Thermal Design of Lithium Bromide-Water Solution

Home , Absorption refrigerator

THERMAL DESIGN OF LITHIUM BROMIDE-WATER SOLUTION

VAPOR ABSORPTION COOLING SYSTEM FOR

INDIRECT EVAPORATIVE COOLING

FOR IT POD

DIGVIJAY RAMKRISHNA SAWANT

Presented to the Faculty of the Graduate School of

The University of Texas at Arlington in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF SCIENCE IN MECHANICAL ENGINEERING

THE UNIVERSITY OF TEXAS AT ARLINGTON

DECEMBER 2014

ii Acknowledgements

I appreciate to my thesis advisor Dr. Dereje Agonafer, for his worthful guidance and corroborative support throughout my thesis. He has always helped me to make things happen which was slightly difficult for me in academics.

I also want to thank my committee members, Dr. Kent Lawrence and Dr.

Haji Sheikh for being in committee. I would like to thank each and every

EMNSPC member at UTA for being with me and my research work. I thank Ms.

Sally Thompson and Debi Barton for being such a excellent supportive staff.

It gives me immense pleasure to thank my roommates and friends for being supportive to each other during happy and sad moments during our such great journey.

Lastly but not least people who gave me a great support for everything I wanted to do, are my family members. I owe them a lot for being such supportive family. My brother Kamlesh and uncle Anil who is just not a brother and uncle but a best guide and friend. I owe them a lot in my life. Behind my most of the successes they always stood behind me. My mother always used to encourage me to do something new and my father was always behind me as a solid rock. My sister in law was always supported me for good thing. Thank you for being such a great, supportive and encouraging family.

November 24, 2014

iii Abstract

THERMAL DESIGN OF LITHIUM BROMIDE-WATER SOLUTION

VAPOR ABSORPTION COOLING SYSTEM FOR

INDIRECT EVAPORATIVE COOLING

FOR IT POD

Digvijay Sawant, MS

The University of Texas at Arlington, 2014

Supervising Professor: Dereje Agonafer

Nowadays with increase use of Internet, mobile there is increase in heat, which ultimately increases the efficient cooling system of server room or IT POD.

Use of traditional ways of cooling system has ultimately increased CO₂ emission and depletion of CFC’s are serious environmental issues which led scientific people to improve cooling techniques and eliminate use of CFC’s. To reduce dependency on fossil fuels and environmental friendly system needed to be design. For being utilizing low grade energy source such as solar collector and reducing dependency on fossil fuel vapor absorption cooling system has shown a great driving force in today’s refrigeration systems. This LiBr-water absorption cooling consists of five heat exchanger namely: Evaporator, Absorber, Solution

Heat Exchanger, Generator, and Condenser. The thermal design was done for a

iv load of 23 kW and the procedure was described in the thesis. There are 120 servers in the IT POD emitting 196 W of heat each on full load and some of the heat was generated by the computer placed inside the IT POD. A detailed procedure has been discussed. A excel spreadsheet was to prepared with varying tube sizes to see the effect on flows and ultimately overall heat transfer coefficient.

v Table of Contents

Acknowledgements ...... iii

Abstract ...... iv

List of Illustrations ...... viii

List of Tables ...... ix

Chapter 1 Introduction to traditional data center and IT POD (Modular data center) ...... 1

1.1 Comparison of IT POD (Modular data center) and Traditional

data center ...... 3

1.1 First Generation Modular data center ...... 4

1.3 Second generation Modular data center ...... 5

Chapter 2 Basic vapor compression refrigeration cycle ...... 6

2.1 Ammonia absorption refrigeration system ...... 9

2.2 Lithium bromide absorption refrigeration cycle ...... 10

2.3 Objective of the thesis ...... 11

Chapter 3 Equilibrium chart for aqueous bromide solutions ...... 12

Chapter 4 Evaporator ...... 13

4.1 Tube side heat transfer coefficient hi ...... 13

4.1.1 Shah’s Method ...... 14

vi 4.1.2 Kandalikar’s Method ...... 16

4.2 Shell Side heat transfer coefficient ho ...... 16

Chapter 5 Absorber ...... 18

5.1 Absorber Analysis ...... 20

5.2 Shell Side Heat Transfer coefficient ho ...... 20

5.3 Tube Side Heat Transfer coefficient hi ...... 21

Chapter 6 Solution heat Exchanger ...... 22

6.1 Solution heat exchanger Analysis ...... 22

6.2 Tubes side heat transfer coefficient hi ...... 23

6.3 Shell Side heat transfer coefficient ho ...... 24

Chapter 7 Generator ...... 25

7.1 Analysis of Generator ...... 26

Chapter 8 Condenser ...... 27

8.1 Condenser Analysis ...... 27

8.2 Tube side heat transfer coefficient hi ...... 27

8.3 Shell side heat transfer coefficient ho ...... 28

Chapter 9 Conclusion and future work ...... 29

References ...... 32

Biographical Information ...... 34

vii List of Illustrations

Figure 1-1 First Containerized data center by Sun Microsystem ...... 2

Figure 1-2 Modular vs Traditional Data Center deployment cost in US$ ...... 2

Figure 1-3 Comparison of Modular data center and Traditional data center ...... 3

Figure 1-4 Sun Microsystem Containerized data center ...... 5

Figure 2-1 Vapor compression refrigeration system ...... 6

Figure 2-2 Pressure enthalpy chart ...... 7

Figure 2-3 Lithium bromide refrigeration system ...... 10

Figure 3-1 Equilibrium chart for aqueous lithium bromide solution ...... 12

Figure 4-1 Evaporator analysis ...... 13

Figure 5-1 Absorber analysis ...... 18

Figure 5-2 Effect of absorber inlet LiBr percentage ratio ...... 19

Figure 5-3 Effect of solution strength ...... 20

Figure 6-1 Solution heat exchanger analysis ...... 22

Figure 7-1 Effect of generator temperature ...... 25

Figure 7-2 Generator analysis ...... 25

Figure 8-1 Analysis of condenser ...... 27

viii List of Tables

Table 9-1 State points of LiBr-Water absorption cooling system ...... 29

Table 9-2 Values of Heat transfer coefficient(W/m^2 K) ...... 30

Chapter 1

Introduction to traditional data center and IT POD (Modular data center)

Data Center is “IT Equipment” which can execute functions like store, process, manage and interchange alphanumerical data and information either individually or simultaneously, in order to effect communication. Along with the fast progress in the economies, industries, technologies around the world, there is an epitomic development in the information management systems. In today’s world, basic activities like payment of utility bills, shopping, fund transfer, travel booking, etc. happen online. To affect this, IT equipment’s are bound to have high computing abilities, fast networking and large storage capacity[10].

A significant research has been observed in data center facilities, since last few years. This transformation has been observed, changes in backbone breaking and low density traditional data center into mobile, highly flexible IT POD. These IT

POD’s are pre-engineered and built inside factory and shifted onsite. As opposite to traditional data center, these IT POD’s are easy to manufacture with containerized platform, easy to manufacture and easy to deploy. This needs low operating and capital cost with high efficiency and profit.

IT POD’s are easy to manufacture and highly efficient as compared to traditional data center. This avoids high capital cost like acquisition of land and commissioning. These IT POD’s are very low maintenance and are considered highly efficient. Thermal conditions inside IT POD are highly depends upon outside dry bulb temperature, wet bulb temperature, locations and same conditions inside IT POD.

Server emits heat while operating. In present study, there are 120 servers which emits heat of 196 W per server and there is CPU installed in one of the rack.

First IT POD was developed by Sun Microsystems, now taken over by Oracle

Corporation, in June 2007 under the name of “Project Black box”.

Figure 1-1 First Containerized data center by Sun Microsystem [2]

Figure 1-2 Modular vs Traditional Data Center deployment cost in US$[8]

Figure 1-3 Comparison of Modular data center and Traditional data center [8]

1.1 Comparison of IT POD (Modular data center) and Traditional data center

Table 1-1 Comparison of IT POD(Modular data center) and traditional data center [2]

# Factor Traditional data center IT POD

1 Deployment time 1 to 2 years with 6 months or less

design and

commissioning

2 Cost of deploy High with capital cost Much more less than

with installation and traditional data center

commissioning depending upon cooling

capacity

Table 1-1 Continued

3 Installation cost and More complex, time Needs crane to lift

time consuming from trailor and

locate on land

4 Realibility Can’t be predictated Predictable because of pre engineered 5 Tax Due to immobility, Due to mobility taxation is high from one place to

another, so does not count under taxation 6 Serviceability Has more space to Limited access to service people service people

The main difference between containerized data center and IT POD (Modular data center) is that containerized data center are made under ISO standards while IT

POD are designed either a prefabricated data center module or a deployment method for delivering data center infrastructure in a modular, quick and flexible method.[8]

1.1 First Generation Modular data center

First generation containers were simply a container full of IT and relied on additional infrastructure to operate[8]. First Modular data center built by Sun

Microsystem was based on first generation.

Figure 1-4 Sun Microsystem Containerized data center[2]

1.3 Second generation Modular data center

Second generation modular solutions had integrated data center cooling technology and came as a complete data center solution implementing evaporative cooling and outside air efficiency [8].

Second generation modular solution consists of a IT POD and cooling system connected through ducting. Types of cooling used are air economizer, waterside economizer, cooling using phase change material (PCM), direct evaporative cooling system, and indirect evaporative cooling system.

Chapter 2

Basic vapor compression refrigeration cycle

The principle of vapor absorption cooling was first invented by Michael Faraday in 1824. This was invented while performing certain experiments to liquefy particular gases. The first vapor absorption refrigeration system was invented by a French scientist

Ferdinand Carre in 1858. Commercial production was started by Ab Artic in 1923 which was taken over by Electrolux in 1925.

A vapor compression refrigeration system is a air refrigeration system with a working substance called as refrigerant. It condenses and evaporates in condenser and evaporator. The refrigerants used are water, R-22, R-134 and many more. In this system, working fluid does not leave the system but re-circulates throughout the system.

In evaporation, refrigerant absorbs latent heat of vaporization while in condensation, it gives latent heat of condensation to the cooling water in the cooler.

Figure 2-1 Vapor compression refrigeration system[3]

Pressure enthalpy (p-h) chart:-

Figure 2-2 Pressure enthalpy chart[3]

Mechanism of basic vapor compression refrigeration system.

1. Compressor:- The low pressure and temperature vapor refrigerant is drawn from

the evaporator into the compressor. In the compressor, refrigerant compresses to

a high pressure and temperature. This refrigerant at high pressure and

temperature is discharge to the condenser.

2. Condenser:- This high pressure and temperature refrigerant flowing from the

compressor looses it latent heat of condensation to the circulating cooling water.

3. The refrigerant leaves the condenser as a high pressure and low temperature

fluid.

4. Receiver: This high pressure and low temperature refrigerant is stored in the

receiver.

5. Expansion valve:- The function of the expansion valve is to direct high pressure

and temperature refrigerant to evaporator by reduced pressure and temperature.

This valve is also called as a expansion valve or refrigerant control valve.

6. Evaporator:- An evaporator consists of cooling coil through which low pressure

and temperature refrigerant flows. This refrigerant absorbed latent heat of

vaporization from the liquid to be cooled and converts into the low pressure and

temperature vapor. This refrigerant again discharge in to the compressor and

cycle continues.

In any compression system, there are two sides according to the magnitude of pressure. 1) High pressure side which consists of discharge from compressor, condenser, receiver and expansion valve and 2) Low pressure side consists of discharge from the expansion valve, evaporator and suction pipe to the compressor.

Advantages and disadvantages of vapor compression refrigeration cycle over air refrigeration cycle:

Advantages

1. For given capacity, the size of the system is small

2. It has low running cost.

3. It can employed to high capacity.

4. Coefficient of performance is quite high.

Disadvantages

1. High initial cost.

2. High leakage problem.

2.1 Ammonia absorption refrigeration system

Ammonia vapor leaves the evaporator and enters to the absorber where is gets absorbed in water to form weak solution of ammonia-water. This absorption process is the exothermic process, which is inversely proportional to temperature. There for to increase the absorption rate some type of cooling is required. This weak solution is pumped through the regenerator towards the generator.

Figure 2-3 Ammonia absorption refrigeration system[3]

In the generator, solution absorbs the some of heat which passes through the rectifier. In rectifier, ammonia vapor gets separated from water and flows towards the condenser where it rejects its heat of condensation to the cooling medium. Then liquefied ammonia passes to the evaporator through expansion valve.

Hot water from rectifier is passed through the regenerator towards absorber and cycle repeats.

2.2 Lithium bromide absorption refrigeration cycle

In lithium bromide absorption refrigeration cycle, refrigerant is saturated water and absorbent is lithium bromide which is highly hydroscopic salt. Lithium bromide has affinity for the water vapor because of its very low vapor pressure.

Figure 2-3 Lithium bromide refrigeration system[11]

2.3 Objective of the thesis

In the IT pod, the heat load is 23 kW. I was told to do a thermal design the vapor absorption cooling system for the IT POD with different sizes of tubes ranging from OD 9.5 mm to OD 50.3 mm.

Chapter 3

Equilibrium chart for aqueous bromide solutions

Figure 3-1 Equilibrium chart for aqueous lithium bromide solution[1]

Chapter 4

Evaporator

In evaporator thermal design, there is always a concern about boiling curve.

It was assumed that refrigerant is flowing through the tubes and water is flowing inside the shell.

Figure 4-1 Evaporator analysis[11]

Boiling curve is available to study saturated pool boiling. Nukiyama has studied different regimes of the boiling curve by varying current flowing through the platinum wire having larger melting point of 1770 ̊ C. The following curve was obtained.

In present thesis, ∆Tе was assumed between 5 ̊ C and 30 ̊ C.

4.1 Tube side heat transfer coefficient hi

It was assumed that refrigerant was flowing through the tubes and according to the calculations ∆Tе was coming between 5 ̊ C and 30 ̊ C.

There are two methods available to calculate tube side heat transfer coefficient.

1) Shah’s Method[6].

2) Kandilkar’s Method[6].

4.1.1 Shah’s Method

The correlation to calculate two phase heat transfer coefficient by Shah’s experimental data was depends on four dimensionless parameters namely, Froude number Frl, Convention number Co, Boiling number Bo and enhancement factor Fo.

Froude number Frl, was defined by

�� = �^2/(��^2 ∗ � ∗ �ᵢ)

It helps to determine whether stratification effects are present or not. If Frl >0.04 then stratification effects are negligible. But if Frl<0.04 then stratification effects are present. This stratification effects were introduced to determine to calculate convention number.

Convection number is given by

�� = [(1 − �)/�]^0.8 ∗ (��/��)^0.5 ∗ ��.

If Frl > 0.04, KFR = 1. But if Frl < 0.04 then KFR is given by

�� = (25 ∗ ��)^(−0.3)

Boling number Bo, is given by

�� = �” / (ṁ ∗ ℎ��. )

Heat flux, q” was given by Rohsenow Equation

〖�" = (µl ∗ hfg ∗ g)[(ρl − ρv)^ /( Ϭ)]〗^(1/2) (((Cpl ∗ ∆Te )/(Csf ∗ hfg

∗ Prⁿ)@))^3

There are different values are available for Csf and n for different types of fluid-surface. The value of Csf and n for water and polished copper was taken as 0.0130 and 1 respectively[5].

For high vapor quality and low boiling number, the convection boiling number was given as following:-

Fᴄᴃ = 1.8 * Co!!.! ………………………..Co<1.0

And for low vapor quality where Co>1

!.! �ᴄᴃ = 1 + 0.8 e !! !" ]

Boiling enhancement factor Fo was given by

Fo = F(1-x) ……………where F = Fᴄᴃ

The liquid heat transfer coefficient, ℎ��, was calculated from Dittus-Boelter correlation as follows:

ℎ�� = 0.023 ��^0.8 ∗ Pr^0.4 ∗ ��/�

So convection boiling coefficient is given by,

ℎᴄᴃ = �� ∗ ℎ��

Martinelli parameter Xtt was given by

1 � �� !.! �� !.! = �� 1 − � !.! ��

One of the correlation for two phase heat transfer coefficient was given by [6]

!! ℎ�� 1 !! = �1 ∗ �� + �2 ℎ��

Where Wright give values for C1 = 6700, C2 = 3.5*10^-4, C3 = 0.67 and C4 = 1

According to Gungor and Winterton[6] the correlation to calculate two phase heat transfer coefficient was given by

ℎ�� = � ∗ ℎ�� + � ∗ ℎ�

Enhancement factor E was given by

1 !.!" � = 1 + 2.4 ∗ 10!��!.!" + 1.37 ��

Suppression factor S is given by

� = 1 + 1.15 ∗ 10!! ∗ �! ∗ ��!.!" !!

Pool boiling term was given by Cooper,

ℎ� = 55 ∗ Pr ^0.12(log ��)^ − 0.55 ∗ �^0.5 ∗ �”^0.67

4.1.2 Kandalikar’s Method

Kandlikar’s gives the relation to calculate two phase heat transfer coefficient, hTP, for horizontal flow and vertical flow inside the tubes based on Shah’s data.

ℎ�� = �1 �� !! + �3 �� !! ∗ ℎ�� ∗ ��…………Vertical flow

ℎ�� = �1 �� !! ∗ 25 �� !! ∗ ℎ�� + �3 �� !! ∗ 25�� !! ∗ ℎ�� ∗ ��

for horizontal flow.

Ffl for water was taken as 1[6].

Values of constant from D1 to D6 were given depending upon value of convention number Co[6].

4.2 Shell Side heat transfer coefficient ho

Laminar flow:

Nusselt for the shell side laminar flow is Nu = 3.66 = ho*De/ K

The equivalent diameter for square pitch is given by

��ₒ! 4 �� − 4 �� = ��ₒ

For turbulent flow:- 2 ∗ 10! < �� = !"∗!" < 1 ∗ 10! !

For fixed tubesheet

Bundle crossflow area As,

�� ∗ � ∗ � �� = ��

Shell side mass flow velocity of given by

ṁ �� = ��

Shell diameter Ds was given by

! �� ∗ �� ! ∗ �� ! �� = 0.637 ∗ �� ∗ ��

For 90̊ and 45̊ , CL = 1

For 1 tube pass CTP = 0.93

Pitch Ratio, PR, is given by = Pt/do

Number of tubes Nt is given by

�� ! �� = 0.785 ∗ �� !��!

Chapter 5

Absorber

Figure 5-1 Absorber analysis[11]

There are two types of absorber. 1) Horizontal tube falling film absorber 2)

Vertical tube falling film absorber. Horizontal tube falling film absorber was selected.

Because it is easy to manufacture.

In the absorber, saturated water vapor produced in the evaporator flows over the array of horizontal tubes. The strong solution flows from the generator through the solution heat exchanger spread on array of horizontal tubes. The weak solution with water vapor is pumped towards generator through the solution heat exchanger.

Figure 5-2 Effect of absorber inlet LiBr percentage ratio[4]

Absorption process is exothermic. As shell side temperature due to exothermic process between strong solution and water vapor increases, there has to be a cooling needed, to avoid the formation of the salt which blocks the piping and pumps. For that reason, a cooling water at 28 ̊ C is supplied through the array of horizontal tubes.

Figure 5-3 Effect of solution strength[4]

5.1 Absorber Analysis

Mass balances around the absorber

ṁ1 = ṁ10+ ṁ6

Energy balance in the absorber is given by:

Q̊ abs = ṁ10h10- ṁ1h1+ ṁ6h6

5.2 Shell Side Heat Transfer coefficient ho

Paitnaik et al[4] suggested Wilke’s correlation can be used to for constant heat flux wall temperature. It was assumed that flow is fully developed in wavy, laminar regime and that the bulk solution temperature profile is linear with respect to the traverse coordinate

�� ℎ� = 0.029 �� !.!" �� !.!"" ᶑ

The film thickness was given by

! 3Г� ! ᶑ = �!�

Solution Reynolds number for horizontal tube was given by:

Г �� = 4 �

Г = mass flow rate per unit of wetted perimeter = m/πDi

In this study, temperature and the enthalpy were carried out at mean temperature and concentration of LiBr solution from the equations suggested by Florides et. al[4].

5.3 Tube Side Heat Transfer coefficient hi

Nusselt number for the tube side laminar flow is Nu = 3.66 = ho*De/ K

For turbulent flow

Petukhov[5] recommends the equation:

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1.07 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

This is valid for 0.5

For the smaller Reynolds number Gnielinski recommends the following equation;

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

Valid for:- 0.5

All the properties are evaluated at mean temperature Tm

Ti + To �� = 2

Chapter 6

Solution heat Exchanger

Figure 6-1 Solution heat exchanger analysis[11]

Solution heat exchanger is provided to heat the LiBr-water solution flowing from the absorber by the heated strong solution of LiBr coming from Generator. This heat exchanger is employed, so that in the generator the temperature required to evaporate the water vapor will be less. So we can employ low temperature heat source in the generator. Here design in done by keeping in mind a of using shell and tube heat exchanger with fixed tube-sheet.

6.1 Solution heat exchanger Analysis

Q ̊shx = ṁ4h4 = ṁ2h2 = U ∗ Ashx ∗ LMTD

�4 − �3 − �6 − �2 �� = �4 − �3 �� 6 − �2

6.2 Tubes side heat transfer coefficient hi

In this study, weak LiBr-water solution from Absorber flows through the tubes and the strong solution LiBr from generator flows through shell.

All the LiBr-water solution properties are evaluated according to expressions proposed by Florides, G.A[4]

It was observed that for tube ID less than 8.1 mm the flow is turbulent flow and of tube ID>12.5 mm the flow is laminar flow.

It was assumed that the flow is Fully developed flow. So for Laminar, fully developed flow with constant surface temperature, Nusselt number is given by

�� = 3.66

For turbulent flow with constant heat flux , Nusselt number is given by

For turbulent flow Petukhov recommends the equation:

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1.07 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

This is valid for 0.5

For the smaller Reynolds number Gnielinski recommends the following equation;

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

Valid for:- 0.5

All the properties are evaluated at mean temperature Tm

Ti + To �� = 2

6.3 Shell Side heat transfer coefficient ho

For shell side it was observed that the flow is Laminar for all tube sizes.

�� = (ℎ� ∗ ��)/� = 3.66

�� = 0.637 ∗ ��(��/��) ∗ ((�� ∗ (��)^2 ∗ ��)/�)^(1/2)

For 90̊ and 45̊ , CL = 1

For 1 tube pass CTP = 0.93

Pitch Ratio, PR, is given by = Pt/do

Tube pitch, Pt = 1.25 do

Number of tubes Nt is given by

�� = 0.785 ∗ (��/��)((��^2)/(��^2 ��^2 ))

� = 1/((��/��) ∗ (1/ℎ�) + (1/2�) ∗ �� ∗ ��(��/��) + (1/ℎ�)

+ (��/��) ∗ �� + ��)

Chapter 7

Generator

Generator is used to evaporate the water from the weak solution of LiBr-water flowing from absorber through solution heat exchanger in the absorber.

Figure 7-1 Effect of generator temperature[4]

Florides et al[4] suggested the a graph of Generator exit temperature vs generator pressure. If the pressure inside the is kept low and the exit temperature is kept in the range 65̊ C to 80̊ C then COP of the system is around 0.8.

Figure 7-2 Generator analysis[11]

Over here, we can use a low temperature heat source such as water heater or water, which was heated by solar collector, flowing through water tube.

7.1 Analysis of Generator

Q ̊gen = ṁ4ℎ4 + ṁ7ℎ7 − ṁ3ℎ3 − ṁ3(ℎ4 − ℎ1)

Heat flux, q”, required to evaporate water vapor from the weak solution of LiBr- water was given by Rohsenow Equation[7]

〖�" = (µl ∗ hfg ∗ g)[(ρl − ρv)^ /( Ϭ)]〗^(1/2) (((Cpl ∗ ∆Te )/(Csf ∗ hfg

∗ Prⁿ)@))^3

∆Te = Ts − Tsat

Chapter 8

Condenser

In condenser, the superheated steam flowing from the generator is directed onto array of horizontal tubes. The un-evaporated water refrigerant flows from the evaporator flows on the same array of horizontal tubes.

Figure 8-1 Analysis of condenser[11]

8.1 Condenser Analysis

Q ̊cond = ṁ7(ℎ7 − ℎ8) = ṁ15(ℎ15 − ℎ16) = U ∗ A ∗ LMTD

�� = (�16 − �15)/ln ((�8 − �15)/(�8 − �16))

8.2 Tube side heat transfer coefficient hi

Cooling water flowing through horizontal tubes at 27 ̊ C. For constant heat flux, for single phase laminar flow, the Nusselt number can be approximated by expression:

��ᴅ = 4.36

For turbulent flow Petukhov recommends the equation:

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1.07 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

This is valid for 0.5

For the smaller Reynolds number Gnielinski recommends the following equation;

��ᴅ = ((�/8) ∗ ��ᴅ ∗ ��)/(1 + 12.7(�/8)^(1/8)(Pr ^(2/3) − 1))

Valid for:- 0.5

All the properties are evaluated at mean temperature Tm

�� = ( Ti + To)/2

8.3 Shell side heat transfer coefficient ho

Condensation on horizontal tube is given by Nusselt theory as

ℎ� = (��/��) ∗ 0.728 ∗ [(��(�� − ��) ∗ ℎ�� ∗ � ∗ ��^3)/(�� (�� − ��)

∗ ��)]^(1/4)

�� = 0.637 ∗ ��(��/��) ∗ ((�� ∗ (��)^2 ∗ ��)/�)^(1/2)

For 90̊ and 45̊ , CL = 1

For 1 tube pass CTP = 0.93

Pitch Ratio, PR, is given by = Pt/do

Tube pitch, Pt = 1.25 do

Number of tubes Nt is given by

�� = 0.785 ∗ (��/��)((��^2)/(��^2 ��^2 ))

� = 1/((��/��) ∗ (1/ℎ�) + (1/2�) ∗ �� ∗ ��(��/��) + (1/ℎ�)

+ (��/��) ∗ �� + ��)

Chapter 9

Conclusion and future work

Table 9-1 State points of LiBr-Water absorption cooling system

Point ṁ (kg/s) P (kPa) T(̊ C) % Remark LiBr 1 0.12 0.87 34.58 55 Weak solution+water

2 0.12 0.87 34.58 55 Weak solution+water

3 0.12 0.87 73.34 55 Weak solution+water

4 0.11 7 83.97 60 Strong solution

6 0.11 0.6 39.58 60 Strong solution

7 9.81E-3 7 73.34 Superheated steam

8 9.81E-3 7 39.03 Saturated Water

9 9.81E-3 7 3.675 Saturated Water

10 9.81E-3 0.87 3.675 Saturated Vapor

11,12 Water Heater

13 0.561 4.4 28 Water

14 0.561 4.4 33 Water

15 3.87 3.564 27 Water

16 3.87 3.564 28.5 Water

17 1.1 1.198 12 Water

18 1.1 1.198 7 Water

Conclusion

Table 9-2 Values of Heat transfer coefficient(W/m^2 K)

Equipment According G.A Soteries et al Anil Sharma

to thesis Florides et (1kW)(7) et al (1 kW)

(23kW) al(1kW)(4) (9)

Evaporater 1110 195 195 2077.68

Absorber 406 400 650 975

Solution 88.6 NA NA NA

Heat

exchanger

Condenser 3480 3265 2980 2467

Values in above table for this thesis work has been given for Cooper Tube of

OD 9.5mm X ID 8.1 mm. From the above table it is observed that the overall heat transfer coefficient for condenser and absorber is in the range of the required. In case of evaporator and solution heat exchanger, the refrigerant is flowing through the number of tubes. So flow is laminar flow. In case of G.A Florides et al, Soteries et al and Anil

Sharma et al. the flow is flowing through a single tube of size OD 9.5 mm x ID 8.1 mm.

So the mass flow rate is not divided, which in divided in this thesis work.

Future Work

In the present study, I have designed a water cooled condenser. In future, cooling can be provided by air. So design of the condenser can be done by assuming air cooling. CFD analysis can be carried out to modeling the system in solid works and running CFD in ANSYS fluent.

References

1. ASHRAE Fundamentals handbook, 2005 and 2009

2. Aurangabadkar, K. A. (2012, November 1). Impact of Louver orientation on air

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Biographical Information

Digvijay Sawant has received his Bachelor’s Degree in Mechanical Engineering from University of Pune, Ganeshkhind Road, Pune, India in June 2009. He completed his Master of Science in Mechanical Engineering at University of Texas at Arlington in

December 2014.

Digvijay has work experience of 1 year 6 months at Alfa Laval I Ltd. He has worked as a Graduate Engineer Trainee (GET) and Company Trainee Engineer in

Planning and scheduling department of Process equipment manufacturing. He is familiar American Society of Mechanical Engineers (ASME) ASME Section VIII,

Divisions 1 and 2 codes, Boiler and Pressure Vessel Design code and Tubular

Exchanger Manufacturing Association (TEMA).

Digvijay has been involved in number of projects such as perform heat emission server test on HP SE1102 server using Prime95 software, modeling and

CFD(Computational Fluid Dynamics) analysis of IT-POD with server racks at different locations to analyze thermal management inside POD funded by NSF (National Science

Foundation) and I/UCRC (Industry/University Co-Operative Research Center) using

Flovent software, modeling and analysis of ASC-15 Direct/Indirect Evaporative Cooling

System with Mestex, division of Mestek Inc. Dallas, Texas and experimental testing of

OxyVap Cooling Pad from Oxycom for direct evaporative cooling.

Digvijay is also a member of ASHRAE.