Augmentation of Heat Transfer and Pressure Drop Characteristics Inside a Double Pipe U-Tube Heat Exchanger by Using Twis
A twisted tape is inserted into a double pipe u-tube heat exchanger with a view to generate swirl flow, thereby enhancing the heat transfer rate of the fluids flowing in it. Experimental investigations of heat transfer enhancement and variation of frictio
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Area of heat transfer m2 Inside tube diameter, m Outside tube diameter, m Twist diameter of inserted tape, m Twist ratio = Pitch/twist diameter
P. V. Durga Prasad (*) Department of Mechanical Engineering, Narsimha Reddy Engineering College, Maisammaguda, Hyderabad, AP, India e-mail: [email protected] A. V. S. S. K. S. Gupta Department of Mechanical Engineering, JNTUH College of Engineering, Hyderabad, AP, India
S. Sathiyamoorthy et al. (eds.), Emerging Trends in Science, Engineering and Technology, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-81-322-1007-8_3, © Springer India 2012
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P. V. Durga Prasad and A. V. S. S. K. S. Gupta
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L1 L2 Δp m Q Cp Thi, Tho Tci, Tco hi h o ΔTLMTD Re Pr Nu K f U
Length of heat transfer test section, m Length of pressure drop test section, m Pressure drop, kg/m2 Mass flow rate, kg/sec Rate of heat transfer, W Specific heat of fluid, KJ/kg-K Inlet and outlet temperature of hot fluid, °C Inlet and outlet temperature of cold fluid, °C Inside heat transfer coefficient, W/m2-k Out side heat transfer coefficient, W/m2-k Log mean temperature difference, °C Reynolds Number Prandtl Number Nusselt Number Thermal conductivity of fluid, W/m−k Friction factor Overall heat transfer coefficient, W/m2−k
1 Introduction In the convective mode of heat transfer involving heat exchangers used in industrial applications, double pipe U-tube heat exchangers find wide usage. Typically, it involves exchange of heat between two fluids separated by a layer of pipes, with one fluid flowing inside the tube and the other fluid flowing outside the tube (called the annulus). As such, a good design of the heat exchanger is to extract maximum possible amount of heat during the heat exchange process. Based on Newton’s law of cooling, the heat transfer coefficient is one parameter which can be enhanced to increase the rate of heat transfer. As the usual economic considerations require a compact design, enhancement of area of heat exchanger serves no purpose. In forced convection under higher Reynolds number, higher heat transfer rates are possible when turbulence or swirl is created in the flow. Hence to achieve this turbulence in the flow, a twisted tape is used as an insert in the pipe with an objective to enhance the heat transfer rates. As the heat exchangers of double pipe U-tube type are frequently used in many applications involving heat transfer between two or more fluids, enhancement of heat transfer rate between the fluids is of great significance for the industry. Besides saving of primary energy, it also leads to reduction in the size and weight of the heat exchanger, thereby saving costs to the users. After a survey of techniques used to enhance the heat transfer rate, an attempt is made in this work to investigate the same using twisted tape inserts. The various techniques of augment convective heat transfer are given by Hong et al. [1] found that in the case of high Prandtl Number fluid in laminar flow, the heat transfer rate increases considerably for a moderate increase in p
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