Class 4 (4th Engineer) MEP 📅 Dec 2023

Exam Question

(a) Sketch, describe and explain the operation of the domestic refrigeration system of a ship using one of the HFC as refrigerant. What kind of maintenance is essential for the system. (8)

(b) Describe the causes for the following in the domestic refrigeration system: (8)

(i) Frequent cut-in and cut-off of the compressor

(ii) Lub oil low pressure cut out of the compressor

(iii) High pressure cut out of the compressor

(iv) Frosting on the compressor suction side

Reference Answer

### (a) Domestic Refrigeration System: Sketch, Operation, and Maintenance
**System Description and Operation**
A ship's domestic refrigeration system operates on the vapor-compression refrigeration cycle. It is designed to maintain low temperatures in provision stores (e.g., meat room, fish room, vegetable room) for preserving food. The system utilizes a Hydrofluorocarbon (HFC) refrigerant, such as R-134a, which has zero Ozone Depletion Potential (ODP). The system consists of the following key components:
1. **Compressor**: This is the heart of the system, acting as a circulation pump for the refrigerant. It draws low-pressure, low-temperature refrigerant vapor from the evaporator and compresses it into a high-pressure, high-temperature superheated vapor. The compressor is typically a reciprocating type for smaller domestic plants and is fitted with safety devices like High Pressure (HP) and Low Pressure (LP) cut-outs, and a lube oil low pressure cut-out.

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