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User manualCapillary Tube Selection Software

CAPILLARY TUBE SELECTION SOFTWAREUSER MANUAL

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1. Introduction

2. Equilibrium of the Cooling System

The capillary tube is one of the most commonly used expansion devices in those cooling systems which work in vapour compression cycles. It is used in all household refrigerators and also in many refrigeration LIGHT commercial appliances. It is the simplest expansion system: Quite often, the capillary selection is based on the practical method of “trial and error”, i.e. testing the different capillaries to determine which one gives the best performance. Although simplified calculation models are available, the final adjustment for a given application should be made by practical laboratory tests. This is simply because the cooling system does not operate under constant conditions and the capillary behaviour is therefore directly affected.

Huayi Compressor Barcelona Software allows the user to calculate a capillary tube for a refrigeration system based on the following ASHRAE publications:

• RP-762: ASHRAE METHOD FOR PREDICTING CAPILLARY TUBE-SUCTION LINE HEAT EXCHANGER PERFORMANCE

• RP-948: PERFORMANCE OF A SUCTION-LINE/CAPILLARY-TUBE HEAT EXCHANGER

Each main element of the system (compressor, condenser, capillary, and evaporator) has its own behavioural characteristics. Once designed and constructed, the equilibrium to some given working conditions is established by the refrigerant charge. Whether this is adequate or not will greatly influence the efficiency of the system.

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Log

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The figure shows a schematic outline, over the enthalpy diagram, of the effects of the different refrigerant charges. Curve 1 corresponds to a low refrigerant gas charge. The low suction pressure results in a low flow from the

A small quantity of refrigerant charge will result in a lower evaporating temperature and poorer use of the evaporator (low flow). On the other hand, an excess of refrigerant gas will result in higher discharge pressures, a decrease in compressor efficiency and an excess of liquid which may appear in the suction line.

compressor which fails to generate sufficient liquid to fill the capillary. As a consequence, a significant quantity of vapour goes through the capillary.

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3. Changes in the Diameter

4. Use of Capillary Tube Selection Software

Z = ( )D 6.098

D0× Z0 Z = ( )D 5.271

D0× Z0

It is possible, with some restriction, to work with different diameters than those indicated in the tables. The following formula will help determine the approximate length of the new capillary when specifying a different diameter than given in the tables.

NOTE: The subindex (0) indicates the given values of the enclosed tables

Capillary tube coiled in the suction line:

Capillary tube not coiled in the suction line:

In curve 2, an increase in the charge raises the pressures and the capillary receives only liquid. In curve 3, if the degree of subcooling is excessive, there is an accumulation of liquid at the outlet of the condenser, which could affect its efficiency with an increase in the discharge pressure. An adequate charge is one which provides a slight subcooling at the outlet of the condenser.

With an excessive charge, there is the increased risk of liquid entering the compressor. This can provoke dilution of the lubricating oil, leading to poor lubrication, wear and, in the case of liquid entering the cylinder, breakage of the valve rendering the compressor useless.

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4.1. Units setting

The capillary tube selection software is available in [W, ºC, mm] and [Btu/h, ºF, inch]. Before starting with the capillary tube calculation, select your unit setting configuration.

4.2. Searching parameters

There are to option to proceed with the capillary tube selec-tion, by Compressor Model or by Cooling Capacity.

• By Compressor Model: Using this option, you have to introduce the concrete Cubigel Compressor® model name.

• By Cooling Capacity: Using this option you have to introduce the Cooling Capacity needed by the system and the refrigerant used (R22, R134a, R404A, R290, R600a, R1234yf, R449A or R452A). The cooling capacity conditions are the conditions introduced by the user in the point 4.3. “WORKING CONDITIONS”.

4.3. Working conditions

The working conditions used by the software to generate the calculations are:

• Evaporating Temperature• Condensing Temperature• Subcooling• Suction temperature

4.4. Capillary tube parameters

The capillary tube calculation can be based in two different assumptions:

• The capillary tube is coiled to the suction line• The capillary tube is not coiled in the suction line

4.5. Results

After the interdiction of all the required data the software shows the optimum capillary tube length for the diameter selected previously. In case of select the option “Capillary tube coiled in the section line” the software also shows the capillary tube length that is necessary to be coiled in the suction line.

Note that this capillary tube calculation is just a first approx-imation; the final adjustment for a given application should be made by practical laboratory tests. This is because the cooling system does not operate under constant conditions and the capillary behaviour is therefore directly affected.

NOTE: According to our experience, the capillary tube length recommended should be between 1.5m and 4.5m. In case of a capillary tube length outside these limits, we recommend to change the capillary tube diameter and run again the capillary calculation software.

Huayi Compressor Barcelona laboratories cannot consider the R449A and R448A as direct drop-in solution for the R404A compressors due to the high discharge temperatures found during the test, this situation can cause motor over-heating and overload protector tripping. The use of these refrigerants means a complete redesign of the application (increasing the fan air flow, increasing the condenser size, etc…) in order to reduce the temperatures and obtain same results as when using R404A. The use of these refriger-ants in the final application needs to be validated by Huayi Application Engineering team case by case in order to guar-antee the reliability and system performances.

The R452A presents a performance more similar to R404A than R449A and could be considered as a drop-in solution.

According to the discharges temperatures, it seems that the use of this refrigerant in Cubigel Compressors® must be validated case by case and the working envelope of the compressor using R452A will be restricted.

The use of the compressors outside the envelope defined by Huayi Compressor Barcelona can cause a reduction in the life time and reliability of the compressor.

R1234yf can be considered an alternative to the full range of R134a compressors. It is also important to note that R1234yf is classified as an A2L refrigerant meaning that it is mildly flammable and therefore subject to charge limita-tions according to international standards.

5. Use of HFC’s Alternative Refrigerants

This calculation method developed by Huayi Compressors has to be considered as a reference tooling. Theoretical resulting

capillary size is recommended to be confirmed by empiric tests in the real appliance.

Huayi Compressors is out of any liability generated as a direct or indirect consequence of above described calculation software.

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Huayi Compressor Barcelona, S.L.Antoni Forrellad, 2 · 08192Sant Quirze del Vallès · BCN · SpainPhone: +34 93 710 60 08Fax +34 93 710 69 58

www.huayicompressor.es

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L · 03/2018