Design of capillary tubes for manufacturers of high and low temperature wet heat test chambers
On the high-pressure side, a reservoir is generally not used. In fact, whether a reservoir is used or not does not depend on what kind of throttling device is used, but on whether the entire system needs to operate, such as a heat pump system or a shutdown and evacuation system. For refrigerators, air conditioners, and other systems, reservoirs are rarely required in their original design.
2. In the suction pipe, a gas-liquid separator is used. For refrigerators, if the return pipe is relatively long, it can ensure that the return air temperature is within the design requirements (recommended by the compressor company as 5oC) and can be omitted. For air conditioners, most air conditioning compressors come with a gas-liquid separator at the factory.
Because when the capillary system is shut down, the high and low pressure sides will balance, causing refrigerant liquid to accumulate in the evaporator. The gas-liquid separator can effectively prevent liquid hammer and refrigerant migration.
3. The high-pressure side can accommodate all the refrigerant charged, which is to prevent damage to the high-pressure pipeline system and compressor when the capillary tube is blocked.
4. Under high load conditions of the evaporator, because the capillary system can provide feedback to the condenser side, the condenser needs to consider whether the condensation pressure will be too high under such conditions, and therefore needs to increase the condensation heat transfer area.
5. Do not accumulate refrigerant liquid in the pipeline between the condenser outlet and the capillary inlet of the high and low temperature wet heat test chamber;
One theory is that when the compressor of the high and low temperature wet heat test chamber stops, this refrigerant liquid will evaporate due to pressure drop, flow into the evaporator and condense, thereby bringing some heat to the refrigeration space, which may have an impact on the enclosed space of the refrigerator. For air conditioning, this heat can be ignored;
Another theory is that this will delay the time for balancing the high and low voltage sides, which may cause problems when the low torque compressor starts again. This can generally be solved by adding a delayed start-up in the control (in fact, this is also beneficial for reducing the impact of starting current on other electrical components or the power grid).
6. A filter must be added to the capillary inlet to prevent blockage, especially for HFC refrigerants such as R134A, R404a, R410a, which are sensitive to moisture and require a dryer in their design.
7. Before entering the capillary tube, the refrigerant in the high and low temperature wet heat test chamber has a certain degree of supercooling. This can be achieved by adding a supercooling tube to the evaporator or exchanging heat with the suction tube, which reduces the gas flash in the capillary tube and increases the cooling capacity while ensuring the refrigerant flow rate.
However, it should be noted that in low-temperature conditions, excessive supercooling may occur due to a slight return of liquid from the suction pipe, resulting in an increase in capillary flow rate and, in turn, an increase in subcooling, which may ultimately cause liquid return.