Design of a Heat Pipe for a Lunar Lander

Buck, Carina

Design of a Heat Pipe for a Lunar Lander

Zusammenfassung

Inhaltsangabe:Introduction:
At the Milwaukee School of Engineering, senior students are required to take part in a Senior Design Project during their final year for 2 to 3 quarters. The project is a group project related to a field in mechanical engineering. Students participating in the exchange program between MSOE and Fachhochschule Lübeck have to be enrolled in the Senior Design Project for 3 quarters. During this time the student has to write his or her diploma thesis as an individual work within the topic of the project.
This Senior Design Project was in the section Energy systems. The task as a group was to design a thermal control system for a Lunar Lander (see Figure 1.1) in cooperation with NASA´s Exploration System Mission Directorate. A Lunar Lander will be exposed to extreme temperature differences. There is a need to control the thermal environment within the lander in order to provide functionality for both personnel and equipment. Previous lunar missions utilized consumable materials for cooling. Future lunar missions will require a more robust thermal control approach, one that allows longer duration missions while minimizing resources. Compared to the previous Lunar Lander, the new lander will be larger to include an additional astronaut as well as additional equipment. The thermal control system must be capable of handling this increase in thermal energy. After the evaluation of a number of possible systems based on research and in depth feasibility in the fall quarter the three most promising systems were chosen by the group to be examined in greater detail. The aim of this project was then to produce a design for each of the remaining thermal control systems until the end of the winter quarter.. The first two quarters ended with a presentation of our accomplishments to a committee of professors at MSOE and an invitation to the Marshall Flight Center in Huntsville, Alabama by NASA to present our designs to a committee of scientists. For the spring quarter we chose two experiments to be performed. One was the building of a vacuum chamber in order to test the thermal properties of the lunar regolith simulant. The other one was the building and testing of the heat pipe design. Inhaltsverzeichnis:Table of Contents:
List of Figures5
List of Tables6
1.Introduction7
1.1The Senior Design Project at MSOE7
1.2The Specifications and Requirements given by NASA8
1.3The Focus of my Thesis10
1.4The Schedule for the Completion […]

Leseprobe

Inhaltsverzeichnis

Carina Buck

Design of a Heat Pipe for a Lunar Lander

ISBN: 978-3-8366-2884-6

Herstellung: Diplomica® Verlag GmbH, Hamburg, 2009

Zugl. Fachhochschule Lübeck, Lübeck, Deutschland, Diplomarbeit, 2008

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http://www.diplomica.de, Hamburg 2009

DIPLOMA THESIS

Carina Buck Page 1 of 90

Abstract

Heat pipes have been used in thermal control systems in several different ways in various

applications.

A wide range of materials and fluids can be used to operate a heat pipe depending on the

applying conditions.

This diploma thesis deals with the development of a heat pipe for an extreme environment

space.

The heat pipe is developed to be part of a system that controls the thermal environment inside a

Lunar Lander and makes it functional for personnel and equipment.

The Lunar Lander will be exposed to extreme temperature differences in which the heat pipe has

to be able to operate in.

In this thesis a heat pipe is designed to meet the applying conditions and requirements.

After the design is completed it is modified to fit conditions applying in a laboratory at the

Milwaukee School of Engineering in order to be able to build a physical model for experimental

purposes.

The goal of this experiment is to prove the functionality of the heat pipe design and therefore

only absolutely necessary chances to the original design are made.

DIPLOMA THESIS

Carina Buck Page 2 of 90

Acknowledgments

I would like to thank the MSOE Senior Design Team 2008 "Concilium Lunare", in particular Mark

Warwick, as well as my advisors Professor Michael Swedish and Professor Dr. John Pakkala for

their support in the past months.

Their help and their input was instrumental in completing this thesis.

I would also like to thank the Fachhochschule Luebeck and the Milwaukee School of Engineering

as well as the initiators of the international exchange program Professor Dr.-Ing. Jürgen

Blechschmidt, Professor Dr.-Ing. Hans Reddemann and Professor Dr. John Pakkala for this

experience and for the effort they put into making this program a success.

DIPLOMA THESIS

Carina Buck Page 3 of 90

Table of Contents

List of Figures ... 5

List of Tables ... 6

Introduction ... 7

1.1

The Senior Design Project at MSOE... 7

1.2

The Specifications and Requirements given by NASA ... 8

1.3

The Focus of my Thesis... 10

1.4

The Schedule for the Completion of the Thesis ... 11

Background Research ... 12

2.1

The History of the Heat Pipe ... 12

2.2

The Principle of a Heat Pipe ... 13

2.3

The Theory of the Preliminary Design of a Heat Pipe ... 16

2.4

Theory of the Design of the Heat Pipe ... 26

2.5

Theory of Building a Heat Pipe ... 28

Preliminary Design of the Heat Pipe for the Lunar Lander ... 29

3.1

The Working Fluid ... 29

3.2

The Material of the Heat Pipe ... 33

3.3

The Limitations for Ammonia at 240 K ... 35

3.4

The Thermal Resistances ... 41

3.5

The Preliminary Design Outcome ... 48

Design of the Heat Pipe for the Physical Model ... 49

4.1

The Viscous Limit ... 49

4.2

The Boiling Limitation ... 50

4.3

The Capillary Limitation ... 51

4.4

The Pressure Limitation ... 52

4.5

The Thermal Resistances ... 53

4.6

The Calculations for the Tube ... 60

4.7

Calculations for the End Caps ... 65

4.8

Drawings ... 71

4.9

The Design of the Wick ... 73

4.10

The Input/ Output Devices ... 73

4.11

The Fill Tube/ Valve ... 73

4.12

The Pressure Gauge ... 74

4.13

The Temperature Device ... 74

DIPLOMA THESIS

Carina Buck Page 4 of 90

4.14

The Working Fluid ... 74

4.15

The Weld ... 74

The Building of the Heat Pipe ... 75

The Experiment ... 77

6.1

The Objective ... 77

6.2

The Theory ... 77

6.3

The First Experiment ... 79

6.4

The Second Experiment... 82

6.5

The Third Experiment ... 85

Conclusion ... 88

Works Cited ... 89

DIPLOMA THESIS

Carina Buck Page 5 of 90

List of Figures

Figure 1.1 "NASA Lunar Lander" ... 7

Figure 1.2 "NASA Lunar Heat Rejection" ... 9

Figure 1.3 "Gantt Chart" ... 11

Figure 1.4 "Gantt Chart - Diagram" ... 11

Figure 2.1 "Heat Pipe Theory" ... 13

Figure 2.2 "Position of the Wick" ... 18

Figure 2.3 "Block Diagram - How to Build a Heat Pipe" ... 28

Figure 3.1 "Merit Numbers for Various Working Fluids" ... 30

Figure 3.2 "Merit Numbers for Ammonia at Various Temperatures"... 31

Figure 3.3 "Thermal Resistances"... 41

Figure 3.4 "Dimension Sketch" ... 48

Figure 4.1 "Thermal Resistances"... 53

Figure 4.2 "P-v Diagram" ... 62

Figure 4.3"Pressure vs. Temperature" ... 63

Figure 4.4 "Interface of MD Solids" ... 64

Figure 4.5 "Pressure vs. Temperature End Caps" ... 67

Figure 4.6 "Stress Distribution" ... 68

Figure 4.7 "Deflection of the End Caps" ... 69

Figure 4.8 "The Assembly of the Container" ... 71

Figure 4.9 "The Container" ... 71

Figure 4.10 "The Tube"... 72

Figure 4.11 "The End Cap 1"... 72

Figure 4.12 "The End Cap 2"... 72

Figure 5.1 "The Tube"... 75

Figure 5.2 "Aluminum Block" ... 75

Figure 5.3 "The End Caps" ... 75

Figure 5.4 "Aluminum Screen Sheet" ... 76

Figure 5.5 "The Wick" ... 76

Figure 5.6 "Aluminum Plate" ... 76

Figure 5.7 "The Carrier"... 76

Figure 6.1 "Experiment Set-up" ... 77

DIPLOMA THESIS

Carina Buck Page 6 of 90

Figure 6.2 "T-v-Diagram" ... 78

Figure 6.3 "The Set-up First Experiment" ... 79

Figure 6.4 "Data First Experiment" ... 80

Figure 6.5 "Data Condenser Side First Experiment" ... 80

Figure 6.6 " Data Evaporator Side First Experiment" ... 80

Figure 6.7 " The Set-up Second Experiment " ... 81

Figure 6.8 " Data Second Experiment " ... 83

Figure 6.9 " Data Condenser Side Second Experiment " ... 83

Figure 6.10 " Data Evaporator Side Second Experiment" ... 83

Figure 6.11 " The Set-up Third Experiment " ... 85

Figure 6.12 " Data Third Experiment " ... 86

Figure 6.13 " Data Condenser Side Third Experiment " ... 86

Figure 6.14 " Data Evaporator Side Third Experiment" ... 86

List of Tables

Table 3-1 "Merit Numbers for Various Working Fluids" ... 29

Table 3-2 "Merit Numbers for Ammonia at Various Temperatures" ... 31

Table 3-3 "Mathematical Model for Various Working Fluids" ... 32

Table 3-4 "Thermal Conductivity" ... 33

Table 3-5 "Fluid Solid Compatibility" ... 34

Table 3-6 "Weight of Material" ... 34

Table 4-1 "Stress Analysis" ... 63

Table 4-2 "Stress Analysis End Caps" ... 66

Table 4-3 "Properties for Solid Works COSMOSXpress Analysis" ... 68

DIPLOMA THESIS

Carina Buck Page 7 of 90

Introduction

1.1

The Senior Design Project at MSOE

At the Milwaukee School of Engineering, senior students are required to take part in a Senior

Design Project during their final year for 2 to 3 quarters. The project is a group project related to a

field in mechanical engineering. Students participating in the exchange program between MSOE

and Fachhochschule Lübeck have to be enrolled in the Senior Design Project for 3 quarters. During

this time the student has to write his or her diploma thesis as an individual work within the topic

of the project.

Figure 1.1 "NASA Lunar Lander" [9]

This Senior Design Project was in the section "Energy systems". The task as a group was to design

a thermal control system for a Lunar Lander (see Figure 1.1) in cooperation with NASA´s

Exploration System Mission Directorate. "A Lunar Lander will be exposed to extreme temperature

differences. There is a need to control the thermal environment within the lander in order to

provide functionality for both personnel and equipment. Previous lunar missions utilized

consumable materials for cooling. Future lunar missions will require a more robust thermal

control approach, one that allows longer duration missions while minimizing resources. Compared

to the previous Lunar Lander, the new lander will be larger to include an additional astronaut as

well as additional equipment. The thermal control system must be capable of handling this

increase in thermal energy. After the evaluation of a number of possible systems based on

research and in depth feasibility in the fall quarter the three most promising systems were chosen

by the group to be examined in greater detail. The aim of this project was then to produce a

design for each of the remaining thermal control systems until the end of the winter quarter."

[23]. The first two quarters ended with a presentation of our accomplishments to a committee of

professors at MSOE and an invitation to the Marshall Flight Center in Huntsville, Alabama by NASA

to present our designs to a committee of scientists. For the spring quarter we chose two

experiments to be performed. One was the building of a vacuum chamber in order to test the

thermal properties of the lunar regolith simulant. The other one was the building and testing of

the heat pipe design.

DIPLOMA THESIS

Carina Buck Page 8 of 90

1.2

The Specifications and Requirements given by NASA

1.2.1

General

NASA provided the Senior Design Group with specifications and requirements for the thermal

control system of the Lunar Lander as guidelines which were considered in the selection of the

three chosen systems:

Power requirements

Heat rejection requirement (11 kW)

Electrical power input requirement (< 1 kW)

Fault operational

The system should still be able to operate if parts of it fail

Thermal control

Anytime / anywhere in the lunar environment

Heating and cooling in the lunar environment

Operation time

More than 7 days duration

Compact

Must be as small as possible to fit in the Lunar Lander

Survival in the lunar environment

Resistant to micrometeoroids

Must be resilient to regolith (moon dust)

Temperatures (100 K to 400 K)

Vacuum

Lightweight

The lighter the cheaper to send it to space

No cost restriction

The right materials are more important than the costs

DIPLOMA THESIS

Carina Buck Page 9 of 90

1.2.2

The Lunar Environment

The Lunar Lander needs to be able to operate in the lunar environment. In order to assure that,

the exact conditions of the lunar environment have to be known. The lunar surface thermal

environment is much more severe than that of the earth, in both magnitude and variation.

The surface temperatures on the sun-lit side of the Moon can reach 390 K at the sub- solar point

while dark side temperatures may plunge below 105 K as it can be seen from Figure 1.2 provided

by NASA.

Most conventional thermal management systems would be seriously compromised or even

rendered useless in such environments.

Figure 1.2 "NASA Lunar Heat Rejection" [9]

DIPLOMA THESIS

Carina Buck Page 10 of 90

1.3

The Focus of the Thesis

The task within the Senior Design Project was to design, build and test a heat pipe for the thermal

control system in the Lunar Lander.

The first step in designing a heat pipe was to perform an in depth background research to get an

overview over the complex topic and all the aspects involved.

The next step was the preliminary design with special consideration of the limitations for the heat

transfer capability, material and fluid properties and compatibilities, thermal resistances as well

as dimensions. This design was made with respect to the specifications and requirements given by

NASA.

After the preliminary design for the use in the Lunar Lander, the heat pipe design was modified to

be able to build and test a physical model of the heat pipe in the laboratory.

Different limitations in regard to feasibility, safety and costs influenced the design.

Due to the toxicity of ammonia, pressure and temperature development in the heat pipe as well

as the heat transfer ability have to be predicted and observed carefully in order to create a safe

experiment.

DIPLOMA THESIS

Carina Buck Page 11 of 90

1.4

The Schedule for the Completion of the Thesis

Figure 1.3 "Gantt Chart"

Figure 1.4 "Gantt Chart - Diagram"

DIPLOMA THESIS

Carina Buck Page 12 of 90

Background Research

2.1

The History of the Heat Pipe

The principle of the heat pipe was first suggested in 1942 by Gaugler of the General Motors

Corporation Ohio, USA, who patented a lightweight heat transfer device in 1944 which was

basically the heat pipe that is present today. The idea was again mentioned in 1962 by Trefehen in

connection with the space program and patented by Wyatt in 1963. However, it was not widely

published until the scientists at the Los Alamos Scientific Laboratory including Grover

independently reinvented the concept in 1964. Grover and his team also demonstrated its

effectiveness as a high-performance heat transfer device, named it the "heat pipe", and

developed its applications.

The first heat pipes consisted of an aluminum or copper container whose inner surfaces have a

capillary wicking material. The first working fluid Grover used was water, shortly after followed by

a liquid sodium heat pipe. 1966 the first cryogenic heat pipe was developed by Haskin of the Air

Force Flight Dynamic Laboratory.

From then on the development and improvement of the heat pipe continued and the heat pipe

gained more and more importance.

Especially NASA took and still takes great interest in its development, since the heat pipe has a

very low weight and is able to operate in a zero gravity environment without great impact on the

performance. The first application of heat pipes in the space program was in thermal equilibration

of satellite transponders. As satellites orbit, one side is exposed to the direct radiation of the sun

and a high temperature while the opposite side is dark and exposed to the very low temperatures

of outer space. This causes severe discrepancies in the temperature of the transponders and

therefore influences the reliability and accuracy. The heat pipe cooling system designed for this

purpose managed the high heat fluxes and demonstrated flawless operation with and without the

influence of gravity. The developed cooling system was the first description and usage of variable

conductance heat pipes to actively regulate heat flow and/or the evaporator temperature.

Publications in 1967 and 1968 by Feldman, Eastman, & Katzoff first discussed applications of heat

pipes to areas outside of government concern that would not fall under the high temperature

classification such as for example air conditioning, engine cooling, and electronics cooling. These

papers also first mentioned flexible, arterial, and flat plate heat pipes.

DIPLOMA THESIS

Carina Buck Page 13 of 90

In 1969 publications introduced the concept of the rotational heat pipe with its applications to

turbine blade cooling and the first discussions of heat pipe applications to cryogenic processes.

Starting in the 1980s, Sony incorporated heat pipes into the cooling schemes for some of its

commercial electronic products instead of the more traditional finned heat sink with and without

forced convection. Heat pipes transferred from a specialized industrial heat transfer component

to a consumer commodity. Modern CPU heat pipes are typically made from copper and use water

as the working fluid.

Heat pipes have many advantages which make them valuable for many different applications in

the cooling and heating business, from Computers over air- conditioning to creating a livable

environment in space.

2.2

The Principle of a Heat Pipe

The principle of the heat pipe can be seen in Figure 2.1. A heat pipe is a closed tube or chamber

that passively transfers thermal energy between a condenser and an evaporator. It can be of

several different shapes and has a porous capillary wick inside.

Figure 2.1 "Heat Pipe Theory" [22]

The wick is saturated with the liquid phase of a working fluid and the remaining volume of the

pipe contains the vapor phase. When heat is applied at the evaporator by an external source, the

working fluid vaporizes. The resulting difference in pressure drives the vapor from the evaporator

to the condenser where it condenses and releases the latent heat of vaporization to a heat sink.

DIPLOMA THESIS

Carina Buck Page 14 of 90

The depletion of liquid by evaporation causes the liquid- vapor interface in the evaporator to

enter into the wick surface where a capillary pressure is developed. This capillary pressure pumps

the condensed liquid back to the evaporator by using the pores and the surface tension of the

wick.

A heat pipe can transport a large amount of heat by having only a small unit size compared to

other systems, but the maximum rate of the heat transfer is still limited by several different

variables. The wick properties like the pore size, the thermal conductivity, and the capillary limit,

which is determined by the pumping capacity of the wick structure, have an effect on the heat

transfer rate as well as the liquid, vapor and material properties.

The viscous limit based on the liquid flow-rate, the sonic limit based on the vapor flow rate, the

entrainment limit based on the friction between the working fluid and the vapor which travel in

opposite directions, the boiling limit based on the pressure difference between the liquid and the

vapor and the physical dimensions of the heat pipe also limit the maximum heat transfer rate and

have to be carefully observed.

Through methods of analysis, the right modification of the characteristics for the heat pipe has to

be found in order to meet the requirements for this project.

The advantages and the uniqueness of this project are given by the conditions in space, the

extreme temperatures, the non-existing atmosphere as well as NASA´s limitations on size and

weight and the non-existing limitations on costs.

DIPLOMA THESIS

Carina Buck Page 15 of 90

2.2.1

The Advantages

A heat pipe is able to transport a large quantity of thermal energy with a relatively small unit size

compared to other common systems.

One of the most important advantages of the heat pipe is clearly its almost total passive

operation, meaning that the system has fewer potential failure points than active systems and

requires no electrical energy in order to operate the system.

The only moving parts required in this heat pipe are due to the fan in the active control, which is

used to increase the coefficient of convection heat transfer from the lander interior.

2.2.2

The Disadvantages

Conditions in space include very low temperatures which require certain working fluid properties.

Most importantly, the triple point of the working fluid must be below the working temperature of

the heat pipe. The chosen fluid, ammonia, is very well able to operate in this environment;

however, ammonia is a hazardous and corrosive substance that requires special precautions if

placed near an area of human occupancy.

There are also several limitations on the heat transfer rate which need to be observed. The type

of limitation restricting the heat transport capability of a heat pipe is determined by which

limitation has the lowest heat transfer rate value at the considered temperature. The limitations

can be divided into two categories, as previously discussed: limitations which result in a failure of

the heat pipe and limitations which do not.

The limitations resulting in a failure of the heat pipe all relate to an insufficient liquid flow into the

evaporator, resulting in the dry-out of the evaporator wick.

DIPLOMA THESIS

Carina Buck Page 16 of 90

2.3

The Theory of the Preliminary Design of a Heat Pipe

2.3.1

The Concept

In order to design a heat pipe, the best combination of fluids, wick structures, wick materials and

container materials should be selected before the detailed design calculations for the dimensions

of the pipe are made. The ideal combination maximizes the performance abilities of the heat pipe.

The selection should be made under the consideration of the state requirements given by NASA

as described earlier.

First Step

Select candidates for working fluid

Select possible wick materials and wick structures to maximize the fluid mass flow-rate

and the thermal conductivity

Select compatible container materials

Second Step

Find necessary equations

Create mathematical test model

Pick starting data for the dimensions

Run and re-run selections from step 1 to find ideal combination

Third Step

Control and observe the limitations

Re-run the test for different combinations if necessary

Fourth Step

Design the dimensions of the heat pipe

Check the limitations

Re-run the test for different combinations if necessary

Fifth Step

Designing the physical model

Drawings

Before starting the detailed design calculations, possible combinations of fluids, wick structures,

wick materials and container materials should be selected. In order to evaluate the candidates

with the mathematical equations, a few assumptions such as the operating temperature have to

be made which have to be corrected or proven in the later design process.

DIPLOMA THESIS

Carina Buck Page 17 of 90

2.3.2

The Working Fluid

The first consideration in the identification of a working fluid is the operating vapor temperature

range. Within this range, several possible working fluids may exist, and a variety of characteristics

must be examined in order to determine the most suitable one. For a heat pipe to operate, its

wick structure must remain saturated with the liquid phase of a working fluid to allow the fluid to

return from the condenser to the evaporator. The selected fluid for the heat pipe must be in the

liquid state when the external heat source is not applied, which means it needs to have a melting

point temperature below and a critical point temperature above the pipe operation temperature.

It should be compatible with the wick and the wall materials and have a good thermal stability, a

high latent heat of vaporization, a high thermal conductivity, low liquid and vapor viscosities, and

a high surface tension. In addition, the vapor pressure cannot be too high or too low over the

operating temperature range. The vaporization and condensation process of the fluid needs to be

balanced to hinder total vaporization and freezing. The liquid flow rate has to be optimized

because it is the flow-rate that will influence the rate of the heat transfer of the whole system.

The liquid fluid will only vaporize at the rate it enters the evaporator.

2.3.3

The Merit Number

The working fluid can be categorized and evaluated by the Merit Number, which is the liquid

transport factor and is a means of ranking heat pipe fluids. It is a parameter based on working

fluid properties indicating the relative suitability of the fluids for various operating temperatures.

The higher merit number is more desirable, because it means that the fluid can transport more

Watt per square meter which in this application is the main task of the liquid. It can be calculated

with equation 2.1 [2].

M =

(2.1)

M Merit Number [W/m

]

Liquid Density [kg/m

]

Latent Heat of Vaporization [J/kg]

Surface Tension of the Liquid [N/m]

Liquid Viscosity [Pas]

DIPLOMA THESIS

Carina Buck Page 18 of 90

2.3.4

The Materials of the Heat Pipe

A major factor for the selection of the right materials for a heat pipe container and the wick are

the compatibility with the working fluid to avoid chemical reaction such as corrosion, erosion or

gas development and an efficient thermal conductivity. For the container the thickness of the

wall, the tensile strength of the material, the material density and the weight also need to be

considered.

2.3.5

The Wick Structure

The purpose of a wick is to provide the necessary flow passages for the return of the condensed

liquid, to provide the surface pores at the liquid- vapor interface for the development of the

required surface tension and the capillary pumping pressure and to provide the heat- flow path

between the inner wall of the container and the liquid- vapor interface. Generally, an effective

wick structure requires small surface pores for large capillary pressure, large internal pores in the

direction normal to the liquid flow for minimal liquid- flow resistance and an uninterrupted highly

conductive heat flow path across the wick thickness for a small temperature drop. The surface

pore size of the wick is proportional to the mesh number, which is the number of pores per

meter. There are two main wick types, the homogenous wick, which consists of a single material

and the composite wick, which consist of more than one material. The position of the wick

depends on the operating temperatures of the heat pipe (see Figure 2.2). Each wick structure has

its advantages and disadvantages. Every wick structure has its own capillary limit. It is important

to select the proper wick structure based on the application.

Figure 2.2 "Position of the Wick"

If the temperature inside the heat pipe is colder than outside the wick should be located in the

center to assist the vaporization. If the temperature inside the heat pipe is warmer than outside

the wick should be located on the wall to assist the condensation.

DIPLOMA THESIS

Carina Buck Page 19 of 90

2.3.6

The Limitations

There are several limitations to observe. The type of limitations restricting the heat transport

capability of a heat pipe is determined by which limitation has the lowest heat transfer rate value

at the considered temperature. The limitations can be divided into two categories, limitations

which do result in a failure of the heat pipe and limitations which do not. The limitations resulting

in a failure of the heat pipe are all connected to an insufficient liquid flow to the evaporator that

therefore results in the dry-out of the evaporator wick.

2.3.7

The Limitations (Failure)

The Capillary Limitations

The capillary limit is the highest heat transfer rate that can be sustained by the capillary pressure

in a heat pipe wick.

When the capillary pressure differences that develop across the liquid- vapor

interfaces cannot provide a sufficient liquid flow anymore, the evaporator wick will dry out.

To find this limit, the heat pipe dimensions, the wick capillary, the frictional characteristics and

the relevant properties of the fluid need to be known. The capillary limit is usually the primary

maximum heat transfer limitation of a low temperature heat pipe.

The capillary limit can be calculated with equation 2.2 [2].

c, max

Cmax

eff

(QL)

(2.2)

C-max

Capillary Limit (W)

(QL)

c, max

Maximum Heat Transfer Factor [W/m]

eff

The Effective Length of the Heat Pipe

The effective length of the heat pipe can be calculated with equation 2.3 [2]

eff

L = (0.5 L + L + 0.5 L )

(2.3)

End Condenser Length [m]

Adiabatic Length [m]

End Evaporator Length [m]

Details

Seiten
Erscheinungsform: Originalausgabe
Jahr: 2008
ISBN (eBook): 9783836628846
Dateigröße: 1.8 MB
Sprache: Englisch
Institution / Hochschule: Fachhochschule Lübeck – Maschinenbau und Wirtschaftsingenieurwesen, Maschinenbau
Erscheinungsdatum: 2014 (April)
Note: 1,0
Schlagworte: heat pipe wärmerohr thermal control system thermodynamics lunar lander

Autor

Carina Buck (Autor:in)

Design of a Heat Pipe for a Lunar Lander

Zusammenfassung

Leseprobe

Inhaltsverzeichnis

Details

Autor

Carina Buck (Autor:in)