Natural convection in a partially open square cavity with internal heat source: An analysis of the opening mass flow

A steady buoyancy-driven flow of air in a partially open square 2D cavity with internal heat source, adiabatic bottom and top walls, and vertical walls maintained at different constant temperatures is investigated numerically in this work. A heat source with 1% of the cavity volume is present in the center of the bottom wall. The cold right wall contains a partial opening occupying 25%, 50% or 75% of the wall. The influence of the temperature gradient between the verticals walls was analyzed for Ra_e = 10³–10⁵, while the influence of the heat source was evaluated through the relation R = Ra_i/Ra_e, investigated at between 400 and 2000. Interesting results were obtained. For a low Rayleigh number, it is found that the isotherm plots are smooth and follow a parabolic shape indicating the dominance of the heat source. But as the Ra_e increases, the flow slowly becomes dominated by the temperature difference between the walls. It is also observed that multiple strong secondary circulations are formed for fluids with a small Ra_e whereas these features are absent at higher Ra_e. The comprehensive analysis is concluded with horizontal air velocity and temperature plots for the opening. The numerical results show a significant influence of the opening on the heat transfer in the cavity.     

Incidence of autochthonous Argentinean mixed starter cultures in ripening of slurry cheese models

The effect of three mixed autochthonous starter cultures in ripening profiles of experimental semihard goat cheeses was evaluated under controlled microbiological conditions. Enterococcus faecium ETC3 and ETC6, Lactobacillus plantarum ETC17 and L. rhamnosus ETC14 were used. Combination of all strains showed the highest level of water soluble nitrogen fraction and total free amino acids (TFAA) at ripening day 1, the lowest level of phosphotungstic acid nitrogen soluble fraction and TFAA at ripening day 64 and the highest global impression. Principal component analyses were performed to establish amino acid profiles relations in the samples.     

TUBE-TO-TUBE HEAT TRANSFER DEGRADATION EFFECT ON FINNED-TUBE HEAT EXCHANGERS

The present work concerns development and application of turbulence models for forced convective heat transfer in ducts. Fully developed flow and temperature fields in straight ducts are considered. The numerical approach is based on the finite volume technique, and a nonstaggered arrangement is employed. The SIMPLEC algorithm is used for handling the pressure-velocity coupling. To achieve fully developed conditions, cyclic boundary conditions are imposed in the main flow direction. The standard k-ε model with wall function is used as a reference. The nonlinear k-ε model of Speziale is applied to calculate the turbulent shear stresses. The turbulent heat fluxes are calculated by three different methods, namely, the simple eddy diffusivity concept, the generalized gradient diffusion hypothesis method and the wealth = earnings × time method. The overall comparison between the methods is presented in terms of the friction factor and average Nusselt number. In particular, the secondary flow field is investigated. The more advanced models show improvement in most cases.     

The Influence of Baffles on the Natural Convection in Trapezoidal Cavities

This article presents an investigation into natural convection in trapezoidal cavities. It examines a cavity whose floor and upper inclined walls are both adiabatic, while the vertical walls are isothermal. For these isothermal walls, we consider two thermal boundary conditions. Under the first condition, the short wall on the left side is heated as the tall one on the right side is cooled. The second condition is the reverse of the first—the short wall is cooled as the tall one is heated. Considering laminar conditions and a two-dimensional system, steady-state computations are carried out to assess the effects of one and two baffles, the baffle's height (H _b ), Rayleigh number, 10³ ≤ Ra ≤ 10⁶, and three Prandtl number values. To demonstrate the various effects, the results from several designed case studies are shown in terms of isotherms, streamlines, and local and average Nusselt numbers in order. Predictions reveal that the second baffle decreases the cavity's fluid flow and heat transfer. As the height of the baffle rises, the heat transfer drops drastically. Also, two baffles produce more pronounced thermal stratification than only one.     

DESIGN AND TUNING OF A FUZZY CONTROLLER FOR INDOOR AIR QUALITY AND THERMAL COMFORT MANAGEMENT

This paper presents the development and testing of a multi objective fuzzy controller. It is dedicated to the control of thermal comfort and indoor air quality while minimising energy consumption and reducing instabilities are other constraints for this controller. After a brief introduction on the difficult task of indoor climate control, the test cell and its corresponding model is described in the second section. The model has been developed within TRNSYS. Section 3 describes the architecture of the fuzzy controller applied to these control objectives in the test cell. A hierarchical architecture has finally been selected since it is a very flexible architecture and it results in reducing the total number of fuzzy rules. The rule optimisation technique, based on genetic algorithms is also presented in the third section. Simulation results are finally presented. They prove that, after optimisation, the fuzzy controller greatly outperforms a typical ON-OFF controller on all control criteria. Energy consumption is in particular reduced by more than 10%. The fourth section of this chapter presents field experiments among 20 subjects of both ON-OFF control and fuzzy control. If major differences are not observed on the thermal comfort and indoor air quality point of view, these experiments however illustrate the importance of on-line tuning of specific fuzzy rules.     

Operating experience with lubricating oils in diesel locomotive engine

Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 10, pp. 21–22, October, 1988.