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As the most widely applied heaters and recuperators in supercritical CO2 (sCO2) power cycles, the Printed Circuit Heat Exchangers (PCHEs) received considerable interests in their transient behavior simulation. After an introduction and comparison about the state-of-art PCHEs numerical simulation approaches, this paper presents a generic one-dimensional (1D) numerical PCHEs modelling methodology featured for 1) ability fulfilling transient simulation; 2) precise capture of the sharp local variations in sCO2 thermo-physical properties. The dynamic simulation ability of the proposed 1D modelling methodology is justified by validating its Modelica implementation against experimental results measured at the Pinjarra Hills High Pressure Loop, the University of Queensland. The proposed PCHE model successfully predicts the changing trends in the temperature and mass flow rate of the working fluids except for a minor time delay. Therefore, the PCHE model is verified as a proper simulation tool for control strategy development for the sCO2 power cycle simulation study. [ABSTRACT FROM AUTHOR]

Dynamic simulation of a Brayton cryocooler is presented as a partial effort of a Korean governmental project to develop 1~3 km HTS cable systems at transmission level in Jeju Island. Thermodynamic design of a 10 kW Brayton cryocooler was completed, and a prototype construction is underway with a basis of steady-state operation. This study is the next step to investigate the transient behavior of cryocooler for two purposes. The first is to simulate and design the cool-down process after scheduled or unscheduled stoppage. The second is to predict the transient behavior following the variation of external conditions such as cryogenic load or outdoor temperature. The detailed specifications of key components, including plate-fin heat exchangers and cryogenic turbo-expanders are incorporated into a commercial software (Aspen HYSYS) to estimate the temporal change of temperature and flow rate over the cryocooler. An initial cool-down scenario and some examples on daily variation of cryocooler are presented and discussed, aiming at stable control schemes of a long cable system. [ABSTRACT FROM AUTHOR]

A test refrigerator based on the modified Reverse Brayton cycle has been developed in the Chinese Academy of Sciences recently. To study the behaviors of this test refrigerator, a dynamic simulation has been carried out. The numerical model comprises the typical components of the test refrigerator: compressor, valves, heat exchangers, expander and heater. This simulator is based on the oriented-object approach and each component is represented by a set of differential and algebraic equations. The control system of the test refrigerator is also simulated, which can be used to optimize the control strategies. This paper describes all the models and shows the simulation results. Comparisons between simulation results and experimental data are also presented. Experimental validation on the test refrigerator gives satisfactory results. [ABSTRACT FROM AUTHOR]

The goal of the overall program is to develop a dynamic numerical model of helium refrigerators and the associated cooling systems based on commercial simulation software. The aim is to give system designers a tool to search for optimum control strategies during the construction phase of the refrigerator with the help of a plant “simulator”. In a first step, a simple Brayton refrigerator has been investigated, which consists of a compressor, an after-cooler, a counter-current heat exchanger, a turboexpander and a heat source. Operating modes are “refrigeration” and “liquefaction”. Whereas for the steady state design only component efficiencies are needed and mass and energy balances have to be calculated, for the dynamic calculation one needs also the thermal masses and the helium inventory. Transient mass and energy balances have to be formulated for many small elements and then solved simultaneously for all elements. Starting point of the simulation of the Brayton cycle is the steady state operation at design conditions. The response of the system to step and cyclic changes of the refrigeration or liquefaction rate are calculated and characterized. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]