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Abstract 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 friction factor have been presented for a typical test section of a u-tube double pipe heat exchanger involving a circular tube filled with a full length insert. The flow is under forced convection with Reynolds Number varying from 3,000 to 31,000. From the experimental data, heat transfer coefficient, friction factor, and ther-mal performance with the twisted tape inserts were calculated and compared with the plain tube data. The results show that there were a significant increase in heat transfer coefficient, friction factor, and it was found that the thermal Performance of smooth tube is better than the full length twisted tape by 2.0–2.2 times.Keywords Heat transfer enhancement • Heat exchanger • Friction factor • 23594
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Performance ratio • Twist ratioNomenclature
A Area of heat transfer m2
di Inside tube diameter, m
d0 Outside tube diameter, m
D Twist diameter of inserted tape, m
H/D Twist ratio = Pitch/twist diameter
P. V. Durga Prasad (*)
Department of Mechanical Engineering, Narsimha Reddy Engineering College,
Maisammaguda, Hyderabad, AP, India
e-mail: pvdurgap@gmail.com
A. V. S. S. K. S. Gupta
Department of Mechanical Engineering, JNTUH College of Engineering, Hyderabad, AP, India
L1 Length of heat transfer test section, m
L2 Length of pressure drop test section, m
Δp Pressure drop, kg/m2
m Mass flow rate, kg/sec
Q Rate of heat transfer, W
Cp Specific heat of fluid, KJ/kg-K
Thi, Tho Inlet and outlet temperature of hot fluid, °C
Tci, Tco Inlet and outlet temperature of cold fluid, °C
hi Inside heat transfer coefficient, W/m2-k
ho Out side heat transfer coefficient, W/m2-k
ΔTLMTD Log mean temperature difference, °C
Re Reynolds Number
Pr Prandtl Number
Nu Nusselt Number
K Thermal conductivity of fluid, W/m−k
f Friction factor
U 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 tur-
bulence in the flow, a twisted tape is used as an insert in the pipe with an objec-
tive 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 signifi-
cance 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