Condensation Temperature Research Articles

Salinity impacts on a unique desalination system embedded with concentrated solar energy for cleaner production

This research comprehensively analyzed a unique solar desalination unit that operates on concentrated solar energy. The analysis primarily focused on evaluating three crucial components: the condenser, flash chamber, and brine heater. Testing was initially performed using seawater sourced from the eastern region of Saudi Arabia. Subsequently, to investigate the influence of salinity on the system performance, the device was tested under variable salinity levels ranging from 15,000 ppm to 35,000 ppm. Key parameters, including condenser temperature, brine heater temperature, and distillate production, were measured throughout the experimentation. The findings unveiled an inverse correlation between salinity and distillate production, as increasing the salinity from 15,000 ppm to 35,000 ppm resulted in a decline in distillate production. The maximum distillate achieved was 2400 ml/h at a salinity level of 15,000 ppm, corresponding to a constant feed rate of 0.2 l/min. The average energy efficiency of the brine heater was determined to be 61.9%. Moreover, the average exergy efficiencies were calculated as 81.3% for the condenser, 4.4% for the brine heater, and 44.3% for the flash chamber. Mathematical models were subsequently developed to establish the relationships between salinity and various system responses. Furthermore, performance metrics such as gain output ratio, energy utilization factor, and specific energy consumption were evaluated. The proposed system has a maximum gain output ratio of 16, a maximum energy utilization factor of 2.2, and a minimum specific energy consumption of 299.3 kWh/m3.

Sodium thermal electrochemical converter coupled with organic Rankine cycle and thermochemical heat storage for power-heat-power application

The inherent intermittency of solar PV and wind sources makes the power supply from renewables unstable. To mitigate this issue, power-heat-power (PHP) systems have been developed in which surplus/cheap electricity can be stored in the form of high-temperature heat, and whenever needed it can be used for electricity generation using a power cycle. The present work focuses on the integration of an innovative combined cycle consisting of a sodium thermal electrochemical converter (Na-TEC) in combination with an organic Rankine cycle (ORC) as a bottoming cycle, with a redox oxide-based thermochemical heat storage (TCHS) system for PHP application. A Multiphysics model is developed to simulate and analyze the performance of the proposed combined cycle. Parametric optimization is performed to achieve optimal system performance. The proposed Na-TEC/ORC achieved a maximum power density of 0.98 W/cm2 and a maximum conversion efficiency of 40 % which is 21.2 % higher in comparison to a standalone Na-TEC device. A maximum exergetic efficiency of 53 % can be achieved while keeping the evaporator temperature at 1150 K and the condenser temperature at 550 K for this cycle. For the maximum conversion efficiency of Na-TEC, a round-trip-efficiency of 36.1 % is calculated for the proposed PHP system provided the TCHS system is 95 % efficient.

Performance analysis and multi-objective optimization of organic Rankine cycle for low-grade sinter waste heat recovery

In order to enhance the sinter waste heat recovery (WHR) rate efficiently, the organic Rankine cycle (ORC) for power production was applied to take the low-grade sinter cooling flue gas (SCFG) expelled from the waste heat boiler as the heat source. The system thermodynamic, thermo-economic and multi-objective optimization models were constructed firstly, and then R245fa was chosen as the ORC working fluid. Furthermore, the variations of system thermodynamic and thermo-economic performances with the ORC thermal parameters under different inlet temperatures of SCFG were analyzed in detail, and the ideal parameter combination was established through the multi-objective optimization approach. The results show that, the optimal inlet temperature of SCFG is determined to be 160 °C, and under the aforementioned condition of inlet temperature of SCFG, the optimal ORC thermal parameters are determined to be 95 °C for the working fluid evaporation temperature, 10 °C for the working fluid superheat degree, 28 °C for the working fluid condensation temperature and 9 °C for the pinch-point temperature difference in evaporator by considering the system thermodynamic and thermo-economic performances comprehensively. Meanwhile, the WHR rate of SCFG under the above ORC parameter combination could reach 64.86 %, showing remarkable energy-saving effect.

Experimental analysis of an ejector assisted dual-evaporator vapor compression system

Condenser split dual-evaporator vapor compression systems (C-DEVCS) have been used to maintain the two evaporators of a single refrigeration system at different temperatures for long. The throttling process occurring in the expansion valve of these systems is irreversible in nature and thus responsible for a part of energy loss. It has been found that the isenthalpic expansion loss can be reduced using ejector as a throttling device which provides isentropic expansion. Moreover, it recovers some of the energy lost in expansion and reduces compressor work. In the current work, an experimental test facility of ejector assisted dual-evaporator vapor compression system (EA-DEVCS) is developed for R-134a working fluid and analyzed for different condenser temperature. The overall COP of EA-DEVCS is found to increase from 1.982 to 2.925 and 9.8 % decrease in compressor power consumption when the water temperature at the inlet of condenser is decreased from 35 °C to 27 °C. The entrainment ratio of the ejector gets increased from 0.396 to 0.701 with the decrease in condenser temperature.

Performance analysis of a dual-ejector enhanced two-stage auto-cascade refrigeration cycle for ultra-low temperature refrigeration

Auto-cascade refrigeration cycle (ARC) is a cost-effective solution for ultra-low temperature refrigeration. This paper proposes a dual-ejector enhanced two-stage auto-cascade refrigeration cycle (ETARC). In ETARC, two ejectors replace the throttle valves at the liquid phase outlet of the two gas–liquid separators in the conventional two-stage auto-cascade refrigeration cycle (CTARC). They are connected in series to recover partial expansion work in the throttling process, aiming to lift the suction pressure of the compressor. The ternary mixture component is selected and R600a/R41/R1150 is supposed to be the working fluid due to the best performance. The mass fraction ratio of the refrigerant mixture components, the quality at the inlet of two separators and the expansion ratio of the throttle valve (EPR) of the two cycles are optimized using particle swarm optimization (PSO) with respect to the maximum COP. The performances of the two cycles at optimum operating conditions are compared using energetic and exergetic methods, and the effect of the evaporation temperature and the condensation temperature on cycle performances and operating characteristics are discussed in detail. The results show that applying the two ejectors effectively improves the performance of ETARC. Compared with the CTARC at the evaporation temperature of −85℃, and the condensation temperature of 45℃, the ETARC cycle exhibits 16.07% improvement in COP, 29.43% increase in the volumetric refrigeration capacity qv, 17.17% reduction in the total exergy destruction rate. ETARC shows significant performance improvement and has a remarkable energy-saving potential.

Searching for Unconventional Superfluid in Excitons of Monolayer Semiconductors.

It is well known that two-dimensional (2D) bosons in homogeneous space cannot undergo real Bose-Einstein condensation, and the superfluid to normal phase transition is Berezinskii-Kosterlitz-Thouless (BKT) type, associated with vortex-antivortex pair unbinding. Here we point out a 2D bosonic system whose low energy physics goes beyond conventional paradigm of 2D homogeneous bosons, i.e., intralayer excitons in monolayer transition metal dichalcogenides. With intrinsic valley-orbit coupling and valley Zeeman energy, exciton dispersion becomes linear at small momentum, giving rise to a series of novel features. The critical temperature of Bose-Einstein condensation of these excitons is nonzero, suggesting true long-range order in 2D homogeneous system. The dispersion of Goldstone mode at long wavelength has the form ϵ(q)∼sqrt[q], in contrast to conventional linear phonon spectrum. The vortex energy deviates from the usual logarithmic form with respect to system size, but instead has an additional linear term. Superfluid to normal phase transition is no longer BKT type for system size beyond a characteristic scale, without discontinuous jump in superfluid density. With the recent experimental progress on exciton fluid at thermal equilibrium in monolayer semiconductors, our work points out an experimentally accessible system to search for unconventional 2D superfluids beyond BKT paradigm.

Economic and binder-free synthesis of NiCo2O4 nanosheets on a Flexible stainless steel mesh as a bifunctional electrode for water splitting

Water as a green source of hydrogen has attracted the attention of researchers considering its potential applications in the energy sector. Thus, developing efficient bifunctional electrocatalysts for water splitting is a potential challenge perceived by researchers exploring the development of sustainable energy technologies. With this motive, the present study focuses on the preparation of the highly active, economic, binder-free, and bifunctional NiCo2O4 nanosheets@ Flexible Stainless Steel Mesh substrate (NCO@FSSM) electrocatalyst via reflux condensation method for the bulk O2 and H2 production. The influence of reflux condensation temperatures (100, 120, 140 °C) on the morphology and electrocatalytic activity is investigated. Electrocatalytic properties for NCO@FSSM synthesized at 120 °C were noted exhibiting smaller overpotentials for oxygen evolution reaction (OER, 310 mV) and hydrogen evolution reaction (HER, 79 mV) at 10 mA cm−2, which were lowest among the previously reported Ni, and Co-based electrodes. Additionally, the scale-up experiments with NCO-120@FSSM film (8 cm X 8 cm) as an anode and FSSM as a cathode and vice-versa, in a specially designed scale-up electrochemical cell revealed steady electrocatalytic performance. The real-time water splitting was studied for 25 h and was noted to produce 7.4 L of (O2) and 11.5 L of hydrogen (H2).

Numerical Analysis of Using R449A Refrigerant Alternative to R404A in Cooling Systems: 3E-Analysis (Energetic, Exergetic, and Environmental)

The direct impact of refrigerants on the environment is largely dependent on the magnitude of global warming potential (GWP) values. In this regard, fluids with low GWP are very important for the environment. Commercial refrigeration accounts for about a third of the world's HFC use. R404A is a derived HFC near an azeotropic mixture. The refrigerant of R404A is widely used in commercial refrigeration systems, especially in supermarkets. As a result of the use of R404A in cooling systems with high GWP, both indirect and direct negative effects on the environment increase. In this study, the energy, exergy, and Life Cycle Climate Performance (LCCP) of R449A, which has a lower GWP value, which can be an alternative to R404A refrigerant, were investigated theoretically. Different evaporator temperatures (-30oC to -5oC) and a condenser temperature (30oC) were used in the analysis. According to the results obtained, while the mass flow rate of R449A is approximately 13% lower than that of R404A, its exergy efficiency is 5% higher. R449A was found to be approximately 5% lower than R404A in LCCP analysis.

Simulation and performance research of absorption heat pump unit based on R134a-DMF working fluid pair

R134a-DMF absorption heat pump unit is an energy-saving heat pump unit that can utilize renewable energy, and has great potential in the refrigeration and heating fields of urban and rural areas. The purpose of this article is to conduct in-depth research on the dynamic characteristics of absorption heat pump units based on R134a-DMF, a new working fluid pair. A mathematical model of the thermophysical properties of the R134a-DMF working fluid pair and the mathematical models of various components of the heat pump unit are constructed. This paper constructs a simulation program, and uses the Control variates to study the change trend of the Coefficient of performance of R134a-DMF absorption heat pump unit affected by the generator outlet concentrated solution temperature, condenser air volume and temperature rise, and chilled water outlet temperature. The results indicate that the established mathematical model for thermophysical properties and the unit model are both accurate models, which can provide guidance for the actual operation and optimization of R134a-DMF absorption heat pump units. Through simulation, it can be concluded that for the three combined forms of R134a DMF (3:2), R134a DMF (1:1), and R134a DMF (2:3), the average increase in COP and refrigeration capacity is 0.85 %, 0.39 %, and 0.42 % for each 1 °C increase in the outlet concentrated solution temperature of the generator, respectively, and the growth rate is relatively slow. The larger the proportion of refrigerant in the binary solution, the greater the COP of the unit under the same operating conditions.

Ammonia heat pumps for district heating: thermo-economic optimization analysis based on evaporator geometry for either direct expansion or chilled water configurations

Electric heat pumps are recognized as a key technology for decarbonization and have received increasing policy support in several countries over the last few years. These devices offer a highly efficient form of electric heating and could make an important contribution to the transition to a low carbon future, especially in case of district heating systems. Within this context, this paper presents a thermo-economic optimization analysis of a 7.35 MW electric heat pump system employed for district heating purposes and using ammonia as working fluid. The implemented code gathers multiple sub-models calibrated ad-hoc from real data or manufacturers’ datasheets. The heat exchangers are simulated by considering phenomenological equations and well-known heat transfer coefficient and pressure drop prediction methods. The optimization analysis is performed at constant condensation temperature that guarantees in/out hot water temperatures of 30/62 °C and is focused on the matching between compressor and evaporator heat exchanger, by considering either a direct expansion system or a chilled water heat pump. Both the coefficient of performance (COP) and the set-up costs are considered as optimization performance indicators for the construction of the Pareto front.

Application of response surface methodology and desirability approach to optimize the performance of an ultra-low temperature cascade refrigeration system

In this paper, multi-objective optimization of an ultra-low temperature cascade refrigeration system is presented using response surface methodology and desirability approach. Evaporation temperature, high-temperature circuit and low-temperature circuit condensation temperature, cascade temperature difference, and superheat degrees of the compressor suction are chosen as the variables, whereas COP, total exergy destruction and exergy efficiency are adopted as the responses that simultaneously maximizing COP and exergy efficiency while minimizing the exergy destruction. The quadratic models for three responses are obtained after the analysis of variance. The interactive influences of the variables on the responses are indicated. The results present that the maximum deviations between the predicted and actual values for the COP and exergy efficiency are 0.84% and 0.96%, whereas the deviations for the exergy destruction are within ± 2% accounting for 96% of the samples. Evaporator temperature, condenser temperature, cascade temperature difference, ect. are found to be important parameters which cause great conflicts among the objective functions. A group of optimum values for the input variables are selected and validated. The derivations between predicted modeling and simulation values for the COP, total exergy destruction, and exergy efficiency are −0.604%, 2.886%, and 0.0452%, respectively, indicating that the method is efficient to optimize the performance.

Two-phase CFD simulations of COSI tests and evaluation of condensation distribution

This study presents the two-phase CFD simulation of experiments carried out on COSI facility in the frame of Pressurized Thermal Shock (PTS). PTS may occur during a cold-water injection, by the Emergency Core Cooling System (ECCS) during a Loss-Of-Coolant Accident (LOCA). The simulations were carried out using the Neptune_CFD code. A sensitivity study on Direct Contact Condensation (DCC) models was performed with a comparison with experimental data. At the end of this study, it appears that the turbulence of the free surface is rather low. Consequently, a low-turbulence heat transfer model is more appropriate. Then, two sensitivity studies on global and local mesh refinement are carried out, with the creation of an optimized mesh. This optimized mesh is used with the low-turbulence model to simulate the 40 test cases with no water level and co-current steam flow. Deviations in temperature and total condensation rate are less than 5% and 25% respectively. Finally, the condensation rate between stratified and non-stratified regions is evaluated. Condensation tends to occur in non-stratified zones, with imbalance that can be very high, reaching almost 80% of total condensation.

The utilizability of non-flammable R471A with low-GWP in air-conditioning systems

<p class="15">The utilizability of non-flammable refrigerant R471A with low-GWP is theoretically investigated in an air-conditioning system. In this context, R410A, R32, and R471A are compared for the evaporation temperatures of 4, 8 and 12 ℃ with the condenser temperatures of 40 and 50 ℃. The results indicate that both the mass flow rate and power consumption of R471A are higher compared to R410A and R32. Although COP of R471A is determined to be smaller than R410A and R32 about by 19% and 22%, R471A can satisfy the restrictions for air-conditioning systems due to its considerable low-GWP compared to R410A and R32 (GWP of R471A is lower by 78% and 93% in comparison with R32 and R410A, respectively). Hence, it should be possible to suppress global warming through the reduction of carbon emissions as a result of using R471A in these systems<span style="font-family: 'Times New Roman';">.</span> Additionally, since R471A is non-flammable, it can be safely used for systems requiring a high amount of refrigerant charge without violating the restrictions.</p>

Heating performance and optimization of ice source heat pump system with supercooled water

An ice source heat pump, which can extract latent heat from the icy water, has a better system performance in low-temperature areas. Cosiderring the disadvantange of ice source heat pump using static ice-making method or scraping ice-making method, an ice source heat pump based on supercooled water method is proposed and its heating performance is measured in the study. Then, a system model is developed to study and optimize the system performance. It concludes: (1) The ice source heat pump system COP decreases with the increasing supercooled water flow rate. The system COP reaches about 3.3 when the condensation temperature is 42 °C. (2) The proper range of supercooled degrees in ice source heat pump is mainly from 2 °C to 3 °C. (3) The rank of local exergy loss rate in ice source heat pump system is listed as follows: compressor > condenser > valve > evaporator > pump. The exergy loss proportion of compressor and condenser is about 65%. (4) The system COP and exergy efficiency of ice source heat pump increase approximately linearly with the increase of capacity. The optimal supercooled degree mainly depends on the rate of change of the compressor power and the pump power concerning the supercooled degree. This work provides insight into the performance of ice source heat pump with supercooled method and guides the design of ice source heat pump system.

Thermodynamic analysis of high temperature cascade heat pump with R718 (high stage) and six different low-GWP refrigerants (low stage)

Decarbonizing industrial heating globally is a significant challenge, driving the integration of high-temperature heat pumps for heat recovery and electrification in the industrial sector. However, current high-temperature heat pumps with low global warming potential refrigerants face limitations in delivering high-temperature heat due to their restricted compressor discharge temperature or require several compressors/intercoolers. To address these issues, a novel high-temperature cascade heat pump system is proposed, utilizing water (R718) in the high stage, while selecting one among six low GWP refrigerants (R1234ze(Z), R1233zd(E), R1336mzz(Z), R600, R600a, R601) in the low stage, with single compressor at each stage. To manage high discharge temperatures of high stage, liquid water injection is applied during high stage compression, modeled for both wet and dry steam. The model is validated against available experimental data with maximum error less than 5 %. Further, the effectiveness of the internal heat exchanger in low stage cycle is assessed for all investigated low stage refrigerants. Results reveal that R718 + R600 offers the optimal refrigerant working pair, achieving a maximum COP × VHC of 2895.1 kJ m−3 for delivering high temperature heat at water condensation temperature of 190 °C and recovering heat from low temperature waste energy of 50 °C.

Hot air recirculation enlarges efficient operating window of reversible solid oxide cell systems: A thermodynamic study of energy storage using ammonia

Energy storage is vital for the energy transition, enabling reliable power grids based on intermittent renewables. Reversible solid oxide cell (rSOC) technology is promising for seasonal energy storage. The novel finding from this work is that optimised air recirculation for rSOC in endothermic electrolyser mode leads to efficiency being nearly independent of current density. Thereby the operating region of highest efficiency is expanded from the thermoneutral point to the entire endothermic region, leading to highly efficient part-load operation. Air recirculation increases fuel cell mode efficiency too, particularly at higher loads. This widens the efficient operating window in both modes. These findings emerge from a thermodynamic study of an rSOC-based energy storage system with ammonia as fuel. A process design is developed and optimised for efficiency, supported with detailed exergy analysis. First, ammonia synthesis subsystem integrated with the rSOC system in electrolyser mode is optimised. Second, rSOC outlet air recirculation is optimised for high system efficiency. Finally, rSOC operating points are optimised for highest round-trip efficiency. We find the least exergy destruction for the ammonia synthesis subsystem at 170bar synthesis pressure and 30°C condensation temperature (without needing refrigeration). The overall system achieves round-trip efficiencies up to 60.3%.

Thermo-Economic Performance of Organic Rankine Cycle-Based Waste Heat Recovery for Power Generation at a Wide Range of Operating Conditions

This study assesses the performance of organic Rankine cycle-based waste heat recovery systems under different working fluids and operating conditions. The basic ORC (BORC) and ORC with recuperator (RORC) are investigated for power generation and economy using toluene and benzene. Thermodynamic and economic indicators are studied at various expander inlet temperatures, expander inlet pressure, evaporation temperature, and condensation temperature. RORC achieves higher ηth by reducing heat source in the evaporator whereas BORC recovers more waste heat and improves Pnet. With toluene, BORC improves Pnet when increasing the expander inlet temperature and pressure. The lowest LCOE of 0.0532 US$/kWh is from BORC operated with toluene at a Pnet of 349 kW and decreases with an increase in expander inlet temperature. The addition of a recuperator adds to the costs of initial investment and LCOE and slightly improves the performance of the ORCs for waste heat recovery.

A study of the optimal conditions for organic Rankine cycles coupled with vapour compression refrigeration using a rigorous approach based on the Helmholtz energy function

VCR-ORC systems combine an organic Rankine cycle (ORC) to produce energy from low-moderate temperature sources and a standard refrigeration cycle (VCRC). Accurate objective functions for the optimal performance of the system are developed based on the Helmholtz energy function and its derivatives. Moreover, the utility of two objective functions is analysed in the search for the optimal conditions of a VCR-ORC system. Finally, it presents a comparative analysis of several working fluids to give the directives in selecting an optimal working fluid and its operation optimal conditions. The method described above uses a set of refrigerants and the PC-SAFT EOS as the prediction model. The results presented in this work show that variables such as the condenser temperature, T1, are fundamental for the optimisation of VCR-ORC systems. Pentane and R1233zd have the best performance for this system. However, the fourth-generation refrigerant shows the best operational condition in all the indicators among the studied fluids despite its wet expansion in optimal operation. In the idealised VCR-ORC cycle, the optimal ORC efficiency links with the optimal COP of the cycle while the extracted heat links with the optimal mechanical work produced by the ORC.

Performance analysis of water refrigerant heat pump with different configurations for high-temperature application

Water is a promising working fluid for high-temperature heat pumps (HTHPs) with the advantages of being cheap, safe, stable, environmentally friendly, non-toxic, and non-flammable. HTHPs using water as a refrigerant not only can reduce greenhouse gas emissions in the industrial sectors by recovering waste heat but also have no adverse effect on the environment if the refrigerant leaks. This article evaluates the safety, energy, and exergy performance of six designed HTHP configurations with water refrigerant by analyzing the discharge superheat, power consumption, heating capacity, COP, and exergy efficiency—at different condensation and evaporation temperatures. The results indicated that water injection and intercooling can effectively decrease the discharge superheat to ensure safety performance. Among these systems, two-stage cycles can supply higher output temperatures and have better system performance compared to single-stage cycles at high-temperature lifts and large compression ratio conditions. The two-stage system with a flash tank (TS-FT) has the biggest heating capacity, the best COP, and the best exergy efficiency. With an evaporation temperature of 80°C and condensation temperature of 140°C, the COP is 4.14 and the exergy efficiency is 70.9% for the TS-FT. Compared with the single-stage ordinary system (SS-OS), the COP of the TS-FT has an increment of 36.6%. The exergy efficiency of the TS-FT is 19.8% higher than that of the SS-OS. Considering the aforementioned theoretical analysis, the TS-FT with the best safety, energy, and exergy performance is the optimal HTHP system with water refrigerant for high-temperature applications.

Innovative experimental approach for the dynamic Multi-Variable investigation of Pulsating heat Pipes

Pulsating Heat Pipes (PHP) are passive two-phase heat transfer devices characterized by a simple structure and high heat transfer capabilities. Despite this, their large-scale application is still hindered by the actual unpredictability of their dynamic behavior during the startup and the thermal crisis. An innovative experimental apparatus is designed to systematically investigate the above-mentioned phenomena. It consists in a square loop made of four borosilicate transparent glass tubes joined at corners by means of brass connectors. The external tube surface is coated with several transparent Indium Tin Oxide heaters. The device is used to topologically reproduce 5, 7, and 11 evaporator/condenser sections PHPs with a 2 mm inner diameter tube, filled with pure ethanol and tested in horizontal position. First a steady-state characterization is performed. The condenser temperature is varied from 10 °C to 40 °C; the input power goes from 10 W to 40 W. Results show that both the increase of number of evaporator sections and condenser temperature enhance the PHP performance in terms of equivalent thermal resistance. Then, the effect of the condenser temperature on the initial liquid phase distribution is analyzed. It is observed that at low condenser temperatures (10 °C, 20 °C), the liquid phase tends to gather in the condenser sections rather than the evaporator sections and it is arranged in short liquid plugs; conversely, for high condenser temperatures (30 °C, 40 °C), the amount of liquid phase in evaporators is higher and it is arranged in long liquid plugs. Finally, the transient behavior is studied in terms of startup time. It is observed that the parameter influencing most the startup time is the initial fluid distribution; the startup time increases with the increase of evaporator sections volume occupied by liquid phase and with the length of liquid plugs; on the other hand, the startup time decreases with the increase of number of menisci in the evaporator sections.