General Equation for the Design of Capillary Tubes

1996 ◽  
Vol 118 (1) ◽  
pp. 150-154 ◽  
Author(s):  
Tuncay Yilmaz ◽  
Saban U¨nal
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
General Equation ◽  
Capillary Tube ◽  
Analytical Equation ◽  
Tube Length ◽  
Capillary Tubes

Capillary tubes are used widely in small refrigeration systems. It is necessary to design the capillary tube, but there does not exist any analytical equation which allows the determination of capillary tube length or mass flow rate for all refrigerants. In this work, an analytical equation is derived which allows to design the capillary tubes. The comparison with existing methods and experimentally obtained values using the refrigerants R12, R22, R113, R114, R134a, and R600a has turned out to be satisfactory.

Experimental Investigation on Flow Characteristic of Stepped Capillary Tube for Heat Pump Type Air Conditioner with R410A

2014 ◽  
Vol 960-961 ◽  
pp. 643-647
Author(s):  
Yan Sheng Xu
Keyword(s):  
Mass Flow Rate ◽  
Heat Pump ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Coefficient Of Performance ◽  
Tube Length ◽  
Air Conditioner ◽  
Capillary Tubes ◽  
Tube Assembly

A stepped capillary tube consisting of two serially connected capillary tubes with different diameters is invented to replace the conventional expansion device. The mass flow rate of refrigerant R410A in stepped capillary tubes with different size were tested. The model of stepped capillary tube is proposed, and its numerical algorithm for tube length and mass flow rate is developed. The experimental results show that the performance comparing between stepped capillary tube system and capillary tube assembly system, the cooling capacity is reduced by 0.3%, the energy efficiency ratio (EER) is equal to each other, the heating capacity is increased by 0.3%, the coefficient of performance (COP) is decreased by 0.3%. That is to say, the performance index of the two kinds of throttle mechanism is almost identical. It indicates that the stepped capillary tube can replace the capillary tube assembly in the R410A heat pump type air conditioner absolutely. The model is validated with experimental data, and the results show that the model can be used for sizing and rating stepped capillary tube.

OPTIMIZATION OF THE RESERVE-TYPE DISTRIBUTOR FOR R410A AIR CONDITIONER

2014 ◽  
Vol 22 (04) ◽  
pp. 1450022 ◽  
Author(s):  
CHI ZHANG ◽  
YING WANG ◽  
JIANGPING CHEN
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Average Length ◽  
Tube Length ◽  
Structural Factors ◽  
Air Conditioner ◽  
Capillary Tubes ◽  
Inlet Tube

Mal-distribution of refrigerant in a cross-flow type evaporator with parallel paths is very important, which can lead to a loss of heat exchanger capacity to 25%. Distributors are used to balance the two-phase refrigerant distributions in each path. Apart from the structural factors, there are other factors influencing the performance of distributor greatly. In this paper, influences of several nonstructural factors on reservoir distributor are investigated experimentally under varied working conditions. The inlet tube configuration, installation orientation and capillary tube length are also studied. One experiment apparatus is developed to measure the refrigerant mass flow rate and the quality based on R410A air conditioner. It is found that influence caused by inlet tube before the distributor is small. The average STD is only 2.76%. Influence caused by orientation is broad. The average STD is less than 9% on the orientation of 15°. On the orientation of 90°, STDs of different conditions are all more than 40%. For orientation, mass flow rate sensitivity is larger than quality sensitivity. Capillary tubes with different length can be used to adjust distribution. Average STD with sizable capillary length difference is 9.47%. It means that only small mal-distribution can be adjusted by using different-length capillary tubes. Capillary tube length sensitivity increases with the increase of difference between outlet tubes or the decrease of average length of outlet tubes.

Assessment of Dimensionless Correlations for Prediction of Refrigerant Mass Flow Rate Through Capillary Tubes — A Review

2017 ◽  
Vol 25 (04) ◽  
pp. 1730004 ◽  
Author(s):  
Mehdi Rasti ◽  
Ji Hwan Jeong
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Capillary Tubes ◽  
Two Phase ◽  
Comprehensive Review ◽  
Wide Range ◽  
Inlet Conditions ◽  
Dimensionless Correlations

Capillary tubes are widely used as expansion devices in small-capacity refrigeration systems. Since the refrigerant flow through the capillary tubes is complex, many researchers presented empirical dimensionless correlations to predict the refrigerant mass flow rate. A comprehensive review of the dimensionless correlations for the prediction of refrigerants mass flow rate through straight and coiled capillary tubes depending on their geometry and adiabatic or diabatic capillary tubes depending on the flow configurations has been discussed. A comprehensive review shows that most of previous dimensionless correlations have problems such as discontinuity at the saturated lines or ability to predict the refrigerant mass flow rate only for the capillary tube subcooled inlet condition. The correlations suggested by Rasti et al. and Rasti and Jeong appeared to be general and continuous and these correlations can be used to predict the refrigerant mass flow rate through all the types of capillary tubes with wide range of capillary tube inlet conditions including subcooled liquid, two-phase mixture, and superheated vapor conditions.

Critical Mass Flow Rate Through Capillary Tubes

2010 ◽  
Author(s):  
A. Nouri-Borujerdi ◽  
P. Javidmand
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Study ◽  
Critical Mass ◽  
Small Diameter ◽  
Critical Conditions ◽  
Tube Length ◽  
Capillary Tubes ◽  
Drift Flux Model

This paper presented a numerical study that predicts critical mass flow rate, pressure, vapor quality, and void fraction along a very long tube with small diameter or capillary tub under critical condition by the drift flux model. Capillary tubes are simple expansion devices and are necessary to design and optimization of refrigeration systems. Using dimensional analysis by Buckingham’s π theory, some generalized correlations are proposed for prediction of flow parameters as functions of flow properties and tube sizes under various critical conditions. This study is performed under the inlet pressure in the range of 0.8 ≤ pin ≤ 1.5Mpa, subcooling temperature between 0 ≤ ΔTsub ≤ 10 °C. The tube diameter is in the range of 0.5 ≤ D ≤ 1.5mm and tube length between 1 ≤ L ≤ 2m for water, ammonia, refrigerants R-12, R-22 and R-134 as working fluids. Comparison between the results of the present work and some experimental data indicates a good agreement. Cluster of data close to the fitted curves also shows satisfactory results.

Numerical Simulation of Capillary Tube for Selected Refrigerants Using Homogeneous Equilibrium Model

2019 ◽  
Vol 27 (01) ◽  
pp. 1950001 ◽  
Author(s):  
Praveen Alok ◽  
Debjyoti Sahu
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Equilibrium Model ◽  
Capillary Tube ◽  
Tube Length ◽  
Mean Deviation ◽  
Choked Flow ◽  
Homogeneous Equilibrium ◽  
The Mean

In this work, a set of computational investigation results of two-phase refrigerant flow through adiabatic capillary are presented. There are various sizes of capillary tubes that can be selected related to commercially available copper tubes. Earlier refrigerants and new refrigerants like R12, R22, R134a, R410A and R32 are used for the flow analysis. Homogeneous-equilibrium model is employed with user-defined properties of the refrigerants for computation using ANSYS CFX. Several important parameters can be predicted rapidly and accurately using this method such as refrigerant mass flow rate, vapor mass fraction, local Mach no. etc. The mean deviation in mass flow rate is found to be [Formula: see text]1.18% for the same length of capillary tube and the mean deviation of tube length is found to be [Formula: see text]1.48% for the same experimental mass flow rate with choked flow condition.

Choked Flow Behavior of CO2 Refrigerant Flowing Through the Spiral Capillary Tube

2020 ◽  
Vol 28 (03) ◽  
pp. 2050024
Author(s):  
Pravin Jadhav ◽  
Neeraj Agrawal
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Graphical Representation ◽  
Capillary Tube ◽  
Flow Behavior ◽  
Tube Diameter ◽  
Tube Length ◽  
Flow Conditions ◽  
Choked Flow

The flow characteristics of CO2 refrigerant are numerically studied for an adiabatic spirally coiled capillary tube employing choked flow conditions. The mass, momentum and energy conservation equations are used to develop a numerical model. The existing model is verified with the published results. The choked flow behavior at various geometric parameters viz. tube diameter and spiral pitch is studied. Similarly, the influence of these parameters on the mass flow rate through the tube is observed. A significant change in mass flow rate is due to a change in tube diameter, whereas a minimal variation is observed with the change in surface roughness and spiral pitch. Moreover, it is observed that the coiling effect has a significant influence on the flow behavior of the spiral capillary tube. As the pressure decreases, from unchoked to the choked pressure in the evaporator by 63.46%, the mass flow rate increases by 9.46% only. The capillary tube choking is circumvented by increasing spiral pitch, tube diameter and decreasing the length of the tube. A unique nomogram is developed that gives the best understanding of choked and unchoked flow conditions, that graphical representation is useful to design the spirally coiled capillary tube. By using that, the choked length is identified for the known mass flow rate, even more, the choked mass flow rate is known for a given tube length. Moreover, for the given tube length and evaporator temperature, a nomogram is useful to the known choked values of mass flow rate and exit values of the evaporator pressure and quality of refrigerant.

scholarly journals Experimental Study on The Effect of Capillary Tube Geometry on The Performance of Vapour Compression Refrigeration System

2014 ◽  
Vol 7 (2) ◽  
pp. 47-60
Author(s):  
Abdul- Kareem R. Abed ◽  
Hassan Jawdat Fadhiel ◽  
Gaydaa Mahsun ◽  
Thabet C. Yassen
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Minor Effect ◽  
Capillary Tubes ◽  
Coil Diameter ◽  
Pitch Distance ◽  
Vapour Compression ◽  
Tube Geometry

A domestic refrigerator of 5 ft3 capacity is used to study the effect of coiled diameter and pitch distance of a capillary tube. Five capillary tubes of 2 mm in diameter and 1500 mm length each are used, as same as original capillary tube of the refrigerator. The capillary tubes is formed in five shapes, each one has different coil diameter (D) namely 25, 50, 75, 100 and 125 mm in diameter, in addition three distances between each coil (pitch (P)) is tested, namely 6, 8 and 10 mm. The pressure at inlet and outlet of capillary are measured to calculate the cycle COP, as well as the power consumed by the cycle compressor is measured to calculate the mass flow rate of refrigerant. The work show that the coiled diameter of capillary tube affect the cycle COP strongly, as the capillary coiled diameter (D) increases from 25 to 100 mm the cycle COP increases from 2.8 to 3.7 when the cabinet temperature equals to 8oC. The increases of coiled diameter more than 100 mm shows insignificant effect on the cycle COP. While the pitch space of capillary tube coiled shows minor effect on the cycle COP. Moreover, to the mass flow rate of refrigerant increases with approximately ranges from 1.2−2.7

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