Lade Inhalt...

Development of Thermal Insulating Textiles. An Innovative IR Reflective Spacer Material

Masterarbeit 2013 127 Seiten

Didaktik - Werken, Textiles Werken

Leseprobe

Table of Contents

1. Introduction
1.2 Problem recognition
1.3 Goal

2. Cold weather effect and technologies
2.1. Cold weather effect on the human body
2.2. Standards for cold weather apparels
2.2.1. Commercial sector
2.2.2. Daily consumer
2.3. Thermal insulation methods
2.3.1. Passive insulation
2.3.1.1. Insulation layer
2.3.2. Active insulation

3. Market analysis
3.1. Market needs
3.1.2. Cold weather textiles
3.1.3. Cold weather sports
3.1.4. Special care for older people
3.1.5. Work related

4. Theories and law’s
4.1. Thermal dynamics
4.1.2. Thermal Conduction principles
4.1.2.1. Thermal conductivity value
4.1.3. Infra-Red
4.2. Human skin
4.3. Ohm’s law

5. Concept development
5.1. Spacer fabric
5.1.1. Reflective layer
5.2. Material
5.2.1. Heat reflection and metals
5.2.1.2. Yarns
5.3. Knitting Technology
5.3.1. Needle notations
5.4. Machines equipment’s
5.4.1. CMS 302 TC knitting machine
5.4.2. Stoll M1 Plus® version 5.4.0.62

6. Material Production
6.1. Material name classification
6.2. Production flow chart
6.3. Production
A-x -1HH
A-x-3HH
C-y-3HH
D-y-3HH
E-z-2HH
F-z-2HH
G-z-2II
G-z-2JI
6.4. Reflective surface comparison

7. Material testing
7.1. Testing of average rate of heat loss
7.1.1. Development map
7.1.2. Setup
7.1.3. Testing method
7.1.4. Evaluation of data
7.2. Testing of thermal resistance value
7.2.1. Development map
7.2.2. Setup
7.2.3. Testing method
7.2.4. Evaluation of data
7.3. Permetest
7.3.1. Testing method
7.4 Sweating guarded hotplate
7.4.1. Testing method
7.5. Other tests
7.5.1. Testing of knitted material
7.5.2. Digital microscope
7.5.3. M-IR spectroscopy

8. Benchmarking process
8.1. Benchmarking material
8.1.1. Duck down material
8.1.2. Omni heat material
8.1.3. Felted wool
8.1.4. Jacket inner lining
8.1.5. Temptrol reflective material
8.1.6. ReF.110x
8.1.7. Non reflective spacer material
8.1.8. Reflective spacer material - G-z-2JI
8.2. Performance comparison

9. Conclusion

Limitation of the thesis

Abstract

Bibliography

Acknowledgment

Though we our live life as individuals life can only be won through collectivism, everyday life reminds us why we are humans. It’s to make a difference.

After more than a year of work, my thoughts would not have become a reality without the support of prof. Dr. rer. nat. Lutz Vossebein and my second professor Prof. Dr.-Ing. Marcus O. Weber. Thank you for directions, support, advice and trusting in me.

Special thank goes to Mr Heisterman, Mr Heimlich, Mr Dorfel and Mrs Aumann for their unwavering support given in development of the material and the testing process.

There are more names to mention than I could write hear, therefore I would like to thank all of the staff at HS Niederrhein for the support they provided me. I would also like to cordially thank staff at HS Niederrhein Offentliche Prüfstelle for helping me with the testing. I would like to pay my gratitude to company Lurex for providing me with free samples of yarns for material production. Special thank goes to Mr Wissling and the staff from Eckart who helped me with advice and IR spectroscopy.

Many thanks goes to my uncle and aunt for being very supportive in my life.

I’m lucky to have been in the company of good people who has made it easy for me make till the end. Through all the difficulties and challenges this thesis has been exciting learning experience to me.

Finally I would like to send gratitude to a person who is no longer among us but who inspired me through difficult times in life. Mr Steve Jobs, not only did you created beautiful world but also inspired a generation. May you rest in peace.

List of Figures

Figure 1-Approximate relation of core and shell compartment at different thermal state. After Lloyd (1994) temperature decreasing from outside to inside

Figure 2-Human body temperature and ambient temperature. (Guyton, Hall, 1996)

F Figure 3-Overview of international standards applicable to cold environment. (HOLMER, 2009)

Figure 4-Contemporary thermal insulation. Prof.Büsgen

Figure 5-Shape memory material. Prof.Büsgen

Figure 6-Uses of heat insulate material

Figure 7-Thermal equilibrium illustration

Figure 8-Electromagnetic spectrum and IR spectrum. (Anon., 2013)

Figure 9- Stretching and bending vibration of an atom. (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

Figure 10-IR active ramen motion. (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

Figure 11. Structure of a spacer fabric

Figure 12 - New material function

Figure 14 - own coated material zoom 2500x

Figure 13 - temptrol zoom 2500x

Figure 15- surface temperature when exposed to IR radiation at 60°C

List of Tables

Table 1-wind chill temperature with wind at 10 m (ISO11079) 15

Table 2-Emissivity coefficient of some materials. (editor.engineeringtoolbox@gmail.com, n.d.)35

Table 3 - Human skin temperature and corresponding wavelengths 53

Table 4 graphical knitting notations 55

Table 5 Layer numbering in needle notation graph 57

Table 6 yarn numbering 59

Table 7 Components for the voltage regulator 88

List of Equations

Equation a- Thermal conductivity (Anon., n.d.)

Equation b-Thermal resistance (Anon., n.d.)

Equation c-Fabric thermal conduction (Saville, 1999)

Equation d-Energy of EMR (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

Equation e-Frequency at a given wavelength (Helmut Günzler, Hans -Ulrich Gremlich , 2002) ..

Equation f-Energy and wavelength relation

Equation g - Wien's displacement law (Hassel, 2010)

Equation h. Celsius to kelvin conversion

Equation i - Radiation conductivity (Saville, 1999)

Equation j - Human body heat loss (Hassel, 2010)

Equation k-Ohm’s law for relation between resistance, voltage and current. (Anon., 2002)

Equation l-Heat generated from electrical energy. (Meier, 2006)

Equation m-correlation of voltage and resistance of material to amount of heat generated

Equation n-average rate of heat loss for once surface

Equation o-tog meter thermal equilibrium. (Saville, 1999)

Special features

Material development chapter contain tables which are used to make it easier to display the results. As such these table are not named after initial discussion.

Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose.

You are already naked.

There is no reason for you to follow your heart.

Steven Paul Jobs

1954 - 2011

Abbreviations

illustration not visible in this excerpt

1. Introduction

Present human needs are becoming more and more complex which makes it hard to offer a single solution to all their needs, but humans have become more and more dependent on the systems and tools which are put in place. Therefore it’s only natural that when using a system or a tool, it should have high degree of reliability in delivering that user experience which should exceeds their expectations.

Apparel industry has been one of the largest industries in the world employing millions of people throughout the textile chain adding values to societies. Some countries are very depended on this industry, country such as Bangladesh, textile industry is the biggest contributor for its GDP. Therefore it’s a very valid assumption to state that textile industry is one of the biggest contributors for the world economy.

World apparel industry showed 2% growth in 2009 with a value of $ 1031.5 billion and is expected to annually grow at 3.1%, the number is expected to reach a level of $ 1162.8 billion by 2014i.

1.2 Problem recognition

Thermal insulating cloths have been part of many people’s lives in many regions around the world. Specifically to maintain needed warmth and allowing them to function normally in cold weather conditions. Considering above facts it’s obvious that thermal insulation apparel sales should accounts for a large number itself.

As a basic need to keep human bodies warm, thermal insulation apparels are a main part of lives of people in cold climate countries. Without such cloths people’s day to day work would come to a halt and endanger their lives. During the period from 1979 to 2002 in America apx. 16313ii cold weather related deaths were recorded according to CSCCC.

According to U.K. office for national statistics only in England and Wales there were estimated 24000 excess winter related deaths and majority of those who died were above the age of 75 year. Several hundred deaths were recorded in winter 2012 in Europe where temperatures dropped more than -32°C iii .

Although there has been a decrees in the annual death rate compared to times before, still the number are high. Like the heavy winter conditions which effected throughout Europe, unexpected climate conditions can take its turn to worse. People might not be prepared enough for any unexpected weather changes.

As developed countries in the world still are coping with the issue of cold weather related deaths, casualties being still higher, people living in under developed parts of the world who cannot afford proper protection against cold weather conditions have less hope. Those who have no proper cold weather protection are likely to suffer. Cause of their deaths may never have been reported.

Human life has the power to change this world and beyond than any other species on this planet. Thus each life is precious for what it holds as contribution to the society no matter how small their part is. Everybody plays a part in the intricate social web allowing us as a species to move forwards and overcome challenges set by our self and the environment around us. Thus the reason to stand against cold weather related deaths justifies itself to be the right of each person who is affected.

1.3 Goal

This thesis will explore the topic in to effects of cold weather conditions on humans, to understand the human body performance. By giving understanding of modern insulation material and their uses in the current market will enlighten the limitations of such material and illustrate existing market opportunities.

All this will be a stepping stone for the heart of the thesis which is to develop a new type of thermal insulating material that could be the future of the industry. In order to achieve that the thesis will explore in to the fundamental analysis of physics that will enable to develop such material. Should the development of such material become a reality then the material shall be benchmarked against other thermal insulation material available in the market. This may give the reader the understanding of how well the development succeeded as well to show how well other materials performed as well.

2. Cold weather effect and technologies.

2.1. Cold weather effect on the human body

illustration not visible in this excerpt

Figure 1-Approximate relation of core and shell compartment at different thermal state. After Lloyd (1994) temperature decreasing from outside to inside

Internal temperature that provides comfort to a human is at 37°C ± 0.5°C. In the figure this can be seen for a non-active person shown with the dark orange colour in the figure. For this individual comfortable skin temperature would be 33-34.5°C. There could be temperature variance throughout body all the while maintaining in the range of 32-35.5°C. Person’s blood flow throughout the body will be optimal under those conditionsiv.

Once in a cold environment the blood flow will stop flowing to the hands and feet. This is depicted by the mid orange colour of the figure. The concentrated blood flows to protect the vital organs necessary for the survival. Cold climate endangers body’s temperature balance and requires actions to control the heat loss this explains shivering which tightness up the skin and the muscles contract and expand rapidly thereby creating temperature that will help to keep the internal organs safer, the function requires lot of energy. This is a last resort when the body cannot not produce heat in any other way. Other environment factors such as snow ice and darkness will increase the stress level. Final stage is indicated with the light coloured area with core temperature of 35°C, if this occurs then the person is about to be hypothermic. The effects can change from person to person depending on the Basel Metabolic Rate. BMR indicates the number of calories you burn if you stayed in bed all dayv. The value changes with age, built of the person and sex.

“Superficial tissue cooling cases discomfort which may affect arousal, vigilance, and concentration more profound cooling for example extremities impairs their function. Neuro- muscular function of hands and fingers is impaired and affects dexterity. Cold feet affects balance and walking and may increase the risk of slippage. Cooling to low skin temperature causes pain, numbness and eventually local frostbite whole body cooling results in a sequel of effects with performance and function, eventually ending up in risk of death by hypothermia during long exposure (HOLMER, 2009).

Healy and Pepter clinch conducted national survey in Ireland in 2002 and found that two third of fuel poor householders demonstrated cold strain, an increase of blood pressure for elderly was observed when the air temperature was 15°C.

Following chart show the correspondence between ambient and body temperature.

illustration not visible in this excerpt

Figure 2-Human body temperature and ambient temperature. (Guyton, Hall, 1996)

Previous image gives an idea about how the human body behaves with the ambient temperature changes which causes effects previously explained.

In addition to cold weather wind also makes the skin feel very colder than it is. Table below illustrate the temperature combination with wind and the felt temperature.

Table 1-wind chill temperature with wind at 10 m (ISO11079)

illustration not visible in this excerpt

The grey areas indicate risk of frost bites. This gives clear understanding why a winter textile not only has to be thermal insulate but also wind proof if it is to give the maximum protection .

From looking at previous data it is obvious of how exposure to cold weather can effect your body very negatively and that it can be even fatal. One must consider all the above mentioned facts when considering to introduce cold climate jacket.

2.2. Standards for cold weather apparels.

Current cold weather textile standards can be separated in to two categories. Commercial sector which focuses on apparels that are made as work ware and are job related apparels, Daily consumer apparels which regards all kinds of jackets that are used in day to day life.

2.2.1. Commercial sector

According to International Standardisation Organisation or ISO a systematic approach for the evaluation and prevention of cold weather related problems at work has been documented. Shown below are the standards in the way it is integrated to handle above mentioned theme.

illustration not visible in this excerpt

Figure 3-Overview of international standards applicable to cold environment. (HOLMER, 2009)

2.2.1.1. Evaluation strategy

This is the first stage of the complete process. A simple observations are first carried out in an orderly fashion, which is stated in step wise and based on this a check list is filled. Main question asked in all of these situations. Are these conditions causing problem with cold? And the answer should be one of which is - no - meaning conditions are acceptable and there is no need for preventive action, Yes slight problem - meaning cold weather conditions are observed which may effect working situation however are not sever and immediate actions are not required, yes sever problem - meaning in order for the safety and health of the employees which result the optimal productivity, such problems should be immediately resolved.

When problems get more serious more details are needed therefore based on the previously mentioned graph more details are takenvi.

2.2.1.2. Metabolic rates

This is the amount of energy used in a period, Measured in Wm² (watt per meter square). Work done is divided in to classes based on the intensity of work. One can look for average metabolic rate for a given tasks from 6 classes, From Resting to very very high.

2.2.1.3. Instruments / cold surfaces

Although this doesn’t define overall comfort or thermal stress but goes in the direction of standardising of recording information which helps determine such indices. Cold surfaces provided information on surface temperatures of different materials that can be touched. The outcome reaction to those metals in different temperature if touched.

2.2.1.4. Clothing

Standards regarding thermal insulation and water vapour resistance of a work ware. It also gives data on evaporation efficiency and for cooling efficiency with textile on human skin.

2.2.1.5. Cold stress

ISO divides this in to two categories

- Whole body cooling
- Local cooling

In whole body cooling there is a method that is introduced to check the adequate clothing required to maintain needed heat balance. Method is known as IREQ to calculate the required clothing insulation this takes lot of factors in to consideration such as wind chill effect, Humidity, ambient temperature and so forth.

Local cooling deals with requirements for accessories such as gloves which will helps a person to carry out tasks without making the fingers numb.

2.2.2. Daily consumer

Although numerous investigations have been carried out on occupational cold weather protective cloths. There seems to be a lack of studies regarding consumer outdoor activities as a whole. Yet certain standards have immerged while producers trying to come up with new types cloths. These are certain basic requirements needed to produce a good winter jacket.

2.2.2.1. Layers

It is considered suitable to have more than a single layer for insulation jackets. Although it should be bared in mind not to add too many layers as this means to reduce flexibility and increase energy needed for movement.

Currently a good multilayer insulation jacket does limit the movement of its wearer thus rendering him/her to use more energy causing to increase the metabolic rate. According to research the increase in energy expense in addition of each layer in a complete system is 4% morevii, also wearing four different layers have shown to increase the metabolism by 5% to 8 % regardless of the friction between the layers were almost not to be found. The weight factor also is an issue while all these additional layers means more material thus more weight. Industry wide it is considered an inch (~2.54 cm) of material is about 4 clo; in metric units 1 cm of insulation equals to 0,24m2 CW-1 this as a rule of thumbviii.

Since these insulations depends upon mobilization of air within the textile structure, the fiber material itself play’s a minor role. Based on research the insulation value depends upon the thickness of layer. “Within the range of ± 10%. This 10% value difference is influence of the fiber, specially the fiber diameter. The fiber radiative heat loss from one fiber to another, however this is to the point until the it equals and will decrease with any deviation of the diameter”ix

2.2.2.2. Breathability

It is crucial to provide proper ventilation to its wearer. If the sweat produced is trapped inside it can be very uncomfortable to the user. Secondly due to the presence of water, heat loss from the body increases. One way to achieve breathability is to wear a jacket that it not too tight. This will allow the sweat to evaporate through the allowed openings such as neck hip or arm openings. Nowadays growing number of jackets allow moisture to pass through the jackets using technologies such as micro pores or membranes.

2.2.2.3. Water/Wind proof

Waterproof jackets provide additional protection to the wearer allowing keeping the body dry and also by keeping internal layers dry.

As previously explained wind chill effect can have negative effect on the person therefore good modern jackets equip a wind proof layer for additional protection.

Additionally making lighter and more flexible jackets with better insulation seems to guide the industry in to the future.

2.3. Thermal insulation methods.

Modern insulation material can be categorised as follows.

illustration not visible in this excerpt

Figure 4-Contemporary thermal insulation. Prof.Büsgen

2.3.1. Passive insulation

For these type of insulations the level of insulation can change for the same material by the effects of the environment, mainly because of moisture gain. There are two methods which are used individually or a combination of them both to help achieve passive insulation. The nature of such material are that the insulation level cannot be changed according to preference or does not self-adjust according to the environment.

2.3.1.1. Insulation layer.

Use of an insulation layer is to trap air in a layer of textile. Air has a thermal conductivity coefficient1 of 0.024 W/m°Cx in comparison felt wool has value of 0.07 W/m°Cxi thus trapping air in combination with a low conductive material is beneficiary to create good thermal insulation layer. Thereby slowing the heat loss and retaining the warmth. Natural and synthetic mater are both used to achieve this. Some of which are explained below.

2.3.1.1.1. Cotton

Before 1900 people were trying the use of cotton as a thermal insulator. This could have been because of the property that cotton can maintain form and space when put in place. This helps to keep warm air trapped inside. In addition cotton was light and has a thermal conductivity value of 0.029 W/m°Cxii.

However it had one major drawback, as cotton absorbs water about 27 times of its weight. This would change its properties completely and it increases the heat loss as well as makes it heavier and very uncomfortable to ware. Not to mention the life time of a product was very short. In US Marine Corps cold weather training manual: “Cotton equal(s) death”.

2.3.1.1.2. Wool

During the same period as cotton was tested as an insulation material potential of wool was also identified. Unlike cotton wool had several advantages such as, although wool can absorb moist its thermal insulation properties will remain very high. Secondly it had a long life span of use, in addition it has self-extinguishing properties when exposed to fire. As a natural fiber it was hard to fulfil the demand just by using wool.

2.3.1.1.3. Down filling

In 1936 Eddi Bauer almost died of hypothermia because of his wool coat when he was on a fishing trip. This inspired him to create the light weighted jacket. Down name was given to feathers used from geese, ducks, swans and many other kinds of birds. Good quality down material has very high thermal insulation that is equal to some of the synthetic material or better. Specially it has a good weight to volume making the jackets very light weighted. It also has a longer life span. It has one a major drawback. When the material absorbs moist the insulation properties goes down drastically. However good the material may be, it carries negative impact as the process of acquiring material means to live pic the feathers out of the birds.

In addition when feathers are packed in to a jacket any opening would result in escaping feathers in to the surrounding.

The market is very low in volume mainly due to the low supply and high price.

2.3.1.1.4. Synthetic insulation

There are wide verities of synthetic insulation materials that are used in apparels, some material outperform natural fibers so well that it is a synthetic material that outperforms all the other material to be the best in the market. Synthetic material which are subject hear uses fibers in the overall structure to achieve the performance.

There are several native advantages in using a synthetic material. Mainly it can be made not to absorb water therefore unlike down material the performance is not greatly reduced. In addition the compact structure is well established and it does not collapse. Synthetic material can be made to transfer water vapour so effectively by using capillary system2. The same capillary system can increase the thermal insulation as it contains air. The overall insulation performance in wet state when compared to down material is high.

When comparing against the best natural thermal insulator synthetic material does not behave physically unstable as the down material. Synthetic material are produced from Poly propylene, polyamide, polyester and different other material are used as flees for jackets. Other methods of production can also be seen.

some of the best performing synthetic insulators are as follows.

Thinsulate

Using fiber with diameter apx.15 microns this material can achieve 1 to 2 times insulation of duck down material. The material uses different mixtures of polymers and is produced by 3M.

Spaceloft

This can be best described as a flexible non porous aerogel blanket. Material is thin and claims to have superior heat insulation of (K value) 14 W/m°C.

2.3.1.2. Reflective layer

Reflective thermal insulation uses the low emissivity principle to reflect the heat back to its source by using special metalized coated surface. Some of such metals used are Copper, Aluminium and silver. Mostly one of these three metals are used in some form of lamination or as a pigment coating on fabric surface to create a reflective surface. As it will be explained later on, it is due to a unique property of these metals which is the low emissivity value that they are capable of achieving thermal reflectivity. Currently in the market there are several apparel manufacturers who are adopting such technologies.

Companies such as Colombia® sports ware uses what they call Omni heat ™ which is a membrane partially coated (apx. 31.5%) with aluminium pigments. There are several other suppliers such as AFM Inc., Innovative insulation which produce similar technologies although there is no indication of this material being used in any apparel.

2.3.2. Active insulation

Active insulation material behaves or can be adjusted to behave differently in different environments according to the preference of it’s user.

2.3.2.1. Not adjustable

These systems although cannot be controlled manually the technology allows these material to behave differently in different environment. Therefore it is not just about keeping the body’s internal heat from escaping in to the colder environment, they are also able to allow body to maintain an equilibrium in warm climate.

2.3.2.1.1. PCM

PCM or phase change materials are mostly used in jackets. These are micro encapsulated paraffin with a size of 2µ to 30µ. This material takes up heat in its melting process in warmer environment and release the temperature when placed in cooler environment. This is ideal for body temperature management for employees who have to work in cool houses where they have to come in and out from cold environment to warm. When the user is in the warm environment PCM takes up heat and melts, once he moves in to the colder environment this heat is released on to the body which allows to keep the body warm.

2.3.2.1.2. Shape memory material

There are two types. They are shape memory polymers or shape memory alloys. These are material that changes its shape when exposed to different temperatures.

illustration not visible in this excerpt

Figure 5-Shape memory material. Prof.Büsgen

Figure above illustrates the behaviour of the material in low and higher temperature. Due to the special chemical properties of these materials, once the material is in temperature that makes it behave in such way the material distance is increased or reduced. Because of this process, if the material is in colder environment the distance between two layers will be increased which increases the thermal insulation, and once its placed in a warmer environment the gap will be reduced allowing the body heat to pass off without any disturbance.

2.3.2.2. Adjustable Insulation

Technology which allows a person to influence their body heat by allowing them to control mechanisms of an apparel has been used since some time. There are several versions of such apparels.

For example Gore-Tex® produces a jacket which consists of air tubes that can be inflated to maximize thermal insulation. These tubes are in cooperated in to the jacket to be inflated.

Certain jacket which follows this principle also uses special gases that have lesser thermal conductivity coefficient. For such technology which uses pumps for the inflation process allows the user to increase or decrease in thermal insulation as needed.

In reverse engineering the technology there are some jackets that uses water or some other liquids to keep the body cooler in required environment.

Companies such as Colombia®, Activheat® are producing different types of jacket3 by embedding them with heat generating material connected to a rechargeable battery. Thermal level can be controlled with these jackets this helps one to maintain the body temperature as needed. Mostly mountain climbers who go in to extreme weather conditions may prefer to use them. The product by Colombia sportswear was recalled due to burning hazard. Such jackets may represent a niche market without any wide public interest.

Price of jacket from Activeheat® starts from 149$ upwards4.

3. Market analysis

The main reasons to have improved thermal insulation material is to help improve lives. This allows people to be more productive and allow them to carry out their daily lives more productively. Materials such as Spaceloft® has a very high insulation levels but with drawbacks. Problem with most of such technologies are that they cannot be incorporated in to an apparel easily. In the case of spaceloft® it is non-breathable. Most of the good materials are not widely available to the mass public. One reason for this could be because it is not economical to be used by mass consumers. Thus most of these technologies only represents only small part of the market.

A recent survey carried out among HS-Niederrhein students showed that more than 50% students inquired were interested of purchasing a new type of material that would be thin and gives better thermal insulation. Due to ever increasing energy costs there are wide verity of uses for thermal insulation material both in consumer and industrial sector. The demand doesn’t seem to be diminishing in any forcible future.

Following graph illustrates the use of thermal insulating textiles in a nutshell. This is only an abstract to enlighten how much impact such materials have in our life. The uses are much broader than what is listed.

illustration not visible in this excerpt

Figure 6-Uses of heat insulate material

By observing the above graph a brief idea of the uses of thermal insulation material can be gained. Although needs of some of the segments are very well provided in others they lack far behind. Therefore there is no single solution that suits most much less all.

E.g. - NATO military uniforms recognize not to use synthetic material with low melting point for military textiles. Because when such materials are exposed to war incidents can create critical situations to the wearer if it melts on the body.

3.1. Market needs

Following are some recognized market needs that exist today. However it is safe to say that there are much more unfulfilled needs.

3.1.2. Cold weather textiles

All though there exists wide verity of materials and technologies that are available in certain markets most preferred insulation materials used are synthetic flees material. This could be largely due to availability and affordability of material that has a longer life span. Yet most of these materials do not fulfil needed thermal insulation properties.

Although material such as down is available they are not as affordable for most of the people. Limitations in wearing bulky jackets are also seen as a reason why people do not prefer heavy jackets. Thus for the average consumer there is a need for thinner and more affordable jacket. Having a more affordable jacket makes it possible to become affordable to many under privileged people who otherwise have no proper choice. In order to provide affordable material production cost have to go down.

3.1.3. Cold weather sports

Sports such as mountain climbing, skiing, camping, hiking and certain other sports require very good thermal insulating apparels. Most of these jackets tend to limit the users movement as well as increase the fatigue thus reduce their performance level. Often fatalities are reported while climbing Himalayan mountains due the extreme cold weather. This due to not having necessary clothing for such extreme conditions.

There is a need in this market to have more lighter, affordable and flexible material.

3.1.4. Special care for older people

As mentioned in the introduction the number of deaths of older people related to cold weather conditions in the UK are very high as with many other countries. One of the major reasons for this is that at old age their bodies cannot generate high metabolism to cope with the rate of heat loss thus vital organs can fail faster. Most people being out of the reach to afford better apparels or not preferring to ware bulky outfits due to un-comfortableness increases the casualties’ level.

3.1.5. Work related

There are many jobs that require wearing thermal insulating apparels. Functional areas such as sailors, researcher or oil platform workers who has to work in extreme weather conditions has to be able to be more flexible and be able to stay without feeling uncomfortable at work. Their productivity is directly related to the thermal comfort.

More specifically military are always looking for new ways in which they can make the solder safer and more efficient in cold environment as this mean the difference between doing the job right and coming home to their loved once. As with previous cases having bulky jackets to ware reduces their dexterity making it harder for them to use their weapon. Soldier who has to perform recon missions can only carry certain amount of food and arms. Due to this it is crucial that they can save energy any way possible. One way to achieve this is by having an efficient and effective thermal insulating clothing system. Having lighter, weather proof better uniforms will allow better movement and also help reduce heat loss thereby reducing the needed food consumption.

4. Theories and law’s

This chapter will continue by introducing all the theories and laws that will become the foundation for this thesis.

4.1. Thermal dynamics

First topic which comes in connection with this topic is thermal equilibrium. To make the whole topic very clear to discuss below graph will be used.

illustration not visible in this excerpt

Figure 7-Thermal equilibrium illustration

When two systems are brought together there will be transfer of energy from one system to the other. This will continue until there will be a thermal equilibrium between either systems, or a state of energy equality. Firstly thermal energy or heat moves from where the thermal energy is more to where it is less and this continues until systems come to equilibrium or equal temperatures. In order to transfer internal energy both systems are involved, this is the first law of thermodynamics. There are four ways in which heat can be lost from body to ambient environment. Convection, conduction, evaporation and radiation are those methods. Above graph illustrates all four types of thermal equilibrium methods.

4.1.1.1. Radiation

Radiation is the method of heat transfer by the means of electromagnetic wave. Human body radiation is not visible to human eye but it certainly can be felt by the skin. In above graph this occurs when the heat is transferred from the hot plate to the metal stand. For this thesis conduction and radiation will be the topic of focus, how to reduce it and measure based on it. As for the discussion of radiation another interesting topic has to be introduced.

4.1.1.2. Convection

Convection is the heat transfer by mass motion of fluids such as water or through gas. It is visible inside of the beaker the heated up water from the bottom goes up heating upper water and once cooled moved back down. For example for a naked body air in contact with the body will receive the heat by conduction and that is carried away from the body by convection.

4.1.1.3. Conduction

Is the transfer of heat from solid material at molecular level without any motion of the material as a whole. In the image this is depicted when the heated metal stand transfers the heat energy to the contacting glass beaker.

4.1.1.4. Evaporation

Changing liquid in to vapour and there by being moved away from the system is this. For this change to occur lot of energy is needed. For the body to evaporate 1g of water it takes about 2424J or 580 calories at body temperature (Anon., n.d.). The process can be seen in the previous figure the water molecules which are on the top which have enough energy breaks free and move as water vapour.

It should be mentioned that Evaporation cannot clearly be taken as a method of heat transfer because but it’s considered as phase change in this case for water. For example a cube of ice once heated will take part of the energy to increase the kinetic energy of ice molecule which will then become water and once more heat is applied it will become vapour. This process requires energy as mentioned before therefore it can be considered method in which heat can be lost from one means to another.

4.1.2. Thermal Conduction principles.

4.1.2.1. Thermal conductivity value.

Thermal conductivity value (also known as thermal conductivity coefficient) is the rate at which the heat is conducted through a material. This is also known as the K value. It is measured by Watt per temperature gradient of one Celsius per Meter thickness. Every material has thermal conductivity vale, even airxiii has a K value of 0.025 W° m-1C-1.

The value for any material can be obtained by applying the following formula.

Equation a- Thermal conductivity (Anon., n.d.)

illustration not visible in this excerpt

4.1.2.2. Thermal resistance value.

Thermal resistance is thickness of material divided by the conductivity value. This gives the R value. The R value changes for the same material depending on the temperature gradient.

Equation b-Thermal resistance (Anon., n.d.)

illustration not visible in this excerpt

This means that the thickness of the material has an overall influence on the R value of a material.

4.1.2.3. Thermal conduction through a fabric.

A fabric is an intricate construction of arranging fibers and/or yarns together. Way in which heat is transmitted through a fabric is complicated and it has to be looked in separately for each method of heat loss.

Thermal conductivity through a fabric can be simplified in to a formula as follows.

Equation c-Fabric thermal conduction (Saville, 1999)

illustration not visible in this excerpt

Based on the formula it can be seen that by using fiber that has a low K value can lead to a lower thermal conductivity. If the fractional fiber volume is less it will decrease the heat loss through the material, leaving only to be conducted through air, radiation or convection.

Heat loss due to radiation is more complex this can be better understood in next chapters.

For all intensive purposes convection and evaporation (evaporation heat loss from the body ~7%xiv) heat loss is neglected for this thesis. Mainly because they account for minimal amount of bodies heat loss.

4.1.3. Infra-Red

Infra-red or IR for short is a part of electromagnetic spectrum and is partially invisible to naked human eye.

illustration not visible in this excerpt

Figure 8-Electromagnetic spe

As illustrated above IR which consists of visible spectrum, U.V., and X-Ray etc.

From moving electrical charges induce magnetic fields and inversely this, that changes of magnetic fields create an electric field. Vibrating electrical charges therefore causes a periodic change electromagnetic fields, which propagates as electromagnetic fields, which propagates as electromagnetic waves linearly in to space with speed of lightxv. For the creation of electromagnetic radiation or EMR some form of energy has to be extended, for example radiation of a white-hot tungsten wire in a light bulb, energy released during this chemical reaction can be emitted as radiation thus EMR is an energy carrier. The energy travels in form of waves.

Energy measuring unit is Joule. Energy and radiation frequency have the following relationship.

Equation d-Energy of EMR (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

illustration not visible in this excerpt

h is the Planks constant. As EMR travel in waves $ is the Frequency or number of oscillations per unit is as given below.

Equation e-Frequency at a given wavelength (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

illustration not visible in this excerpt

Where λ the corresponding wavelength and c is speed of light which is 2.997×108 ms-1 in a

vacuum. λ As it appeared on the Figure 8-Electromagnetic spectrum and IR spectrum. Changes from left to right with decreasing wavelength on the EM spectrum.

Based on the previous two equation following can be derived for the energy level at a given point of the EMR.

Equation f-Energy and wavelength relation

illustration not visible in this excerpt

Therefore we can see that the radiation frequency and energy are directly proportional.

Near IR is the closest to the visible spectrum and as shown before contains most of the energy out of the IR portion of the spectrum. This is detectable by the naked eye and further it goes in to middle range it becomes undetectable to naked eye. The categorisation of the IR is done according to ISO 204735 scheme.

Sir Frederick William Herschel, born in Hanover, Germany was famous musician and an astronomer. He discovered infrared in 1800 while a study of light refraction through a prism. Parts of the suns energy received to earth arrive in the form IR radiation. All objects which are above absolute zero6 or -273 °C emit IR radiation. A warm body emits wide range of IR meaning they have different wavelength. As the previous argument goes the wavelength and the energy relation can be establish. This explains why different temperatures of the IR radiation has corresponding wavelengths thus in order to understand a specific temperature effect the wavelength is important.

4.1.3.1. Absorption and reflection of IR

A molecule consists of two or more atoms. As such the whole world consists of atoms and although solid substances seem solid and in state of relaxations, the atoms inside of them are in constant motion with each other. Specially the electrons of an atom changes its position by moving up or down from what is fictionally known as an energy level within an atom. These motions mean that an atom release or absorb energy during this process. Atoms themselves when bonded move relative to each other. For the simplest form of two atom molecule there are two types of basic motions that can be recognized. They are stretching vibrations and bending vibrations. Below diagram illustrates the motion.

illustration not visible in this excerpt

Figure 9- Stretching and bending vibration of an atom. (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

These vibrations or motions can be either symmetric or Asymmetric and this is one key to IR absorption. The atoms are in motion relative to a hypothetical centre of a linear mass. Nature of such motions can be two fold. Consider CO² molecule, assume the following as an easy structure. Consider the distance of space between depicted as how the motion occurs.

illustration not visible in this excerpt

In the symmetric molecular movement the atoms in dipole movement moves equal distance around the centre. This is also known as raman inactive movement. Sum of the movement from both sides is equal to zero as the atoms travel the same distance on both sides. Thus this stretch is called IR inactive.

In an asymmetric movement there is a change in the dipole movement one side from the other. This is known as raman active movement. Hear the sum of the movement is in either direction has value and creates additional energy. Therefore these molecules absorb IR radiation and is known as IR active.

When a raman active motion happens then there is a difference between the energy of the two vibrations. Energy state E² and another to an energy state E³, E³ having a higher rotational quantum number7 or energy value. Absorption of IR occurs only if the energy of the incident photon8 coincides exactly with the energy difference between the vibrations (E³-E²). A graph illustrates this below.

illustration not visible in this excerpt

Figure 10-IR active ramen motion. (Helmut Günzler, Hans -Ulrich Gremlich , 2002)

Above graph shows the corresponding quantum number for the molecules rotational movement and as it is indicated the IR wave energy emitted is absorbed by a raman active rotational. This energy absorbed by the material leads to a gain in temperature by increased molecular movement.

4.1.3.2. Emissivity

Is the ratio of the radiation absorbed by a surface to the radiation emitted by a blackbody at the same temperature. The emissivity coefficient value ranges 0 to 1. Close to 0 being almost non absorption of IR radiation whereas closer it gets to 1 it means there is perfect harmony of absorption of radiation and re-emitting of the radiation from that material.

Table 2-Emissivity coefficient of some materials. (editor.engineeringtoolbox@gmail.com, n.d.)

illustration not visible in this excerpt

4.1.3.3. Black body

Is any object that is able absorb the entire spectrum of electromagnetic spectrum which falls on it. To imagine this think of staring in to the abyss of a dark cave on sunny day.

4.1.3.4. Black body radiation

Refers to an object like mentioned before it absorbs all radiation which falls upon it but not only does it absorb but it comes to an equilibrium state by re-emitting the radiation. This is a character of this system independent of the source or type of radiation which the blackbody is exposed to.

According to Stefan Boltzmann radiation law when the temperature of the black body increases wavelength decreases, the overall radiation energy increases and the peak of the radiation curve moves to shorter wavelengths.

4.1.3.5. Wien’s displacement law

Wien derived formula which was initially developed by Nobel prize winning physicist Max Plank. Based on observation made before the radiation law he derived a simple formula which states that temperature T times the wavelength λ of the maximum intensity is a constant.

Temperature should be calculated in Kelvin.

Equation g - Wien's displacement law (Hassel, 2010)

illustration not visible in this excerpt

Equation h. Celsius to kelvin conversion

illustration not visible in this excerpt

4.1.3.6. Radiation heat loss through a material.

In the conductive principle in previous chapter, thermal conduction through a fabric was discussed. Conduction is only a part of the heat loss principle. Radiation heat loss through a fabric is more complicated. Following formula is used to establish a simplified relationship to find out radiation heat loss through a thick fabric.

Equation i - Radiation conductivity (Saville, 1999)

illustration not visible in this excerpt

Not to be misunderstood with fiber volume fraction, which deals with composite material. FFV is the complete fiber volume within volume space of a material.

4.2. Human skin

Skin is the largest organ of a human being, out of several purposes some of its functions are to control evaporation and heat regulation of the body. The skin area of average human being is around 1.85m²xvii. As previously mentioned average mean skin temperature ranges around 34°C with variations across the body. Our body produces apx. 1.2°C an hourxviii given the heat loss body manages to maintain the right core temperature of ~ 37°C. Human skin radiates IR, this is one way in which human body maintains its thermal equilibrium, and it accounts for 54%-60% of all the heat loss from the body (Saville, 1999).

[...]


1 How much thermal energy is transferred through an m² are of 1m thick material.

2 Tubular fiber that can transport moisture

3 Price not available for Colombia jacket.

4 http://activheat.com/index_files/Batteryheatedapparel.htm

5 Optics and photonics—Spectral band. 2007

6 -273°C or 0°K

7 Rotational quantum number is given to different motions associated with the nucleus of rotations molecule.

8 Photon is a discreet packet of energy associated with EMR. In this case the incident energy of the corresponding IR radiation.

Details

Seiten
127
Jahr
2013
ISBN (eBook)
9783656834014
ISBN (Buch)
9783656834021
Dateigröße
7.8 MB
Sprache
Englisch
Katalognummer
v283424
Institution / Hochschule
Hochschule Niederrhein in Mönchengladbach
Note
1.0
Schlagworte
Thermal Insulation Thermal Insulation Coating IR reflective textiles Thermal insulating spacer material Thermal insulating textiles

Autor

Teilen

Zurück

Titel: Development of Thermal Insulating Textiles. An Innovative IR Reflective Spacer Material