RHEOLOGICAL PROPERTIES OF
FRUITS AND FRUIT PRODUCTS
4. 1 . INTRODUCTION
Most processed and lots of freshly consumed fruits get some type of heat or cooling down during controlling or making. Design and operation of processes regarding heat transfer needs special attention due to heat sensitivity of fruits. The two theoretical and empirical relationships used when designing, or functioning, heat techniques need familiarity with the heat properties with the foods into consideration. Food cold weather properties can be explained as those real estate controlling the transfer of heat within a specified food. These homes are usually classified (Perry and Green, 1973) into thermodynamical properties, viz, specific volume level, specific heat, and enthalpy; and high temperature transport houses, namely, energy conductivity and thermal diffusivity. When considering the heating or perhaps cooling of foods, various other physical houses must be regarded because of their inbuilt relationship while using вЂвЂpure'' thermal properties pointed out, such as denseness and viscosity. Therefore , a grouping of thermal and related homes, known as thermophysical properties, give a powerful application for design and prediction of heat transfer operation during handling, finalizing, canning, and distribution of foods (Fig. 4. 1). Abundant information concerning thermophysical houses of foodstuff (Polley ou al., 1980; Wallapapan ou al., 1983; Choi and Okos, 1986; Rahman, 1995) is available towards the design industrial engineer. However , getting relevant data is usually the controlling part of the design of specific food operation, and the best answer may be the experimental determination. This chapter provides data and information intended for thermal method calculation intended for fruits and fruit goods, including a brief description of more commonly utilized methods for measurement and dedication of thermophysical properties.
4. 2 . THERMOPHYSICAL PROPERTIES' IDENTIFICATION
Thermophysical real estate include different types of parameters linked to the temperature transfer procedures present during fruit control. It is well known that warmth can be transferred by three ways: radiation, louage, and convection. Radiation is a transfer of heat by electromagnetic waves. The range of wavelength 0. 8вЂ“400 mm is referred to as thermal light, since this infrared radiation is quite readily 73
Fresh fruit Manufacturing
e (W/mв€’1/ Kв€’1)
a (m2/ sв€’1)
r (kg / mв€’3)
cp (kJ/kgв€’1/ Cв€’1)
m (Pa s)
Heat transfer properties
Figure 4. 1 ) Thermophysical houses associated to fruit finalizing.
absorbed and converted to heat energy. A body giving out or absorbing the maximum likely amount of radiant energy is known as a вЂвЂblack body. '' Energy emitted by a dark body is given by the StefanвЂ“Boltzmann law:
Q Вј sitting 4
wherever s may be the StefanвЂ“Boltzmann continuous; A the location of copy, and To the absolute temperature. For not any вЂвЂperfect'' black bodies, because real body are, Frequency. (4. 1) is fixed by since factor noted a emissivity (В«):
Queen Вј sВ«AT 4
Emissivity values of foods are inside the range 0. 5вЂ“0. 97 (Karel ain al., 1975). Conduction is a movement of heat by direct transfer of molecular strength within solids (for case in point, heating of any fruit pulp by direct fire through metal containers). Convection is definitely the transfer of heat by groups of molecules that move because of a Вґ
gradient of density or agitation (for example, the stirring of tomato puree). Heat copy may take place: (i) in steady-state method by keeping frequent the heat difference between two elements or (ii) under unsteady-state way when the temperature is continually changing. Computation of heat transfer under these conditions is extremely...
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