function and a linear function of the axial coordinate. The temperature distribution within the fluid and the local and mean Nusselt number have been evaluated analytically
Effect of a magnetic field on the couette forced convection of a buongiorno’s nanofluid over an embedded cavity
Full text linkThe paper investigates the effect of a magnetic field on the forced convection of a nanofluid in a channel with an embedded cavity. The nanofluid is described by the Buongiorno’s model, and a fixed temperature boundary condition is prescribed. The governing equations are written in a dimensionless form and solved numerically by employing COMSOL Multiphysics. The obtained velocity, temperature and concentration fields are presented as function of the governing parameters, and the Nusselt number on the upper boundary is evaluated as well. Particular attention is paid to the effect of the inclination angle of the magnetic field, showing that variations up to 40% may affect the Nusselt number
A concentrated-parameter model for the validation of a tractor heating system during artificial winter conditions
Full text linkIn the present paper, a concentrated-parameter model is presented, in order to simulate the behavior of a climatic chamber suitably designed for testing tracked and wheeled tractors. Reference is made to standard-severe winter conditions (–18°C), i.e., the tractor dissipates thermal power in a climatic chamber that reproduces winter temperature and humidity conditions. The software package Matlab-Simulink is utilized and the system under investigation consists of 5 blocks. The dynamic modeling first covers a 10 hours period to reach the prescribed conditions for the climatic test chamber. Then, after this preparation period, the tractor’s engine is supposed to work. The simulations show that higher values of the adduction coefficient are preferable since they allow obtaining quickly, and with a lower heating power, the desired comfort conditions for the machine’s cabin
The scop of an air source heat pump: Comparison between on-off and inverter heat pump
Full text linkThe paper investigates the seasonal performance of electric air-to-water heat pump comparing an on-off heat pump with an inverter-driven variable speed compressor. Reference is made to a heat pump for domestic space heating installed in Bologna, and the bin-method proposed by UNI/TS 11300-4 is employed in order to investigate the effect of external temperature. The analysis shows that the inverter heat pump performs better than the on-off one, displaying higher values of SCOP about at least 10%
Replacement of gas boilers with air source heat pumps: An economic analysis based on a trnsys evaluation and on the actual energy prices in Italy
Full text linkIn this work, we investigate the replacement of a gas boiler with an electric air-to-water heat pump (AWHP) as a heating generation system for a detached single-family house. Attention is paid to the recent increase in energy prices in Italy. The evaluation of the energy consumption is done via a dynamic analysis performed by employing Trnsys. The investment results are economically advantageous only if the thermal energy demand is quite high, and the recent energy price increase (for both natural gas and electricity) leads to disadvantages in replacing the heat generation system in all the considered cases
Accoppiamento fluido-parete nella convezione forzata in un canale piano parallelo con flusso termico sinusoidale
No full textConjugate forced convection heat transfer in a plane channel: Longitudinally periodic regime
No full textEntropy optimization of a FENE-P viscoelastic model: a numerically guided comprehensive analysis
Full text linkThe influence of polymers on entropy generation processes is substantial, particularly in the fields of fluid dynamics and rheology. The FENE-P (Finitely Extensible Nonlinear Elastic-Peterlin) model describes the polymer’s dynamics as a result of the interaction between the stretching caused by the velocity gradient and the elastic force that restores the polymer to its equilibrium position. Models such as FENE-P aid in understanding and predicting polymer flow behaviour allowing for the reduction of entropy generation by optimizing system designs. A continuum approach is employed to express the heat flux vector and polymer confirmation tensor of the model. The study investigates the complex relationship between polymer conformation, flow dynamics, and heat transfer taking into account the thermophoresis (Soret effect) and mass diffusion-thermal diffusion coupling (Dufour effect) phenomena to optimize processes by reducing entropy. This study illuminates polymer’s significance in entropy minimization, improving engineering design methodologies and applications in materials science, chemical engineering, and fluid dynamics. As result, the presence of polymers leads to a substantial decrease in the total entropy of the system. This understanding provides opportunities for enhancing heat transfer systems, thereby facilitating the development of more efficient and sustainable technology
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