Evaporating Temperature Range Research Articles

Trade-off working fluid selection for heat pumps

Nowadays heat pump systems are used to recover the heat from waste water from different sources and produce hot water for household and communal purposes. In this research comparative thermodynamic analysis of performance for a water-to-water single-stage vapor compression heat pump using several HCs, HCFCs and HFCs which belong to refrigerants of different generations is presented. A multi-criteria approach for optimal selection of refrigerants was used as scientific tool. Results of theoretical experiments of vapor compression heat pump system with the evaporator temperature range 0…25°C and condenser temperature 60°C and 83°C showed that the COP of R1234ze was higher than that of R600a, R152b by about 6.7…17.3%, 8.25…20.5%, and 1.7…14.4%, respectively, at condenser temperature 60 °C; however results are different if at condenser temperature is 83°C: the average COP of R600a was higher than that of R1234ze and R152b by about 7.7…14.7%, 9.3…15.8%, and 7.5…15.6%, respectively. COP displays a positive correlation with the evaporator temperature as well as a negative correlation with the condenser temperature. The complete analysis of all factors, including environmental safety, indicates that R1234ze and R600a refrigerants should be preferred as the working fluids for using in the water-to-water single-stage vapor compression heat pump for the hot water supply and heating purposes in industrial applications.

Exergetic Analysis of a New Direct Steam Generation Solar Plant Using Screw Expanders

Screw expanders are volumetric machines particularly suitable in energy conversion with steam–liquid mixtures and for the exploitation of low temperature heat sources. This study explored the main criteria to evaluate the thermodynamic advantages and exergetic assessment of an innovative solar electricity generation system: Screw expanders are utilized as power machines and parabolic trough collectors as a thermal source. Such a direct steam generation solar system, which is based on the Rankine cycle, offers benefits in comparison with usual power plants with dynamic expanders: The best exploitation of low temperature heat sources, satisfactory thermal efficiency with steam–liquid mixtures, lower evaporation pressures, and reduced size. Under real working conditions, screw expanders can work at part-load operating conditions; thus, the chief purpose of the present paper was to analyze the exergetic advantages of the planned solar power system when solar radiation and off-design working conditions fluctuate. Initially, the polytropic expansion phase with a specific numerical model is described to evaluate the energy losses that affect the thermodynamic performance of screw expanders when installed in the planned renewable energy power plant. Subsequently, to explore the exergy harnessing in the exhausted steam at off-design working conditions and then to appraise the maximum exergetic efficiency of the proposed screw expander-based solar thermal electricity plant, numerical optimization was performed in a broad range of evaporation and condensation temperatures.

Thermodynamic properties and performance evaluation of [EMIM] [DMP]‐H 2 O working pair for absorption cooling cycle

The combination of ionic liquid-refrigerant based [EMIM][DMP]-H2O as an alternative working pair for single effect vapor absorption cycles (VACs) is assessed and optimized by using energy and exergy based performances. Thermodynamics properties of binary mixture of [EMIM] [DMP]-H2O like Dühring's (P-T-x1) and h-T-X1 plots are computed from the activity coefficient based non-random two-liquid model (NRTL) model. Further modeling and simulation of VACs are accomplished in open source Scilab as mathematical programing software and used to ascertain the optimal generator temperature established on energetic and exergetic COP. Optimal results include an extensive range of temperatures like Te from 2.5 to 15°C and Ta and Tc from 30 to 45°C. Simulation of the single effect VAC with SHE by using [EMIM][DMP]-H2O mixture at Te = 10°C, Tg = 100°C, Ta = 30°C, and Tc = 40°C were evaluated and compared with the 5 working fluids. Simulation outcomes depicted greater COP of 0.82 for [EMIM][DMP]-H2O in comparison with NH3-H2O, EMISE-H2O, [EMIM][BF4]-H2O and nearly equal to LiBr-H2O (COP = 0.83). In addition, the effect of Tg on the COP, ECOP f, and composition are compared and optimized for the evaporation temperature range from 2.5 to 15°C, Ta/Tc from 30 to 45°C and cooling water (CW) flow in series and parallel. Additionally, the optimal Tg exhibited distinction based on energy and exergy analysis. Thus, it resulted in optimized performances of [EMIM] [DMP]-H2O that can be suitable to replace corrosive aqueous LiBr in VACs.

Performance analysis of R1234yf/ionic liquid working fluids for single-effect and compression-assisted absorption refrigeration systems

Due to the disadvantages of conventional working pairs (NH3/H2O and H2O/LiBr) in the absorption-refrigeration cycles, 2,3,3,3-Tetrafluoroprop-1-ene(R1234yf)/ionic liquid (IL), which possessed of remarkable properties, has received more and more attention. In this work, the thermodynamic performance of single-effect and compression-assisted absorption refrigeration cycles were analyzed using R1234yf as refrigerant and ILs (including [emim][BF4], [hmim][BF4], [omim][BF4], [hmim][Tf2N], [hmim][PF6] and [hmim][TfO]) as absorbent, the thermodynamic properties of working pairs was estimated by the NRTL model. The effects of generation, evaporation, condensation and absorption temperature as well as compression ratio on the cooling performance and circulation ratio were studied in various working conditions. Compared to the single-effect cycle, the compression-assisted cycle effectively improves the cooling performance, reduces the circulation ratio and extends the operation range of generation, evaporation and absorption temperatures. At the same working condition, [hmim][Tf2N] performs the best while [emim][BF4] has the lowest COP, the cooling performance of [hmim][BF4], [omim][BF4], [hmim][TfO] and [hmim][PF6] is similar.

Experimental study on evaporative heat transfer and pressure drop of R-134a in a horizontal dimpled tube

The heat transfer and pressure drop characteristics of R-134a during evaporation in smooth and dimpled tubes are experimentally examined. All test sections used in this study are double-tube heat exchangers, where the hot water in an annulus transfers its heat to R-134a in the inner tube. The experiments are conducted in a mass flux range of 300–500 kg/m2 s, heat flux range of 20–30 kW/m2, and evaporating temperature range of 7–13 °C. Smooth and dimpled tubes with a length of 1500 mm and an inner diameter of 8.1 mm are tested. The results indicate that the tube with protrusions enhance the heat transfer up to 70% along with a pressure drop increase up to 587% over the smooth tube. The effects of relevant parameters on heat transfer and pressure drop are explored. In this experiment, the heat transfer enhancement factor falls in the range of 1.26–1.7, while the pressure drop penalty factor fluctuates between 3.78 and 6.87. In addition, the efficiency index is applied to estimate the performance of dimpled tube. It is found that all efficiency index values are in the range of 0.18–0.42.

Experimental Investigation of Ejector-Assisted Vapor Compression System

The performance of an ejector as an expansion device rather than the conventional expansion valve or capillary tube in a vapor compression system is experimentally analyzed. Experiments have been conducted using 28 ejectors of different dimensions at the same condenser and evaporator temperatures, and it has been observed that for utmost performance, an optimum area ratio of the ejector is required. One of the ejector geometry has been experimented further for a wide range of condenser and evaporator temperatures. The coefficient of performance is found to be enhanced by at least 10% in comparison to the conventional vapor compression system for the considered range of condenser and evaporator temperatures and the maximum improvement in COP obtained is 12.83% at 14.3∘C evaporator temperature and 32.4∘C condenser temperature with 17.9211 ejector area ratio. The refrigerant R134a has been used as the working substance.

Experimental and Numerical Study of Double-Pipe Evaporators Designed for CO2 Transcritical Systems

The performance of a CO2 double-pipe evaporator was studied through experiments and a simulation model that was established by the steady-state distribution parameter method and experimentally verified while using a CO2 transcritical water‒water heat pump system. The effects of different operating parameters on heat transfer performance were studied over a range of evaporation temperatures (−5 to 5 °C), mass velocity (100‒600 kg/m2s), and heat flux (5000‒15,000 W/m2). It was found that the dryout quality increased at a small evaporation temperature, a large mass velocity, and a small heat flux. The simulation yield means relative error (RE) of heat transfer for the evaporation temperature and that of the CO2 pressure drop for the chilled water inlet temperature were 5.21% and 3.78%, respectively. The effect of tube diameter on the performance of CO2 double-pipe evaporator is probed through simulations. At the same time, this paper defines a parameter α , which is the proportion of the pre-dryout region to the whole heat transfer region. A larger α value is desirable. A further theoretical basis is provided for designing an efficient and compact CO2 evaporator.

Conductive Recyclable Organogel Composites

AbstractAs the use of automation in industry accelerates, the development of flexible, electrically conducting materials with the requisite environmental resilience for impact‐resistant sensors, foldable electronics, and electrostatic shielding are needed; simultaneously, recyclability for these materials remains a crucial attribute. Traditional conductive stretchable materials, such as rubbers, are not recyclable, and hydrogel materials have limited applications due to water evaporation and operating temperature range. Comparatively, organogels can be formulated with enhanced tunability, matrix recyclability, and the ability to support many conductive fillers. Here, rheology, mechanical testing, and electrochemical impedance spectroscopy (EIS) characterize the nanoscale interactions between carbon fillers, the liquid phase, and the network matrix in hemiaminal dynamic covalent network (HDCN) organogels. HDCN chemical equilibria are shown to strongly influence macroscopic gel properties, while HDCN composites exhibit very high conductivities up to 9.95 mS cm−1 appropriate for sensing applications, demonstrating promise as recyclable alternatives for conductive stretchable materials.

Mass Spectrometry of a Xylitol Molecule

The technique and results of a mass spectrometric study on the yield of positive ions formed upon ionization of xylitol molecules by electron impact are discussed. The mass spectra of xylitol are studied in the range of mass numbers of 10–160 Da and in the range of bombarding electrons energies of 5–80 eV. Based on the analysis of the measured mass spectra, a scheme of xylitol fragmentation is proposed, which contains the most probable channels of formation of ion-fragments upon electron impact, when the energy of the incident electrons significantly exceeds the ionization potential of the molecule. The appearance energies of ionized fragments of xylitol are determined for the first time from the energy dependences of the effective cross-section formation of the ions upon electron impact. The dynamics of ionized fragment formation is studied in the temperature range of the initial substance evaporation of 340–410 K. The behavior of the temperature dependence indicates that the formation processes of water and oxonium cations compete with each other.

Масс-спектрометрия молекулы ксилита

AbstractThe technique and results of a mass spectrometric study on the yield of positive ions formed upon ionization of xylitol molecules by electron impact are discussed. The mass spectra of xylitol are studied in the range of mass numbers of 10–160 Da and in the range of bombarding electrons energies of 5–80 eV. Based on the analysis of the measured mass spectra, a scheme of xylitol fragmentation is proposed, which contains the most probable channels of formation of ion-fragments upon electron impact, when the energy of the incident electrons significantly exceeds the ionization potential of the molecule. The appearance energies of ionized fragments of xylitol are determined for the first time from the energy dependences of the effective cross-section formation of the ions upon electron impact. The dynamics of ionized fragment formation is studied in the temperature range of the initial substance evaporation of 340–410 K. The behavior of the temperature dependence indicates that the formation processes of water and oxonium cations compete with each other.

Thermodynamic considerations for optimal thermal compressor design

A unified framework for the modeling of the thermal compressor of a single-effect ammonia–water absorption system is developed. An optimal thermal compressor configuration is found through a comparative assessment of various desorption and rectification configurations, and pertinent figures of merit are defined. The diabatic distillation column configuration is shown to achieve the highest thermal compressor performance. Parameters relevant to quantitative thermal compressor characterization are identified. Two optimal operating temperatures are identified, for the optimization of energetic and exergetic objectives, respectively. Statistical regression and artificial neural network analyses from thermodynamic simulations over a wide range of ambient and evaporator temperatures provide accurate prediction of thermal compressor performance and are compared. These results facilitate the assessment of absorption technology through simple predictive tools at the cycle design stage. This framework could also yield a design tool and could guide system design, optimal control, and flexible operation.

Estimation of performance of a J-T refrigerators operating with nitrogen-hydrocarbon mixtures and a coiled tubes-in-tube heat exchanger

The exergy efficiency of Joule-Thomson (J-T) refrigerators operating with mixtures (MRC systems) strongly depends on the choice of refrigerant mixture and the performance of the heat exchanger used. Helically coiled, multiple tubes-in-tube heat exchangers with an effectiveness of over 96% are widely used in these types of systems. All the current studies focus only on the different heat transfer correlations and the uncertainty in predicting performance of the heat exchanger alone. The main focus of this work is to estimate the uncertainty in cooling capacity when the homogenous model is used by comparing the theoretical and experimental studies. The comparisons have been extended to some two-phase models present in the literature as well.Experiments have been carried out on a J-T refrigerator at a fixed heat load of 10 W with different nitrogen-hydrocarbon mixtures in the evaporator temperature range of 100–120 K. Different heat transfer models have been used to predict the temperature profiles as well as the cooling capacity of the refrigerator. The results show that the homogenous two-phase flow model is probably the most suitable model for rating the cooling capacity of a J-T refrigerator operating with nitrogen-hydrocarbon mixtures.

Sensory quality of milk fat with low cholesterol content fractioned by molecular distillation.

Anhydrous milk fat (AMF) is a valuable ingredient in several industries, but its cholesterol content is a disadvantage because it is associated with several diseases. The objective of this study was to remove the largest possible amount of cholesterol from AMF by molecular distillation and to analyze the sensory properties of the obtained product. AMF was subjected to various molecular distillation arrangements. The first set of experiments involved molecular distillations performed over a range of evaporation temperatures. Then, according to the outcome of the first set of experiments, a second set of experiments was carried out in order to study the effect of the feeding flow rate. Finally, the number of distillation stages was modified. The best results were obtained in a three-stage arrangement, in which ∼60% of cholesterol was removed with a 30.48% distillate yield. The sensory properties of this distillation cut were also the most similar to those of the untreated milk fat. © 2018 Society of Chemical Industry.

A Perspective Evaluation Methodology for Economic Feasibility of Low Temperature Sustainable Energy Source in Heating Mode Technology

The economical and clean environment issues for a sustainable energy source at low temperature (LT) were considered and compared to natural gas technology as a fossil fuel source. The friendly environment refrigerants R410A, R407C, R717, R134a, and R600a were analyzed in an approximately 500 kW heating load output cascade heat pump. The heat pump was investigated at an intermediate temperature of 35 °C, high temperature (HT) cycle condenser at 70 °C, and compressors isentropic efficiency of 70%. All analyzed refrigerant pairs exhibited high heating season performance factor (HSPF), and it was ranged between 7 and 8.5. The thermal performance comparison revealed that the HSPF for R717/R600a showed the highest values among other refrigerant pairs. The results showed that at LT cycle evaporator temperature range of −10 to −2 °C, the natural gas technology revealed a higher season heating cost values than that of the heat pump plant by up to 10%. On the contrary at lower LT evaporator temperature, the heat pump plant technology exhibited a higher season heating cost lied in the range of 4–13.6% than that of the natural gas system. At compressors isentropic efficiency of 90%, the seasonal heating cost of the heat pump plant was lower than that of the natural gas technology by the range of 9–25% at test conditions. The mean seasonal CO2 amount released by the natural gas firing technology from all tested refrigerant pairs ranged between 2.1 and 2.5 times that of the heat pump plant technology for the investigated LT evaporator temperature range.

Cut-off temperature evaluation and performance comparison from energetic and exergetic perspective for NH3-H2O absorption refrigeration system

This study represents the thermodynamic analysis and optimization of single effect aqua-ammonia absorption cooling system. Mathematical models are derived from thermodynamic theory to compute the optimum performance parameters. Cut-off temperature to operate the system is obtained at various operating temperatures. Analysis depicts that with raise in evaporator temperature from −5 to 5°C, the required cut-off temperature decreased from 72°C to 59°C. Through realistic comparison between thermodynamic first and second law analysis, optimum generator temperature corresponding to maximum COP and minimum exergy destruction is evaluated. It is found that the optimum generator temperature corresponding to exergy approach is 11°C lower as compared to energy approach. Optimum generator temperature is a strong function of evaporator and condenser temperature. Hence, it is feasible to determine optimum generator temperature for certain range of evaporator and condenser temperatures. Contours of optimum generator temperature for various combinations of condenser and absorber temperatures are presented.

Performance Investigation of Natural Refrigerant R290 as a Substitute to R22 in Refrigeration Systems

Abstract Use of natural refrigerant R290 can play a vital role in fulfilling the objectives of the international protocols like Montreal and Kyoto. Because of environmental problems such as ozone depletion and global warming, R22 needs to be phased out on urgent basis. This paper analyzes the possibilities of R290 as a potential substitute to R22. Thermodynamic performance analysis of refrigerants R290 and R22 was carried out using standard vapour compression cycle, with evaporating temperature range of -25°C to 10°C for the condensing temperature of 45°C, based on analytical calculations. Refrigerant properties were obtained from REFPROP 9.0. Performance parameters like, discharge temperature, volumetric refrigerating capacity and required mass flow of refrigerant were found to be lower with R290 when compared to R22. Coefficient of performance with R290 is slightly lower than that of with R22. However, higher COP can be expected by especially designed system pertaining to the properties of R290. Overall, R290 can be a better substitute to R22 in real applications because of its excellent environmental and thermo-physical properties.

Effects caused by the internal heat exchanger at the low temperature cycle in a cascade refrigeration plant

This work analyses and quantifies the effects caused by the use of an internal heat exchanger (IHX) at the CO2 subcritical cycle in an HFC134a/CO2 cascade refrigeration plant that incorporates a gas-cooler at the exit of the low temperature compressor. Previous theoretical and experimental studies showed that the IHX reduces the refrigeration capacity and COP of the subcritical cycle, however, it has been seen that it also lowers the heat to be rejected at the condenser. This reduction, when the cycle is a part of a cascade system, allows reducing the heat load of the high temperature cycle, modifying the working conditions of the cascade plant. The modifications result in an increment of the overall coefficient of performance of the cascade system. The analysis here presented is based on the evaluation of an experimental HFC134a/CO2 refrigeration plant, which has been analysed with and without internal heat exchanger in an evaporating temperature range from −40 to −30°C and in a condensing one from 30 to 50°C. The plant incorporates a gas-cooler at the exit of the CO2 compressor. The experimental results confirm that the IHX slightly reduces the cooling capacity but it can increment the overall COP up to 3.7%.

Performance Study of Refrigeration Units That Use the Refrigerant R-404A by Using Computer Simulation

The performance parameters of vapor compression refrigeration units that used the refrigerant R-404A were studied by developing a computer simulation algorithm. The various performance parameters investigated per one kilowatt of refrigeration capacity, such as the mass flow rate, the compressor power consumption, the condenser heat rejection rate, the compressor exit temperature and the coefficient of performance. Two refrigeration cycles were tested under various evaporating and condensing temperatures: the standard cycle and the ideal cycle with superheating and sub-cooling. The results of the present work reveal that the compressor power variation over the evaporating temperature range from –10℃ to 15℃at Tc = 40℃ is decreased by 38.8% for standard cycle and by 43.8% for ideal cycle. The compressor power variation over the condensing temperature range from 30℃ to 50℃ at Te = 10℃ is increased by 122% for standard cycle and by 54.5% for ideal cycle. On the other hand, the COP for the ideal cycle with 5℃ superheating and sub-cooling is approximately 25% higher than that of the standard cycle at Te = 10℃ and Tc = 40℃ for the refrigerant R-404A.

Prediction of energetic and exergetic performance of double-effect absorption system

The solar cooling technology is a promising alternative to the conventional electrical driven air conditioners, and one of the optimum systems is solar double-effect absorption system. The main objective of this research is to predict, analyze and optimize the performance of the double-effect absorption system. Also it is required to predict the coefficient of performance (COP) and exergetic efficiency (ηex) of the system, and to formulate them in equations as functions of the operating parameters of the cycle. A computer program has been developed by EES (Engineering Equation Solver) software to describe the mathematical model of the used absorption system to carry out the energy and exergy analyses, which were used to analyze the thermodynamic performance of the system. By studying the energetic and exergetic performance of the double-effect absorption cycle for evaporator temperature range of 2–10 °C, absorber and condenser temperature range of 28–45 °C, and HPG temperature range of 100–200 °C, two equations, which are functions of the operating temperatures, have been developed to predict the performance of the cycle.

First law analysis of a novel double effect air-cooled non-adiabatic ammonia/salt absorption refrigeration cycle

This paper thermodynamically analyzes an air-cooled type double effect absorption refrigeration system using ammonia/lithium nitrate and ammonia/sodium thiocyanate solutions as working pairs and driven by high temperature heat source such as waste heat energy, innovatively, an air-cooled type non-adiabatic absorber is implemented in the system to improve the cycle performance. Comparing to the single effect absorption refrigeration system, the double effect system is designed not only to directly and efficiently utilize high temperature waste heat energy for cycle performance improvement, but also to greatly extend the application occasion to high ambient temperature condition. Parametric analysis of the present system show that COP of the double effect system is 30–60% higher than the single effect system under air cooling working condition and the high pressure generating temperature of the double effect system can be extended to as high as 220°C. Influences of high pressure generator temperature, low pressure generator temperature, absorber outlet solution temperature as well as other system working parameters on cycle performance are numerically simulated and parametric optimization is provided in the present model. Cycle performance comparison of NH3/LiNO3 system with NH3/NaSCN system has been carried out. According to the simulation results, COP of NH3/NaSCN system is found to be 10–15% higher than that of NH3/LiNO3 system in evaporating temperature range of -10°C<Te<5°C. However in low evaporating temperature conditions, Te⩽-10°C, NH3/LiNO3 systems are found to be more competitive than that of NH3/NaSCN system. The main concern of the present study is that implementation of non-adiabatic absorbers in air-cooled type double effect ammonia/salt absorption refrigeration systems is essential, and only under non-adiabatic absorption conditions can the double effect ammonia/salt system realize miniaturization.