DOMRAC 1 PART 2

• Refrigeration


  The absence of heat
• Btu


  British thermal unit
• Conduction


  A method of heat transfer in which heat moves from one molecule of a substance to another molecule of the same or different substance
• Convection


  A method of heat transfer that occurs in fluid, where the molecules are free to move around
• Radiation


  A method of heat transfer which is the same as light waves
• Btu is the unit of heat
• Cold is the absence of high temperature
• Convection is a method of heat transfer that occurs in fluid
• Radiation is a method of heat transfer that is the same as light waves
• Btu stands for British thermal unit
• Heat


  Moves from a warm substance to a cooler substance
• Btu


  The amount of heat energy required to increase the temperature of one pound of water by one degree Fahrenheit
• Conduction


  Heat moves by passing from one molecule of a substance to another molecule of the same or different substance
• Convection


  Heat transfer that occurs in fluid, where the molecules are free to move around
• Radiation


  Heat transfer which flows through wave motion like light waves, where energy is transmitted from one body to another
• Specific heat


  The amount of heat needed to raise the temperature of one pound of a substance by one degree Fahrenheit
• Not all substances have the same specific heat
• Specific heat of various substances


  • Most fruits and vegetables: 0.92 Btu/lb
  • Beef: 0.77 Btu/lb
  • Fish and Poultry: 0.82 Btu/lb
  • Lamb/Pork: 0.66 Btu/lb
  • Milk: 0.92 Btu/lb
  • Butter: 0.64 Btu/lb
  • Egg: 0.76 Btu/lb
• Calculating heat required to change temperature

  1. Q = W x S (t2 - t1)

  2. Where: Q = heat (Btu), W = weight (lb), S = specific heat (Btu/lb), t2 = final temperature, t1 = initial temperature
• Sensible heat


  Heat added or removed from a substance that can be measured by a change in temperature, without changing state
• Latent heat


  Heat added or removed from a substance to cause a change in state without a change in temperature
• How heat transferred to one substance to another substance?
• Pressure is defined as the force per unit area (P = F/A).
• Psi

  Pound per square inch
• Water boils at normal atmospheric pressure of 14.7 Psi, with a temperature of 212'F. When it is under the pressure of 20 Psi, its boiling point will become 258'F, while in a vacuum of 20 inches of mercury will boil at 180'F.
• Pressure and temperature relationship chart R-12 and R-22 in ratio
• What is pressure?
• How pressure and heat is being combined
• Unit of pressure


  Psi