Emanuele Habib

Natural Convection Heat and Momentum Transfer in Rectangular Enclosures Heated at the Lower Portion of the Sidewalls and the Bottom Wall and Cooled at the Remaining Upper Portion of the Sidewalls and the Top Wall

Laminar natural convection inside air-filled, rectangular enclosures heated from below and cooled from above, with the lower portions of both sidewalls maintained at the temperature of the bottom wall, and the remaining upper portions of the sidewalls maintained at the temperature of the top wall, is studied numerically. A control volume formulation of the finite-difference method is used for the solution of the mass, momentum, and energy transfer governing equations. Simulations are performed for height-to-width aspect ratios of the cavity from 1 to 5, Rayleigh numbers based on the height of the cavity from 5 × 102 to 5 × 106, and values of the heated fractions of both sidewalls from 0 to 1. It is found that when the heated portions of the two sidewalls are different in length, a steady-state solution is reached, with a basic three-cell flow pattern. In contrast, when the heated fractions of the sidewalls are the same, the asymptotic solution may be either stationary, with a flow field consisting of two pairs of superimposed roll cells, or periodic, with a flow pattern consisting of a primary cell and two secondary cells that pulsate about the center of the enclosure. Dimensionless heat transfer correlating equations are proposed.

Demand Side Management in Microgrids for Load Control in Nearly Zero Energy Buildings

The paper presents a feasible model of architecture for the technical building systems (TBS) particularly suitable for nearly zero energy buildings (NZEBs). The suggested model aggregates the users around an electric node in order to reach up the threshold value of electric power, and to get a more virtuous and flexible cumulative load profile. Present proposal is a full electric common smart micro grid with a single point of connection, with heating and domestic hot water generated by a centralized electric heat pump system. The renewable energy is provided by a photovoltaic field connected to the common grid. A building automation control system operates those electric TBS modulating the global load for a building demand response (DR). The effectiveness of the proposed model consists of exploiting thermal inertia as an energy storage, by forcing both local and central set points of heating and air conditioning systems. The control is based on the integrated and common operation of all users and all systems of the building as one unique “large user.” The integrated management of the grid is operated to control the whole electric demand exploiting the self-consumption, avoiding peaks, and maintaining a flat load profile. The suggested microgrid model allows concretely the possibility to realize a building DR with benefits for the end-users in a consumer view point. A study of the effect of these control opportunities on whole electric demand is done by simulation on a case study.

Correlating equations for laminar free convection from misaligned horizontal cylinders in interacting flow fields

Steady laminar free convection in air from a pair of misaligned, parallel horizontal cylinders, i.e., a pair of parallel cylinders with their axes set in a plane inclined with respect to the gravity vector, is studied numerically. A specifically developed computer code based on the SIMPLE-C algorithm is used for the solution of the dimensionless mass, momentum, and energy transfer governing equations. Results are presented for different values of the center-to-center cylinder spacing from 1.4 up to 10 diameters, the tilting angle of the two-cylinder array from 0 deg to 90 deg, and the Rayleigh number based on the cylinder diameter in the range between 10 3 and 10 7 . It is found that the heat transfer rates at both cylinder surfaces may in principle be traced back to the combined contributions of the so-called plume effect and chimney effect, which are the mutual interactions occurring in the vertical and horizontal alignments, respectively. In addition, at any misalignment angle, an optimum spacing between the cylinders for the maximum heat transfer rate, which decreases with increasing the Rayleigh number, does exist. Heat transfer dimensionless correlating equations are proposed for any individual cylinder and for the pair of cylinders as a whole.

Smart micro grids for Nearly Zero Energy Buildings

The paper presents a feasible model of architecture for the technical building systems (TBS) particularly suitable for Nearly Zero Energy Buildings (NZEBs). NZEBs are buildings where the energetic consumption are optimized by means of solutions that drastically reduce both electric and thermal demand, while residual required energy has to be provided by local renewable generation. The suggested model aggregates the users around an electric node in a common microgrid in order to reach up the threshold value of electric power and to get a more virtuous and flexible cumulative load profile. The building (or a group of buildings) represents the natural limit of the aggregation of the electric systems, like in the heating systems. Present proposal is a full electric smart micro grid with heating and domestic hot water generated by a centralized electric heat pump system. The renewable energy is provided by a photovoltaic field. The authors suggest to control the whole electric demand of the building by exploiting its thermal inertia as an energy storage by forcing both local and central set points of heating and air conditioning systems and time shifting opportunities of smart appliances. A case study is presented.

Free Convection Heat Transfer from a Row of Horizontal Cylinders

Steady laminar free convection in air from parallel circular cylinders set side-by-side is studied numerically. The SIMPLE-C algorithm is used for the solution of the mass, momentum, and energy transfer governing equations. Simulations are performed for tube-arrays consisting of 10 equally-spaced cylinders, for different center-to-center separation distances in the range between 1.4 and 6 cylinder-diameters, and for Rayleigh numbers spanning between 101 and 105.

Demand side management in mixed residential/commercial buildings with PV on site generation

Buildings with mixed residential and commercial units show relevant power peak that re further enhanced by shifting to electric source of nowadays gas-driven systems. The proposed solution is to organize a microgrid for such kind of buildings, aggregating different users with a common electric distribution system with a unique connection to the grid, a local common generation and a common heating/cooling system (electric-driven). This approach upgrades a group of independent several small users with rigid loads and chaotic behavior, to a large user with a flexible and controlled profile. A central building automation control system (BACS) managing all built-in technical systems and smart appliances may control load minute by minute, shifting in time plannable and controllable ones merging different kinds of load, obtaining a flatter diagram. The authors consider the suggested approach convenient to realize demand side management (DSM) for residential/commercial buildings. DSM exploits the flexibility of smart appliances and the thermal inertia of the structure, by imposing local and central set-points of heating and cooling systems according to the actual global net load and generation at a given moment. In the present paper, main aspects of the proposed control system are presented and simulations for a given case study with local PV generation are provided. Results show that this approach may lead to power peak reduction up to 20% even in the unfavorable case of combining commercial and residential units. Moreover, full self-consumption of locally generated energy from RES may be achieved.

Experimental and theoretical analysis of water uptake and swelling kinetics of trabecular tissue from human femur head: some preliminary results

In this paper we firstly illustrate the measurement of the swelling of a single trabecula from human femur heads during water imbibition. Moreover, since the swelling is caused by water diffusing from external surfaces to the core of the sample, by measuring the sample swelling over time, we obtained direct information about the transport of fluids through the intimate constituents of bone, where the mineralization process takes place. We developed an apparatus to measure the free expansion of the tissue during the imbibition. In particular, we measured the swelling along three natural axis (length L, width W and thickness T) of the trabecula. To this aim, a 3D analytical model of the water uptake by the sample was performed according to Fickian transport mechanism. The results have been utilized to fit the measured swelling along the three sample directions (L, W, T) and the apparent diffusion coefficients DT,DW and DL.

Heat Transfer Features of a Horizontal Slot Jet Impinging in Mixed Convection

The mutual interactions occurring between a laminar confined slot jet impinging on a isothermal vertical wall and the natural upward draft promoted by the same target wall, as well as their effects on the local and average heat transfer rates at the target surface, are studied numerically. A specifically developed computer code based on the SIMPLE-C algorithm is used for the solution of the governing equations. Results are presented for different values of the Reynolds number based on the nozzle width in the range between 0 and 400, the Grash of number based on the target wall length in the range between 0 and 108 , and a complete range of geometry parameters (jet nozzle width, length of the target wall, and nozzle-to-target spacing).© 2006 ASME

Natural Convection From a Pair of Parallel Horizontal Circular Cylinders Set in Free Air With Different Alignments

Steady laminar free convection in air from a pair of parallel horizontal cylinders set in a plane inclined with respect to the gravity vector, with the horizontal and vertical positions as special cases, is studied numerically. A specifically developed computer-code based on the SIMPLE-C algorithm is used for the solution of the dimensionless mass, momentum, and energy transfer governing equations. Results are presented for different values of the center-to-center cylinder spacing from 1.4 up to 10 diameters, the tilting angle of the array from 0° to 90°, and the Rayleigh number based on the cylinder-diameter in the range between 103 and 107 .Copyright