Modelling and Simulation of the Freezing Systems and Heat Pumps Using Unisim ® Design C
Abstract—The paper describes the modeling and simulation of the heat pumps domain processes. The main objective of the study is the use of the heat pump in propene–propane distillation processes. The modeling and simulation instrument is the Unisim® Design simulator. The paper is structured in three parts: An overview of the compressing gases, the modeling and simulation of the freezing systems, and the modeling and simulation of the heat pumps. For each of these systems, there are presented the Unisim® Design simulation diagrams, the input–output system structure and the numerical results. Future studies will consider modeling and simulation of the propene–propane distillation process with heat pump.
A COMPRESSOR SURGE CONTROL SYSTEM: COMBINATION ACTIVE SURGE CONTROL SYSTEM AND SURGE AVOIDANCE SYSTEM
A novel method for combining active surge control system (ASCS) and surge avoidance system (SAS) for a centrifugal compressor is presented. ASCS is a promising method to improve compressor operating area by stabilizing surge. However, this method is not applied yet in industrial compressors. Safety issue is considered in implementing the ASCS. A failure in ASCS may endanger the compressor by entering deep surge as the compressor is allowed to operate in the stabilized surge area. Combination of ASCS and SAS is proposed to improve the safety by utilizing the SAS as a back-up system. SAS is a reliable method in surge control and widely applied in industrial compressors. However, the compressor operating area is reduced by applying the SAS. An ASCS by using piston actuation is used as a case study and performance evaluations of the combined system are done by simulations.
Urea removal strategies for dialysate regeneration in a wearable artificial kidney.
The availability of a wearable artificial kidney (WAK) that provides dialysis outside the hospital would be an important advancement for dialysis patients. The concept of a WAK is based on regeneration of a small volume of dialysate in a closed-loop. Removal of urea, the primary waste product of nitrogen metabolism, is the major challenge for the realization of a WAK since it is a molecule with low reactivity that is difficult to adsorb while it is the waste solute with the highest daily molar production. Currently, no efficient urea removal technology is available that allows for miniaturization of the WAK to a size and weight that is acceptable for patients to carry. Several urea removal strategies have been explored, including enzymatic hydrolysis by urease, electro-oxidation and sorbent systems. However, thus far, these methods have toxic side effects, limited removal capacity or slow removal kinetics. This review discusses different urea removal strategies for application in a wearable dialysis device, from both a chemical and a medical perspective.