Analysis of the reasons of lack of oil in constant temperature and humidity test chamber compressor
If the constant temperature and humidity test chamber compressor is short of oil, the consequence is that the compressor is stuck or early wear occurs. The lack of oil in the compressor can be explained by the following two reasons: 1. The compressor is not returning oil well; 2. The compressor is bubbling during shutdown.
(1) Compressor oil return is not good:
A small portion of the oil mixes with the refrigerant gas and circulates in the system. To avoid accumulation of oil in the system and to ensure the maximum circulating flow rate of refrigerant in the pipeline. It is generally believed that the circulation of oil and gas mixtures with a mass flow of less than 1% of refrigerant gas in the system is permissible. For example, a 1.5HP compressor may have a cycle of 1 kg of oil per hour, which means that 1.2 times the amount of oil replenished in the system. The compressor manufacturer selects and certifies certain refrigeration oils in order to obtain a good mutual solubility between the refrigerant and the oil. However, in the mechanical design, it is necessary to provide a good return of the compressor with a minimum flow rate of the refrigerant gas, that is, the pipe size, particularly the suction line size, must be carefully selected. That is, the pipe diameter must be balanced between pressure drop and good oil return.
Here we recommend the following minimum refrigerant flow rate: For horizontal pipes (and graded pipes), the refrigerant flow rate is 4m/s. The rising line refrigerant flow rate 8m/s. However, the maximum flow rate must be less than 15m/s to reduce the pressure drop and avoid refrigerant flow noise. For pipelines that are less than 30 meters long, there is no need to install a trap. It is recommended to install a horizontal pipe with a gradient of 0.8 cm per meter in the direction of the refrigerant flow.
(2) Blistering during shutdown of the constant temperature and humidity test chamber compressor
The refrigerant oil in the compressor is more or less miscible with the refrigerant gas. This mutual solubility is related to pressure and temperature. According to the principle of thermodynamics, it is known that a gas can be transferred from the hottest place in the system to the coldest place. The situation is that during shutdown, the compressor is the coldest part of the system. Therefore, after the oil reaches full saturation, the refrigerant sinks at the bottom of the compressor housing. The consequence will be wear or jamming of the compressor parts. This will be further analyzed below. When the compressor starts, the suction pressure drops, so that the refrigerant in the oil can be decomposed, or the refrigerant sinking at the bottom of the compressor shell evaporates out of the oil and brings out a large amount of oil. At this point the compressor housing is quickly filled with foam (oil and refrigerant mixture) and is drawn in through the cylinder and out of the compressor. The entire amount of oil can flow out of the compressor in seconds. So even if the system design is very good, if the press can not return oil, its mechanical parts will be seriously worn.
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