The process of heat transfer

Many industrial procedures involve the heat transportation. Heat transportation is a procedure by which internal energy from one substance transportations to another substance. The heat transportation occurs when bing of temperature difference between two parts. The heat transferA is usually occurs from a highA temperature part to a lower temperature part. There are three manners of heat transportation. There are conductivity, convention and radiation. The conductivity manner is the transportation of heat in solids or fluids at remainder conditions. The convention manner is occurs at fluids near a solid surface. While the radiation manner is the transportation of heat through the electromagnetic moving ridges without medium required. The procedures of heat tranfer cover a big scope of temperatures and force per unit area. There are devices to execute heat transportations procedure called heat money changers.

Heat money changers are devices that carry oning heat transportation between two fluids at difference temperatures ( Kirk, 1999 ) . In many types of heat money changer, the two fluids are separated by a solid wall to forestall they are non in direct contact with each other. The primary heat transportation manners in heat money changers are convention and conductivity. The convention occurs in the boundary bed between the fluids on each side of the solid wall and the conductivity occurs in the solid wall itself. Double pipe heat money changer is one of the illustrations of heat money changer applications. To maximise conductivity heat transportation, the heat money changer devices such as dual pipe heat money changer usage liquid coolants to tranfer the heat. Therefore, heat money changer public presentation depends on the effectivity of the heat tranfer fluids.

The heat transportation fluids play an of import function in the development of heat money changer equipment. However, the conventional coolant fluids such as ethene, H2O and oil offer low heat transportation belongingss. Therefore, the advanced heat transportation fluids development with higher heat transportation belongingss is in a strong demand. Therefore, to obtain higher heat transportation belongingss, a new coevals of heat transportation fluids have been developed which is called nanofluid.

2.2 ) Double pipe

Double pipe is the 1 of heat money changer applications. Double pipe heat money changer is made of homocentric inner and outer pipe ( Sadik et al, 2002 ) . Cold and hot liquid severally flows in the spread of interior pipe and exchanges heat at the same clip. U decompression sicknesss are used for inter connexion inner pipe. The construction of dual pipe heat money changer is simple and heat transmittal is big.

Figure 1: Double pipe heat money changer in industry ( www.brighthub.com )

Figure 2: the construction of dual pipe heat money changer ( www.wikimedia.org )

The dual pipe heat money changer can be arranged as in figure 2. There are two shells joined at one terminal through return bend lodging. In the interior of return crook lodging, the cardinal tubing is dead set or welded into a U-shape with the U-bend for this constellation. It will do the shell side fluid to flux in series through each of two shells. The lodging has a removable screen to let remotion or interior tubings.

The dual pipe heat money changer is besides known as hairpin heat money changer. These hairpins are based on modular rules. They can set up in series ( Figure 3 ) , parallel ( Figure 4 ) or series parallel combinations to accomplish the responsibility of application.

Figure 3: An oil ice chest with two hairpin subdivisions arranged in series. ( Sadik et al, 2002 )

Figure 4: An oil ice chest with two dual pipe units in series on the shell side and analogue on the tube side ( Sadik et al, 2002 ) .

2.2.1 ) Purpose of dual pipe heat money changer

By and large, the dual pipe heat money changer used for high flow rate, temperature and force per unit area conditions. The heat transportation rate is high. The dual pipe heat money changer was developed to suit applications that are excessively little country and subdivisions. They can be used in fouling conditions for easy to clean and care. When little heat transportation countries are required, dual pipe heat money changer is first-class for heating and chilling fluids procedure. They are besides really suited for the fluids at high force per unit area due to the smaller diameter of the pipes.

2.2.2 ) Type of dual pipe heat money changer

The dual pipe heat money changer is made by fall ining tubings ( Sarit, 2005 ) . The design buildings produce difference types of dual pipe units. The types of dual pipe heat money changers are listed in Figure 5.

Double Pipe Heat Exchanger

Two tubings unit

Multi-tubes unit

Multipass

U-tube

Single base on balls

Parallel-series

Series-series

Parallel-parallel

Figure 5: Types of dual pipe heat money changer ( Sarit, 2005 ) .

There are the inside informations types of dual pipe heat money changer ( Sarit, 2005 ) :

Single base on balls unit

This is the simplest type of the dual pipe heat money changer. It made by infixing one tubing into another pipe and sealing decently. This unit is non really popular because of comparatively big length for a given responsibility and required big infinite even though the care is easier. Normally, this type is used in little application such as inline warming of furnace oil for little domestic boiler. Figure 6 shows one of illustrations for individual base on balls unit.

U-tube unit

This is the most popular design of dual pipe heat money changer. Figure 7 shows a U-tube unit. It is arranged by two interior tubings are jointed at the terminal pipe with U-bend by welding. The two outer tubings are joined by a return crook lodging. This type is allowed thermic enlargement since the terminal of the pipe is joined with U-bend.

Multi-tube unit

Multi-tube dual pipe are similar to the U-tube but different in utilizing one inner pipe to a package of tubing. For low force per unit area application, the tubing sheet is sealed both on the shell side fluids. This type is suited for low force per unit area and non-hazardous units. This type is shown in Figure 8.

Figure 6: A Single base on balls two-base hit pipe heat money changer

Figure 7: A U-tube dual pipe heat money changer

Figure 8: Multi tubing double pipe heat money changer

2.2.3 ) The advantages of dual pipe heat money changer

There are the advantages of dual pipe heat money changer ( Hewit et al, 1994 ) :

They are inexpensive and readily available due to simplicity building in its typical applications.

Thermal enlargement did non happen because of the U-tube type of building

Easy of cares since shell circuit can be inspected and steam or automatically cleaned due to simple building and flanged articulation.

They are flexible in any status because come in with multi-pass tubing circuit agreement that can be adjusted either add up the connection or take it.

Capable of defying thermic applications and support in high temperature and force per unit area applications.

They allow countercurrent heat exchange in which the cold fluids can be heated to a higher temperature since there are the hot fluids at the issue.

2.2.4 ) The applications of dual pipe heat money changer.

There are several applications for dual pipe heat money changer ( Guy, 1978 ) :

Oil and gas production.

Engine and transmittal oil ice chests.

Chemical and H2O warming applications.

Steam to liquid applications.

Marine fuel ice chest.

In this undertaking, the dual pipe heat money changer application in H2O warming for territory warming installation is used to analyze.

2.3 ) Nanofluid

Nanofluid is the name conceived by Argonne National Laboratory to depict a fluid in which nanometre sized atoms are suspended. The nanofluid is new sort of heat medium incorporating nanoparticles which is uniformly and stably distributed in a base fluid ( Mohorianu et al, 2006 ) . Nanofluid are engineered by suspending nanoparticles with mean sizes below 100nm in common base fluids ( Wenghua et al. 2007 ) . Common base fluids are normally conventional coolants like H2O, oil and ethanediol. Figure 9 shows that the one illustration of nanofluid type, aluminum oxide, Al2O3 is smaller than 30 A± 5 nanometer.

Figure 9: Alumina, Al2O3 nanoparticles dispersed in H2O ( Ji-Hwan Lee et al. , 2007 )

2.3.1 ) Production of nanofluid

The development of modern engineering allows the fiction of stuffs at the nanometre graduated table. Nanoparticles used in nanofluids have been made from many stuffs. The illustration of nanoparticles stuffs are oxide ceramics, nitride ceramics, carbide ceramics, metals and composite stuffs.

There are two techniques to bring forth nanofluids which are the two measure technique and the individual measure technique ( Wenhua et al. 2007 ) . The two measure technique starts with nanoparticles, produced by one of the physical or chemical synthesis techniques descried antecedently and so returns to scatter them into a base fluid. Meanwhile, the individual measure technique at the same time makes and disperses the nanoparticles straight into the base fluid.

2.3.2 ) Nanofluid in heightening thermic public presentation

Nanofluid is nanotechnology-based heat transportation fluids that are derived by stably suspending nanometre sized atoms with typical length graduated tables of 1 to 100nm in conventional heat transportation fluids. Research consequences from research workers show that nanofluids have thermic belongingss that are different from conventional heat transportation fluids.

For the high public presentation in thermic conduction, several research workers have done some experimental and analysis survey. For illustration, Masuda et Al. ( 1993 ) has showed that the thermic conduction of extremist all right suspensions of aluminum oxide, silicon oxide and other oxides in H2O increased by up to 30 % for a volume fraction of 4.3 % . Wang et Al. ( 1999 ) reported that thermic conduction for aluminum oxide and cuprous oxide enhanced with a assortment of basal fluids including H2O and ethene ethanediol. They observed a upper limit of 12 % addition in the conduction with a volume fraction of 3 % of alumina atoms. On the other manus, the viscousness showed an addition of 20 % -30 % for the same volume fraction. Choi, et Al. ( 2001 ) stated that the add-on of a little sum of nanoparticles to conventional heat transportation liquids increased the thermic conduction of the fluids up to about two times. Eastman et Al ( 2001 ) found that the thermic conduction of ethene ethanediol nanofluid incorporating 0.3 % volume fraction of Cu atoms can increased up to 40 % . Pantzali et Al. ( 2009 ) have conducted probe the efficaciousness of nanofluids in home base heat money changer. They found that when the nanofluid is added in coolant, the thermic conduction is increased.

The convention heat transportation coefficient besides has been studied and investigated by the researches. Choi ( 1995 ) reported a possibility to increase convention heat transportation coeffients is by utilizing nanoparticles suspended in liquids. Byung et Al. ( 2008 ) have conducted an experiment on consequence of aluminum oxide in dual pipe heat money changer. They found that the add-on of nanoparticles in the fluid increase the mean heat transportation coefficient of the system in laminar flow. They besides stated that the factors of heightening the heat transportation of nanofluids are surface belongingss of nanoparticles, atoms lading and atom form. Leong et Al. ( 2010 ) have investigated thermic public presentation of an automotive auto radiator operated with nanofluids based coolants. They have concluded that with the increasing in volume concentration of nanofluids, the heat transportation rate is increased.

The researches have performed the probe on the consequence of nanofluids belongingss such as volume concentration to better the thermic public presentation. Xuan and Li ( 2003 ) performed experimental survey on Cu-water nanofluids up to 2 % volume concentration and developed a Nusselt figure correlativity. They found that Cu-water dilute nanofluids have about same force per unit area bead as H2O under same Reynolds figure. Hwang et Al. ( 2007 ) reported that thermic conduction of the nanofluids depends on the volume fraction of atoms and thermic conduction of atoms and base fluids. The thermic conduction of aqueous aluminum oxides ( Al2O3 ) nanofluids with low concentration has been investigated by Lee et Al. ( 2008 ) . This aluminum oxide ( Al2O3 ) nanofluids produced by two measure technique. They indicated that the thermic conduction of aqueous nanofluids increases linearly with the add-on of aluminum oxide atoms.

Mintsa et Al. ( 2009 ) researched the consequence of temperature, atom size and volume fraction on thermic conduction of H2O based nanofluids of Cu oxide and aluminum oxide. They have suggested that to heighten the thermic conduction was by increasing the atoms volume fraction, temperature and atoms size. When smaller atoms are used in the same volume fraction, the contact surface country of atoms with fluid and Brownian gesture can be increased. Therefore, this increased thermic conduction of nanofluids. An experimental survey on the heat transportation public presentation and force per unit area bead of TiO2-water nanofluids fluxing in disruptive flow government has conducted by Duangthongshuk and Wongwises ( 2010 ) . They stated that the force per unit area bead of nanofluids was higher than the base fluid and increased with the increasing volume concentrations.

Table 2: The sum-up of literature surveies in thermic public presentation operated with nanofluids.

Mention

Atoms

Fluids

Findingss

Masuda et Al. ( 1993 )

Al2O3, SiO2

Water

30 % betterment for volume fraction of 4.3 % .

Wang et Al. ( 1999 )

Al2O3, CuO

Water, EG

12 % betterment for volume fraction of 3 %

Choi, et Al. ( 2001 )

– about two times increment

Eastman et Al ( 2001 )

Copper

EG

40 % betterment for 0.3 % volume fraction

Pantzali et Al. ( 2009 )

Thermal conduction increased

Choi ( 1995 )

Convection heat transportation coefficient addition

Byung et Al. ( 2008 )

Al2O3

Average heat transportation coefficient addition

Leong et Al. ( 2010 )

Copper

EG

Heat transportation rate increased

Xuan and Li ( 2003 )

Copper

Water

Pressure bead increased for 2 % volume fraction

Hwang et Al. ( 2007 )

Increasing depending on volume fraction per centum

Lee et Al. ( 2008 ) .

Al2O3

Water

Thermal conduction increased

Mintsa et Al. ( 2009 )

CuO, Al2O3

Water

Increasing depending on volume fraction per centum

Duangthongshuk and Wongwises ( 2010 )

Increasing depending on volume fraction per centum

Note: EG: ethene ethanediol

2.3.3 ) Thermal belongingss of nanofluids

The thermic conduction of nanofluids was the chief focal point in the phases of nanofluids research. In any instance, the belongingss of nanofluids depend on the thermic conduction, specific heat, denseness and dynamic viscousness. Vasu et Al. ( 2008 ) has listed some of the belongingss of nanoparticles and based fluids in Table 3. Pantzali et Al. ( 2009 ) has consistently measured the thermophysical of the nanofluids. Some belongingss of nanofluids and base fluids are shown in Table 4.

Table 3: Thermophysical belongingss of nanofluids and base fluids ( Vasu et al, 2008 )

Property

Water

Ethylene

ethanediol

Copper

Al2O3

CuO

TiO2

C [ J/kgK ]

4179

2415

385

765

535.6

686.2

I? [ kg/m3 ]

997.1

1111

8933

3970

6500

4250

K [ W/mK ]

0.605

0.252

400

40

20

8.9538

I± [ m2/s ]

1.47

93

1163

1317

57.45

30.7

Table 4: Measured thermophysical belongingss of H2O and nanofluids at 25IS degree Celsiuss ( Pantzali et al. 2009 )

Index

Thermal conduction, kn ( W/mK )

Density

I?n ( kg/m3 )

Heat capacity cp, n ( J/kgK )

Viscosity

Aµn ( mPas )

Base fluid: H2O

0.607

998

4180

1.0

Al2O3-4

0.648

CuO-3

0.643

CNT

0.628

Al2O3-3

0.643

1050

3910

2.9

TiO2

0.643

1030

3960

2.0

CuO-8

0.720

1510

2700

5.6

CuO-4

0.669

1250

3280

2.0

CuO-2

0.631

1130

3720

1.3

2.3.4 ) The advantages of nanofluids

Since the solid in nano-sized atoms ( 1-100nm ) are suspended in the base fluid, it has higher thermic conduction heat transportation coeffients compare to other conventional coolants. There are other advantages ( Choi, 1995 ) :

Improved heat transportations

Heat transportation system size decrease

Minimal clogging

Miniaturization of the systems

2.3.5 ) Applications of nanofluids

In assortment of thermic system, nanofluids can be used to better heat transportation and energy efficiency. Many applications have been used nanofluids since the production companies see the potency of nanotechnology in industrial applications. The illustrations of application are ( Wenghua et al. 2007 ) :

Transportation system sectors

The nanofluid is added up in automotive engine coolant to increase the thermic conduction.

The nanofluid has been applied to the chilling of automatic transmittals to better heat transportations from transmittal chilling ( Tzeng et al. 2005 ) .

In automotive lubricators applications, nanoparticles stably dispersed in mineral oil to cut down wear and heightening burden transporting capacity ( Zhang and Que. 1997 ) .

Electronicss chilling industry

Nanofluid has been used as working fluid for heat pipes in electronic chilling applications ( Tsai et al. 2004 ) .

Nanofluids have been investigated on the heat capableness of an hovering heat pipe ( Ma et al. 2006 ) .

Defense mechanism development

Nanofluid have possible to supply chilling in military system like power electronic device, directed energy arm, military vehicles, pigboats and high power optical maser rectifying tube.

Space researching

The power of denseness is really high makes nanofluids attractive in general electronic chilling.

The magnitude addition in the critical heat flux in pool boiling utilizing nanofluids ( You et al. 2003 & A ; Vassalo et Al. 2004 )

Nuclear systems chilling

The possible impacts of the usage of nanofluids are on the safety, neutronic and economic public presentation of atomic system.

Biomedicine

Iron based nanoparticles used as bringing vehicles for drugs or radiations without damaging nearby healthy tissue during malignant neoplastic disease intervention.

Nanofluids could besides used for safer surgery by bring forthing effectual chilling around the surgical part.

In contrasting application to chilling, nanofluids could be used to bring forth a high temperature around tumours to kill malignant neoplastic disease cells without impacting nearby healthy cells ( Jordan et al. 1999 ) .

Other applications

In edifices where additions in energy efficiency could be realized without increased pumping power.

Nanofluids coolants besides have possible application in major procedure industries such as stuffs, chemicals, nutrient and drink, paper, fabrics and etc.