Figure 12.1(c) illustrates a simple distributor. Its purpose is to give a uniform distribution of refrigerant throughout the evaporator. Thorough mixing of the liquid and vapour leaving the expansion valve is achieved by the turbulence created when the mixture passes at high velocity through the nozzle in the distributor. A homogeneous mixture then flows past the conical deflector and through multiple, small-diameter pipes, of equal friction, that connect the outlet of the distributor to the inlet tubes on the evaporator. The distributor may be located horizontally or vertically but the latter gives better distribution.
The significant pressure drop across a distributor causes some of the liquid passing to flash to vapour, increasing turbulence and helping to improve mixing. The total pressure drop across an expansion valve and distributor is the same as would occur across an
Expansion valve used alone, for an equal refrigerating effect. Pressure drop varies with the load on the evaporator and this cannot be compensated for by adjusting the setting of the thermostatic expansion valve.
Distributors should always be close to their own expansion valves and external pressure — equalising lines must be used. When a hot gas valve is used (see section 12.9) the gas is sometimes injected at the distributor through a side connection between the nozzle and the cone. Turbulence and mixing is improved when hot gas enters under partial load conditions. Distributors are not always adopted for very small installations.
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