Decreasing Condensation Temperature Research Articles

Steam distillation process for flavor enhancement of milk coffee: Effects of condensation temperature on volatile compounds and flavor characteristics.

To enhance the flavor characteristics of milk coffee, steam distillation was applied to roasted ground coffee to obtain extracts that were then added to the hot water extract of the residue. The effects of different condensation temperatures for steam distillation on the volatile compounds of condensates and the flavor characteristics of the milk coffees prepared with each condensate were investigated. The volatile compounds were analyzed by gas chromatography/mass spectrometry, and principal component analysis (PCA) was performed on the mean peak areas of the volatiles that showed significant differences between the samples. The five types of milk coffees prepared with/without condensates were evaluated by consumer panelists using the check-all-that-apply question combined with the milk coffee flavor lexicon. The results showed that the concentration of volatile compounds tended to be higher in response to decreasing condensation temperature in steam distillation. The volatile compounds were grouped into four patterns based on their concentration in the condensates, which was affected by the volatility of the compounds and the duration of the condensation process in steam distillation. PCA clarified the characteristic volatile compounds that contribute to differences between the three condensates. The check-all-that-apply results indicated that the samples prepared with the condensates enhanced some specific coffee flavors, although acceptances for them were not enhanced. Implementing a steam distillation step in the milk coffee production process could lead to enhancing the coffee flavor strength of milk coffee products, and changing the condensation temperature for steam distillation was effective for providing different flavor characteristics of milk coffee. PRACTICAL APPLICATION: Changing the condensation temperature for steam distillation is effective in differentiating the flavor characteristics of milk coffee. Increasing the condensation temperature resulted in decreased concentrations of volatile compounds, which enhanced the milk and rich flavor. Decreasing the condensation temperature resulted in increased concentrations of volatile compounds, which provided a stronger coffee flavor to the milk coffee, possibly leading to a reduction in the use of coffee for milk coffee production. The check-all-that-apply question combined with the milk coffee flavor lexicon could effectively evaluate consumers' perceptions of the milk coffee flavor characteristics and their acceptances in a single survey.

Visualization study on the condensation in a propylene loop heat pipe operating at condenser temperatures between 153 and 283 K

A cryogenic loop heat pipe (CLHP) is an effective means of temperature control at low temperatures, but the physical properties of cryogenic working fluids are quite different from those of room-temperature working fluids, and their phase change and heat transfer characteristics need to be further studied. In this paper, a test system for evaluating the loop heat pipe (LHP) heat transfer performance and visualizing the condensation phenomenon in the condenser was fabricated. The performance of a propylene LHP with 20 W of heat exchange was tested as the condenser temperature was varied from 283 to 153 K, and the flow patterns and heat transfer characteristics during condensation were obtained. With the decreasing condenser temperature, slug flow disappeared, and pseudo-slug flow occurred and transitioned into wavy-annular flow, which was mainly caused by the increase of density ratio and viscosity ratio of the liquid to vapor. These change of flow pattern further affected the two-phase heat transfer and the performance of the CLHP. Pseudo-slug flow was observed at a condenser temperature of 273 to 203 K and it had a notable influence on the condensation pressure drop. The heat transfer coefficient of the two-phase region ranged from 2500 to 5500 W/m2K. When the condenser temperature ranged from 203 to 173 K, the transition of flow pattern and the fluctuation in the system caused a large deviation between the obtained and predicted heat transfer coefficients, and at other condenser temperatures, the obtained values were consistent with the predicted values for the corresponding flow patterns.

Condensation heat transfer and pressure drop characteristics of zeotropic mixtures of R134a/R245fa in plate heat exchangers

Zeotropic mixtures have shown great potential to improve the system efficiency compared with the use of pure fluids as the working fluids. However, there is a lack of analysis of the heat transfer during the phase change of zeotropic mixtures in plate heat exchangers, which is a common heat transfer device used as the evaporator and condenser in these systems. This paper presents an experimental analysis of the flow condensation heat transfer and pressure drop characteristics of zeotropic mixtures in a plate heat exchanger. The objectives are to obtain prediction methods for the heat transfer coefficient and frictional pressure drop and to quantify the degradation of the heat transfer coefficient by using mixtures. Zeotropic mixtures of R134a/R245fa with five different quantitative compositions were experimentally tested with the bubble point temperatures of 30°C to 50°C and various mass fluxes. The experimental results indicate that condensation of the mixtures is governed by a shear-controlled process, similar to what happens with pure fluids. Moreover, the heat transfer degradation of the zeotropic mixture caused by the mixture effects increases with decreasing condensation temperature and mass flux. There is a 48% maximum decrease in the heat transfer coefficient for the mixture of R134a/R245fa with 0.431/0.569 in mass fraction. A modified Silver-Bell-Ghaly method provides a good prediction for the heat transfer data with a mean absolute percentage deviation of 12.2%. A pure-fluid correlation developed in a previous work by the authors enables a prediction with an 8.6% mean absolute percentage deviation for the pressure drop data.

Performance evaluation of an electric vehicle thermal management system with waste heat recovery

Widespread adoption of electric vehicles is limited by their mileage, which is severely shortened by the positive temperature coefficient (PTC) heater in cold weather. To alleviate this difficulty, an electric vehicle thermal management system (EVTMS) with waste heat recovery from motor and controller unit is presented in this study. Utilizing a simulation model, the performances of EVTMS are investigated from the aspects of energy, exergy, and thermo-economy. In addition, the effects of waste heat amount and condensation temperature on EVTMS performances are exposed and discussed. It is indicated that increasing waste heat amount and decreasing condensation temperature would contribute to EVTMS performance improvement. Results show that the EVTMS with waste heat recovery leads to, in the best case, the coefficient of performance (COP) increase of 13.2%, the exergy destruction reduction of 20.01%, and the driving mileage improvement of 33.64%. With the waste heat varying in 0–2 kW and condensation temperature varying in 30–45 °C, the COP ranges from 2.05 to 4.71 and the system exergy efficiency varies in 28.63%~40.05%. Compared with the PTC heater, EVTMS with waste heat recovery could save the annual operation cost of 162.31–249.44 €. Base on the operation cost savings, the payback period of EVTMS ranges from 4.57 to 6.77 years.

Performance assessment and optimization of a novel multi-generation system from thermodynamic and thermoeconomic viewpoints

Multi-generation systems are promising technologies for multiple production applications to reduce the waste heat of the basic system. For this purpose, a novel multi-generation system using geothermal heat source is proposed which produces different commodities of cooling, heating, power and freshwater, simultaneously. The system comprises of a Kalina cycle, an absorption refrigeration cycle, a humidification-dehumidification desalination system, and a domestic water heater unit system. Exergoeconomic optimization of the proposed system is conducted, showing that the optimum thermal efficiency, exergy efficiency and total SUCP (sum unit cost of the product) can be obtained 94.84%, 47.89%, and 89.95 $/GJ, respectively. Moreover, a comprehensive parametric study showed that the Gained-Output-Ratio, freshwater, thermal efficiency and exergy efficiency can be optimized based on the desalination mass flow rate ratio. In addition, it is demonstrated that a higher thermal efficiency can be obtained by increasing vapour generator pinch point temperature difference, turbine inlet pressure, and evaporator temperature or decreasing condenser temperature, absorber temperature, basic ammonia concentration, desalination top temperature, desalination bottom temperature, and heater terminal temperature difference. Whereas, a higher exergy efficiency can be attained at high evaporator temperature, basic ammonia concentration, and desalination bottom temperature or low vapour generator pinch point temperature difference, turbine inlet pressure, condenser temperature, absorber temperature, desalination top temperature, and heater terminal temperature difference.

Experimental Investigation of the Condensation Heat Transfer Coefficient of R134a inside Horizontal Smooth and Micro-Fin Tubes

The condensation heat transfer coefficient of R134a was experimentally studied inside two smooth and four micro-fin tubes. The working conditions and structural parameters of the test tubes were selected as the influencing factors, and the experiment was conducted under mass velocities of 400–1100 kg·m−2·s−1, condensation temperatures of 35–45 °C and water-testing Reynolds numbers of 8000–22,000, with an inlet superheat of 1–2 °C and outlet subcooling of 1–2 °C at the test section for the refrigerant. Experimental results indicate that the heat transfer coefficient increases with increasing mass velocity and decreasing condensation temperature and water-testing Reynolds number. The heat transfer coefficient of the micro-fin tube with a helix angle of 28° is the highest and that of smooth tube is the lowest for test tubes with the same inner diameter. Tube diameter has a small influence on the heat transfer coefficient for the smooth tubes while the heat transfer coefficient increases with decreasing tube diameter for the micro-fin tubes. The heat transfer coefficient inside the test tube was compared with some well-known existing correlations, and results show that correlations by Cavallini et al., Thome et al., Shah and Akers et al. can estimate the experimental data with mean absolute deviation of less than 30%, and correlations of Dobson and Chato et al. and Jung et al. cannot be used to capture the heat transfer coefficient with mean absolute deviations of 140.18% and 146.23%, respectively. While the Miyara et al. correlation overestimates the heat transfer coefficient, correlations of Cavallini et al., Koyama et al. and Oliver et al. all underestimate the experimental data for the micro-fin tube. Their deviations are from 25 to 55% for micro-fin tubes 3 and 4, while their deviations keep to within 30% for micro-fin tubes 5 and 6. Finally, to improve the correlation prediction accuracy, a dimensionless parameter was introduced to the correlations of Dobson and Chato et al. and Jung et al., and correlations of Cavallini et al., Koyama et al. and Oliver et al. were modified by enhancing the turbulence effect. The prediction accuracy of all modified correlations can be controlled to within 30%.

Energy and Entropy-Based Optimization of a Single-Stage Water–Lithium Bromide Absorption Refrigeration System

Thermodynamic optimization of single-stage water–LiBr absorption system was performed earlier both from first- and second-law points of view. However, a realistic comparison between the two approaches is essential to identify the superior one. Hence a theoretical model is developed to optimize the absorption chiller for identifying conditions corresponding to maximum system coefficient of performance (COP) and minimum entropy generation rate. Optimum generator temperature for minimum entropy generation is found to be lower than that corresponding to maximum COP, with absorber having a dominant role in enhancing irreversibility in system. Optimal generator temperature decreases with increasing evaporator temperature and decreasing condenser temperature. Thus, it is possible to identify optimum value for any combination of condenser and evaporator temperature from both the energy and entropy points of view. Concerned contour maps are presented. Adoption of an entropy-optimized map is suggested, owing to higher sensitivity of entropy generation to the changes in condition compared to COP.

Extraction of Aluminum by AlCl Disproportionation Process in Vacuum

The extraction of aluminum by the AlCl disproportionation process in vacuum was researched using the furnace designed by ourselves. The features of aluminum products were characterized by X-ray diffraction, scanning electronic microscope and energy-dispersive X-ray spectroscopy. The results indicated that the purity of aluminum products increased with decreasing condensation temperature; aluminum products could be oxidized as their size was too small; the residues of the extraction of aluminum from alumina could be further treated with this process to generate metallic aluminum with a little carbon; aluminum products with high Al4C3, C and Al2O3 impurities could be purified by this process. The conclusions could provide bases for the industrial application of the process.

Energetic and Ecological Benefits of Heat Pump Application in Energy Transformation Systems

In 1900, Nikola Tesla published a paper: The problem of increasing human energy, stressing that generating electricity from burning of coal we would be destroying material, which would be a barbarous process. This message is still vitally important, and one method to mitigate the barbarous effects is e.g., application of heat pump. Its benefits are twofold: economic and ecological. Heat pump reduces fuel consumption and lessens the burden on the environment through combustion products. As example, we have quantified its application in the area of heating, but the results obtained are extendable to any energy system. The most significant parameters are the efficiency of the energy conversion process and the COP of the heat pump. When the product of these two parameters is equal to one, part of energy losses, occurring in the energy conversion process which is associated with the heat pump application, can be completely utilised by the heat pump as useful heat. This is of paramount importance for reduction of energy conversion losses and protection of the environment. In general, both the fuel consumption and amount of combustion products decrease with increasing COP, that is, with increasing evaporation temperature and/or decreasing condensation temperature of the working fluid used in the heat pump.

First and second laws analysis of the heat pipe/ejector refrigeration cycle

Abstract Integration of the heat pipe with an ejector will result in a compact and high performance system. The concept of the heat pipe/ejector refrigeration cycle is discussed, in this paper. The needed driving capillary forces are firmly established. The basic characteristics of the system, such as entrainment ratio, coefficient of performance, exergy efficiency and thermal efficiency of the system are evaluated. Also, the zero-dimensional constant pressure mixing theory is applied to ejector. In this study, water is used as the working fluid. Whenever the mixed flow is supersonic, a normal shockwave is assumed to occur upstream of diffuser inlet. The simulation results indicate that, the coefficient of performance can reach about 0.30 at T e = 10 °C, T c = 30 °C and T g = 100 °C. Also, the second law efficiency of the heat pipe/ejector refrigeration cycle increases with increasing evaporator temperature and decreasing condenser temperature. It is seen that, the maximum heat pipe cooling capacity obtains for large heat pipe diameters, near the small heat pipe lengths. It has proven that, this refrigeration system can be widely used in many areas, especially in renewable energy utilization such as solar energy.

Experimental study on the performance of a solar driven steam jet ejector chiller

This study experimentally investigated the performance of a solar driven (by parabolic trough collector) steam jet ejector chiller (SJEC) having a cooling capacity of 1 kW. The experiments show the particular characteristics of a SJEC with the strong influence of the condenser temperature, T cond, and evaporator temperature, T evap, on the coefficient of performance (COP). A decrease in the condenser temperature by 12 °C, in case of an evaporator temperature of T evap = 7 °C the COP was increased by 57%, while for T evap = 13 °C the COP was increased by 41% and for T evap = 17 °C the COP was increased by 34.4%, respectively. While at a constant condensation temperature an increase in the evaporator temperature, T evap, from 7 to 13 °C, leads to increased COP values ranging from 14% to 56.7%, and increases T evap from 7 to 17 °C, lead to increases in COP values ranging from 53% to 132%, respectively. These results in general indicate that the COP increases with decreasing condenser temperature, which is determined by the source temperature of the cooling medium and it has the limiting factors controlling the operation of the solar steam ejector refrigeration system.

Comment on “Assessing the implications of K isotope cosmochemistry for evaporation in the preplanetary solar nebula” by E. Young

Young [1] has presented an ablative^diiusive model to reinterpret the K isotopic data of Humayun and Clayton [2], arriving at signi¢cantly diierent conclusions. Here, I show that Young's model [1] fails to explain the ubiquitous presence of volatile element depletion, and that his interpretations of the K isotopic data of [2] are achieved by replacing an intensive variable used by [2] with an extensive variable developed by [1] that traces mass loss but not volatile element depletion. Further discrepancies introduced by [1] also in£uence the outcome. It is shown here that the ablative^diiusive model of Young [1] has no cosmochemical applications. The intellectual foundations of K isotope cosmochemistry rest upon decades of work (summarized by [2^4]) by E. Anders, S.R. Taylor, H. Wa«nke, H. Palme, and others that showed that the chemical compositions of Earth, Moon and meteorites exhibit distinct volatile element depletion relative to Si, and refractory elements, when compared with CI chondrite compositions. These eiects are characterized by an increasing order of depletion with decreasing condensation temperature, such that the order of depletion in the Earth is La6 Si6K6Rb6Cs6Pb [3,4], and were recognized to be caused by processes such as partial evaporation or incomplete condensation, which had operated selectively on the basis of condensation temperature. Young [1] proposes an inherently non-selective process: evaporation so intense that both volatile elements and major elements are lost su¤ciently rapidly to constitute an ablative process, in which evaporative losses are restricted to a diiusively limited boundary layer on the exterior of the body experiencing the intense thermal event. The chemical composition of the body inwards of the boundary layer is identical to its initial chemical composition prior to the thermal event. However, the ablative nature of the process drives the boundary layer inwards at a rate, dr/dt, which (if not arrested by termination of the heating event) would eventually consume the entire object. The model developed by Young [1] has a characteristic non-dimensional number, the `ablative^ diiusive Peclet number' :

Density, refractive index and sorption capacity of solid CO 2 layers

The density and refractive index of solid CO 2 layers were measured by an interferometric method, as was the sorption capacity of these layers for hydrogen, as a function of the condensation conditions such as temperature, growth rate and layer thickness. These properties, i.e. the density ϱ, refractive index n and sorption capacity, are strongly influenced by the condensation temperature. Above ≈70 K, ϱ and n of solid CO 2 layers agree well with those given in the literature for the bulk crystal, but below 70 K they decrease monotonically with decreasing condensation temperature. The charges of ϱ and n for a condensation temperature of 10 K are 40% and 16%, respectively. Below about 50 K, the sorption capacity of solid CO 2 layers for H 2 becomes measurable and increases considerably with decreasing condensation temperature indicating a porous structure of these layers. At about 20 K the maximum value of 220 mmol H 2/mol CO 2 has been measured. Below about 10 K drastic changes of the layer properties occur; the sorption capacity reduces considerably and an increase of the density is observed. This behaviour is due to spontaneous transitions of the layer structure during the CO 2 condensation, which can be observed by a sudden increase of the layer temperature as well as by an abrupt change of the interference pattern. The frequency of these spontaneous transitions increases with decreasing condensation temperature and increasing deposition speed. The released energy was measured by 7 K and estimated to be ≈ 1% of the total condensation energy of the CO 2 quantity condensed after a previous transition.

Reply to Edward Anders: A discussion of alternative models for explaining the distribution of moderately volatile elements in ordinary chondrites

The high observed abundances of Na and Cu in chondrules indicate that the amount of loss during chondrule formation was minor and possibly negligible, consistent with the view that loss was controlled by diffusion kinetics rather than equilibrium volatility, and that the surface of the chondrule quickly cooled to temperatures at which diffusional transport was negligible. Ordinary chondrite/CI abundance ratios appear to be randomly distributed in the range 0.9-0.1. Very few values are observed in the 0.36–0.70 range, but this is not statistically significant, nor is it predicted by the two-component (chondrule-matrix) model. If CI chondrite abundances are representative of mean solar-system material, the very low chondrule content in CM chondrites (<5% of high-temperature materials) indicates that the observed volatile distribution resulted from incomplete accretion of volatile carriers (perhaps a fine aerosol). At the ordinary chondrite formation location the fraction of an element sited in unaccreted carriers increased with decreasing condensation temperature. At the CM location a similar trend is observed for elements less volatile than S, but the unaccreted fraction of more volatile elements was nearly constant.

Optical absorption spectra of matrix isolated silver atoms and their dependence on matrix properties

The isolation of silver atoms in rare gas matrices has been studied as a function of the condensation parameters, such as condensation temperature, gas flow rate and dilution ratio, and of the matrix temperature. This was done to establish defined experimental conditions, which allow a comparison between the spectra of isolated species in various gas matrices. The isolation of silver atoms is increasingly favoured by decreasing condensation temperature, increasing gas : metal ratio and within the series from Ne to Xe. The tendency of the Ag atoms to become trapped at various sites increases with these trends resulting in broad and only partially resolved spectra. Owing to the substantial change in matrix structure with the condensation temperature TK, the form of the spectra depends strongly on TK. Annealing of these layers at temperatures up to 0.4 of the matrix triple point temperature results in well resolved atomic spectra indicating that most of the various sites are unstable at higher temperatures. The conditions are also given, at which metal aggregation is favoured.

Influence of condensation temperature on microstructure and tensile properties of titanium sheet produced by high-rate physical vapor deposition process

The influence of condensation temperature from 1000° to 275°C on the microstructure and tensile properties of titanium sheet produced by the high-rate physical vapor deposition process was studied. Deposition rates of 1 mil (250.000°A) per min were obtained. The microstructure varied with decreasing condensation temperature in the following sequence: above 883°C, transformed β; from 883° to 850°C, coarse columnar α; around 840°C, predominantly whisker growth; below 740°C, fine columnar α; below 450°C, very fine grained columnar α of less than theoretical density. The yield strength of the distilled sheet from 27,000 psi to 62,000 psi as the grain diameter decreased from 32 to 1 μ. The yield strength vs (grain diameter)-1/2 plot is linear.