Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
COMPARISONS BETWEEN TWO TRANSIENT SIMULATION APPROACHES APPLIED TO A DUAL-EVAPORATOR REFRIGERATOR
Submission Author:
Guilherme Zanotelli , SC
Co-Authors:
Guilherme Zanotelli, Christian Hermes
Presenter: Guilherme Zanotelli
doi://10.26678/ABCM.COBEM2021.COB2021-0759
Abstract
The present work focuses on the comparison between two distinct strategies for modeling the transient behavior of a refrigerator: quasi-steady and complete transient. Both modeling strategies were employed to simulate the behavior of a refrigerator with two evaporators arranged in parallel (one for the fresh-food, the other for the freezer and ice maker). In addition to the two evaporators with forced convection, the system is comprised of an oil-free linear compressor, a forced air condenser, a 3-way valve upstream of two capillary tubes – one for the freezer and one for the fresh-food – and a check valve at freezer evaporator outlet. For the heat exchangers, first-principles models were proposed following a moving boundaries scheme for the evaporators and finite volumes for the condenser. For the capillary tube, an artificial neural network was trained using results from a first-principles model. A semi-empirical model was developed for the linear compressor, where the capacity control is achieved by varying the piston displacement. The closing parameters of the mathematical models, such as overall thermal conductance and heat capacity of the refrigerated compartments, performance curves of the heat exchangers, air flow rates in the refrigerated compartments were determined experimentally using a climatized chamber as well as wind tunnels available at POLO facilities. The models were implemented in the Modelica language, which allows for the temporal solution of the differential and algebraic equations system through the high-performance integrator DASSL. The model estimates were compared with each other and with experimental results. As regard as the experiments, the complete transient model proved to be more accurate, particularly during the pull-down regime, presenting, however, some numerical instabilities. On the other hand, the quasi-steady approach proved to be as accurate as fully the transient during the cyclic regime, but much more robust. In comparison to the experimental data, an RMS error of 5 % was observed for energy consumption and 2°C for temperatures in both cases. Regarding the simulation speed, the quasi-steady method, which was capable of simulating about ∼13 min/sCPU, was approximately 6 times faster than the completely transient method (∼2 min/sCPU).
Keywords
Household Refrigerator, Numerical transient simulations., Multiple evaporators, Linear compressor, Modelica
