Search Results (51)

The electrification of the industrial sector is an important pathway to decarbonizing the industry and achieving a sustainable society. High-temperature heat pumps (HTHPs) are critical devices for providing industrial heat and consuming green electricity. The goal of the present work is the theoretical thermodynamic analysis of a reverse Brayton HTHP that operates with novel working fluids. Specifically, the idea of using mixtures of working fluids with CO₂ is studied for the first time with the aim of suggesting new candidates to increase the performance of industrial HTHPs. A model of an HTHP with an internal heat exchanger is developed and verified in the MATLAB programming language. Nine different mixtures are studied: CO₂/R152a, CO₂/R1234ze(E), CO₂/Propane, CO₂/Butane, CO₂/Isobutane, CO₂/Pentane, CO₂/Isopentane, CO₂/Hexane and CO₂/Heptane. The examined industrial heat production temperatures are 150 °C, 200 °C and 250 °C, while the waste heat stream temperatures that drive the heat pump are considered to be 80 °C and 100 °C. The results prove that the application of the mixtures can enhance the COP, especially in the case of lower temperature lifts. CO₂/R152a seems to be a promising choice compared to pure CO₂, presenting performance enhancements ranging from 4.12% to 64.02% among the studied scenarios. Full article

Organic Rankine Cycles (ORCs) are widely recognized as an effective solution for waste heat recovery (WHR). However, the design and optimization of these systems must address the tradeoff between computational efficiency and the need to capture complex component behavior. This requires moving beyond purely energetic 0D modeling approaches to account for constructional, spatial, and operational constraints. This work presents a novel modeling framework with a specific focus on the expansion device. Radial inflow turbine stages are selected for their capability to achieve high pressure ratios while maintaining compactness and high efficiency. Heat exchangers follow a generic one-dimensional counterflow configuration, with a shell-and-tube geometry adopted for sizing purposes. The turbine stages are modeled by resolving several internal sections in order to capture local thermofluid dynamic conditions. The framework predicts turbine efficiency and incorporates a newly developed formulation for shock-induced losses, improving performance prediction under trans-sonic flow conditions. After validation against experimental data, the model is applied to a WHR system integrated with an internal combustion engine fueled by biofuels. The results highlight the existence of optimal operating conditions arising from competing physical mechanisms. The analysis also shows the transition from single-stage to two-stage turbine configurations at high pressure ratios and emphasizes the role of real gas effects in determining stage performance and optimal expansion distribution. The results of simulations carried out for three different working fluids (ethanol, toluene, and R1234ze(E)) highlight that the available mechanical power ranges from 10 to 22 kW for single-stage turbine configurations and from 24 to 36 kW for two-stage configurations, with total system volumes varying between approximately 600 and 9000 L. Among the working fluids considered here, ethanol provides the best overall performance for the present case study. Overall, the proposed approach provides a reliable and computationally efficient tool for the preliminary design and optimization of ORC-based WHR systems. Full article

This study analyzes four alternative cycle configurations for the traditional vapor compression system used in conventional, hybrid, and electric vehicles, taking low-GWP alternatives for the substitution of R134a. These are cycle with an internal heat exchanger and thermostatic expansion valve (IHX + TEV); cycle with an internal heat exchanger and short tube (IHX + ST); cycle with an ejector (EC); and cycle with an ejector and internal heat exchanger (EC + IHX). Similarly, the energy, exergy, exergoeconomic, and environmental impact of these configurations were analyzed using synthetic refrigerants with a GWP of less than 150. The results indicate that, using the EC + IHX configuration, the COP for refrigerants R1234yf, R1234ze(E), R1243zf, and R516A is the highest, increasing by more than 20%. Using R1243zf in the EC configuration can reduce the total cost ratio compared to other refrigerants. On the other hand, the use of IHX cycle configurations with R444A and R445A decreases the exergy efficiency and increases the total cost ratio by up to 35% and 70%, respectively. Additionally, the Total Equivalent Warming Impact (TEWI) analysis showed reductions up to 20% for ejector cycle configurations using R1234ze(E), R1234yf, R1243zf, and R516A. Full article

Vapour-compression refrigeration and cooling systems represent a significant share of global electricity consumption, being estimated to account for approximately 10% to 20% of the worldwide electricity demand, which highlights their critical impact on energy efficiency and sustainability. In this context, improving the thermodynamic and exergoeconomic performance of refrigeration cycles, as well as the appropriate selection of the refrigerant, has become a key research priority. Therefore, this work aims to comparatively evaluate the energy, exergy, exergy cost, and exergoeconomic performance of three vapour-compression refrigeration cycle configurations: a simple cycle, a two-stage cycle with a flash tank, and a two-stage cycle with a flash tank and a mixing chamber. Six refrigerants (R134a, R600a, R290, R1234yf, R1234ze (E), and R717) were analysed under evaporation temperatures of 228–238 K and condensation temperatures of 298–308 K. The performance evaluation was carried out using the Fuel–Product–Residue (FPR) methodology, considering the coefficient of performance (COP), exergy efficiency, system irreversibilities, and exergy and exergoeconomic costs. The results indicate that the incorporation of the mixing chamber increases the COP by up to 7% and the exergy efficiency by up to 6% compared to the simple cycle, while reducing exergoeconomic costs by up to 10% for the most favourable refrigerants. Among the working fluids analysed, R600a exhibits the best overall performance (COP up to 4.3 and an exergy efficiency of 33%), followed by R290 and R717, whereas R1234yf shows the lowest efficiencies (COP ≈ 3.7 and exergy efficiency ≈ 28%) and the highest exergoeconomic costs. These findings demonstrate that the design of vapour-compression refrigeration systems should involve the joint selection of the cycle configuration and the refrigerant based on integrated energy, exergy, and exergoeconomic criteria. Overall, the results highlight that both the refrigerant and the cycle configuration must be selected simultaneously, considering energy, exergy, and exergoeconomic criteria, to achieve more efficient and sustainable industrial applications. Full article

Combining Organic Rankine Cycles (ORC) with cooling cycles offers a promising approach to achieving greater outputs within a single system. In this study, a novel directly combined ORC-VCC system has been designed to not only meet the cooling demand using a geothermal heat source but also generate power. The proposed novel ORC-VCC system has been analyzed for its energetic performance using four selected fluids: R290, R600a, R601, and R1234ze(E). Parametric analysis has been conducted to investigate the effects of parameters of heat source temperature, heat source mass flow rate, cooling capacities, condenser temperature, ORC evaporator temperature, pinch point temperature difference and isentropic efficiencies on net power production. Among the working fluids, R290 has provided the highest net power production under all conditions in which it was available to operate. Additionally, the results have been analyzed concerning a reference cycle for comparative evaluation. The proposed novel cycle has outperformed the reference cycle in all investigated cases in terms of net power production such as demonstrating an improvement of approximately from 8.7% to 57.8% in geothermal heat source temperature investigations. Similar improvements have been observed over the reference cycle at lower heat source mass flow rates, where net power increases by up to 50.8%. Full article

This paper presents a banana ripening chamber system for Romania. The system comprises two main parts: the refrigerating unit, with a cooling capacity of 47.5 kW, and a fresh air supply system for ethylene exhaust during the ripening process (1000 m³/h). The proposed solution replaces the classical one-stage vapor compression with R134a. The new solution presented in this study has a proven fruit ripening solution that includes the 3Es; it is eco-friendly (low GWP refrigerant R1234ze(E)), economical, and energy efficient (AHU with heat recovery). The advantage of the new system results from an increasing coefficient of performance, with 7.34% owing to decreasing the power consumption of the compressors. Regarding heat recovery, the annual energy consumption for ventilation is lower, using (annual average) 41% less energy than without heat recovery. Full article

The study presents the results of an experimental investigation aimed at evaluating the performance of a water-to-water heat pump utilising R1234ze(E) and R515B in a drop-in application. Several operating conditions are tested, varying the mass flow rates and temperatures of the secondary fluids that pass through the heat exchangers while maintaining the compressor shaft rotational frequency and the vapour superheating at the evaporator outlet constant. Overall, when compared to R1234ze(E), the utilisation of R515B results in capacity and COP variations within −6.81% to +2.46% and −2.41% to +6.29%, respectively. Regarding the performance of the compressor, R515B exhibits comparable volumetric and overall efficiency, while a slightly lower refrigerant temperature at the compressor discharge is found, with differences ranging from −3.1 °C to −0.5 °C. Overall, R515B appears to be more suitable than R1234ze(E) for applications in the high-temperature range. Full article

Background/Objectives: The purpose of this systematic review was to assess the global prevalence of sleep bruxism and awake bruxism in pediatric and adult populations. Methods: This systematic review was conducted by analyzing studies published from 2003 to 2023. The following keyword combination was utilized: prevalence, epidemiology, population, and bruxism. The PubMed database was analyzed, supplemented by manual searches using the Google search. Additionally, the snowballing procedure method was applied. A double assessment of the quality of publications was carried out to preserve the highest possible quality of evidence (e.g., Joanna Briggs Institute critical appraisal checklist). Analyses were conducted using the R statistical language. Results: The global bruxism (sleep and awake) prevalence is 22.22%. The global sleep bruxism prevalence is 21% and awake prevalence is 23%. The occurrence of sleep bruxism, based on polysomnography, was estimated at 43%. The highest prevalence of sleep bruxism was observed in North America at 31%, followed by South America at 23%, Europe at 21%, and Asia at 19%. The prevalence of awake bruxism was highest in South America at 30%, followed by Asia at 25% and Europe at 18%. Conclusions: One in four individuals may experience awake bruxism. Bruxism is a significant factor among women. It was observed that age is a significant factor for the occurrence of sleep bruxism in women. Among the limitations of the study is the lack of analysis of the prevalence of bruxism in Africa and Australia due to not collecting an adequate sample for analysis. The study was registered in the Open Science Framework (10.17605/OSF.IO/ZE786). Full article

Centrifugal compressors are commonly used in heating, ventilation, and air conditioning (HVAC) systems. The current generation of refrigerants in HVAC systems have very low ozone depletion potential, but most of them are still considered as containing high global warming potential (GWP) chemicals. Facing the regulatory pressure to eliminate the high-level GWP refrigerants, some of the existing HVAC systems will need to switch to low-GWP refrigerants. In this paper, we studied the performance changes in a refrigerant centrifugal compressor when switching from R134a to R1234ze(E) and R1234yf through a method that combined numerical simulation and an 1D meanline code. By combining these two methods, a reliable compressor performance change prediction was generated using limited results from the computational fluid dynamics (CFD) simulations. The results show that the property differences in the working fluid can significantly change the refrigerant compressor performance, including the compressor efficiency, pressure ratio, power consumption, working range and cooling capacity. Full article

Due to the impact of global warming and climate change, more and more people are starting to have a clearer understanding and vigilance about greenhouse gases. To prevent further deterioration of the global environment, this study examines the coefficients of performance of 21 currently available refrigerants with very low global-warming potential and zero ozone-depleting potential under evaporation temperatures of 10, −20, −40, and −60 °C and condensation temperatures of 30, 40, and 50 °C, respectively. It is found that the use of pure refrigerant in a two-stage refrigeration system to replace the single-stage refrigeration system, in addition to mixing it into an appropriate mixture, can effectively improve the performance coefficient of the refrigeration system. For single-stage vapor compression refrigeration systems, R1234ze(Z), R601, and R1233zd(E) have the best refrigeration performances among the environmentally friendly refrigerants studied, while R441A performs the worst for T_eva = 10 °C and −20 °C. Moreover, RE170 has the highest COP of the refrigeration system for T_eva = −40 °C and −60 °C. However, R1234yf performs worse in COP when the evaporation temperature is lower, and it ranks last for T_eva = −60 °C. When a double-stage vapor compression refrigeration system is employed instead, the percentage increase in the COP of the system using R1234yf becomes the largest for T_eva = −40 °C and −60 °C. However, the growth rate of R717 ranks last for T_eva = −60 °C. For an R717/R1234yf mixture at an optimum mass fraction of 0.25, the COP of the refrigeration system can be increased up to 25.8% despite an increase of 15.2% in operating pressure compared to R1234yf. The discharge temperature may rise; however, there will be no overheating problem for the compressor. Full article

Due to its environmental benefits, CO₂ shows great potential in refrigeration systems. However, a basic CO₂ transcritical (BCT) refrigeration system used for airconditioning in buildings might generate massive indirect carbon emissions for its low COP. In this study, a novel CO₂ transcritical/two-stage absorption (CTTA) hybrid refrigeration system is broadly investigated, and both energy efficiency and life cycle climate performance (LCCP) are specifically engaged. The theoretical model shows that optimal parameters for the generator inlet temperature (T_G2), intermediate temperature (T_m), and discharge pressure (P_c), exist to achieve maximum COP_tol. Using the LCCP method, the carbon emissions of the CTTA system are compared to six typical refrigeration systems by using refrigerants, including R134a, R1234yf and R1234ze(E) etc. The LCCP value of the CTTA system is 3768 kg CO_2e/kW, which is 53.6% less than the BCT system and equivalent to the R134a system. Moreover, its LCCP value could be 3.4% less than the R1234ze(E) system if the COP of the CO₂ subsystem is further improved. In summary, the CTTA system achieves ultra-low carbon emissions, which provides a potential alternative to air conditioning systems in buildings that can be considered alongside R1234yf and R1234ze(E) systems. Full article

The use of heat pumps is increasing worldwide, and knowledge of their properties is becoming more and more important. Although numerous tests regarding heat pumps have been performed, due to the large number of influencing variables, the entire range of input parameters is not covered, and there is no overall picture regarding the range of the coefficient of performance (COP) of heat pumps and their output parameters. This study extends existing research and provides a much more detailed comparison of results for the application of R1234yf and R1234ze(E) refrigerants, including the pressure drop across the evaporator, condenser, and internal heat exchanger (IHX). The appropriate mathematical model for the selected components was defined and verified experimentally. A total of 60 series of measurements were performed at different evaporating and condensing temperatures. The deviation of the numerical simulation results from the experimentally determined results was up to 7.4% for cooling capacity, 8.1% for heating capacity, 7.2% for COP and 6.8% for compressor energy consumption. This study shows that COP increases from 4.77% to 10.73% for R1234ze(E) compared to R1234yf. The use of an IHX in the thermal cycle further increases COP for both refrigerants between 2.61% and 4.99%. Full article

Microfin tubes are widely used to enhance heat transfer in heat exchangers in order to reduce volumes, costs and refrigerant charge. Much experimental work has been published for the flow of liquids, while some experimental work is available for the flow of gases for the chemical, refrigeration and air conditioning industry. This work reviews the literature and presents new experimental friction factors for the flow of the superheated vapor of R1234ze(E) in a 5 mm outside diameter microfin tube. The authors have also collected an extensive data bank of heat transfer coefficients (around 648 points from different research laboratories) and friction factors (around 536 points), covering 45 different geometries of inner finned tubes. After comparing the predictions from available correlations with experimental data, the present paper suggests the best performing equations for the calculation of the friction factor and of the Nusselt number during forced convection flow of liquids and gases. The suggested model for friction factor estimates the experimental values with a relative and absolute deviation of −0.3% and 7.9%, respectively, whereas the suggested model for the heat transfer coefficient predicts the experimental data bank with a relative and absolute deviation of −3.3% and 13.9%, respectively. The validity range of the two correlations is extremely wide, covering microfin tubes with diameters from 2.6 mm to 24.4 mm, and Reynolds number from about approximately 1000 to 300,000 for the friction factor, and from 3000 to 1,000,000 for the heat transfer coefficient. Full article

This study proposes the experimental evaluation of alternative refrigerants with low global warming potentials (GWPs) such as R1234ze(E), R513A, and the mixture R516A as a drop-in replacement for R134a in a domestic refrigerator with a volumetric capacity of 513 L. Initially, the optimal charge for each refrigerant was defined based on the minimum energy consumption of the refrigerator, then the thermal and energy performance of the refrigerator was evaluated. Finally, a total equivalent warming impact analysis (TEWI) was performed. The main results indicated that the optimal charge of the alternative refrigerants was below that corresponding to R134a (105 g), of which R516A (86 g) presented the greatest charge reduction. Regarding the average temperature of the refrigerator compartments, very adequate thermal conditions were observed; thus, the alternative refrigerants showed very similar conditions to R134a. For the coefficient of performance (COP) and considering R134a as a reference, it was observed that R513A presented the greatest reduction of around 28%, while R1234ze(E) showed an increase of 13% in relation to R134a. Finally, the TEWI analysis showed R1234ze(E) as the refrigerant with the least impact. Full article

Heat pump electricity costs grow with a power relationship as the evaporator temperature in the cycle decreases. The thermo-economic study of a solar thermal-assisted heat pump and storage system determines the minimum cost of the coupled system for an evaporator temperature. Through two case studies, one for the dairy industry and the other for 2G bioethanol production, the coupled system was evaluated for different temperatures in the evaporator, from 30 to 90 °C, and the minimum cost of the coupled system was determined. For the dairy industry, the lowest levelized total cost of a heat pump (LCOE) at 50 °C is 0.0799 USD/kWh. The evaluation carried out allowed us to determine the best operating conditions of the heat pump: 50 °C in the evaporator, COP = 4.2, and the work of the compressor of 211.3 kW. In the case of 2G anhydrous bioethanol production, the lowest levelized energy cost is 0.0409 USD/kWh for an evaporator temperature of 30 °C and a payback of 1.8 years. The study carried out makes it possible to guarantee the supply of the heat load at the operating temperature of the process and determines the impact of environmental conditions on the cost of the heat pump assisted with solar thermal energy. Full article