09. Industrial Processes - Heating

dielectric heating

It is also sometimes called high frequency capacitance heating.

TRUE

(TRUE or FALSE) If non-metallic materials i.e., insulators such as wood, plastics, china clay, glass, ceramics etc are subjected to high voltage AC current, their temperature will increase in temperature is due to the conversion of dielectric loss into heat.

10-50MHz

What is the range of the supply frequency required for dielectric heating?

20 kV

What is the applied voltage for dielectric heating?

50%

What is the overall efficiency of dielectric heating?

TRUE

(TRUE or FALSE) The dielectric loss is dependent upon the frequency and high voltage. Therefore, for obtaining high heating effect, high voltage at high frequency is usually employed.

U.S. Patent 2,147,689 (application by Bell Telephone Laboratories, dated 1937)

It states "This invention relates to heating systems for dielectric materials and the object of the invention is to heat such materials uniformly and substantially simultaneously throughout their mass. It has been proposed therefore to heat such materials simultaneously throughout their mass by means of the dielectric loss produced in them when they are subjected to a high voltage, high frequency field."

U.S. Patent 2,147,689 (application by Bell Telephone Laboratories, dated 1937)

This patent proposed radio frequency (RF) heating at 10 to 20 megahertz (wavelength 15 to 30 meters).

TRUE

(TRUE or FALSE) A changing electric field across the material causes energy to be dissipated as the molecules attempt to line up with the continuously changing electric field.

TRUE

(TRUE or FALSE) The energy you get from discharging a capacitor will be slightly less than the energy it took to charge it - the difference going into heating the capacitor.

TRUE

(TRUE or FALSE) With increase in electric field strength the degree of polarization is increased. At a certain value of electric fields all electric dipoles align themselves. In this condition the dielectric material is said to be saturated.

• Frequency

• Relative permittivity of dielectric

• Area of the electrode plates

• Power factor

• Square of the Supply Voltage

The amount of heat generated in dielectric heating is directly proportional to these factors (HINT: FRAPS)

the distance between two electrodes

The amount of heat generated in dielectric heating is inversely proportional to?

TRUE

(TRUE or FALSE) RF dielectric heating is increasingly used as a way to kill pests in certain food crops after harvest.

TRUE

(TRUE or FALSE) RF heating can heat foods more uniformly than with microwave heating.

TRUE

(TRUE or FALSE) RF Heating is used in the wood industry to cure glues used in plywood manufacturing

TRUE

(TRUE or FALSE) RF heating can be used to speed up drying lumber.

short wave diathermy machines

It is used as a form of physical therapy and in surgical procedures.

Thermex dielectric heating systems

These are widely acclaimed for their rugged dependability and engineering superiority.

induction heating

It is caused by eddy currents in imperfect dielectrics.

dielectric heating

It depends on the electrostatic effect.

200-500kHz

What is the order of operating frequencies in induction heating.

1-50MHz

What is the range of operating frequencies in dielectric heating.

induction heating

It is termed surface heating.

dielectric heating

It is termed volume heating.

TRUE

(TRUE or FALSE) The cost of equipment required in induction heating is low.

TRUE

(TRUE or FALSE) The cost of equipment required in dielectric heating is comparatively high.

TRUE

(TRUE or FALSE) A microwave open is also known as microwave.

microwave oven/heating

It is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation. These radiations are in the microwave spectrum.

TRUE

(TRUE or FALSE) In microwave heating, the process involves polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating.

TRUE

(TRUE or FALSE) In microwave heating, intermolecular friction gives rise to heat and that heat is utilized for heating the substance itself.

TRUE

(TRUE or FALSE) MIcrowave ovens heat food quickly and efficiently.

TRUE

(TRUE or FALSE) A microwave oven heats food by passing microwave radiation through it.

TRUE

(TRUE or FALSE) Microwaves are a form of non-ionizing electromagnetic radiation with a frequency higher than ordinary radio waves but lower than infrared light. This oven use frequencies in one of the ISM (industrial, scientific, medical) bands.

The frequency used is about 2.45 GHz and a wavelength of 12.2 cm.

(TRUE or FALSE) What is the frequency and wavelength used in microwave heating?

Ionizing radiation

It can remove tightly-bound electrons from atoms, causing them to become charged, is less risky in very tiny amounts (such as x-rays) but can cause problems when exposure is high (think burns and even DNA damage).

TRUE

(TRUE or FALSE) Microwaves emit non-ionizing radiation.

non-ionizing radiation

It is a type of radiation that has enough energy to move atoms around within a molecule but not enough to remove electrons.

TRUE

(TRUE or FALSE) Because microwaves interact directly with the contents of a reaction mixture, energy transfer occurs more efficiently than with conventional heating techniques

dipolar rotation

A molecule rotates back and forth constantly, attempting to align its dipole with the ever-oscillating electric field; the friction between each rotating molecule results in heat generation.

ionic conduction

A free ion or ionic species moves translationally through space, attempting to align with the changing electric field. Like in dipolar rotation, the friction between these moving species results in heat generation

microwave furnace/heating

• energy conversion

• internal heating

• inside to outside

• material dependent

• highly efficient

conventional furnace/heating

• energy transfer

• external heating source

• heat flow: outside to inside

• material independent

• energy losses

• Pasteurization

• Flash pasteurization

• Microwave chemistry

• Sterilization

• Food preservation

• Microwave thermotherapy, use of microwave

  heating to treat cancer

microwave heating applications:

microwave hyperthermia - tumor and cancer treatment

In 1990, Dr. Alan J. Fenn, an electrical engineer at the Massachusetts Institute of Technology’s Lincoln Laboratory developed a concept for heating deep tumors by means of adaptive microwaves.

TRUE

(TRUE or FALSE) Microwave energy is very effective in heating cancerous tumors, because tumors typically have high-water content. Such tissue heats very rapidly when exposed to high-power microwaves.

TRUE

(TRUE or FALSE) Microwave energy generated by the magnetron (Domestic microwave ovens operate at a frequency of 2450 MHz with a power usually ranging from 500 to 1100 watts) is transferred to the oven cavity through a waveguide section A mode stirrer spreads the microwave energy more or less evenly throughout the oven.

Center for Devices and Radiological Health (CDRH)

CDRH meaning

FDA through its Center for Devices and Radiological Health (CDRH)

It sets and enforces standards of performance for electronic products to assure that radiation emissions do not pose a hazard to public health.

Federal Standard (21 CFR 1030.10)

It limits the amount of microwaves that can leak from an oven throughout its lifetime to 5 milliwatts (mW) of microwave radiation per square centimeter at approximately 2 inches from the oven surface. This limit is far below the level known to harm people. Microwave energy also decreases dramatically as you move away from the source of radiation. A measurement made 20 inches from an oven would be approximately 1/100th of the value measured at 2 inches from the oven.

TRUE

(TRUE or FALSE) Microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn.

TRUE

(TRUE or FALSE) Two areas of the body, the eyes and the testes, are particularly vulnerable to RF heating because there is relatively little blood flow in them to carry away excess heat. Additionally, the lens of the eye is particularly sensitive to intense heat, and exposure to high levels of microwaves can cause cataracts.