Compression Work Research Articles

Impact of space utilization and work time flexibility on energy performance of office buildings

This study investigates the impact of different space utilization on energy use intensity, heating load, cooling load, and thermal comfort of occupants using a combination of empirical data gathering and simulation-based studies. The increasing worldwide preoccupation with energy consumption and environmental sustainability has led to increased attention on optimizing interior spaces to mitigate total energy demand. The considered case study for conducting this research was the Norwegian living lab namely Zero Emission Building (ZEB) Flexible Lab in Trondheim, Norway. In this study, 10 different scenarios of occupancy schedules based on flexible arrangements from standard workweeks to extensive remote work configurations were designed and analyzed using IDA ICE 5.0. The findings demonstrate significant reductions in energy use across scenarios with increased teleworking and compressed work weeks. The remote scenario achieved the most significant decrease in Energy Use Intensity (EUI), with a reduction of 46 % compared to the base case. Similarly, the implementation of flexible hours and remote working in scenarios resulted in a reduction of electric heating demand by up to 23 %, underscoring the potential of occupancy-based strategies in enhancing building energy efficiency. However, uncomfortable hours increased by 59 % in the 2-day remote working scenario compared to the base case, demonstrating the need to consider climate conditions when implementing remote work. The research offers valuable insights into the complex connections between flexible arrangements and energy efficiency, considering many elements such as occupancy schedule and use dynamics. This article offers a comprehensive analysis that may give architects, building managers, and policymakers valuable insights. This study contributes to the developing sustainable architecture by emphasizing the impact of dynamic occupancy on the energy performance of office buildings.

Modelling and optimization of combined supercritical carbon dioxide Brayton cycle and organic Rankine cycle for electricity and hydrogen production

Hydrogen as a clean fuel, is key energy carrier for sustainable development, and its production via water electrolysis is most desirable for its carbon free nature. Nuclear power provides good opportunity to satisfy the huge energy demand associated with the process, in addition to electrical power generation. Modelling an efficient and cost effective nuclear based power and Hydrogen cogeneration system and optimizing it to enhance its performance is the core academic problem addressed in the present study. It proposes a power plant cycle aided by a nuclear reactor, providing 300 MW thermal power input. Supercritical CO2 Brayton cycle is used as the main cycle, instead of traditional Helium Brayton cycle or steam Rankine cycle. To increase the cycle efficiency, by reducing the compression work and by reducing the cold source loss, main compression intercooling and waste heat recovery by an Organic Rankine Cycle (ORC) is introduced together with recompression Brayton cycle arrangement. The power coming from recovered waste heat goes to a Proton Exchange Membrane Electrolyzer (PEME), which facilitates the production of Hydrogen by splitting water via electrolysis. Additional attention is given to ORC fluid selection by employing and comparing the performance of widely acknowledged R245fa together with its more eco friendly replacements, R1233Zd(E) and R1234Ze(Z). The evaluation of the system performance is conducted through the lenses of Energy, Exergy, and Economics. Essential parameters are scrutinized to gauge their impact on two pivotal objectives. Overall Exergy Efficiency(ηex) takes care of the thermodynamic performance and the economic aspect is scrutinized by Levelized Cost of Energy (LCOEn). Notably, by employing R245fa as the ORC working fluid, the system attains peak Energy efficiency of 42.13% and Exergy efficiency of 58.32%, and a minimum LCOEn of 0.063 USD/kWh. Of all the components associated with the system nuclear reactor tops the chart for maximum exergy destroyed(40.8% of total) as well as maximum investment cost(65.7% of total). Pump contributes least to exergy destruction(0.03% of the total) and heat exchangers hold least share(1.1% of total) for investment cost. Furthermore, a multiobjective optimization exercise is executed to fine-tune the system’s operational parameters. This optimization results in a 3.12% increase in Overall Exergy Efficiency and a 9.79% decrease in LCOEn compared to the base operating condition with R245fa used as the ORC fluid. The ηex & LCOEn in best possible operating condition are 58.25% & 0.0645 USD/kWh using R245fa as ORC fluid, 58.23% & 0.0645 USD/kWh using R1233Zd(E) as ORC fluid and 58.22% & 0.0644 USD/kWh using R1234Ze(Z) as ORC fluid. If same amount of electrical Power is supplied to PEME for both with and without ORC configuration, having an ORC is advantageous both in terms of superior Exergy Efficiency and lower LCOEn. The proposed configuration is also economically more lucrative with higher Net Present Value(NPV) and Benefit to Cost Ratio(BCR). For example, when PEME power input for both the cases is 10 MW, proposed system has NPV = 201.79 Million USD & BCR = 1.70 compared to NPV = 164.03 Million USD & BCR = 1.58 for without ORC configuration. Even if in without ORC configuration, no electrical power is supplied to the electrolyzer, adding an ORC to produce Hydrogen will still achieve maximum 1.57% Exergy Efficiency increment, compared to only electrical power production by sCO2 Brayton cycle. It is seen that in base condition, the NPV is still superior for the proposed configuration (203.03 to 189.32 Million USD), and the BCR dips only slightly from 1.72 to 1.71.

Mechanistic Model of Fatigue in Ultrasonic Assisted Machining.

Anti-fatigue design in the machining process of aviation material requires advanced processes to enhance the surface integrity and a holistic model which can optimize the process aiming at maximum fatigue life. In the present study, the axial ultrasonic assisted milling process was utilized to machine the Inconel 718 while the process executes the thermomechanical cutting and peening action simultaneously. To optimize the process factors, a hybrid model using a combination of regression analysis and an analytical model was developed to correlate the machining factors, i.e., vibration amplitude, cutting velocity and feed rate to fatigue life. Herein, the former was used to map the process inputs to surface integrity aspects (SIAs), viz. roughness, hardness and residual stress; then, the SIA was mapped to fatigue life through a stress-based approach. The obtained results revealed that there is close agreement between the measured and predicted values of fatigue life where the prediction error is less than two times the dispersion. On the other hand, applying ultrasonic vibration at the highest amplitude together with the maximum feed rate and cutting velocity yield significant improvement in fatigue life, i.e., three times the same condition without ultrasonic vibration in light of the enhancement of compressive residual stress and work hardening of the surface layers.

Optimizing cascade refrigeration systems with low GWP refrigerants for Low-Temperature Applications: A thermodynamic analysis

This study offers a comprehensive thermodynamic analysis of a cascade refrigeration system conducted for low-temperature applications, focusing on the use of low-GWP and zero-ODP refrigerants to improve efficiency and sustainability. The target of this study is to explore the performance of the system using a combination of refrigerants: low-temperature cycle refrigerants such as R744, while high-temperature cycle refrigerants such as R717, R1234yf, R1234ze(E), R1336mzz(E), and R1336mzz(Z), respectively. The ECS model incorporating in REFPROP 10.0a tool was utilized to extract the data through coding for analysis. The assessment of this system involves the examination of various parameters such as its coefficient of performance, total compressor workload, total exergy, and exergy efficiency across various operational conditions. The results are compared with and without superheated and subcooled conditions to understand the impact of these parameters on the system performance. The system with R744 in the low-temperature cycle and R717, R1234yf, R1234ze(E), R1336mzz(E), and R1336mzz(Z) in the high-temperature cycle provides a higher COP and lower total compressor work compared to the conventional cascade refrigeration system. In optimal CRS, the R744-R717 pair attains the highest COP of 2.05 at the lowest possible compressor work from 9.53 to 4.87 kW than other refrigerants pair while evaporator temperature shifting from −55 °C to −20 °C. The exergy efficiency of R744/R717 is found at 26.47 % at an evaporator temperature of −55 °C, but it extends to a peak of 51.73 % at −20 °C. The study also shows that the superheating and sub-cooling of the refrigerants have a significant impact on the performance of the cascade refrigeration system. Superheating and sub-cooling at 10 °C, improves the COP of the system by reducing the compressor work and increasing the heat transfer efficiency. The research offers valuable insights into the system’s thermodynamic performance when employing low GWP refrigerants in low-temperature applications. These findings have the potential to guide the design and optimization of cascade refrigeration systems over the range of low-temperature applications.

Numerical and Performance Analysis of R290 Heat Pump Driven Air Conditioning System for Heating and Cooling

The demand for heating and air conditioning is rising due to rapidly changing climatic conditions. The market for heat pumps and air conditioning systems is seeing a steady increase in low global warming potential. There is a growing need to use environment-friendly refrigerants. Contemporary Refrigerants (HCFCs) such as those found in heat pump air conditioning systems have the potential to cause global warming and ozone depletion. Using more environmentally friendly refrigerants, including hydrocarbon and blend refrigerant mixtures, is one way to lower Global Warming Potential (GWP) and Ozone depletion potential. This study examines the performance of several alternative refrigerants, including R32, R134A, R410A, R22 and R290. To examine the performance of R290, theoretical and simulation results are compared for various refrigerants while taking into account several performance parameters, including the refrigerant energy efficiency ratio, mass flow rate, coefficient of performance, cooling capacity and compressor work for One Ton of Refrigeration (1TR) air conditioners. One player with a very low GWP is R290. However, the only drawback is that it can catch fire and is hazardous to use in split-type commercial heat pump air conditioning applications. The environmental and thermo physical properties of R290 are significantly better than those of other materials, according to theoretical and simulation studies utilising Cool Pack software, hence it is a viable replacement.

Adaptive sparse structure development with pruning and regeneration for spiking neural networks

Spiking Neural Networks (SNNs) are more biologically plausible and computationally efficient. Therefore, SNNs have the natural advantage of drawing the sparse structural plasticity of brain development to alleviate the energy problems of deep neural networks caused by their complex and fixed structures. However, previous SNNs compression works are lack of in-depth inspiration from the brain development plasticity mechanism. This paper proposed a novel method for the adaptive structural development of SNN (SD-SNN), introducing dendritic spine plasticity-based synaptic constraint, neuronal pruning and synaptic regeneration. We found that synaptic constraint and neuronal pruning can detect and remove a large amount of redundancy in SNNs, coupled with synaptic regeneration can effectively prevent and repair over-pruning. Moreover, inspired by the neurotrophic hypothesis, neuronal pruning rate and synaptic regeneration rate were adaptively adjusted during the learning-while-pruning process, which eventually led to the structural stability. Experimental results on spatial and temporal datasets demonstrate that our method can flexibly learn appropriate compression rate for various tasks and effectively achieve superior performance while massively reducing the network energy consumption. Specifically, for the neuromorphic DVS-Gesture dataset, 98.56% accuracy with 1.45% improvement is achieved by our method when the compression rate reaches 61.10%. Our code is available at: https://github.com/BrainCog-X/Brain-Cog/tree/main/examples/Structural_Development/SD-SNN.

Wet shot peening effects on surface integrity and very high cycle fatigue of TC17 titanium alloy

With the increasing reliability requirements of aerospace equipment, very high cycle fatigue of TC17 titanium alloy has gained significant attention. This study investigates the effects of different wet shot peening treatments on the surface integrity and very high cycle fatigue performance of TC17 titanium alloy, elucidating the underlying mechanisms. Experimental results show that wet shot peening exacerbates surface defects, increases roughness, creates a plastic deformation layer, and induces compressive residual stress and work hardening. The combined effect of these factors reduces the fatigue performance. However, post-peening polishing significantly enhances the very high cycle fatigue performance by reducing stress concentration from surface defects while retaining the beneficial effects of compressive residual stress. Therefore, polishing after wet shot peening is concluded to be the most effective method for improving the very high cycle fatigue performance of TC17 titanium alloy.

1D models of an active magnetic regeneration cycle for cryogenic applications

In investigation of an active magnetic regenerator (AMR) cycle operating at room temperatures, 1D models have been extensively used to accurately computing its performance metrics. However, extending these models to simulate an AMR cycle at cryogenic temperatures introduces inherent complexities and challenges. The broad temperature span and low operating temperatures required for cryogenic applications, such as hydrogen liquefaction, lead to significant density variations of the working fluid within the AMR that cannot be overlooked. In this work, two 1D AMR models assuming a compressible working fluid operating at cryogenic temperatures are demonstrated which address the large density variations and the numerical stiffness of the equations. The models exhibit good agreement with experimental and 2D numerical results of an AMR configuration designed for hydrogen liquefaction. A comparative study is conducted between the developed models and an incompressible AMR model at cryogenic temperatures shows that the incompressible model predicts cooling powers that are higher by a factor of up to 10 at high values of utilization, highlighting the error of assuming an incompressible fluid on estimating the performance metrics.

Heat pump assisted sorption carbon capture with steam condenser heat recovery in a decarbonised coal-fired power plant

More than 50% energy input of coal-fired power plant is lost in the condensation of steam turbine in a temperature range of 30–35 ℃. Carbon capture technology has a negative influence on power generation efficiency of coal-fired power plant. Thus, it is essential to find an efficient method for waste heat recovery and increase the overall energy efficiency in coal-fired power plant with carbon capture. A novel integrated system including absorption heat pump and adsorption carbon capture based on coal-fired power plant is then presented. Waste heat from steam condenser is recovered by absorption heat pumps driven by steam extracted from low pressure steam turbine. The output hot medium from the absorption heat pumps is further heated to desorption temperature for the regeneration process of adsorbents by the extracted steam. The results show that heat penalty increases with the increase of the desorption temperature, and the heat recovery amount has an opposite trend. Compared with the conventional coal-fired power plant, thermal efficiency of the integrated system increases by 0.854%. The efficiency decrease of the compression work accounts for over a half of the total efficiency decrease due to the compression and the capture process. External heat recovery is applied in flue gas and the multi-compression process, and the thermal efficiency increase can be improved to 1.453% when compared with 0.725% of the system without external heat recovery. It proves that absorption heat pump could play a significant role in the energy saving of adsorption carbon capture system.

Enhanced strength and toughness of carbon fiber reinforced aluminum matrix composite prepared via novel indirect extrusion method

The fabrication of large-sized, high-performance CF/Al composites presents significant challenges for the aerospace industry. This study introduces a novel indirect extrusion (IE) method for the high-quality production of CF/Al composites. The study investigates the infiltration mechanism of the alloy liquid during the IE process, highlights the technique's advantages, and systematically analyzes the mechanical properties and failure mechanisms of CF/Al composites. Results show that the aluminum liquid initially fills the interlayers and subsequently penetrates the fiber bundles, effectively shortening the infiltration distance. At a casting temperature of 800°C and an infiltration pressure of 40 MPa, the composite exhibits excellent forming quality and microstructural integrity. Compared to direct extrusion (DE) CF/Al composites, IE-CF/Al composites show significant improvements in compressive strength (16.72 %), flexural strength (16.87 %), fracture toughness (43.18 %), and work of fracture (90.61 %). The interlayer alloy and increased fiber spacing in IE-CF/Al composites enhance energy absorption capacity and reduce the risk of brittle fracture. This process lays a solid foundation for the high-quality production and application of CF/Al composites.

Performance Evaluation of Novel Advanced Recompression Absorption Refrigeration Systems Equipped with Ejector and Vapor Injection Technology

The absorption refrigeration cycle (ARC) faces challenges considering its decreased working pressure and COP. By integrating Recompression technology (RAC) into ARC, these issues are partly addressed. To address these inefficiencies, in this study, ejector and vapor injection techniques are incorporated into refrigerant side of the RAC cycle, resulting in the development of advanced systems: Refrigerant ejector enhanced recompression absorption cycle (RE-RAC) and Vapor injection enhanced recompression absorption cycle (VI-RAC). Key metrics assessed are 1st and 2nd law efficiency, system exergy destruction rate, compressor load, and generator heat requirements. Conclusively, under analogous operating conditions, RE-RAC and VI-RAC demonstrate a substantial improvement in COP, achieving 76 % and 63 % enhancements, respectively, over the standard RAC system. Compared to the conventional solution ejector-based SE-RAC, these systems show performance increases of 28 % and 19 %, respectively. The findings also highlight the sensitivity of these systems to parameters such as generator temperature and pressure, evaporator temperature, absorber temperature, evaporator recovery and normal pressure ratio. At higher evaporator temperature and lower generator temperature, the performance of these systems as well as enhancement of RE-RAC over VI-RAC is higher observed. The optimal value of generator pressure and recovery pressure ratio for maximum efficiency and minimum total exergy destruction rate is also dependent upon these. At a generator temperature of 67 °C and an evaporator temperature of 8 °C, RE-RAC exhibits a 35 % higher COP compared to VI-RAC. However, at −10 °C evaporator temperature, changes in external generator heat input and compressor work reduce the COP enhancement to 5 %.

You get what you expect: assessing the effect of a compressed work schedule on time pressure, fatigue, perceived productivity, and work-life balance

ABSTRACT With a refreshed surge of interest in alternative work schedules, such as the compressed workweek, as a tool to increase employer attractiveness, the question of the effects of such work arrangements recurs. In light of inconsistent research findings, we examined the effects of the implementation of a four-day compressed workweek on time pressure, fatigue, perceived productivity, and work-life balance within a construction company. Moreover, we investigated the effect of employee expectations. Drawing on longitudinal data (N = 247) and using Latent Change Score Modelling (LCSM), we found that work-life balance increased while fatigue and time pressure decreased. Three months after implementing a compressed work schedule, perceived productivity remained stable. These effects were contingent on individuals’ expectations regarding the effect of the compressed schedule. The results highlight the importance of employee expectations in shaping the outcomes of the adoption of alternative work schedules.

Compact Heat Exchangers With Curved Fins for Hydrogen Turbofan Intercooling

Abstract Hydrogen is being considered as a possible path toward carbon-neutral aviation. There are additional advantages besides its main benefit of CO2-free combustion. One application is to use it for aero engine heat management due to its cryogenic temperature and high heat capacity, including intercooling and exhaust heat recuperation. The focus of this paper is on the design of a compact heat exchanger (HEX) integrated into an intermediate compressor duct (ICD), which could decrease compression work and specific fuel consumption (SFC). This compact heat exchanger features curved fins to promote flow turning and decrease pressure losses compared to more conventional straight fin heat exchangers. Conceptual design and duct shape optimization has been carried out which produced integrated ICD heat exchanger designs with significantly lower air-side total pressure losses compared to their conventional straight fin counterparts, which could improve system level integration and engine performance. A direct outcome of this study is a pressure loss correlation, which can be used in future engine system-level trade studies.

Thermodynamic Analysis of Modelled and Simulated Heat Pump Drying System Using Azeotropic Mixture of Organic Working Fluids

It is well-known that the choice of working fluid significantly impacts the performance, cost estimation, and environmental effect of a heat pump. In this study, the performance of pure working fluids (dimethyl ether and ethanol) was compared with that of azeotropic mixture working fluids used in vapor compression heat pumps. The study also examined the effect of compression ratio and different compressor models on the performance of a vapor compression heat pump for heating processes and drying tomato slices at an air temperature of 40 °C and an air flow rate of 200 kg/hr. Using ethanol as the working fluid at evaporating and condensing temperatures of 10 °C and 15 °C, respectively, the specific moisture extraction rate was 0.2112 kg/kWh, and the Carnot coefficient of performance was 57.60. The study demonstrated a COP improvement of more than 15% for azeotropic mixtures compared to a pure working fluid. The maximum overall energy efficiency and exergy efficiency, achieved with Mixture II, were 5.68% and 27.32%, respectively. As suction pressure increased while maintaining constant discharge pressure, the compression ratio and work done by the compressor decreased, while the system's overall energy efficiency, and overall exergy efficiency improved under the given conditions.

Feasibility of solar-powered air-conditioning system using natural refrigerants

This research focuses on low carbon dioxide alternatives to air-conditioning systems that use sustainable and low-power drives. This detailed research takes into account a 1 t capacity air-conditioning system using several refrigerants based on vapor compression. Natural refrigerants should be used instead of all-synthetic ones due to their environmentally favorable properties. Using the CoolPack software platform, a comparative analysis was conducted, and it was found out that the natural refrigerants R290 and R600a exhibited promising results in terms of heat removal from the evaporator (Q e (kW)), heat removal from the condenser (Q c (kW)), work done by the compressor (W (kW)) and coefficient of performance when fixed temperatures of 10°C for the evaporator and 50°C for the condenser were maintained. For the refrigerant R600a, superheating at the compressor (inlet) suction by 5°C was necessary to maintain the running cycle within a practical working zone. Given that a 1 t vapor compression cycle air-conditioning system based on R290 has a compressor work consumption of 640 W, the motor power input for a single-phase induction motor will be roughly 1000 W. In contrast, direct-current (DC) motors require about 30% less power (770 W) and can be readily driven by solar photovoltaic systems (DC). Thus, by presenting solar thermal (required for R600a) and solar photovoltaic power (DC) applications for the natural refrigerants R290 and R600a, the present work will contribute to a sustainable environment and demonstrate the capabilities of dependable operation with optimal power usage.

AI-Based Detection of Surge and Rotating Stall in Axial Compressors via Dynamic Model Parameter Estimation

Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak of their performance curves. These fluid dynamic instabilities can cause drops in efficiency, stress on the blades, fatigue, and even failures. Compressors are handled therefore by operating with a safety margin far from the surge line. Moreover, models able to predict onset instabilities and to reproduce them are of great interest. A dynamic system able to describe successfully both surge and rotating stall is the model presented by Moore and Greitzer That model has also been used for developing control laws of the compressor dynamics. The present work aims at developing an artificial neural network (ANN) approach able to predict either the permanence of the system in stable working condition or the onset instabilities from a time sequence of the compressor dynamics. Different solutions were tried to find the most suitable model for identifying the system, as well as the effects of the duration of the time sequence on the accuracy of the predicted compressor working conditions. The network was further tried for sequences with different initial values in order to perform a system analysis that included multiple variations from the initial database. The results show how it is possible to identify with high accuracy both rotating stall and surge with the ANN approach. Moreover, the presence of an underlying fluid dynamic model shares some similarities with physically informed AI procedures.

Calculated purpose of the distance between the expansion joints of cement concrete pavements of roads

Problem. The article discusses current issues of increasing the efficiency and quality of construction of cement concrete pavements for highways. It is shown that the regulatory documents in force in Ukraine recommend reducing the distances between compression joints and expansion joints during the construction of roads made of cement concrete. However, such a reduction leads to a slowdown in the pace of road construction and a significant increase in construction costs. The increase in cost occurs due to frequent stoppages of a set of concrete-laying machines and the formation of a large amount of concrete waste. The cost of this waste can reach UAH 200 thousand per 1 kilometer of road. In addition, frequent stops of a set of machines when laying cement concrete pavements of highways slow down the time it takes to put roads into operation. Purpose of the work. The aim is to calculate the expansion of cement concrete pavement when heated under operating conditions. Methodology. The work used formulas for thermophysical calculations during thermal expansion of concrete. The paper presents the results of thermophysical calculations of the expansion of cement concrete pavements of highways during their operation at elevated temperatures. It has been shown that when there are a large number of compression joints, they can partially compensate for the space required for concrete expansion. At the same time, they can act as compression joints during low temperatures. A design of double expansion seams has been proposed, which allows increasing the distance between them. The joint work of compression and expansion seams makes it possible to increase the distance between expansion seams. Due to this, it is possible to reduce their number, while simultaneously increasing the speed of construction and maintaining the quality indicators of the coating concrete. Originality: The article presents the results of a production test of thermophysical calculations. It is shown that two experimental sections of road surfaces were built. The concept of the maximum value of thermal expansion of concrete was further developed. Practical value: On one of them, the distance between expansion joints was 101 m, and on the other – about 300 meters. In this case, the distance between the expansion joints in the double seam was 1.5 meters. These parameters were sufficient for efficient and high-quality operation of double expansion joints.

Development of Ti-Zr-Mn based AB2 type metal hydrides alloys for an 865 bar two-stage hydrogen compressor

This study reports the development of a new Ti-Zr-Mn-based AB2 type hydrogen storage alloys for a two-stage metal hydride hydrogen compressor (MHHC). The hydrogen storage alloys are designed to compress hydrogen from 35 to 865 bar within a temperature difference of 115 °C. High-pressure PCT measurements up to 700 bar were carried out to test the performance of the alloys. The alloys' hysteresis and the plateau slope were reduced by optimizing the composition. The introduction of fugacity correction into the Van't hoff equation reduces the deviation between calculation and actual pressure to 24 bar at a pressure above 350 bar. A precise relation between the Ti/Zr ratio and the desorption pressure is described and helps make a correct design of the alloy composition. The designed alloy shows looses less than 1% of the capacity over 3000 full cycles. The desorption plateau pressure of the alloy is constant within 92% during the whole cycling process. A 2 stages compressor working with two types of alloys offers compression with a temperature range between -20 and 95 °C for the refueling hydrogen vehicles up to 865 bar.

Empirical modelling of a semihermetic reciprocating compressor for different CO2-based mixtures

Mixing CO2 with other refrigerants gives carbon dioxide new thermophysical properties, such as higher critical temperature or lower working pressures.However, most of these new mixtures havenotyetbeenevaluatedexperimentally, introducing a lack of knowledge about how the main components of a refrigerating plant will operate with these blends.One clear example is the compressor, whose operationdirectly affects the performance and energy consumption of theplant. Accordingly, this work evaluates experimentally the behaviour of a CO2 semi-hermetic reciprocating compressor working with four different CO2-based mixtures of CO2/R32, CO2/R290, CO2/R1270 and CO2/R1234yf. The analysis covers the parameters of volumetric and global efficiency, discharge temperature, mass flow rate, and electrical power consumption, where noticeable differences are shown in terms of efficiencies, affecting the mass flow rate and the electrical power consumption significantly, and, to a lesser extent, the discharge temperature. The experimental results are compared with the standardized models from UNE-12900 and AHRI-540, proposing a simplified empirical model with a prediction error below 4% for all analysed mixtures and an extensive model for other CO2-based mixtures.

Exploring the Work Motivational Factors of Generation Z Workforce in Selected BPO Companies: Basis For Job Satisfaction

This qualitative study explored the work motivational factors of the Generation Z workforce. Herzberg’s Approach guided the study in relating situations where Generation Z participants perceived themselves as motivated (job satisfaction) with their work and, equally, in circumstances where they felt demotivated (job dissatisfaction). Hygiene factors (extrinsic) identified for motivating and satisfying this generation at work included a conducive work environment, favorable policies, supportive leaders and teammates, and a competitive salary. For the intrinsic motivating factors, Generation Z participants expressed a desire for continuous personal and career growth, as well as aspirations for job promotions. Regarding demotivators, Generation Z participants perceived issues related to salary disputes, changes in work conditions like remote work (WFH), undesirable interactions with teammates, and unsupportive leaders. They also mentioned lack of rewards and recognition in terms of employee engagement from their company. Additionally, they were demotivated by the absence of training and development opportunities. This study recommended programs for BPO companies aimed at motivating and satisfying Generation Z in the workplace. These included work schedule options, recognition and rewards, and training and development. Work schedule options encompassed flexible scheduling and compressed work weeks, while recognition and rewards consisted of flexible reward options and employee-driven recognition programs. Finally, training and development programs focused on technology utilization, leadership, and team building. Implementing these programs would assist BPO companies in adapting to Generation Z behavior, thereby retaining them in the workforce.