Browsing by Keyword "Heat transfer"
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Item Calibration procedures for multidimensional heat transfer models based on on-site experimental data(2015-11-01) Garay, Roberto; Uriarte, Amaia; Apraiz, Inés; Martinez, Roberto Garay; Arrien, Amaia Uriarte; Egaña, Ines Apraiz; Tecnalia Research & Innovation; EDIFICACIÓN DE ENERGÍA POSITIVAAn experimental and numerical approach to the characterization of thermal bridges is presented, based on on-site taken measurements. Commonly on-site applied numerical thermal assessments perform one-dimensional heat transfer analysis over planar elements such as facades. However, it is well known that within thermal bridges in a building one-dimensional heat transfer analysis cannot be applied. A procedure is proposed, based on the creation of a numerical 2D thermal model which is calibrated against experimental data from several temperature and heat flux sensors which are located at specific points in the thermal bridge elements. Results of one particular implementation of this method are discussed.Item Disaggregation process for dynamic multidimensional heat flux in building simulation(2017-08-01) Garay, Roberto; Riverola, Alberto; Chemisana, Daniel; Martinez, Roberto Garay; Tecnalia Research & InnovationHeat transfer across envelopes (façade, roof, glazed areas) represents a big share of the energy flow within the heat balance of buildings. This paper focuses on areas of the envelope where multi-dimensional heat transfer occurs. These areas are commonly defined as thermal bridges, due to a localized reduction of thermal resistance of constructions in these places. This paper reviews common standardized methods to assess heat transfer in buildings, under various modelling assumptions: one-dimensional, multi-dimensional, steady state and dynamic. Within presently developed modelling and assessment methods, a need for improvement has been identified over existing methods for the thermal assessment of multi-dimensional heat transfer under dynamic conditions. A phasorial approach to differential heat transfer in thermal bridges has been developed, which serves as the dynamic extension of steady-state thermal bridge coefficients. This formulation is applied to the junction of a masonry wall with a concrete slab.Item Experimental Thermal Performance Assessment of a Prefabricated External Insulation System for Building Retrofitting(ELSEVIER SCIENCE BV, SARA BURGERHARTSTRAAT 25, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, 2017) Garay, Roberto; Arregi, Beñat; Elguezabal, PeruExternal Thermal Insulation Composite Systems (ETICS) are increasingly used for the energy-efficient retrofit of buildings. This paper evaluates the in-situ thermal performance of a prefabricated composite panel made of PIR and concrete, by full scale testing of a prototype installed at the KUBIK test facility. Experimental results from measurement show a reduction in the thermal resistance of the ETICS assembly compared to theoretical design values. A number of phenomena have been identified causing multidimensional heat flow of conductive and convective nature,such as thermal bridges at floor slabs and anchors, and thermal bypass of the insulation causing airflow behind the ETICS.Item Rapid simulation models for aluminium furnaces design(2017-07-04) Anglada, Eva; Vicario, Iban; de Landia, Leonor; Mendizabal, Gorka; Toledo, Nagore; CIRMETAL; PROMETALThe minimisation of energy consumption in aluminium metal casting industries requires an appropriate design of the furnaces to reduce as possible the heat losses through the walls. Detailed simulation models have been developed that allow the in-depth study of furnace behaviour, but these models are too complex and slow for some industrial necessities. To make possible a fast evaluation during preliminary phases more agile models are needed. This agility may be achieved by simplified models, but the results could be affected by a lack of accuracy. The work presented hereafter shows how the steady state analysis of the furnace walls with simplified models of finite elements may give sufficiently accurate and fast results. The simulation models have been validated against experimental results, thus confirming their ability to adequately reproduce the thermal behaviour of the walls of several furnaces regardless of their composition or heating system.Item Simplified Models for High Pressure Die Casting Simulation(2015) Anglada, Eva; Meléndez, Antton; Vicario, Iban; Arratibel, Ernesto; Cangas, Gaizka; CIRMETAL; Tecnalia Research & Innovation; PROMETALThe simulation of the High Pressure Die Casting (HPDC) process is a complex type of simulation. The industrial procedure is based on consecutive manufacturing cycles that must be taken into account in the simulation. Moreover the part geometries use to be complex and the alloy is injected at really high velocities. All of that usually implies long calculation times that in complex cases can lead to several days. Sometimes, the circumstances require to have available a fast solution despite involve a loss of accuracy. The work presented hereafter discusses different possibilities to simplify the HPDC simulation models together with their benefits and drawbacks. The simplified simulation models have been validated against a detailed 3D simulation model, previously correlated with experimental results. The comparative, shows that the use of simplified models may be a solution that makes possible a big reduction in calculation times maintaining a reasonable level of accuracy.