Project on Pressure Drop Analysis in a Capillary Tube

A capillary tube is a long, narrow tube of constant diameter. The word “capillary” is a misnomer since surface tension is not important in refrigeration application of capillary tubes. The capillary tube is used as an expansion device in a vapor compression refrigeration system. In this project, you are going to calculate pressure drop in the various capillary tube for R22 refrigerant and air by varying capillary tube diameter keeping the length of the tube constant and varying the tube length keeping the diameter of tube constant with the help of control valve.

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This project deals with the pressure drop analysis in a capillary tube. The capillary tube is made of copper. You are going to work on a capillary tube of dia 0.31mm, 0.45mm, 0.55 mm and you are going to analyze how pressure drop varies with varying diameter. The refrigerant you are going to use is Air and R22 with a mass flow rate of 6.5kg/cm2.

To implement this project, you will be requiring the following components,

1. Three capillary tubes of dia 0.31mm, 0.45mm and 0.55 mm.
2. Eight control valves
3. Two pressure gauge
4. Long copper pipe
5. Two storage tanks
6. One air compressor
7. One litter R22 refrigerant

Project Description:

1. Air Compressor: An air compressor is a device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. The inlet sucks air in for the piston to compress. The compressed air is then released through the discharge valve. In certain air compressor models, the pressure is produced with rotating impellers. Compressed air is air kept under a pressure that is greater than atmospheric pressure. It serves many domestic and industrial purposes. You will be needing a single stage reciprocating air compressor.
2. Storage Tank: Storage tank is where refrigerants are being stored in high pressure. You can easily find these in domestic refrigerators.
3. R22 refrigerant: Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22 or R-22. It is commonly used as a propellant and refrigerant These applications are being phased out in developed countries due to the compound's ozone depletion potential (ODP) and high global warming potential (GWP), although global use of R-22 continues to increase because of high demand in developing countries R-22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene. R-22 cylinders are coloured light green.
4. Pressure Gauge: Pressure gauge is the device using which you are going to measure the pressure at the inlet and outlet sections of a capillary tube.

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Project Implementation:

1. At first, build the experimental setup as shown in the figure. Then circulate air inside the capillary tube.
2. Then perform a leakage test with the help of a soap bubble and water.
3. If you are finding any leakage is present then eliminate the leakage then and there.
4. Close the outlet valve and fill up of air inside the first tube (diameter - 0.31mm)at a particular pressure(max 6.5 kg/cm2).
5. Then close the inlet valve and measure the drop in pressure and keep a record of it. Perform the same in the other two capillary tubes with air as a refrigerant.
6. By varying the diameter and length of capillary tube you have to observe the pressure drop in a similar procedure as above.
7. Then follow the same procedure for refrigerant r22.
8. At the end plot graphs such as Diameter Vs Pressure drop, Length Vs Pressure drop and Diameter Vs Mass flow rate for observing the changes occurred.

Project Brief: After successful completion of the project, you can observe the following things,

• At a constant length of the capillary tube by varying the diameter we observe that pressure drop is less in large diameter capillary tube and vice versa.
• At constant diameter, by varying the length of the capillary tube we observe that pressure drop is high in small length capillary tube.
• For air at low pressure, the pressure drop is negligible in a capillary tube.
• At high pressure, the pressure drop is comparatively large.

Software requirements:

Minitab: You can use this software for plotting and comparing your result data.

• Three capillary tubes of diameter 0.31 mm
• 0.45 mm and 0.55 mm
• Eight control valves
• pressure gauge
• Long copper pipe
• Two storage tanks
• One air compressor
• One litter R22 refrigerant

• Refrigeration

Pressure Drop Analysis in a Capillary Tube