Thermodynamic analysis of an ejector–vapour compressor cascade refrigeration system

Using the framework of the first and second law of thermodynamics, an ejector–vapour compressor cascade refrigeration system is studied. The criteria for refrigerant selection are examined, with R134a and R410A selected as the refrigerant for the ejector and compressor sub-cycle, respectively. The effects of generator temperature, evaporator temperature, condenser temperature, intercooler temperature and intercooler temperature difference are examined. The results demonstrate that a combined cycle can improve 30.8% when compared to the COP of single compressor cycle and 122% when compared to the single ejector cycle. In addition, intercooler temperature can be set at 26.5 °C for minimizing total exergy loss.

     

Exergy analysis of a domestic refrigerator using eco-friendly R290/R600a refrigerant mixture as an alternative to R134a

The aim of the present work is to bring out an exergy analysis of the hydrocarbon refrigerant mixture of R290/R600a as an alternative to R134a on the performance of a domestic refrigerator which is originally designed to work with R134a. The performance of both refrigerants was evaluated using an exergy analysis. The effects of evaporator temperature on the coefficient of performance (COP), exergy loss, exergic efficiency, and efficiency defect in the four major components of the system for R134a and R290/R600a mixture were experimentally investigated. The results obtained showed that the COP of R290/R600a mixture was improved up to 28.5 % than that of R134a. The highest average exergic efficiency of the system (42.1 %) was obtained using R290/R600a mixture at an evaporator temperature of 263 K (?10 °C). The overall efficiency defect in the refrigeration cycle working with R290/R600a mixture was consistently better than R134a.     

Exergy analysis of vapor compression refrigeration system using R450A as a replacement of R134a

This paper experimentally investigated exergetic performance analysis of vapor compression refrigeration system using R450a as a replacement for R134a at different evaporator and condenser temperatures within controlled environmental conditions. The exergetic performance analysis of the vapor compression refrigeration system with test parameters including efficiency defects in the components, total irreversibility, and exergy efficiency of the refrigeration system was performed. Findings showed that the total irreversibility and exergy efficiency of the vapor compression refrigeration system using R450A refrigerant were lower and higher than R134a by about 15.25–27.32% and 10.07–130.93%, respectively. However, the efficiency defect in the condenser, compressor, and evaporator of the R450A refrigeration system was lower than R134a by about 16.99–26.08%, 5.03–20.11%, and 1.85–15.85%, respectively. Conversely, efficiency defect in the capillary tube of the R450A refrigeration system was higher than R134a by about 14.66–78.97% under similar operating conditions. Overall, it was found that the most efficient component was the evaporator, and the least efficient component was the compressor for both refrigerants.

     

Exergy analysis and experimental study of a vapor compression refrigeration cycle

This article presents a detailed experimental analysis of 2TR (ton of refrigeration) vapor compression refrigeration cycle for different percentage of refrigerant charge using exergy analysis. An experimental setup has been developed and evaluated on different operating conditions using a test rig having R22 as working fluid. The coefficient of performance, exergy destruction, and exergetic efficiency for variable quantity of refrigerant has been calculated. The present investigation has been done by using 2TR window air conditioner and the results indicate that the losses in the compressor are more pronounced, while the losses in the condenser are less pronounced as compared to other components, i.e., evaporator and expansion device. The total exergy destruction is highest when the system is 100% charged, whereas it is found to be least when the system is 25% charged.     

Thermodynamic analysis of a direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22

The thermodynamic analysis of direct expansion solar-assisted heat pump system working with R290 as a drop-in substitute for R22 was carried out under the metrological conditions of Calicut, India. A prototype of a DXSAHP system consists of a compressor, an air-cooled condenser with evaporator–collector and thermostatic expansion valve. The experiments were carried during the winter months of 2016. The artificial intelligence technique artificial neural network integrated with genetic algorithm model was presented to predict energy and exergy performance of a system. The energy performance ratio of a system was found to be 5.75% higher and reduced heating capacity of about 6.8% when compared to R22. Similarly, the second law analysis (exergy analysis) of a total system working with R290 was found to be better when compared to baseline refrigerant. The selected alternative working fluid is a hydrocarbon and has zero ozone depletion and negligible global warming potential. Hence, R290 can be used as a drop-in substitute for R22 in DXSAHP systems.

     

Thermodynamic performance of automobile air conditioners working with R430A as a drop-in substitute to R134a

The refrigerant R134a is to be phasing out soon in automobile air conditioning applications due to its high global warming potential of 1430. Hence, it is essential to identify a sustainable alternative refrigerant to phase out R134a in automobile air conditioners. This paper presents the experimental thermodynamic performance of R430A (composed of R152a and R600a, in the ratio of 76:24, by mass) as a drop-in substitute to replace R134a in automobile air conditioners. The experiments were carried out in an automobile air conditioner test setup equipped with a variable frequency drive electrical motor. During experimentation, the ambient temperature and ambient relative humidity were maintained at 35?±?1 °C and 65?±?5%, respectively. The compressor speed was varied in the range between 1000 and 3000 rpm. The results showed that the coefficient of performance of an automobile air conditioner working with R430A was found to be 12–20% higher with 6–11% reduced compressor power consumption when compared to R134a. The R430A has 2–6 °C higher compressor discharge temperature when compared to R134a. The physical stability of the lubricant used in the compressor was retained while operating with R430A. The maximum exergy destruction occurs in the compressor (0.28 kW for R134a and 0.24 kW for R430A) followed by evaporator (0.16 kW for R134a and 0.14 kW for R430A), condenser (0.14 for R134a and 0.12 kW for R430A) and expansion valve (0.043 kW for R134a and 0.039 kW for R430A) at a compressor speed of 1000?±?10 rpm. The exergy destruction of the system operating with R430A was found to be 12–28% lower when compared to R134a systems due to its favorable thermo-physical properties. The total equivalent warming impact of R430A was found to be lower when compared to R134a by about 47.3%, 35% and 32.4% for LPG, petrol and diesel vehicles, respectively. The results confirmed that R430A is a good drop-in substitute to replace R134a in existing automobile air conditioning systems.

     

Thermodynamic evaluation of heat recovery through a Canopus heat exchanger for vapor compression refrigeration (VCR) system

This communication deals with the waste heat recovery from the industrial refrigeration and air-conditioning system by introducing Canopus heat exchanger. There is a considerable amount of low-grade heat available in large-capacity systems. To recover this low-grade heat, a Canopus heat exchanger is introduced between compressor and condenser components. The system feasibility is studied with various operating parameters and its effect on heat recovery factor and overall COP of the system. The parametric results obtained for different eco-friendly working fluids, such as R-134a and R-507a, have been presented. It is found that, in general, overall COP of the system is improved without affecting the actual performance of the system. The potential of low-grade heat availability is increased with increasing cooling capacity.     

Solar adsorption refrigeration system using different mass of adsorbents

In this investigation, a prototype model of the solar adsorption refrigeration system was constructed and its performance was evaluated with different mass ratios of adsorbents in the laboratory for possible field application. The main components of the solar-driven cooling system were vacuum tube collector, adsorption bed, condenser, evaporator, chilling chamber, and temperature data logger. The experimental study was conducted to analyze the performance of solar cooling unit using different mass ratios of activated carbon–methanol from 0.250 to 2.50. A minimum cooling temperature of 12.2 °C was obtained with the manually prepared activated carbon–methanol with mass ratio of 1.00. The cooling coefficient of performance and specific cooling potential was also evaluated from performance calculations.     

Distillation of LiCl from the LiCl–Li2O molten salt of the electrolytic reduction process

Electrolytic reduction of the uranium oxide in LiCl–Li₂O molten salt for the treatment of spent nuclear fuel requires the separation of the residual salt from the reduced metal product, which contains about 20 wt% salt. In order to separate the residual salt and reuse it in the electrolytic reduction, a vacuum distillation process was developed. Lab-scale distillation equipment was designed and installed in an argon atmosphere glove box. The equipment consisted of an evaporator in which the reduced metal product was contained and exposed to a high temperature and reduced pressure; a receiver; and a vertically oriented condenser that operated at a temperature below the melting point of lithium chloride. We performed experiments with LiCl–Li₂O salt to evaluate the evaporation rate of LiCl salt and varied the operating temperature to discern its effect on the behavior of salt evaporation. Complete removal of the LiCl salt from the evaporator was accomplished by reducing the internal pressure to <100 mTorr and heating to 900 °C. We achieved evaporation efficiency as high as 100 %.     

Influence of the addition of aluminium nanoparticles on thermo-rheological properties of hydroxyl-terminated polybutadiene-based composite propellant and empirical modelling

The heat transfer performance and entropy analysis are done in a compact loop heat pipe (CLHP) with Al₂O₃/water and Ag/water nanofluid. A compact loop heat pipe having a flat square evaporator with dimensions of 34 mm (L)?×?34 mm (W)?×?19 mm (H) has been fabricated and tested for the heat load ranging from 30 to 500 W. The experimental tests are conducted by keeping the CLHP in the vertical orientation with distilled water, silver (Ag)/water and aluminium oxide (Al₂O₃)/water nanofluid having low volume concentrations of (0.09% and 0.12%). The effect of wall and vapour temperature, evaporator and condenser heat transfer coefficient, thermal resistance on the applied heat loads is experimentally investigated and compared. The experimental results showed that the evaporator thermal resistance is reduced by 34.70% and 20.21%, respectively, for 0.12 vol% of Ag, Al₂O₃ nanoparticles when compared with that of the distilled water. For the same volume concentrations of Ag, Al₂O₃ nanoparticles, an enhancement of 34.52%, 23.7%, 39.27% and 30.8%, respectively, observed for the convective heat transfer coefficients at the evaporator and condenser. The entropy is also reduced by 19.08% and 11.58% when Ag and Al₂O₃ nanofluids are used as the operating fluid. From the experimental tests, it is found that the addition of small amount of Ag nanoparticles in the working fluid enhanced the operating range by 15% when compared with that of Al₂O₃/water nanofluid without the occurrence of any dry-out conditions.

     

Modeling of a MED-TVC desalination system by considering the effects of nanoparticles: energetic and exergetic analysis

In this study, the energetic and exergetic analysis of a multi-effect desalination system with a thermal vapor compression desalination system has been numerically evaluated. For this purpose, the mass, energy, and exergy balance equations for the thermo-compressor, first effect as well as middle effects, and condenser have been developed. The effects of motive steam pressure and number of effects on yield, gained output ratio (GOR), performance ratio (PR) and irreversibility have been examined. Nanoparticles were used to improve the heat transfer properties at different stages. The highest rate of exergy destruction with 61.67% is concerned with thermo-compressor, owing to the large difference between the motive steam pressure and the entrained steam. The lowest exergy losses rate among the various components was 4.89% for the condenser, due to the fact that much of the final distillate steam entrained the thermo-compressor. As the number of effects increased from 1 to 7, the yield, GOR as well as PR, improved by approximately 590% and the irreversibility reduced by 1.88%. As the motive steam pressure increased from 400 to 1290 kPa, the yield decreased by 25.45% while the GOR and PR improved by 12.62 and 14.8%, respectively. From the second law viewpoint, irreversibility intensified by 16.11% which in turn diminished the second efficiency by 3.17%.

     

Molecular distillation

Molecular distillation was studied for the separation of tocopherols from soya sludge, both experimentally and by simulation, under different operating conditions, with good agreement. Evaporator temperatures varied from 100°C to 160°C and feed flow rates ranged from 0.1 to 0.8 kg/h. The process pressure was maintained at 10⁻⁶ bar, the feed temperature at 50°C, the condenser temperature at 60°C, and the stirring at 350 rpm. For each process condition, samples of both streams (distillate and residue) were collected and stored at −18°C before tocopherols analyses. Owing to the differences between molecular weights and vapor pressures of free fatty acids and tocopherols, tocopherols preferentially remained in the residue at evaporator temperatures of 100°C and 120°C, whereas for higher temperatures (140°C and 160°C) and lower feed flow rate, tocopherols tended to migrate to the distillate stream.     

Dielectric modes in antiferroelectric liquid crystal observed at low temperatures

A broad temperature antiferroelectric binary mixture has been investigated by means of dielectric spectroscopy. The sample was cooled down to –70°C. It was found that the sample was still in antiferroelectric phase. This is the widest antiferroelectric mixture ever seen (～170°) in which three well-separated modes have been detected at room temperature. In addition, the bias field influence on existing modes has been observed. All modes change their strengths with bias field. Results show that the fastest mode, called X mode previously, gradually disappears around –30°C. When the temperature decreases below –40°C, one can indisputably observe additional mode, faster than X mode. This mode (named as Y mode) observed for extra low temperatures is bias independent. It can be the molecular mode, connected with rotation around long molecular axis. The rotation around short molecular axis seems to be blocked in antiferroelectric packing. To calculate parameters of observed modes, Cole–Cole model was used. The parameters of Y mode are discussed in this article.     

A high performance liquid chromatography – inductively coupled plasma-mass spectrometry interface employing desolvation for speciation studies of platinum in chemotherapy drugs

A novel interface between high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS) is described. The eluent from the HPLC is nebulised into a heated cyclone spray-chamber and the solvent removed using a Nafion membrane drier, held at 75 degrees C, and a cryogenic condenser. The condenser consists of 6 Peltier heat pumps connected to liquid cooled aluminium blocks. At a nebuliser gas flow rate of 0.6 l min(-1), the membrane drier removes 58% of the vapour and the Peltier condenser 75% of the remaining vapour, i.e. a total desolvation efficiency of 89%. This enables the use of HPLC solvents which otherwise would destabilise the ICP, e.g. 100% acetonitrile or methanol, and permits the use of solvent gradients with minimal baseline drift. The system has been applied to the determination of platinum species in an organoplatinum drug used for chemotherapy in human plasma ultrafiltrate of patients treated with this new drug (JM-216). The limit of detection for platinum species has been 0.6 ng nl(-1) (i.e. 120 pg of Pt) and several species have been separated with good resolution.     

Influence of temperature on thymine-to-solvent vibrational energy transfer

At the instant following the non-radiative deactivation of its ππ* electronic state, the vibrational modes of thymine possess a highly non-equilibrium distribution of excitation quanta (i.e., >4 eV in excess energy). Equilibrium is re-established through rapid (5 ps) vibrational energy transfer to the surrounding solvent. The mechanisms behind such vibrational cooling (VC) processes are examined here using femtosecond transient grating and two-dimensional photon echo spectroscopies conducted at 100 K and 300 K in a mixture of methanol and water. Remarkably, we find that this variation in temperature has essentially no impact on the VC kinetics. Together the experiments and a theoretical model suggest three possible mechanisms consistent with this behavior: (i) vibrational energy transfer from the solute to solvent initiates (directly) in intramolecular modes of the solute with frequencies >300 cm(-1); (ii) the relaxation induced increase in the temperature of the environment reduces the sensitivity of VC to the temperature of the equilibrium system; (iii) the time scale of solvent motion approaches 0.1 ps even at 100 K. Mechanism (i) deserves strong consideration because it is consistent with the conclusions drawn in earlier studies of isotope effects on VC in hydrogen bonding solvents. Our model calculations suggest that mechanism (ii) also plays a significant role under the present experimental conditions. Mechanism (iii) is ruled out on the basis of long-lived correlations evident in the photon echo line shapes at 100 K. These insights into photoinduced relaxation processes in thymine are made possible by our recent extension of interferometric transient grating and photon echo spectroscopies to the mid UV spectral region.     

High-performance system for partial nitritation of reject water resistant to temperature fluctuation

A sequencing batch reactor (SBR) applying partial nitritation for reject water treatment was operated for 330 days at a laboratory scale. The system was repeatedly exposed to sudden temperature drops from 24 to 17 °C. The nitrogen loading rate (NLR) was increased incrementally from 0.4 to 1.5 kg/(m³ day) with the aim to evaluate temperature stability of the process at different NLR value. Total nitrite nitrogen (TN^IIIN) represented 94–99% of oxidised nitrogen in the effluent throughout the entire operation of the reactor. It was found that the pH profile during the SBR cycle, nitrogen removal efficiency and concentration of N-species in the effluent did not show significant changes following temperature decreases occurring within the entire applied range of the NLR. Simultaneously, the nitrogen removal rate increased proportionally with the NLR where the nitrogen oxidation efficiency reached 48–58% regardless of actual temperature and NLR. These observations clearly demonstrate the temperature stability of applied partial nitritation system during the tested temperature fluctuations.     

Synthesis of a New Modification of Lithium Chloride Confirming Theoretical Predictions

In accordance with prior calculations, the new polymorph β‐LiCl (wurtzite structure type) has been synthesised, by the low‐temperature atomic‐beam‐deposition (LT–ABD) technique, in a mixture with α‐LiCl (rock salt structure type) by depositing LiCl vapour (2 to 5.3 × 10^–4 mbar) onto a cooled substrate (–30 to –60 °C). The maximum β‐LiCl fraction of 53 % was obtained using a sapphire (0001) substrate at –50 °C and 3.7 × 10^–4 mbar LiCl vapour pressure. The proportion of the new polymorph contained in the bulk sample decreases as temperature or vapour pressure deviate from these values, until finally the rock salt type LiCl is found exclusively. When the samples are warmed up to room temperature, β‐LiCl irreversibly transforms to α‐LiCl. The X‐ray diffraction pattern of the two phase LiCl sample measured at –50 °C has been indexed and refined based on a hexagonal unit cell for β‐LiCl with the lattice constants a = 3.852(1) Å and c = 6.118(1) Å and a cubic unit cell for α‐LiCl with the lattice constant a = 5.0630(8) Å. By Rietveld refinement the wurtzite type ofstructure (P6₃mc, No. 186) was suggested for the new hexagonal modification of LiCl with the Li–Cl distances (2.32 and 2.34 Å) being 8 % smaller than those of α‐LiCl. Moreover, the cell volume decreases as much as 16 % during the transition from β‐LiCl to α‐LiCl. Both the shifts in bond lengths and volume correspond well with the situation encountered for LiBr and LiI. Besides the variation of LiCl vapour pressure and substrate temperature, also different substrate materials were employed for testing their influence on formation of the β‐LiCl polymorph.     

Analysis of operation mode of reflective liquid crystal display devices

The reflective liquid crystal display device having one polarizer was studied with the dynamic parameter space method. Device operation mode was analysed for both normally black and normally white operation conditions. The electro-optical responses and reflectance spectra were also studied for different operation modes. It was found that the optimized normally white modes for twist angles 180° and 220° of the reflective liquid crystal device have satisfactory contrast ratios and dispersion properties. For these twist angles, two equivalent normally white modes exist. The polarizer angles β₁ of the first mode and β₂ of the second mode have the simple relation β₂ = 90° + β₁.     

Asymmetric induction radical copolymerization of optically active l-menthyl vinyl ether with vinylene carbonate and indene

The copolymerizations of l-menthyl vinyl ether (l-MVE) with the monomers vinylene carbonate (VCA) and indene (IN) were carried out in benzene with azobisisobutyronitrile (AIBN) as an initiator to obtain optically active copolymers. The optically active l-menthyl residue from the copolymer main chain was removed using dry hydrogen bromide gas. After the ether cleavage reaction, the copolymers prepared (VA–VCA and VA–IN) were still optically active, and hence it was found that asymmetric induction had taken place in the copolymer main chain. The optical rotatory dispersion (ORD) and circular dichroism (CD) data of the original and ether-cloven copolymers were also determined.