Effect of harvest time and drying on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was grown under field conditions in South-East Queensland to study the effects of harvest time and drying conditions on seed quality. Cobs were harvested at different times to obtain seed with two moisture percentage ranges (20-30% and 40-50%) and dried to 12% moisture under different combinations of drying temperatures (30 degrees C, 40 degrees C and 50 degrees C) and air velocities (1.25 m/s, 2.75 m/s and 4.30 m/s). Dried seed was stored at 30 degrees C with bimonthly monitoring of seed quality for 12 months. For standard as well as cold test germinations, statistical analysis yielded significant main effects for temperature, air velocity and harvest moisture content and significant interactions for drying temperature by harvest moisture and drying temperature by air velocity. Germination at the beginning of storage was unaffected by drying temperatures up to 40 degrees C regardless of harvest moisture but was lower at 50 degrees C for higher moisture. However, germination at the end of the storage period of 12 months was greatest for seed harvested at higher moisture and dried at temperatures up to 40 degrees C. Germination was not affected by air velocity for drying temperatures up to 40 degrees C but at 50 degrees C it generally decreased with increase in air velocity. To slow down seed deterioration during storage, it is recommended that sweet corn seed should be harvested at a higher moisture range (40-50%) and dried at 40 degrees C and 4.30 m/s air velocity. The drying temperature can be raised to 50 degrees C for seed harvested at a low moisture range (20-30%) provided the air velocity is kept low (1.25 m/s).

Drying of porous building materials: hydraulic diffusivity and front propagation

One-dimensional drying of a porous building material is modelled as a nonlinear diffusion process. The most difficult case of strong surface drying when an internal drying front is created is treated in particular. Simple analytical formulae for the drying front and moisture profiles during second stage drying are obtained when the hydraulic diffusivity is known. The analysis demonstrates the origin of the constant drying front speed observed elsewhere experimentally. Application of the formulae is illustrated for an exponential diffusivity and applied to the drying of a fired clay brick.

Parameters affecting the performance of wetting and drying in a two-dimensional finite element long wave hydrodynamic model

The marsh porosity method, a type of thin slot wetting and drying algorithm in a two-dimensional finite element long wave hydrodynamic model, is discussed and analyzed to assess model performance. Tests, including comparisons to simple examples and theoretical calculations, examine the effects of varying the marsh porosity parameters. The findings demonstrate that the wetting and drying concept of marsh porosity, often used in finite element hydrodynamic modeling, can behave in a more complex manner than initially expected.

Effect of addition of maltodextrin on drying kinetics and stickiness of sugar and acid-rich foods during convective drying: experiments and modelling

The effect of addition of maltodextrin on drying kinetics of drops containing fructose, glucose, sucrose and citric acid individually and in mixtures was studied experimentally using single drop drying experiments and numerically by solving appropriate mass and heat transfer equations. The numerical predictions agreed with the experimental moisture and temperature histories within 5-6% average relative (absolute) errors and average differences of +/- 1degreesC, respectively. The stickiness of these drops was determined using the glass transition temperature (T-g) of the drops' surface layer as an indicator. The experimental stickiness histories followed the model predictions with reasonable accuracy. A safe drying (non-sticky) regime in a spray drying environment has been proposed, and used to estimate the optimum amount of addition of maltodextrin for successful spray drying of 120 micron diameter droplets of fruit juices. (C) 2003 Elsevier Ltd. All rights reserved.

Drying front in a sloping aquifer: Nonlinear effects

[1] The profiles for the water table height h(x, t) in a shallow sloping aquifer are reexamined with a solution of the nonlinear Boussinesq equation. We demonstrate that the previous anomaly first reported by Brutsaert [1994] that the point at which the water table h first becomes zero at x = L at time t = t(c) remains fixed at this point for all times t > t(c) is actually a result of the linearization of the Boussinesq equation and not, as previously suggested [Brutsaert, 1994; Verhoest and Troch, 2000], a result of the Dupuit assumption. Rather, by examination of the nonlinear Boussinesq equation the drying front, i.e., the point x(f) at which h is zero for times t greater than or equal to t(c), actually recedes downslope as physically expected. This points out that the linear Boussinesq equation should be used carefully when a zero depth is obtained as the concept of an average'' depth loses meaning at that time.

The drying of sewage sludge by immersion frying

The objective of this work was to dry sewage sludge using a fry-drying process. The frying experiments were carried out in commercial fryers modified by adding thermocouples to the setup. During frying, typical drying curves were obtained and it was verified that, in relation to the parameters: oil temperature, oil type and shape of the sample, the shape factor the most effect on the drying rate, at least within the range chosen for the variables studied. Oil uptake and calorific value were also analyzed. The calorific value of the samples increased with frying time, reaching values around 24MJ/kg after 600s of frying (comparable to biocombustibles such as wood and sugarcane bagasse). The process of immersion frying showed great potential for drying materials, especially sewage sludge, obtaining a product with a high energy content, thereby increasing its value as a combustible.

Optimization of co-current spray drying process of sugar-rich foods. Part I - Moisture and glass transition temperature profile during drying

A steady state mathematical model for co-current spray drying was developed for sugar-rich foods with the application of the glass transition temperature concept. Maltodextrin-sucrose solution was used as a sugar-rich food model. The model included mass, heat and momentum balances for a single droplet drying as well as temperature and humidity profile of the drying medium. A log-normal volume distribution of the droplets was generated at the exit of the rotary atomizer. This generation created a certain number of bins to form a system of non-linear first-order differential equations as a function of the axial distance of the drying chamber. The model was used to calculate the changes of droplet diameter, density, temperature, moisture content and velocity in association with the change of air properties along the axial distance. The difference between the outlet air temperature and the glass transition temperature of the final products (AT) was considered as an indicator of stickiness of the particles in spray drying process. The calculated and experimental AT values were close, indicating successful validation of the model. (c) 2004 Elsevier Ltd. All rights reserved.

Modeling dimensional shrinkage of shaped foods in fluidized bed drying

Three particular geometrical shapes of parallelepiped, cylinder and sphere were selected from cut beans (length : diameter = 1: 1, 2:1, 3: 1), potatoes (aspect ratio = 1:1, 2:1, 3:1) and peas, respectively. The dimensional shrinkage behavior was studied in a batch fluidized bed at three drying temperatures of 30, 40 and 50C. Relative humidity of hot air was kept at 15%. Dimensional shrinkage was plotted using a nondimensional moisture ratio and the shrinkage behavior of the selected foods was modeled with simple mathematical models.

Relating the stickiness property of foods undergoing drying and dried products to their surface energetics

Stickiness is a common problem encountered in food handling and processing, and also during consumption. Stickiness is observed as adhesion of the food to processing equipment surfaces or cohesion within the food particulate or mass. An important operation where this undesirable behavior of food is manifested is drying. This occurs particularly during drying of high-sugar and high-fat foods. To date, the stickiness of foods during drying or dried powder has been investigated in relation to their viscous and glass transition properties. The importance of contact surface energy of the equipment has been ignored in many analyses, despite the fact that some drying operations have reported using low-energy contact surfaces in drying equipment to avoid the problems caused by stickiness. This review discusses the fundamentals of adhesion and cohesion mechanisms and relates these phenomena to drying and dried products.

A glass transition temperature approach for the prediction of the surface stickiness of a drying droplet during spray drying

The development of surface stickiness of droplets of sugar and acid-rich foods during spray drying can be explained using the notion of glass transition temperature (T-g). In this work, criteria for a safe drying regime have been developed and their physical basis provided. A dimensionless time (psi) is introduced as an indicator of spray dryability and it is correlated with the recovery of powders in practical spray drying. Droplets with initial diameters of 120 mum were subjected to simulated spray drying conditions and their safe drying regime and 41 values generated. The model predicted the recovery in a pilot scale spray dryer reasonably well. (C) 2004 Elsevier B.V. All rights reserved.

Life Cycle Assessment (LCA) Applied to the Design of an Innovative Drying Process for Sewage Sludge

Most adverse environmental impacts result from design decisions made long before manufacturing or usage. In order to prevent this situation, several authors have proposed the application of life cycle assessment (LCA) at the very first phases of the design of a process, a product or a service. The study in this paper presents an innovative thermal drying process for sewage sludge called fry-drying, in which dewatered sludge is directly contacted in the dryer with hot recycled cooking oils (RCO) as the heat medium. Considering the practical difficulties for the disposal of these two wastes, fry-drying presents a potentially convenient method for their combined elimination by incineration of the final fry-dried sludge. An analytical comparison between a conventional drying process and the new proposed fry-drying process is reported, with reference to some environmental impact categories. The results of this study, applied at the earliest stages of the design of the process, assist evaluation of the feasibility of such system compared to a current disposal process for the drying and incineration of sewage sludge.

Heat and mass transfer during fry-drying of sewage sludge

Deep-frying, which consists of immersing a wet material in a large volume of hot oil, presents a process easily adaptable to dry rather than cook materials. A suitable material for drying is sewage sludge, which may be dried using recycled cooking oils (RCO) as frying oil. One advantage is that this prepares both materials for convenient disposal by incineration. This study examines fry-drying of municipal sewage sludge using recycled cooking oil. The transport processes occurring during fry-drying were monitored through sample weight, temperature, and image analysis. Due to the thicker and wetter samples than the common fried foods, high residual moisture is observed in the sludge when the boiling front has reached the geometric center of the sample, suggesting that the operation is heat transfer controlled only during the first half of the process followed by the addition of other mechanisms that allow complete drying of the sample. A series of mechanisms comprising four stages (i.e., initial heating accompanied by a surface boiling onset, film vapor regime, transitional nucleate boiling, and bound water removal) is proposed. In order to study the effect of the operating conditions on the fry-drying kinetics, different oil temperatures (from 120 to 180 degrees C), diameter (D = 15 to 25 mm), and initial moisture content of the sample (4.8 and 5.6 kg water(.)kg(-1) total dry solids) were investigated.

Effect of drying conditions on pyrethrins content

Windrowed pyrethrum stems were air dried under a range of storage conditions to examine whether the current commercial practice of drying crop material is conducive to pyrethrins' degradation. Crop material was stored for up to 12 days in a commercial windrow, a shed receiving indirect light or a dark, 5 degrees C cool-room. Analysis of pyrethrins extracted from flowers of all treatments demonstrated that pyrethrins were not degrading in windrowed crops, plant material stored in the shed or in the 5 degrees C cool-room. The small differences obtained in pyrethrins content among the treatments can be explained by the natural variation in pyrethrins content of pyrethrum crops. The observation that the achenes were unchanged during this drying period supported the pyrethrins analysis. These results demonstrate that pyrethrins in planta do not degrade as rapidly as extracted pyrethrins. (C) 2005 Elsevier B.V. All rights reserved.