Thermal Food Engineering Operations. NITIN KUMAR

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      1 Surface temperatures of heating and receiving bodies or materials,

      2 Surface characteristics of both bodies or materials,

      3 Shapes of the emitting and receiving materials.

      Quantities indicate infrared radiations are the perfect source of energy for heating purposes. They indicate the factors such as larger heat transfer capacity, heat penetration directly into the product, no heating of surrounding air, and fast process control. A perfect balance required for optimal heating between the body and surface heating is attained with IR. The parameters that are important to control to achieve optimal heating results are radiator temperature, infrared penetration characteristics, radiator efficiency, and infrared reflection or absorption properties.

       1.3.1.2 Advantages of IR Heating

      There are several advantages of IR over traditional heating techniques: [1].

      Instant heat: Electric IR system forms heat instantly so there is no need for heat build-up.

      Reduced operating costs: The energy can reach 50%, depending upon the insulation, types of construction, and other factors. Furthermore, operations maintenance is limited to the cleaning of reflectors and heat source changing.

      Clean and safe: Operating IR is a low-risk task and there is no production of by-products.

      Zone control: The IR energy is absorbed only where it is directed and does not propagate. Other advantages of IR are as follows:

      1 Quick heating rate

      2 Shorter residence time

      3 Uniform drying temperature

      4 A high degree of process control

      5 Higher thermal efficiency

      6 Cleaner work environment

      7 Alternate source of energy

      The utilization of IR technique in the food sector is still developing; many attempts are continuously growing for the development of IR technologies and the future research is focusing on process control and equipment design development, expanding the areas of applications of IR heating and understanding the interaction between heating process and product characteristics.

       1.3.1.3 Applications of IR Heating

There are wide applications for IR (infrared radiation) which include medical, paper industries dye, automobile, and others. Table 1.1 discusses the several application of IR heating [1]. In industrial applications, medium to long-range wavelengths seem to be beneficial, for all materials to be heated or dried give the largest absorption in the 3-10 mm region. Moreover, the applications in short waves are continuously evolving. Applications of IR are mostly within the area of food for drying and many other processes during the period from the 1950s to the 1970s from the Soviet Union, the United States, and the Eastern European countries. During the 1970s, much research was performed about industrial frying or meat products cooking and the utilization of near-infrared (NIR) techniques is initiated [28, 43]. In the 1970s and 1980s, several types of research were carried out to apply this technique in the sector of food, mostly at [Swedish Institute of Food and Biotechnology] and gained a set of knowledge. Recent work is experimental in nature and performed in Japan, Taiwan, and several other countries. Applications are mostly from areas such as dehydration, drying of vegetables, fish, rice, roasting of coffee, cocoa, and cereals, heating of floor, frying of meat, baking of pizza, biscuits, and bread, enzymes, and pathogens inactivation. Also, for thawing, blanching, sterilization, pasteurization of packing materials, and surface pasteurization, these techniques have been used.

      The major effects on food involve the quick heating of food surfaces sealed in moisture and aroma compounds. Variation to components of food surfaces is equivalent to those that happen during baking.

      1.3.2 Microwave Heating

       1.3.2.1 Principal and Mechanism

      With the increasing demand for healthy foods, there is a repeated effort given to enhance and optimize different processing techniques in food, to meet the expectations of consumers. With the advancement of emerging technologies, microwave energy has become an indispensable part of every household system. The use of microwave has expanded from heating and defrosting to thawing, blanching, sterilization, drying, etc., in food industries [20, 69]. Microwave is electromagnetic waves with a frequency which ranges from 300 Mhz to 300 GHz. Frequency of microwave used for domestic purposes is 2.45 GHz, whereas the frequency for industrial purposes is 915 MHz [8].

Table 1.1 Applications of Infrared heating: [1].

Industry	Methods
Agriculture	Incubation and warming
Bottling	Drying
Glass	Drying, curing the varnish or paint on back—mirrors and tempering layers
Medical-applications	Incubation and warming
Environmental chambers	Heating
Food	Toasting, cooking, food warming, drying, broiling, and melting
Pharmaceutical	Drying water from powder—tablets
Metal treatment	Preheating—aluminum; steel
Paper	Laminating Calendaring—rolls Adhesive—labelsDrying water from—towels
Paint	Primer, topcoat alkyd, acrylic—steel panels, Drying—bicycles, vehicles bodies, aluminiumbodies
Textiles	Moisture elimination—carpets Latex and PVC backingMoisture elimination from dyes
Plastics	Laminating Annealing FormingEmbossing

Microwave is a varying magnetic field that generates heat on interaction with, and absorption by, certain dielectric materials, and with the positioning of the direction of the electric field, the native thermal motion of the polarity molecule changes [26]. Water, the dominant polar molecule, consists of separated molecules of an oxygen atom with a negative charge and hydrogen atom with a positive charge which combinedly structure into an electric dipole. When these dipoles fluctuate swiftly back and forth from positive to negative in the direction of the electric field numerous times per second, these express reversals produce frictional heat. This implies that the polar molecules in food play a vital role in the heating performance of food in the СКАЧАТЬ