buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

72 Ion Zabet and Graţiela-Maria Ţârlea
2002). In the same time we will try to define the point where injection process
take place on the: isentropic process, isochoric process or between them. The
work is conducted in two phases: the first phase of the rig consists in the set-up
of a test rig, its instrumentation, the calibration of the measurements devices,
the set-up of the data acquisition system and a few verification tests; the second
phase consists in the achievement of the 100 tests. On this test rig we mount a
pressure sensor on the evaporator supply and a new system of expansion valves.
This new system of the expansion valves allow us to extend the tests matrix to a
wide range of capacities and a higher control over the system. The expansion
valves are mounted three on the evaporator and two on the injection evaporator.
2. Description of Experimental Model
The schematic representation of the test rig is given in Fig. 1. The
refrigerant circuit (Zabet, 2011) comprises a main evaporator, an injection
evaporator, the compressor, a condenser and different expansion valves. The
refrigerant is R407C.
The main evaporator and injection evaporator are fed by a glycol water
closed loop.
Glycol water is an aqueous solution 50% of propylene glycol. The glycol
water loop is composed of a pump, an electrical boiler, an expansion tank, a bypass
loop and different manual control valves (at the inlet and outlet of the main
evaporator and the injection evaporator). The condenser is cooled by tap water.
Two type of test was performed: with injection and without injection. The
compressor characteristics are: type scroll; injection mode vapour; swept
volume 166 cm 3 ; N= 2900 rpm. The main evaporator is a helical heat
exchanger.
The second evaporator is a helical heat exchanger which is used for heat
the refrigerant liquid to be injected in the compressor. The boiler is built by
using two concentric cylinders. The internal cylinder is completely closed and
filled with gaseous nitrogen. Glycol water circulates upwards between the
external and the internal cylinders. Glycol water is heated by 10 electrical
resistances (6 resistances of 9 kW and 4 resistances of 6 kW). A flow sensor is
installed at the boiler exhaust, to protect the boiler if no water movement is
detected. The nominal flow rate of the pump is 40m 3 /h.
The boiler is equipped with a temperature regulation system, which
allows maintaining a stable temperature set point at the boiler exhaust (by
switching on and off some resistances). On the second evaporator it was
mounted two expansion valves and two different orifice types in order to
varying the injected refrigerant mass flow. On the main evaporator it was
mounted three expansion valves with different orifice size. The expansion
valves are mounted in parallel for both types of evaporator. The condenser is
shell and tubes heat exchanger and use tap water for refrigerant condensation.