Unit 25 - (Ch. 113-114) Thermodynamics & Refrigerants

Which of the following is an example of an increase of latent heat? 1. water evaporating 2. ice melting 3. refrigerant evaporating 4. air cooling.

*1, 2, 3* 1. water evaporating 2. ice melting 3. refrigerant evaporating

The ratio, Refrigeration Effect/External Energy supplied is called? A) The refrigeration efficiency. B) The refrigeration ratio. C) The refrigeration capacity. D) The compressor efficiency. E) The coefficient of performance.

E) The coefficient of performance. ????????????

Refrigeration is the transfer of heat energy: A) to any substance B) from a lower temperature substance to a higher surrounding. C) any combination of all given answers. D) from any substance. E) from a higher temperature substance to a lower surrounding.

b * This is an incomplete answer.

Which of the following is/are NOT physical properties of refrigerants? 1. Toxicity. 2. Odour. 3. Leakage tendency. 4. Corrosiveness. 5. Miscibility. 6. Entropy. 7. Moisture Reaction. 8. Flammability/Explosiveness. 9. Density.

*4, 6 & 9* 4. Corrosiveness. 6. Entropy. 9. Density.

The refrigerating effect of a refrigerant is: A) equal to its latent heat of vaporization. B) greater than its latent heat of vaporization. C) less than its latent heat of vaporization. D) equal to its specific heat capacity. E) less than its net-refrigerating effect.

A) equal to its latent heat of vaporization.

The rate at which a system will remove heat from the refrigerated medium is defined as: A) coefficient of performance. B) net refrigerating effect. C) refrigeration capacity. D) compression ratio. E) differential efficiency.

B) net refrigerating effect.

The larger the difference between the temperature of the liquid refrigerant entering the evaporator and the actual evaporator temperature: A) the larger the refrigerating effect will be. B) the smaller the refrigerating effect will be. C) the larger the latent heat will be. D) the smaller the latent heat will be. E) the smaller the sensible heat will be.

B) the smaller the refrigerating effect will be.

For R-22, the refrigerant enters the evaporator as a saturated liquid and leaves as a saturated vapour at standard conditions. If 433.6 kJ of heat is removed every second, what is the flow of refrigerant in kg/min? A) 867.2 kg/min B) 44.6 kg/min C) 120 kg/min D) 2 kg/min E) 18.6 kg/min

C) 120 kg/min ???????????

Ammonia is explosive in concentrations between? A) 5 to 10 % B) 11 to 14 % C) 16 to 25 % D) 26 to 31 % E) 32 to 40 %

C) 16 to 25 % But according to Mathesongas.com, AFC International, and engineeringtoolbox.com this range is actually 15-28%.

The latent heat of fusion of ice is: A) the sensible heat required to melt ice. B) 335 kJ per 1 tonne. C) 335 kJ per 1 kg. D) the latent heat required to evaporate ice.

C) 335 kJ per 1 kg.

Group "A" refrigerants are: A) Non-flammable B) Low-flammable C) Low-toxicity D) Low-toxicity and flammable E) High-toxicity and flammable

C) Low-toxicity

It is not required that the ideal refrigerant should have: A) a non-corrosive action on metals. B) a non-flammable nature. C) a high sensible heat. D) an inoffensive odour. E) a low condensing pressure.

C) a high sensible heat.

Ammonia is the only commonly used refrigerant which has the physical property of _____________________. A) miscibility B) enthalpy C) flammability D) density E) low condensing pressure

C) flammability

Ammonia, as well as being toxic, is also: A) miscible. B) odourless. C) flammable. D) dense. E) a low pressure refrigerant.

C) flammable.

A rise of temperature within any substance is due to: A) total heat. B) conductive heat. C) sensible heat. D) latent heat. E) radiant heat.

C) sensible heat.

At standard refrigeration conditions, the condenser pressure would be ____________ kPa absolute or greater for the refrigerant ammonia to condense. A) 368 kPa B) 496 kPa C) 833 kPa D) 1166 kPa E) 1355 kPa

D) 1166 kPa

The amount of heat absorbed by water when it evaporates at atmospheric pressure is A) 99.63 kJ/kg B) 335 kJ/kg C) 417.46 kJ/kg D) 2257 kJ/kg E) 2675.5 kJ/kg

D) 2257 kJ/kg

Which one of the following is not a trait of an ideal refrigerant? A) A low boiling point at atmospheric pressure. B) A high latent heat capacity: that is, it should require a large amount of heat to convert it from a liquid to a gas after its boiling point has been reached. C) A fairly low condensing pressure. D) An offensive odour. E) A non-poisonous nature. F) A noncorrosive action on metals. G) A nonflammable and nonexplosive nature when mixed with air. H) A reasonable price.

D) An offensive odour.

The property which has to be known for the calculation of the size of control valves and piping etc. is __________________. A) Specific gravity. B) Enthalpy. C) Refrigerating effect. D) Density. E) Boiling point.

D) Density.

Ammonia refrigerants: A) have high sensible heat capacity. B) mix well with oil. C) are very expensive. D) are well suited for industrial refrigeration. E) are ideally suited to copper piping system.

D) are well suited for industrial refrigeration.

The ideal refrigerant should: A) have a low latent heat capacity. B) have a high boiling point. C) have high condensing pressure. D) be environmentally friendly. E) be easily detected because of its strong odour.

D) be environmentally friendly.

Leakage tendency is determined by: A) Operating pressure B) Viscosity C) Density D) Molecular mass E) All of the above

E) All of the above

One of the following is a thermodynamic property of heat: A) Entropy. B) Enthalpy. C) Density. D) Volume. E) All of the above.

E) All of the above.

Which of the following has the highest boiling point at atmospheric pressure? A) Ammonia B) Freon 12 C) Freon 22 D) Freon 113 E) Water

E) Water

R-22 refrigerant is: A) not miscible with oil. B) mostly used in packing plants. C) corrosive on copper. D) corrosive on aluminum. E) a heat transferring medium.

E) a heat transferring medium.

Which of the following thermodynamic properties apply to refrigerants? A) Entropy. B) Enthalpy. C) Density. D) Volume. E) all of the above

E) all of the above ??????????

The ability of a refrigerant to be dissolved into oil and vice versa is called _________________________. A) moisture reaction B) enthalpy C) density D) leakage tendency E) miscibility

E) miscibility

Which of the following refrigerants do not damage the ozone layer? A) R-11 B) R-12 C) R-22 D) R-113 E) R-141 F) R-717

F) R-717 (ammonia) CFC's are the worst, HCFC's second, HFC's (not listed) have minimal impact R-134a has largely replaced R-22 because of the reduced action on the ozone layer.

Identify the group for each of the following refrigerants: 1. R-11 is in group _______. 2. R-22 is in group _______. 3. R-134a is in group _______. 4. R-142b is in group _______. 5. R-152a is in group _______. 6. R-290 is in group _______. 7. R-600 is in group _______. 8. R-714 is in group _______. 9. R-764 is in group _______.

1. R-11 is in group A1. 2. R-22 is in group A1. 3. R-134a is in group A1. 4. R-142b is in group A2. 5. R-152a is in group A2. 6. R-290 is in group A3. 7. R-600 is in group A3. 8. R-714 is in group B2. 9. R-764 is in group B1.

In a refrigeration system: *(choose all that are correct)* 1. flashed refrigerant into vapour in an evaporator can be as high as 30%. 2. the flashed refrigerant takes part in the actual refrigeration process. 3. the flashed refrigerant amount depends on the temperature difference between the liquid refrigerant before the control valve and the evaporator. 4. the net refrigerating effect of a refrigerant must be calculated under the standard conditions.

3, 4 *Practice quiz shows this group as being correct. 1 should also be correct as per the statement on page 172

The refrigerant with the highest refrigerating effect per kg on any refrigerant is: A) Propane B) Ammonia C) Carbon Dioxide D) Sulfur Dioxide E) Water

??????????? E) Water

The amount of liquid that may flash into vapor can be as high as? A) 30% B) 40% C) 50% D) 60% E) 70%

A) 30%

Which of the following characteristics is common in all of the group B refrigerants? A) High toxicity. B) High flammability. C) Non-toxic but highly flammable. D) Low Toxicity. E) Low flammability.

A) High toxicity.

The standard refrigeration cycle is used to compare refrigerants and machines operating under comparable conditions. These standard conditions are: A) 1030 kPa and atmospheric pressure. B) 30°C condensing and -15°C evaporating. C) 30 kPa and atmospheric pressure. D) -30°C condensing and 15°C evaporating. E) 30 kPa and atmospheric temperature.

B) 30°C condensing and -15°C evaporating.

If the first column of a refrigeration table lists the saturation temperature of a refrigerant, which column will most likely list the saturation pressure? A) Column 1 B) Column 2 C) Column 3 D) Column 4 E) Column 5

B) Column 2

Which column in the refrigerant table lists the absolute pressure in kPa? A) Column 1. B) Column 2. C) Column 3. D) Column 4. E) None of the above.

B) Column 2.

The molecular mass of a refrigerant is a factor in which of the following refrigerant characteristics? A) Miscibility. B) Leakage tendency. C) Toxicity. D) Flammability. E) Explosiveness.

B) Leakage tendency.

Which of the following is NOT a requirement for an ideal refrigerant? A) A fairly low condensing pressure. B) Light in weight. C) A low boiling point. D) A non-toxic nature. E) A non-corrosive action on metals.

B) Light in weight.

The refrigerant that has the following characteristics is ______________? It is non-flammable, odorless, non-toxic, it does not have a corrosive effect on metal if water is present and at atmospheric pressure, it has a boiling point of approximately -40.6°C. A) Ammonia B) R-22 C) R-744R D) R-134a E) R-290

B) R-22

The enthalpy of a vapour is A) Sensible heat of a liquid. B) Sensible heat of a liquid plus latent heat of evaporation. C) Latent heat of evaporation.

B) Sensible heat of a liquid plus latent heat of evaporation.

The net refrigerating effect of a refrigerant is the amount of heat: A) discharged by the condenser. B) absorbed by the refrigerant in the evaporator. C) absorbed by the refrigerant in the condenser. D) discharged by the refrigerant in the evaporator. E) absorbed by the evaporator.

B) absorbed by the refrigerant in the evaporator.

A refrigerant in the "B" Group that is used more than others in its group in refrigeration systems is ______________. A) R-290 B) ammonia C) R-134a D) R-22 E) CO2

B) ammonia

If moisture is present in a refrigerant it is most likely to form ice in the ____________________________. A) condenser B) expansion valve C) receiver D) compressor suction E) evaporator

B) expansion valve

Because of a ruptured ammonia tank, the concentration of ammonia gas in a room exceeds 3%. The wearing of a gas mask, as the only protective device by a person entering a room: A) is recommended, because the gas mask alone is sufficient protection. B) is not recommended, because ammonia will severely irritate the skin. C) is not recommended, because the gas mask is not effective at concentrations above 3%. D) is not recommended, because ammonia is flammable.

B) is not recommended, because ammonia will severely irritate the skin. ?????????????