Already a subscriber?
MADCAD.com Free Trial
Sign up for a 3 day free trial to explore the MADCAD.com interface, PLUS access the
2009 International Building Code to see how it all works.
If you like to setup a quick demo, let us know at support@madcad.com
or +1 800.798.9296 and we will be happy to schedule a webinar for you.
Security check
Please login to your personal account to use this feature.
Please login to your authorized staff account to use this feature.
Are you sure you want to empty the cart?
ASHRAE Standard 28 Methods of Testing Flow Capacity of Refrigerant Capillary Tubes, 1996
- 28_1996_RA2010_text.pdf [Go to Page]
- FOREWORD
- 1. PURPOSE
- 2. SCOPE
- 2.1 This standard prescribes two test methods, a traditional method and an alternative method, for determining the flow capacity of capillary tubes such as are used for refrigerant metering in refrigeration systems. Both methods use dry nitrogen and ...
- 2.2 The results obtained by the prescribed procedures are indicative of the refrigerant flow characteristics of the tube but are not intended to represent the actual refrigerant flow characteristics in a refrigerating cycle.
- 2.3 The scope of this standard does not include specifications of tolerances on tube diameters or nitrogen flow capacity; however, acceptable variation in test results is suggested.
- 3. DEFINITIONS
- 4. APPARATUS FOR TRADITIONAL METHOD
- 5. TEST PROCEDURE FOR TRADITIONAL METHOD
- 5.1 The tube shall be incorporated into the test apparatus, arranged as shown in Figure 1. Unless otherwise dictated by design considerations, the tube shall preferably be tested as a straight length. If the limitations of the test apparatus make it ...
- 5.2 Adjust the ambient temperature of the apparatus and the tempering coil temperature to the specified value of 21°C +3°C (70°F + 5°F).
- 5.3 Adjust the inlet pressure to the desired value. The inlet pressure for various lengths and inside diameter shall be selected using Figure 2 as a guide. (Refer to Section 5.7 if multipoint nitrogen flow capacities are desired.)
- 5.4 Allow nitrogen to flow through the meter during two complete revolutions of the indicator.
- 5.5 Check and adjust as necessary the water level in the wet- test meter according to the manufacturer’s specification.
- 5.6 Each test run shall consist of determining the time (to the nearest 0.1 second) it takes a predetermined volume of nitrogen to pass through the wet-test meter.
- 5.7 If multipoint dry nitrogen flow capacities are desired, flow rates shall be determined at additional values of inlet pressure as guided by Figure 2.
- 5.8 A laboratory standard capillary tube developed in-house after equipment installation and calibration should be kept for subsequent equipment check.
- 6. DATA TO BE RECORDED FOR TRADITIONAL METHOD
- 6.1 Record a volume of not less than 30 L (1.1 ft3) during a period of not less than 120 seconds during any test.
- 6.2 Observe the time for four consecutive metered volumes and compute each flow rate.
- 6.3 Record the ambient temperature, the nitrogen temperature at the tube inlet, and the pressure and temperature at the wet-test meter.
- 6.4 Record the barometric reading and the temperature of the barometer. Correct the barometric reading for temperature only.
- 7. CORRECTION TO STANDARD BASIS FOR TRADITIONAL METHOD
- 7.1 Average the four rates obtained in section 6.2, then correct the average for the calibration of the wet-test meter (see Section 4, item (i)).
- 7.2 The flow rate of dry nitrogen (Qs) for the tested tube, corrected to standard barometric pressure at tube discharge and expressed in L/s (cfm) when the volume is measured at standard temperature and pressure, shall be obtained from Equation 1.
- 8. PRESENTATION OF DATA
- 8.1 The dry nitrogen flow capacity for a capillary tube shall be reported as follows:
- 8.2 If multipoint nitrogen flow capacities are obtained, they shall be presented by means of a curve as shown in Figure 4. The phrase “Dry nitrogen flow rate corrected to standard barometric pressure 101.325 kPa abs (14.696 psia) at tube discharge...
- 9. SUGGESTION FOR ACCEPTABLE VARIATION IN TEST RESULTS
- 10. APPARATUS FOR ALTERNATIVE METHOD
- 11. TEST PROCEDURE FOR ALTERNATIVE METHOD
- 11.1 The capillary tube shall be incorporated into the test apparatus, as shown in Figure 5. Unless otherwise dictated by design considerations, the tube shall preferably be tested as a straight length. If the limitations of the test apparatus make i...
- 11.2 With the main solenoid valve off and no flow, install the capillary tube as shown in Figure 5 in the quick-connect fixture.
- 11.3 Adjust the pressure gauge (7) and flowmeter (8) to zero as recommended by the manufacturer.
- 11.4 Open the nitrogen supply (1) and turn on the main solenoid switch (2).
- 11.5 Adjust the inlet pressure indicated on the pressure gauge (7) by using the pressure regulator (3). If the inlet pressure is less than 350 kPa gauge (50.8 psig), turn on the solenoid (5) to bypass the main line and direct the nitrogen flow throug...
- 11.6 The nitrogen volumetric flow rate converted to the condition of 101.325 kPa abs (14.696 psia) and 21°C (70°F) shall be read from the flowmeter (8). A flow reading shall be taken only when the flowmeter shows no fluctuations.
- 11.7 For data presentation, see Section 8.
- 11.8 A laboratory standard capillary tube developed in- house after equipment installation and calibration should be kept for subsequent equipment check.
- 12. CORRECTION TO STANDARD BASIS FOR ALTERNATIVE METHOD
- 12.1 The flow rate obtained in section 11.6 shall be corrected for the barometric pressure during the test being different from the standard pressure of 101.325 kPa abs (14.696 psia). Equation 2 shall be used.
- 13. REFERENCES [Go to Page]