Sakamon Devahastin

A Comparative Study of Low-Pressure Superheated Steam and Vacuum Drying of a Heat-Sensitive Material

Abstract Using carrot cubes as a model heat-sensitive material, experimental investigations were conducted to examine the drying kinetics and various quality parameters of the dried product undergoing both low-pressure superheated steam and vacuum drying. Effects of operating parameters such as pressure and temperature on the drying characteristics as well as quality attributes, i.e., volume, shrinkage, apparent density, color, and rehydration behavior, of the dried product underwent the two drying processes were also evaluated and compared. Although low-pressure steam drying required longer dwell time to achieve the same final moisture content than vacuum drying, some of the quality attributes were superior to those obtained in vacuum drying.

Drying Kinetics and Quality of Shrimp Undergoing Different Two-Stage Drying Processes

Abstract An innovative two-stage drying concept is presented in this article. The work considered drying of shrimp using a superheated steam dryer followed by a heat pump (SSD/HPD) or a hot air dryer (SSD/AD) both from drying kinetics and dried product quality points of view. The experiments were performed using the first-stage superheated steam drying temperature of 140°C while the second-stage heat pump drying (or hot air drying) was performed at 50°C. The moisture content of shrimp at the end of the superheated steam drying stage was varied between 30 and 40% (w.b.). The effect of tempering between SSD/HPD was also investigated. Shrinkage, color, rehydration behavior, texture (toughness and hardness), and microstructure of dried shrimp were measured. The results showed that SSD/HPD dried shrimp had much lower degree of shrinkage, higher degree of rehydration, better color, less tough and softer, and more porous than single-stage SSD dried shrimp. It was also found that SSD/AD gave redder shrimp compared to shrimp dried in a single-stage superheated steam dryer. No improvement in terms of shrinkage and rehydration behavior was observed, however.

Study of Intermittent Low-Pressure Superheated Steam and Vacuum Drying of a Heat-Sensitive Material

Low-pressure superheated steam drying (LPSSD) has recently been applied to drying of various heat-sensitive foods and bioproducts with success. Several studies have shown that the quality of LPSSD-dried products is superior to that obtained using conventional hot air or vacuum drying. However, drying time and energy consumption for LPSSD is generally greater than that for vacuum drying. Therefore, it is necessary to examine different methodologies to improve the energy efficiency of LPSSD. An intermittent drying scheme is one possible method to reduce the energy consumption of the process while maintaining the desired product quality. In this study, the effect of intermittent supply of energy (through an electric heater and steam injection to the dryer) and vacuum (through the use of a vacuum pump) at various intermittency values or on:off periods (10:5, 10:10 and 10:20 min in the case of intermittent supply of energy and 5:0, 5:5, and 5:10 min in the case of intermittent supply of vacuum) at the on-period setting temperatures of 70, 80, and 90°C on the drying kinetics and heat transfer behavior of the drying samples (banana chips) was studied. The effects of these intermittent drying schemes and conditions on the quality parameters of dried banana chips; i.e., color, shrinkage, texture, and ascorbic acid retention, were also studied. Finally, the energy consumption values for intermittent LPSSD and vacuum drying were monitored through the effective (or net) drying time at various intermittent drying conditions and compared with those using continuous LPSSD and vacuum drying.

Enhanced heat transfer in free convection-dominated melting in a rectangular cavity with an isothermal vertical wall

Abstract Free convection-dominated melting of a phase change material in a rectangular cavity with an isothermally heated vertical wall is simulated using the streamline upwind/Petrov–Galerkin finite element technique in combination with a fixed-grid primitive variable method. The enthalpy–porosity model is employed to account for the physics of the evolution of the flow at the solid/liquid interface. A penalty formulation is used to treat the incompressibility constraint in the momentum equations. Inverting of the container at an appropriate stage during the melting process is proposed as a simple but effective technique for enhancement of free convection-controlled heat transfer in the phase change material. The technique results in more than 50% increase of the energy charge rate during the melting process for some specific cases.

A numerical study of flow and mixing characteristics of laminar confined impinging streams

Numerical simulations were performed to study the flow and mixing characteristics of two-dimensional laminar confined impinging streams. By solving the time-dependent conservation equations for mass, momentum and energy, Reynolds numbers beyond which the flow becomes oscillatory and even random were determined for different geometric configurations. Simulations were also performed for cases with jet Reynolds numbers in the stable regime to study the mixing characteristics of the system. It is found that both the inlet jet Reynolds number and the geometry of the system have strong effects on mixing in impinging streams.

Comparative Evaluation of Physical Properties of Edible Chitosan Films Prepared by Different Drying Methods

Edible films are alternative packaging, which have recently received much attention due mainly to environmental reasons. Edible films may be formed from edible biomaterials such as polysaccharides, proteins, or lipids. Among these biopolymers, chitosan is of interest because it has a good film-forming property and is biodegradable, biocompatible, and nontoxic. Several techniques have been used to prepare edible chitosan films with various degrees of success. However, it is always interesting to find an alternative technique to produce films of superior quality at shorter processing (drying) time. In this study, the influences of different drying methods and conditions on the drying kinetics and various properties of chitosan films were investigated. Drying at control conditions (ambient air drying and hot air drying at 40°C) as well as vacuum drying and low-pressure superheated steam drying (LPSSD) at an absolute pressure of 10 kPa were carried out at different drying temperatures (70, 80, and 90°C). The properties of chitosan films, in terms of color, tensile strength, percent elongation, water vapor permeability (WVP), glass transition temperature (T g ), and crystallinity, were also determined. Based on the results of both the drying behavior and film properties, LPSSD at 70°C was proposed as the most favorable conditions for drying chitosan films.

Fractal Characterization of Some Physical Properties of a Food Product under Various Drying Conditions

The present work was aimed at monitoring and studying the relationship between microstructural changes of a food product and its physical property changes during two different types of drying; i.e., conventional hot air drying and low-pressure superheated steam drying, using fractal analysis. The external changes of a model food product, viz. carrot, which were represented in terms of the percentage of shrinkage and the rehydration behavior, correlated well with its microstructural changes, which were represented by the rate of change of the fractal dimension of the microstructural images. The changes of physical properties and microstructure of carrot could be divided into two periods, which are periods of uniform and nonuniform deformation. The microstructural changes of the samples undergoing different drying techniques were quite different, however. Fractal dimension of carrot undergoing drying increased with drying time for both hot air drying and low-pressure superheated steam drying cases. Fractal dimension was found to be a good indicator of the microstructural changes of a product undergoing different drying techniques and conditions.

Effects of Drying Temperature and Particle Size on Hydration Properties of Dietary Fiber Powder from Lime and Cabbage By-Products

The use of by-products from fruit and vegetable processing plants as sources of dietary fiber and bioactive agents is currently of interest, both from the waste management and from the production of value-added products points of view. This work aimed at studying the use of lime residues and outer leaves of white cabbage to produce dietary fiber powder, which included the study of the product pretreatment and preparation, drying, and grinding dried residues into powder. Dietary fiber content during each processing step was determined to calculate the loss of functionality of the products through the process. Hydration properties, i.e., water holding capacity (WHC) and swelling capacity (SWC), of the two residues were also determined after hot air drying at 60–80°C. The effect of particle size of dietary fiber powder, which was obtained by grinding dried residues, in the range of 63–450 μm, on the hydration properties was also evaluated and discussed.

Evaluation of bioactive compounds and bioactivities of soybean dried by different methods and conditions

Soybean has attracted significant research and commercial interests due to its many health-promoting bioactive compounds, especially isoflavones (β-glucosides, malonyl-β-glucosides, acetyl-β-glucosides and aglycones). Isoflavones possess antioxidant activity and α-glucosidase inhibitory activity, which has proved effective in the treatment of type 2 diabetes mellitus. Prior to its use, however, soybean needs to be dried to extend its storage life and to prepare the material for subsequent food or pharmaceutical processing. The present study investigated the effects of drying methods and conditions on the drying characteristics, isoflavones, antioxidant activity and α -glucosidase inhibitory activity of dried soybean. Hot-air fluidized bed drying (HAFBD), superheated-steam fluidized bed drying (SSFBD) and gas-fired infrared combined with hot air vibrating drying (GFIR-HAVD) were carried out at various drying temperatures (50, 70, 130 and150°C). The results showed that higher drying temperatures led to higher drying rates and higher levels of β-glucosides and antioxidant activity, but to lower levels of malonyl-β-glucosides, acetyl-β-glucosides and total isoflavones. At the same drying temperature GFIR-HAVD resulted in the highest drying rates and the highest levels of β-glucosides, aglycones and total isoflavones, antioxidant activity as well as α-glucosidase inhibitory activity of dried soybean. A drying temperature of 130°C gave the highest levels of aglycones and α-glucosidase inhibitory activity in all cases. The relationships between all the studied parameters were monitored and simple correlations between them were determined.

Some hydrodynamic and mixing characteristics of a pulsed spouted bed dryer

A modified spouted bed, viz. pulsed spouted bed, was developed to offset some of the limitations of the conventional spouted bed. Experiments were performed to study several hydrodynamic characteristics of this device, i.e., spouting mechanism, solid circulation rates, and maximum spoutable bed height. Mixing of particles under various operating conditions was investigated experimentally. Results show that there exists a range of the pulse frequency in which this device performs better than the conventional spouted bed in terms of the maximum spoutable bed depth, solid circulation rates and mixing behavior.