Marcelo Moreira Ganzarolli

Natural convection in rectangular enclosures heated from below and symmetrically cooled from the sides

Steady natural convection in an enclosure heated from below and symmetrically cooled from the sides is studied numerically, using a streamfunction-vorticity formulation. The Allen discretization scheme is adopted and the discretized equations were solved in a line by line basis. The Rayleigh number based on the cavity height is varied from 103 to 107. Values of 0.7 and 7.0 for the Prandtl number are considered. The aspect ratio LH (length to height of the enclosure) is varied from 1 to 9. Boundary conditions are uniform wall temperature and uniform heat flux. For the range of the parameters studied, a single cell is observed to represent the flow pattern. Numerical values of the Nusselt number as a function of the Rayleigh number are reported, and the Prandtl number is found to have little influence on the Nusselt number. A scale analysis is presented in order to better understand the phenomenon.

Natural Convection in an Array of Vertical Channels with Two-Dimensional Heat Sources: Uniform and Non-Uniform Plate Heating

An experimental and numerical analysis was performed to investigate the conjugated conduction–convection heat transfer problem in an array of vertical, parallel plates forming open channels with heated protruding elements attached to one of the walls. Uniform and non-uniform heating of the plates was analyzed. Both the distance between plates and power dissipated per plate was varied. In non-uniform heating in each plate and for a specified total heat generation rate, one element was electrically supplied with a different power level from the others, and the influence of the location of this element on the temperature distribution was investigated. The SIMPLEC algorithm, based on the finite volume method, was used to solve the pressure velocity coupling. Numerical and experimental temperature profiles were compared and good agreement was observed.

Optimum Fins Spacing and Thickness of a Finned Heat Exchanger Plate

The thermal design of a counterflow heat exchanger using air as the working fluid was performed with two distinct goals: minimum inlet temperature difference and minimum number of entropy generation units. The heat exchanger was constituted by a double-finned conductive plate closed by adiabatic walls at the fin tips on both sides. The hot and cold air flows were considered in the turbulent regime, driven by a constant pressure head. The thermal load was constant, and an optimization was performed to obtain the optimum fin spacing and thickness, according to the two design criteria. A computer program was employed to evaluate the optimum conditions based on correlations from the literature. The results obtained from both design criteria were compared to each other. A scale analysis was performed considering the first design goal and the corresponding dimensionless parameters were compared with the results from the correlations.

Nitrogen charge temperature prediction in a gas lift valve

The operation of a class of retrievable gas-lift valves (GLV) is controlled by the axial movement of a bellows. One force acting on the bellows is due to the pressure exerted by the nitrogen gas contained in the GLV dome. It depends on the nitrogen temperature, which is influenced by both the production fluid and the injection gas temperatures in the well. This work investigated this dependence for a GLV installed in a side pocket mandrel tube. Three independent procedures were used for this purpose, comprising a compact thermal model, an experimental investigation with a thermal mockup and a numerical analysis. From these, a correlation for the nitrogen temperature was proposed, based on the local production fluid and injection gas temperatures, and on their convective coefficients with the mandrel tube surfaces.

NUMERICAL SIMULATION OF A THERMALLY- DRIVEN OPEN CAVITY WITH A SHROUDING WALL

Natural convection in a square open cavity with and without the presence of a shrouding wall is analyzed. One vertical wall is heated and the horizontal walls are adiabatic. The other vertical wall is open to the ambient or a fluid reservoir. A shrouding wall is placed in front of this open wall forming a vertical open channel. Laminar and two-dimensional flow is assumed for the Rayleigh number ranging from 103 to 107 and the problem is solved numerically by using the Finite Volume-SOLA method. The average Nusselt number is reported for different values of the Rayleigh number and the distance of the shrouding wall to the open cavity.Copyright

Aspect Ratio Effect in a Thermally-Driven Rectangular Open Cavity With an Isothermal Shrouding Wall

Natural convection in a rectangular open cavity with the presence of an isothermal shrouding wall is investigated. The horizontal walls of the cavity are adiabatic. One vertical wall is heated uniformly and another is open to a fluid reservoir. The isothermal shrouding wall is placed in front of this opening forming a vertical channel. Laminar and two-dimensional flow is assumed for a Rayleigh number ranging from 103 - 106 . The numerical solution is carried out with the Finite Volume-SOLA method. The cavity aspect ratios considered are B = L/H = 0.5, 3.0 e 6.0, where L and H are the cavity width and cavity height, respectively. The distance b/H between the isothermal shrouding wall and the cavity opening is considered as 0.5 and 0.2. The effects of the Rayleigh number Ra, the cavity aspect ratios B and the ratio b/H, on the streamlines, isotherms and average Nusselt number are reported.Copyright