Experimental Investigations of Low-temperature Driven Ejector for Isobutane

The paper describes experimental and numerical investigation of ejection refrigeration system dedicated for short time storage of food products for local retail market, especially in rural areas. This work was sponsored by US Dept. of Agriculture under Phase I SBIR program. This novel method does not use electricity and is cleaner for the environment than other refrigeration techniques. One of the crucial problems of the retail market of perishable foodstuff is a lack of efficient and appropriate refrigerated storage capacity. The existing technology in most cases uses conventional refrigeration systems that consume a large amount of electricity, they are expensive as well as use harmful working substances (usually artificial GHG gases that have high greenhouse warming potential in comparison with most of the natural substances). In addition, ensuring required storage conditions in terms of the stability of the product temperature and humidity may be a challenge for most of the existing short time storage refrigerators.  Responding to these challenges we developed an ejector based refrigeration system that 1) utilizes solar or waste heat (below 100C temperature) as a main source of energy, 2) eliminates the mechanical compressor, which is a main user of electricity and the main contributor to maintenance and reliability issues in cooling systems and 3) operates without any ozone depletion effects and any greenhouse gas (GHG) emissions, when used with natural refrigerants. Until recently, ejector use in refrigeration systems was considered as controversial because most of the research conducted in the past has yielded only theoretical results without visible, commercial products. The main issue was a relatively low value of coefficient of performance (COP) in comparison with classical compression systems. Selection of the working fluid for the refrigeration or air-conditioning system is the crucial problem because the system efficiency is strongly influenced by the thermodynamic properties of the refrigerant. We found that the maximum efficiency can be achieved with natural refrigerants, of which isobutane is by far the most favorable. However, primarily due to its flammable nature, isobutane is not currently allowed in commercial systems in USA and Canada although it has been used for many years in all domestic refrigerators in Germany and other EU countries where appropriate safety precautions and regulations were developed. For US market, we identified two other environmentally friendly equivalents to isobutane: R245fa and R1234ze both with zero ozone depletion potential. The research described here had overcome another limitation - a lack of appropriate methods for the design of ejector geometry. Such methodology was developed and tested in a variety of thermodynamic cycles for cooling, heating and heat pumps. The test stand and the experimental results of investigation for isobutane as a working fluid along with CFD modelling results are shown and discussed in the paper in details.

Design and baseline characteristics of the finerenone in reducing cardiovascular mortality and morbidity in diabetic kidney disease trial

Background: Among people with diabetes, those with kidney disease have exceptionally high rates of cardiovascular (CV) morbidity and mortality and progression of their underlying kidney disease. Finerenone is a novel, nonsteroidal, selective mineralocorticoid receptor antagonist that has shown to reduce albuminuria in type 2 diabetes (T2D) patients with chronic kidney disease (CKD) while revealing only a low risk of hyperkalemia. However, the effect of finerenone on CV and renal outcomes has not yet been investigated in long-term trials. Patients and Methods: The Finerenone in Reducing CV Mortality and Morbidity in Diabetic Kidney Disease (FIGARO-DKD) trial aims to assess the efficacy and safety of finerenone compared to placebo at reducing clinically important CV and renal outcomes in T2D patients with CKD. FIGARO-DKD is a randomized, double-blind, placebo-controlled, parallel-group, event-driven trial running in 47 countries with an expected duration of approximately 6 years. FIGARO-DKD randomized 7,437 patients with an estimated glomerular filtration rate >= 25 mL/min/1.73 m(2) and albuminuria (urinary albumin-to-creatinine ratio >= 30 to <= 5,000 mg/g). The study has at least 90% power to detect a 20% reduction in the risk of the primary outcome (overall two-sided significance level alpha = 0.05), the composite of time to first occurrence of CV death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for heart failure. Conclusions: FIGARO-DKD will determine whether an optimally treated cohort of T2D patients with CKD at high risk of CV and renal events will experience cardiorenal benefits with the addition of finerenone to their treatment regimen. Trial Registration: EudraCT number: 2015-000950-39; ClinicalTrials.gov identifier: NCT02545049

Development of delayed equilibrium model for CO2 convergent-divergent nozzle transonic flashing flow

The one-dimensional implementation of the Delayed Equilibrium Model (DEM) is known as a relatively simple yet accurate approach for prediction of critical mass flow rate, pressure and void fraction distri- butions for two-phase water transonic flows in ducts of variable geometry. However, the direct applica- tion of DEM equipped with original saturation index evolution law and Lockhart-Martinelli approach (the original setup) is incapable of accurate prediction of CO 2 transonic flow. Moreover, the Darcy friction fac- tor approach has a significant impact on the simulation results. Consequently, this paper presents a new law of the saturation index evolution and a new frictional pressure gradient approach for CO 2 transonic two-phase flows together with experimental validation and discussion of obtained data. A comparative analysis of the developed DEM setup and the referential Homogeneous Equilibrium Model revealed that application of the proposed approaches decreases the mean maximal discrepancy between experimental and calculated static pressure values by a factor of app. 2, with simultaneous decrease of the standard deviation by a factor of app. 4. That proves that both the frictional pressure gradient approach and the proper introduction of the thermal non-equilibrium effects are substantial for accurate modelling of the flashing process in CO 2 flows

Measurement approach of mean heat transfer coefficient for packed bed of vegetables

The non-invasive measurement approach of the mean heat transfer coefficient for the packed bed of vegetables may be thought as still open issue. There is a clear need for the assessment of heat transfer conditions for various types of fruits and vegetables in order to accurately predict the thermal load that is necessary to select refrigeration equipment for cold storage chamber. Additionally, there is significant development in numerical modelling of heat and mass transfer processes in cold storage chambers for fruits and vegetables which requires precise heat transfer prediction. The theoretical basis for the indirect measurement approach of mean heat transfer coefficient for the packed bed of vegetables that is based on single blow technique is presented and discussed in the paper. The approach based on the modified model of Liang and Yang was presented and discussed. The testing stand consisted of a dedicated experimental tunnel along with auxiliary equipment and measurement system are presented. The geometry of the tested vegetables bed were presented. Selected experimental results of heat transfer are presented and discussed for the packed bed of carrots. These results were presented as dimensionless relationship. The obtained results were compared with the existing dimensionless relationships developed for the packed bed consisting of elements of various regular shapes

A study of transcritical carbon dioxide cycles with heat regeneration

The paper presents an efficiency analysis of two transcritical CO2 power cycles with regenerative heaters. For the proposed cycles, calculations of thermal efficiency are given for selected values of operating parameters. It was assumed that the highest working temperature and pressure are in the range from 600 to 700°C and 40 to 50 MPa, respectively. The purpose of the calculations was optimization of the pressure and mass flows in the regenerative heaters to achieve maximum cycle efficiency. It follows that for the assumed upper CO2 parameters, efficiency of 51-54% can be reached, which is comparable to the efficiency of a supercritical advanced power cycle considered by Dostal

A defnition of near-critical region based on heat capacity variation in transcritical heat exchangers

In the paper, a method for determination of the near-critical region boundary is proposed. The boundary is evaluated with respect to variations of specific heat capacity along isobars. It is assumed that the value of specific heat capacity inside the near-critical region exceeds by more than 50% the practically constant value typical for fluids under normal conditions. It appears that large variations of heat capacity are also present for high-pressure subcritical states sufficiently close to the critical point. Therefore, such defined near-critical region is located not only in supercritical fluid domain but also extends into subcritical fluid. As an example, the boundaries of the near-critical region were evaluated for water, carbon dioxide and R143a

Numerical modelling of ejector operating with isobutane

The rapid growth of various applications of the ejection refrigeration systems could be observed recently. Because of possibility of the application of solar or waste energy to supply the motive energy they can be thought as a real alternative to compression devices in air-conditioning technologies. Ejection system can effectively compete with absorption system under temperature of the motive heat source lower than 80°C. The paper deals with CFD numerical simulation along with experimental investigations carried out on a specially constructed prototype/stand for the case of isobutane as a working fluid under motive vapour temperature below 75°C. The numerical and experimental results of entrainment ratio were compared. A good accuracy between numerical and experimental results was observed. The divergent of the results are lower than 20% for tested series. The exemplary pressure and velocity field were presented. Also it was shown that predicted by numerical simulation pressure distribution at ejector wall fits well with experimental pressure distribution

Exergy analysis of operation of two-phase ejector in compression refrigeration systems

Paper deals with theoretical analysis of possible efficiency increase of compression refrigeration cycles by means of application of a two-phase ejector. Application of the two phase ejector in subcritical refrigeration system as a booster compressor is discussed in the paper. Results of exergy analysis of the system operating with various working fluids for various operating conditions have been shown. Analysis showed possible exergy efficiency increase of refrigeration compression cycle