2: Ohmic Heating Flashcards

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1
Q

What is ohmic heating?

A
  • Ohmic heating is also known as resistance heating and involves direct contact of electrodes to the food.
  • The heat is generated based on electrical resistance.
  • Ohmic heating is ideal for liquid products.
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2
Q

What are the factors that affect resistance?

A
  • Temperature: Resistance decrease with increasing temp.
  • Direction of electric current
  • Physicochemical properties of food.
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3
Q

What are the factors that affect the efficiency of ohmic heating?

A
  • Electrical resistance of product (Low moisture content will be heated faster)
  • Ways of product flow
  • Residence time
  • Distance of electrodes
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4
Q

What is a product’s critical current density?

A

The maximum current density that can be carried by a product. Flash-over will likely occur if current density exceeds the critical limit.

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5
Q

Why is the design of an ohmic heater product specific?

A
  • Because different products will have different physicochemical properties, leading to differing heating efficiency.
  • Ohmic heater design is dependent of several factors such as, product type, flow rate, heating rate, holding time, power requirement, cost and type of current (AC or DC).
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6
Q

What are some advantages of ohmic heating?

A
  • Rapid and even heat transfer
  • High temperature can be achieved
  • No hot surfaces needed
  • High efficiency
  • Uniform heating of liquid products with particulates
  • Applicable to heating viscous liquids
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7
Q

Describe the techniques to achieve optimum ohmic heating in products containing solid particulates.

A
  • Pasteurize/sterilize liquid carrier and transfer the carrier to liquid containing suspended solid particulates.
  • Ensure the balance between particulates and carrier liquid to ensure homogenous suspension
  • Avoid turbulent flow for mixing. Turbulent flow introduces air bubbles into the liquid and reduces efficiency of heating.
  • Non-homogenous liquid will heat unevenly where temperature is higher near solids.
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8
Q

What are the product factors to be considered for ohmic heated products?

A
  • Moisture content
  • Size and shape
  • Solid to liquid ratio
  • Viscosity
  • pH
  • Thermal conductivity
  • Specific heat
  • Amount and type of electrolyte
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