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The heat transfer capacity of a convectional heat exchanger needs to be increased to minimize size and cost. Inserts are a promising way to enhance heat transfer at a bearable penalty in pressure drop. The objective of this study is to evaluate experimentally the thermal-hydraulic characteristics of a heat exchanger tube inserted with a novel alternatively twisted swirl generator (ATSG) tape. The experimental data has been collected for nine distinct combinations of ATSG tapes, includes the tapes with three twist angles (45°, 60°, and 90°) and three twist ratios (3, 4 and 5) for Reynolds numbers of 4,000 to 20,000. The use of ATSG tapes resulted in a considerable improvement in heat transfer rate compared to simple twisted tapes (TT). Over the range evaluated, heat transfer coefficient, pressure drop and thermal performance factor (TPF) with ATSG tapes in a tube are, respectively, 1.57–1.82, 1.58–2.54, and 1.22–1.46 times to that of simple TT in a tube. The maximum TPF achieved is 1.52 for ATSG tape with twist ratio of 3 and twist angle of 90°. The TPF for any combination of ATSG tapes is greater than one, which signifies that it is an efficient approach. [ABSTRACT FROM AUTHOR]

The experimental and numerical analysis is arranged to evaluate thermal hydraulic performance analysis with entropy generation on nanofluid flow in helical screw inserts in the tube with single and double strip and different twist ratios (TRs) in laminar flow. Single strip insert is also compared with double strip of helical screw inserts. Maximum enhancement of 421% in the values of Nusselt number is found with double strip helical screw insert in the flow of nanofluid at 1.5 of TR and 300 of Re as compared with plain tube inflow of water. Correlations are generated for Nu and f. Entropy production number is found lower value with double strip inserts than single strip helical screw inserts at low value of twist ratio in the flow of nanofluid than water. Thermal performance factor is achieved higher values with double strip insert at all flow rates at 2.5 of TR than single strip inserts, whereas found maximum value of 2.38 with double strip insert at twist ratio of 2.5 and Reynolds number of 300 in the flow of nanofluid. Optimum design of double strip inserts attained low entropy production number and higher value of thermal performance factor in the flow of nanofluid. [ABSTRACT FROM AUTHOR]

Abstract: Artificial roughness in the form of ribs is a convenient method for enhancing thermal performance of solar air heaters. This paper presents the experimental investigation of heat transfer and friction factor characteristics of a rectangular duct roughened with W-shaped ribs arranged at an inclination with respect to the flow direction on its underside on one broad wall. W ribs have been tested both pointing in downstream W-down and upstream W-up to the flow. The range of parameters for this study has been decided on the basis of practical considerations of the system and operating conditions. The duct has a width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/Dh ) of 0.03375 and angle of attack of flow (α) of 30–75°. The air flow rate corresponds to Reynolds number between 2300–14,000. The heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition and thermo-hydraulic performance has been investigated. Thermo-hydraulic performance comparison for different angle of attack of flow shows that W-down arrangement with angle of attack of flow as 60° gives best thermo-hydraulic performance. In addition heat transfer and friction factor correlations have been developed. [Copyright &y& Elsevier]

Abstract: Artificial roughness in form of ribs is convenient method for enhancement of heat transfer coefficient in solar air heater. This paper presents experimental investigation of heat transfer and friction factor characteristics of rectangular duct roughened with W-shaped ribs on its underside on one broad wall arranged at an inclination with respect to flow direction. Range of parameters for this study has been decided on basis of practical considerations of system and operating conditions. Duct has width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/D h) 0.018–0.03375 and angle of attack of flow (α) 30–75°. Air flow rate corresponds to Reynolds number between 2300–14,000. Heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition to determine thermo-hydraulic performance. Correlations have been developed for heat transfer coefficient and friction factor for roughened duct. [Copyright &y& Elsevier]

Abstract: An experimental investigation has been carried out to study the heat transfer and friction characteristics in solar air heater by using discrete W-shaped roughness on one broad wall of solar air heater with an aspect ratio of 8:1, the roughened wall being heated while the remaining three walls are insulated. The experiment encompassed Reynolds number (Re) range from 3000 to 15,000, relative roughness height (e/Dh ) in the range of 0.0168–0.0338, relative roughness pitch (p/e) 10 and the angle of attack (α) in the range of 30–75°. The effect of parameters on the heat transfer and friction are compared with the result of smooth duct under similar flow conditions. Correlations for heat transfer and friction have been developed as a function of roughness and flow parameters. [Copyright &y& Elsevier]