Nicolas Galanis - Academia.edu (original) (raw)

Papers by Nicolas Galanis

Revue Générale de Thermique, 1997

In this work, we study numerically the heat transfer and fluid flow inside a circular inclined tu... more In this work, we study numerically the heat transfer and fluid flow inside a circular inclined tube. The thermal boundary condition is that of a constant and uniform (axially and circumferentially) heat flux on the tube wall. A finite volume method is used to solve, in dimensionless form, the parabolic equations of mixed convection. The results, obtained for water with

International Journal of Refrigeration-revue Internationale Du Froid, Dec 1, 2012

ABSTRACT This paper presents the performance of an ammonia-water absorption chiller. This single-... more ABSTRACT This paper presents the performance of an ammonia-water absorption chiller. This single-stage 10 kW absorption chiller is cooled with a water-ethylene glycol solution. The required heat source is hot water between 75 degrees C and 85 degrees C. Different operating conditions can be imposed by varying temperatures and flow rates of secondary circuits and the flow of the rich solution. This equipment, designed for solar air conditioning applications, was tested under various operating conditions to assess its performance. This study shows that the performance of the absorption chiller decreases significantly with the evaporator temperature. This is due to a problem of partial evaporation in the evaporator when the absorption machine is operated outside its design specifications. Cooling capacity oscillations, caused by refrigerant expansion control, were also observed. Absorption chiller performance is also influenced by heat source temperature, cooling temperatures and flow of the rich solution.

The active water-circulation solar heating system of an experimental house near the city of Quebe... more The active water-circulation solar heating system of an experimental house near the city of Quebec, Canada, is simulated numerically using the TRNSYS program (Klein et al., 1978) to evaluate the effects of various modifications on the efficiency. Configurations modeled are the classic system (CS) with on-off freeze-protection control, CS with an optimized continuous-flow control, a modified system (MS) as proposed

HAL (Le Centre pour la Communication Scientifique Directe), 2005

ABSTRACT Purpose - To determine the axial evolution of the hydrodynamic and the thermal fields fo... more ABSTRACT Purpose - To determine the axial evolution of the hydrodynamic and the thermal fields for mixed convection in inclined tubes and to investigate the presence of flow reversal. Design/methodology/approach - The elliptical, coupled, steady state, three-dimensional governing partial differential equations for heated ascending laminar mixed convection in an inclined isothermal tube were solved numerically using a finite volume staggered grid approach. Findings - The axial evolution of the velocity profiles and fluid temperatures show that upstream diffusion has an important effect near the inlet of the heating region. As a result, both the wall shear stress and the Nusselt number are affected upstream of the heating zone. Flow reversal occurs of GF=9?×?10 5 . The shape and size of the region with negative velocities depends strongly on the value of the Grashof number. The effect of the Grashof number on the axial evolution of the wall shear stress and the Nusselt number is shown to be very important in the region of developing flow. Research limitations/implications - The results have been calculated for one Reynolds number (Re=100), a single fluid (air) and one tube inclination (45°). Practical implications - Further results of this type can be mapped and would be useful for heat exchanger design. Originality/value - This is the first time that flow reversal has been calculated numerically for inclined tubes. Most previous studies concern horizontal or vertical tubes and use axially parabolic equations which are easier to solve but can not calculate the flow field in the region with backflow.

HAL (Le Centre pour la Communication Scientifique Directe), 2008

International audienc

Transactions of The Canadian Society for Mechanical Engineering, Jun 1, 2002

This paper presents a numerical study of periodic, developing, laminar, incompressible flow in a ... more This paper presents a numerical study of periodic, developing, laminar, incompressible flow in a straight horizontal tube subject to low frequency oscillations about the vertical diameter at its entrance. The three-dimensional flow field is influenced by the tangential and Coriolis forces and is governed by three independent parameters: the flow Reynolds number Re, the oscillation Reynolds number Reω (based on the tub’s oscillation frequency ω) and the angular amplitude A of the tube’s oscillation. It is characterized by a periodic secondary transverse flow, normally consisting of two symmetrical vortices, and an oscillating axial field. The local friction factor exhibits large variations along the tube;s circumference. Its average value is higher than the corresponding value for stationary tubes, and increases with both Reω and A. At high Reω the tube’s oscillation can induce flow reversal, the limits of this flow reversal have been established in terms of the three governing parameters. Finally, the exi...

ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Associat... more ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

Ashrae Transactions, 1986

Inconsistencies are shown to exist in the presentation and formulation of the ASHRAE solar radiat... more Inconsistencies are shown to exist in the presentation and formulation of the ASHRAE solar radiation model. To remove them, it is proposed: 1. To include in the Fundamentals Handbook the clearness number in the expressions for the direct and, in particular, the sky diffuse irradiation under cloudless conditions, and 2. To rewrite the expressions for cloud sky conditions so that

Ashrae Transactions, 1985

Hourly values of the global and diffuse solar radiations incident on a horizontal surface, calcul... more Hourly values of the global and diffuse solar radiations incident on a horizontal surface, calculated with the ASHRAE and WON models at four locations in eastern Canada, are compared to the corresponding measured values. The comparison is carried out monthly for the period 1973 through 1976. The agreement is good for the summer months, but large discrepancies are observed during

International Journal of Thermal Sciences, Jul 1, 1999

The developing flow with mixed laminar convection in an inclined tube has been studied numericall... more The developing flow with mixed laminar convection in an inclined tube has been studied numerically for four different thermal boundary conditions: a uniform heat flux is applied over the entire circumference or its top half at either the outer tube surface or the fluid-solid interface. The calculated results for local parameters (circumferential distribution of the interfacial temperature, axial velocity profile, etc.) and for average variables (circumferentially average values of the Nusselt number and of the interfacial shear stress) are quite different, especially for high values of Grashof number. Thus, for Gr = 106, Re = 500 and Pr = 7, the asymptotic average Nusselt number for a uniform heat flux applied over the entire outer tube surface is 16.47; the corresponding values for a heat flux applied on the fluid-solid interface is 26.14 for uniform flux over the entire circumference and 29.71 for a heat flux applied only on the top half of the interface.

Energy and Buildings, May 1, 2009

A model of the transient heat transfer between the ground under and around the foundations of an ... more A model of the transient heat transfer between the ground under and around the foundations of an indoor ice rink and the brine circulating in pipes embedded in the concrete slab under the ice has been coupled with a previously developed model calculating heat fluxes towards the ice by convection, radiation and phase changes. Subroutines calculating the energy consumption for heating and humidifying (or cooling and reheating) the ventilation air have also been added to the model. The resulting simulation tool has been used to calculate monthly refrigeration loads and energy consumption by the ventilation system, the lights, the brine pump, the radiant heating system of the stands and the underground electric heating used to prevent freezing and heaving for four North American cities with very different climates. Correlations expressing the energy consumption of the ventilation air stream in terms of the sol-air temperature are formulated.

International Journal of Heat and Mass Transfer, Feb 1, 2009

WIT transactions on engineering sciences, Apr 10, 2002

fins is significantly greater than that from the bottom fins. and hydrodynamic fields are quite d... more fins is significantly greater than that from the bottom fins. and hydrodynamic fields are quite different and that the heat loss from the top linearly with the temperature of the solid, show that the corresponding thermal numerically for bare and finned tubes. The results, for heat losses varying a horizontal tube and conduction in the surrounding solid have been solved The coupled non-linear PDEs modeling developing laminar mixed convection in 1. Introduction considerably in the entrance regionof the tube. than the corresponding value for forced convection and that it varies show that the heat transfer coefficient, or Nusselt number, is significantly higher the solid-fluid interface or at the outer surface of the tube. All of these studies 4, 51 for isothermal and uniform or non-uniform flux conditions applied at either thermal fields have been investigated experimentally [ l , 2 1 and numerically 13, flow induced by the buoyancy force and its effects on the hydrodynamic and many applications such as solar collectors and nuclear reactors. The secondary Combined free and forced convection in the entrance region of tubes occurs in strongly dependent on the local flow conditions. The performance of flat plate temperature fields are three-dimensional and that the heat transfer coefficient is have confirmed the results for bare tubes, namely that the hydrodynamic and in tubes with longitudinal internal fins 161 or with external annular fins 171. They Several other studies have investigated the hydrodynamic and thermal fields

Mechanics Research Communications, Mar 1, 2006

... 1a, has received much attention from the researchers. In the past, many experimental solar po... more ... 1a, has received much attention from the researchers. In the past, many experimental solar ponds have been constructed, operated and instrumented around the world; see in particular (Folchitto, 1997, Alagao, 1994, Al-Marafie, 1991, Reid, 1989 and Joyce, 2001). ...

Numerical Heat Transfer Part A-applications, Feb 1, 1998

Laminar upward and downward flows with mixed convection in a thin vertical tube with a short unif... more Laminar upward and downward flows with mixed convection in a thin vertical tube with a short uniformly heated section were investigated numerically. Calculations were performed by solving the elliptic Navier-Stokes and energy equations for slow flows of air ( Pr = 0.7) corresponding to low Reynolds numbers from 20 to 500 and a wide range of Grashof numbers. Results reveal

International Journal of Numerical Methods for Heat & Fluid Flow, Mar 27, 2009

PurposeThe aim is to study the conjugate problem of developing laminar mixed convection flow and ... more PurposeThe aim is to study the conjugate problem of developing laminar mixed convection flow and heat transfer of water‐Al2O3 nanofluid inside an inclined tube submitted to a uniform wall heat flux.Design/methodology/approachThe set of non‐linear, coupled and fully elliptic governing equations has been solved using a “finite‐control‐volume” numerical method, the classical power‐law scheme for computing heat and momentum fluxes staggered and non uniform grids for spatial discretization of various regions of the tube.FindingsNumerical results have shown that the presence of nanoparticles slightly intensifies the secondary flow due to buoyancy, in particular in the developing region. It also increases the average Nusselt number and decreases slightly the product ReCf with respect to those of water. For the horizontal inclination, two new correlations have been proposed to calculate these two variables in the fully developed region, for Grashof number ranging from 103 to 105 and particle volume concentrations up to 7 per cent.Practical implicationsThe results of this study can be employed for various practical heat transfer and thermal applications using nanofluids.Originality/valueThe present study constitutes an original contribution to the knowledge of nanofluid thermal behaviour.

Applied Energy, Apr 1, 2010

A parametric study and optimization is performed on a transcritical power cycle using six perform... more A parametric study and optimization is performed on a transcritical power cycle using six performance indicators: thermal efficiency, specific net output, exergetic efficiency, total UA and surface of the heat exchangers as well as the relative cost of the system. The independent parameters are the maximum temperature and pressure of the cycle as well as the net power output. Results show that it is impossible to simultaneously optimise all six performance indicators, i.e. that the values of the independent parameters are not the same for all the optimizations. The design value for these parameters is therefore a matter of choice, or compromise, among the combinations optimising the performance indicators. For a limited low temperature heat source the parametric studies reveal the existence of a maximum value for the net power output of the system and of another net power output minimising the cost per kW. A comparison of optimised results for three working fluids (CO 2 , ethane, R125) shows that the better fluid depends on the optimised indicator and clearly indicates that a simple first law analysis is not sufficient for the selection of a working fluid. In summary, this paper demonstrates the need to achieve a multi-point optimization and comparison in order to study adequately a transcritical power system.

Journal of Solar Energy Engineering-transactions of The Asme, Aug 1, 1984

An algorithm based on daily hours of bright sunshine has been developed and used to evaluate the ... more An algorithm based on daily hours of bright sunshine has been developed and used to evaluate the performance of active solar heating systems for different values of system parameters (collector area and efficiency curves; orientation and inclination; storage capacity; heating load). Comparisons of monthly and annual results with those obtained by other methods using measured values of global horizontal radiation show good results. The results were used to construct charts (for southern Que´bec in this case) which do not require values of solar radiation for the prediction of the system’s performance.