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Consider the following statements: 1. The operation of a refrigerator unit at more than one temperature can be accomplished by using different throttling valves and a separate compressor for each ‘temperature range’. 2. The refrigerated space must be maintained above the ice point to prevent freezing. 3. In domestic refrigerators, the refrigerant is throttled to a higher pressure in the freezer followed by full expansion in the refrigerated space. Which of the above statements are correct? 

Consider the following statements: 1. The operation of a refrigerator unit at more than one temperature can be accomplished by using different throttling valves and a separate compressor for each ‘temperature range’. 2. The refrigerated space must be maintained above the ice point to prevent freezing. 3. In domestic refrigerators, the refrigerant is throttled to a higher pressure in the freezer followed by full expansion in the refrigerated space. Which of the above statements are correct?  Correct Answer 1 and 2 only

A multi-evaporator system with individual compressors and multiple expansion valves is shown below.

[ alt="F3 M.J Madhu 04.05.20 D1" src="//storage.googleapis.com/tb-img/production/20/05/F3_M.J_Madhu_04.05.20_D1.png" style="width: 437px; height: 306px;">

[ alt="F3 M.J Madhu 04.05.20 D2" src="//storage.googleapis.com/tb-img/production/20/05/F3_M.J_Madhu_04.05.20_D2.png" style="width: 361px; height: 266px;">

It can be seen that in the multiple evaporator system there is a separate compressor and expansion valve for each temperature range of the evaporator.

A simple refrigerator and freezer unit is shown in the figure below.

[ alt="F3 M.J Madhu 04.05.20 D3" src="//storage.googleapis.com/tb-img/production/20/05/F3_M.J_Madhu_04.05.20_D3.png" style="width: 403px; height: 348px;">

Most refrigerated goods have a high water content and the refrigerated space must be maintained above ice point to prevent freezing. The freezer compartment, however is maintained at about -18°C. Therefore the refrigerant should enter the freezer at about -25°C which would cause ice formation in the neighbourhood of the evaporator coils and dehydration procedure. This problem can be eliminated by throttling the refrigerant to a higher pressure (hence temperature) for use in the refrigerated space and then throttling it to the minimum pressure for use in the freezer. The entire refrigerant leaving the freezer compartment is subsequently compressed by a single compressor to the condenser pressure.

[ alt="F3 M.J Madhu 04.05.20 D5" src="//storage.googleapis.com/tb-img/production/20/05/F3_M.J_Madhu_04.05.20_D5.png" style="width: 292px; height: 227px;">

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