S. Lazzari

Transient Heat Transfer from an Offshore Buried Pipeline during Start-up Working Conditions

The 2D heat transfer from offshore, completely buried pipelines is studied with reference to transient working conditions. In particular, the start-up case is considered (i.e., the case of a pipeline initially at equilibrium with the surrounding soil). Two different start-up cases are investigated: the step-rising case and the smooth-rising case. (In the latter, the steady-state wall temperature is reached in a finite time.) The energy balance equation is written in a dimensionless form and solved numerically by means of a finite element method. The dimensionless temperature field in the soil and the thermal power exchanged per unit length by the pipeline with the soil are determined. A comparison with a simpler one-dimensional model of the phenomenon (“extra-soil layer” approximation) is performed.

Non-axisymmetric forced and free flow in a vertical circular duct

Abstract The fully developed laminar mixed convection in a vertical circular duct is studied analytically, with reference to non-axisymmetric boundary conditions such that the fluid temperature does not change along the axial direction. The Boussinesq approximation is applied by taking the average temperature in a duct section as the reference fluid temperature. The dimensionless momentum and energy balance equations are solved by employing Fourier series expansions of the temperature and the velocity fields. The solution shows that the temperature field is not influenced by the velocity distribution and that the Fanning friction factor is not affected by buoyancy. On the other hand, the velocity field is strongly influenced by the buoyancy forces and may display flow reversal phenomena. Two special cases are studied in detail: a duct with a sinusoidal wall temperature distribution; a duct subjected to an external convection heat transfer with two environments having different reference temperatures.

Design of a Nearly Zero Energy One-Family House in North-Centre Italy

The thermal design of a nearly zero energy one-family house, in North-Centre Italy, is described. The house has a timber frame, a wood-fiber thermal insulation for the roof and a wood-fiber plus YTONG blocks thermal insulation for the lateral walls. Forced ventilation with high efficiency heat recovery is employed. Heating and cooling is provided by an air-to-water heat pump connected to floor radiant panels. Domestic Hot Water is supplied by a thermal solar collector and a heat pump for DHW. The electric energy for the heat pumps and for the forced ventilation system is supplied by PV collectors, which provide also most of the electric energy for lighting and appliances. The thermal design is based on dynamic simulations performed through the code TRNSYS 16.

Closed Form Solutions For Mixed Convection With Magnetohydrodynamic Effect in a Vertical Porous Annulus Surrounding an Electric Cable

Mixed convection Darcy flow in a vertical porous annulus around a straight electric cable is investigated. It is assumed that the flow is fully developed and parallel. Moreover, the Boussinesq approximation is used. The magnet i c field with a steady electric current in the cable is radially varying according to the Biot―Savart law. Two fiow regimes are investigated. The first is mixed convection with negligible effects of internal heat generation due to Joule heating and viscous dissipation. The second is forced convection with important effects of heat generation. In these two special cases, closed form expressions of the velocity profile and of the temperature profile, as well as of the flow rate and the Nusselt number, are obtained. The main features of these solutions are discussed.