At the end we will know about......

• Concept of Capillary tube

• Vapour compression system

• Thermodynamic analysis of system

• Literature review

• Properties of refrigerants

• Scope of theory

Capillary Tube• The capillary tube is a copper tube of very small

internal diameter. • The internal diameter of the capillary tube varies

from 0.5 to 2.28 mm.• It is of very long length and it is coiled to several

turns so that it would occupy less space. • And length from 2 to 6 m• Capillary tube used as the throttling device in the

domestic refrigerators, deep freezers, water coolers and air conditioners.

• Primarily there are two kinds of capillary tubes

1. Adiabatic Capillary tube

2. Non-Adiabatic Capillary tube

When the pressure of the refrigerants in capillary tubes drops below the saturation value, a part of the refrigerant flashes into vapor.

This results in two-phase flow Due to high frictional resistance to flow of refrigerant , the pressure

of liquid refrigerant decreases

Vapor compression system

• The vapor-compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and rejects that heat elsewhere.

Saturated vapor

Superheated vapor

Saturated liquid

Saturated vapor

Thermodynamic analysis of the system

Advantages• The capillary tube is a very simple device that can be manufactured easily.

• It does not have any moving parts hence it does not require maintenance

• Inexpensive .

• The capillary tube limits the maximum amount of the refrigerant that can be charged in the refrigeration system.

• Cause the compressor to start at a low torque as the pressures across the capillary tube.

• When the refrigeration plant stops the pressure across the capillary tube becomes same and also along the whole refrigeration cycle the pressure is constant.

Limitations

• Capillary tube is susceptible to clogging by foreign particles due to small bore.

• Once the particular bore and length of capillary is selected for a particular system, it cannot adjust to the variations in discharge pressure.

• During off-cycle liquid refrigerant flows to evaporator because of pressure difference between condenser and evaporator. The evaporator may get flooded and the liquid refrigerant may flow to compressor and damage it when it starts.

Literature review

AUTHORNAME

TYPE OFSTUDY

REFRIGE-RANT

CAPILLARYDIMENSION

REMARKS

Yuanguang Li, Zhiyi

Wang, Buyun Jing

Analysis on the adiabatic flow in

capillary tube

R407C 1.6mm R-407C has similar capillary behavior to that

of R-22.

S. M. Sami, Ph.D.,

P.E., H. Maltais

and D. E. Desjardins

Influence of Geometrical

Parameters on Capillary Behavior

R-410BR-407C R-410A

2.159mm1.778mm

R-410B has the highest-pressure

drop and temperature

drop.

Analysis on the adiabatic flow of R407C in capillary tube

• R407C - a non-azeotropic mixture (23% R32/25% R125/52% R134a)

• A theoretical analysis is made and a numerical model is presented.• The equations of energy, continuity and pressure drop through a

capillary tube are presented• Pressure variations with length of tube are shown and compared to

R22 in the paper• Compared with the performance data of R22, the results show that

this numerical model is adequately precise and is available to provide an effective means by which to analyze components performance in optimizing and controlling a R407C air-conditioning system.

• R407C is most widely used one of the alternatives to R22

Influence of Geometrical Parameters on Capillary Behavior

• R-410B (R32/R125: 45/55%),• R-407C (R32/R125/R134a: 23/25/52%)• R-410A (R32/R125: 50/50%)• All these refrigerants are studied and their temperature and

pressure behaviour are plotted against length of capillary tube• R-410B has the highest-pressure drop along the capillary tubes

compared to the alternatives under question and also has the highest temperature drop along the capillary tube.

• The data also showed that R-407C has similar capillary behavior to that of R-22.

• Also the pressure drop decreases with increase in capillary diameter.

• Authors-S. M. Sami, Ph.D., P.E., H. Maltais and D. E. Desjardins

Other literature reviews…AUTHOR

NAMETYPE OF

STUDY

Sukkarin Chingulpitak, Somchai Wongwises Two-phase flow model of refrigerants flowing through helically coiledcapillary tubes

Bo Gu *, Yuanguang Li, Zhiyi Wang, Buyun Jing Analysis on the adiabatic flow of R407C in capillary tube

Zhou Guobing a,*, Zhang Yufeng b Numerical and experimental investigations on the performanceof coiled adiabatic capillary tubes

Robert R. Bittle a , Duane A. Wolf b & Michael B. Pate c A Generalized Performance Prediction Method forAdiabatic Capillary Tubes

M. Fatouh Theoretical investigation of adiabatic capillary tubes workingwith propane/n-butane/iso-butane blends

Neeraj Agrawal1 and Souvik Bhattacharyya2 Study of helically coiled adiabatic capillarytubes for transcritical CO2 expansion

R. R. Bittle a , J. A. Carter b & J. V. Oliver c Extended Insight into the Metastable Liquid RegionBehavior in an Adiabatic Capillary Tube

Properties of RefrigerantsRequired Properties of Ideal Refrigerant:

• The refrigerant should have low boiling point and low freezing point.

• It must have low specific heat and high latent heat.

• It must have high critical pressure and temperature to avoid large power

• requirements.

• It should have low specific volume to reduce the size of the compressor.

• It must have high thermal conductivity to reduce the area of heat transfer in evaporator and condenser.

• It should be non-flammable, non-explosive, non-toxic and non-corrosive.

• It should not have any bad effects on the stored material or food, when any

• leak develops in the system.

• It should give high COP in the working temperature range. This is

necessary to reduce the running cost of the system.

• It must be readily available and it must be cheap also.

Scope

• In respect of this , our project is a little effort to design such a capillary tube which will work efficiently with new alternative refrigerants

• We al know r22 is the main reason for the depletion of ozone layer. So we need a eco-friendly refrigerant.

• And we are in search of that.

Referances• [1] Lorentzen G. Revival of carbon dioxide as a refrigerant. Int J Refrig 1994;17:292–300.• [2] Bansal PK, Rupasinghe AS. A homogeneous model for adiabatic capillary• tubes. Appl Thermal Eng 1998;18:207–19.• [3] Gu B, Li Y, Wang Z, et al. Analysis on the adiabatic flow of R407C in capillary• tube. Appl Thermal Eng 2003;23:1871–80.• [4] Chen Y, Gu J. Non-adiabatic capillary tube flow of carbon dioxide in a• novel refrigeration cycle. Appl Thermal Eng 2005;25:1670–83.• [5] Khan MK, Kumar R, Sahoo PK. Flow characteristics of refrigerants• flowing through capillary tubes—a review. Appl Thermal Eng 2009;29:1426–39.• [6] Park C, Lee S, Kang H, et al. Experimentation and modelling of refrigerant• flow through coiled capillary tube. Int J Refrig 2007;30:1168–75.• [7] Valladares G. Numerical simulation and experimental validation of coiled• adiabatic capillary tubes. Appl Thermal Eng 2007;27:1062–71.• [8] Madsen KB, Poulsen CS, Wiesenfarth M. Study of capillary tubes in a• transcritical CO2 refrigeration system. Int J Refrig 2005;28:1212–8.• [9] Silva DL, Hermes CJL, Melo C, et al. A study of transcritical carbon dioxide• flow through adiabatic capillary tubes. Int J Refrig 2009;32:978–87.• [10] Hermes CJH, Silva DL, Melo C, et al. Algebraic solution of transcritical• carbon dioxide flow through adiabatic capillary tube. Int J Refrig• 2009;32:973–7.• [11] Agrawal N, Bhattacharyya S. Adiabatic capillary tube flow of carbon dioxide• in a transcritical heat pump cycle. Int J Energy Res 2007;31:1016–30.• [12] Gorasia JN, Dubey N, Jain KK. Computer aided design of capillaries of• different configurations. ASHRAE Trans 1991;97:132–8.• [13] Mori Y, Nakayama W. Study on forced convection heat transfer in• curved pipes (2nd report turbulent region). Int J Heat Mass Transf• 1967;10:37–59.