The Deposition of Nanoparticles on Heat Transfer Surfaces
Table of Contents
Description Page #
- Abstract 3
- Introduction 4
- Problem Statement 7
- Significance of the Problem 8
- Purpose of the project 9
- Definitions 10
- Delimitations 11
- Limitations 12
9. Literature Review 13
10. Equipment and Procedures 22
10-1) Experiment Design 22
10-2) Experiment Parameters 22
10-3) Calculations to Determine the Gage of Nichrome wire 22
10-4) Equipment 23
10-5) Heating Element Fabrication 25
10-6) Experiment set up 26
10-7) Nanofluid Preparations 27
10-8) Experiment Procedures 28
10-9) Data Collection 28
10-10) Data Analysis 40
10-11) Experiment Errors 41
11. Conclusions and Recommendations 42
12. References 44
13. Appendix 46
- Abstract
Nanofluids have been seriously studied to work as a heat transfer medium during the past few decades.Nanoparticles are a microscopic particle with at least one dimension less than 100 nm. Nanofluid is a mixture of nano-sized particles of less than 100 nmsuspended in liquid medium.Currently, the research focused on substituting heat transfer nanofluid in industrial applications. Some researchers state that addition of nano-particles to base fluid will increase the thermal conductivity by as much as 160%.This project focuses on the deposition of nano-particles of different concentrations on the heat transfer surfaces. In this project, a series of experiments will be performed to obtain the heat transfer advantage of using nanofluids instead of water. The variables in this research are the different types of nanoparticles at different concentrations in the base fluid which is water. The research attempts to develop a model to observe the change of the Critical Heat Flux (CHF) in different nanofluidsconcentrations and various temperatures.
- Introduction
In industrial applications, boiling is commonly used to transfer heat. Water is the most commonly used liquid in boiling applications since it is easily available, cheap, and safe. The conventional heat transfer fluids have poor thermal conductivity compared to solids. In order to improve heat transfer efficiency, techniques are required to enhance the conductivity of the fluids. The thermal conductivity of the nanofluids is higher than the base fluid (water).Therefore, dispersing nano-particles will enhance the heat transfer efficiency of fluids (Kevin G. 2010).
Nano-particles are particles less than 100 nm in size that increases the thermal conductivity for any fluid after being dispersed in it. One of the most interesting properties of nanofluids is their boiling heat transfer behavior. Experiment is necessary to investigate the heat transfer behavior in nanofluids, will be designed in this study.
The ability of nanofluids to increase the efficiency of heat transfer will help in reducing the power cost and environmental impact. Nanotechnology is a developing technology, and will help the industry economy if the mechanism of heat transfer in nanofluids is investigated more.
There are only a few researches citation that have been directed to-date on convective and boiling heat transfer in nanofluids. Most of these investigations exposed conflicting results. Additional investigation is necessary to fully understand the behavior of nanofluids under boiling Heat Flux.
Over the past few years, the use of nanofluids in industrial applications has become more common. The main concept of dispersing nano-particles in base fluids is to enhance thermal conductivity and its history can be traced back to Maxwell in the 19th century (Eapen, J. 2007). Since then, the research in critical Heat Flux (CHF) of nanofluids has been of interest to the scientists working on nano-particles.
The nano-particles that are commonly used in heat transfer area include metal oxides alumina, Titanium, copper, etc.To investigate the deposition of nanoparticles on solid surface during heat transfer, a nichrome wire will be used.
The following properties of nichrome make it a more suitable candidate for this purpose:
- Electrical Resistivity at room temperature: 1.0 x 10-6 to 1.5 x 10-6 ohm m
- Thermal Conductivity: 11.3 W/moC
- Magnetic Attraction: None
- Thermal Expansion Coefficient (20oC to 100oC): 13.4 x 10-6/oC
- Temperature Coefficient of Resistivity (25oC to 100oC): 100 ppm/oC
- Specific Gravity: 8.4
- Density: 8400 kg/m3
- Melting point: 1400oC
- Specific Heat: 450 J/kgoC
- Modulus of elasticity: 2.2 x 1011 (Swapnil S. (2009))
The deposition of nano-particles around the heating element in each experiment run may cause increase in heat transfer rate. This feature needs to be investigated more through this research. This experiment is expected to provide information regarding the observations in change in the Critical Heat Flux (CHF) of nanofluids.
- Problem Statement
Water is the most common fluid which been used in heating system and boiling at industry field. Hence, the energy cost of heating is expensiveexpectation which made most companies looking for cheaper system. So, the problem is the high cost of energy consumption. Ability of nanfluids in transfer heat better than water was determining last few decades. However, the study of nanofluids is still at its infancy, comprising primarily in heat transfer researches. More research need to conduct understand the deposition of nano-particles over the heating element, if itseffectthe heat transfer efficiency or no. To utilize the nanofluids usefully in heat transfer applications, research is necessary to understand and determine the deposition of nano-particles on heat transfer surfaces at different concentrations and temperatures. Once this understanding is achieved, it should enable the use of nanofluids at appropriate concentrations in heat transfer applications.
- Significance of the Problem
It’s important to know the properties of nanofluids that can affect the Critical Heat flux (CHF). Some of these proprieties are thermal conductivity, surface tension, viscosity, density, pH, and heat of vaporization. To obtain better CHF, it’s necessary to understand how thermal conductivity of nano-particles affects the heat transfer efficiency. Developing a proper model which is applicable toobtain the boiling heat transfer characteristics in nanofluids is significant. Using readily available nanofluids determination of enhance heat transfer characteristics in applications is possible. This understanding will result in decreasing energy costs in heat transfer applications.
- Purpose of the Project
The purpose of this project is to study and further understand the role of nanofluids in heat transfer, particularly the deposition on heat surfaces. The performance of nanofluids will be evaluated using variable nanofluids of different chemical composition and concentration during boiling. The major variables to be studied in this project are the types of the nano-particles and the concentration in the base fluid which is water. An experiment set up was designed and fabricated to confidently measure heat transfer characteristics in nanofluids. The result of nanoparticles deposition on heat transfer surface will be studied.
- Definitions
CuO Copper oxide
Al2O3 Aluminum oxide
CHF Critical heat flux
hlvLatent heat of vaporization, [J/kg]
q” Heat flux (kW/m2)
λ Thermal conductivity ratio
Greek Symbols
Δ TsatSurface superheat: Tw-Tsat [K]
Δ Difference
Ώ Resistance unit, [ohm]
σ Surface tension, [N/m]
ρ Density, [kg/m3]
Subscripts
l Saturated liquid
nano Nanofluid
sat Saturated condition
v Saturated vapor
cp Composite particles
np Nanoparticles
kp Particle thermal conductivity
k1 Liquid thermal conductivity
The particle volume fraction of the suspension
- Delimitations
Some of the delimitations of this study are Purity of water, type of the nano-particles. A digital thermo cable temperature reader was used instead of normal thermocouple temperature reader to obtain the exact reading. Nichrome wires were used to speed up the heating process and thus avoid some common mistakes encountered during prolonged heating.Another delimitation might be the use of a tube that houses the nichrome wire that may not fit properly. The dispersion and deposition of nano-particles around the heating element at each experiment run will also be delimitation.
- Limitations
This experiment was limited to laboratory conditions. First of all, financial limitations were our prime concern. The fabrication was done using existing or used components. Due to cost consideration the nanofluids usewas restricted to copper oxide (CuO) and aliuminum oxide (Al2O3).Testing was restricted to only two concentrations of nanofluids to accommodate the time schedule.
9. Literature Review
Nanofluids are suspensions of nanoparticles in a base fluid, typically water. The term nanoparticle comes from the Latin prefix ‘nano’. It prefix is used to denote the 10-9 part of a unit. In this context, nano-particles can be termed as the particles with a size in the range of a few nanometers. Traditionally, nanoparticles have a size between 100-2500 nm. Particles smaller than 100 nm are termed ultrafine. These objects are being extensively explored due to their possible applications in medical, optical and electronics fields.
The most popular nano-particles that use to produce nanofluids are: aluminum oxide (Al2O3), copper (II) oxide (CuO), copper (Cu). Water, oil, decene, acetone and ethylene glycol are the most common base fluids being used in producing nanofluids.
“Nano-particles can be produced from several processes such as gas condensation, mechanical attrition or chemical precipitation techniques. Gas condensation processing has an advantage over other techniques.” (“Critical Review of heat transfer….,” 2007)
In this project one type of nanofluids from the previous weretested. CuO and Al2O3 are the once which is available in our lab. Water is the base fluid which will be used in this experiment.
Preparation of a nanofluid is done by straight mixing of nano-particles with the base fluid. Nanofluid preparation has various requirements such as an even, durable, stable suspension, low agglomeration of particles, and no chemical change of the fluid. Following approaches have been suggested to stabilize the suspensions of nanofluids: using ultrasonic vibration, changing the pH value of suspension, and using surface activators and/or dispersants. These approaches will change the surface properties of base fluids, particularly the heat transfer characteristics. The required application of the nanofluid will verify the type of approach needed to be used. Choice of the appropriate activation of dispersants depends primarily on the characteristics of particles and solutions. (“Critical Review of heat transfer….,” 2007)
Information about how nanofluids Preparation mentioned were cooperative. In our work, similar process was followed. Analytical scale to weight the nanofluids and water volumes is needed. Matrices beaker were used to measure the quantity of water.
Particles can break or compose after mixing into the liquid. To observe the characteristics of particles while dispersed in liquid, Transmission Electron Microscopy (TEM) is commonly used. Some other researchers use ultrasonic vibration techniques in watching the particles, but ultrasonic vibration techniques can break agglomerates.
High resolution camera was our watching device to picture the deposition of nanofluids on nichrome wire. So many pictures were taken while the experiment in running. These observations will help in analyze the relation between depositions of nanoparticles on heat element surface and temperature change.
Nichrome wire is the best electrical wire to be used in heating, because of its high capability of heat storing and high resistivity. Nichrome is providing so many options of different gages and diameters. Calculated of nichrome wire specifications were done at the experiment preparation section of this paper.
The following properties of nichrome make it a more suitable candidate for this purpose:
- Electrical Resistivity at room temperature: 1.0 x 10-6 to 1.5 x 10-6 ohm m
- Thermal Conductivity: 11.3 W/moC
- Magnetic Attraction: None
- Thermal Expansion Coefficient (20oC to 100oC): 13.4 x 10-6/oC
- Temperature Coefficient of Resistivity (25oC to 100oC): 100 ppm/oC
- Specific Gravity: 8.4
- Density: 8400 kg/m3
- Melting point: 1400oC
- Specific Heat: 450 J/kgoC
- Modulus of elasticity: 2.2 x 1011 (Swapnil S., 2009)
Water is the most commonly used solvent. It is also one of the most common base fluids used in heat transfer applications use for boiling. It is a non-toxic and inexpensive liquid. Its low viscosity makes it easy to pump through tunnels and pipes. But the bad part of water is that it has a low boiling point and a high freezing point, comparatively though. Moreover, if its pH is little away from neutral point (pH = 7), it can be corrosive (Heat Transfer Fluids…, n.d.).
The base fluid which was used in the experiment is water ether tap water or De-ionizedwater. Result of nanofluids runs is going to be compared with water result.
Thermal conductivity (λ) is the intrinsic property of a material which relates its ability to conduct heat. This means that thermal conductivity is the factor that affects heat transfer rate of each material. Nanofluids have higher thermal conductivity than the pure liquid (water). Experimentally, suspending the nanoparticles wasenhancing the base fluids thermal conductivity, thus leading to high heat transfer rate.
Thermal Conductivity = heat × distance / (area × temperature gradient)
λ = Q × L / (A × ΔT)
Research has been conducted in the field of heat transfer over the past several years to improve the use of heat transfer enhancement methods. The benefit of adding Nano-particles is a method applied to increase the heat transfer performance of base fluids. Massachusetts institute of technology (MIT) is one of the institutions working on this research in concentration. The field of nanofluids with respect to heat transfer is quite new. As a new material, nanoparticles are being used in suspension in conventional heat transfer fluids. Nanofluids are fluids having small solid-particles suspended in them. The nanoparticles suspended in the fluids werechanging the heat transfer physical characteristics and transference properties of the base fluid. This research was review and summarizes the recent improvements on the heat transfer characteristics of nanofluids.
As nano-particles help in increasing the thermal conductivity of conventional fluids, many researchers expected that nano-particles would enhance the boiling heat transfer. These studies brought out several experimental investigations on the pool boiling characteristics of nanofluids. Disperse Nano-particles as a chemical suspended into the base fluid is a method that can help improve heat transfer. Enhancing the thermal conductivity is the method to improve the heat transfer characteristics of conventional fluids. Since the nano-particles have a larger thermal conductivity than a base fluid (water), disperse nano-particles into the base fluid is possible to increase the thermal conductivity of that fluid. According to Visinee T. et al (2005),
“The enhancement of thermal conductivity of conventional fluids by the suspension of solid particles, such as millimeter- or micrometer-sized particles, has been well known for more than 100 years.” (“Critical Review of heat transfer….,” 2007)
However, because of some problems such as sedimentation, erosion, fouling and increased pressure drop of the flow channel, this area has not drawn the attention and interest of researchers. The modern advances in materials technology has made it possible to produce nano-particles that can help in solving these problems. Nano-particles suspended in base fluids is a new Innovative called ‘nanofluids’. These nano-particles were make changes in the thermal and transference properties of the base fluid. The main goal of this paper is to study the result of nanoparticles deposition on heat transfer surfaces after many times of heating.
Natural convection of small-nanoparticles dispersed fluids has been used in many industrial applications such as chemical, food, and also in solar collectors. Absolutely, the natural convection of nanofluids is not the same as the pure fluids. From unbalanced density distribution of liquid due to temperature differences and the distribution of the nano-particles concentration due to sedimentation, the natural convection of nanofluids is determined. There are not enough studies reporting the natural convection of nanofluids with sedimentation. Putra ethaspresented the experimental observations they made on the natural convection of two oxides (Al2O3 and CuO)–water based nanofluids inside a horizontal cylinder heated from one end and cooled from the other. The requirements of parameters such as nano-particles concentration, nano-particles material and geometry of the test tube were examined at steady-state surroundings. The nano-particles concentration and the absence of stratification concentration layers were make the difference between convection of nanofluids and pure fluid. At same ratio, length and diameter of tube wereaffecting the natural convective heat transfer of nanofluids and the base fluid. Most of the researchers have focused on application of nanofluids as heat transfer medium for a single-phase heat transfer, taking advantage of the high thermal conductivity of nanofluids (Gilberto M. Jr., 2005).
Obviously, the natural convective heat transfer of nanofluids was changed while increasing Nano-particles concentration, aspect ratio of test tube, and nano-particle density. Nano-particles size of CuO is smaller than that of Al2O3. Therefore, the drop in heat transfer rate should be larger for Al2O3. This is because the nano-particles density of CuO is greater than that of Al2O3. The nanofluid in the enclosure is assumed to be in single phase, that is, both the fluid and nano-particles are in thermal equilibrium. The effect of suspended nano-particles on the heat transfer wire will be analyzed. It wasillustrated that the heat transfers rate increase as the nano-particles volume fraction increases at any given Grashof number. The expectation of increase the deposition of nanoparticles on heat surfaces isto increase the heat transfer rate.
The research conducted by Lee et al (1999) studied the effects of dispersing CuO and Al2O3 nanoparticles on the thermal conductivity of water and ethylene glycol. Their results confirmed that the thermal conductivity of the nanofluids is higher than that of pure liquids. They also reported that the thermal conductivity of ethylene glycol increased by more than 20% when CuO nanoparticles were dispersed in it (Lee et al, 1999).
Another similar work reported an increase in the thermal conductivity of ethylene glycol by 40% when copper nanoparticles were dispersed in it at 0.3% volume concentration (Eastman et al, 2001). The above studies made use of spherical nanoparticles. In another study, carbon nanotubes were dispersed in oil. The thermal conductivity of this nanofluid was 2.5 times greater than that of pure oil (Choi et al, 2001).
In this experiment, we were evaluating the pool boiling of two different nanofluids, Aluminum oxide (Al2O3) and copper oxide (CuO). We were also study the effects of heater thickness, size and nature of nano-particles and surface roughness of the heater, on the boiling characteristic of nanofluids. The expectation are to somewhat enhance the heat transfer characteristic during pool boiling, and the boiling curves of nanofluids should be shifting to upper left part. The change of the curve means that the nanofluids are absorbing more heat than water so it starts boiling faster.