[0001] The present invention relates to a refrigerating plant comprising a plate-type flooded
evaporator.
[0002] Evaporators are known as "flooded" evaporators when the exchange surface is completely
covered with refrigeration liquid. A phase separator is normally used downstream of
the evaporator to receive the biphasic mixture coming from the evaporator and the
condensed liquid supplied by the thermal expansion valve. The biphasic mixture is
separated in the separator due to the force of gravity and the liquid phase is recirculated
in the evaporator with the condensed liquid that flows through the valve, while the
vapour is drawn out by the compressor.
[0003] The uniform distribution of the fluid in the ducts flowing into the evaporator is
helped by the fact that it is a liquid rather than a low mass fraction biphasic mixture,
thus avoiding the possibility of some ducts being supplied with vapour only, which
would result in a drastic reduction in heat exchange.
[0004] Due to the particular way in which they work, flooded evaporators require a condensate
expansion valve to guarantee a constant level of liquid in the separator.
[0005] In particular, flooded evaporators can be smaller than dry evaporators in that an
area of the surface is not used for overheating, but they need more refrigeration
liquid.
[0006] Moreover, in flooded evaporators the evaporating fluid and that to be cooled usually
flow in the same direction, so that the maximum differences in temperature correspond
with the low heat exchange coefficients of the fluid in the liquid phase with low
vapour concentrations. The main characteristic of flooded evaporators is that they
allow small differences in temperature between the evaporating fluid and the fluid
to be cooled so that, with the same output temperature of the fluid to be cooled,
the evaporator achieves higher vaporization temperatures and thus a higher performance
coefficient.
[0007] Despite the advantages of flooded evaporators over dry evaporators, plate-type flooded
evaporators are difficult to use in refrigerating plants.
[0008] With a plate-type flooded evaporator in a refrigerating plant comprising a traditional
regenerative exchanger, for instance a tube-in-tube or spiral heat exchanger, the
degree of sensitivity with which the temperature is measured would produce an "oscillatory"
phenomenon corresponding with an opening and closing phase of the flow of the refrigeration
liquid controlled by the thermal expansion valve and thus result in sudden and exaggerated
reactions of the plant to external stress factors. In other words, the behaviour of
the thermal expansion valve affects the action of the regenerative exchanger creating
a vicious cycle both in the case of low overheating and in the case of high overheating
causing the aforesaid oscillation.
[0009] The object of the present invention is to provide a refrigerating plant comprising
a plate-type flooded evaporator that overcomes the problems typical of the prior art
solutions.
[0010] The object of the present invention is a refrigerating plant the essential characteristics
of which are claimed in Claim 1, and the preferred and/or secondary characteristics
are claimed in Claims 2-5.
[0011] In order to better understand the present invention, some non-limiting embodiments
thereof will now be described by way of example with the help of the figures in the
accompanying drawing, in which:
figure 1 is a schematic illustration of a refrigerating plant according to the present
invention; and
figure 2 is a schematic illustration of another refrigerating plant according to the
present invention.
[0012] In figure 1 designated as a whole by number 1 is a refrigerating plant with some
parts removed for the sake of simplicity.
[0013] The plant 1 comprises a plate-type flooded evaporator 2, a compressor 3, a condenser
4, a regenerative exchanger 5 and a thermostatic vale 6 of the self-adjusting mechanical
type.
[0014] As the evaporator 2 is of the flooded type, the purpose of the thermostatic valve
6 is to guarantee a constant level of liquid in said evaporator 2.
[0015] The thermostatic valve 6 receives the warm refrigeration liquid from the regenerative
exchanger 5 which, in turn, receives it from the condenser 4.
[0016] In particular, as well as receiving the warm refrigeration liquid coming from the
condenser 4, the regenerative exchanger 5 also receives the biphasic liquid/vapour
mixture coming from the evaporator 2 and having a vapour concentration of approx.
0.95. Inside the regenerative exchanger 5 the mixture coming from the evaporator 2
evaporates completely and the resulting vapour is carried into the compressor 3 to
continue the refrigeration cycle. A temperature and pressure sensor 7 is arranged
to read the temperature and pressure of the vapour leaving the regenerative exchanger
5.
[0017] The vaporization phase inside the regenerative exchanger 5 according to the present
invention takes place by means of a high thermal inertia of the condensed refrigeration
liquid independent of the operation of the thermostatic valve 6. Said effect is obtained
by means of a regenerative exchanger comprising a flow path of the biphasic mixture
to be vaporized immersed in a volume of pressure-condensed refrigeration liquid. The
ratio in volume of the flow path of the biphasic mixture to be vaporized and the volume
of the condensed refrigeration liquid is such to guarantee said high thermal inertia.
In particular, the above flow path consists of a spiral tube 8 arranged with its axis
in a horizontal or vertical position and immersed in a cylindrical tank 9 full of
pressure-condensed refrigeration liquid.
[0018] In figure 2 designated as a whole by number 11 is a refrigerating plant with some
parts removed for the sake of simplicity. The parts identical to those of the plant
1 in figure 1 are indicated by the same numbers and not described again.
[0019] In the specific case, the plant 11 differs from the plant 1 due to the presence of
a microprocessor 12 capable of guaranteeing the electronic control of overheating
by the management of the software of an electric expansion-type valve 13.
[0020] It will be apparent to the person skilled in the art that with the plant according
to the present invention overheating can be controlled by means of the thermostatic
valve without the oscillatory phenomenon typical of plants using a traditional regenerative
exchanger. The mass of warm refrigeration liquid ensures considerable stability in
relation to the exchange of heat between the biphasic mixture to be evaporated and
said warm refrigeration liquid.
1. Refrigerating plant (1; 11) comprising a flooded evaporator (2), a compressor (3),
a condenser (4) and a thermal expansion valve (6); said refrigerating plant being
characterized in that said flooded evaporator (2) is of the plate type and in that it comprises a regenerative exchanger (5), connected to said evaporator through said
thermal expansion valve (6; 13) for letting the refrigeration liquid through and for
receiving the refrigeration liquid coming from the condenser (4); there taking place
in said regenerative exchanger (5) a vaporization step of the biphasic mixture coming
from said flooded evaporator (2) by means of a high thermal inertia of the condensed
refrigeration liquid.
2. Refrigerating plant (1; 11) according to Claim 1, characterized in that said regenerative exchanger comprises a flow path of the biphasic mixture to be vaporized
immersed in a volume of pressure-condensed refrigeration liquid.
3. Refrigerating plant (1; 11) according to Claim 2, characterized in that the flow path is a spiral tube (8), whose axis is horizontally or vertically arranged,
and which is immersed in a cylindrical reservoir (9) full of pressure-condensed refrigeration
liquid.
4. Refrigerating plant (1) according to any one of the preceding Claims, characterized in that said thermal expansion valve (6) is a self-adjusting mechanical thermostatic expansion
valve.
5. Refrigerating plant (11) according to any one of Claims 1-3, characterized in that it comprises a microprocessor (12) to guarantee the electronic control of overheating
by the management of the thermal expansion valve (13) software; said thermal expansion
valve (13) being of the modulating type with electrical control.