EP2857778A1

EP2857778A1 - Refrigerator with a non-azeotropic mixture of hydrocarbons refrigerants

Info

Publication number: EP2857778A1
Application number: EP13187230.1A
Authority: EP
Inventors: Enzo Rivis; Marco Gavioli
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2013-10-03
Filing date: 2013-10-03
Publication date: 2015-04-08
Also published as: US20150096325A1

Abstract

A refrigerator with a refrigerant circuit using a non-azeotropic mixture of hydrocarbons refrigerants comprises a compressor, a condenser, an expansion device , a first evaporator downstream the expansion device, a second evaporator downstream the first evaporator, a first heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first evaporator, on one side, and refrigerant downstream the first evaporator and upstream the second evaporator, on the other side, and a second heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first heat exchanger, on one side, and refrigerant downstream the second evaporator (19) and upstream the compressor (10), on the other side, the expansion device being a capillary tube that is integral part of both heat exchangers as a side of exchangers, where the capillary tube is parallel and in contact with a tube of the circuit or it is wrapped around such tube.

Description

The present invention relates to a refrigerator with a refrigerant circuit using a non-azeotropic mixture of hydrocarbons refrigerants. More particularly, the present invention relates to a refrigerator in which said refrigerant circuit comprises a compressor, a condenser, an expansion device, a first evaporator downstream the expansion device, a second evaporator downstream the first evaporator, a first heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream the first evaporator, on one side, and refrigerant downstream the first evaporator and upstream the second evaporator, on the other side, and a second heat exchanger to cause heat exchange between refrigerant downstream the condenser and upstream said first heat exchanger, on one side, and refrigerant downstream the second evaporator and upstream the compressor, on the other side.
This kind of refrigerator, known also as "dual evaporator" or "sequential evaporator" type refrigerator, uses a non-azeotropic mixture of two different refrigerants, for instance propane (R-290) and n-butane (R-600), which has an appropriate gliding temperature difference (GTD) during evaporation and condensation phases. With a refrigeration cycle using the above mixture, known also as Lorenz-Meutzner cycle, it is possible to have identical or at least similar energy saving performances of a dual evaporator refrigeration circuit using a mono-component refrigerant and a by-pass two-circuit cycle, where a 3-way electrovalve is used.
A refrigerator of the type mentioned at the beginning of the description is disclosed by US 5 207 077 and EP 2 592 366 . In both the above documents the expansion device is placed immediately upstream the first evaporator, i.e. the low-temperature evaporator. In US 5207077 the expansion device is identified in the drawing as an expansion valve, while in EP 2592366 the expansion device is a capillary tube arranged at the side of the first evaporator. In said first solution the presence of the valve does increase the overall cost of the appliance, and it may create problem of condensation on suction tube. In the second solution, as it is also disclosed in "Performance optimization of a Lorenz-Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer", IJR, N. 35, Issue 1, Jan 2112, pages 36-46, the optimum capillary tube length is of the order of 10 - 15 m if similar energy consumption performances of a bypass two-circuit cycle are to be obtained.
In the above documents the sub-cooling from second evaporator and compressor and the additional one required using these mixtures (tube connection between first and second evaporator) is obtained through use of heat exchangers made with two tubes. In EP 2 592 366 it is explained that these tubes work better in case one is inside the other and in counter-flow.
On the above mentioned publication and patents are given also indications on modification required by a refrigerator/freezer product using a non-azeotropic mixture. In the above mentioned article "Performance optimization of a Lorenz-Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer" are given also information on modification in length of capillary (required at least 10m) in order to have benefits in energy and correct behavior of product.
It is an object of the present invention to provide a refrigerator with a refrigeration circuit designed for a modified Lorenz-Meutzner cycle which does not present the above problems and has a low cost.
Such object is obtained thanks to the features listed in the appended claims.
One of the main features of the invention is the use of a capillary tube for the two heat exchangers required for this cycle. In other words, the capillary tube is used as one side of both heat exchangers. According to a preferred feature of the invention, the capillary tube is used externally to the other tubes of the refrigerant circuit, and the refrigerant flow in the capillary tube is in counter flow with reference to the refrigerant flow in the tube of the refrigerant circuit. According to a different embodiment, the capillary tube is used internally to the other tube.
According to a preferred feature of the invention, the capillary tube has a length comprised between 2.5 and 5 meters, and an internal diameter comprised between 0,6 and 0,8 mm.
The use of a capillary tube with a reduced length does reduce the overall cost of the appliance and increases the simplicity of the layout of the refrigerant circuit, with related advantages in term of reliability and reduced overall volume of the circuit.
Even if different kind of refrigerant mixtures can be used, the applicant has found that a mixture of 80% and 20% by mass in liquid phase of n-butane and propane respectively has the advantage of not requiring a different compressor (i.e. the same for iso-butane R600a can be used).
Further advantages and features of a refrigerator according to the present invention will be clear from the following detailed description, provided by way of non limiting example, with reference to the attached drawings in which:

Figure 1 is a schematic view of a refrigerant circuit of a refrigerator according to the present invention;
Figure 2 is a detail of a cross-section of one of the two heat-exchangers of figure 1 according to a first embodiment, and
Figure 3 is a detail similar to figure 2 and referring to a second embodiment of the invention.

With reference to the drawings, the refrigerant circuit according to the invention comprises a compressor 10, a condenser 12, usually placed on back wall of the refrigerator, cooled by natural convection or with forced air, a drier 14 as normally used on a domestic refrigerator / freezer appliance.
Downstream the drier, the circuit comprises a capillary tube 16 of from 2.5 to 5 m (depending on the total volume of the cells, the type of compressor etc.), with an internal diameter comprised between 0.60 and 0.80mm.
The circuit comprises a first heat exchanger 18 and a second heat exchanger 20. The first heat exchanger 18 present a first side made by a capillary tube portion 16a in contact with a portion 22 of the circuit tube between first or low temperature evaporator 17 (placed in the freezer compartment - not shown) and second or high temperature evaporator 19 (placed in the fridge compartment - not shown). The section of such heat exchanger is shown in figure 2, and applicant has determined through experimental tests that the length of this tube/tube heat exchanger is preferably between 0,5 and 1 m. Internal diameter of the suction tube 22 is preferably comprised between 5 and 8 mm.
As shown in figure 2, the capillary tube portion 16a and the portion 22 of the refrigerant circuit tube are in contact one with another, and they are covered by a layer of aluminum foil 23 which may be a self-adhesive aluminum tape which assures a correct placement of the two parts of the heat exchanger and helps increasing the thermal efficiency thereof.
According to a further embodiment shown in figure 3, the capillary tube 16a is wrapped around the tube 22 of the refrigerant circuit without use of any aluminum layer.
The second heat exchanger 20 is similarly composed of a capillary tube portion 16b and a portion 24 of suction tube upstream the compressor 10. The length of such double-pipe heat exchanger 20, particularly in the embodiment shown in figure 2, is preferably comprised between 1,5 and 3 m. Internal diameter of the suction tube 24 is preferably comprised between 5 and 8 mm. The section of the second heat exchanger 20 is identical to the section of the first heat exchanger 18 shown in figure 2 or 3.
For the first evaporator 17 (freezer evaporator - low temperature) the applicant has found that the same evaporator used in refrigerators with the bypass two-circuit cycle (where aR600a is used as refrigerant) can be adopted. For the second evaporator 19 (fridge Evaporator - high temperature), the applicant has found that an increased surface of about 10 / 30 % vs. the surface of an evaporator used in a bypass two-circuit cycle is beneficial for energy saving performances.
The use of capillary 16 also as a second heat exchanger tube 16b improves the sub-cooling of the tube connection from second evaporator 19 (at high temperature) and compressor 10. With the solution according to the invention it is possible to have equivalent or even improved energy reduction if compared to prior art, particularly EP 2592366 , but with a length of capillary reduced (max 5 meters) and with a reduced length of suction tube (tube connection between high temperature evaporator and compressor (max 3,5m), simplifying the refrigerant cycle and reducing the overall cost of the appliance.
The solution according to the invention can be applied to direct cooled evaporator products (static evaporators in freezer and fridge compartments) and hybrid products (no frost freezer and static fridge).

According to the tests carried out by the applicant in a refrigerator (with freezer and fridge compartments) having a total internal volume around 300 liters, the main benefits obtained applying the cycle according to the invention on a bottom mount freezer built-in product are as follows:
a) Energy saving

	Refrigerator / Freezer Hybrid	Refrigerator Freezer Direct Cooled
Reference using R600a (Wh/24h)	920 (*)	860 (*)
Result obtained using mixture R290/R600 (20/80) (Wh/24h)	814 (*)	770 (*)
Energy Benefit	11,5 %	10,5%
(*) According procedure EN 62552

Therefore an energy reduction around 11% has been obtained on both typologies of products.
b) Low temperatures in freezer compartment Comparison of temperatures obtained in freezer (in air), having compressor running 100% at 32 °C ambient:

	Refrigerator / Freezer Hybrid	Refrigerator Freezer Direct Cooled
Reference with R600a (°C)	-29.8	-29.6
Result obtained using mixture R290/R600 (20/80) (Wh/24h) (°C)	-32,0	-35.6

Low temperatures in freezer have not only a positive impact on energy saving performances, but they improve the freezing ability of products: in term of capacity (more quantity can be frozen on product in the same time) and in quality (faster freezing improves the quality of food frozen).
In addition the applicant has verified that the use of mixture of refrigerants is able to maintain the same level of noise and of electrical performances of products.

Claims

Refrigerator with a refrigerant circuit using a non-azeotropic mixture of refrigerants and comprising a compressor (10), a condenser (12), an expansion device , a first evaporator (17) downstream the expansion device, a second evaporator (19) downstream the first evaporator (17), a first heat exchanger (18) to cause heat exchange between refrigerant downstream the condenser (12) and upstream the first evaporator (17), on a first side (16a), and refrigerant downstream the first evaporator (17) and upstream the second evaporator (19), on a second side (22), and a second heat exchanger (20) to cause heat exchange between refrigerant downstream the condenser (12) and upstream the first heat exchanger (18), on a first side (16b), and refrigerant downstream the second evaporator (19) and upstream the compressor (10), on a second side (24), characterized in that the expansion device is a capillary tube (16, 16a, 16b) that is adapted to act as said first side (16a, 16b) of both heat exchangers (18, 20).
Refrigerator according to claim 1, wherein both the first and second heat exchangers (18, 20) are shaped as double-pipe exchangers formed by said capillary tube (16, 16a, 16b) in a heat exchange relationship with corresponding portions (22, 24) of tube of the refrigerant circuit.
Refrigerator according to claim 2, wherein said capillary tube (16a, 16b) is externally in contact with said portions of tube (22, 24).
Refrigerator according to claim 2 or 3, wherein the capillary tube has a total length comprised between 2 and 5 m.
Refrigerator according to claim 4, wherein the capillary tube (16, 16a, 16b) has an internal diameter comprised between 0,6 and 0,8 mm.
Refrigerator according to claim 4 or 5, wherein the length of the first heat exchanger (18) is comprised between 0,5 and 1 m.
Refrigerator according to claim 4 or 5, wherein the length of the second heat exchanger (20) is comprised between 1,5 and 3 m.
Refrigerator according to any of claims 2-7, wherein both heat exchangers (18, 20) are covered by an aluminum layer (23).
Refrigerator according to any of claims 3-7, wherein the capillary tube (16, 16a, 16b) is wrapped around the other portions of the tube (22, 24).
Refrigerator according to any of the preceding claims, wherein both evaporators (17, 19) are static evaporators placed in a freezer compartment and in a fridge compartment respectively.
Refrigerator according to any of claims 1-9, wherein the second evaporator (19) is a static evaporator placed in a fridge compartment, and the first evaporator (17) is a no-frost evaporator placed in a freezer compartment.
Refrigerator according to any of the preceding claims, wherein the refrigerant is a mixture of propane and butane of 20 to 80 % by mass in liquid phase.