Sensing Bulb Charge Characteristics
Ability of the liquid charged TXV keep the evaporator is filled with refrigerant, without considering its temperature or pressure has some disadvantages. Although this feature is desirable in that it provides full and efficient use of the entire surface of the evaporator under any conditions of load, is undesirable in that it also allows for an overload of the compressor motor. Overload occurs whenever the excessive evaporator pressures and temperatures, which are the result of intense heat load. Another disadvantage of TXV is its tendency to spread open, when the compressor initially cycles, thus, overfeeding of the evaporator. Overfeeding when you start occurs when the evaporator pressure drops quickly when the compressor starts sensing lamps of a high pressure, because overheating vety high. Valve corresponds to the opening of completely, allowing the fluid to flood the evaporator and enter the suction line. Valve continues to overfeed the evaporator die until the temperature of the lamp has cooled to normal operating temperature.
This reaction can lead to damage of the compressor. These operational difficulties will be overcome by the use of different charges TXVs sensing bulb.
The type of charge used in the sensing bulb determines how TXV responds to changes in demand. Balls will be charged as direct liquid contain the same refrigerant in the system. The amount of liquid charge enough to sustain liquid-vapor mixture in a bulb, capillary tube and thermostatic element throughout its design range of exploitation. This type of lamp experiences increase of superheat, temperature and pressure die evaporator reduction. This back characteristic creates overheating 20F (11C) at -20F (29C) evaporator temperature, which decreases to 5 F (3C) overheating with 40F (4.4C) coils. This type of sensing lights used in the average temperature, since it limits the ability of the flood-back when the system starts.
Cross liquid charged bulbs contain other refrigerant, than that used in the system. The amount of liquid charge enough to sustain liquid-vapor mixture in a bulb, capillary tube and thermostatic element throughout its design range of exploitation. These lamps have a relatively flat response curve. They generate overheating 12F (6.6C) at -20F (-29C) temperature of the evaporator and 8F (4.4C) overheating 40 F (4.4C) the temperature of the coil. They are used in average temperatures between 0 and 40F (18 and 4.4C). At temperatures below 0F (-18C), low temperature fluid cross charge is used, which are directly proportional response increasing from 5F (3C) superheat at the evaporator temperature -40 F 23F (40C to 13C) overheating in the coil temperature of 30 F (1C). This feature prevents flooding back during startup, because overheating increases as the evaporator warms, modulating valve in direction closed. These TXVs are normally used in low and medium temperatures.
Right gas (steam) is charged bulbs contain the same refrigerant in the system. The amount of liquid is limited so that at this temperature, all the refrigerant in the bulb, capillary tube and thermostatic element is a vapor. If overheating rises above this temperature, pressure change is so small that it no longer affects the position of the needle. Consequently, the flow of the refrigerant in the evaporator remains constant until the load is reduced. Because the refrigerant flow remains constant pressure in the evaporator reaches the maximum limit. This pressure-limiting characteristic is used in applications for limiting the power of the compressor in periods of high load. These bulbs also experience an increase in their superheat set point as the temperature and pressure in the evaporator increase. This is directly linked feature creates overheating 5F (3C) in the evaporator temperature of 40F (4.4C) and 15F (8C) overheating in 60F (16C) the temperature of the coil. These TXVs are widely used in high-temperature applications.
Cross gas (steam) is charged bulbs contain different refrigerant from that used in the system. The amount of fluid is limited so that at a given temperature of the refrigerant in the bulb, capillary tube and thermostatic element is a vapor. These lamps have a relatively steep response curve in response to the overheating of 25 F (14C) evaporator temperature 30 (-1C) overheating 35F (19.4C) at a coil temperature of 37 F (3C). These characteristics limit their use in medium temperature...
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