Capillary Tubes PDF

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Capillary tubes...

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CAPILLARY TUBES Capillary Tube Installation The pressure drop is inversely proportional to the diameter of and directly proportional to the length. When choosing a capillary tube, its diameter should be chosen with the largest dimension possible in order to reduce the risks of blocking with small impurities present in the system. Any increase in diameter must be compensated with a greater length of the capillary tube. Capillary Tube Calculation For selection, the designer of a new or modified refrigeration unit that use a capillary type expansion system, you must select its diameter and length, such that the compressor and the capillary find the equilibrium point for the temperature of desired evaporation. The most used technique is "cut and test". First, a capillary longer than usual will be installed, the equipment is turned on and after a time in which the system stabilizes, the temperature is taken of the evaporator, if the desired temperature is not reached, the process must be cut and repeated, return to Turn on the equipment and check the evaporator temperature. There are numerous methods for sizing capillaries, some of them are specified in the literature they are based on empirical equations and others apply the principle of fluid dynamics. The

problem is further complicated when the capillary tube joins the suction line forming a heat exchanger as occurs in most refrigeration systems, since the flow to through the capillary tube in these cases it is not adiabatic, for this reason they are based on tests experimental.

For the first approximation, tables or graphs can be used. Once the capillary had been selected, its resistance is fixed, therefore, the flow of the coolant through it is proportional to the pressure difference between the condenser and evaporator. Since the capillary tube and the compressor are connected in series, the flow capacity of the tube must be necessarily equal to the pumping capacity of the compressor, as long as it is running. An imbalance condition between these two components must necessarily be temporary, for this reason must be taken care when selecting the filter since it could serve as a container, accumulating refrigerant in liquid phase or that this element is another resistance for the fluid refrigerant. Its best use is for systems that have a relatively constant load. Nor should they Use with open type compressors, due to the loss of refrigerant that may be through of the stamps. The use of capillaries in remote systems should be avoided, as these systems are difficult load accurately. Although the capillary tube is self-compensating under certain operating conditions, it will operate itself. maximum efficiency, only when the working conditions for which it was dimensioned. The same They are designed for a set of operating conditions and any change, whether in condensation and evaporation as selected at the time of design, will represent a decrease in the efficiency of the refrigeration cycle.

Advantages of capillary tubes  Simple.  They have no moving parts.  They are inexpensive.  They allow to equalize the pressures very quickly after the stop, allowing the motor to have low starting torque. Disadvantages of capillary tubes  Poor performance when departing from working conditions.  They are susceptible to being covered with foreign matter.  Require the refrigerant charge to be kept within certain limits.  Trial-and-error installation

The calculation of the capillary tube can be done by various methods or using different tables. For this we must take into account:  Refrigerating power of the compressor.  Evaporator temperature.  Condensation temperature.  Type of refrigerant.

GLOSSARY OF TERMS -Refrigerant: It is any body or substance that acts as a cooling agent absorbing heat from one place and delivering it to another place where it is not needed. -Heat: Energy that is manifested by an increase in temperature and comes from the transformation of other energies; is caused by the vibratory movements of atoms and the molecules that form the bodies. -Latent Heat: Latent heat is the energy required by a quantity of substance to change phase, from solid to liquid or liquid to gas. -Sensitive heat: It is one that receives a body or an object and causes its temperature to rise without affect its molecular structure and therefore its state....