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Introduction

 

Material Model

 

       The current material model supports two types of materials. One is generic material type and the other is generic food type.

 

Generic Material Type

 

       For a generic material type you don’t need to know the composition of the material. The absolute dry material is treated as one whole substance.

       For drying related balance simulation you only need to provide the specific heat of the absolute dry material. The specific heat of the material with moisture content is a weighted average of the absolute dry material and the moisture

                                                                                  (1)

where CWetMat, CDryMat,  CMoisture represent specific heats of wet material, absolute dry material, and moisture liquid, respectively, and w stands for the moisture content of the material.

       When evaporation related balance simulation is involved you need to provide the duhring lines of the material solution to account for boiling point rise in addition to the specific heat of the absolute dry material. It needs to be noted that Equation 1 is also used to calculate the specific heat of material solution in evaporation related balance calculation.

 

Generic Food Type

 

       For a generic food material you need to know the basic compositions of the material. There are 5 basic components to constitute a generic food material in addition to its moisture. The 5 basic components are Carbohydrate, Ash, Fiber, Fat and Protein.

       For drying related balance simulation you need to provide the mass fraction for each of the 5 basic components.

       The specific heat of a generic food material without moisture content is a weighted average of each of the 5 basic components. The specific heat as a function of temperature for each of the 5 basic components is listed in Table 1 (Unit Operations in Food Engineering, Chapter 11--Thermal Properties of Food).

 

Carbohydrate

Ash

Fiber

Fat

Protein

 

Table 1 Specific Heat of Generic Food Components

 

       Please note that the unit of temperature T is oC and that of Cp is kJ/kg. oC in Table 1.

       The specific heat of a generic food material with moisture is a weighted average of absolute dry food material and the moisture, which can be calculated by Equation 1.

       For evaporation related balance simulation you need to provide the duhring lines of the material solution to account for the boiling point rise.

 

Flowsheet and Materials

 

Creating a new material

 

       Materials can be created independent of any flowsheet. Any time before or after you create a flowsheet, you can go to the materials catalog to create a material that you want to model, and add it to the materials catalog. Here are some steps to create a generic food material:

 

There is no flowsheet open. Clicking Materials/Drying Materials… will open the Drying Materials window.

 

Here there is already one material in the catalog. Clicking the Add button will open the New Drying Material window.

 

After we give a name, choose the type, and normalize, we can define the duhring lines.

 

Here we can define the duhring lines. After closing the Duhring Lines window and New Drying Material window, we can see our newly created material in the catalog.

 

We can now close the catalog window.

 

 

Specifying the material to be used on a flowsheet

 

       Before a new flowsheet is created, a material needs to be specified first. After the flowsheet is created with the specified material, you cannot switch to another material. However, you can modify the material’s specific heat of absolute dry material or the duhring lines, and the flowsheet will be recalculated and updated after you finalize the modification. Here are the steps to set a material before using it on a flowsheet:

 

There is no flowsheet open. Clicking Materials/New Flowsheet Settings… will open the New Flowsheet Settings window.

 

Here we need to select the material that we want to use on a new flowsheet, by selecting the appropriate row under “Select Drying Material” and then clicking the Set button. After closing this window we can create a new flowsheet. We can see the material used on the flowsheet by clicking Flowsheet/Options…

 

Clicking Flowsheet/Options… will open the Flowsheet Options window.

 

Here we can see what material is used by the flowsheet. In this case, the Drying Material is “My Generic Food 1”.