International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
Experimental Study onHeat Transfer
andPressure Drop In Micro-Fin Tubes withand
Without Coiled Wire Insert
R. S. Lavate1* A. M. Patil2
1
*PG Student, M. E (Heat Power Engineering)
P.V.P.I.T College of Engineering, Budhgaon, Dist.-Sangli 416416 (India)
2
Associate Professor and Vice-Principal
P.V.P.I.T College of Engineering, Budhgaon, Dist.-Sangli 416416 (India)
ABSTRACT
The coiled wire inserts in microfin tubes are a typical technique that offers a higher heat transfer increase and, at the same
time, only a mild pressure drop penalty. This study investigates the heat transfer characteristics and pressure drop in a microfin
tube with and without coiled wire insert. Coiled wire insert has been used as one of the passive heat transfer enhancement
techniques and are the most widely used tubes in several heat transfer applications. The experiments are conducted using two
heat exchangers, contains microfin tube with coil wire inserts and microfin tube without coil wire insert.It contains the microfin tube in which Coiled wire insert is fabricated by bending iron wire into coil wire with coil diameter of 7.80 mm, coil pitch
of 3.2 mm and length 610 mm. The tests are performed at the cold and hot water mass flow rates ranging between 0.01667 and
0.06667 kg/s. The inlet cold and hot water temperatures are between 20 0C and 250Cand between 40 0C to 45 0C, respectively.
The experimental investigation and the calculations are discussed in this paper. Effect of different Reynolds numbers on the
heat transfer rate, overall heat transfer rate, Heat transfer coefficient results, pressure drop and friction factor for microfin
tube with and without coil wire insert are investigated.
Keywords:- coiled wire insert, Heat transfer augmentation technique, Micro fin tube, Passive methods,
1. INTRODUCTION
Heat exchangers have several industrial and engineering applications. The design procedure of heat exchangers is quite
complicated, as it needs exact analysis of heat transfer rate and pressure drop estimations apart from issues such as
long-term performance and the economic aspect of the equipment. Whenever inserts are used for the heat transfer
enhancement, along with the increase in the heat transfer rate, the pressure drop also increases. Therefore, any
augmentation device should optimize between the benefits due to the increased heat transfer coefficient and the higher
cost involved because of the increased frictional losses.The present paper includes various heat transfer augmentation
techniques. A literature review of heat transfer augmentation using passive techniques has been included.
Augmentation techniques increase convective heat transfer by reducing the thermal resistance in a heat exchanger. Use
of Heat transfer enhancement techniques lead to increase in heat transfer coefficient but at the cost of increase in
pressure drop.Experimental work on heat transfer augmentation using coiled wire inserts and a new kind of insert is
carried out. Inserts when placed in the path of the flow of the liquid, create a high degree of turbulence resulting in an
increase in the heat transfer rate and the pressure drop. The work includes the determination of heat transfer coefficient
and pressure drop in micro-fin tube with coil wire insert and without coil wire insert. The results of micro-fin tube with
coiled wire insert are compared with the values for the micro-fin tube without coiled wire insert
2. OBJECTIVES
 Investigating the heat transfer characteristics in Micro-fin tube with and without coiled wire insert.
 To determine the pressure drop in Micro-fin tube with and without coiled wire insert.
3.METHODOLOGY (ACTION PLAN)
 Preparation of test rig with required measuring instrumentation.
 Experimentation will be carried out by varying percentage of fluid (Refrigerant), mass flow rate and by using
micro-tube with and without coiled wire inserted.
 Obtained data will analyze with various parameters of micro-tube with and without coiled wire inserted.
 Validation of results with available literature.
Volume 4, Issue 3, March 2015
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
4.EXPERIMENTAL SETUP
A schematic diagram of the experimental apparatus is shown in Fig 1. The test loop consists of a test section,
refrigerant loop, hot water loop, and cold water loop and data acquisition system. The test section is a Shell and Tube
type heat exchanger shown in fig. 2. The shell is made up of mild steel having diameter 100 mm and length 750 mm.
the shell is insulated with SS 304 Nitrile rubber. Inside the shell 7 number of microfin tubes are placed. The inner and
outer diameters of the micro-fin tube are 8.92 and 9.52 mm respectively. The microfin tubes are made up of copper.
The length of microfin tube is 610mm. Coiled wire insert is fabricated by bending a 1mm diameter iron wire into coil
wire with coil diameter of 7.80 mm and coil pitch of 3.2 mm the length of coil wire is 610 mm.
Fig- 1: Block Diagram of experimental setup
The close loops of hot and cold water consist of the storage tanks, electric heaters controlled by adjusting the voltage,
and a cooling coil immerged inside a cold storage tank. R134a is used as the refrigerant for chilling the water. The hot
water is adjusted to the desired level and controlled by a temperature controller the temperature of hot water maintain
in between 400C to 450C. The temperature of cold water ranges from 200C to 250C. After the temperature of the cold
and hot water are adjusted to achieve the desired level, the water of each loop is pumped out of the storage tank and is
passed through a flow meter, test section, and returned to the storage tank. In this test rig two rotameters with the flow
range 1 to 10 LPM, are used to measure flow of cold water and hot water. The flow of water is controlled through ball
valves. To measure pressure drop across the microfin test section the manometer is used. One end of manometer is
connected to inlet section of microfin tube and other end is connected to outlet of microfin tube with flexible pipe.
To measure the temperature 12 different thermocouples are used. T1, T2, T3, T4 are the temperature after evaporation,
compression, condensation and expansion respectively. T5, T6 be the temperature of hot water at inlet and outlet and T 7,
T8 be the temperature of cold water at inlet and outlet for microfin tube with coil wire insert. Similarly, T 9, T10 be the
temperature of hot water at inlet and outlet and T11, T12 be the temperature of cold water at inlet and outlet for microfin
tube without coil wire insert. In addition to the loop component, a full set of instruments for measuring and control of
temperature and flow rate of all fluids is installed at all important points in the circuit.
Experiments were conducted with various flow rates of hot water and cold water entering the test section. Hot water at
about 40°C is allowed to pass through the tube side of heat exchanger at a flow rates ranging from 0.01667 Kg/s to
0.06667 Kg/s and Cold water is now allowed to pass through the annulus side of heat exchanger in Counter current
direction at flow rates ranging from 0.01667 Kg/s to 0.06667 Kg/s.The water inlet and outlet temperature for both hot
water and cold water are recorded only after temperature of both the fluids attains a steady state
5. DATA DEDUCTION
5.1 For Reynolds Number
Where, ρ – Density (kg/ m3), - Velocity of water (m/s), di -Inside diameter of the test tube (m)
5.2 For Prandlt Number
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
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Where, - Dynamic Viscosity, (Kg/m.s), - specific heat, KJ/ (kg 0C), - Thermal conductivity of fluid, (w/ m°C)
5.3 For Average Heat Transfer Rate and Overall Heat Transfer Rate
5.4 Pressure Drop and Friction Factor Calculation
ΔP - Pressure Drop, di -Inside diameter of the test tube (m), L- Length of the test section, m - Density, kg/ m3,
Velocity of water (m/s),
5.5 Heat transfer coefficient
-
6. RESULTS AND DISCUSSION
Graph -1: Heat transfer rate Vs Reynolds Number
From graph 1 shows the variation of the heat transfer rate with hot water Reynolds number for different types of test
section at mass flow rate of hot (mh) and cold water (mc) varies from 0.01667 kg/s to 0.06667 kg/s at a specific
temperature of hot and cold water entering the heat exchanger. Due to higher heat transfer surface area, the heat
transfer rates obtained from the Micro-fin tube with coil wire insert are higher than those micro-fin tubes without coil
wire insert. From graph 1 it is clear that the coiled wire insert can enhance heat transfer rate. This is because the coiled
wire insert has a significant effect on the mixing of fluid in the boundary layer. Therefore, the heat transfer rates
obtained from micro-fin tube with coiled wire insert are higher than those from micro-fin tube without coiled wire
insert.
Graph - 2: Heat Transfer Coefficient Vs Reynolds Number
Volume 4, Issue 3, March 2015
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
The average heat transfer coefficient increases with increasing hot water mass flow rate. This is because the heat
transfer coefficient depends directly on the heating capacity of the hot water.
Graph - 3: Heat Transfer Coefficient Vs Reynolds Number
Graph 3 shows the variation of the heat transfer coefficients with hot water Reynolds number at various types of the test
section. The heat transfer coefficients obtained from the micro-fin tube with coiled wire insert are the higher as
compared with those from the micro-fin tube without the coiled wire insert.
Graph – 4:Pressure Drop Vs Reynolds Number
Graph 4 shows the coiled wire insert has significant effect on the pressure drop. The pressure drop in microfin tube
with coil wire insert is greater than that of microfin tube without coil wire insert at same mass flow rate of hot and cold
water
Graph - 5:Friction Factor Vs Hot water mass flow rate
From graph 5 shows the variation of Friction factor with hot water Reynolds number for mass flow rate of cold water
mc= 0.01667 kg/s and mass flow rate of hot water mh varies from 0.01667 kg/s to 0.06667 kg/s at a specific temperature
of hot and cold water entering the heat exchanger. From above graph it is clear that trends of friction factor slightly
decrease as mass flow rate of hot water increase for the micro-fin tube with and without coiled wire insert.
Graph - 6 :Friction Factor Vs Reynolds number
Volume 4, Issue 3, March 2015
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 4, Issue 3, March 2015
ISSN 2319 - 4847
From graph 6 shows the variation of Friction factor with hot water Reynolds number for mass flow rate of cold water
(mc) and mass flow rate of hot water (mh) varies from 0.01667 kg/s to 0.06667 kg/s at a specific temperature of hot and
cold water entering the heat exchanger. The coiled wire insert has significant effect on the friction factor. The friction
factor in microfin tube with coil wire insert is greater than that of microfin tube without coil wire insert at same mass
flow rate of hot and cold water
7. CONCLUSION
The experimental investigation and the calculations are discussed in this paper. Effect of different Reynolds numbers
on the heat transfer rate, overall heat transfer rate, Heat transfer coefficient results, pressure drop and friction factor for
microfin tube with and without coil wire insert are investigated. Then the comparative study is carried out. The heat
transfer enhancement techniques can be improved heat transfer or thermal performance of heat exchangers. Coiled wire
insert has been used as one of the passive heat transfer enhancement techniques. Coiled wire insert enhance heat
transfer rates, heat transfer coefficients, pressure drop, friction factor. When the pressure drop increases, the pumping
power cost also increases, thereby increasing the operating cost.
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