Influence of equilibrium relative humidity and plasticizer concentration on the water content and glass transition of starch materials

Polymer ◽  
1997 ◽  
Vol 38 (21) ◽  
pp. 5401-5406 ◽  
Author(s):  
D. Lourdin ◽  
L. Coignard ◽  
H. Bizot ◽  
P. Colonna
Keyword(s):  
Glass Transition ◽  
Relative Humidity ◽  
Water Content ◽  
Equilibrium Relative Humidity ◽  
Plasticizer Concentration

Modeling Vapor Transport in a Hollow Fiber Membrane Humidifier Using ε-NTU Approach

2020 ◽  
Author(s):  
Hoang Nghia Vu ◽  
Xuan Linh Nguyen ◽  
Sangseok Yu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Fuel Cell ◽  
Relative Humidity ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Water Content ◽  
Vapor Transport ◽  
Overall Mass Transfer Coefficient ◽  
Mass Exchanger

Abstract In a fuel cell vehicle, the water content of the gas supply within certain ranges plays a key role in improving the performance of a proton exchange membrane. The lower limit of water content in the air supply is to avoid the problem of drying-out, while the upper prevents flooding. Water management can be accomplished by a membrane humidifier which allows water vapor to permeate the mixture from the side having the higher water concentration, moving to the other side of the membrane. In this study, the variation in water content collected at the outlet of a membrane humidifier is investigated with a one-dimensional mass exchanger model and various operating variables. The vapor concentration of outlet flows is affected by operating temperature and relative humidity of the membrane humidifier. Relative humidity of the dry side at the point of outlet flow, to be supplied to the fuel cell module, is the key characteristic. The analogy of the effectiveness-NTU approach for heat transfer is used to analyze the characteristics of the mass exchanger. Mass flux through the membranes is estimated with an overall mass transfer coefficient which represents vapor transport characteristics moving through the membrane module. This coefficient has a similar role to the overall heat transfer coefficient in heat exchanger analysis. This parametric study is conducted to understand the effects of different variables. The Effectiveness-NTU methodology of mass transfer uses the overall mass transfer coefficient and the mass transfer rate, as evaluated experimentally. Simulink software is then employed to deliver outcomes of the model for different operating conditions.

scholarly journals Assessment of lettuce quality during storage at low relative humidity using Global Stability Index methodology

2012 ◽  
Vol 32 (2) ◽  
pp. 366-373 ◽  
Author(s):  
María Roberta Ansorena ◽  
María Victoria Agüero ◽  
María Grabriela Goñi ◽  
Sara Roura ◽  
Alejandra Ponce ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Relative Humidity ◽  
Global Stability ◽  
Water Content ◽  
Relative Water Content ◽  
Storage Time ◽  
Stability Index ◽  
Total Chlorophyll ◽  
External Zone ◽  
Relative Water

During postharvest, lettuce is usually exposed to adverse conditions (e.g. low relative humidity) that reduce the vegetable quality. In order to evaluate its shelf life, a great number of quality attributes must be analyzed, which requires careful experimental design, and it is time consuming. In this study, the modified Global Stability Index method was applied to estimate the quality of butter lettuce at low relative humidity during storage discriminating three lettuce zones (internal, middle, and external). The results indicated that the most relevant attributes were: the external zone - relative water content, water content , ascorbic acid, and total mesophilic counts; middle zone - relative water content, water content, total chlorophyll, and ascorbic acid; internal zone - relative water content, bound water, water content, and total mesophilic counts. A mathematical model that takes into account the Global Stability Index and overall visual quality for each lettuce zone was proposed. Moreover, the Weibull distribution was applied to estimate the maximum vegetable storage time which was 5, 4, and 3 days for the internal, middle, and external zone, respectively. When analyzing the effect of storage time for each lettuce zone, all the indices evaluated in the external zone of lettuce presented significant differences (p < 0.05). For both, internal and middle zones, the attributes presented significant differences (p < 0.05), except for water content and total chlorophyll.

Relationship Between Equilibrium Relative Humidity and Deterioration of Shelled Corn

1995 ◽  
Vol 38 (4) ◽  
pp. 1139-1145 ◽  
Author(s):  
H. F. Ng ◽  
R. V. Morey ◽  
W. F. Wilcke ◽  
R. A. Meronuck ◽  
J. P. Lang
Keyword(s):  
Relative Humidity ◽  
Equilibrium Relative Humidity

scholarly journals Physical state of 2-methylbutane-1,2,3,4-tetraol in pure and internally mixed aerosols

2018 ◽  
Vol 18 (21) ◽  
pp. 15841-15857 ◽  
Author(s):  
Jörn Lessmeier ◽  
Hans Peter Dette ◽  
Adelheid Godt ◽  
Thomas Koop
Keyword(s):  
Glass Transition ◽  
Relative Humidity ◽  
Oxidation Product ◽  
Secondary Organic Aerosols ◽  
Glassy State ◽  
Organic Aerosols ◽  
Lower Troposphere ◽  
Tropospheric Temperature ◽  
Transition Temperatures ◽  
Glass Transition Temperatures

Abstract. 2-Methylbutane-1,2,3,4-tetraol (hereafter named tetraol) is an important oxidation product of isoprene and can be considered as a marker compound for isoprene-derived secondary organic aerosols (SOAs). Little is known about this compound's physical phase state, although some field observations indicate that isoprene-derived secondary organic aerosols in the tropics tend to be in a liquid rather than a solid state. To gain more knowledge about the possible phase states of tetraol and of tetraol-containing SOA particles, we synthesized tetraol as racemates as well as enantiomerically enriched materials. Subsequently the obtained highly viscous dry liquids were investigated calorimetrically by differential scanning calorimetry revealing subambient glass transition temperatures Tg. We also show that only the diastereomeric isomers differ in their Tg values, albeit only by a few kelvin. We derive the phase diagram of water–tetraol mixtures over the whole tropospheric temperature and humidity range from determining glass transition temperatures and ice melting temperatures of aqueous tetraol mixtures. We also investigated how water diffuses into a sample of dry tetraol. We show that upon water uptake two homogeneous liquid domains form that are separated by a sharp, locally constrained concentration gradient. Finally, we measured the glass transition temperatures of mixtures of tetraol and an important oxidation product of α-pinene-derived SOA: 3-methylbutane-1,2,3-tricarboxylic acid (3-MBTCA). Overall, our results imply a liquid-like state of isoprene-derived SOA particles in the lower troposphere at moderate to high relative humidity (RH), but presumably a semisolid or even glassy state at upper tropospheric conditions, particularly at low relative humidity, thus providing experimental support for recent modeling calculations.

WATER RELATIONS OF ASEXUAL SPORES OF SPHAEROTHECA MACULARIS (WALLR. EX. FR.) COOKE AND ERYSIPHE POLYGONI DC.

1965 ◽  
Vol 11 (3) ◽  
pp. 531-538 ◽  
Author(s):  
J. S. Jhooty ◽  
W. E. McKeen
Keyword(s):  
Relative Humidity ◽  
Water Content ◽  
Osmotic Pressure ◽  
Water Relations ◽  
Erysiphe Polygoni ◽  
Significant Change ◽  
Sphaerotheca Macularis ◽  
Glass Surfaces

The conidia of Sphaerotheca macularis germinate best at a relative humidity (R.H.) of 99 and 100% on glass surfaces, and germination does not occur if the R.H. is below 93%. Conidia of Erysiphe polygoni DC. germinate at 3% R.H. The water content of conidia of S. macularis and E. polygoni is 53 and 69% respectively. The osmotic pressure of S. macularis conidia is about 18 atm and their density varies from 1.10 to 1.11 g/ml. There is no significant change in the diameter and length of the conidia during germination.

scholarly journals Raoult’s law revisited: accurately predicting equilibrium relative humidity points for humidity control experiments

2016 ◽  
Author(s):  
Michael G. Bowler ◽  
David R. Bowler ◽  
Matthew W. Bowler
Keyword(s):  
Relative Humidity ◽  
Vapour Pressure ◽  
Control Device ◽  
Raoult’S Law ◽  
Simple Argument ◽  
Humidity Control ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Equilibrium Relative Humidity ◽  
Raoult's Law

AbstractThe humidity surrounding a sample is an important variable in scientific experiments. Biological samples in particular require not just a humid atmosphere but often a relative humidity (RH) that is in equilibrium with a stabilizing solution required to maintain the sample in the same state during measurements. The controlled dehydration of macromolecular crystals can lead to significant increases in crystal order, which often leads to higher diffraction quality. Devices that can accurately control the humidity surrounding crystals on a beamline have led to this technique being increasingly adopted, as experiments become easier and more reproducible. Matching the relative humidity to the mother liquor is the first step to allow the stable mounting of a crystal. In previous work, we measured the equilibrium relative humidity for a range of concentrations of the most commonly used precipitants and showed how this related to Raoult’s law for the equilibrium vapour pressure of water above a solution. However, a discrepancy between measured values and those predicted by theory could not be explained. Here, we have used a more precise humidity control device to determine equilibrium relative humidity points. The new results are in agreement with Raoult’s law. We also present a simple argument in statistical mechanics demonstrating that the saturated vapour pressure of a solvent is proportional to its mole fraction in an ideal solution: Raoult’s Law. The same argument can be extended to the case where solvent and solute molecules are of different size, as is the case with polymers. The results provide a framework for the correct maintenance of the RH surrounding samples.SynopsisThe equilibrium relative humidity values for a number of the most commonly used precipitants in biological macromolecule crystallisation have been measured using a new humidity control device. A simple argument in statistical mechanics demonstrates that the saturated vapour pressure of a solvent is proportional to its mole fraction in an ideal solution (Raoult’s Law). The same argument can be extended to the case where solvent and solute molecules are of different size.

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