Coefficient Of Performance Research Articles

Energy/freshwater sustainability in urban areas through a novel solar-driven system with H2 production/liquefaction: Techno-economic evaluation and multi-objective optimization

The application of solar-based power plants systems in cities offers various advantages. These include reducing reliance on fossil fuels, declining carbon emissions, and supporting efforts to address climate change. Additionally, solar energy enhances energy resilience, promotes economic growth, and generates employment opportunities through investments in solar infrastructure. The primary goal of the current investigation is to meet the daily energy requirements of environmentally friendly urban areas. The setup includes the utilization of various processes such as LNG regasification, parabolic trough solar collectors, dual-loop power cycles, reverse osmosis, and a unit for liquefaction and hydrogen production. The analysis shows that the evaluated plant generates a net output electricity of 1994 kW and has a levelized cost of electricity (LCOE) of 5.1 Cent/kWh. Furthermore, the system effectively caters to the water demand of 32.21 kg/s and cooling requirement of 392 kW for residential purposes. In addition, it exhibits the capability to generate hydrogen at a rate of 9.49 kg/h, which is subsequently stored in a liquid state. The study findings indicate that adjusting the pressure of the compressor has a substantial influence on liquefaction work. Initially, the work increases with increasing pressure, reaches a peak, and subsequently declines. It is crucial to maintain the recommended pressure level of approximately 5 MPa for optimal performance. This pressure level leads to an efficiency of 17.01% and a coefficient of performance (COP) of 0.16. According to the multi-objective optimization, the optimized system demonstrates a shorter payback period of 3.38 years compared to the baseline system's 4.03 years, despite having higher initial costs. Over a 20-year lifespan, the optimized system is more profitable, surpassing the baseline system by approximately $2.4 million.

Performance Evaluation of Water Cooled Condenser of Air Conditioner Working on VCRS

VCRS commonly known as (Vapour Compression Refrigeration System) is widely adopted method for air conditioning of buildings, in pharmaceutical industry for storage of medicine, in hospitals, automobiles etc. There are several methods for increasing the efficiency% (COP) of an VCRS cycle. Some of the modification can be done in Compressor, Condenser, Evaporator, and in Refrigerant . In this experiment, we adopted method of Subcooling to reduce Compressor work. This study investigates the implementation of subcooling in the condenser of a Vapour Compression Refrigeration System (VCRS) to enhance its efficiency and reduce power consumption. The traditional condenser design is modified by submerging it in a water tank, allowing for subcooling of the refrigerant. The subcooling process involves lowering the temperature of the refrigerant below its saturation temperature, which improves the system’s Coefficient of Performance (COP) by increasing the density of the refrigerant entering the expansion valve. This modification aims to optimize the heat rejection process and enhance the overall performance of the refrigeration system .Experimental result demonstrate a significant reduction in power consumption and an improvement in COP, highlighting the effectiveness of the condenser subcooling method in enhancing the efficiency of VCRS. Keywords : Compressor, Condenser, Expansion Valve, Evaporator.

Natural refrigerant mixtures in low-charge heat pumps: An analysis of the potential for performance enhancements

The study investigated the characteristics of different natural refrigerants and their mixtures in a residential heat pump with low refrigerant charge. Three main evaluation criteria were utilized for comparing different mixtures: Coefficient of Performance (COP), Volumetric Heating Capacity (VHC), and a newly proposed indicator, the heating capacity at charge limit. Propane was used as a reference refrigerant. It was found that some mixtures significantly improved both COP and the heating capacity at charge limit while maintaining similar volumetric heating capacity and operating conditions. Alternative multi-criteria decision-making techniques were adopted to rank the best refrigerant mixtures. Mixtures rich in Dimethyl Ether (DME), such as DME-CO2 [0.96-0.04] and DME-Propylene [0.75-0.25] were found consistently among the best options. Those were followed by Propylene-rich mixtures such as Propylene-CO2, Propylene-Isobutane and Propylene-Butane. The levelized cost of heat (LCOH) could be improved by up to 12 %. To accelerate the transition to natural refrigerants, without compromises on efficiency and costs, further research and certification activities on non-fluorinated refrigerants based on Dimethyl Ether (R-E170), CO2 (R-744) and Propylene (R-1270) are recommended.

Assessment of using different ozone-friendly R22 alternative refrigerants in residential air conditioners in a high-ambient temperature country

The performance of a vapor compression refrigeration system (VCRS)-based residential air conditioner operating in a high-ambient temperature (HAT) country was investigated using six zero-ODP (ozone depletion potential) refrigerants as replacements to R22. The non-flammable alternative refrigerants considered in the present research were R134a, R404A, R407C, R410A, R448A, and R507A. Using the basic conservation laws, the VCRS was modeled during steady-state operation and solved using engineering equation solver (EES) software. Coefficient of performance (COP), pressures and temperatures at compressor suction and discharge, Global Warming Potential (GWP), critical pressure and temperature, compressor pressure ratio, volumetric cooling capacity (VCC) specific cooling capacity (SCC), and refrigeration effect were utilized as assessment criteria for the alternative refrigerants considered. From these refrigerants, the highest values of suction pressure, discharge temperature, and condenser pressure were attained by R410A. In addition, the discharge temperatures for all refrigerants, except R134a, were all higher than their corresponding critical values, causing a quicker drop in the VCRS’s performance. As an alternative refrigerant, R407C showed the highest SCC of 141.0 kJ/kg followed directly by 139.2 and 138.0 kJ/kg for R410A and R448A, respectively. A reverse trend was found for VCC with respective values of 4722 and 3775 kJ/m3 for R410A and R448A. Lower volume flow rates and smaller-sized compressors are expected for higher VCC refrigerants. The same trend was found for the compressor’s specific work input and condenser’s specific heat transfer with values of (51.14, 46.82, and 45.38 kJ/kg) and (190.3, 187.8, and 183.4 kJ/kg) for R410A, R407C, and R448A, respectively. For applications in HAT countries, larger condenser’s specific heat transfer makes the refrigerant more applicable. Conversely, with respect to COP, refrigerant R134a with a value of 3.075 was the superior alternative followed by R448A and R407C with respective COPs of 3.042 and 3.011. Based on the overall assessment in terms of environmental obligation, COP, compressor input power, refrigerant flow rate required, and all the evaluations made in this research, refrigerant R448A was recommended as the most appropriate substitute to R22 which can effectively be used in residential air conditioners in a HAT country.

Assessment of a hybrid solar water heating system: environmental impact and economic viability

ABSTRACT Conventional methods of space heating are not only expensive but also environmentally harmful, as they emit greenhouse gases that contribute to global warming. To tackle this issue, a hybrid solar water heating system assisted by a solar evacuated tube collector has been developed at the Madhav Institute of Technology and Science in Gwalior, India. Experiments conducted from November to February 2022–23 (winter season) revealed promising results. Throughout the winter season, the system achieved a daily average effective solar heat collection of 2.85 kWh, with a daily average collector efficiency of 45.5%. The average coefficient of performance (COP) of the solar water heat exchanger was 3.5. Additionally, the system demonstrated an energy payback time of 1.2 years, shorter than that of conventional systems. Over its lifetime, the developed winter heating system is estimated to mitigate 127.9 tonnes of CO2 emissions, earning a carbon credit of $1408. Economic analysis further revealed a favorable benefit-to-cost ratio for the hybrid system, ranging from 3.13 to 3.36, with a payback period varying from 5.03 to 4.47 years for an inflation rate of 6–13%. These findings affirm the feasibility and efficacy of a solar-powered hybrid active winter heating system.

Energy, exergy and sustainability analysis of a photovoltaic-thermal solar system with nano-enhancement and thermal energy storage integration

As a result of using various energy sources such as fossil fuels, harmful gases emerge and endanger the world's future. The search for different energy sources is to diminish the dangers that may arise in the future. Renewable energy sources are also the most basic for a sustainable future. This study aims to increase the performance of photovoltaic thermal collectors (PVT), which are used to obtain thermal energy from solar energy and produce electrical energy. The novelties of this experimental work are the analysis of a combination of a solar air heater and thermal energy storage via a phase change material technology and surface modifications on absorber plates, including a nanotechnological amendment. Furthermore, the adverse impacts on the environment of the manufactured systems were taken into account with the help of such parameters as waste exergy ratio and sustainability index. Initially, PVT with a V-grooved absorber surface (V-PVT) was built. In the second stage, nano-enhanced V-grooved PVT (NE/V-PVT) was produced, in which the absorber plate was coated by graphene nanoparticles. Then, a thermal energy storage entity was mounted onto the system, and the V-grooved PVT with the thermal energy storage entity (TS/V-PVT) was developed. 40 W absorber fans were used to provide airflow in these manufactured collectors. In addition, Styrofoam insulation material was used for the collector case, and a low-cost system was designed. Simultaneous experiments for each PVT were carried out. The waste exergy ratio (WER) and the sustainability index (SI) were also considered. Based on the experimental results, thermal efficiency was calculated as 40.60%, 54.01%, and 53.90% for V-PVT, NE/V-PVT, and TS/V-PVT, respectively. Furthermore, the coefficient of performance (COP) values were obtained as 2.67 for V-PVT, 4.28 for NE/V-PVT, and 3.49 for TS/V-PVT. The findings illustrated that nano-coating and V-grooved modifications on solar collectors substantially increased the system performance.

Heating performance of a vapor compression heat pump cascaded with a thermoelectric heat pump

Air source heat pumps (ASHPs) are widely utilized for heating and cooling in residential buildings; however, their effectiveness in heating mode is compromised during extreme weather conditions. Extensive research endeavors have been undertaken to develop, test, and assess a cost-effective vapor compression ASHP suitable for cold climate regions. This study takes an innovative approach by developing component and system prototypes for a cold climate heat pump. This design combines a thermoelectric heat pump (TEHP) with a traditional residential split ASHP to augment heating capacity in low ambient temperature conditions. The component and system prototypes underwent experimental testing in the psychrometric chambers. The experimental findings revealed a 13.6 % to 13.7 % increase in total heat pump heating capacity, accompanied by a 3.1 % to 5.0 % decrease in the coefficient of performance (COP) at ambient temperatures of −15 °C and −19 °C, when compared to the original ASHP. The COP of the TEHP is relatively constant, ranging from 1.63 to 1.76. This prototype offers a solution to address the challenges associated with reduced heat pump capacity at low ambient temperatures. The experimental results indicated that the lower the ambient temperature, thermoelectric heat pump auxiliary heating can increase the heating efficiency 60 % in comparison to electric resistance.

Limits of coefficient of performance of adsorption cooling cycle based on refrigerant’s type

This research work discusses how the thermodynamic properties of refrigerant constrain the upper limit of the coefficient of performance (COP) of adsorption cooling (AC) cycle. A mathematical model is developed based on the mass and energy balance across the adsorption bed and used to estimate the maximum COP. Langmuir model is used to derive the ideal COP. Besides, Carnot COP and exergy efficiency are derived to evaluate the adsorption cooling cycle further. These new parameters are applied to the available cycles in the open literature to assess how much room for improvement is still left in the adsorption technology based on the refrigerant type. Water, ammonia, methanol, ethanol, Butane, R134a, R32, CO2 and R1234ze are used in this study. The maximum cooling COP cannot exceed 1.0 for cooling applications and is always less than 2.0 for heat pumps. Results show that AC cycles using water or ethanol as refrigerants achieve the highest exergy efficiency. The AC cycle using water as an adsorbate and silica gel as an adsorbent has the highest relative COP, about 80 % at 85 °C regeneration temperature. In turn, CO2 exhibits the lowest one. This work is merely an attempt to save experimental effort and time by identifying the most suitable refrigerant based on its physical and thermal properties and the cycle operating conditions.

Self-oscillating polymeric refrigerator with high energy efficiency.

Electrocaloric1,2 and electrostrictive3,4 effects concurrently exist in dielectric materials. Combining these two effects could achieve the lightweight, compact localized thermal management that is promised by electrocaloric refrigeration5. Despite a handful of numerical models and schematic presentations6,7, current electrocaloric refrigerators still rely on external accessories to drive the working bodies8-10 and hence result in a low device-level cooling power density and coefficient of performance (COP). Here we report an electrocaloric thin-film device that uses the electro-thermomechanical synergy provided by polymeric ferroelectrics. Under one-time a.c. electric stimulation, the device is thermally and mechanically cycled by the working body itself, resulting in an external-driver-free, self-cycling, soft refrigerator. The prototype offers a directly measured cooling power density of 6.5 W g-1 and a peak COP exceeding 58 under a zero temperature span. Being merely a 30-µm-thick polymer film, the device achieved a COP close to 24 under a 4 K temperature span in an open ambient environment (32% thermodynamic efficiency). Compared with passive cooling, the thin-film refrigerator could immediately induce an additional 17.5 K temperature drop against an electronic chip. The soft, polymeric refrigerator can sense, actuate and pump heat to provide automatic localized thermal management.

Thermodynamic performance analysis and environmental impact assessment of cascade refrigeration cycles using eco-friendly nano-refrigerants

There is a lack of research in the literature on the application of nanoparticles to different cascade cycle configurations with environmental refrigerants in ultra-low temperature refrigeration applications. This study is the first on the use of nano-refrigerants in cascade refrigeration cycles. In this study, the effect of 2 wt.% of CuO to RE170 and R170-pure refrigerant utilization in cascade vapor compression refrigeration cycle (CVCRC), cascade ejector refrigeration cycle (CERC) and cascade ejector intercooler refrigeration cycle (CEIRC) are investigated to achieve higher performance values in ultra-low temperature applications. For CVCRC, CERC and CEIRC, the increases in terms of coefficient of performance (COP) with the use of nano-refrigerant were found to be 12.77 %, 8.20 %, and 6.37 %, respectively, and 18.55 %, 14.05 %, and 6.07 %, for exergy efficiency. Upon scrutinizing the results with nano-refrigerant in relation to the COP, the analysis revealed that the CEIRC cycle exhibited an improvement ranging from 13.43 % to 20.49 % in comparison to CERC. Additionally, with nano-refrigerant, the CEIRC cycle demonstrated an increase ranging from 42.39 % to 75.41 % when compared to CVCRC in COP. It was observed that the utilization of CEIRC led to a 13.03 % decrease in kg CO2 emissions in compared to CERC and a reduction of 32.53 % compared to CVCRC with using nano-refrigerant.

Experimental evaluation of Adsorption Heat for Water vapour/Silica gel pair for chiller application

Isosteric adsorption heat is crucial in assessing adsorption cycle performance. Typically, adsorption heat is indirectly estimated from the isotherm equation fitted to the experimental uptake data. This indirect method is susceptible to the accuracy and choice of isotherm equation. Consistency of this indirect method with actual adsorption heat measurements is rarely examined. Present work addresses this research gap by simultaneously measuring adsorption uptake and heat. This is achieved by incorporating heat flux sensors within an existing constant volume variable pressure (CVVP) setup. The measurements are carried out for water vapour/RD-silica gel pair with temperature and pressure ranging from 298 to 363 K and 0.15 kPa to 6.3 kPa respectively. Two popular isotherms viz. Dubinin–Astakhov (D–A) and Tóth isotherm equation are used to estimate the indirect adsorption heat. Both isotherm equations show a good fit with the experimental uptake (< 5% deviation). Interestingly, indirect adsorption heat estimated using Tóth isotherm fails to predict (∼15% deviation) the uptake dependent adsorption heat trend shown by calorimetric data, whereas D–A isotherm agrees well (<5% deviation). Therefore, the present work forms fundamental basis for identifying suitable isotherm equation, which is consistent with experimental adsorption uptake as well as heat data. Subsequently, a comparison of theoretical coefficient of performance (COP) for water vapour/RD-silica gel adsorption chiller is undertaken, based on indirect adsorption heat values available in the literature. The comparison reveals that COP prediction is sensitive to adsorption heat. This further emphasizes the necessity for experimentally measuring adsorption heat.

Enhanced Elastocaloric Effects in γ-Graphyne.

The global emphasis on sustainable technologies has become a paramount concern for nations worldwide. Specifically, numerous sustainable methods are being explored as promising alternatives to the well-established vapor-compression technologies in cooling and heating devices. One such avenue gaining traction within the scientific community is the elastocaloric (eC) effect. This phenomenon holds promise for efficient cooling and heating processes without causing environmental harm. Studies carried out at the nanoscale have demonstrated the efficiency of the eC effect, proving to be comparable to that of state-of-the-art macroscopic systems. In this study, we used classical molecular dynamics simulations to investigate the elastocaloric effect for the recently synthesized γ-graphyne. Our analysis goes beyond obtaining changes in eC temperature and the coefficient of performance (COP) for two species of γ-graphyne nanoribbons (armchair and zigzag). We also explore their dependence on various conditions, including whether they are deposited on a substrate or prestrained. Our findings reveal a substantial enhancement in the elastocaloric effect for γ-graphyne nanoribbons when subjected to prestrain, amplifying it by at least 1 order of magnitude. Under certain conditions, the changes in the eC temperature and the COP of the structures reach expressive values as high as 224 K and 14, respectively. We discuss the implications of these results by examining the shape and behavior of the carbon-carbon bond lengths within the structures.

Numerically investigating the effect of using nanofluids on the thermal performance and coefficient of performance of a U-tube deep borehole ground source heat pump

In this study, a deep-borehole ground source heat pump was simulated using computational fluid dynamics (CFD) method. The thermal performance and coefficient of performance (COP) of the vertical ground source heat pump simulated with accuracy using CFD for water and 4 different nanofluids as working fluids were investigated. Two nanofluids contained silver and copper metallic nanoparticles and the other two nanofluids contained copper and aluminum oxide nanoparticles. For each of these nanofluids as well as water, the heat exchange rate, total exchanged heat, outlet temperature and COP were calculated and the results were compared together. The results showed that using nanofluids leads to increased exchanged heat. Nanofluids based on aluminum oxide, copper oxide, copper and silver nanoparticles resulted in 4.83, 5.76, 6.9, 7.69 percent increase in total exchanged heat, respectively. In addition to increased exchanged heat, using nanofluids increased the outlet temperature. Also, the results showed that the maximum and minimum increase in COP were 36.5% and 5.2% which were related to using silver and aluminum oxide nanoparticle-based nanofluids, respectively.

Experimental investigation on frosting performance of a microchannel heat exchanger in heat pump system for electric vehicles

Frosting of outdoor heat exchangers deteriorates the heat transfer performance of the electric vehicle (EV) heat pump system. The frosting performance of the outdoor heat exchanger in an EV heat pump air-conditioning system was investigated experimentally, considering different flow configurations, tube arrangements, and frontal air volume. The purpose of the study was to establish the optimal tube arrangements and flow configurations for minimizing frost formation and maximizing system performance. The results indicate that a three-flow configuration outperforms a two-flow setup under frosting conditions. Specifically, a flow sequence of 14-21-35 increases the heat capacity by 15.05 %–20.64 % compared to that of the reverse flow of 35-21-14. Additionally, the coefficient of performance (COP) increases by 1.19 %–3.55 %. Higher airflow reduces frost formation. A significant correlation exists between the refrigerant distribution within the heat exchanger and the corresponding frost distribution on the surface of the microchannel heat exchanger. The frost formation rate was slower for the flat tube vertical arrangement. Furthermore, horizontal tube arrangements were more conductive than vertical ones, providing a more uniform temperature distribution and higher heat transfer rates (an increase of 2.7% in heat transfer and 3.4% in heat capacity). The COP of the vertical arrangement system was consistently higher than that of the horizontal arrangement by 1.4 %–3 %.

Performance improvement of the phase change material-assisted earth-air heat exchanger in summer

Studies confirmed that phase change material (PCM) can improve the cooling potential of an earth-air heat exchanger (EAHE). However, the poor utilization of the PCM unit’s latent heat storage (LHS) capacity and insufficient understanding of energy efficiency hinder its applications in EAHE. To solve these problems, this study made a structural improvement to the PCM unit and proposed a centrally located hollow cylindrical PCM-assisted EAHE (CHCPCM-EAHE). Then, numerical simulations were conducted on this CHCPCM-EAHE through a 3-D model built on the ANSYS FLUENT, and its cooling performance in Chongqing (China) summer was comparatively studied. The results found that the LHS performance of the PCM unit in this CHCPCM-EAHE was improved despite the significant reduction in material volume. Compared to the PCM unit in the previous PCM-assisted EAHE, the maximum liquid fraction and average charged latent heat in all charge–discharge cycles of the PCM unit in this CHCPCM-EAHE were increased by 56.82 % and 10.46 %∼56.43 %, respectively. The results also found that the CHCPCM-EAHE performed better in cooling potential and coefficient of performance (COP). Compared to the conventional EAHE and previous PCM-assisted EAHE, its average cooling capacity increased by 60.12 %∼70.75 % and 4.05 %∼10.96 %, and average COP increased by 47.22 %∼49.02 % and 6.88 %∼8.18 %, respectively.

An examination of the vapour compression refrigeration system performance utilizing several environmentally friendly refrigerants and the effect of nanoparticles- a review

The refrigeration system stands out as a significant contributor to the escalating trend in energy consumption. Therefore, implementing energy-saving measures is considered one of the most effective strategies for addressing this challenge. Nanofluids demonstrate remarkable promise in enhancing refrigeration systems' thermodynamic and mechanical efficiency. In contemporary times, there is a global emphasis on exploring nano refrigerants to enhance the heat transfer properties of cooling systems. Household and industrial refrigeration systems commonly utilize Hydrofluorocarbons (HFCs) because of their exceptional thermodynamic attributes. Nevertheless, the Kyoto Protocol has classified HFCs as contributors to global warming because of their high (GWP) value, which stands at 1300., their improved Coefficient of Performance (COP), and, critically, a lower GWP while having zero Ozone Depletion Potential (ODP). Integrating nanoparticles with high thermal conductivity into traditional refrigerants has revealed compelling outcomes. These include heightened heat transfer coefficients, enhanced (COP), and reduced energy consumption by compressors in household refrigerators. This article explores the use of environmentally friendly refrigerants and the impact of nanoparticles on refrigeration systems.

Effect of geometry on the coefficient of performance of Ni–Ti elastocaloric parts manufactured via powder bed fusion

This study investigates the greater coefficient of Performance (COP) exhibited by the Ni–Ti lattice geometry (LS) over the solid geometry (SS) for solid-state heating and cooling. The LS's advantageous COP can be attributed to factors including variations in phase transformation behavior, a larger surface area facilitating enhanced heat transfer, and a greater volume of water heated per cycle owing to the cavities. Moreover, the LS demands lower compression forces due to its lower mass and geometry, which contribute to its heightened energy efficiency. Remarkably, the LS achieved a maximum temperature span of 11.2 °C at 40 kN compression force, whereas the SS required 80 kN to attain a similar 12.9 °C span. Both the SS and LS showcased a non-linear correlation with compression force which was attributed to Lauder's transformation and pseudo-elastic behaviors. Additionally, the temperature span of the SS exhibited symmetrical behavior during heating-cooling cycles. Conversely, the LS displayed asymmetry, with a more substantial temperature change during the cooling phase than the heating phase.

Solar adsorption cooling system operating by activated–carbon–ethanol bed

One efficient way to convert small thermally energized into effective cooling is through adsorption cooling technology, which increases energy efficiency and reduces environmental pollution. This study's primary goal is to hypothetically examine the thermal coefficient of performing the solar adsorptive refrigerator machine operated with an activating carbon/Ethanol operating dual. The impact of different operating situations and design factors on the machine's performance is inspected and evaluated. The present double-bed solar energy adsorptive-cooler unit is modeled by thermodynamic methodology. Then, it was analyzed to evaluate its effectiveness work under Baghdad climate conditions. For the current study, the two-bed solar adsorption cooling unit with 0.5 kW capacity input heat 11893 that operates at 5 °C for the evaporator and 45 °C for the condenser is presented. The Engineering-Equation-Solver (EES) simulation program was created and used to solve the modeling equations that predict the optimal cycle performance and evaluate the optimum reasonable values of the operation parameters of the proposed system. The pressure range for the refrigeration cycle is 2.408 kPa for the evaporation state and 23.14 kPa for the condensation state. The findings demonstrate that an optimum coefficient of performance (COP) is 0.702 at 95 °C, a 20% performance increase, which generates 39.4 of cooling water. It produced 1 kg of chilled water for 2.463 kg of activated carbon at a temperature of 5°C. The improved solar-powered adsorption systems and refrigeration technologies are appealing substitutes that can satisfy energy demands in addition to meeting needs for cooling, ice production, air conditioning, and refrigeration preservation and safeguarding of the environment with Iraq's climate conditions.

Modelling of the refrigerant distribution in a critically charged propane heat pump cycle for performance evaluation

The investigation of heat pumps employing natural refrigerants as working fluids has gained substantial momentum, driven by increasingly stringent regulations addressing the global warming potential (GWP) and ozone depletion potential (ODP) of refrigerants. Propane (R290) stands out as an attractive option due to its low GWP and zero ODP. However, a major drawback of propane lies in its flammability. When using propane as working fluid, it will therefore be necessary to limit the total refrigerant charge within the system, without compromising on the heat pump performance. This study endeavors to address this challenge by developing a model of the refrigerant charge distribution in a critically charged heat pump system consisting of an evaporator, a compressor, a condenser, and an expansion valve. In the model, the charge distribution in the two heat exchangers is modelled in detail using a suitable void fraction correlation. For the compressor and expansion valve, a simplified model is employed, in which no refrigerant charge is calculated. Using an iterative procedure, the model can then be used to determine the coefficient of performance (COP), evaporator- and condenser pressure for a heat pump with an established total charge and heat capacity. The influence of different design and operation parameters, such as the degrees of subcooling and superheat, the volume ratio of the evaporator and the condenser, etc., can be assessed.

Optimal charge amount for semiconductor chiller applying eco-friendly refrigerant R-744

The refrigerants used to cool the heat generated in semiconductor production are Freons, which are now subject to regulation because of their high ozone depletion potential (ODP) and global warming potential (GWP). Therefore, R-744 is considered an eco-friendly refrigerant. This study experimentally analyzed the effect of the refrigerant charge amount based on the temperature discharged after cooling objects when operating a brine chiller using R-744 under subcritical conditions. The results showed that the optimal charge amount in terms of the coefficients of performance (COP) differed from that in terms of the maximum cooling capacity. In case of the apparatus used in this study, the optimal refrigerant charge amount with maximum cooling capacity was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and −10 °C and at 9.2 kg when the temperature of the cooling object was 0 °C. However, in terms of COP, the optimal refrigerant charge amount was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and 0 °C. This difference was attributed to the variation in the required evaporation heat capacity with the target temperature of the cooling object.