Heat Transfer of Nanofluids Through
HEAT TRANSFER OF NANOFLUIDS THROUGH
DOUBLE PIPE HEAT XCHANGER
ABSTRACT:
Due to the various speculated uses of nanofluids, it has become important to know more about their properties hence the objective of the present study is to investigate the forced convection of nanofluids.
The investigation was conducted by using double pipe heat exchanger in counter flow arrangement and the flow was turbulent. Water based nanofluids containing Al2O3 nanoparticles of various concentrations will be tested.
INTRODUCTION:
Nanofluids are dispersions of nanometer sized metal/metal oxide, carbon nanotubes, diamond or any other nanoparticles in a liquid medium.
These fluids have shown a significant increase in the thermal conductivity compared to the base fluid.
These fluids have a great potential to replace current coolants and heat transfer fluids in a variety of applications.
Heat-Transfer Challenges:
The heat rejection requirements are continually increasing due to trends toward smaller features (to <100 nm) for microelectronic devices, more power output for engines.
Cooling becomes one of the top technical challenges facing high-tech industries such as microelectronics, transportation, manufacturing, and metrology.
Conventional method to increase heat flux rates:
extended surfaces such as fins and micro-channels
increasing flow rates increases pumping power.
Nanofluids are promising to meet and enhance the challenges
Why use nanoparticles?
The concept of dispersing solid particles in fluids to enhance thermal conductivity is not new-it can be traced back to Maxwell
The major problem is the rapid settling of these particles (mm or micro) in fluids.
The small size of nanoparticles should markedly improve the stability of suspensions
The agglomeration of nanoparticles into larger particles that are found in liquids is a serious challenge.
Figure .1
DOUBLE PIPE HEAT EXCHANGER:
A double pipe heat exchanger, in its simplest form is just one pipe inside another larger pipe. One fluid flows through the inside pipe and the other flows through the annulus between the two pipes. The wall of the inner pipe is the heat transfer surface. The pipes are usually doubled back multiple times as shown in the diagram at the left, in order to make the overall unit more compact.
The term 'hairpin heat exchanger' is also used for a heat exchanger of the configuration in the diagram. A hairpin heat exchanger may have only one inside pipe, or it may have multiple inside tubes, but it will always have the doubling back feature shown. . Some heat exchanger manufacturers advertise the availability of finned tubes in a hairpin or double pipe heat exchanger. These would always be longitudinal fins, rather than the more common radial fins used in a crossflow finned tube heat exchanger. The actual double pipe heat exchanger is as shown in the figure.2
Figure.2
EXPERIMENTAL SETUP:
Figure.3
WORKING:
The experimental setup is as shown in the figure.3 consist of double pie heat exchanger, computer, two reservoirs, one heater, wheatstone bridge circuit, two pumps, valves etc. The second reservoir consisting of the nanofluid which is passed through the pum2 through the flowmeter2 when valve2 is opened. First the nanofluid passthrough the double pipe heat exchanger through inner pipe of diameter 17mm.The reservoir consisting of the water based nanofluids AL2O3 nanoparticles. The nanoparticles are of different concentrations like 1%nanofluid and 4%nanofluid is used. The fluid is heated in reservoir2 by using heater and then send to the double pipe heat exchanger of another side through the pump1, flowmeter1 when valve1 is opened.
The water is used as the fluid in heat exchanger then the operation is carried out at 40˚c then the calculations are done by the computer through data transmitter with the required inputs. The nusselt number and then heat transfer coefficient or film coefficient are determined by using the Reynolds number and other parameters. Like this at 50˚c and60˚c the values are determined.
The nanofluid1% and 99% water is next used as the fluid of the heat exchanger and then the properties of the fluid are determined, and then with different concentrations of the nanofluids are used and then heat transfer rate is determined. The flowmeters are used to find out the flow of the fluid and then pumps are used to circulating the fluid with the required velocity.
Finally by observing the results the heat transfer rate is increased by using the nanofluids with different concentrations of nanoparticles with base fluids.
MEASUREMENT OF CONVECTIVE HEAT TRANSFER COEFFICIENT:
By using the below relation we determine the overall heat transfer coefficient .
RESULTS AND DISCUSSIONS:
- 40 oC
- 50 oC
- 60 oC
TEMPERATURE DEPENDANCE:
Xuan and Li proposed new correlation concerning forced convection of nanofluids flowing in the tube by considering the microconvection and microdiffusion effects of the suspended nanoparticles:
CONCLUSION:
nanofluids have a bright future to be used as an effective heat transfer fluids,
nanofluids with relatively small concentration of solid particle can give meaningful enhancement of convective heat transfer coefficient
the enhancement of heat transfer convective coefficient compared to the base fluids: 6-10% for 1% particles concentration and 7-17% for 4% particles concentration
The use of Al2O3 nanoparticles as dispersed in water can enhance the convective heat transfer coefficient in the turbulent regime and the enhancement increase with Reynolds number, particles volume concentration, and temperature as well under the condition of experiment.