Search

Highlights • Mass fraction difference as the driving force for the mass transfer. • New variable to fit experimental data for absorption chillers. • Linear relation of cooling capacity to mass fraction difference. • Less deviation compared to characteristic temperature function. Abstract Absorption chillers are considered as heat transfer devices and hence most commonly modeled as heat transfer processes. The absorption of the refrigerant vapor though inherently involves mass transfer into the absorbent, which in comparison to the heat transfer usually is a slow transport process. Modeling absorption chillers, however, usually does not include this mass transfer process. This in fact neglects the dominant process in absorption chillers which is addressed in the present paper. [ABSTRACT FROM AUTHOR]

The present paper analyzes the feasibility of an exhaust gas driven jet-ejector cooling system for charge air cooling of turbocharged gasoline engines in addition to the conventional charge air cooler to increase the engine efficiency. Thereto, steady-state experiments of a jet-ejector cooling system and an exhaust gas heat exchanger prototype working with the refrigerant R134a are used to analyze the operation and control of the compound system and determine feasible cooling capacities, charge air temperatures, thermal COP th and hydraulic COP h . Moreover, the cooling system is rated regarding its power densities and engine backpressure. The exhaust gas waste heat recovery, system power densities, and engine backpressure are acceptable. However, the hydraulic COP h and the amount of reject heat need to be improved, necessitating for instance a multi-staging of the jet-ejection. [ABSTRACT FROM AUTHOR]

A comparison of absorption and desorption is conducted using a detailed model describing heat and mass transfer. First, the influences of various assumptions have been evaluated. Second, typical conditions for both absorption chillers and heat transformers have been defined. The performance of absorption and desorption processes have been analysed for a flow length of 0.1 m. In an absorption chiller, during desorption, the viscosity is lowered and the mass diffusivity is increased. These circumstances cause a 46% higher transfer rate as compared to absorption. Thus, the overall performance of the process is determined by the absorber component. In a heat transformer, during absorption at an elevated pressure and temperature level, the viscosity is lower and mass diffusivity is higher as compared to desorption. Therefore, the transfer rate of during absorption is 10% higher as compared to desorption. Hence, the desorber performance is somewhat more influential to the overall system performance. [ABSTRACT FROM AUTHOR]

Due to their simplicity, jet-ejector cooling systems have been investigated for different applications despite their lower thermal COP th in comparison to alternative thermally-driven cooling technologies. The present paper aims at the derivation of a simple method of representation of the operation characteristics of a jet-ejector cooling system for changing boundary conditions. Thereto, a jet-ejector cooling system operating with the refrigerant R134a has been experimentally investigated in double choking operation of the jet-ejector. The jet-ejector operation is characterized by the entrainment ratio μ in dependence of the adequate stagnation pressure ratios. The results are discussed in a non-dimensional graph as a three dimensional surface from which characteristic lines may be deduced. In several graphs, the motive, condenser and evaporator pressures are linked with the entrainment ratio μ , the cooling capacity Q ˙ 0 , the thermal COP th and the hydraulic COP h allowing a comprehensive determination of the system operation. [ABSTRACT FROM AUTHOR]

The geometrical simplicity of a jet-ejector is in stark contrast to the complexity of the flow phenomena occurring in ejector operation. The available flow models range from empirical models to models based on computational fluid dynamics, differing considerably in complexity and thus explanatory power. The one-dimensional flow models of semi-empirical nature are based on experiments at comparatively low motive pressures and thus on ideal gas equations. In contrast, a one-dimensional, experimentally validated model of a jet-ejector in critical double choking operation which includes real gas effects and relies on a single physically interpretable loss coefficient is introduced in the present paper. Real gas effects impact on the state quantities and the critical mass flow of the expansion in the supersonic nozzle in particular which should be considered in the determination of the entrainment ratio or the absolute motive and suction mass flows of the ejector and in ejector design. [ABSTRACT FROM AUTHOR]

Introduction The pathophysiology of aortic stenosis (AS), the most common acquired valvulopathy, is not fully understood and there is to date no treatment to slow or stop the progression of the disease. To define new therapeutic strategies, reproductible and adequate animal models of AS remain essentials and is lacking. A new mouse model has been proposed consisting of a single-nucleotide homozygous substitution mutation in the gene encoding EGFr, known as C57BL6 Egfr Wa2/Wa2 . However, it has been recently shown that aortic regurgitation (AR) remained prevalent, and that AS was rare or absent. Objective The aim of this study was to evaluate the effect of a high fat diet (HFD) and vitamin D 3 supplementation in this model. Methods C57BL6 Egfr Wa2/Wa2 mice were fed with HFD and were subcutaneous injected with vitamin D 3 (16 UI/kg UI, 3 times a week, n = 16) during eighteen weeks. We used as control C57BL6 Egfr Wa2/Wa2 mice fed without HFD and vitamin D 3 ( n = 12). Echocardiography was performed 3 and 6 months later. Blood serum 25(OH) 2 D 3 , 1,25(OH) 2 D 3 , calcium, total cholesterol, phosphates and creatinine were analyzed, and histology/IHC were performed at 6 months to assess valvular fibrosis, calcification and inflammation. Results Echocardiographic analysis did not show any improvement of the model with HFD and vitamin D 3 supplementation. We observed pure severe AS in only two animals in each group and predominant AR in remaining animals. The different variables studied by echocardiography are represented in Table 1 . Vitamin D 3 supplementation and HFD did not affect inflammation and calcification, although total cholesterol level was increased. Conclusion These results suggest that HFD and vitamin D 3 supplementation had no effect on the C57BL6 Egfr Wa2/Wa2 mice model. This model essentially mimics AR and no AS. Further studies are needed to find a reliable animal model of AS. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the heat transfer occurring during reflux condensation of refrigerant R134a in an inclined micro-fin tube (0.008 m OD, 0.5 m length). The experiments were carried out at a system pressure of 0.74 MPa and at inclination angles of 30°, 38°, 45°, 60° and 90° from the horizontal. The experiments indicated that the inclination angle has a significant effect on heat transfer during reflux condensation. The maximum reflux heat transfer coefficient was found at 30° inclination angle. At this arrangement, the heat transfer increased by a factor of 2.45 compared to the vertical case. A comparison with previous studies suggests that the heat transfer in a micro-fin tube is 2.2 times better than that in a plain tube, and 1.34 times better than that in a plain rectangular channel both at 30° inclination. [ABSTRACT FROM AUTHOR]