Vapor Compression Cycle Research Articles

Exergy and parametric analysis of freeze desalination with reversed vapor compression cycle

Freezing desalination is one of the recent technologies that tries to contribute in water shortage problems. The idea of desalination by freezing is quite new and still needs more deep investigation for better understanding and proposing new enhancements in the system’s technology. This paper aims to present exergy and parametric analysis for different operational parameters of a small-scale desalination by freezing unit working on a reversed vapor compression cycle. Operating parameters including freezing ratio, temperature and salt concentration are investigated. These parameters variations are critical to determine the working design parameters effects on the overall cycle performance. Salinity range from 5000 to 45000 ppm was tested using a heat pump of a C.O.P range from 3.8 to 8.2. Results showed that the energy consumption for this system range was 14.5 and 68.7, kWh per meter cube water production at 5000 and 45000 ppm, respectively. Exergy analysis showed that recovering larger quantities of the expelled brine is more efficient and useful due to more contributions in increasing the energy efficiency of the operating cycle. The proposed system proved to give higher thermal efficiency compared to alternative desalination systems such as reverse osmosis with membranes or flash systems. The system recorded a high thermal efficiency of 44% at 25 °C and 50% icing ratio. The output results from the system analysis given in this paper could significantly help to implement an actual optimized desalination system working on a reversed vapor compression cycle.

Energetic, exergetic and exergeoeconomic assessment of a hybrid solar/biomass poylgeneration system: A case study of a rural community in a semi-arid climate

Abstract In this work, a polygeneration system combining a compound parabolic collectors’ solar field, a thermocline thermal energy storage system, biomass boilers, an ORC, a reverse osmosis unit, a vapor compression cycle and a hybrid air/water condenser, is investigated considering energetic, exergetic and exergoeconomic indicators. The studied system is assessed for the case of a 40 households community located in a semi-arid region (Benguerir, Morocco) characterized by a good solar potential (DNI of 2239 kWh/m2/y) and the presence of brackish groundwater. Results show that the proposed system could meet a significant part of the community’s requirements with an annual biomass consumption of 342 T and an average solar contribution of 20%. The weekly plant’s overall energy efficiency is varying between 15 and 44%, while its corresponding exergy efficiency is in a range between 5 and 2.9%. Results also report that the use of R1336mzz(Z) as an ORC working fluid could reduce the weekly biomass consumption by 13.4%, while the use of R1234ze(Z) could lead to an increase of this value by 8.94%. Finally, a parametric study highlighted that considerable cost reductions should be fulfilled at the solar field’s level to make its aperture increase economically viable.

Energy, economic and environmental evaluation of a novel combined cooling and power system characterized by temperature and humidity independent control

A novel combined cooling and power system with independent control of temperature and humidity was presented to meet the energy supply demand in buildings. The energy, economic and environmental characteristics of the organic Rankine cycle powered two-stage vapor compression cycle with sixteen organic working fluids were discussed at variable geothermal fluid temperature. The results showed that organic Rankine cycle powered two-stage vapor compression cycle had certain advantages in improving refrigeration performance. Taking the critical mass flow rate as the boundary, the cooling and electricity output of the system could be controlled by adjusting the mass flow rate of refrigeration device. As far as the output power of the system was concerned, R1234yf, R134a, R600a, R600, R123 and R601 were suitable for different temperature ranges of geothermal fluids, while in terms of refrigeration performance, R1234ze, R245fa, R123, and R601 were respectively suitable for different geothermal fluid temperatures. The system with N-heptane had the optimal techno-economic performance, which electricity production cost decreases from 0.1543 $/kWh to 0.0484 $/kWh. Therefore, the novel combined cooling and power system can meet the seasonal cooling and electricity demand of the building and maximize the use of dry hot rock resources.

Optimal arrangement of a micro-CHP system in the presence of fuel cell-heat pump based on metaheuristics

ABSTRACT The current energy crisis in today's world has pushed human vision to the optimal use of available energy, and experts have always taken steps to realise this important issue. One of these solutions is the use of cogeneration cycles. The main purpose of this study is to present a multi-objective methodology to select the optimal arrangement of a heat pump (HP)-based CHP system. The optimal arrangement is based on select of the best model of three different HP technologies, trans-critical R744 cycle, Peltier device, and vapour compression cycle (VCC) to achieve the best efficiency for the hybrid HP-based and fuel cell-based micro-CHP system. The optimisation process is performed based on a developed model of the Coyote Optimization Algorithm (COA) by considering two dissimilar objectives: maximising the performance of the hydrogen energy consumption and minimising the combined yearly maintenance and capital costs. The final results indicate that the VCC technology gives the best performance with regards to its low-cost and efficient features.

The effect of stage number on the performance of a vapor compression refrigeration cycle using refrigerant R32

In the refrigerant cycle of Air-Conditioning (AC) unit the mainly used cycle is vapor compression cycle. The performance of the refrigerant, named as Coefficient of Performance (COP), need to be improved by using modification. The modification by using multi stage is one of the potential solutions. In the present study, the effect of number of stage to the performance will be explored. A simple vapor compression cycle that is typically used in the AC unit is taken into study. IN the cycle the refrigerant is difluoromethane R32. Three different stages are examined, they are single stage, two-stages, and three stages. The numerical analyses are carried out using commercial Aspen One software. The COP, mass flow rate of the refrigerant and compressor power will be discussed. The result shows that increasing the number of stages related to increasing the COP.

A Comparative Study of Solar-Driven Trigeneration Systems for the Building Sector

The utilization of solar irradiation in the building sector is vital to create sustainable systems. Trigeneration systems are highly efficient systems that usually produce electricity, heating and cooling which are the main energy needs in the buildings. The objective of this work is the energetic and financial investigation of three different solar-driven trigeneration systems that can be applied in buildings with high energy needs (e.g., hospitals or commercial buildings). The parabolic trough solar collector (PTC) is selected to be used because it is the most mature solar concentrating technology. The examined configurations practically are different combinations of organic Rankine cycle (ORC) with heat pumps. System 1 includes a PTC coupled to an ORC which feeds an absorption heat pump machine. System 2 includes a PTC which simultaneously feeds an ORC and absorption machine. System 3 includes a PTC which feeds an ORC and a heat exchanger for heating, while the ORC is fed with and electricity a vapor compression cycle for cooling production. The simple payback period of System 1 is 5.62 years and it is the lowest, with System 2 to have 7.82 years and System 3 to have 8.49 years. The energy efficiency of the three systems is 78.17%, 43.30% and 37.45%, respectively, while the exergy efficiency 15.94%, 13.08% and 12.25%, respectively. System 1 is the best configuration according to energy, exergy and financial analysis. This study is performed with developed thermodynamic models in Engineering Equation Solver and a dynamic model in FORTRAN.

Performance Results of a Solar Adsorption Cooling and Heating Unit

The high environmental impact of conventional methods of cooling and heating increased the need for renewable energy deployment for covering thermal loads. Toward that direction, the proposed system aims at offering an efficient solar powered alternative, coupling a zeolite–water adsorption chiller with a conventional vapor compression cycle. The system is designed to operate under intermittent heat supply of low-temperature solar thermal energy (<90 °C) provided by evacuated tube collectors. A prototype was developed and tested in cooling mode operation. The results from the testing of separate components showed that the adsorption chiller was operating efficiently, achieving a maximum coefficient of performance (COP) of 0.65. With respect to the combined performance of the system, evaluated on a typical week of summer in Athens, the maximum reported COP was approximately 0.575, mainly due to the lower driving temperatures with a range of 75 °C. The corresponding mean energy efficiency ratio (EER) obtained was 5.8.

OPTIMIZATION OF THE PERFORMANCE OF VAPOUR COMPRESSION CYCLE USING LIQUID SUCTION LINE HEAT EXCHANGER

One of the most commonly used refrigeration systems is vapour compression refrigeration system. As saving energy remains a challenge, researchers are putting a lot of efforts into finding efficient solution to improve the performance of vapour compression refrigeration systems. Mechanical subcooling and Liquid Suction Line Heat Exchanger (LSLHX) are approaches that have shown to improve the performance of Vapour Compression Cycle (VCC) systems. This experimental study is conducted to achieve two objectives. First objective is to optimize the heat source and heat sink water volumetric flow rate combination that results in the best performance. In order to evaluate the effect of using subcooling cycle and LSLHX cycle, different flow rate combinations are studied and analysed. Then, to optimize the heat source and heat sink water volumetric flow rate combination that outcome in the optimum performance. Second objective is to optimize the system performance through implementing subcooling and LSLHX. At the optimum water flow rates, the basic VCC performance of the designed system showed better performance compared to the published data. The system performance was improved by 10% at the optimum flow rate when solely subcooling was used while deteriorated by 47.5% at full LSLHX.

A novel storage system for cooling stand-alone photovoltaic installations

Stand-alone photovoltaic systems usually use batteries to adjust energy yield to energy demand. An alternative energy storage system for stand-alone photovoltaic installations is proposed for three cooling applications: air conditioning, food preservation and freezing. A thermally insulated storage tank with ammonia in saturated mixture phase is integrated into the vapour-compression cooling cycle. A thermodynamic model and an economic assessment based on typical costs and cost sensitivity are included to assess the proposed system performance in comparison with a conventional stand-alone photovoltaic system with a vapour-compression cycle. Results show that the proposed storage strategy is an affordable option, especially in hot climates and for food preservation and freezing applications.

Investigation and Analysis of R463A as an Alternative Refrigerant to R404A with Lower Global Warming Potential

This research presents the development of R463A refrigerant, a nonflammable refrigerant that was retrofitted to replace R404A. R463A is primarily composed of hydrofluorocarbons/hydrocarbons/carbon dioxide (HFCs/HCs/CO2), and has global-warming potential (GWP) of 1494. It is a nonazeotropic mixture of R32 (36%), R125 (30%), R134a (14%), R1234yf (14%), and R744 (6%). R463A is composed of polyol ester oil (POE), and it is classified as a Class A1 incombustible and nontoxic refrigerant. R463A has a higher cooling capacity (Qe) than that of R404A, as it is composed of hydrofluorocarbons (HFCs) R32 and carbon dioxide (CO2) R744, and has lower GWP than that of R404A due to the use of hydrofluoroolefins (HFOs) from R1234yf. The results of this research showed that R463A can be retrofitted to replace R404A due to its composition of POE, Class A1 incombustibility, and lower toxicity. The properties of R463A and R404A, as analyzed using national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software, are in accordance with the CAN/ANSI/AHRI540 standards of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). The normal boiling point of R463A was found to be higher than that of R404A by 23%, with a higher cooling capacity and a 63% lower GWP value than that of R404A. The critical pressure and temperature of R463A were found to be higher than those of R404A; it can be used in a high-ambient-temperature environment, has higher refrigerant and heat-rejection effects, and has lower GWP than that of R404A by 52% due to the HFOs from the R1234yf component. The cooling coefficient of performance (COPc) of R463A was found to be higher than that of R404A by 10% under low-temperature applications. R463A is another refrigerant option that is composed of 7% carbon dioxide (CO2), and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs, HFOs, HCs, and natural refrigerants, which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Design, manufacturing and testing of a Beta Stirling machine for refrigeration applications

As the concern for CO2 emissions and global warming raises, the Stirling machine appears as a candidate alternative technology to vapor compression cycles that use refrigerant fluids. In this paper, we present the design, manufacturing and testing of a Beta Stirling machine for refrigeration applications. The first part of the paper presents the principle of the Stirling cycle, the mechanical configuration of the designed machine, and the key design parameters. The second part describes the experimental test bench and instrumentation of the Stirling machine. The last part of the paper presents experimental results. The prototype typical performance is a 450 W heat lift at 4°C and a COP of 0.9 when Nitrogen is used as the working gas. Cold end temperature variation as a function of heat lifts and charge pressure are presented. Coefficient of Performance is also discussed. Mechanical power, instantaneous torque and velocities curves are reported.

Synergetic cascade-evaporation mechanism of a novel building distributed energy supply system with cogeneration and temperature and humidity independent control characteristics

Low and medium grade heat sources, such as geothermal energy, solar energy, and various waste heat sources, can only usually meet the independent demand of electricity, cooling or heating in the building. However, the demand for different forms of energy exists simultaneously. Therefore, a novel distributed building energy supply system is presented and cascade evaporation is used for combined cooling, heating and power. Two-stage evaporation is adopted to realize the temperature and humidity independent control. The coupling effect of the cascade evaporation and the building energy supply ability is illustrated through the multi-parameter optimization of system power generation and refrigeration performance as well as the simulation analysis of cooling and power control strategies. The results show that the organic Rankine cycle (ORC) as the power source of the vapor compression cycle (VCC) eliminates the mechanical work and electrical energy conversion process between the ORC and VCC. The low-temperature stage of VCC dehumidifies the outdoor fresh air, while the high-temperature stage cools the indoor return air, realizing the independent control of temperature and humidity and increasing the equivalent evaporation temperature of VCC. The proposed energy supply system can simultaneously meet the cooling, heating and electricity demand of the building, so it can be promoted in practical engineering applications.

Comparison of optimal oriented façade integrated solar cooling systems in Australian climate zones

Solar cooling technologies have been proven to have great potential for energy saving during cooling season. Meanwhile, glass has become one of the primary structural materials used in building construction since the middle of the 20th century. Although common glass adds to the aesthetic appeal of a building, it has serious drawbacks, such as creating heat traps, preventing natural ventilation and causing glare. Highly glazed façades would cause unwanted heat transmission from the ambient, which must be extracted to outside using an air-conditioning system. Internal heat resulting from façade configurations can be responsible for up to 45% of a building’s cooling requirements. A façade integrated solar cooling system can simultaneously improve building’s energy efficiency, utilise solar energy and still maintain a high level of architectural and aesthetic quality. This investigation presents a consistent approach for optimising and comparing façade integrated solar cooling systems in terms of technical and financial performance. Four systems (a vapour compression cycle (VCC) chiller driven by semi-transparent photovoltaics (STPV) arrays, a single-stage absorption chiller, an adsorption chiller and a vapour compression chiller coupled with organic Rankine cycle (ORC) driven by evacuated tube solar collectors) were assessed and compared with a conventional electric vapour compression chiller. The systems investigated were modelled in TRNSYS and the models were applied to predict performance parameters in various climate zones (seven cities) in Australia. The solar fraction (SF) and unit cooling cost (UCC) were the two parameters applied to quantify the technical and financial aspects of each solar cooling system in seven cities in Australia. It was found that among the systems investigated, the VCC chiller with STPV system has the highest SF (100% except in Darwin) and lowest UCC ($0.21 kWhr−1) for all seven cities in Australia. In general, due to the grid as a virtual storage, ORC-VCC system has higher SF (40% and 50%) and lower UCC (5% and 10%) compared with adsorption and absorption chiller respectively in subtropical and temperate climate zones.

Multi-objective optimization for the proper selection of the best heat pump technology in a fuel cell-heat pump micro-CHP system

In this paper, a new multi-objective technique has been proposed for optimal analysis of three different candidate heat pump solutions including the vapor compression cycle (VCC), trans-critical R744 cycle, and Peltier device to determine which one gives the best configuration and better performance on a hybrid heat pump and fuel cell-based micro-CHP system. Here, a sunflower optimization algorithm is utilized to provide two different objectives: minimizing the combined yearly maintenance and capital costs and maximizing the performance of the hydrogen energy consumption. Simulation results show that using the VCC, according to its efficient and low-cost characteristics for cell stack and lithium battery maintenance, gives the best solution for the presented hybrid system.

Range control MPC with application to Vapor Compression Cycles

A range control MPC formulation is presented for control of Vapor Compression Cycles (VCC). Variation in system dynamics is handled through application of range control which is a generalization of a tracking problem whereby the set-point for the system output is replaced by a funnel (time-varying upper and lower bounds on the system output) which is implemented as a set of soft constraints. Vapor cycle is optimized to maximize device efficiency while ensuring feasibility of operation. Experimental validation of the control design, embedded in a heat-pump controller, is presented.

Energy study of edamame freezing process at PT Mitratani Dua Tujuh Jember

Knowledge of the cooling load of products that will be stored frozen in cold storage needs to be known. The purpose of this research was to analyse the cooling load in cold storage, calculate the freezing time of the product, calculate the amount of heat in the vapor compression cycle and the coefficient of performance (COP). PT. Mitratani Dua Tujuh is a company engaged in the processing of frozen fast food and edamame as one of the leading frozen products in this company. The maximum capacity of cold storage used was 190 tons with an air speed of 0.9 m/s and used two compressors with R-404A refrigerant type. The results of the analysis found that the freezing time per package on the product was 5.28 hours. Cold storage cooler load of 55, 432 kW or equivalent to 15.75 tons of refrigeration. The amount of heat in the compression cycle consisted of compression, condensation, expansion and evaporation were 6, 45 kW, 34, 17 kW, 17, 18 kW and 27, 72 kW, and the coefficient of performance (COP) was 1, 237.

Probabilistic borderwork

ABSTRACTHow are borders made porous? In Turkey's Kurdish borderlands, smugglers are not just agents who operate under cover of night, but city‐based traders whose legal practices create a third space in between legality and illegality. Kurdish oil traders accused of smuggling work closely with lawyers to perform what I call probabilistic borderwork. This is a deliberate counterstate political strategy that uses scientific uncertainty to challenge smuggling charges, achieve nonillegality, and legally disrupt the state's border enforcement. Going beyond existing categories of law and politics, probabilistic borderwork is not a rights‐claiming political‐legal action. Rather, it is a form of techno‐legal political agency involving collaboration between otherwise disparate professional groups. [oil, borders, law, techno‐politics, the Kurds, Turkey]

Performance simulation of membrane heat pumps based on vacuum membrane dehumidification system

An alternative technology that surpasses the efficiency of conventional vapor compression cycle is necessary to meet the increasing demand for air conditioning. One of the candidates, membrane heat pump (MHP), can decrease energy consumption through the separation of the air-conditioning process into dehumidification and sensible heat cooling. Humid air is dehumidified through a vapor-permeable dense membrane and cooled by a water-cooling cycle. When dehumidifying, a vacuum membrane system can be utilized in the heat pump system. In this study, two typical systems, water vapor discharge and condenser-combined vacuum membrane dehumidification (VMD) systems, are elucidated, and MHPs that consist of each VMD system are designed. Their performance are simulated and compared. The MHP with water vapor discharge VMD system has an improved coefficient of performance in general.

Experimental study of a personal cooling system integrated with phase change material

Personal cooling is attracting more attention recently because they focus on conditioning the micro-environment around occupants rather than the entire building space, leading to building energy savings while satisfying thermal comfort. In this study, a novel portable personal cooling system integrated with phase change material (PCM) for active thermal storage was investigated. A PCM embedded in a graphite matrix is integrated into the condenser of the vapor compression cycle while an evaporator provides the localized cooling. The vapor compression cycle is operated in a reverse cycle for the regeneration of PCM. The effects of the thermostat setting, PCM recharge rates, and cooling time on system performance were experimentally studied. Results show that the personal cooling system can provide a cooling capacity of 160 W for 4.5 h, the increase in thermostat setting can lead to higher cooling capacity, and the increase in cooling time leads to fast coefficient of performance degradation in both cycles. Besides, the higher compressor speed is recommended to reduce recharge time and increase the overall coefficient of performance.

Dynamic Control of Pressure Drop Oscillation in a Microchannel Cooling System

While microchannel evaporator based cooling systems are efficient in removing high heat fluxes they are prone to the instability mechanism called pressure drop oscillation. The instability can lead to poor cooling performance, system fatigue and even mechanical failure of the cooling system. To address this challenge, a system level approach with dynamic control of cooling performance is studied in this paper. This approach provides an efficient and reliable technique for thermal management and avoidance of flow instability, even in the presence of large and time-varying heat loads. This study considers a system operating on a vapor compression cycle consisting of a microchannel evaporator, compressor, condenser, electronic expansion valve, and an accumulator. The stability and cooling performance of the system is analyzed under different operating conditions via computational simulation of fluid flow and heat transfer. Based on the understanding gained from this analysis, a dynamic control strategy is developed to stabilize and maintain the system at the optimum operating conditions using feed-forward and feed-back controllers.