Overview of nanofluid
Nanofluid is fluid which consists of a base fluid with nano-sized. The nano-sized particles (1–100 nm) dispersed in the base fluid. In the application of heat transfer enhancement in nanofluid, metal or metal oxide nano particles are used. As we know that metal and metal oxide increase conduction and convection. In the past few decades, nanotechnology’s rapid advancement has led to the emerging of a new generation of coolants called nanofluids.
If we analyze the regular solid-liquid dispersion, nanofluid has higher effective surface area and therefore higher effective heat transfer surface between particles and fluids. Nanotechnology is being utilized or considered for some, applications focused to give more productive energy supplies and employments.
While many of these applications may not influence heat energy transfer directly, each has the potential to reduce the need for the electrical energy, petroleum distillate fuel, or natural gas that would otherwise be moved through the energy transmission system. More efficient energy generation and use may decrease the amount of construction, maintenance and decommissioning activities.
Thermal conductivity of nanofluids is found to be an attracting characteristic for many applications. It can be defined as the ability of a material to conduct or transfer heat. Numerous researchs have been completed on this subject
Thermal conductivity of 0.3% copper nanoparticles of ethylene glycol (EG) nanofluids is raised up to 40% contrasted with the base liquid. Authors stressed that this property plays a vital role in the construction of energy-efficient heat transfer system. Higher thermal conductivity is higher and surface area of copper (Cu) nanoparticles are attributed to this improvement.
However, the surface to volume ratio (A/V) of nanoparticles is a dominant factor influencing the nanofluids’ thermal conductivity rather than nanoparticles thermal conductivity. Surface to volume proportion (A/V) is expanded with more lesser sizes of nanoparticles.
Heat transfer using nanofluid
The high heat-generating processes have generated an increased requirement for the latest technology to increase heat transfer. Many methods are available to increase heat transfer in processes.
The heat transfer in a process can be calculated as follows:
Q = h* A*∆T
Q is the used for heat transfer rate, h is the heat transfer coefficient, A is the effective heat transfer area, and ∆T is the temperature difference. It is observed that from this equation that heat transfer possible to enhance by:
(i) Increase ΔT
(ii) Increase A
(iii) Increase h
Heat transfer improvements can also be increased by increasing the heat transfer coefficient h. By developing more efficient heat transfer methods or improving the transport properties of the material used for heat transfer.
From the transportation industry to energy production units, nanofluid can be used widely in all range also in electronics systems like microprocessor, micromechanical, electrical system and the biotechnology field.
The improvement in properties of nanofluid
In most cases, an increase in thermal conductivity has been observed. Abnormal trends in case of viscosity have been seen with nanofluid. The viscosity found to increase when nanoparticles are dispersed in the base fluid.
For higher volume concentration, nanofluid behaviour found shear thinning for less attention it’s Newtonian loading. Many disagreements are seen in many works, but even though we can say that force convection in case of nanofluid is increased than base fluid. This increase because of nanofluid is not dependent on conventional theories.
For example, the properties of CuO nanoparticles are shown.
|Average Particle Size (nm)||30-50|
|True Density (kg/m3)||6400|
|Specific Heat (J/kgK)||531.02|
|Thermal Conductivity (w/mK)||20|
Suppose we see nanofluid in case of natural convection. It can be said that deterioration in results seen in nanofluid, increase in volume concentration result in an increase in deterioration. More experiments are required to conduct on metallic particles and with low volume concentration. Even for specific heat, it has been noted that it lower over base fluid, More research is required to be done on specific heat as it is essential parameters in the heat transfer field.
Comparison of various nanofluid
The nanofluid thermal conductivity is dependent on its metallic particle properties. Different types of Nanofluids used to enhance heat transfer in the Heat exchanger (TiO2, Al2O3, SiO2, CuO, CeO2 etc.)
There are so many experiments result available to compare different nanofluid. Let’s see some graphical comparison of various nanofluids. The comparison of three working fluid water, CuO/water, MgO/water can be seen in the figure given below.
The graphical result presented between heat transfer rate (Q) and Inlet temperature of nanofluid. It can be easily observed from graph CuO nanofluid shows superior heat transfer compared with MgO nanofluid and water. The graph is plotted for three different temperatures 70, 80 and 90 °C.
Let’s take a second example to understand more about another nanofluid comparison. The graphical representation, including a comparison of water, Al2O3/water, CuO/water is shown figure below.
It can be noticeable clearly from the above graph that CuO nanofluid performs better heat transfer rate as compared to the other two.
Now, let’s observe result analysis in the table given below,
mc is the mass flow rate of coolant in litre per minute (What is the mass flow rate? Refer click ). Qavg is calculated heat transfer rate for water, Al2O3/water and CuO/water. The unit of heat transfer rate is kW (kJ/s) (What is heat transfer rate? Refer click )
The study of the result table makes us know that CuO nanofluid performs better heat transfer at every condition of mass flow rate. If we do cost comparison, then Al2O3 nanofluid is cheaper than CuO nanofluid.
The heat transfer difference is not very high between Al2O3 nanofluid and CuO nanofluid. For cost-effective, the Al2O3 nanofluid can be commercial fluid to get enhanced heat transfer.
Applications of nanofluid in heat transfer
Nanofluid has been used or considered for many applications to give more efficient energy supplies and uses. Nanofluid has been used or considered for many applications to give more efficient energy supplies and uses. These applications not influencing energy transmission completely yet they can lessen the preliminary requirement for Petroleum fuel, electricity, oil distillate fuel, or flammable gas. It would somehow be traveled through the energy transmission framework. Coming up next are a few instances of nanofluid for explicit applications
The recent researches in electronic cooling demonstrate the use of nanofluid to enhance the heat transfer rate. The vapour chamber used in electronic cooling is filled with nanofluid for better heat transfer.
The jet impingement is the possible technology to cool some electronics devices. The water is sprayed over the heat sink device to absorb more heat from it. The use of nanofluid instead of water can extract more heat from the heat sink.
The radiator is compact type cross-flow heat exchanger and used for engine cooling. The space management is significant issues in every automobile vehicle. The size reduction of cooling components can be possible if the component’s function gets enhanced in heat transfer. The nanofluid is the superior and modern coolant which can meet the requirement for compactness.
Parabolic solar collector and other solar thermal devices
The working fluid is circulated through the solar thermal system by absorbing solar radiation. The solar energy absorbed by working fluid is generally transferred to the heat exchanger for other applications. The use of nanofluid as a working fluid in the solar thermal system improves its performance and efficiency.
The transformer is widely used electrical equipment for power transmission. The cooling oil is used in the transformer to absorb heat generated due to resistance. The performance of cooling oil can be improved by adding nanoparticles in oil. Here, the base fluid is oil which supports the stability of nanofluid.
Some of the other applications of nanofluid in the area of cooling and heat transfer are as given below:
The refrigeration system works on various thermodynamic cycles. The refrigerant is the working fluid in the refrigeration system. There are certain experiments carried out to use nanoparticles with refrigerant. The researchers observed good agreement results using nanofluid in some refrigeration system.
Nuclear reactor cooling
The tremendous amount of heat is generated in the nuclear reactor core. To provide sufficient cooling, the water is circulated through the condenser system. The nuclear system requires better heat transfer formula for the cooling system. The nanofluid is an option to enhance the cooling system of the nuclear reactor.
Engine transmission system cooling
In an internal combustion engine (IC), the engine oil is circulated through all transmission parts including gearbox, valves, crankshaft, cylinder etc. The purpose of transmission oil is to provide cooling and lubrication to various parts of the IC engine.
The nanofluid has shown superior stability in oil. The use of nanofluid in IC engine transmission system is a new era for researchers.
Waste heat recovery system in the boiler
The higher temperature flue gas is exhausted from a chimney in the boiler. The boiler efficiency can be increased by absorbing heat which is wasted by flue gas. The waste heat recovery system is installed to fulfil energy efficiency. The use of nanofluid as a working fluid in the waste heat recovery system to increase system’s absorbing efficiency.
Solar evaporation enhancement
Solar distillation is used to convert saline or wastewater into fresh drinkable water. The saline water is evaporated by using solar energy, and the evaporated water is then condensed to get fresh water.
The carbon nanoparticle is having higher solar radiation absorptivity. The use of carbon nanoparticle in saline water increases the evaporation rate, which leads to the superior performance of solar water distillation.
Feasibility as a thermal fluid
The nanofluid is advance thermal fluid for heat transfer application. The advancement in power generating and power electronics devices produce a tremendous amount of heat. The generation of heat is reducing the performance of the device. To meet this requirement, the nanofluid is invented to enhance heat transfer and device performance.
The nanofluid shows superior performance on heat transfer. It can be feasible to use nanofluid for small scale application. For large or industrial scale, more number of researches still required to be done. The preparation of nanofluid plays a vital role in its feasibility. The stability of nanofluid is an essential factor affecting its feasibility.
The higher stable nanofluid can be more feasible as thermal fluid.
Questions & Answers
Why nanofluid possess heat transfer characteristic?
Nanofluids have higher explicit surface area and accordingly more heat conduction surface among particles and liquids.
Definition: Thermal conductivity
The Thermal conductivity can be characterized as capacity of a material to direct or move heat.
Which are the ways to increase heat transfer?
There are three ways to increase heat transfer based on heat transfer expression:
- Increase ΔT (temperature difference)
- Increase A (Effective surface area)
- Increase h (heat transfer coefficient)
What is the volume concentration of nanofluid?
The volume concentration is a term used to state the proportion of nanoparticles in a prepared nanofluid.
Which of the nanofluid is performing higher heat transfer in given examples?
Copper Oxide (CuO) nanofluid.
Which nanofluid is cost-effective?
Aluminium Oxide (Al2O3) nanofluid.
Which of the three nanofluids used in this article?
Followings are three naonofluids used in this articles :
- MgO/ water
Give the unit of heat transfer.
The unit of heat transfer is kW (kilowatt) or kJ/s (kilo Joule/second)
In which of the electronic device, the use of nanofluid is possible?
The nanofluid can be used in vapour chamber and jet impingement setup for electronic cooling.
What is the specific name of the radiator in the field of the heat exchanger?
Compact type cross-flow heat exchanger
What is the dominant factor of nanofluid for feasibility?
The stability of nanofluid is the dominant factor for feasibility.
What is the use of carbon nanoparticles?
The carbon nanoparticles are good absorber of solar radiations. It can be used in solar distillation units for evaporation enhancement of water.
This article is useful for students and researcher to get a basic idea of some nanofluid and its properties. The article is also helpful for the student to find a research topic related to nano science and its applications. The comparison of few fluids is presented in this article to create a base for advance fluid and parameters study. The future scope of nanofluid is comprehensive and attractive. The nanofluid will be the key to increase any equipment efficiency.
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