# Shared Flashcard Set

## Details

Ch 1 Heat Transfer
RETA BK 2-Ch01
17
Mechanical Engineering
Professional
06/12/2018

Term
 1. Which of the following factors listed below does not affect heat transfer? a. Temp difference b. Surface area c. Thermal conductivity d. Density
Definition
 d. Density 1-2
Term
 2. An example of a poor conductor of heat is a. aluminum tubing b. schedule 40 steel pipe c. wood d. water.
Definition
 c. wood 1-3
Term
 3. Thermal conductivity ('k') is a. exactly the same value for any metal b. the number of BTUs that will pass in one hour through a material 1" thick with an area of 1 ft2 if the temp difference from one side to the other is 1F. c. a measure of the total energy (heat content) per pound of refrigerant measured in BTUs d. a relationship between heat and temp that is useful in determining discharge temps.  it is the heat moved into or out of the process, divided by the absolute temp in BTUs/lb/R
Definition
 b. the number of BTUs that will pass in one hour through a material 1" thick with an area of 1 ft2 if the temp difference from one side to the other is 1F. 1-6
Term
 4. Which is not a common source of fouling of a heat exchange surface? a. water b. oil c. frost d. dirt
Definition
 a. water 1-9, 10
Term
 5. Which statement is true? a. the higher the k factor, the greater the thermal conductivity b. the lower the k factor, the greater the thermal conductivity c. the higher the k factor, the lower the thermal conductivity d. the k factor is not associated with thermal conductivity
Definition
 a. the higher the k factor, the greater the thermal conductivity 1-6
Term
 6. Optimum u factor for the given material that the heat exchanger is made of results when a. there is no impeding substance such as ice, dirt or oil on the surfaces of the heat exchanger tubes b. maximum airflow across the evap is achieved c. the system is operating with the design recirculation ratio d. the system is maintaining temp.
Definition
 a. there is no impeding substance such as ice, dirt or oil on the surfaces of the heat exchanger tubes 1-8
Term
 . When air flow is decreased across a heat exchange surface, cooling capacity is a. reduced b. increased c. not changed because area is not changed d. not changed because evaporator temp is not changed
Definition
 a. reduced 1-10
Term
 8. Centrifugal fans have an advantage over propeller fans in that they ________ than prop fans a. require less physical space b. consume more hp per CFM of air moved c. are quieter d. have fewer components to maintain
Definition
 c. are quieter 1-12
Term
 9. The operating engineer a. cannot change the k factor of the metal but has some control of the overall u factor for the evap as a unit b. can increase k factor by increasing air velocity over the evap and has some control of the overall u factor for the evap as a unit c. should allow frost to collect on the evap to increase k factor d. can increase k factor by starting another compressor
Definition
 a. cannot change the k factor of the metal but has some control of the overall u factor for the evap as a unit 1-7
Term
 10. The limiting factor of an evps capacity that the operator cannot control is a. suction temp b. suction pressure c. evap size d. refrigerant liquid feed flow
Definition
 c. evap size 1-9
Term
 11. The best way to keep an evap from being affected by oil build-up is to a. operate the system at the correct evap temp b. periodically remove oil from the oil collection points c. set hot gas defrost cycle for a minimum of 30 minutes d. increase air flow across the evaporators
Definition
 b. periodically remove oil from the oil collection points 1-9
Term
 12. The effectiveness of a heat transfer surface depends on several factors. One factor the operator has control over is: a. Evaporator surface area b. material the evaporator is made of c. type of fans used d. cleanliness of the evaporator
Definition
 d. cleanliness of the evaporator 1-9
Term
 13. One advantage of using axial type fans is a. quieter operation b. they require less motor horsepower per CFM c. they can move air further across the space to be cooled d. they can work against a higher static pressure.
Definition
 b. they require less motor horsepower per CFM 1-12
Term
 14. Which of the following is not a result of scale build-up on a condenser coil? a. reduced heat transfer b. increased operating cost c. increased u value d. increased condensing temperatures
Definition
 c. increased u value 1-13
Term
 15. If R value is doubled, what will happen to the heat transfer rate (assuming the temperature difference and the area do not change)? a. the rate of heat that is transferred will be double b. the rate of heat that is transferred will be cut in half c. the rate of heat transfer does not change d. the conductance is doubled so the heat transfer rate is increased
Definition
 b. the rate of heat that is transferred will be cut in half 1-4
Term
 16. What happens to the theoretical capacity of an evaporator in a 0F freezer if the ammonia evaporating pressure is dropped from 8.96 psig to 6.11 psig? a. the capacity of the evap is reduced by 50% b. the capacity of the evap is doubled c. the capacity of the evap is not changed d. the capacity of the evap is increased by 50%
Definition
 d. the capacity of the evap is increased by 50% 1-6
Term
 . Damaged insulation on the suction line in an ammonia refrigeration system will a. not change the efficiency of the system because the suction pressure will not change b. cause efficiency loss and potential damage to the suction line c. look bad but will not cause any major problems d. cause an efficiency loss but will not cause any other problems.
Definition
 b. cause efficiency loss and potential damage to the suction line 1-15, 16
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