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ACRC Technical Report 235PDF


Title:Simulation Analysis of Thermal Systems and Components
Author(s):Jain, G.; Bullard, C.W.
Subject(s):stationary air conditioning system analysis
Abstract:Issues involved in the solution of thermal system problems within a Newton-Raphson framework have been addressed. The physical limitations of Newton-Raphson variables and limited range of thermodynamic property calculation routines were identified as key factors in the stability and robustness of the solution algorithm. A general guideline is presented to be used while solving thermal system problems. A validation study for two R134a condensers and one 3 slab CO2 gas cooler was done using finite volume based heat exchanger models. The finite volume sequential marching algorithm resulted in excellent agreements with the heat transfer data (within ±5%). The models however underpredicted refrigerant side pressure drop by as much as 80% for the gas cooler and by 50% for the condensers. Nitrogen flow tests were conducted and it was found that for single-phase flow the steeplechase arrangement of microchannel tubes in the headers contribute about 10% to the total pressure drop. Through a systematic analysis the observed discrepancies in pressure drop were attributed largely to the effect of high quantity of oil present in the gas cooler. The interaction of two-phase refrigerant with microchannel headers and oil were suspected to be the possible reason for the same in R134a condensers. The effect of capillary tube-suction line heat exchanger (ctslhx) geometry on system performance was explored at various design and off-design conditions by embedding it in a system model. A detailed finite-volume model of the capillary tube and suction line, capable of handling all the phase-change complexities was used. All the ctslhx configurations considered meet the design constraints and had little effect on the design COP. Captubes with large inlet sections and relatively small outlets were found to give best performance at all the simulated off-design perturbations.
Issue Date:2004-10
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-235
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 69
Date Available in IDEALS:2009-06-22

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