Gianni Comini - Academia.edu (original) (raw)

Papers by Gianni Comini

Journal of Heat Transfer, 1982

In this paper we describe a system of computer programs based on the finite element method, which... more In this paper we describe a system of computer programs based on the finite element method, which can be used for the calculation of coupled velocity and temperature fields during freezing and thawing of soils in the presence of seepage flow. In the programs, the mass and energy conservation equations are solved simultaneously, without the use of too limiting assumptions. The results of the computations are compared with experimental measurements made on a laboratory model of a soil freezing system, and the agreement between measured and computed values is good.

Journal of Heat Transfer, 1977

In many practical situations, adequate thermal design of pavement structures in seasonal frost ar... more In many practical situations, adequate thermal design of pavement structures in seasonal frost areas can be done by utilizing a model based on heat conduction alone. In this paper we present a system of computer programs which allow the solution of practically any nonlinear heat conduction problem in soils, provided that a two-dimensional description, plane or axisymmetric, is possible. The finite element method, together with the empirical correlations for thermal properties and boundary conditions, is used in the simulations. Predictions of the thermal regime in different structures are favorably compared with the results of experimental measurements, both for long-term and short-term temperature variations.

Numerical Heat Transfer Part B-fundamentals, 1997

The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems ... more The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems in two-dimensional incompressible flows. The Bubnov-Galerkin finite-element method and a sequential procedure are employed to discretize and solve the governing differential equations. Very accurate results are obtained by employing “advective derivative conditions” at the outflow for all the variables involved. The boundary conditions for the streamfUnction at internal walls are imposed during the assembly process, and the vorticity at inflow and wall boundaries is evaluated in the framework of the stream/unction equation. The accuracy of the approach is demonstrated by the solution of two well-known benchmark problems concerning forced convection over a circular cylinder in cross flow and mixed convection in a plane channel heated from below.

Numerical Heat Transfer Part B-fundamentals, 1996

The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin fini... more The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin finite-element methods. The accuracy reached is estimated on the basis of five test problems for which exact analytical solutions are available. The comparison concerns the calculation of temperature distribution and the computation of nodal heat flow rates over external and internal boundaries. In the numerical solution, rectangular elements of

… of Numerical Methods for Heat …, 2002

... Article Type: Research Paper. Keyword(s): Numerical simulation; Convection; Heat transfer. Jo... more ... Article Type: Research Paper. Keyword(s): Numerical simulation; Convection; Heat transfer. Journal: International Journal of Numerical Methods for Heat & Fluid Flow. Volume: 12. ... Two wavychannels of finite width have been investigated by Ali and Ramadhyani (1992). ...

International Journal of Refrigeration, 1978

La methode des elements finis dans la technique du from La rnethode des elements finis, tout d'ab... more La methode des elements finis dans la technique du from La rnethode des elements finis, tout d'abord developee pour resoudre des problemes d'elasticite, est maintenant employee largement dans la technique du froid pour la resolution des problemes de conduction lineaire et non lineaire. On donne dans le texte quelques exemples d'application de la methode dont on presente aussi les developpements possibles se rapportant a la technique du froid.

Letters in Heat and Mass Transfer

ABSTRACT

International Journal of Numerical Methods for Heat & Fluid Flow, 2003

By neglecting the influence of tubes, this paper adopts a simplified two-dimensional approach to ... more By neglecting the influence of tubes, this paper adopts a simplified two-dimensional approach to deal with laminar convection of air through wavy finned-tube exchangers. Pressure drop and heat transfer characteristics are investigated in the fully developed region of the flow channels between adjacent fins. The solutions are presented for several space ratios (height over length of a module) and two

International Journal of Numerical Methods for Heat & Fluid Flow, 1999

ABSTRACT Three-dimensional flows over backward facing s.tif are analysed by means of a finite ele... more ABSTRACT Three-dimensional flows over backward facing s.tif are analysed by means of a finite element procedure, which shares many features with the SIMPLER method. In fact, given an initial or guessed velocity field, the pseudovelocities, i.e. the velocities that would prevail in the absence of the pressure field, are found first. Then, by enforcing continuity on the pseudovelocity field, the tentative pressure is estimated, and the momentum equations are solved in sequence for velocity components. Afterwards, continuity is enforced again to find corrections that are used to modify the velocity field and the estimated pressure field. Finally, whenever necessary, the energy equation is solved before moving to the next step.

ABSTRACT Most compact heat exchangers and heat dissipating components rely on convection enhancem... more ABSTRACT Most compact heat exchangers and heat dissipating components rely on convection enhancement mechanisms that reduce the continuous growth of boundary layers. Usually surface irregularities, in the form of interruptions and/or vortex generators, are introduced in the flow passages. The resulting geometric configurations are periodic in space and, after a short distance from the entrance, induce velocity and thermal fields that repeat themselves from module to module. The numerical models presented here consider the space-periodicity and allow flows that are stationary at sub-critical values of the Reynolds number, but become time-periodic, or quasi periodic, above the critical value of the Reynolds number. Space discretizations are achieved by an equal order finite element procedure based on a projection algorithm. Two-dimensional schematizations are employed to analyze the effects of surface interruptions and transverse vortex generators, while three-dimensional schematizations are employed for longitudinal vortex generators.

Journal of Heat Transfer, 1979

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1993

Finite-element formulations for coupled conduction and convection problems are obtained by a dire... more Finite-element formulations for coupled conduction and convection problems are obtained by a direct approach based on energy balances, at both element and node levels. This way, clear physical interpretations are provided for all the essential steps of conventional finite-element procedures of the Galerkin type. In the examples, the finite-element formulation is validated first by comparison with the analytical solution of

Numerical Heat Transfer, Part B: Fundamentals, 2000

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1997

The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems ... more The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems in two-dimensional incompressible flows. The Bubnov-Galerkin finite-element method and a sequential procedure are employed to discretize and solve the governing differential equations. Very accurate results are obtained by employing “advective derivative conditions” at the outflow for all the variables involved. The boundary conditions for the streamfUnction at internal walls are imposed during the assembly process, and the vorticity at inflow and wall boundaries is evaluated in the framework of the stream/unction equation. The accuracy of the approach is demonstrated by the solution of two well-known benchmark problems concerning forced convection over a circular cylinder in cross flow and mixed convection in a plane channel heated from below.

Numerical Heat Transfer, Part B: Fundamentals, 1996

The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin fini... more The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin finite-element methods. The accuracy reached is estimated on the basis of five test problems for which exact analytical solutions are available. The comparison concerns the calculation of temperature distribution and the computation of nodal heat flow rates over external and internal boundaries. In the numerical solution, rectangular elements of

Numerical Heat Transfer, Part B: Fundamentals, 1985

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1988

ABSTRACT A finite-element procedure for the prediction of laminar forced convection in three-dime... more ABSTRACT A finite-element procedure for the prediction of laminar forced convection in three-dimensional parabolic flows is presented. The procedure, based on the parabolized simplification of the complete Navier-Stokes equations, is first validated by comparing computed results with the available literature data for thermally and hydrodynamically developing flows in flat channels. Then, new results are presented for simultaneously developing flows in square duels, with ,and, and ,and boundary conditions and Prandtl number ranging from 0.1 to 10.

Numerical Heat Transfer, Part B: Fundamentals, 1982

... by using the proper form of algorithm (39) and the values of the stream function can be ... T... more ... by using the proper form of algorithm (39) and the values of the stream function can be ... Theformulation in the preceding section is general and applicable to any type of finiteelement ... A simpleFEM generator routine was also used to speed up the preparation of geometric input ...

Numerical Heat Transfer, Part B: Fundamentals, 1981

A finite-element marching procedure is presented for the calculation of transport processes in th... more A finite-element marching procedure is presented for the calculation of transport processes in three-dimensional parabolic flows. As in corresponding finite-difference procedures, equations are solved one after the other. Similarly, longitudinal and cross-stream pressure gradients are uncoupled. Velocity fields are determined by first calculating intermediate velocity values based on estimated pressure gradient distributions and then obtaining appropriate corrections so as to

Numerical Heat Transfer, Part B: Fundamentals, 1979

This paper presents a generally applicable approach to laminar heat transfer problems in the entr... more This paper presents a generally applicable approach to laminar heat transfer problems in the entrance region of ducts. Consideration is given to the general situation in which ducts have arbitrary but constant cross sections. The finite-element method is used in the simultaneous step-by-step integration of the momentum and energy equations. Several illustrative examples demonstrate the versatility of the proposed technique and permit an evaluation of its accuracy.

Journal of Heat Transfer, 1982

In this paper we describe a system of computer programs based on the finite element method, which... more In this paper we describe a system of computer programs based on the finite element method, which can be used for the calculation of coupled velocity and temperature fields during freezing and thawing of soils in the presence of seepage flow. In the programs, the mass and energy conservation equations are solved simultaneously, without the use of too limiting assumptions. The results of the computations are compared with experimental measurements made on a laboratory model of a soil freezing system, and the agreement between measured and computed values is good.

Journal of Heat Transfer, 1977

In many practical situations, adequate thermal design of pavement structures in seasonal frost ar... more In many practical situations, adequate thermal design of pavement structures in seasonal frost areas can be done by utilizing a model based on heat conduction alone. In this paper we present a system of computer programs which allow the solution of practically any nonlinear heat conduction problem in soils, provided that a two-dimensional description, plane or axisymmetric, is possible. The finite element method, together with the empirical correlations for thermal properties and boundary conditions, is used in the simulations. Predictions of the thermal regime in different structures are favorably compared with the results of experimental measurements, both for long-term and short-term temperature variations.

Numerical Heat Transfer Part B-fundamentals, 1997

The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems ... more The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems in two-dimensional incompressible flows. The Bubnov-Galerkin finite-element method and a sequential procedure are employed to discretize and solve the governing differential equations. Very accurate results are obtained by employing “advective derivative conditions” at the outflow for all the variables involved. The boundary conditions for the streamfUnction at internal walls are imposed during the assembly process, and the vorticity at inflow and wall boundaries is evaluated in the framework of the stream/unction equation. The accuracy of the approach is demonstrated by the solution of two well-known benchmark problems concerning forced convection over a circular cylinder in cross flow and mixed convection in a plane channel heated from below.

Numerical Heat Transfer Part B-fundamentals, 1996

The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin fini... more The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin finite-element methods. The accuracy reached is estimated on the basis of five test problems for which exact analytical solutions are available. The comparison concerns the calculation of temperature distribution and the computation of nodal heat flow rates over external and internal boundaries. In the numerical solution, rectangular elements of

… of Numerical Methods for Heat …, 2002

... Article Type: Research Paper. Keyword(s): Numerical simulation; Convection; Heat transfer. Jo... more ... Article Type: Research Paper. Keyword(s): Numerical simulation; Convection; Heat transfer. Journal: International Journal of Numerical Methods for Heat & Fluid Flow. Volume: 12. ... Two wavychannels of finite width have been investigated by Ali and Ramadhyani (1992). ...

International Journal of Refrigeration, 1978

La methode des elements finis dans la technique du from La rnethode des elements finis, tout d'ab... more La methode des elements finis dans la technique du from La rnethode des elements finis, tout d'abord developee pour resoudre des problemes d'elasticite, est maintenant employee largement dans la technique du froid pour la resolution des problemes de conduction lineaire et non lineaire. On donne dans le texte quelques exemples d'application de la methode dont on presente aussi les developpements possibles se rapportant a la technique du froid.

Letters in Heat and Mass Transfer

ABSTRACT

International Journal of Numerical Methods for Heat & Fluid Flow, 2003

By neglecting the influence of tubes, this paper adopts a simplified two-dimensional approach to ... more By neglecting the influence of tubes, this paper adopts a simplified two-dimensional approach to deal with laminar convection of air through wavy finned-tube exchangers. Pressure drop and heat transfer characteristics are investigated in the fully developed region of the flow channels between adjacent fins. The solutions are presented for several space ratios (height over length of a module) and two

International Journal of Numerical Methods for Heat & Fluid Flow, 1999

ABSTRACT Three-dimensional flows over backward facing s.tif are analysed by means of a finite ele... more ABSTRACT Three-dimensional flows over backward facing s.tif are analysed by means of a finite element procedure, which shares many features with the SIMPLER method. In fact, given an initial or guessed velocity field, the pseudovelocities, i.e. the velocities that would prevail in the absence of the pressure field, are found first. Then, by enforcing continuity on the pseudovelocity field, the tentative pressure is estimated, and the momentum equations are solved in sequence for velocity components. Afterwards, continuity is enforced again to find corrections that are used to modify the velocity field and the estimated pressure field. Finally, whenever necessary, the energy equation is solved before moving to the next step.

ABSTRACT Most compact heat exchangers and heat dissipating components rely on convection enhancem... more ABSTRACT Most compact heat exchangers and heat dissipating components rely on convection enhancement mechanisms that reduce the continuous growth of boundary layers. Usually surface irregularities, in the form of interruptions and/or vortex generators, are introduced in the flow passages. The resulting geometric configurations are periodic in space and, after a short distance from the entrance, induce velocity and thermal fields that repeat themselves from module to module. The numerical models presented here consider the space-periodicity and allow flows that are stationary at sub-critical values of the Reynolds number, but become time-periodic, or quasi periodic, above the critical value of the Reynolds number. Space discretizations are achieved by an equal order finite element procedure based on a projection algorithm. Two-dimensional schematizations are employed to analyze the effects of surface interruptions and transverse vortex generators, while three-dimensional schematizations are employed for longitudinal vortex generators.

Journal of Heat Transfer, 1979

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1993

Finite-element formulations for coupled conduction and convection problems are obtained by a dire... more Finite-element formulations for coupled conduction and convection problems are obtained by a direct approach based on energy balances, at both element and node levels. This way, clear physical interpretations are provided for all the essential steps of conventional finite-element procedures of the Galerkin type. In the examples, the finite-element formulation is validated first by comparison with the analytical solution of

Numerical Heat Transfer, Part B: Fundamentals, 2000

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1997

The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems ... more The streamfunction-vorticity formulation is used to analyze unsteady laminar-convection problems in two-dimensional incompressible flows. The Bubnov-Galerkin finite-element method and a sequential procedure are employed to discretize and solve the governing differential equations. Very accurate results are obtained by employing “advective derivative conditions” at the outflow for all the variables involved. The boundary conditions for the streamfUnction at internal walls are imposed during the assembly process, and the vorticity at inflow and wall boundaries is evaluated in the framework of the stream/unction equation. The accuracy of the approach is demonstrated by the solution of two well-known benchmark problems concerning forced convection over a circular cylinder in cross flow and mixed convection in a plane channel heated from below.

Numerical Heat Transfer, Part B: Fundamentals, 1996

The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin fini... more The two-dimensional heat conduction equation is solved by control-volume and Bubnov-Galerkin finite-element methods. The accuracy reached is estimated on the basis of five test problems for which exact analytical solutions are available. The comparison concerns the calculation of temperature distribution and the computation of nodal heat flow rates over external and internal boundaries. In the numerical solution, rectangular elements of

Numerical Heat Transfer, Part B: Fundamentals, 1985

ABSTRACT

Numerical Heat Transfer, Part B: Fundamentals, 1988

ABSTRACT A finite-element procedure for the prediction of laminar forced convection in three-dime... more ABSTRACT A finite-element procedure for the prediction of laminar forced convection in three-dimensional parabolic flows is presented. The procedure, based on the parabolized simplification of the complete Navier-Stokes equations, is first validated by comparing computed results with the available literature data for thermally and hydrodynamically developing flows in flat channels. Then, new results are presented for simultaneously developing flows in square duels, with ,and, and ,and boundary conditions and Prandtl number ranging from 0.1 to 10.

Numerical Heat Transfer, Part B: Fundamentals, 1982

... by using the proper form of algorithm (39) and the values of the stream function can be ... T... more ... by using the proper form of algorithm (39) and the values of the stream function can be ... Theformulation in the preceding section is general and applicable to any type of finiteelement ... A simpleFEM generator routine was also used to speed up the preparation of geometric input ...

Numerical Heat Transfer, Part B: Fundamentals, 1981

A finite-element marching procedure is presented for the calculation of transport processes in th... more A finite-element marching procedure is presented for the calculation of transport processes in three-dimensional parabolic flows. As in corresponding finite-difference procedures, equations are solved one after the other. Similarly, longitudinal and cross-stream pressure gradients are uncoupled. Velocity fields are determined by first calculating intermediate velocity values based on estimated pressure gradient distributions and then obtaining appropriate corrections so as to

Numerical Heat Transfer, Part B: Fundamentals, 1979

This paper presents a generally applicable approach to laminar heat transfer problems in the entr... more This paper presents a generally applicable approach to laminar heat transfer problems in the entrance region of ducts. Consideration is given to the general situation in which ducts have arbitrary but constant cross sections. The finite-element method is used in the simultaneous step-by-step integration of the momentum and energy equations. Several illustrative examples demonstrate the versatility of the proposed technique and permit an evaluation of its accuracy.