Modelling of the bladed disk vibration with damping elements in blade shroud

The requirement for wide operation range of steam turbine can cause, that the blades work close to resonant frequency. For decreasing of blade’s vibration there are placed damping elements in the blade shroud. These elements are calculated for dissipation of the vibration energy. The analytical method of blade and bladed disk modal analysis is introduced. The method enables to include blades both with and without damping elements in shroud. The mathematical model of the bladed disk is prepared for including damping effects in contact planes

Blade dynamic stress analysis of rotating bladed disks

The paper deals with mathematical modelling of steady forced bladed disk vibrations and with dynamic stress calculation of the blades. The blades are considered as 1D kontinuum elastic coupled with three-dimensional elastic disk centrally clamped into rotor rotating with constant angular speed. The steady forced vibrations are generated by the aerodynamic forces acting along the blade length. By using modal synthesis method the mathematical model of the rotating bladed disk is condensed to calculate steady vibrations. Dynamic stress analysis of the blades is based on calculation of the time dependent reduced stress in blade cross-sections by using Hubert-Misses-Hencky stress hypothesis. The presented method is applied to real turbomachinery rotor with blades connected on the top with shroud

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Abstracts of papers from scientifical and professional journals (In Czech)

Measurement of HGB beer colloidal ageing and tannoid content development using complex turbidimetric analysis.

Measurements of HGB beers were carried out in concentrated and blended samples to analyse the chill haze and tannoid content development during the thermal forced ageing process. The measurements were performed by the method of complex turbidimetric analysis (CTA), based on a single instrumentation for beer chill haze determination in commercial bottles and polyvinylpyrrolidone/tannoid content titration of beer samples in usual reaction tubes. For illustration of the efficiency of the CTA method, the initial values of saturated ammonium sulphate precipitation limits (SASPL) and sensitive protein (SP) levels were determined, too. The CTA method confirmed enhanced colloidal stability of the blended HGB final product due to lower content of the high molecular weight haze active proteotannic complexes. An almost linear correlation between the chill haze and tannoid content development during beer ageing process, starting from some concentration threshold level after a certain lag time was revealed.The correlation between the tannoid content of HGB beer in blended and non blended state was found also linear. The CTA method can be effectively used for the evaluation and prediction of the HGB beer colloidal ageing process and diagnostics of the causes of production inhomogeneity.Measurements of HGB beers were carried out in concentrated and blended samples to analyse the chill haze and tannoid content development during the thermal forced ageing process. The measurements were performed by the method of complex turbidimetric analysis (CTA), based on a single instrumentation for beer chill haze determination in commercial bottles and polyvinylpyrrolidone/tannoid content titration of beer samples in usual reaction tubes. For illustration of the efficiency of the CTA method, the initial values of saturated ammonium sulphate precipitation limits (SASPL) and sensitive protein (SP) levels were determined, too. The CTA method confirmed enhanced colloidal stability of the blended HGB final product due to lower content of the high molecular weight haze active proteotannic complexes. An almost linear correlation between the chill haze and tannoid content development during beer ageing process, starting from some concentration threshold level after a certain lag time was revealed.The correlation between the tannoid content of HGB beer in blended and non blended state was found also linear. The CTA method can be effectively used for the evaluation and prediction of the HGB beer colloidal ageing process and diagnostics of the causes of production inhomogeneity

Stir Bar Sorptive Extraction - New Approach for the Determination of Some Beer Flavours.

For the determination of beer flavours well-established methods require sample preparation steps such as liquid/liquid extraction, solid phase extraction or distillation techniques. During the past years the microextraction procedures become popular e. g. solid phase microextraction (SPME) or stir bar sorptive extraction (SBSE). This work presents the simple and rapid possibility of the determination of some beer flavours using stir bar sorptive extraction. A commercially available small stir bar (10 mm length, 1,3 mm OD) is coated with polydimethylsiloxane and produced by Gerstel GmbH and it is known as Twister. The Twister is placed directly in the beer sample and stirred. Then the stir bar is removed, rinsed with distilled water and eluted with 200 μl of organic solvent for gas chromatographic analysis.Validated parameters of the optimised method are shown in this work.For the determination of beer flavours well-established methods require sample preparation steps such as liquid/liquid extraction, solid phase extraction or distillation techniques. During the past years the microextraction procedures become popular e. g. solid phase microextraction (SPME) or stir bar sorptive extraction (SBSE). This work presents the simple and rapid possibility of the determination of some beer flavours using stir bar sorptive extraction. A commercially available small stir bar (10 mm length, 1,3 mm OD) is coated with polydimethylsiloxane and produced by Gerstel GmbH and it is known as Twister. The Twister is placed directly in the beer sample and stirred. Then the stir bar is removed, rinsed with distilled water and eluted with 200 μl of organic solvent for gas chromatographic analysis.Validated parameters of the optimised method are shown in this work

Thermogravimetric determination of moisture in brewing raw materials. Part II. - Possibilities of application of thermogravimetric method to determine the moisture in hops and hop products.

As it has been already mentioned in the first part of this work devoted to the moisture determination in barley, green and finished malt, the thermogravimetric determination of moisture content in natural samples by means of the HR 83 moisture analyser of the company Mettler - Toledo is based on the principles of halogen warm-up and automatic monitoring of the course of the drying curve. This part describes the results related to the elaboration and validation of the method for thermogravimetric moisture determination in whole hops and hop products. At the same time, comparisons of results obtained by this method with the results obtained by the official method of moisture determination in hops and hop products were made (EBC 7.2, MEBAK 5.2.3 and IOB 2.2). Based on the findings it can be stated that the results of the thermogravimetric method coincided with the results obtained by the official method and therefore this moisture meter can be fully recommended for the needs of hop plants and brewery laboratories.As it has been already mentioned in the first part of this work devoted to the moisture determination in barley, green and finished malt, the thermogravimetric determination of moisture content in natural samples by means of the HR 83 moisture analyser of the company Mettler - Toledo is based on the principles of halogen warm-up and automatic monitoring of the course of the drying curve. This part describes the results related to the elaboration and validation of the method for thermogravimetric moisture determination in whole hops and hop products. At the same time, comparisons of results obtained by this method with the results obtained by the official method of moisture determination in hops and hop products were made (EBC 7.2, MEBAK 5.2.3 and IOB 2.2). Based on the findings it can be stated that the results of the thermogravimetric method coincided with the results obtained by the official method and therefore this moisture meter can be fully recommended for the needs of hop plants and brewery laboratories

Determination of chlorinated phenols in brewing liquor and beer using SPE.

A method for the determination of chlorinated phenols in brewing liquor and beer is described. Solid phase extraction technique for the sample preconcentration was used. Then the analytes were derivatized and determined by gas chromatographic analysis coupled with electron capture detector. SPE columns LiChrolut EN (ethyl vinyl benzene - divinyl benzene copolymer with an extremely large specific surface) and LiChrolut RP-18 were tested. The dependences of recovery on the eluent volume were investigated. Validated parameters of the optimized method for the determination of chlorinated phenols in brewing liquor and beer are shown in this work.A method for the determination of chlorinated phenols in brewing liquor and beer is described. Solid phase extraction technique for the sample preconcentration was used. Then the analytes were derivatized and determined by gas chromatographic analysis coupled with electron capture detector. SPE columns LiChrolut EN (ethyl vinyl benzene - divinyl benzene copolymer with an extremely large specific surface) and LiChrolut RP-18 were tested. The dependences of recovery on the eluent volume were investigated. Validated parameters of the optimized method for the determination of chlorinated phenols in brewing liquor and beer are shown in this work

Characterizing a Czech-Type Beer.

The article maps in detail the situation in Czech brewing industry at the beginning of the new millennium and characterizes the differences between Czech beers and foreign lager- or Pils-type beers. On the basis of an extensive set if analytical and sensory data we defined a so-called "Czech-type" beer, which differs from the majority of foreign beers in many attributes. The "Czech-type" beer is specific by the presence of unfermented extract, higher bitterness and colour, higher polyphenol content and higher pH values. Considering the sensory attributes, it is typical by its higher fullness, bitterness, longer bitterness fading and lower presence of foreign flavours and aromas. Technologically, the most important factors are the composition of the grist, extent of hopping and their attuning to the choice of the yeast strain and the fermentation process used.The article maps in detail the situation in Czech brewing industry at the beginning of the new millennium and characterizes the differences between Czech beers and foreign lager- or Pils-type beers. On the basis of an extensive set if analytical and sensory data we defined a so-called "Czech-type" beer, which differs from the majority of foreign beers in many attributes. The "Czech-type" beer is specific by the presence of unfermented extract, higher bitterness and colour, higher polyphenol content and higher pH values. Considering the sensory attributes, it is typical by its higher fullness, bitterness, longer bitterness fading and lower presence of foreign flavours and aromas. Technologically, the most important factors are the composition of the grist, extent of hopping and their attuning to the choice of the yeast strain and the fermentation process used

Thermogravimetric determination of moisture in brewing raw materials. Part I. - Possibilities of utilizing the thermogravimetric method to determine the moisture in barley and malt.

Thermogravimetric determination of the moisture content in native samples with the aid of HR 83 (Mettler Toledo) analyser is based on the concept of halogen heating and an automated monitoring of the course of the kilning curve. The possibility of utilizing this instrument in the field was tested on real samples of barley, green malt and malt. Validation of the methods for determining dry matter in barley, green and finished malt was performed. Based on the obtained observations, it can be stated that this instrument can be recommended to malting and brewing laboratories.Thermogravimetric determination of the moisture content in native samples with the aid of HR 83 (Mettler Toledo) analyser is based on the concept of halogen heating and an automated monitoring of the course of the kilning curve. The possibility of utilizing this instrument in the field was tested on real samples of barley, green malt and malt. Validation of the methods for determining dry matter in barley, green and finished malt was performed. Based on the obtained observations, it can be stated that this instrument can be recommended to malting and brewing laboratories

Determination of the Fatty Acids in Beer by SPME.

An escalated content of fatty acids during fermentation can influence the quality of final beer. So it is necessary to use the suitable analytical method for the determination of their concentrations in beer or hopped wort. This work presents the simple and rapid possibility of the selective determination of the free fatty acids (C6-C12) in beer or wort by Solid Phase Microextraction (SPME) and gas chromatography. The free fatty acids C6-C12 were extracted by SPME fiber placed in the headspace of vial containing the sample of beer with the addition of salt. Analytes were thermally desorbed from the coated fiber of the SPME in the hot injector of the GC equipped with a fused silica capillary column SPB-1000 and a flame ionisation detector. For the quantitation of these medium-chain fatty acids heptanoic acid and undecanoic acid were used as internal standards. Validated parameters of the optimalized method for the determination of medium-chain fatty acids from beer are shown in this work. This method is time saving, low cost, does not require solvents and provides high sensitivity and reproducibility. It can be recommended for routine control analyses in brewery laboratories.An escalated content of fatty acids during fermentation can influence the quality of final beer. So it is necessary to use the suitable analytical method for the determination of their concentrations in beer or hopped wort. This work presents the simple and rapid possibility of the selective determination of the free fatty acids (C6-C12) in beer or wort by Solid Phase Microextraction (SPME) and gas chromatography. The free fatty acids C6-C12 were extracted by SPME fiber placed in the headspace of vial containing the sample of beer with the addition of salt. Analytes were thermally desorbed from the coated fiber of the SPME in the hot injector of the GC equipped with a fused silica capillary column SPB-1000 and a flame ionisation detector. For the quantitation of these medium-chain fatty acids heptanoic acid and undecanoic acid were used as internal standards. Validated parameters of the optimalized method for the determination of medium-chain fatty acids from beer are shown in this work. This method is time saving, low cost, does not require solvents and provides high sensitivity and reproducibility. It can be recommended for routine control analyses in brewery laboratories