Surface Vapor Pressure Research Articles

Uncertainties in historical changes and future projections of drought. Part I: estimates of historical drought changes

How drought may change in the future are of great concern as global warming continues. In Part I of this study, we examine the uncertainties in estimating recent drought changes. Substantial uncertainties arise in the calculated Palmer Drought Severity Index (PDSI) with Penman-Monteith potential evapotranspiraiton (PDSI_pm) due to different choices of forcing data (especially for precipitation, solar radiation and wind speed) and the calibration period. After detailed analyses, we recommend using the Global Precipitation Climatology Centre (GPCC) or the Global Precipitation Climatology (GPCP) datasets over other existing land precipitation products due to poor data coverage in the other datasets since the 1990s. We also recommend not to include the years after 1980 in the PDSI calibration period to avoid including the anthropogenic climate change as part of the natural variability used for calibration. Consistent with reported declines in pan evaporation, our calculated potential evapotranspiration (PET) shows negative or small trends since 1950 over the United States, China, and other regions, and no global PET trends from 1950 to 1990. Updated precipitation and streamflow data and the self-calibrated PDSI_pm all show consistent drying during 1950–2012 over most Africa, East and South Asia, southern Europe, eastern Australia, and many parts of the Americas. While these regional drying trends resulted primarily from precipitation changes related to multi-decadal oscillations in Pacific sea surface temperatures, rapid surface warming and associated increases in surface vapor pressure deficit since the 1980s have become an increasingly important cause of widespread drying over land.

Directed energy missions for planetary defense

Directed energy for planetary defense is now a viable option and is superior in many ways to other proposed technologies, being able to defend the Earth against all known threats. This paper presents basic ideas behind a directed energy planetary defense system that utilizes laser ablation of an asteroid to impart a deflecting force on the target. A conceptual philosophy called DE-STAR, which stands for Directed Energy System for Targeting of Asteroids and exploration, is an orbiting stand-off system, which has been described in other papers. This paper describes a smaller, stand-on system known as DE-STARLITE as a reduced-scale version of DE-STAR. Both share the same basic heritage of a directed energy array that heats the surface of the target to the point of high surface vapor pressure that causes significant mass ejection thus forming an ejection plume of material from the target that acts as a rocket to deflect the object. This is generally classified as laser ablation. DE-STARLITE uses conventional propellant for launch to LEO and then ion engines to propel the spacecraft from LEO to the near-Earth asteroid (NEA). During laser ablation, the asteroid itself provides the propellant source material; thus a very modest spacecraft can deflect an asteroid much larger than would be possible with a system of similar mission mass using ion beam deflection (IBD) or a gravity tractor. DE-STARLITE is capable of deflecting an Apophis-class (325m diameter) asteroid with a 1- to 15-year targeting time (laser on time) depending on the system design. The mission fits within the rough mission parameters of the Asteroid Redirect Mission (ARM) program in terms of mass and size. DE-STARLITE also has much greater capability for planetary defense than current proposals and is readily scalable to match the threat. It can deflect all known threats with sufficient warning.

Cloud effects on surface energy and mass balance in the ablation area of Brewster Glacier, New Zealand

Abstract. The effect of clouds on glacier surface energy balance (SEB) has received increased attention in the last decade, but how clouds interact with other meteorological forcing to influence surface mass balance (SMB) is not as well understood. This paper resolves the SEB and SMB at a site in the ablation zone of Brewster Glacier over a 22-month period, using high-quality radiation data to carefully evaluate SEB terms and define clear-sky and overcast conditions. A fundamental change in glacier SEB in cloudy conditions was driven by increased effective sky emissivity and surface vapour pressure, rather than a minimal change in air temperature and wind speed. During overcast conditions, positive net long-wave radiation and latent heat fluxes allowed melt to be maintained through a much greater length of time compared to clear-sky conditions, and led to similar melt in each sky condition. The sensitivity of SMB to changes in air temperature was greatly enhanced in overcast compared to clear-sky conditions due to more frequent melt and changes in precipitation phase that created a strong albedo feedback. During the spring and autumn seasons, the sensitivity during overcast conditions was strongest. To capture these processes, future attempts to explore glacier–climate interactions should aim to resolve the effects of atmospheric moisture (vapour, cloud, and precipitation) on melt as well as accumulation, through enhanced statistical or physically based methods.

Experimental investigations on surface vapor pressure models for LiCl–CaCl2 desiccant solutions

The surface vapor pressure of desiccant solutions is the key parameter for modeling the liquid desiccant system. Usually, the simple mixing rule (SMR) model and the nonrandom two-liquid (NRTL) model are employed by people to calculate the surface vapor pressure of mixture desiccant solutions during simulating the performance of a liquid desiccant system. However, there is little literature caring about the calculation accuracy of the two models for surface vapor pressure of mixture desiccant solution under different circumstances. In this paper, an experimental system is built to measure the surface vapor pressure of LiCl–CaCl2 desiccant solutions under various conditions including temperatures ranging from 25°C to 75°C, total mass concentrations ranging from 5% to 40% and three mass mixing ratios of LiCl to CaCl2 (e.g., 1:1, 1:2, 2:1). The two models for surface vapor pressure of mixture desiccant solution (i.e., the SMR and the NRTL) are compared with the test data. It is found that the SMR model has much better accuracy than the NRTL model in forecasting the surface vapor pressure of LiCl–CaCl2 mixture desiccant solution when the solution mass concentration is lower than 10%, and it is the opposite for the case when the solution mass concentration is higher than 30%. Afterwards, the revised equations for the SMR and the NRTL model are proposed according to the test data within the conditions concerned in this study. The calculation accuracy of the two vapor pressure models is proved to be greatly improved after the revisions.

A method for sensible heat flux model parameterization based on radiometric surface temperature and environmental factors without involving the parameter KB−1

Sensible heat flux is a key component of land–atmosphere interaction. In most parameterizations it is calculated with surface-air temperature differences and total aerodynamic resistance to heat transfer (Rae) that is related to the KB−1 parameter. Suitable values are hard to obtain since KB−1 is related both to canopy characteristics and environmental conditions. In this paper, a parameterize method for sensible heat flux over vegetated surfaces (maize field and grass land in the Heihe river basin of northwest China) was proposed based on the radiometric surface temperature, surface resistance (Rs) and vapor pressures (saturated and actual) at the surface and the atmosphere above the canopy. A biophysics-based surface resistance model was revised to compute surface resistance with several environmental factors. The total aerodynamic resistance to heat transfer is directly calculated by combining the biophysics-based surface resistance and vapor pressures. One merit of this method is that the calculation of KB−1 can be avoided. The method provides a new way to estimate sensible heat flux over vegetated surfaces and its performance compares well to the LAS measured sensible heat and other empirical or semi-empirical KB−1 based estimations.

Selection of optimal mixed liquid desiccants and performance analysis of the liquid desiccant cooling system

Liquid desiccant cooling system is an energy-conservative and environment-friendly air-conditioning system. Its performance is strongly influenced by the thermal properties of liquid desiccant, especially the surface vapor pressure. Mixed liquid desiccant may have better dehumidification efficiency, lower material cost and lower energy consumption. But it is difficult to analyze its thermal properties. To improve on this, our paper proposes a method based on the NRTL equation to predict the vapor pressure of mixed liquid desiccants. Six absorbent solutions (LiBr/LiCl + CaCl2/MgCl2 + water/methanol) have been analyzed, and systems employing them have also been investigated. The results show that the dehumidification efficiency of mixed liquid desiccant was higher than that of a single solution. The LiBr–CaCl2–water system can obtain higher COP compared with other systems under the condition of the same dehumidification performance in summer. Moreover, the LiCl–methanol–water may be a potential absorbent for energy saving. The results are meaningful for the selection of suitable liquid desiccants and engineering design.

Study on mass transfer of droplets in narrow space

Combinatorial or high-throughput experimentation is improving numerous scientific domains intensely, such as biological chemistry, material science, catalysis. In the past research, most of researchers focus on the novel configuration and microfabrication rather than the transfer mechanism in the microcosm. In this study, we proposed a mass transfer model among droplets in a narrow space. In the derivation, the molecular mass flow rate (JM) formula was used to calculate droplet mass transfer rate, which was controlled by the concentration gradient of the surface vapor pressure (PS) near the droplets. Especially, in the simplification of the expression of the simulating results, all droplets were divided into groups following their radii subtly. In order to assess the accuracy and predictive capability of the proposed model, we carried out some designed experiments to investigate distribution and size changes of the droplets at different temperatures and times. After capturing and analyzing the images of the droplets gathering on a hydrophobic glass slide in an airtight narrow space, we verified the simulating results with the experimental data. The less than 5% deviation indicated the proposed mass transfer model could describe the mass transfer phenomenon among droplets in a narrow space reliably. Furthermore, we found that the total droplet number (ND) decreases with the running time, which should be taken into account discreetly when designing the parallel micro-reactors.

A Remote Sensing Method for Estimating Surface Air Temperature and Surface Vapor Pressure on a Regional Scale

This paper presents a method of estimating regional distributions of surface air temperature (Ta) and surface vapor pressure (ea), which uses remotely-sensed data and meteorological data as its inputs. The method takes into account the effects of both local driving force and horizontal advection on Ta and ea. Good correlation coefficients (R2) and root mean square error (RMSE) between the measurements of Ta/ea at weather stations and Ta/ea estimates were obtained; with R2 of 0.77, 0.82 and 0.80 and RMSE of 0.42K, 0.35K and 0.20K for Ta and with R2 of 0.85, 0.88, 0.88 and RMSE of 0.24hpa, 0.35hpa and 0.16hpa for ea, respectively, for the three-day results. This result is much better than that estimated from the inverse distance weighted method (IDW). The performance of Ta/ea estimates at Dongping Lake illustrated that the method proposed in the paper also has good accuracy for a heterogeneous surface. The absolute biases of Ta and ea estimates at Dongping Lake from the proposed method are less than 0.5Kand 0.7hpa, respectively, while the absolute biases of them from the IDW method are more than 2K and 3hpa, respectively. Sensitivity analysis suggests that the Ta estimation method presented in the paper is most sensitive to surface temperature and that the ea estimation method is most sensitive to available energy.

Spatial and temporal variability of water vapor content during 1961–2011 in Tianshan Mountains, China

Based on the climate factors data and surface vapor pressure (SVP) data of 44 weather stations in Tianshan Mountains during the years 1961-2011, this paper establishes a water vapor content (WVC) estimation model according to the relationship between monthly WVC of radiosonde and corresponding SVP and analyzes the spatial and temporal variability of WVC and their causes. The results show that the WVC is linearly and negatively related to the elevation and longitude (Vertical zonality and Longitude zonality), while it was not linearly related to the latitude. The westerly wind, geographical situation and sea level elevation composed complex surface conditions to influence the spatial distribution of WVC in the Tianshan Mountains. The Mann-Kendall (M-K) statistical test shows a significant increasing trend in the mean annual WVC in Tianshan Mountains during 1961-2011(P < 0.001), with a rate of 0.23 mm/decade, and indicates an abrupt turning pointin 1985 (P < 0.001). Correlation analysis shows that the WVC are significantly correlated to the temperature, especially during the winter, but the summer WVC are significantly correlated to the precipitation. In addition, the North Atlantic Oscillation Index (NAOI) and the Arctic Oscillation Index (AOI) are significantly correlated to the winter WVC in the Tianshan Mountains. As a new Microwave radiometric profilers (MWRPs) instrument, the MP-3000A provides continuous, real-time and high temporal resolution atmospheric profiles up to 10 km. In order to monitor water vapor and atmosphere profiles in Tianshan Mountains, an MP-3000A was established in Urumqi (43.8°N, 87.58°N) in May 2008. The results indicated that the MP-3000A was applicable to this area, and the evolutionary process of water vapor and the WVC peak values of MP-3000A were a strong signal for rainstorm and flood forecasts for Urumqi and the Tianshan Mountains.

IMS-MS and IMS-IMS investigation of the structure and stability of dimethylamine-sulfuric acid nanoclusters.

Recent studies of new particle formation events in the atmosphere suggest that nanoclusters (i.e, the species formed during the early stages of particle growth which are composed of 10(1)-10(3) molecules) may consist of amines and sulfuric acid. The physicochemical properties of sub-10 nm amine-sulfuric acid clusters are hence of interest. In this work, we measure the density, thermostability, and extent of water uptake of <8.5 nm effective diameter dimethylamine-sulfuric (DMAS) nanoclusters in the gas phase, produced via positive electrospray ionization. Specifically, we employ three systems to investigate DMAS properties: ion mobility spectrometry (IMS, with a parallel-plate differential mobility analyzer) is coupled with mass spectrometry to measure masses and collision cross sections for <100 kDa positively charged nanoclusters, two differential mobility analyzers in series (IMS-IMS) are used to examine thermostability, and finally a differential mobility analyzer coupled to an atmospheric pressure drift tube ion mobility spectrometer (also IMS-IMS) is used for water uptake measurements. IMS-MS measurements reveal that dry DMAS nanoclusters have densities of ∼1567 kg/m(3) near 300 K, independent of the ratio of dimethylamine to sulfuric acid originally present in the electrospray solution. IMS-IMS thermostability studies reveal that partial pressures of DMAS nanoclusters are dependent upon the electrospray solution concentration ratio, R = [H2SO4]/[(CH3)2NH]. Extrapolating measurements, we estimate that dry DMAS nanoclusters have surface vapor pressures of order 10(-4) Pa near 300 K, with the surface vapor pressure increasing with increasing values of R through most of the probed concentration range. This suggests that nanocluster surface vapor pressures are substantially enhanced by capillarity effects (the Kelvin effect). Meanwhile, IMS-IMS water uptake measurements show clearly that DMAS nanoclusters uptake water at relative humidities beyond 10% near 300 K, and that larger clusters uptake water to a larger extent. In total, our results suggest that dry DMAS nanoclusters (in the 5-8.5 nm size range in diameter) would not be stable under ambient conditions; however, DMAS nanoclusters would likely be hydrated in the ambient (in some cases above 20% water by mass), which could serve to reduce surface vapor pressures and stabilize them from dissociation.

Fluid dynamic and heat transfer processes between solid surfaces and non-Newtonian liquid droplets

This paper addresses the experimental and theoretical description of the fluid dynamic and thermal behaviour of non-Newtonian (shear-thinning) droplets impacting onto smooth and micro-patterned heated surfaces. The shear-thinning liquids are mixtures of water + xanthan gum prepared with different concentrations of the gum, namely 0.05%, 0.10%, 0.15% and 0.35%wt. For droplet impacts over the surfaces heated bellow the boiling temperature of the liquid, the shear-thinning effect is clearly governed by the concentration of the non-Newtonian component, which is associated to the consistency coefficient of the constitutive model describing the viscous behaviour of the flow. In line with this, models predicting the spreading of Newtonian droplets are revisited and an alternative one is proposed, which integrates the non-Newtonian behaviour. The results suggest that heating the surface (and consequently the liquid) alters the rheology of the non-Newtonian mixture and reverses the increase of the zero viscosity, which is observed for impacts onto non-heated surfaces, thus allowing a larger spreading diameter and a significant recoiling phase for droplets with high concentrations of the non-Newtonian component. The heat transferred at droplet–surface interaction, during the spreading of the droplet is also evaluated. The analysis evidences the strong coupling between the heat transfer process and the spreading dynamics, for the non-Newtonian droplets. Further heating the surface above the boiling temperature of the liquid, the droplets impact the surfaces within the nucleate boiling regime and thermal induced atomization occurs. In this case, Phase Doppler measurements are taken to characterize the size of the secondary droplets generated within this process. The results show that the thermal induced atomization is mainly triggered by the force balance between surface tension and vapour pressure forces, so the viscosity plays a secondary role.

Measuring and Modeling the Retreat of the Summit Ice Fields on Kilimanjaro, East Africa

Terrestrial laser-scanning surveys of the south-facing cliff of the northern Ice Field on the summit crater of Kilimanjaro were taken on three occasions, in September 2004, January 2006, and August 2008. By comparing the three scans, the rates of lateral cliff retreat and surface lowering can be assessed. During 2004–2006, the mean lateral retreat was 1.39 m yr-1, falling to 0.89 m yr-1 during 2006–2008. These rates are broadly comparable with previous work using ablation stakes. Surface lowering is much less rapid, at 0.65 and 0.25 m yr-1, respectively. Analysis of seasonal forcings (radiation on a south-facing cliff, radiation on a flat surface, surface vapor pressure, and relative humidity) shows that most of the lateral retreat occurs during the austral summer, when direct radiative input is considerably higher on the south-facing ice cliff. On the ice surface, however, high-sun periods around the equinoxes dominate the surface lowering. Lowering is more during the wet than the dry seasons, which suggests that the current moisture availability on Kilimanjaro is not frequent enough to prevent lowering year round.

Representing moisture fluxes and phase changes in glacier debris cover using a reservoir approach

Abstract. Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a CMB model adapted for debris-covered glaciers. We present the results of two point simulations, using both our new "moist" and the conventional "dry" approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former year coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass-balance dynamics. When water and ice are considered, heat transmission to the underlying glacier ice is lower, as the effective thermal diffusivity of the saturated debris layers is reduced by increases in both the density and the specific heat capacity of the layers. In combination with surface heat extraction by QL, subdebris ice melt is reduced by 3.1% in 2008 and by 7.0% in 2011 when moisture effects are included. However, the influence of the parameterization on the total accumulated mass balance varies seasonally. In summer 2008, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total ablation increases by 4.0%. Conversely, in fall 2011, the modulation of basal debris temperature by debris ice results in a decrease in total ablation of 2.1%. Although the parameterization is a simplified representation of the moist physics of glacier debris, it is a novel attempt at including moisture in a numerical model of debris-covered glaciers and one that opens up additional avenues for future research.

Development, calibration and validation of a mathematical model for the low-pressure-vaporization of the water in porous media

This paper reports the development, calibration and validation of a mathematical model of the low-pressure-vaporization process in different types of porous media. This model aims to improve models developed by other authors in this area, namely by considering some aspects that have not been addressed, such as: the vapor pressure is not equal in the whole chamber; the interfacial vapor pressure is not equal to the saturation pressure; the surroundings have a significant influence on the vaporization phenomena in all zones of the porous media; and the first stage of the process is not characterized only by diffusion vaporization. For that purpose, an experimental calibration procedure was made involving the definition of several LPV parameters: vaporization coefficient of the porous medium εPM, vaporization coefficient at the liquid–vapor interface within the porous medium εi,PM, free surface vapor pressure Pv,FS, vapor pressure of the free layer Pv,FL, interfacial vapor pressure Pv,i, volume of the vaporization layer VVL and volume of the free layer VFL. These parameters were represented by a set of multivariable functions and determined from a series of experiments in different types of porous media, each one characterized by a different initial water temperature. Thus, in this work an enhanced physical model of the LPV in porous media is proposed, concerning two distinct stages. The experimental set-up comprises two main components: the vacuum chamber (VC) and the depressurization system (DS). Part of the VC volume is occupied by an open container for porous media, which is isolated from the VC walls.The results obtained show that the multivariable functions determined through the vaporization coefficient have a good agreement with experimental results (e.g., R2 varies within 0.9581–0.9903) and also that this parameter describes well all regimes of the second stage of the LPV process. The importance of the capillary effect and of the surface tension forces on the superheating degree and, consequently, on the LPV evolution was demonstrated, as well as the effect of the amount of water initially contained in the porous medium. From the validation based on the measured water temperature evolutions, deviations within ±5% are found, which confirm the good agreement between experimental and simulated values. Thus, it is possible to conclude that the calibrated mathematical model describes well the experimental results and it is a good model of reference to various studies and applications.

Effect of flexibility on liquid-vapor coexistence and surface properties of tangent linear vibrating square well chains in two and three dimensions

The effect of flexibility on liquid-vapor and interfacial properties of tangent linear vibrating square well chains is studied. Surface tension, orthobaric densities, vapor pressures, and interfacial thicknesses are reported and analyzed using corresponding states principles. Discontinuous molecular dynamics simulations in two and three dimensions are performed on rigid tangent linear vibrating square well chains of different lengths. In the case of two dimensions, simulation results of completely flexible tangent linear vibrating square well chains are also reported. Properties are calculated for chains of 2-12 monomers. Rigidity is controlled by trapping the first and last monomer in the chain in a vibrating well at half of the distance of the whole chain. Critical property values are reported as obtained from orthobaric densities, surface tensions, and vapor pressures. For the fully flexible chains, the critical temperatures increase with chain length but the effect saturates. In contrast, the critical temperatures increase for the rigid chains until no more critical point is found.

Liquid-vapor equilibrium and interfacial properties of square wells in two dimensions

Liquid-vapor coexistence and interfacial properties of square wells in two dimensions are calculated. Orthobaric densities, vapor pressures, surface tensions, and interfacial thicknesses are reported. Results are presented for a series of potential widths λ* = 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5, where λ* is given in units of the hard core diameter σ. Critical and triple points are explored. No critical point was found for λ* < 1.4. Corresponding states principle analysis is performed for the whole series. For λ* = 1.4 and 1.5 evidence is presented that at an intermediate temperature between the critical and the triple point temperatures the liquid branch becomes an amorphous solid. This point is recognized in Armas-Pérez et al. [unpublished] as a hexatic phase transition. It is located at reduced temperatures T* = 0.47 and 0.35 for λ* = 1.4 and 1.5, respectively. Properties such as the surface tension, vapor pressure, and interfacial thickness do not present any discontinuity at these points. This amorphous solid branch does not follow the corresponding state principle, which is only applied to liquids and gases.

Atmospheric constraints for the CO2partial pressure on terrestrial planets near the outer edge of the habitable zone

In recent years, several potentially habitable, probably terrestrial exoplanets and exoplanet candidates have been discovered. The amount of CO2 in their atmosphere is of great importance for surface conditions and habitability. In the absence of detailed information on the geochemistry of the planet, this amount could be considered as a free parameter. Up to now, CO2 partial pressures for terrestrial planets have been obtained assuming an available volatile reservoir and outgassing scenarios. This study aims at calculating the allowed maximum CO2 pressure at the surface of terrestrial exoplanets orbiting near the outer boundary of the habitable zone by coupling the radiative effects of the CO2 and its condensation at the surface. These constraints might limit the permitted amount of atmospheric CO2, independent of the planetary reservoir. A 1D radiative-convective cloud-free atmospheric model was used. CO2 partial pressures are fixed according to surface temperature and vapor pressure curve. Considered scenarios cover a wide range of parameters. Results show that for planets in the habitable zone around K-, G-, and F-type stars the allowed CO2 pressure is limited by the vapor pressure curve and not by the planetary reservoir. The maximum CO2 pressure lies below the CO2 vapor pressure at the critical point of pcrit =73.8 bar. For M-type stars, CO2 pressures above pcrit are possible for almost all scenarios considered across the habitable zone. This implies that determining CO2 partial pressures for terrestrial planets by using only geological models is probably too simplified and might over-estimate atmospheric CO2 towards the outer edge of the habitable zone. (abridged)

Water-based conditions for the microscale parallel synthesis of bicyclic lactams

We report efficient miniaturized conditions to prepare arrays of bicyclic lactams for screening. The nature of the solvent is usually an important factor of reactivity. At a small synthesis scale, when automated pipetting devices are required, physical properties of the solvent, such as surface tension and vapor pressure also become very important. After having shown that a complete evaporation of a solution of reagents in water or a mixture of ethanol and water yields the expected lactams, we exemplified the reaction and procedure with the preparation of a library of 80 members. Our synthesis scheme is validated for synthesis scales from 1 to 100mg. Therefore, it can be used both to produce rapidly test samples for HTS as well as to prepare intermediates for the synthesis of more elaborated nature-inspired compounds.

Nucleation of ethanol, propanol, butanol, and pentanol: A systematic experimental study along the homologous series

We present homogeneous vapor-liquid nucleation rates of the 1-alcohols (C(n)H(2n+1)OH, n = 2-4) measured in the well-established two-valve nucleation pulse chamber as well as in a novel one-piston nucleation pulse chamber at temperatures between 235 and 265 K. The nucleation rates and critical cluster sizes show a very systematic behavior with respect to the hydrocarbon chain length of the alcohol, just as their thermo-physical parameters such as surface tension, vapor pressure, and density would suggest. For all alcohols, except ethanol, predictions of classical nucleation theory lie several orders of magnitude below the experimental results and show a strong temperature-dependence typically found in nucleation experiments. The more recent Reguera-Reiss theory [J. Phys. Chem. B 108(51), 19831 (2004)] achieves reasonably good predictions for 1-propanol, 1-butanol, and 1-pentanol, and independent of the temperature. Ethanol, however, clearly shows the influence of strong association between molecules even in the vapor phase. We also scaled all experimental results with classic nucleation theory to compare our data with other data from the literature. We find the same overall temperature trend for all measurement series together but inverted and inconsistent temperature trends for individual 1-propanol and 1-butanol measurements in other devices. Overall, our data establishe a comprehensive and reliable data set that forms an ideal basis for comparison with nucleation theory.

Investigation on feasibility of ionic liquids used in solar liquid desiccant air conditioning system

The corrosion problem of traditional liquid desiccants hinders the development of solar liquid desiccant air conditioning system. Ionic liquids (ILs) could be a possible substitute because of their low corrosion to metals. According to the characteristic of cation and anion, two ILs 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and 1,3-dimethylimidazolium acetate ([Dmim]OAc) were selected for possibility investigation. The experimental results demonstrated that the surface vapor pressure of [Bmim]BF4 aqueous solution was so high that it was not suitable for dehumidification. With comparing the structure of [Bmim]BF4 and 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4), it was found that for imidazole salts with the same anion, as the alkyl chain of the cation becomes shorter, the surface vapor pressure of its aqueous solution would be lower. In addition, simulation model was used to compare the dehumidification performance of [Dmim]OAc and [Emim]BF4 with that of the traditional desiccants lithium Chloride (LiCl) and lithium bromide (LiBr). The results showed that in the same condition, [Dmim]OAc with an inlet mass concentration of 81.7% and [Emim]BF4 of 85.5% could reach the same dehumidification rate as LiCl of 40.9% and LiBr of 45.0% mass concentration. Better dehumidification performance of [Dmim]OAc than that of [Emim]BF4 was achieved, thus, like [Emim]BF4, [Dmim]OAc can also be a promising substitute for traditional desiccant.