How much do you know about the diameter of the refrigeration system and the return of the upstream pipe When the refrigeration equipment is under low load, if it is found that the oil return cannot be normal, it can be calculated according to the minimum return oil flow rate. Whether the diameter of the upstream pipe is too thick, so that the steam flow rate is too low due to the reduction of refrigerant circulation at low load. Therefore the oil cannot be brought back. In the calculation, the cooling capacity that appears in the device can be calculated according to the number of cylinders and cooling conditions of the current compressor. In addition to calculating the diameter of the suction pipe according to the above method, the minimum return oil cooling capacity can also be used for calculation. Because the amount of refrigerant circulation in the system is related to the cooling conditions and cooling capacity of the device, the less the cooling capacity, the less the amount of refrigerant vapor passing through the suction pipe, so as long as the suction pipe of different diameter is limited The minimum return oil cooling capacity is equivalent to limiting the minimum return oil flow rate. In addition, the amount of refrigerant circulation and the specific volume of steam increases as the evaporation temperature decreases. Therefore, at the same minimum return oil cooling capacity, the lower the evaporation temperature, the greater the actual flow rate of refrigerant vapor in the suction pipe. The trend is the same as the relationship between the minimum return oil flow rate and the evaporation temperature. . Although this method is not as accurate as the direct calculation of flow rate, it is practically more convenient. In order to ensure normal oil return at low load, the upward suction pipe has to use a pipe with a smaller diameter. However, if the diameter of all the suction pipes is the same as that of the upward suction pipes, and the thin pipes are used, the resistance pressure drop of the suction pipes may exceed. At this time, the horizontal and descending parts of the suction pipe can be thicker in diameter and compensated by reducing the resistance of these parts, so that the pressure drop of the suction pipe resistance at full load remains within 1°C. When the horizontal pipe is thicker than the upstream pipe, an eccentric reducer (1/8-32) is needed at the connection between the lower end of the upstream pipe and the lower horizontal pipe to prevent oil from accumulating at the bottom of the horizontal pipe, while the upstream pipe and the upper horizontal pipe Standard shrinkage is used at the connection, so that the oil will not flow back after flowing out of the up pipe.
Generally speaking, when the length of the upward pipe is short and the minimum load of the device is not less than 25% of the full load, the pipeline resistance will not be excessive after taking the above measures to enlarge the diameter of the horizontal pipe section. But if the upward pipe is long and thin, and the minimum load is small, especially when the evaporation temperature is low, even if the horizontal pipe diameter is enlarged, sometimes the resistance is still too large. At this time, the double-up-pipe arrangement method can be used, and this method is now more commonly used in the refrigeration equipment of the cold storage of the ship's refrigerated cabin. The so-called double up-pipe arrangement is to use two up-pipes of different thickness in parallel together. When the load is high, both up-pipes are put into work, and the cut-off valve is set when the load is low, which is controlled by the operator according to the situation. In this way, an oil trap is provided at the bottom of the thick ascending pipe. When the load is reduced, the oil will accumulate in the oil trap due to the reduction of the vapor flow rate, and the thick pipe is automatically sealed. To ensure normal oil return. When the load is increased, due to the increased resistance of the thin tube, the pressure difference between the two ends of the ascending tube increases, the oil storage in the oil trap is washed away, the oil seal is lifted, and the thick tube is automatically put into work. When installing, pay attention to that the upstream pipe should be connected from the top of the horizontal pipe, so that after the oil flows out of the upstream pipe, it will not flow back again. When the upstream pipe is long, you can also bend the pipe into an oil trap in the middle. If the oil slides down the middle of the upstream, there will be an intermediate oil trap. When the product becomes an oil seal, due to the increased pressure difference between the two sides of the oil seal, the oil can be washed away, so that the oil can go up through two relays, which is more conducive to the return of lubricating oil. The resistance of valves, elbows, etc. in the pipeline is very large. For example, in a pipeline with a diameter of 63 mm, the resistance of a straight-through ball valve that is fully open during operation is equivalent to 21 meters of pipe length, and a fully open angle valve It is equivalent to 10 meters, an elbow is equivalent to 2 meters, and a tee joint is also equivalent to the resistance of 4 meters of pipe length. The larger the pipe diameter, the more the length of the folded pipe. For example, when the pipe diameter is 310 mm, the straight pipe is wide. The resistance of the angle valve, elbow and tee is 100, 50, 10, and 1120 meters. Therefore, the valve parts in the pipeline should be installed as little as possible. Gate valves and cocks are generally not allowed in refrigeration systems, they are only used in refrigerant water lines.
