29 research outputs found
Lyophilization model of mannitol water solution in a laboratory scale lyophilizer
No full textThe paper reports on the development of a numerical model for the simulation of a lyophilization process in a vial. Experimental analysis is presented of lyophilization dynamics inside a single vial in a laboratory scale lyophilizer. The problems of lyophilization modelling of a mannitol water solution are covered in detail. The effects of the small scale of the laboratory device with respect to a correct definition of boundary conditions for the numerical simulations are described, especially the effect of the comparatively high temperatures of the chamber walls. In the numerical model, a 1D vial approximation of the governing equations of heat and mass transport with moving front between the frozen and porous part of the cake is used and solved in a time stepping nonlinear iteration procedure. A water vapour diffusion model, implemented in the mass conservation equations, based on the Knudsen model of diffusivities, is applied and linked to the typical pore size of the porous cake. A front tracking scheme with moving computational grid is applied, and a dedicated sub-model of surface layer ice sublimation is introduced, based on the one-sided vapour diffusion model. The comparison of the numerical and the experimental results show that the developed numerical model is able to capture the transition points from primary to secondary drying very accurately, with accompanying accurate capturing of the temperature levels inside of the drying material
Effects of controlled nucleation on freeze-drying lactose and mannitol aqueous solutions
No full textThe lyophilization of lactose and mannitol aqueous solutions was investigated with an emphasis on analyzing the effects of controlled nucleation, temperature of nucleation, and pore size distribution on the freeze-drying process. The experimental procedure involved the depressurization technique of controlled nucleation, in-vial temperature measurements as well as measurements of the chamber pressure, which allowed the analysis of the product batch, loaded in the laboratory lyophilizator. The average pore enlargement was 93 and 58% with the incorporation of the controlled nucleation step in the lyophilization of 6 wt% lactose and 6 wt% mannitol solutions, respectively. Consequently, the primary drying times were lowered from 450 to 500 min in both cases. The pore sizes were determined to be as important as the solid material itself in the scope of the sublimation rates. Namely, the average equivalent diameter of the pores was larger in the dried mannitol cake compared to the lactose cake. However, despite the higher porosity of the dried mannitol cake, the end of the sublimation in the primary drying step was observed approximately 500 min earlier during the lyophilization of the lactose solution with the same initial concentration as the mannitol solution in a comparable freeze-drying protocol. In addition, an increase in mannitol concentration from 3 to 12 wt% was found to substantially extend the time required for the sublimation phase of the lyophilization
Numerical and experimental modeling of lyophilization of lactose and mannitol water solutions in vials
No full textThe paper reports on the development of a numerical model for the simulation of a lyophilization process in a vial. Lactose and mannitol-water mixtures are used as the working media. Experimental analysis of the lyophilization dynamics inside a single vial in a laboratory scale lyophilizer is reported, with the main focus on the primary drying phase. In order to assess the primary drying kinetics, the temperature distribution along the vertical axis of the samples is measured. In the numerical model, a one-dimensional (1D) vial approximation is used, and governing equations of the heat and water vapor transport with moving front between the frozen and the porous part of the filling are solved by a finite difference method in a time stepping nonlinear iteration procedure. A dedicated mapping of heat transfer boundary conditions, derived for the axisymmetric vial case, is applied for the case of the 1D vial geometry approximation. The main difference in the drying of lactose and mannitol solutions lies in the fact that the lactose shows undercooling effects during the primary drying phase, which is not the case for the mannitol solution. This effect is a consequence of shrinking behavior of the lactose porous cake, leading to a loss of contact with the vial side and hence to a decrease in the overall heat input to the vial. In order to account for the shrinking process in the numerical model, a linear approximation of the decrease of the heat transfer from the vial side wall during the simulation is introduced. The comparison of the numerical and experimental results shows that the developed numerical model is able to accurately capture the movement of the sublimation front, dividing the frozen from the porous part of the filling, at typical locations inside the vial, accompanied also by an accurate capturing of the temperature levels inside the drying material, with the derived numerical model also able to reproduce the temperature drop during the primary drying of the lactose solution
A HIGH RESOLUTION TEMPERATURE CLIMATOLOGY FOR THE GREATER ALPINE REGION (GAR)
No full textThe Greater Alpine Region (the GAR) covering the area between 4-19°E and 43-50°N and an altitude range between 0 and more than 4000 m asl. offers a challenging climate worth to be studied in any detail. However, it is surprising that up to now no comprehensive Alpine Temperature Climatology covering the whole region is existing. To overcome this deficiency as a first step we want to produce monthly temperature maps for this region in spatial resolution as high as possible. The period under investigation will be 1961-1990. In this paper we will describe the first steps of our initiative as well as the further plans
A new instrumental precipitation dataset for the greater alpine region for the period 1800-2002
No full textThe paper describes the development of a dataset of 192 monthly precipitation series covering the greater alpine region (GAR, 4-18°E by 43-49°N). A few of the time series extend back to 1800. A description is provided of the sometimes laborious processes that were involved in this work: from locating the original sources of the data to homogenizing the records and eliminating as many of the outliers as possible. Locating the records required exhaustive searches of archives currently held in yearbooks and other sources of the states, countries and smaller regional authorities that existed at various times during the last 200 years. Homogeneity of each record was assessed by comparison with neighbouring series, although this becomes difficult when the density of stations reduces in the earliest years. An additional 47 series were used, but the density of the sites in Austria and Switzerland was reduced to maintain an even coverage in space across the whole of the GAR. We are confident of the series back to 1840, but the quality of data before this date must be considered poorer. Of all of the issues involved in homogenizing these data, perhaps the most serious problem is associated with the differences in the height above ground of the precipitation gauges, in particular the general lowering of gauge heights in the late 19th century for all countries, with the exception of Italy. The standard gauge height in the early-to-mid 19th century was 15-30 m above the ground, with gauges being generally sited on rooftops. Adjustments to some series of the order of 30-50% are necessary for compatibility with the near-ground location of gauges during much of the 20th century. Adjustments are sometimes larger in the winter, when catching snowfall presents serious problems. Data from mountain-top observatories have not been included in this compilation (because of the problem of measuring snowfall), so the highest gauge sites are at elevations of 1600-1900 m in high alpine valley locations. Two subsequent papers will analyse the dataset. The first will compare the series with other large-scale precipitation datasets for this region, and the second will describe the major modes of temporal variability of precipitation totals in different seasons and determine coherent regions of spatial variability
HISTALP - historical instrumental climatological surface time series for the Greater Alpine Region
No full textThis paper describes the HISTALP database, consisting of monthly homogenised records of temperature, pressure, precipitation, sunshine and cloudiness for the 'Greater Alpine Region' (GAR, 4-19 degrees E, 43-49 degrees N, 0-3500m asl). The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness to the 1840s and sunshine to the 1880s. A systematic QC procedure has been applied to the series and a high number of inhomogeneities (more than 2500) and outliers (more than 5000) have been detected and removed. The 557 HISTALP series are kept in different data modes: original and homogenised, gap-filled and outlier corrected station mode series, grid-1 series (anomaly fields at 1 degrees *1 degrees , lat * long) and Coarse Resolution Subregional (CRS) mean series according to an EOF-based regionalisation. The leading climate variability features within the GAR are discussed through selected examples and a concluding linear trend analysis for 100, 50 and 25-year subperiods for the four horizontal and two altitudinal CRSs. Among the key findings of the trend analysis is the parallel centennial decrease/increase of both temperature and air pressure in the 19th/20th century. The 20th century increase (+1.2 degrees C/+1.1 hPa for annual GAR-means) evolved stepwise with a first peak near 1950 and the second increase (1.3 degrees C/0.6hPa per 25 years) starting in the 1970s. Centennial and decadal scale temperature trends were identical for all subregions. Air pressure, sunshine and cloudiness show significant differences between low versus high elevations. A long-term increase of the high-elevation series relative to the low-elevation series is given for sunshine and air pressure. Of special interest is the exceptional high correlation near 0.9 between the series on mean temperature and air pressure difference (high-minus low-elevation). This, further developed via some atmospheric statics and thermodynamics, allows the creation of 'barometric temperature series' without use of the measures of temperature. They support the measured temperature trends in the region. Precipitation shows the most significant regional and seasonal differences with, e.g., remarkable opposite 20th century evolution for NW (9% increase) versus SE (9% decrease). Other long- and short-term features are discussed and indicate the promising potential of the new database for further analyses and applications
Daily dataset of 20th century surface air temperature and precipitation series for the European Climate Assessment
No full textWe present a dataset of daily resolution climatic time series that has been compiled for the European Climate Assessment (ECA). As of December 2001, this ECA dataset comprises 199 series of minimum, maximum and/or daily mean temperature and 195 series of daily precipitation amount observed at meteorological stations in Europe and the Middle East. Almost all series cover the standard normal period 1961-90, and about 50% extends back to at least 1925. Part of the dataset (90%) is made available for climate research on CDROM and through the Internet (at http://www.knmi.nl/samenw/eca). A comparison of the ECA dataset with existing gridded datasets, having monthly resolution, shows that correlation coefficients between ECA stations and nearest land grid boxes between 1946 and 1999 are higher than 0.8 for 93% of the temperature series and for 51% of the precipitation series. The overall trends in the ECA dataset are of comparable magnitude to those in the gridded datasets. The potential of the ECA dataset for climate studies is demonstrated in two examples. In the first example, it is shown that the winter (October-March) warming in Europe in the 1976-99 period is accompanied by a positive trend in the number of warm-spell days at most stations, but not by a negative trend in the number of cold-spell days. Instead, the number of cold-spell days increases over Europe
