MD160Y - Process for foodstuff drying - Google Patents

Abstract

The invention relates to the food industry, namely to a drying process of foodstuffs in the electromagnetic field by impulses of overload frequency. The process, according to the invention, includes the treatment of foodstuffs in an electromagnetic field, using an active period with impulsive frequencies for heating and a rest period without phase transfers, with the elimination of moisture from the surface of the product, at the same time the treatment is performed alternating the periods , until the required moisture is reached in the product, and the duration of the periods is calculated using the formula (1) for the active period of impulses and (2) for the rest period: The result consists in reducing the energy consumption by creating the maximum temperature gradient in the active period of heating and humidity removal without phase transfers during the passive period.

Description

The invention relates to the food industry, namely to a process for drying food products in an electromagnetic field using ultra-high frequency pulses.

The process of drying with pulse currents in an electromagnetic field is known, which includes drying cherries by convection at a drying agent temperature of 100…105°C simultaneously with drying with pulse currents in an electromagnetic field with a frequency of 2450 MHz, the irradiation power being 1.5 kW, the pulse duration of 5 s and the pause between them of 25 s [1].

The disadvantage of this method is that the duration of the pulses and the pause between them are determined for a specific product (cherry) and cannot be applied to other products. At the same time, the mentioned durations of the pulses and the pause between them are determined for the reasons of being maintained within fixed limits.

The problem solved by the invention consists in the possibility of choosing the drying process for different products, due to the calculation of the optimal duration of the pulses of application of ultra-high frequency energy and the pause between them depending on the power of the energy source and the thermophysical properties of the product.

The problem is solved by the fact that the food drying process includes treating food products in an electromagnetic field, using an active period with ultra-high frequency pulses for heating and a rest period without phase transfers, with the elimination of moisture from the surface of the product, at the same time the treatment is performed by alternating the periods, until the required moisture is reached in the product, and the duration of the periods is calculated using the formula (1) for the active period of the pulses and (2) for the rest period:

,\tab\tab(1)

,\tab\tab\tab\tab(2)

where:

τA - duration of the active period of the pulses, s;

α - thermal diffusion coefficient, m2/s;

c - specific heat capacity, J/kg·K;

ρ - product density, kg/m3;

d - product layer thickness, m;

TS - product surface temperature, K;

TM - ambient temperature, K;

λ - thermal conductivity coefficient, W/m·K;

Qv - intensity of heat released, W/m3,

τp - duration of the rest period, s;

αp - molar diffusion coefficient of water, m2/s.

The result is reduced energy consumption by creating the maximum temperature gradient during the active heating period and eliminating humidity without phase transfers during the passive period.

The advantages of this process are: the possibility of calculating drying periods for different products; increasing product quality and reducing energy consumption.

During the active period in the product, the maximum temperature gradient is achieved, so the most intensive transfer of moisture in the liquid state occurs without the transfer of the liquid-vapor phase from the inner layers of the product to the periphery. Then the energy source of the ultrahigh frequency field is interrupted for a period of time τp. During this period, due to the accumulated energy, the removal of moisture from the surface of the product and the relaxation of the pressure inside it occurs. After this, the cycle repeats.

Exceeding the τp value of the rest period (pause) creates a pressure drop inside the product that absorbs air along with moisture from the product-environment boundary layer inside.

Example of implementation

The table presents the sunflower seed parameters necessary for calculating the active and passive periods for drying.

Table

Parameters Symbol Unit of measurement Humidity 33% 15% thermal diffusion coefficient α m2/s 0.89 0.68 specific heat capacity c J/kg·K 2292 1955 product density ρ kg/m3 817 744 product layer thickness d m 0.005 0.005 product surface temperature TS K 346 346 ambient temperature TM K 293 293 thermal conductivity coefficient λ W/m·K 0.150 0.137 heat release intensity QV W/m3 4.2·104 3.9·104 water molar diffusion coefficient αp m2/s 4.4·10-8 4.9·10-8

When sunflower seeds have reached 33% moisture, the duration of the active period is:

= = = (s)

and the duration of the passive period is:

= = =71(s).

When sunflower seeds have reached 15% moisture, the duration of the active period is:

= = = (s)

and the duration of the passive period is:

= = =64(s).

Therefore, knowing the power of the energy source and the thermophysical parameters of sunflower seeds, presented in the table, the duration of the active and passive period of application of the ultra-high frequency field energy can be calculated according to relations 1 and 2. Using relations 1 and 2, the periods of application of the ultra-high frequency field energy can be calculated for different products.

1. MD 2656 C2 2005.01.31

Claims (1)

Process for drying food products, which includes treating them in an electromagnetic field using an active period with ultra-high frequency pulses for heating and a rest period without phase transfers, with the elimination of moisture from the surface of the product, at the same time the treatment is carried out by alternating the periods, until the required moisture is reached in the product, and the duration of the periods is calculated using the formula (1) for the active period of the pulses and (2) for the rest period: ,\tab\tab(1) ,\tab\tab\tab\tab(2) where: τA - duration of the active period of the pulses, s; α - thermal diffusion coefficient, m2/s; c - specific heat capacity, J/kg·K; ρ - product density, kg/m3; d - product layer thickness, m; Ts - product surface temperature, K; Tm - ambient temperature, K; λ - thermal conductivity coefficient, W/m·K; Qv - intensity of heat released, W/m3, τp - duration of the rest period, s; αp - molar diffusion coefficient of water, m2/s.