2. Radiation heat transfer, its governing laws and its
application in Food ProcessingPresented by: Malathi A.N Jr M.tech
Dept. of PFE CAE Raichur. Under the guidance of : Dr.Ramchandra.C.T
2 3. Introduction Heat transfer It is transfer of thermal energy
from one place to another. When an object is at a different
temperature from its surroundings, heat transfer occurs so that the
body and the surroundings reach the same temperature at thermal
equilibrium.3Such spontaneous heat transfer always occurs from a
region of high temperature to another region of lower temperature
as required by the second law of thermodynamics. 4. Modes of Heat
Transfer: 1) Conduction, or heat transfer by molecular scale
vibration and rotation. 2) Radiation, or heat transfer by photons.
3) Convection, or heat transfer by large-scale fluid motion (liquid
or gas).4 5. Conduction Heat conduction occurs as hot, rapidly
moving or vibratingatoms and molecules interact with neighboring
atoms and molecules, transferring some of their energy (heat) to
these neighboring atoms. In other words, heat is transferred by
conduction whenadjacent atoms vibrate against one another, or as
electrons qkAdTx move from one atom dx another. to5 6. Convection
This is the process of moving heat around by moving themolecules
that contain the heat. E.g. Boiling water in a pan produces
convection cells. The waterat the bottom gets heated and it rises
to the top, forcing the cool water down, where it gets heated. The
water at the top sends its heat into the air so the
cycleiscontinuous. q = h A (Tf-Ts) q=amount of heat h=surface heat
transfer coefficient6 7. Radiation Thermal radiation is the
transfer of heat energy throughempty space by electromagnetic
waves. No medium is necessary radiation takes place even in and
through a perfectvacuum.For instance, the energy from the Sun
travels through the vacuum of space before warming the earth.
Radiation is the onlyform of heat transfer that can occur in the
absence of any form of medium 7(i.e., through a vacuum). 8. If
consider any body totalincident radiation on the body is absorbed,
partly reflected and partly emitted.Incident radiationReflected
radiation As per the nature of body itcan be8classified into four
types Opaque Body t = 0 ; a + r =1 Black Body a =1 ; t =0; r=0
White Body r=1 ; a=0; t=0 Transparent BodyAbsorbed
radiationTransmitted radiation 9. Reflectivity () is defined as the
ratio of reflectedenergy to the incident energy. Transmissivity ()
is defined as the fraction of the incident energy that is
transmitted through the object. Absorptive () is defined as the
fraction ofthe incident energy that is absorbed by the object.
Emmisivity ()The ratio of theemissive power of real body (E) to the
blackbody emissive power ( Eb at the same temperature is the
hemispherical emissivity of the surface. E b9 10. The radiation
laws for black-body radiation 1.Plancks law 2.Wiens
law3.Stefan-Boltzmann law10 11. Plancks Law This law governs the
intensity of radiation emitted byunit surface area into a fixed
direction (solid angle) from the blackbody as a function of
wavelength for a fixed temperature. 2 hc 2 1 E ,T hc 5 ekT1 h =
6.625 X 10-27 erg-s (Planck Constant) K = 1.38 X 10-16 erg/K
(Boltzmann Constant) C = Speed of light in vacuum11Max Planck
1858-1947 12. Wien's Law:Displacement Atany given wavelength, the
black body monochromatic emissive power increases with temperature.
The wavelength at which the monochromatic emissive power is a
maximum is found by setting the derivative of Plancks Equation with
respect to K TT2897 . 8 mKWien Where k is a constant equaling
2897.8mk (1864-1928)12max 13. Stefan-Boltzmann Law The radiation
energy per unit time from a blackbody is proportional to the fourth
power of the absolute temperature and can be expressed with
Stefan-Boltzmann Law asq = T4 A Where, q = heat transfer per unit
time (W) = 5.6703 10-8 (W/m2K4) Stefan-Boltzmann Constant T =
absolute temperature Kelvin (K) A = area of the emitting body (m2)
13Josef Stefan 1835-1893Ludwig Boltzmann 1844-1906 14. Application
of Radiation in Food Processing14 15. Approval of radiation
processing of food in India In 1994 Government of India amended
Prevention ofFood Adulteration Act (1954) Rules, and
approvedirradiation of onion, potato and spices for domestic
market. Additional items were approved in April 1998 and2001. 15
16. What is radiation processing? Radiation processing is
controlled application of energy ofshort wave length radiations of
the electromagnetic spectrum
knownasionizingradiationsandincludesgammarays, accelerated
electrons and X-rays to have desired effecton the product. About
5,00,000 tons of food items are irradiated per year16world wide in
over 40 countries. 17. Uses of radiation processing? Some of the
major objectives of radiation processing are:1.Sterilization of
medical and packaging products 2.Insect disinfestations of food
products 3.Inhibition of sprouting in tubers, bulbs and rhizomes
4.Delay in ripening of fruits 5.Enhancement in shelf life by
destruction of spoilage microbes in foods 6.Elimination of
pathogens and parasites in foods 17 18. Food Irradiation Exposure
of foods to ionizing radiation in form ofgamma radiation, X-rays
and electron beams to destroy pathogenic microorganism SI unit of
irradiation is Gray (Gy). 1Gray = 1 joule of energy absorbed per kg
of food material.18 19. Applications low Dose Applications (up to 1
kGy)1.Sprout inhibition in bulbs and tubers 0.03-0.15 kGy 2.Delay
in fruit ripening 0.25-0.75 kGy 3.Insect disinfestation parasites
0.07-1 kGy19and elimination of food borne 20. Medium Dose
Applications (1 kGy to 10 kGy)1.Reduction of spoilage microbes to
prolong shelf-life of meat, poultry and seafoods under
refrigeration 1.53 kGy 2.Reduction of pathogenic microbes in fresh
and frozen meat, poultry and seafood's 37 kGy. 3.Reducing the
number of microorganisms in spices 10 kGy. 20 21. High Dose
Applications (above 10 kGy)1.Sterilization of packaged meat,
poultry, and their products that are shelf stable without
refrigeration 25.00-70.00 kGy 2.Sterilization of Hospital diets
25.00-70.00 kGy21 22. Technologies 1. Electron irradiation 2.
X-rays irradiations 3. Gamma irradiations Electron irradiation
Electron irradiation uses electrons accelerated in an electric
field to a velocity close to the speed of light. Electrons are
particulate radiation and, hence have cross section many times
larger than photons, so that they do not penetrate the product
beyond a few inches, depending on product density.22 23. Gamma
irradiation : Gammaradiation is a part of electromagnetic spectrum.
The radiation is obtained through the use of radioisotopes.
(cobalt-60 or, caesium-137). Presently,caesium-137 is used only in
small hospital units to treat blood before transfusion to prevent
Graft-versus-host disease. Food irradiation using Cobalt-60 is the
preferred23method by most processors, because the deeper
penetration enables administering treatment to entire industrial
pallets reducing the need for material handling. 24. X-ray
irradiation : Similar to gamma radiation, X-rays are photon
radiation of awide energyspectrum and an alternative to
isotopebased irradiation systems X-ray irradiators are scalable and
have deep penetrationcomparable to Co-60. They also permit dose
uniformity. Nominal X-ray energy is usually limited to 5 MeV. USA
has provisions for up to 7.5 MeV, which increases 24conversion
efficiency 25. Effect of Irradiation on Microbes The high energy
rays of irradiation directly damagethe DNA of living organisms,
inducing crosslinkages and other changes that make an organism
unable to grow or reproduce. When these rays interact with water
molecules in anorganism, they generate transient free radicals that
can cause additional indirect damage to DNA. 25 26. Effectiveness
and Benefits of Irradiation From the obvious improvements in food
safety through destruction of pathogens, irradiation provides other
benefits. Some of these contributions include increasing shelf life
of meats Improving quality of fruits and vegetablesProviding a
suitable alternative to chemical treatments (e.g., methyl bromide
and ethylene oxide), especially for decontamination of fruits and
vegetables.Providing economic savings due to reduced incidence of
26illness 27. Un irradiated productsirradiated products Straw
BerriesVegetablesCherries 27 28. It kills bacteria's , fungus
,insects . It will not harmful to human health. Delay in ripening
and sprouting of vegetable. Irradiated materials are used
forpackaging offood. No reaction with the packaging when stored. It
will not effect the nutritional value. Foods can be treated after
packaging Perishable foods can be kept longer without noticeable
quality loss. 28 29. 1. The process is costly 2. There will be risk
to human beings exposing to the radiations 3. Large energy sources
is required .29 30. Radiation process spices Most spices get
heavily contaminated with microbes, including pathogenic bacteria
during processing while drying in open. Since radiation processing
does not involve increase in temperature and humidity. It extends
shelf life of spices in packed form retaining colour, aroma and
other sensory properties and at the same time eliminates bacteria
and microbes without leaving any chemical residues.30 31. Non
Ionizing Radiations Non-ionizing radiationrefers to any type of
electromagnetic radiation that does not carry enough energy per
quantum to ionize atoms or molecules. Ultraviolet,visiblelight,
infrared, microwave, radio waves are allexamples of non-ionizing
radiation. 31 32. 32 33. Far Infrared Radiation FIRheating can be
classified into 4 majorcategories: baking, drying, thawing and
pasteurization Using FIR heating, baking time can be
shortened,energy consumption can be reduced, and nutrition and
appearance can be better preserved.
FIRheatinghelpsreducebeta-carotenechlorophyll degradation in the
heating process. 33and 34. Advantage s FIRheating achieved more
uniform surface heating than air convection heating. FIR at 80C was
found to be the best dryingcondition with a good compromise between
drying time and colour of the product.34 35. MICROWAVE HEATING MW
are electromagnetic waves generated bymagnetrons and klystrons.
Frequency 300MHz Wavelength from 1mm to 1m industrial heating
purposes the availablefrequencies are 915 and 2450MHz35 36.
Microwaves are absorbed and penetrate the food. The energy of these
electromagnetic radiationsexcite the water molecules (in food)
which bear a positive electrical charge in one position and a
negative charge at another position of the molecules (dipole). When
the electric field of the microwave interact with the dipole, the
water molecules begin to vibrate very rapidly in food. These
vibration produces a friction that creates heat with in the food,
thereby cooking it.36 37. Applications Dehydration Pasteurization
Sterilization Cooking Baking37 38. How can radiation processed
foods be identified in the market ? Irradiatedfood cannot be
recognized by sight, smell, taste or touch. Codex Alimentarius
Commission has endorsed a green irradiation logo.38 39. As per the
PFA (Fifth Amendment) Rules, 1994, allpackages of irradiated foods
to be marketed in India will be labeled with this logo, along with
the words Processed by Irradiation method , and the date of
irradiation, license number of the facility and the purpose of
irradiation. Consumers will have a free choice to buy radiation
processed or non- radiation processed commodity.39 40. 40
