Numerical analysis of the two-phase heat transfer in the heat exchanger of a mixed refrigerant Joule–Thomson cryocooler

Published Date
Cryogenics
December 2015, Vol.72:103–110, doi:10.1016/j.cryogenics.2015.09.010

• Author 

• R.M. Damle ^a
• P.M. Ardhapurkar ^b
• M.D. Atrey ^a,,

• aRefrigeration and Cryogenics Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India
• bS.S.G.M. College of Engineering, Shegaon 444203, India

Received 3 August 2015. Revised 26 September 2015. Accepted 28 September 2015. Available online 8 October 2015. 

Highlights

• •
  Two-phase heat transfer in the heat exchanger of an MR J–T cryocooler is simulated.
• •
  One-dimensional steady state model developed for numerical simulation.
• •
  Numerical model validated with experimental data for nitrogen–hydrocarbons mixtures.

Abstract

The recuperative heat exchanger is the most critical component of a mixed refrigerant Joule–Thomson cryocooler. The heat transfer process in such a heat exchanger takes place under two-phase conditions due to simultaneous boiling of the cold stream and condensation of the hot stream. This results in higher heat transfer coefficients as compared to single phase heat exchange. Moreover, depending on the composition of non-azeotropic mixtures, the boiling and condensation take place over a range of temperatures. In this work, the two-phase heat transfer in the recuperative heat exchanger of a mixed refrigerant Joule–Thomson cryocooler is studied. A numerical model is developed to simulate the heat transfer in a helically coiled tube-in-tube heat exchanger with nitrogen–hydrocarbons mixtures. The heat transfer coefficients for the two-phase flow under boiling and condensation are evaluated with the correlations available in the literature. The physical properties of the mixtures are evaluated at local conditions of temperature and pressure. The numerical results obtained with the developed model are compared with the experimental data reported in the literature. Additionally, the model predictions are also compared with new experimental data reported in the present work.

Keywords

J–T cryocooler

Mixed-refrigerant

Heat-exchanger

Numerical

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Nomenclature

A

cross-sectional area (m²)

CV

control volume

Cp

specific heat (J/kg K)

d

characteristic dimension (m)

dx

CV length (m)

G

mass velocity (kg/m² s)

h

heat transfer coefficient (W/m² K)

H

enthalpy (J/kg)

k

thermal conductivity (W/m K)

L

length of the finned tube/external annulus (m)

wetted perimeter (m)

m

mass (kg)

mass flow rate (kg/s)

given mass flow rate (kg/s)

Nu

Nusselt number

Pr

Prandtl number

p

pressure (N/m²)

Re

Reynolds number

T

temperature (K)

maximum temperature difference (K)

temperature glide (K)

V

velocity (m/s)

gas phase velocity (m/s)

liquid phase velocity (m/s)

Martinelli parameter

gas mass fraction

Greek symbols

viscosity (Ns/m²)

density (kg/m³)

wall shear stress (N/m²)

Subscripts

bub

bubble point

dew

dew point

c

cold gas in the external annulus

cond

condensation

eq

equivalent

g

gas

h

hot gas in the inner tube

in

inlet

l

liquid

lo

liquid only

m

mixture

out

outlet

w

tube wall

(–)

average over CV

Fig. 1.

Fig. 2.

Fig. 3.

 Table 1

Table 1.

 Table 2

Table 2.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

 Table 3

Table 3.

 Table 4

Table 4.

 Table 5

Table 5.

• ⁎ 
  Corresponding author. Tel.: +91 (22)2576 7522; fax: +91 (22)2572 6875.

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