Thermal performance of double pipe heat exchanger

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Conventional heat transfer fluids such as water and ethylene glycol play an important role in many industrial fields such as chemical production, power generation, air-conditioning and transportation. However, these conventional coolants offer low thermal conductivity. Due to the development of nanotechnology and thermal engineering, various methods have been made to improve the heat transfer. One of the approaches including development of new generation of heat transfer fluids called nanofluids.

Nanofluids are new kind of heat transfer medium containing nanoparticles which is uniformly and stably distributed in a base fluid (Mohorianu et al, 2006). Typical base fluids are include water, oil and ethylene glycol. Since the solid in nano-sized particles (1-100nm) are suspended in the base fluid, it has higher thermal conductivity compared to other conventional coolants. Therefore, when these nanofluids are used as coolant, heat transfer process will be more efficient.

Heat transfer is a process which internal energy from one substance transfers to another substance. Double pipe heat exchanger is one of the examples of heat transfer applications. Double pipe heat exchanger consist two pipes with one of the pipe placed concentrically inside another one pipe which has larger diameter. The larger diameter pipe served as the shell to lead the flow from one section to another section (Sadik et al, 2002). The double pipe heat exchanger was developed to fit in small applications.

Thus, this project studied on the thermal performance of double pipe exchanger operated using nanofluids. The double pipe thermal performance operating with nanofluids were compared to other conventional coolants such as water. Another criterion studied in this study was the effect of the volume fraction of nanoparticles to the double pipe heat exchanger thermal performance. This study was applied analytical study method.

Some of input data are needed to perform the analytical study. It included nanofluids thermal properties such as thermal conductivity, density, specific heat and viscosity and double pipe specification such as length, diameter and flow rate. This study was focused on the analysis study of heat transfer coefficient, pumping power, pressure drop, Prandtl number (Pr) and Nusselt number (Nu) related to the thermal performance of double pipe exchanger.

1.2 Objective

The objectives of this project are listed as follows:

To study the thermal performance of double pipe exchanger operated using nanofluids.

To determine the effect of the copper nanoparticles volume fraction to the thermal performance of double pipe heat exchanger.

To study the effect of operating temperature to the thermal performance of double pipe heat exchanger.

To estimate possible size reduction of the double pipe heat exchanger when using nanofluids.

1.3 Scope of work

The scopes of work for this project are shown below:

Only one application of heat exchanger was investigated. The application considered was double pipe heat exchanger in cooling lubricating oil at gas turbine engine.

Only one type of nanofluids was considered. The type of nanofluids chosen in this study was copper based water nanofluids.

Only analytical study method was focused in this study.

Input data such as thermal conductivity, double pipe specification and etc were obtained from literature and mathematical formulations.

The thermal properties of nanofluids such as thermal conductivity, density and viscosity which to apply in double pipe heat exchanger were assumed same with the thermal properties of nanofluids in researches conducted in laboratory.

1.4 Background of Study

The heat exchanger device such as double heat exchanger faces challenges to obtain the best thermal performance. The thermal performance of heat exchanger device plays important role in the performance of cooling system. The conventional coolants offer lower thermal conductivity. The list of several solids and liquids for thermal conductivity are shown in Table 1.1. The study of nanofluids is important to improve the thermal performance system in heat exchanger.

Solids/liquids

Materials

Thermal conductivity (W/m K)

Metallic solids

Silver

429

Copper

401

Aluminium

237

Non-metallic solids

Diamond

3300

Carbon nanotubes

3000

Silicon

148

Alumina (Al2O3)

40

Metallic liquids

Sodium

72.3

Non-metallic liquids

Water

0.613

Ethylene glycol (EG)

0.253

Engine oil (EO)

0.145

Table 1.1 Thermal conductivity of various solids and liquids (Eastman et.al.1997)

Since the increasing of thermal performance is important, this study was investigated the thermal performance of heat exchanger operated using nanofluids. The application of heat exchanger for this study was double pipe heat exchanger. The double pipe was chosen since it required less space and easy for maintenance. The type of nanofluids chosen was water based copper nanofluids. A copper nanoparticle was chosen in this study since it has higher thermal conductivity compared to other nanoparticles such as alumina. This study applied analytical study method. Almost similar study was done by Leong et al. (2010) and Vasu et al. (2008). However, their studies focused on radiator thermal performance.

The mathematical formulations were calculated the thermal performance of double pipe heat exchanger such as heat transfer coefficient, heat transfer rate, pressure drop and pumping power. These formulations required the thermal properties of nanofluids such as heat conductivity, specific heat, density and viscosity. In addition, the analysis study on Prandtl number (Pr), Nusselt number (Nu) and heat transfer coefficient also conducted in this study. It was expected that the thermal performance of double pipe heat exchanger are increased when operated using water based copper nanofluids as coolant.

1.5 Statement of Problem

Do the nanofluids increase the thermal performance of double pipe exchanger?

Which is more efficient for double pipe heat exchanger thermal performance operated using nanofluids or using other conventional coolant?

What is the effect of nanoparticles volume fraction to the performance of double pipe exchanger?

Can the size of the double pipe heat exchanger be reduced when using nanofluids?

What are the advantages using nanofluids in heat exchanger system?