What are the symptoms of the leaky valves in a refrigeration compressor?
1. Noisy compressor
2. Bubbles in sight glass
3. Motor starts and stops rapidly
4. Compressor operating at low discharge pressure
5. Compressor operating at high suction pressure
a) 3,4,5
b) 1,3,5
c) 1,2,4
d) 1,4,5
e) 2,3,5
Answer: D
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Power Engineering
- The work done in a constant pressure expansion can be determined by:
- If 10.4 m³ of air is compressed at a constant temperature to 5.1 m³ and 750 kPa gauge. Calculate how much work is done on the gas, assuming atmospheric pressure to be 100 kPa.
- Boyle's Law is one of constant:
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- If the volume of a confined gas is constant then the absolute pressure is directly proportional to the absolute temperature according to:
- Find the characteristic constant for a gas if 112 kg of the gas has a volume of 5.7 m³ at 1500 kPa absolute and 27.5°C.
- If 24,500 kJ of work is done in a cylinder when 115 kg of a perfect gas is expanded isothermally at 210°C from 0.035 m³ to 6.9 m³. Find the characteristic constant for this gas.
- A gas at 1000 kPa gauge pressure and 30°C is transferred from a cylindrical vessel 1.5 m in diameter and 3 m long to another cylindrical vessel 2.5 m in diameter and 5 m long. If the new gauge pressure is 150 kPa, calculate the new temperature. Note: Assume atmospheric pressure to be 100 kPa for this calculation.
- If 0.25 m³ of a gas at 4000 kPa gauge pressure is expanded until the gauge pressure is 500 kPa and the expansion is polytropic with n = 1.35. Find the final volume the gas will occupy. Note: Assume atmospheric pressure = 100 kPa
- The equation (PV/T) = mR or PV = mRT is called the:
- The Characteristic Constant of each perfect gas is
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- If 10.4 m³ of air is compressed at a constant temperature to 5.1 m³ and 750 kPa gauge. Calculate how much work is done on the gas, assuming atmospheric pressure to be 100 kPa.
- Compression and expansion in real life cases will always follow the polytropic process that is described by the formula(s):
- The formula Work = (P1V1 - P2V2) / n - 1 is used to describe expansion during:
- To "expand a gas" means the gas is:
- The work done in a constant pressure expansion can be determined by:
- A perfect gas is compressed under conditions of constant temperature to a volume of 30 m³. If the final pressure of the gas is 450 kPa gauge and the initial volume was 135 m³, what was the initial pressure? (Assume atmospheric pressure to be 101.3 kPa)
- Gases such as air, nitrogen and oxygen can be roughly defined as perfect gases because they:
- The General Gas Law can be written using the formula/s:
- The pressure-volume diagram of a typical air compressor will have a curve drawn:
- Absolute pressure can be defined as:
- How much work is required to compress a gas polytropically from 195 kPa abs to 1600 kPa abs while reducing the volume to 0.8 m3? Use the value of "n" for this gas as 1.35.
- If 1.45 m³ of air at 100 kPa abs and 12°C is compressed to 950 kPa abs while following the law PV1.34 = C. Taking R for air = 0.287 kJ/kg K, find the final volume of air and the mass of air compressed.
- The characteristic constant for a gas is given as: