Refrigeration Trade Theory N3 — Document
August 2018 — N3 — Refrigeration Trade Theory
N3
2018
Nated Engineering
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Q1— Section header —
1.1Indicate whether the following statements are TRUE or FALSE. Cho ose the answer and write only 'True' or 'F alse' next to the question number (1.1.1
1.1.10\the ANSWER BOOK.
1.1.1The COP of a domestic refrigerator is less than 1.
1.1.2Critical temperature is the temperature above which a gas will immediately liquefy.
1.1.3Presence of moisture i n a refrigerant affects the working of the expansion valve.
1.1.4A thermostatic valve is used as an expansion device by a domestic refrigerator working on the vapour compression cycle.
1.1.5The bank of tubes at the back of a domestic refrigerat or is condenser tubes.
1.1.6Condensing temperature in a refrigerator is the temperature at which refrigerant gas becomes liquid.
1.1.7In a flooded evaporator refrigerator, an accumulator at the suction of the compressor is used to superheat the vapour.
1.1.8he latent heat of vaporisation of a refrigerant increases t lower temperatures and pressures
1.1.9A refrigerant should be a good electric conductor.
1.1.10
1.2Explain the following two refrigeration systems.
1.2.1Compound (4\
1.2.2Cascade (6\ [20] 1104158320
Q2— Section header —
2.1Identify each of the following refrigeration components by writing th e answer next to the letter (A \the ANSWER BOOK
2.2Draw a neat, labelled sketch of an evaporative condenser. (12\ [19
Q3— Section header —
3.1The cooling capacity of a refrigeration plant is 50 kW. The coefficient of performance of the plant is 5. The refrigerant enthalpy gain in the evaporator is 140 kJ /kg
3.1.1The refrigerant mass flow rate (2\
3.1.2The work of compression (2\
3.1.3The power required by the compressor motor if the efficiency is 85% (2\
3.1.4The total amount of heat reje cted by the condenser (2\ 11041583
3.2A defrost thermostat is a commonly installed component in any refrigeration system. Answer the following questions relating to a defrost thermostat
3.2.1What is the primary f unction of a defrost therm ostat? (2\
3.2.2List the THREE variables a defrost thermostat works on and briefly explain how it works when using each variable. (3 2\ (6\
3.3Steel is commonly used fo r water piping in refrigeration. ame THREE t ypes of steel piping that can be used. (3\
3.4Give ONE disadvantage of a constant pressure expansion valve. (2\ [21
Q4— Section header —
4.1State THREE methods that are used to control capacity on DX evaporators. (3\
4.2List FOUR basic functi ons of refrigerant oils (4\
4.3State the function of a heat exchanger as well as where it should be installed in a refrigeration system. (6\
4.4Name THREE possible causes of the following condition and state the corrective measures to be t aken: A c
4.5Give ONE purpose of item E in FIGURE 1 in refrigeration. (1\ [20 11041583
Q5— Section header —
5.1Refer to FIGURE 2 and answer the following questions.
5.1.1Name the type of pump shown in FIGURE 2. (1\
5.1.2Label the parts in dicated on FIGURE 2 by writing the answer next to the letter (A E\the ANSWER BOOK. (5\ 11041583
5.2The diagram in FIGURE 3 is applicable to the selection and operation of centrifugal pumps. Label the curves A, B and C and point D i ndicated on the diagram by writing the answer next to the letter (A
5.3Refer to FIGURE 4, the Crankcase Press ure Regulator and answer the following questions.
5.3.1A Crankcase Pressure Regulator (CPR\ is an outlet pressure regulator and will not allow the crankcase pressure to rise above a predetermined level. Give FIVE considerations that affect its selection for installation and use on a particular refrigeration
5.3.2Figure 4 below shows schematic of a Crankcase Pressure Regulat or (CPR\. Label the parts by writing the answer next to the letter (A E\the ANSWER BOOK. (5\ FIGURE
Mark Allocation
Total100 marks
Sections20 + 20 = 40 marks
Paper information
TitleDocument
SubjectRefrigeration Trade Theory
LevelN3
Document typeQuestion paper
Year2018
MonthAugust
Pages15
Downloads2
Examination context
Decade2010s
Years ago8y
SeasonWinter (SH)
Start dayWednesday
Exam periodAugust 2018
Days since exam2,992
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