1,721,015 research outputs found
Optimization of ventilated roofs for livestock housing
No full textThis paper aims at optimizing the performance of roofing components equipped with a ventilated interspace in order to reduce the heat load inside the animal houses. By means of a theoretical model and experimental tests, the three-dimensional profile of the air temperature in the duct is determined. Consequently the air temperature inside a typical house for livestock is calculated. The air flow is considered uniform inside the rectangular duct and the thermal problem is solved by adopting H2 boundary conditions. The air temperature in the house is then calculated and the optimal duct thickness minimizing it was determined
La rete inversa nel teleriscaldamento urbano
No full textVengono confrontate tre possibili configurazioni di reti di teleriscaldamento, con particolare riguardo alla rete inversa, confrontandone costi di impianto e di esercizi
Validation of the NASGE ThermoHydraulic Code by the PGV Experimental Results
No full textTranslating the steam generator functional requirements intospecific design criteria requires a deep knowledge of thermo fluid dynamical behaviour of both sodium (in the external channels) and water. These features are to be emphasized, since the prediction of speed, pressure, temperature in the sodium and water flow can lead to new design criteria aimed at improving the steam generator performance and avoid dangerous and inefficient operating conditions. Hence it is suitable to have computer codes at one’s disposal, to predict the thermo-fluid dynamics of the fluids in the various operating conditions, for steam generators of any size.This paper is devoted to present a preliminary study on a steam generator code, based on a numerical solution of a channel flow model, predicting the pressure, speed and temperature in any external channel, for water and sodium. The approach used to derive the mathematical model is based on the usual channel flow method.The results are compared with two sets of experimental data performed the first on a plexiglass device by Alsthom Tecnique des Fluides, the second on a real prototype by the Electricite de France; the agreement is very satisfactory
Numerical Transient Analysis of Parallel and Counter Flow Heat Exchangers
No full textNumerical transient solutions of parallel and counter current heat transfer processes are obtained by the use of a finite element technique. Solutions provide the one dimensional temperature profile for both fluids of the heat exchangers.The results are verified with steady state and transient analytical or numerical solutions available in literature. The numerical method is applicable to the thermal analysis of anykind of parallel and counter flow heat exchanger with arbitraryinitial and inlet conditions.The main features of the mathematical model, adopted to solve the energy balance equations, is the use of the Galerkin finite elements method to linearize the system of partial differential equations.Very satisfactory results in extremely low computation time arerealized on a medium size computer
LMFBR fuel rod response in natural convection heat decay removal
No full textThis paper describes the fuel rod response in a pool type liquid metal fast breeder reactor, in shutdown natural convection heat removal. The fuel rod response is studied resorting to a finite element technique; the transient temperature and thermal stresses profiles are found.For this aim the code FENHT (Finite Element Nuclear Heat Transfer), has been developed: it is based on a one-dimensional three nodal finite element subdivion of the fuel rod and the solution of the pertinent heat transfer equations is performed by the Crank-Nicholson integration method. Although the strongly non linearities, arising from the thermal properties of the system and from the boundary conditions,the computing time is very low and the numerical solution isreached without undesiderable oscillatio
Exact solution to the conjugate problem of nonuniform cooling of fuel rods
No full textIn this article, the analytical solution to a conjugate heat transfer problem is presented.The temperature distribution of the cladding of a fuel rod is determined, assuming, that the internal heat generation rate is constant, while the local heat transfer coefficient isvariable along the cladding perimeter, because of contact between adjacent rods. The contact occurs in one point (four-cusp channel) or along a line of the wetted perimeter.Due to asymmetric geometry, the heat transfer coefficient depends on the blocking percentage of the channel and vanishes at the points of contact between adjacent rods.The energy balance equation is solved in two regions (h=0 in the former, and h given by a quadratic form in the latter) of the rod perimeter. This quadratic form was deduced by Turner et al. in 1982, solving numerically the fluid-flow problem. The solution of the thermal problem is obtained resorting to the use of Green's function; the results are given in terms of parabolic-cylinder functions.Some graphs are obtained and discussed; the results show satisfactory agreement with other data available in the literature. Numerical work was performed by personal computer
Accident analysis in LMFBR fuel rods by the FENHT code
No full textThis paper describes the code capability related to the safety requirements in nuclear plants. The code solves the non-linear transient heat-transfer problem for the fuel element of a nuclear reactor, in order to simulate any accidental, operational and emergency power transient with arbitrary initial conditions. The temperature distribution in the fuel, gap and cladding is obtained by a finite-element technique based on minimizing the thermal potential with respect to the temperature vector at the nodes of the finite elements. The non-linear differential matricial equation is linearized by an iterative procedure and solved by the Crank—Nicholson method. Also the thermoelastic stresses in the cladding are valued, by the usual Hooke's law. The code has been applied to the analysis of two reference accidents (incidental power transients) occurring in a liquid-metal fast-breeder reactor (LMFBR); the results are reported and briefly discusse
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