An experimental study of the flow of R-134a inside an adiabatic spirally coiled capillary tube Mohd. Kaleem Khan, Ravi Kumar*, Pradeep K. Sahoo Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee, Uttarakhand 247 667, India article info Article history: Received 29 August 2007 Received in revised form 9 January 2008 Accepted 13 January 2008 Published online 3 February 2008 Keywords: R-134a Refrigerant Capillary Adiabatic Flow Pitch Correlation abstract This paper presents an experimental investigation for the flow of R-134a inside an adia- batic spirally coiled capillary tube. The effect of various geometric parameters like capillary tube diameter, length and coil pitch for different capillary tube inlet subcoolings on the mass flow rate of R-134a through the spiral capillary tube geometry has been investigated. It has been established that the coil pitch significantly influences the mass flow rate of R- 134a through the adiabatic spiral capillary tube. The effect of providing pressure taps on the capillary tube surface has a negligible effect on the mass flow rate through the capillary tube. It has been concluded that the effect of coiling of capillary tube reduces the mass flow rate by 5–15% as compared to those of the straight capillary tube operating under similar conditions. The data obtained from the experiments are analyzed and a semi-empirical correlation has been developed. The proposed correlation predicts more than 91% of the mass flow rate which is in agreement with measured data in an error band of 10%. ª 2008 Elsevier Ltd and IIR. All rights reserved. Etude expe ´ rimentale sur l’e ´ coulement de R-134a a ` l’inte ´ rieur d’un capillaire adiabatique en spirale Mots cle ´s : R-134a ; Frigorige ´ ne ; Capillaire ; Adiabatique ; E ´ coulement ; Inclinaison ; Corre ´ lation 1. Introduction Capillary tubes are being used as an expansion device in the low capacity refrigerating machines like domestic refrigerators and window type room air conditioners. These are narrow drawn copper tubes of 0.5–2.0 mm bore and 2–6 m length. Owing to the simplicity, low cost, zero maintenance and requirement of a low starting torque motor to run the compressor, capillary tubes have been used in a variety of vapour compression systems. The various flow aspects of the capillary tube were in- vestigated by a number of researchers since past six decades. Bolstad and Jordan (1948) pioneered the investigations on capil- lary tubes. They studied the effect of oil entrainment on the mass flow rate through the capillary tube. It was found that the use of oil separator in the system decreases the flow rate by 8% in comparison to that when no oil separator was used. Mikol (1963) carried out an extensive experimental investigation on the capillary tube to explore the various flow phenomena like * Corresponding author. Tel.: þ91 1332 285740; fax: þ91 1332 285665. E-mail address: ravikfme@iitr.ernet.in (R. Kumar). www.iifiir.org available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ijrefrig 0140-7007/$ – see front matter ª 2008 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2008.01.008 international journal of refrigeration 31 (2008) 970–978