Heat transfer and fluid flow characteristics of double pipe heat exchanger with passive techniques

Abstract

The present dissertation reports the experimental study pertaining to thermohydraulic characteristics of double pipe heat exchanger with passive enhancement techniques. The objective of the present study is to analyze the thermal performance of double pipe heat exchanger integrated with passive enhancement techniques for various practical applications such as solar air heating, air conditioning, space heating, chemical and petrochemical industries, food processing and power industries. A test facility has been developed to analyze the thermohydraulic characteristics in the annulus of double pipe heat exchanger with passive techniques. Test facility includes the test specimen, water flow and air flow system and instrumentation scheme. Water flows in the inner tube of the test specimen while air is allowed to flow in the annulus in the opposite direction that of water flow. Initially, tests have been performed to study the heat transfer and pressure drop characteristics of annuli formed by smooth inner tube and corrugated outer tube in counter flow conditions for the different diameter ratios (0.53, 0.44 and 0.40), different pitches (10 mm, 20 mm, and 30 mm) for varied range of Reynolds number (3500-10500). Nusselt number, friction factor and thermal performance factor are estimated from the present test data. Correlations have been proposed for friction factor, Nusselt number and thermal performance factor as a function of various modeling parameters. Next, the double pipe heat exchanger involving plain surface disc turbulators are considered for the Investigation. Tests are performed to examine the effect of various parameters namely, diameter ratio (DR = 0.42, 0.475 and 0.53), pitch ratio (8.42, 9.79 and 11.79) and Reynolds number (3200 - 10500) on the thermal performance. Nusselt number, friction factor and thermal performance factor are estimated from the test data. Also, correlations are proposed to evaluate various parameters such as Nusselt number, friction factor and thermal performance factor. Based on encouraging results, efforts have been made to estimate the thermohydraulic behavior using helical surface disc turbulators in the annulus of double pipe heat exchanger. Tests are performed for various diameter ratio (DR = 0.42, 0.475 and 0.53), different pitch ratio (8.42, 9.79 and 11.79), various helix angle (ɸ = 20o, 30o and 40o) and varied range of Reynolds number (3500 - 10500). Correlations are proposed for friction factor, Nusselt number and thermal performance factor as a function of various modeling parameters. Keywords: Double pipe heat exchanger, corrugated tube, plain surface disc turbulator, helical surface disc turbulator, heat transfer, Nusselt number, Reynolds number, friction factor, thermal performance factor.