T. Langrish - Academia.edu (original) (raw)
Papers by T. Langrish
Powder technology, 1993
... Eng. Sci., 1 (1952) 259. 2 A. Afacan and JH Masliyah, Powder Technol., 61 (1990) 179. ... 8 W... more ... Eng. Sci., 1 (1952) 259. 2 A. Afacan and JH Masliyah, Powder Technol., 61 (1990) 179. ... 8 WH Press, BP Flannery, SA Teulolsky and WT Vetterling, Numerical RecOs: The Art of Scientific Computing Cambridge University Press, MA, p. 550. References. 1H. ...
Journal of Zhejiang University SCIENCE A, 2007
... Drying Technology, 21(7):1253-1272. [30] Ozmen, L., Langrish, TAG, 2005. An experimental inve... more ... Drying Technology, 21(7):1253-1272. [30] Ozmen, L., Langrish, TAG, 2005. An experimental investigation into wall deposition of milk powder in spray dryers. ... Geothermics, 18(1-2):327-335. [40] Zimon, AD, 1969. Adhesion of Dust and Powder. Plenum Press, New York, p.110. ...
Atomization and Sprays, 2008
Drying Technology, 2014
The effects of different humidities on process yields and degrees of crystallinity have been stud... more The effects of different humidities on process yields and degrees of crystallinity have been studied for spray-dried powders from the spray drying of lactose with humid air in a straight-through system. According to Williams-Landel-Ferry (WLF) kinetics, it was suggested that a higher particle temperature and lower glass transition temperature would increase the crystallization rates of the particles during the spray-drying process. Freshly humidified air produced by a Buchi-B290 spray dryer as a humidifier before the main spray dryer decreased the particle glass transition temperature (T g ), while allowing the particle temperature (T p ) to reach higher values by using an insulated drying chamber. The results showed that higher T p À T g , as a result of applying humid air, improved the process yield from 21 AE 4% to 26 AE 2% and the lactose crystallinity by decreasing the latent heat of crystallization for the powder products from 43 AE 1 J/g to 30 AE 11 J/g. It has been found in this study that the humidity of the inlet air should be adjusted in such a way as to not exceed relative and absolute humidities of 2.7-3% and 65-70 g/kg DA , respectively, at the outlet of the drying chamber, to give the most crystalline particles.
International Journal of Pharmaceutics, 2010
The aim of this study was to develop a method for converting an amorphous drug to a crystalline f... more The aim of this study was to develop a method for converting an amorphous drug to a crystalline form to enhance its stability and inhalation performance. Spray-dried amorphous salbutamol sulphate powder was conditioned with supercritical carbon dioxide (scCO 2 ) modified with menthol. The effect of menthol concentration, pressure, temperature and time on the characteristics of the resulting salbutamol sulphate powder was investigated. Pure scCO 2 had no effect on the physical properties of amorphous salbutamol sulphate; however, scCO 2 modified with menthol at 150 bar and 50 • C was efficient in converting amorphous drug to crystalline form after 12 h of conditioning. The average particle size of powders decreased slightly after the conditioning process because of reducing agglomeration between particles by increasing surface roughness. Emitted dose measured by the fine particle fraction (FPF emitted ) of amorphous salbutamol sulphate was enhanced from 32% to 43% after conditioning with scCO 2 + menthol and its water uptake was significantly decreased. This study demonstrates the potential of scCO 2 + menthol for converting amorphous forms of powders to crystalline, while preserving the particle size.
Powder Technology, 2007
The relative amounts of wall deposition between skim milk and maltodextrin have been compared in ... more The relative amounts of wall deposition between skim milk and maltodextrin have been compared in a pilot-scale spray dryer of 1.5 m height, equipped with a two-fluid atomizer. The atomizer air pressure was 200 kPa, the inlet air temperature was 230 °C, the liquid feed flowrate was 1.6 L h−1, and there was no swirl at the air inlet. Both maltodextrin and skim milk,
Developments in Chemical Engineering and Mineral Processing, 2008
Journal of Zhejiang University SCIENCE A, 2007
The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of ... more The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of a pilot-scale spray dryer was predicted using simple correlations for particle depositions in pipes. The predicted particle deposition fluxes of these materials were then compared with the measured deposition fluxes. The predicted particle deposition regimes of the spray dryer were expected to be in the
Wood Science and Technology, 1997
An investigation has been carried out into whether the internal moisture movement inside Australi... more An investigation has been carried out into whether the internal moisture movement inside Australian hardwood timber is best described by a diffusion model with driving forces based on gradients in moisture content or in partial pressure of water vapour. Experimental data from two sets of drying schedules applied to timber from three species of Australian hardwoods (yellow stringybark, spotted gum and ironbark) reported in Langrish et al. (1997) have been used to assess the use of the two driving forces, and the standard error has been used as the criterion for goodness of fit. Moisture-content driving forces have fitted the data better than a model based on vapour-pressure driving forces alone. The use of moisture-content driving forces with diffusion parameters obtained from data from one drying schedule is also better in predicting the drying behaviour with another schedule than vapour-pressure driving forces for yellow stringybark and ironbark. These results may be due to the complexity of the moisture-movement process through timber, with more than one moisturetransport mechanism being active, so that the use of only one driving force for moisture movement is at best only an approximation to the true behaviour. Symbols D diffusion coefficient, m 2 s -1 (moisture-content gradient), m 3 s kg < (vapour-pressure gradient) De activation energy, K Dr pre-exponential factor m 2 s -1 (moisture-content gradient), m3s kg -1 (vapourpressure gradient) J mass flux of water divided by density, m s -1 t time, s x position, m X moisture content, kg kg -1
Wood Science and Technology, 2000
This work examines the applicability of mathematical models for correlating the visco-elastic str... more This work examines the applicability of mathematical models for correlating the visco-elastic strains during kiln drying of radiata pine (Pinus radiata D. Don) sapwood at various temperatures and moisture contents. The eventual aim is to use a mathematical model incorporating these strains to optimise the drying schedules and minimise the degradation. Data sets from previous experiments (Keep 1998) obtained at temperatures from 20 to 140°C for sapwood at 5, 15 and 20% moisture contents (dry basis) were analysed. The data were ®tted for various theoretical models, namely the Maxwell, Kelvin and Burgers models, and the Bailey-Norton equation. The parameter values and standard errors for the above models over the range of experimental data have been determined. The results indicate that the Maxwell model did not ®t the experimental data well, having only one parameter. In most cases, the Bailey-Norton equation was inadequate, as it is a power-law model with a predicted continuous increase in creep with time and does not predict a plateau in the creep strain, as has been observed for most of data. The Kelvin model gave a better ®t than the Bailey-Norton equation for most of the data sets. From visual inspection of the plots for the experimental data and the model predictions with time, it was found that both the Kelvin and Burgers models ®tted the data satisfactorily. However, the three-parameter Burgers model was not a signi®cant improvement over the two-parameter Kelvin model at the 0.01 level of signi®cance, as shown by an analysis of variance.
Journal of Food Engineering, 2006
The migration of lactose, protein and fat within milk droplets and particles in a spray dryer is ... more The migration of lactose, protein and fat within milk droplets and particles in a spray dryer is investigated with a view to eventually modelling this process using computational fluid dynamics. Both protein and fat accumulate preferentially at the surface of the milk particles as they dry, at the expense of lactose. This has repercussions for the rate of particle agglomeration
Journal of Food Engineering, 2009
This paper reviews the different levels and scales of mathematical modelling that can be applied ... more This paper reviews the different levels and scales of mathematical modelling that can be applied to spray dryers. These scales range from the whole dryer level (coarsest scale), represented by a well-mixed assumption, through plug-flow reactor approximations (and mixed well-mixed/plug-flow views, a finer scale), to the finest scale, computational fluid dynamics (CFD). All levels have some value, and the approach is suggested here of applying the coarsest scale first, where well-mixed approaches can give some useful information about the occurrence of wall deposition in short-form dryers. Parallel-flow approaches give some insights into trends in crystallinity and direct wall deposition from an atomizer. CFD, as a means of studying the finest scale phenomena, has been heavily used recently for studying the wall deposition process and for suggesting new designs for dryers. the approach, which aims to calculate the outlet temperature and moisture content in a dryer. The stickiness or otherwise of the solids can be assessed because, if the dryer is well mixed, then these outlet conditions represent the conditions for the solids inside the equipment.
Experiments in Fluids, 2004
An experimental study of a simple jet flow, which contains a dispersion of fine droplets, has bee... more An experimental study of a simple jet flow, which contains a dispersion of fine droplets, has been carried out in order to investigate the effect of turbulence, evaporation and coalescence on the droplet size distributions within the jet. Very little evaporation occurs in the potential core of the jet, while in the far-field, where the potential core has vanished and the droplets disperse more readily, evaporation occurs predominantly in the outer portions of the spray. Evidently, turbulence enhances the evaporation rate of droplets at the edges of the spray, and fresh air entrained from the outer regions increases the evaporative driving force. Coalescence has also been observed within the spray, although this effect is rather subtle compared to the evaporation effect in the dilute jets investigated here. Nevertheless, sufficient measurements have been taken to validate, at least partially, any coalescence models, in addition to any turbulence and evaporation models for dilute poly-disperse sprays.
Education for Chemical Engineers, 2006
B ased on results of our own research and stakeholder surveys, the School of Chemical and Biomole... more B ased on results of our own research and stakeholder surveys, the School of Chemical and Biomolecular Engineering at The University of Sydney has identified a number of imperatives for curriculum change, and has used this stimulus to embark on the task of curriculum renewal. First, the desired graduate attributes were determined, followed by the design of mechanisms needed to integrate these within the curriculum. The curriculum was designed to incorporate an integrated framework for teaching all core concepts, enabling technologies and engineering practice paradigms. The new curriculum was introduced in stages, commencing in 2004. Each unit of study comprises several modules, most supported by problem-based learning. Integration within, and between semesters is vitally important, and is enhanced by team teaching, which has also helped to provide a sense of peer-support. Assessment against sets of competencies rather than differentiated grading was introduced for core technical courses. Students progress between years of study with a greater understanding of the inter-relationship between the analytical, synthesis and practice components of the curriculum. There are a few issues to resolve, but several positive features have emerged so far. The positive reviews of the new curriculum by the Accreditation Panels of both Engineers Australia and the Institution of Chemical Engineers, as well as comments from student representatives, have been significant confirmations of our approach.
Drying Technology, 2013
ABSTRACT Lactose crystallization may occur during spray drying, depending on the operating condit... more ABSTRACT Lactose crystallization may occur during spray drying, depending on the operating conditions for drying, and this work reviews previous and new evidence for the effects of different additives or plasticizers on retarding or accelerating the rate of crystallization. The effects of different operating conditions during spray drying are also considered in the experimental work reviewed and performed here, which was mainly carried out with Buchi B-290 laboratory-scale spray dryers (Buchi, Flawil, Switzerland), although some work on pilot-scale equipment is also discussed. The additives used and reviewed in this article include milk proteins, such as casein and whey protein isolate, polyethylene glycol, and ascorbic acid. The key physical properties, such as glass transition temperature and drying characteristics of the material, are discussed, allowing degrees of amorphicity in spray-dried lactose to be controlled over a wide range, from close to 0% to nearly 100%.
Drying Technology, 2006
The accuracy of the Lagrangian approach for predicting droplet trajectories and evaporation rates... more The accuracy of the Lagrangian approach for predicting droplet trajectories and evaporation rates within a simple spray has been addressed. The turbulent dispersion and overall evaporation rates of droplets are modelled reasonably well, although the downstream velocity decay of the larger droplets is under-predicted, which is attributed to a poor estimate of the radial fluctuating velocity of these droplets at the inlet boundary. Qualitative agreement is found between the predicted and experimental evolution of the droplet size distribution downstream of the nozzle. These results show that smaller droplets evaporate preferentially to larger droplets, because they disperse more quickly towards the edge of the jet, where the entrainment of fresh air from the surroundings produces a significant evaporative driving force. Droplet dispersion and evaporation rates are highly influenced by the rate of turbulence generation within the shear layer. This work demonstrates the potential of the Lagrangian approach for analysing particle trajectories and drying within the more complex spray dryer system.
Drying Technology, 1993
Two different methods for calculating the heat of somtion of timber are compared. One method uses... more Two different methods for calculating the heat of somtion of timber are compared. One method uses thermodynamic expieasions together with the sorption equilibrium relationship given by Simpson and Rosen (1981). while the other is based on the direct measurements made by Kelsev end Clarke (1956). The latter method is most reliable for moisture contents below 0.07 kg kg, where the
Powder technology, 1993
... Eng. Sci., 1 (1952) 259. 2 A. Afacan and JH Masliyah, Powder Technol., 61 (1990) 179. ... 8 W... more ... Eng. Sci., 1 (1952) 259. 2 A. Afacan and JH Masliyah, Powder Technol., 61 (1990) 179. ... 8 WH Press, BP Flannery, SA Teulolsky and WT Vetterling, Numerical RecOs: The Art of Scientific Computing Cambridge University Press, MA, p. 550. References. 1H. ...
Journal of Zhejiang University SCIENCE A, 2007
... Drying Technology, 21(7):1253-1272. [30] Ozmen, L., Langrish, TAG, 2005. An experimental inve... more ... Drying Technology, 21(7):1253-1272. [30] Ozmen, L., Langrish, TAG, 2005. An experimental investigation into wall deposition of milk powder in spray dryers. ... Geothermics, 18(1-2):327-335. [40] Zimon, AD, 1969. Adhesion of Dust and Powder. Plenum Press, New York, p.110. ...
Atomization and Sprays, 2008
Drying Technology, 2014
The effects of different humidities on process yields and degrees of crystallinity have been stud... more The effects of different humidities on process yields and degrees of crystallinity have been studied for spray-dried powders from the spray drying of lactose with humid air in a straight-through system. According to Williams-Landel-Ferry (WLF) kinetics, it was suggested that a higher particle temperature and lower glass transition temperature would increase the crystallization rates of the particles during the spray-drying process. Freshly humidified air produced by a Buchi-B290 spray dryer as a humidifier before the main spray dryer decreased the particle glass transition temperature (T g ), while allowing the particle temperature (T p ) to reach higher values by using an insulated drying chamber. The results showed that higher T p À T g , as a result of applying humid air, improved the process yield from 21 AE 4% to 26 AE 2% and the lactose crystallinity by decreasing the latent heat of crystallization for the powder products from 43 AE 1 J/g to 30 AE 11 J/g. It has been found in this study that the humidity of the inlet air should be adjusted in such a way as to not exceed relative and absolute humidities of 2.7-3% and 65-70 g/kg DA , respectively, at the outlet of the drying chamber, to give the most crystalline particles.
International Journal of Pharmaceutics, 2010
The aim of this study was to develop a method for converting an amorphous drug to a crystalline f... more The aim of this study was to develop a method for converting an amorphous drug to a crystalline form to enhance its stability and inhalation performance. Spray-dried amorphous salbutamol sulphate powder was conditioned with supercritical carbon dioxide (scCO 2 ) modified with menthol. The effect of menthol concentration, pressure, temperature and time on the characteristics of the resulting salbutamol sulphate powder was investigated. Pure scCO 2 had no effect on the physical properties of amorphous salbutamol sulphate; however, scCO 2 modified with menthol at 150 bar and 50 • C was efficient in converting amorphous drug to crystalline form after 12 h of conditioning. The average particle size of powders decreased slightly after the conditioning process because of reducing agglomeration between particles by increasing surface roughness. Emitted dose measured by the fine particle fraction (FPF emitted ) of amorphous salbutamol sulphate was enhanced from 32% to 43% after conditioning with scCO 2 + menthol and its water uptake was significantly decreased. This study demonstrates the potential of scCO 2 + menthol for converting amorphous forms of powders to crystalline, while preserving the particle size.
Powder Technology, 2007
The relative amounts of wall deposition between skim milk and maltodextrin have been compared in ... more The relative amounts of wall deposition between skim milk and maltodextrin have been compared in a pilot-scale spray dryer of 1.5 m height, equipped with a two-fluid atomizer. The atomizer air pressure was 200 kPa, the inlet air temperature was 230 °C, the liquid feed flowrate was 1.6 L h−1, and there was no swirl at the air inlet. Both maltodextrin and skim milk,
Developments in Chemical Engineering and Mineral Processing, 2008
Journal of Zhejiang University SCIENCE A, 2007
The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of ... more The particle deposition behaviour of skim milk, water and maltodextrin in the conical section of a pilot-scale spray dryer was predicted using simple correlations for particle depositions in pipes. The predicted particle deposition fluxes of these materials were then compared with the measured deposition fluxes. The predicted particle deposition regimes of the spray dryer were expected to be in the
Wood Science and Technology, 1997
An investigation has been carried out into whether the internal moisture movement inside Australi... more An investigation has been carried out into whether the internal moisture movement inside Australian hardwood timber is best described by a diffusion model with driving forces based on gradients in moisture content or in partial pressure of water vapour. Experimental data from two sets of drying schedules applied to timber from three species of Australian hardwoods (yellow stringybark, spotted gum and ironbark) reported in Langrish et al. (1997) have been used to assess the use of the two driving forces, and the standard error has been used as the criterion for goodness of fit. Moisture-content driving forces have fitted the data better than a model based on vapour-pressure driving forces alone. The use of moisture-content driving forces with diffusion parameters obtained from data from one drying schedule is also better in predicting the drying behaviour with another schedule than vapour-pressure driving forces for yellow stringybark and ironbark. These results may be due to the complexity of the moisture-movement process through timber, with more than one moisturetransport mechanism being active, so that the use of only one driving force for moisture movement is at best only an approximation to the true behaviour. Symbols D diffusion coefficient, m 2 s -1 (moisture-content gradient), m 3 s kg < (vapour-pressure gradient) De activation energy, K Dr pre-exponential factor m 2 s -1 (moisture-content gradient), m3s kg -1 (vapourpressure gradient) J mass flux of water divided by density, m s -1 t time, s x position, m X moisture content, kg kg -1
Wood Science and Technology, 2000
This work examines the applicability of mathematical models for correlating the visco-elastic str... more This work examines the applicability of mathematical models for correlating the visco-elastic strains during kiln drying of radiata pine (Pinus radiata D. Don) sapwood at various temperatures and moisture contents. The eventual aim is to use a mathematical model incorporating these strains to optimise the drying schedules and minimise the degradation. Data sets from previous experiments (Keep 1998) obtained at temperatures from 20 to 140°C for sapwood at 5, 15 and 20% moisture contents (dry basis) were analysed. The data were ®tted for various theoretical models, namely the Maxwell, Kelvin and Burgers models, and the Bailey-Norton equation. The parameter values and standard errors for the above models over the range of experimental data have been determined. The results indicate that the Maxwell model did not ®t the experimental data well, having only one parameter. In most cases, the Bailey-Norton equation was inadequate, as it is a power-law model with a predicted continuous increase in creep with time and does not predict a plateau in the creep strain, as has been observed for most of data. The Kelvin model gave a better ®t than the Bailey-Norton equation for most of the data sets. From visual inspection of the plots for the experimental data and the model predictions with time, it was found that both the Kelvin and Burgers models ®tted the data satisfactorily. However, the three-parameter Burgers model was not a signi®cant improvement over the two-parameter Kelvin model at the 0.01 level of signi®cance, as shown by an analysis of variance.
Journal of Food Engineering, 2006
The migration of lactose, protein and fat within milk droplets and particles in a spray dryer is ... more The migration of lactose, protein and fat within milk droplets and particles in a spray dryer is investigated with a view to eventually modelling this process using computational fluid dynamics. Both protein and fat accumulate preferentially at the surface of the milk particles as they dry, at the expense of lactose. This has repercussions for the rate of particle agglomeration
Journal of Food Engineering, 2009
This paper reviews the different levels and scales of mathematical modelling that can be applied ... more This paper reviews the different levels and scales of mathematical modelling that can be applied to spray dryers. These scales range from the whole dryer level (coarsest scale), represented by a well-mixed assumption, through plug-flow reactor approximations (and mixed well-mixed/plug-flow views, a finer scale), to the finest scale, computational fluid dynamics (CFD). All levels have some value, and the approach is suggested here of applying the coarsest scale first, where well-mixed approaches can give some useful information about the occurrence of wall deposition in short-form dryers. Parallel-flow approaches give some insights into trends in crystallinity and direct wall deposition from an atomizer. CFD, as a means of studying the finest scale phenomena, has been heavily used recently for studying the wall deposition process and for suggesting new designs for dryers. the approach, which aims to calculate the outlet temperature and moisture content in a dryer. The stickiness or otherwise of the solids can be assessed because, if the dryer is well mixed, then these outlet conditions represent the conditions for the solids inside the equipment.
Experiments in Fluids, 2004
An experimental study of a simple jet flow, which contains a dispersion of fine droplets, has bee... more An experimental study of a simple jet flow, which contains a dispersion of fine droplets, has been carried out in order to investigate the effect of turbulence, evaporation and coalescence on the droplet size distributions within the jet. Very little evaporation occurs in the potential core of the jet, while in the far-field, where the potential core has vanished and the droplets disperse more readily, evaporation occurs predominantly in the outer portions of the spray. Evidently, turbulence enhances the evaporation rate of droplets at the edges of the spray, and fresh air entrained from the outer regions increases the evaporative driving force. Coalescence has also been observed within the spray, although this effect is rather subtle compared to the evaporation effect in the dilute jets investigated here. Nevertheless, sufficient measurements have been taken to validate, at least partially, any coalescence models, in addition to any turbulence and evaporation models for dilute poly-disperse sprays.
Education for Chemical Engineers, 2006
B ased on results of our own research and stakeholder surveys, the School of Chemical and Biomole... more B ased on results of our own research and stakeholder surveys, the School of Chemical and Biomolecular Engineering at The University of Sydney has identified a number of imperatives for curriculum change, and has used this stimulus to embark on the task of curriculum renewal. First, the desired graduate attributes were determined, followed by the design of mechanisms needed to integrate these within the curriculum. The curriculum was designed to incorporate an integrated framework for teaching all core concepts, enabling technologies and engineering practice paradigms. The new curriculum was introduced in stages, commencing in 2004. Each unit of study comprises several modules, most supported by problem-based learning. Integration within, and between semesters is vitally important, and is enhanced by team teaching, which has also helped to provide a sense of peer-support. Assessment against sets of competencies rather than differentiated grading was introduced for core technical courses. Students progress between years of study with a greater understanding of the inter-relationship between the analytical, synthesis and practice components of the curriculum. There are a few issues to resolve, but several positive features have emerged so far. The positive reviews of the new curriculum by the Accreditation Panels of both Engineers Australia and the Institution of Chemical Engineers, as well as comments from student representatives, have been significant confirmations of our approach.
Drying Technology, 2013
ABSTRACT Lactose crystallization may occur during spray drying, depending on the operating condit... more ABSTRACT Lactose crystallization may occur during spray drying, depending on the operating conditions for drying, and this work reviews previous and new evidence for the effects of different additives or plasticizers on retarding or accelerating the rate of crystallization. The effects of different operating conditions during spray drying are also considered in the experimental work reviewed and performed here, which was mainly carried out with Buchi B-290 laboratory-scale spray dryers (Buchi, Flawil, Switzerland), although some work on pilot-scale equipment is also discussed. The additives used and reviewed in this article include milk proteins, such as casein and whey protein isolate, polyethylene glycol, and ascorbic acid. The key physical properties, such as glass transition temperature and drying characteristics of the material, are discussed, allowing degrees of amorphicity in spray-dried lactose to be controlled over a wide range, from close to 0% to nearly 100%.
Drying Technology, 2006
The accuracy of the Lagrangian approach for predicting droplet trajectories and evaporation rates... more The accuracy of the Lagrangian approach for predicting droplet trajectories and evaporation rates within a simple spray has been addressed. The turbulent dispersion and overall evaporation rates of droplets are modelled reasonably well, although the downstream velocity decay of the larger droplets is under-predicted, which is attributed to a poor estimate of the radial fluctuating velocity of these droplets at the inlet boundary. Qualitative agreement is found between the predicted and experimental evolution of the droplet size distribution downstream of the nozzle. These results show that smaller droplets evaporate preferentially to larger droplets, because they disperse more quickly towards the edge of the jet, where the entrainment of fresh air from the surroundings produces a significant evaporative driving force. Droplet dispersion and evaporation rates are highly influenced by the rate of turbulence generation within the shear layer. This work demonstrates the potential of the Lagrangian approach for analysing particle trajectories and drying within the more complex spray dryer system.
Drying Technology, 1993
Two different methods for calculating the heat of somtion of timber are compared. One method uses... more Two different methods for calculating the heat of somtion of timber are compared. One method uses thermodynamic expieasions together with the sorption equilibrium relationship given by Simpson and Rosen (1981). while the other is based on the direct measurements made by Kelsev end Clarke (1956). The latter method is most reliable for moisture contents below 0.07 kg kg, where the