Heat Exchanger Tube Constructional Materials

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This heat exchanger is a very important part of the nuclear reactor. It is used to transfer energy from one fluid circuit to another, which from a nuclear reactor perspective, from the primary circuit that contains heavy pressurized water to the second one that has the water to be converted to steam. It is therefore very important to ensure efficiency and utmost effectiveness. However, heat exchangers are sometimes affected by issues of efficiency, damage to equipment and fatigue to the construction material which hampers their effectiveness and consequently the performance of the nuclear reactor.

This is a research proposal about a project that looks to address this heat exchanger issues. The project will be about studying the heat exchanger tube constructional materials to establish their properties with the aim of choosing the best material.

The various materials in use today will be studied. Herein in this paper is the purpose of the study, a review of the relevant literature, the proposed methodology and how the project is to be conducted and the time frame of the project.

Purpose

This part of the proposal explains why the project is being conducted, its significance and the objectives of the project. The main aim of the proposed project will be to compare the various materials (including the physical, thermal, chemical and mechanical attributes) used in the construction of heat exchanger and come up with the most suitable material with the most desirable characteristics to improve the efficiency and general effectiveness of the earlier stated heat exchanger. This part will also state the expected milestones of the proposed project.

Methodology and literature review

This section of the proposals deals with the proposed methods, procedures and exact materials that are going to be addressed by the project. A literature review of the nuclear reactor, heat exchanger and its constituent construction materials will also be addressed in this section.

Time frame

The proposal also includes the proposed working timetable clearly showing the expected dates of accomplishing the various milestones of the proposed project.

INTRODUCTION

With increase in global population, technological growth and general modernization of almost all aspects of human life, there has been a resultant exponential growth in energy needs in the world. There have also emerged environmental concern issues. To satisfy this ever increasing energy debt, it is of huge importance to not only tap into nuclear energy source but to ensure effectiveness, sustainability and overall efficiency in the energy generation process. With this knowledge, it is extremely vital to not only design nuclear reactors properly, but to also select wisely the materials used in the construction of the reactor components.

Heat exchanger is one of the most important parts of a nuclear reactor. Its main role is to transfer heat from one fluid to another without need for the two coming into contact. In nuclear power plants, heat exchangers should be designed to ensure maximum heat transfer between the primary circuit which is the pressurized water reactor and the secondary circuit which is where water is converted in to the wanted steam.

This project looks to compare the materials used to construct the heat exchanger for purposes of increasing both the efficiency and durability of the stated components. It will look to perform a thorough analysis of the qualities of the materials used to construct the heat exchanger. This comparison of their properties will include the advantages and limitations, differences and similarities, effectiveness, efficiency and durability among others. The materials will be studied under varied conditions that simulate the operating conditions of a nuclear reactor. This conditions can be mildly exaggerated to establish the suitability of the materials during normal operations and at also during fault conditions that are characteristic of the nuclear plant.

BackgroundHeat exchangers in nuclear reactors are prone to corrosion, fatigue, mechanical breakdown and overall damage reducing its life span and efficiency. Due to this it is of utmost importance to select the best materials which will be used for heat exchangers. The materials should increase thermal efficiency and be able to meet the environmental and economic factors. The loss in capacity due to the heat exchanger is estimated at 3.2% which is high.

Heat exchanger design and its analysis involve the use of conduction and convention in heat transfer. The materials used should therefore be able to allow for conduction to take place. The major issues to be considered in the heat exchange material selection are the physical, chemical and mechanical properties of the materials in question.

In this research I will be looking at properties of different materials and comparing them in order to select that which has the best properties to act as a heat exchanger material.

The research will be carried out between February 20eth 2016 to March 20eth 2016. I will target experts from the nuclear sector and also use library resources and the web.

PURPOSE

The main aim objective of this project is to compare various materials used in the construction of heat exchangers today in order to select the best and most suitable one so to increase and overall efficiency. The aim is to bring the efficiency of the heat exchange process as close as possible to 100%. Heat exchangers play a huge role in many processes. These processes include chemical, nuclear power plants and fossil, refrigeration, fertilizers and desalination. They are of utmost importance in the industries and due to the increase in the energy needs it is of paramount importance.

Other objectives include reviewing the properties of the materials used in order to suggest future improvements and to select materials that are both durable, strong and that will suit the operational needs of the heat exchanger fully.

In addition, the project will aim to acquire knowledge on next generation heat exchanger materials that will not only fit the future generations of nuclear reactors with the purpose of identifying unsuitable materials that are currently in use and suggesting their replacement.

I shall also look to identify tubing materials that will help improve the heat exchanger. I shall look at two aspects when looking into the tubing materials, that is, the resistance to corrosion when exposed to conditions in the environment that are as a result of a steam or water leak in the sodium. The other aspect will be loss of mechanical strength as a result of decarbulisation of 2.25Cr-1Mo in Sodium.

Irrespective of the reactor types, the key to efficiency will be achieved by use of highly effective heat exchanger. There is high demand for construction integrity since the combination of the temperature and pressure in a reactor requires this. For the next generation reactors to be successful they need highly effective and highly compact heat exchangers.

Scope of the project

The project scope will be the analysis of existing materials being currently used and to gain insight as to why they are in use. Durability, efficiency and capability of improvement will be covered. The project will also look to cover their general impact on the environment.

The project will not however provide the cost analysis of the various materials. The overall focus of the project will be on the effectiveness, efficiency, suitability and availability of improvements and not the economic impact of the above named aspects.

Milestones

There expected milestones during the project are acquisition of information relevant to the project, starting and completing the project in due time and writing the project report.

METHODOLOGYSince the project looks to compare between various constructional materials of the heat exchangers currently in use, properties of the following materials will be studied; copper alloys (both ferrous and non-ferrous), carbon steel, stainless steel, Inconel, haste alloy and titanium.

The above mentioned materials will be studied to establish their thermal, chemical and mechanical properties.

Thermal properties

This part of the project will look to analyze the response of materials to the large amounts of heat energy present in the nuclear reactor during the operation of the heat exchanger. It will look to provide an in-depth insight to the behavior of the various materials under very high temperatures to establish the one thats most suitable. This behaviors include thermal conductivity, thermal expansivity,

Thermal conductivity refers to the ability of a material to allow heat to pass through. The material used to build a heat exchanger should be as a good conductor as possible. This is to ensure the heat exchanged from one fluid circuit to another is as close to maximum as possible. Relevant research will be conducted to establish the best heat conductor that can be used in the heat exchanger.

In my research I will take into consideration the changes that will occur in the future. The materials will be subjected to higher temperatures in the future than they are subject to today. This is due to the loss in strength due to metallurgical changes that will occur to the structures. The materials that will be considered in my research will be those that can be able to withstand temperatures of up to 1000 degrees Celsius.

I shall also look into the thermal efficiency of the materials. The heat loss to the surrounding environment should be low so as to increase the thermal efficiency.

Mechanical propertiesA material will be studied to establish its mechanical strength, durability, malleability, weld ability, fatigue and resistance to fracture. The project will look to identify a heat exchanger material that can survive the stress and strain that are due to the physical forces being applied on the heat exchanger tubing.

Research will be conducted to also determine the time the materials are in use to establish the one that lasts the longest. Apart from durability, the resistance of the material to fracture and the time frame fatigue. With the next generation nuclear systems the life span of the heat exchanger will be expected to increase to up to 60 years. In my research, I will choose the material with the highest durability in order for it to last for that long. The material should also resist fracture due to fatigue.

The material should be able to get...