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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 pressure drop.
Eiamsa-ard et al. [2] for experimentally investigating the effect of twisted tape insert on heat transfer in the tube side of a double pipe heat exchanger measured
the heat transfer without twisted tape [3]. Twisted tape techniques have been used to
augment heat transfer in double pipe heat exchanger. Ahmed et al. [4] measured the
tube side heat transfer coefficient for turbulent flow of air in a smooth tube for the
purpose of investigating the heat transfer enhancement using twisted tape inserts.
An overview of hundred research works of enhancement heat transfer rate by using
twisted tape was reported by Dewan et al. [5]. Anil Singh Yadav [6] investigated
heat transfer and the pressure drop characteristics in a double pipe heat exchanger
with full length twisted tape inserts. Naphon [7] reported heat transfer results from
the plain tube for comparing with those from coil-wire inserted tube [8]. Heat trans-
fer and pressure drop characteristics of Laminar flow through a circular tube fitted
with regularly spaced twisted tape elements with multiple twists.
The objective of this paper is to study heat transfer and pressure drop charac-
teristics of the U-tube double pipe heat exchanger with and without twisted tape
inserts. The effect of various relevant parameters on heat transfer characteristics
and pressure drop are also investigated. The experiments on heat transfer and
pressure drop characteristics for the U-tube double pipe heat exchanger with full
length twisted taped insert have been analysed for their suitability to practical
applications in industries.
2 Experimental Equipment and Procedure
2.1 Description of Experimental Equipment
The schematic representation of experimental set up is shown in Fig. 1a. It con-
sists of, Water tank with heater of 0.64 m3 capacity placed on floor, Double pipe u
bend heat exchanger, measuring devices like totalizer, temperatures, Water pumps
for pumping hot water, and cold water (0.25 HP). The heat exchanger consists of
2 m long tubes of stainless steel (304 SS), 0.019 m inner diameter, and 0.025 m
outer diameter. The heat transfer test section is fitted with jacket (annulus) for
admitting hot water. Over the jacket asbestos rope is wound to a thickness of 1
inch to minimize heat loss.
Two RTD PT 100 type temperature sensors one just before the test section and
other after the test section are placed to measure the inlet and outlet of fluid. A
hot water tank (insulated with asbestos rope) with the in built PID controller and
heater (1 kW) is provided to supply hot water at constant temperature. The tem-
perature of hot water is maintained at 75 °C with the deviation of plus or minus
2 °C by thyristor controlled heating. Also two more RTD PT 100 type temperature
sensors, one at the inlet and another at the outlet of jacket are placed to measure
the hot fluid temperatures.
The cold water at room temperature is being taken at different Reynolds numbers
ranging from 3,000 to 33,000 with the aid of a centrifugal pump. The by-pass valve attached to totalizer is used to regulate the flow rate to the test section. The two ends
of the U-tube manometer pressure tapes, one just before the test section and the other
just after test section are provided for pressure drop measurement. Mercury is used
as the manometric liquid for determining the pressure drop at different flow rates.The photo of twisted tape inserted into the tube and schematic