1
Distributor
陈江平
上海交通大学制冷研究所
《制冷原理与装置》讲义
What’s it? What is its function?
The refrigerant distributor is a
device connected to the outlet
of a thermostatic expansion
valve (TEV). The outlet of the
distributor is machined to
accept tubing which connects
the distributor to each
evaporator coil circuit.
The refrigerant distributor
equally distributes refrigerant
flow from the thermostatic
expansion valve (TEV) into each
circuit of a multi-circuit
evaporator coil.
The refrigerant distribution problem
in evaporators
A portion of the liquid refrigerant passing through the
thermostatic expansion valve (TEV) normally flashes,
resulting in two-phase (liquid and vapor) flow at the
valve outlet, see Figure 1. This mixture is
predominately liquid by weight, but the vapor
occupies most of thevolume. For a typical R-22
application, the percentage, by weight and volume, of
liquid and vapor flow entering the evaporator coil are
listed below:
The above values are based on 110°F liquid
refrigerant entering the TEV, and a 45°F
evaporating temperature. In this example,
liquid represents 77% of the flow by weight,
though it only amounts to 7% of the flow
volume. An additional problem arises due to
the fact that liquid and vapor move at different
velocities.
More…
This is sometimes referred to as slip, since gravity has a greater influence on the liquid portion
of the flow. If a simple header is used to divide the flow into each of the evaporator circuits,
the circuits will not receive equalamounts of refrigerant. The lower circuits of the evaporator
invariably receive the most liquid, possibly causing TEV hunting and floodback problems.
The upper circuits are then starved, reducing the effective evaporator surface, see Figure 2.
To achieve proper distribution…
The liquid portion of the two-phase flow must be divided equally to each evaporator coil
circuit. The solution:
[1] mix the liquid and vapor portions of the refrigerant flow;
[2] maintain a homogeneous two-phase mixture until equal portions of the flow are
divided into each evaporator circuit.
Some Pictures
2
Very important
External Equalizer
TEV is needed if
distributor is used,
because of its high
pressure-drop
