| Popis: |
To overcome difficulties (slip, sample disturbance) associated with traditional sensors, a semi-empirical method was developed to allow the use of a 4-bladed vane sensor in small strain oscillatory testing. It was assumed that the vane sensor acted as a bob with an acting radius, RV, different from the actual radius of the vane (0.02005 m). To solve for RV, the complex modulus obtained using a concentric cylinder sensor from reference viscoelastic fluid, was set equal to the complex modulus equation for vane sensor. RV values were grouped into three phase shift ranges from 5° to less than 16°, from 16° to less than 60°, and from 60° to 90° and they were 0.01883, 0.01869, and 0.01850 m, respectively. These values were used in the calculation of viscoelastic properties of eight commercial food products, which resulted in complex modulus values within 15% of those obtained using a concentric cylinder sensor. Results showed that this particular vane and cup system can be used to directly measure the storage and loss moduli of viscoelastic material and phase shift within the upper frequency value of 6.28 rad/s. Above 6.28 rad/s, there is an inconsistency in phase shift angles measured using vane method. This method is ideal for testing thixotropic food systems because disturbance is minimal during sample loading, giving more accurate viscoelastic measurements. |
