Frost Loss and Anti-freezing Measures of Shell and Tube Heat Exchanger
Shell and tube for refrigerationHeat ExchangerAccidents often occur that the refrigeration system is paralyzed and huge economic losses are caused by the rupture of the heat exchange tube. One of the most common reasons for the rupture of the heat exchange tube is that the heat exchange tube is broken or crushed due to the ice expansion on the water side in the heat exchanger. Generally, the ice support of the heat exchange tube is damaged in condensers and flooded evaporators, and the ice pressure damage of the heat exchanger tube is common in dry evaporators. The main reasons for the freezing of water in the heat exchanger are as follows:
1. The machine is shut down for a long time, and the water is not discharged or not discharged cleanly. When the ambient temperature is lower than 0 ℃, the water stored in the heat exchange tube will freeze and expand to break the heat exchange tube. The preventive measure for this situation is to require users to drain the water from the heat exchanger when it is shut down for a long time. The lower part of the end cover of the water chamber of the condenser and the flooded evaporator and the lower part of the dry evaporator shell are equipped with Drain valve or drain plug, equipment maintenance personnel can discharge the water in the heat exchanger from here. For the air-cooled heat pump system, when it is running in winter, some occasions will shut down for a short time, but the ambient temperature is low, and the water temperature will quickly drop below the freezing point, but it is troublesome for maintenance personnel to drain water frequently. For such a system, it is recommended Set the antifreeze operation control mode, start the antifreeze operation mode in the shutdown mode, and automatically start the pump cycle when the water temperature is lower than a certain value, if the water temperature continues to drop, automatically start the heating mode and turn on the compressor until the water temperature rises to a safe range.
2. When repairing the equipment, the water in the heat exchanger is not discharged clean before recovering and filling the refrigerant, or the water pump is not turned on to let the water flow, which causes the refrigerant to evaporate rapidly and absorb the heat in the water. The water in the heat exchanger does not flow, and it will freeze soon, resulting in rupture and damage of the heat exchange tube. The preventive measure for this situation is to require the equipment maintenance personnel to recover and charge the refrigerant in the state of no water or water in the flow of the heat exchanger.
3. The refrigerant in the refrigeration system is undercharged or leaked, which leads to the deviation of the evaporation pressure. The evaporation temperature is operated below 0 ℃ for a long time. When the water flow rate in the evaporator is low and the water flow dead zone tends to freeze, This leads to damage to the ice support or ice pressure of the heat exchanger tube. The preventive measure for this situation is that the refrigeration system must be filled with sufficient refrigerant, and a low-pressure alarm device is set, the evaporator outlet should be set with a freezing point protection switch, and the equipment maintenance personnel should always check the pressure value of the system to ensure timely detection of refrigerant Leakage.
4. Since the water system is not equipped with a cut-off protection device, when the water pump fails or other reasons cause the water system to suddenly cut off when the equipment is running, the compressor is still running and there is no time for load reduction and shutdown, and the refrigerant in the evaporator is still evaporating continuously. Often, the low-pressure protection device and freezing point protection are too late to react, and the water in the evaporator has frozen, resulting in rupture and damage of the heat exchange tube. The preventive measure for this situation is to be sure to set up a water flow switch or water pressure difference switch and other cut-off protection devices on the water system.
5. Due to the failure of the sensor or related protection device of the equipment, there is no timely alarm and shutdown when the equipment is abnormal, especially the temperature sensor fails and cannot reflect the accurate temperature value. When the actual water temperature reaches the load reduction interval or shutdown interval, while the temperature sensed by the sensor is still in the maintenance interval or loading interval, the water temperature will drop sharply until it freezes, resulting in damage to the heat exchange tube. For this situation, the preventive measure is that the water temperature sensor is recommended to use a sensor with high precision and reliable quality, and then set up a freezing point protection sensor or temperature switch to take double protection measures to prevent sensor failure. In addition, equipment maintenance personnel should often calibrate the temperature sensor with a thermometer. If the sensor is found to be inaccurate, the sensor should be replaced in time.