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U sklopu rada analiziran je amonijačni rashladni sustav industrijskog pogona za preradu i skladištenje mesa. Rashladni sustav sastoji se od direktnog sustava hlađenja s dvostupanjskom kompresijom i indirektnog sustava hlađenja s propilen glikolom kao rashladnim medijem. Proveden je proračun navedenih sustava u projektnim radnim uvjetima, te analiza godišnje potrošnje energije za pogon kompresora. Kompresori oba sustava spojeni su na evaporativni kondenzator na kojemu se održava konstantna temperatura kondenzacije 35°C. Predložena je rekonstrukcija regulacije sustava uz implementaciju varijabilne temperature kondenzacije, čija bi vrijednost ovisila o vanjskim uvjetima. Simulacija rada sustava s varijabilnom temperaturom kondenzacije, te proračun ušteda energije proveden je u računalnom programu Matlab, korištenjem satne metode. Zbog niskih temperatura zraka u komorama za skladištenje duboko smrznutog mesa dolazi do zaleđivanja isparivača. Pregled istraživanja o utjecaju leda na rashladni proces i opis odleđivanja isparivača pregrijanim parama dan je u sklopu rada. Dinamički model odleđivanja isparivača vrućim parama razvijen je u računalnom programu Simulink. Cilj rada je razvoj modela koji će dati optimalno vrijeme trajanja odleđivanja i učinkovitost odleđivanja u ovisnosti o različitim utjecajnim parametrima. Model odleđivanja opisan je za element isparivača duljine cijevi 12 mm, s pripadnim dijelom lamele površine 92 x 79 mm. Odleđivanje je unutar modela podijeljeno u pet faza: zagrijavanje, odleđivanje cijevi, odleđivanje cijevi i lamele, odleđivanje lamele i suho grijanje. Rezultati simulacije pokazali su da vrijeme odleđivanja isparivača raste s porastom početne debljine i gustoće leda. Vrijeme odleđivanja i razmak između dva odleđivanja ovise o strukturi i gustoći leda, koje su funkcije relativne vlažnosti ulaznog zraka. Smanjenjem temperature kondenzacije povećava se vrijeme odleđivanja isparivača. Opisana je regulacija odleđivanja temeljem temperature isparivača, te dan pregled toplinskih gubitaka i ukupne učinkovitosti isparivača. As part of the work, the ammonia cooling system of the industrial plant for meat processing and storage was analyzed. The cooling system consists of a direct cooling system with two-stage compression and an indirect cooling system with propylene glycol as cooling medium. The calculation of design load conditions of the mentioned systems was carried out, as well as the analysis of the annual energy consumption of compressors. The compressors of both systems are connected to an evaporative condenser where a constant condensation temperature of 35°C is maintained. An improvement of system control was proposed with the implementation of variable condensation temperature, the value of which would depend on external air conditions. The simulation of system operating with variable condensation temperature, and the calculation of energy savings was carried out in the computer program Matlab, using the hourly method. The evaporators freeze due to the low air temperatures in the deep-frozen meat storage chambers. An overview of the research on the influence of ice on the cooling process and a description of the defrosting of the evaporator with superheated vapors is given as part of the paper. A dynamic model of evaporator defrosting with hot vapor gases was developed in the computer program Simulink. The goal of the paper was to determine the optimum duration and efficiency of defrosting depending on various parameters. The defrosting model is described for an evaporator element with a pipe length of 12 mm, with a corresponding lamella area of 92 x 79 mm. Defrosting process is divided into five phases within the model: heating, pipe defrosting, pipe and lamella defrosting, lamella defrosting and dry heating. The simulation results showed that the defrosting time increases with the increase in the initial thickness and density of the ice. The time of defrosting and the duration between two defrosting processes depends on the structure and density of the ice, which are functions of the relative humidity of the incoming air. Decreasing the condensation temperature increases the defrosting time. The control of defrosting process acording to evaporator temperature is described, and an overview of heat losses and the overall efficiency of the evaporator is given in the paper. |
