A new, fast and flexible, time-dependent, one-dimensional numerical model was developed in order to study in detail the operation of an active magnetic regenerator (AMR). The model is based on a coupled system of equations (for the magnetocaloric material and the heat-transfer fluid) that have been solved simultaneously with the software package MATLAB. The model can be employed to analyze a wide range of different operating conditions (mass-flow rate, operating frequency, magnetic field change), different AMR geometries, different magnetocaloric materials and heat-transfer fluids, layered and single-bed AMRs, etc. This paper also presents an optimization of the AMRA news geometry, where the AMR consists of a packed-bed of grains (spheres) of gadolinium (Gd). The optimization of the mass-flow rate and the operating frequency of the AMR were performed by studying five different diameters of Gd spheres.
COBISS.SI-ID: 11935003
The cooling degree days concept is a tool to estimate and analyze weather related energy consumption in buildings, i.e. the cooling system electric energy consumption. The main problem with applying this method is that it disregards latent cooling loads. This paper deals with an approach for monitoring electric energy consumption due to cooling in buildings based on cooling degree days, which allows an estimation of latent loads. In addition to applying methods for determining base temperature to base humidity, a new technique is introduced, which is based on a significance test of the enthalpy latent days partial regression coefficient. Analogous to the performance line concept, the influence of latent loads can be presented in the form of a performance surface graph. The performance surface is a plot of electric energy consumption as a function of cooling degree days and latent enthalpy days. The above methods are tested on data sets consisting of electric energy consumption data obtained from two buildings and hourly meteorological data.
COBISS.SI-ID: 11808027
Wall temperatures were measured by high-speed IR thermography during the sequential chain coalescence of bubbles from four nucleation sites in 4 ms to form a single large hovering bubble during pool boiling of water at atmospheric pressure on an electrically-heated titanium foil 25 m thick. Interactions between bubbles before and during coalescence were significantly affected by asymmetries in bubble growth rate or size, and by the thermal response of the thin wall to previous heat transfer. Liquid was redistributed over the contact area of a coalesced bubble, maintaining heat transfer. Outward movement of the shared wall contact line at the instant of horizontal coalescence of two attached bubbles caused localized increases in wall heat flux but continuing oscillations following coalescence and during declining coalescence between an attached bubble and a detached bubble did not affect the wall heat flux in these studies. During the contraction of the contact area leading to detachment, there was a reduction in heat flux at the contact line and sometimes a reversal in heat flux at the contact line.
COBISS.SI-ID: 11996187