Basic Construction Of A Typical Pem Fuel Cell Engineering Essay

Research tendency presents are more on the alternate beginning of energy. The aim of the research is to develop a nature friendly and portable beginning of energy. One of the illustrations of the beginning is Polymer Electrolyte Membrane ( PEM ) fuel cell. Fuel cells are devices that produce electricity through electrochemical reactions. The basic buildings of a PEMFC are shown in Figure 1-1 schematically. The fuel is hydrogen gas and ambient air or pure O is the oxidizer. This reaction merely produces heat and H2O. Sing their high energy transition efficiency, zero emanation potency, low noise and possible usage of renewable fuels, fuel cells are considered as future devices for Mobile, stationary, and portable power applications. However, PEMFC systems are non presently cost effectual ; so there are legion survey related to PEM fuel cell runing conditions to better the efficiency of the cell so it can be commercialize.

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Figure 1-1: Basic building of a typical PEM fuel cell [ 2 ] .

The complex procedure of PEMFC operation can be described as the conveyance of mass, impulse, energy, species and charges that take topographic point at the same time. Fuel cells are still undergoing intense development, and the combination of new and optimized stuffs, improved merchandise development, fresh architectures, more efficient conveyance procedures, and design optimisation and integrating are expected to take to major additions in public presentation, efficiency, dependability, manufacturability and cost-effectiveness.

1.1 Influence of Temperature on Fuel Cell Performance and chilling methods

A simple manner to better the public presentation of a fuel cell is to run the system at its upper limit allowed temperature. At higher temperature, electrochemical activities addition and reaction takes topographic point at a higher rate, which in bend increases the efficiency. On the other manus, runing temperature affects the maximal theoretical electromotive force at which a fuel cell can run. Higher temperature corresponds to take down theoretical maximal electromotive force and lower theoretical efficiency [ 2 ] .

Temperature in the cell besides influences cell humidness and besides membrane ionic conduction. Therefore, temperature has an indirect influence on the cell end product power through its impact on the membrane H2O content. When a PEMFC operates at low force per unit area the maximal operating temperature should be less than 100A°C.

As a consequence, the operating temperature is selected by sing the lastingness of the membrane electrolyte and the safety border for thermic transeunt response of the fuel cell. The chief intent of thermic direction in fuel cell systems is to guarantee the stack operation within a dependable temperature scope and to supply a more unvarying temperature distribution in the stack. A elaborate apprehension of the stack thermic behavior is hence necessary for design and development of an efficient chilling solution. Research done by Oosterkamp [ 3 ] shows some of the heat transportation issues for both PEM based systems. To analyse the effectivity of different thermic direction schemes, developing a thermic theoretical account is indispensable.

Problem statement

A legion survey of design and fiction were conducted and their nonsubjective chiefly focused on the efficiency of the system, the on the job conditions and many more. It is of import to come out with an thought of how to find the temperature of an air-cooled PEM fuel stack so that the method can be used in design consideration and system efficiency survey.

In position of the expected troubles that would be encountered in the experimental finding of the inside informations of temperature distribution, the usage of the numerical simulation provides a extremely attractive rating tool. Therefore, the Commercial CFD Code Fluent will be used for the intent.

Aims

The chief aim is to analyze thermic public presentation of an air-cooled PEM fuel cell tonss. The focal point is on air-cooled PEMFCs. Air-cooled fuel cell systems combines the chilling map with the cathode flow field and therefore eliminates many of the subsidiary systems required for conventional fuel cell designs and by this average lowers the overall cost. Other nonsubjective is to suggest chilling channel design for air-cooled PEMFC.

Significant of survey

The significance of this survey is:

a ) Using Commercial ANSYS Code Fluent, the simulations are able to supply extremely accurate consequences for PEM fuel-cell stack temperature. The outlook is that this numerical attack will lend to a better rational design of PEM fuel-cell in the hereafter.

B ) It is besides the purpose that the consequences from the current work will better the thermic public presentation of PEM fuel-cell, therefore increase the quality of design.

Scope of survey

a ) This survey focused on bipolar home base for polymer electrolyte membrane fuel cell ( PEMFC ) with dimension of 136mm X 242.5mm X 4.82mm and with consecutive constellation of chilling channel with different facet ratio.

B ) The general purpose of this survey is to place which chilling channel design will chill effectivity for PEM fuel cell.

degree Celsius ) In order to accomplish the high heat transportation rate, several design of chilling channel will be simulated utilizing ANSYS Fluent. The simulation on the bipolar home base theoretical account will be conducted in simple 3D steady province analysis affecting heat transportation and fluid flow with conductivity and convection utilizing laminal flow theoretical account.

vitamin D ) This survey will affect in temperature at recess and mercantile establishment and besides the inside part of the chilling channel, and the surface temperature of the bipolar home base. This survey will sing the changeless heat flux generated.

vitamin E ) The simulation does non take into history the electrochemical reactions and attendant heat effects at the membrane bed.

Chapter II

LITERATURE REVIEW

2.0 Introduction

This chapter focuses on the old survey done by a few researches. Some related old researches were reviewed to understand what already have been done. The thought was to see how the old survey had been developed in term of methodological analysis and consequence.

2.1 Operation of PEMFC

The basic rules of operation of the fuel cell is similar to that of the electrolyser in that the fuel cell is constructed with two electrodes with a conducted electrolyte between them.

The bosom of the cell is the proton carry oning solid PEM. It is surrounded by two beds, diffusion and a reaction bed. Under changeless supply of H and oxygen the H diffuses through the anode and the diffusion layer up to the Pt accelerator, the reaction bed. The ground for the diffusion current is the inclination of H O reaction.

Two chief electrochemical reactions occur in the fuel cell. One at the anode ( anodal reaction ) and the other at the cathode.

At the anode, the reaction releases hydrogen ions and negatrons whose conveyance is important to energy production.

H2a†’2H+ + 2e-

The H ion on its manner to the cathode passes through the polymer membrane while the lone possible manner for the negatrons is through an outer circuit. The H ion together with the negatrons of the outer electric circuit and the O which has diffused through the porous cathode reacts to H2O.

2H+ + A? O2 + 2e- a†’H2O

The H2O ensuing from this reaction is extracted from the system by the extra air flow. The reaction is:

H + A? O2 a†’H2O

This procedure occurs in all types of fuel cells.

2.1.1 Partss of a Fuel Cell

Polymer electrolyte membrane ( PEM ) fuel cells are are made from several beds of different stuffs, as shown in the Figure 2.1.1. The three key beds in a PEM fuel cell include:

Membrane electrode assembly

Catalyst

Bipolar home base

Other beds of stuffs are designed to assist pull fuel and air into the cell and to carry on electrical current through the cell.

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Figure 2.1.1: Partss of PEM fuel cell

Membrane Electrode Assembly

The electrodes ( anode and cathode ) , accelerator, and polymer electrolyte membrane together form the membrane electrode assembly ( MEA ) of a PEM fuel cell.

Anode.

The anode is the negative side that operate the negatrons that are released from the H molecules. Channelss etched into the anode spread the H gas every bit over the surface of the accelerator.

Cathode.

The cathode is the positive side of the fuel cell. It besides contains channels that distribute the O to the surface of the accelerator. It conducts the negatrons back from the external circuit to the accelerator, where they can recombine with the H ions and O to organize H2O.

Polymer Electrolyte Membrane

The polymer electrolyte membrane ( PEM ) is a specially treated stuff that conducts merely positively charged ions and blocks the negatrons.

Catalyst

It is normally made of Pt pulverization really thinly coated onto C paper or fabric. The accelerator is unsmooth and porous so the maximal surface country of the Pt can be exposed to the H or O. The platinum-coated side of the accelerator faces the PEM.

Bipolar home base

The bipolar home bases are made of a extremely conductive stuff such as C, black lead or conductive metals and are responsible for:

aˆ? Collecting and transporting negatrons from the cell to an external electrical circuit.

aˆ? Transporting portion of the merchandise heat to the environment and to the chilling subdivision of a stack.

2.2 Stack Cooling Methods

There are different chilling methods that can be used in fuel cell systems to keep a changeless temperature. These include heat spreaders, chilling with cathode air flow, chilling with separate air flow, H2O chilling, and chilling with antifreeze/coolant [ 2 ] .

2.2.1 Passive Methods

Passive chilling refers to plan characteristics used for chilling without power ingestion.

Heat spreaders

Installing heat spreaders with high thermic conduction in a PEMFC stack is one of illustrations of inactive chilling method. By utilizing heat spreaders, heat can be transferred more expeditiously outside the stack. Heat spreaders can be used to transport heat out of the stack through conductivity, so to disperse the heat to environing air through natural or forced convection.

Figure 2.2.1.1: Heat Spreader [ 2 ]

Heat pipes

A heat pipe is one of the inactive heat transportation device that combines the rules of thermic conduction and stage alteration and has an highly high effectual thermic conduction. Faghri and Guo [ 4 ] studied recent applications of heat pipe engineering in fuel cell systems, which include new stack designs with heat pipes to better heat transportation every bit good as work on fuel cell system degree design. In their survey, in one design, a bipolar home base was designed with holes, into which micro-heat pipes were inserted and bonded.

Figure 2.2.1.2: Heat Pipe [ 4 ]

Natural chilling with cathode air flow

For a little fuel cell, the cathode air flow can work in one of two manners: natural convection or forced convection. Natural convection is the simplest manner to chill the cell and evaporate H2O at the cathode. This is done with a reasonably unfastened construction at the cathode sides, which will increase the volume of the stack. For little PEM fuel cells ( less 10 than 100W ) , natural convection from air external respiration can be sufficient to keep the cell temperature.

2.2.2 Active Methods

Forced chilling with cathode air flow

Forced convection is one of the chilling methods that use to take unwanted heat out of the stack. This will ensue in a more compact stack construction and increase the chilling capableness. However, really high cathode air flow speed or a really big gas channel is necessary for remotion of waste heat. When the power of the fuel cell is high, a more effectual chilling attack must be applied.

Since the specific heat of air is low, high air flow rate is needed to take the generated heat. Temperature distribution within the stack could be more unvarying and the heat remotion would be more efficient by utilizing H2O chilling method ; nevertheless, this method needs more accoutrements and complicated control strategies.

The chief applications of the air-cooled fuel cell is in portable and backup power coevals, where fuel cell solutions have many advantages over conventional lead-acid batteries and Diesel generators, including extended runtime, high dependability, high efficiency, and decreased environmental impact.

Cooling with separate air flow

Increasing reactant air flow can take more heat, but excessively much reactant air may dry out the proton exchange membrane [ 1 ] . Generally, in those instances fuel cells need a separate reactant air supply and chilling system.

Water chilling

For H PEMFCs larger than 10 kilowatt, it is by and large necessary to utilize H2O chilling. Unit of measurements below 2 kilowatts can be air cooled, and cells between 2 kilowatts and 10 kilowatts need a careful pick sing whether air or H2O chilling should be used [ 5 ] . Water chilling requires a more complex design: the temperature and force per unit area of the chilling H2O must be monitored and the flow of chilling H2O must be supplied by a H2O pump. The H2O chilling of PEMFCs gives rise to jobs associated with H2O direction such as forestalling the merchandise H2O from stop deading, and quickly runing any frozen H2O during start-up when the fuel cell system is operated in sub-freezing conditions. In such state of affairss, an antifreeze/ coolant is used alternatively of normal H2O in the chilling system.

2.3 Thermal Management

Thermal direction in PEM fuel cell is really important as the stack demand to be maintained as the individual cell temperature must be unvarying with the other individual cell. Furthermore the PEMFC operates at optimal temperature scope 60 to 80 A°C [ 10 ] . As when the cells exceed 80A°C, thermic harm of the membrane may happen. Thus, a mean of efficient chilling system demand to be used to let the PEM fuel cell to remain at the coveted temperature scope.

Sangseok Yu and Dohoy Jung [ 6 ] wrote a paper sing on the thermic direction scheme for PEMFC system with a big active cell country discoursing the importance of thermic direction of PEM. The authors stated that the fuel cell temperatures need to be maintained at proper runing temperature. A decision made from their survey were the maximal temperature of the fuel cell was suggested as the representative operating temperature, the fuel cell runing temperature can be efficaciously controlled by seting chilling far operation, and eventually the mention value of the operating temperature is system dependent and should be determined by sing membrane lastingness and system safety border.

Yong Hun Park and Jerald A.Caton [ 7 ] conducted an experiment on several chilling method and the consequence of chilling in the stack. The consequence of the simulation shows that the chilling method should be used to keep the inside temperature inside, public presentation and lifetime of the fuel cells. The research worker added that a chilling method adds the complexness to the system and therefore, a simple chilling method are used.

.

Chapter III

Methodology

3.0 Introduction

CFD can be described as the usage of computing machines to bring forth information about the ways in which fluids flow in given state of affairss. It is the analysis of systems affecting fluid flow, heat transportation and associated phenomena such as chemical reactions by agencies of computer-based simulation ( Versteeg 1995 ) . The range of this undertaking is based on the CFD simulation. There are a few stairss need to be follow as the consequences are important in order to accomplish the aims of this undertaking.

3.1 Flow Chart

The flow chart trades with the readying of experimental plants to be carry out for this analysis. The experiment apparatus, parametric quantities designation and experiments and informations analysis is explained in this flow chart. The experimental plants as stated in specific criterion referred is besides explained and discussed. Figure 3.1 nowadays the flow chart of experimental plants to be carry out in this probe.

Literature Review

Preliminary Solid Modeling

Datas Roll uping

Simulation

Decision

Consequence

Fail

Passed

Design 1

Design 2

Chart 3.1: Flow chart

3.2 Computational Fluid Dynamics ( CFD ) methodological analysis

CFD is one of the methods of analysis. It is the usage of computing machine to work out and analyze job that involve fluid flows. The basic methodological analysis of CFD is express by the FIGURE 3.2.1 below.

Figure 3.2.1: CFD methodological analysis

Import Geometry

Define Boundary Condition

Generate Mesh

Initialize Solution

Run Solver

Consequence

Figure 3.2.2: Pre-processing Flow Chart

3.2.1 Pre-processing

3D modeling

There are many computing machine aided design package available to be used to plan the theoretical account. For the survey, patterning package CATIA is used to develop the 3D theoretical account for the bipolar home base. The geometry of the theoretical account is taken from the instance survey. Below is the theoretical account done by utilizing CATIA. Besides the item drawing will be included to give better position of the theoretical account.

Cooling channel

Figure 3.2.1.1: Isometric View of 20 channels home base

Cooling channel

Figure 3.2.1.2: Isometric View of 40 channels home base

3.2.2 Procedure

3.2.2.1 Engaging

A mesh of points has to be produced within the volume of the fluid to supply discretization of the infinite in which the flow takes topographic point ( Shaw 1992 ) . When the finite volume method is used, as with Fluent, the points are arranged so that they can be grouped into a set of volumes and the PDEs can be solved by comparing assorted flux footings through the faces of the volumes.

Table 3.2.2.1 shows the parametric quantities such as the size of the mesh that need to be adjusted to acquire the most acceptable mesh for the simulation. The quality of the mesh plays a important function in the truth and stableness of the numerical calculation. Regardless of the type of mesh used in the sphere, look intoing the quality of mesh is indispensable. One of import index of mesh quality that ANSYS FLUENT allows you to look into is a measure referred to as the extraneous quality ( Table 3.2.2.2 ) . Extraneous Quality ranges from 0 to 1, where values near to 0 correspond to low quality. Other quality aspect that needs to be considered in FLUENT is skewness value ( Table 3.2.2.2 ) . The maximal values that lower than 0.9 is somehow can be said hold a good quality of mesh.

Table 3.2.2.1: Settings on ANSYS Mesh

Table 3.2.2.2: Mesh Statistic and Orthogonal Quality

Table 3.2.2.3: Lopsidedness Parameters

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Figure 3.2.2.1: Close View on Bipolar Plate engagement

3.2.2.1.1 Grid Independence Test

It was of import to set up that the consequences of the simulations were mostly independent of the size of the grid. It would be highly time-consuming to transport out grid independency trials for each instance studied. In the grid independency trials, the initial grid was refined by about duplicating the figure of elements. The values for force per unit area, air speed and temperature were checked. This process was carried out until the same tendencies were observed on analyzing graphical consequences. In add-on it was ensured that the consequences between the concluding grids were meeting to a sensible grade.

The undermentioned tabular arraies present a sum-up of the consequences. In all instances presented, refined grid-2 was chosen as sufficiently grid independent. ANSYS Fluent that presently used can non manage mesh more than 500000 cells because the licence available is for non-commercialize usage.

Table 3.2.2.1.1: Grid Independence Test for Bipolar Plate

Initial Grid

Refined grid-1

Refined grid-2

Entire no. of cells

187969

327615

478482

Average Temperature ( A° C )

154.84

151.1

129.3

3.3 Simulation

The theoretical account was imported to ANSYS work bench from CATIA by IGS format. Channels for chilling were being imprinted with another organic structure to enable the channel to be assign with boundary status. After engaging procedure is complete the simulation of FLUENT can be started. First, the energy equation and Laminar in flow theoretical account is enabled. Further accounts of the theoretical accounts will be discussed in the following chapter. Figure 3.3.1 and 3.3.2 give the position of the equation theoretical account of the simulation.

Figure 3.3.1: Energy Equation Model

Figure 3.3.2: Flow Equation Model

The boundary status was assigned to the solid sphere which is the bipolar home base and the fluid which is the chilling air.

After that the theoretical accounts proceed with convergent thinker processing. The halting standard is 1000 loops. The loop was set to 1000 because there were no alterations in the surface temperature such as in the figure 3.3.3 below. The residuary secret plan of energy and continuity converged and remain changeless such in figure 3.3.4.

Figure 3.3.3: Surface Temperature Monitor Graph

Figure 3.3.4: Residual Plots of Continuity and Energy Equation

The consequence obtained from the convergent thinker station processing. The het surface temperature, air temperature, and heat transportation rate were observed and roll up. Further treatment on abstracting informations from the station processor will be discuss in chapter 5.

The simulation was done with the remainder of the design with same boundary status. The consequence was analysed to happen the consequence of the designs to the surface temperature of the bipolar home base, chiefly by find the chilling effectivity.

Chapter IV

GEOMETRY DESIGN AND SIMULATION CONDITION

4.0 Introduction

In this chapter, both the 20 channels design and 40 channels design for chilling channel geometry of the individual bipolar home base which simulated utilizing ANSYS-Fluent was discussed in item. The boundary conditions were besides stated in this chapter. The boundary conditions that were used in simulation are stated.

4.1 Air Cooling Channel Design

For this survey, two geometry designs were constructed in. The thought of the design was to increase the air flow speed enter the recess channel. By increasing the speed, the sum of heat transportation will be increased due to increase in Reynolds figure, therefore addition in Nusselt figure. The standard dimension of bipolar home base is 136mm ten 242.5mm ten 4.82mm are show in the figure 4.1.

In this survey the air channel will be maintained at 136mm in length and 2mm in tallness for both channel design. The lone difference between the designs is the aspect ratio. The elaborate drawing can be referred in Appendix A.

Table 4.1: Table of Channel Specifications

Width, millimeter

Height, millimeter

Length, millimeter

Gap between channels

Aspect ratio

No. of channels

20 Channelss

7.90

2.00

136

1.00

0.07

20

40 Channelss

3.45

2.00

136

1.00

0.025

40

4.1.1 Bipolar Plate Geometry Design

4.1.1.1 20 Channelss Design

For the 20 channels design the dimension of the recess geometry is 7.90mm breadth and 2mm tallness. The channel length from recess to outlet is 136mm. The inlet subdivision of this design is merely a consecutive rectangular form ( calculate 4.2 ) . The item drawing can be referred in Appendix A.

Figure 4.2: 20 channels Bipolar Plate

Figure 4.3: Dimension of Bipolar home base 20 Channels in millimeter

4.1.1.2 40 Channelss Design

For the standard air chilling impart the dimension of the recess geometry for every channel is 3.45mm breadth and 2mm tallness and 1mm distance from the following channel. The channel length from recess to outlet is 136mm. The entire Numberss of air channels are 40 channels. The inlet subdivision of this design is merely a consecutive rectangular form ( calculate 4.4 ) . The item drawing can be referred in Appendix A.

Figure 4.4: 40 Channels Bipolar Plate

Figure 4.5: Dimension of Bipolar home base 40 channels Channel in millimeter

4.2 Boundary Conditionss

All the design was simulated with same boundary status. In this survey there are two types of boundary status. First is air boundary status, and another one is bipolar home base boundary status.

4.2.1 Air Boundary Conditionss

The simulation was conducted for five values of air speed which is taken from assorted Reynolds figure and the illustration of computation for the speed will be discuss in the following subject

.

The temperature of the air come ining the chilling channel was set to 30 grade Celsius based on the mean ambient local temperature.

The force per unit area of air was set to 1 standard pressure, where the value is obtained for 30 degree Celsius ambient temperature at sea degree height. The value was taken from Table A-9 ( see Appendix A ) . The force per unit area at mercantile establishment is set to zero and the procedure will presume it is changeless force per unit area.

4.2.2 Bipolar Plate Boundary Conditionss

The value of denseness 2240 kg/m3, specific heat 710 J/kg.K and the thermic conduction 20 W/m.K was based on the material type of bipolar home base. The bipolar home base is made from the C black lead.

The wall or heated surface heat flux value is 1025.6 W/m2. The wall heat flux is defined as the rate of the heat transportation per unit country from the wall to the fluid. This value of heat flux will discourse at the subdivision 4.3.

The values of the boundary conditions are summarized in the tabular array below ;

Table 4.1: Boundary Condition Valuess

Boundary Condition

Value

Air

Inlet Velocity, Vin

Temperature, Tinitial

30A° C

Pressure, Pair

1 standard pressure

Bipolar Plate

Material type

Carbon Graphite

Density, I?

2240 kg/m3

Thermal Conductivity, K

20 W/m.K

Specific Heat, Cp

710 J/kg.K

Heat Flux, Q

1025.6 W/m2

4.3 Assumption Calculation

4.3.1 Heat Flux Calculation

The information for heat generated in a fuel cell operation is based on [ xx ] which is an experimental-based information on a similar fuel cell home base design. For the simulation purpose the value of entire heat generated is 32 Watt at burden 20A and 55 % efficiency.

Area of Bipolar Plate ;

From the new heat transportation rate and bipolar home base are, calculate the rate of heat transportation per unit country or heat flux for het surface,

So approximated the heat flux value is 1025.6 W/m2.

4.3.2 Laminar Flow Calculation

For this survey, the air flow assumed as laminar flow. The ground was air behaves as ideal gas and since the characteristic Reynolds Number in the air channels are low which is below the scope of turbulent flow for internal flow instance. For the internal flow the scope of Reynolds figure indicated as Re & lt ; 2300 for laminar flow, 2300 & lt ; Re & lt ; 4000 for transient flow and Re & gt ; 4000 for turbulent flow.

These values were proven from the computation below ;

Reynolds figure ;

Where V = Air flow speed, D = features length of the geometry, and I? = kinematic viscousness of the fluid.

For flow through rectangular channels, the Reynolds Number is based on the hydraulic diameter Dh defined as

For 20 channel design ;

For 40 channels design ;

The value of I? = 1.789 x 10-5 was taken from Table A-9 ( see Appendix A ) . The value of speed is take from the maximal value of speed that fan provided for this simulation.

From the computation above, the Reynolds figure is 200 are low than 2300. So the speed satisfied and proven as laminar flow. Second premise is assumed the surface of the bipolar home base was level by non sing the channel at the top and underside of the bipolar home base. Third premise is considered the air blowing into the chilling channel is in one way which is perpendicular to the recess of the chilling channel.

Chapter V

RESULT AND DISCUSSION

5.0 Introduction

In this chapter, consequences such as temperature and heat transportation rate from the simulations of the PEM fuel cell bipolar home base was obtained in order to analyze the important of the design. Then the consequences were compared with the standard design. For the analysis, the focal point is on the alterations in temperature from the recess distance of the recess geometry.

5.1 Consequence

From the simulation, the air temperature and heat transportation rate at every design were taken. The value of temperatures was taken from five different Reynolds figure which are 200, 400, 600, 800 and 1000. The heat transportation rate was obtained from the heat transportation of the overall distance. Form the information the chilling effectivity of the bipolar home base can be calculated. All the informations were tabulated and presentable in graph.

The consequence of simulation can be viewed in the tabular arraies at the Appendix B. Below is illustration figure of bipolar home base temperature distribution consequence from simulation on speed 2.2 m/s or Reynolds figure 400. For the full bipolar home base temperature distribution consequence of all simulations please mention to Appendix.

Table 5.1: Bipolar Plate Temperature Contour

Rhenium

20 Channelss

Cooling Rate

40 Channelss

Cooling Rate

Re-200

967.7

666.6

Re-400

956.7

668.7

Re-600

951.4

672.8

Re-800

947.9

673.8

Re-1000

945.4

677.6

Note: Effective internal convection chilling rate obtained in simulation is taken at air-solid boundary.

5.2 Calculation

5.2.1 Heat Transfer Rate Analytical Validation

CpairI”T

Cpair ( Toutlet – Tinlet )

5.2.1.1 Example Calculation for 20 Channelss design

For illustration computation, information is taken from simulation on 20 channels design at air speed 1.12 m/s.

= 0.002 kg/s

Cpair = 1007 J / kg.K

Toutlet = 54.64 A° C

Tinlet = 30 A° C

= 0.002 ten 1007 x ( 54.64 – 30 )

= 49.62 Watt

5.2.1.2 Example Calculation for 40 Channelss Design

For illustration computation, information is taken from simulation on 40 channels design at air speed 1.41 m/s.

= 0.002 kg/s

Cpair = 1007 J / kg.K

Toutlet = 61.90 A° C

Tinlet = 30 A° C

= 0.002 ten 1007 x ( 50.35 – 30 )

= 41 Watt

5.2.2 Percentage Mistake

Percentage mistake between simulation consequence and analytical computation.

5.2.2.1 Example Calculation for 20 Channelss Design

The heat transportation rate value is taken from simulation file and from analytical computation informations on 20 channels design at speed 1.12 m/s as shown in Figure 5.2.2.1.1.

Figure 5.2.2.1.1: Entire Heat Transportation from Fake Files

5.2.3 Cooling Effectiveness ( a?? )

5.2.3.1 Example Calculation of Cooling Effectiveness

Heat transportation rate of het surface is same for every simulation which is 32 Watt. This is because the heat flux that set in the simulation is changeless for every simulation file. For illustration computation, the heat transportation rate value is taken from simulation on 20 channels design at speed 3.3 m/s. The value of fake heat flux is taken as shown in Figure 5.2.3.1.1.

Figure 5.2.3.1.1: Heat Flux of Air

5.3 Discussion for 20 Channel Design Bipolar Plate

The chief aim of this survey is to imitate the fresh design of air chilling channel of a fuel cell bipolar home base by fixing two geometry designs of the air chilling channel. By fixing standard chilling channel as a control simulation, a consequence such as temperature distribution, air temperature alterations, air speed alterations, and heat transportation rate can be compared with the new designs. In this survey, the heat flux were set as changeless value, the difference is the recess air speed.

The consequences of changing the air Reynolds Number are plotted in Figure 5.3.1. By increasing the air recess speed, the mean plate temperature drops well, as expected. Proving the phenomena, the increasing values of chilling effectivity shows that the higher air speed absorb more heat from the home base. The highest chilling effectivity that is 94.35 % gives the lowest mean temperature of the home base which is 95.6 ISC.

Figure 5.3.1: Home plate temperature with variable Reynolds figure graph

The similar profile of temperature distribution shows in figure 5.3.2 explained on the alterations of temperature along the home base. The temperature bit by bit increasing as traveling farther the chilling channels and at one point it can be state that it starts to keep the temperature. This is because the nature of air that can merely absorb heat at certain sum merely. The maximal temperature of the home base before it traveling changeless is pointed at figure 5.3.3. For illustration the temperature at Reynolds figure 200 will keep when it reaches 135.5 A°C.

Rhenium 1000

Re 800

Re 600

Re 400

Re 200

Figure 5.3.2: Graph of Temperature Distribution on Bipolar home base

Figure 5.3.3: Graph of Maximum Plate Temperature

The temperature bead at the initial distance between the recess can be seen at figure 5.3.1 and the alterations is plotted in the Figure 5.3.4 below. The temperature bead alterations with the fluctuation of Reynolds figure.

Figure 5.3.4: Graph of Temperature Drop at Initial distance

Figure 5.3.5: Graph of temperature gradient

When there exists a temperature gradient within a organic structure, heat energy will flux from the part of high temperature to the part of low temperature.

Sample computation for temperature gradient at Re 200:

I”T =

=

= 0.325

From the Figure 5.3.5 we can state that the temperature gradient decreases with fluctuation of Reynolds figure. It shows that the rate of heat transportation tend to acquire lower when the air speed increases as the heat soaking up from the home base is more with high air speed. This status satisfies Fourier ‘s Law of heat conductivity where heat flows down a temperature gradient.

5.4 Discussion for 40 Channels Design Bipolar Plate

%

a-¦c The consequences of changing the air Reynolds Number are plotted in Figure 5.4.1. By increasing the air recess speed, the mean plate temperature drops well, as expected. Proving the phenomena, the increasing values of chilling effectivity shows that the higher air speed absorb more heat from the home base. The highest chilling effectivity that is 66.1 % gives the lowest mean temperature of the home base which is 115.9 ISC.

Figure 5.4.1: Home plate temperature with variable Reynolds figure graph

The similar profile of temperature distribution shows in figure 5.4.2 explained on the alterations of temperature along the home base. The temperature bit by bit increasing as traveling farther the chilling channels and at one point it can be state that it starts to keep the temperature. This is because the nature of air that can merely absorb heat at certain sum merely. The maximal temperature of the home base before it traveling changeless is pointed at figure 5.4.3. For illustration the temperature at Reynolds figure 200 will keep when it reaches 135.5 A°C.

Re 200

Rhenium 1000

Re 800

Re 600

Re 400

Figure 5.4.2: Graph of Temperature Distribution on Bipolar home base

Figure 5.4.3: Graph of Maximum Plate Temperature

The temperature bead at the initial distance between the recess can be seen at figure 5.4.1 and the alterations is plotted in the Figure 5.4.4 below. The temperature bead ranges between 1.5 and 1. The temperature bead can be said has a similar profile.

Figure 5.4.4: Graph of Temperature Drop at Initial distance

Figure 5.4.5: Graph of temperature gradient

When there exists a temperature gradient within a organic structure, heat energy will flux from the part of high temperature to the part of low temperature.

Sample computation for temperature gradient at Re 200:

I”T =

=

= 0.19

From the Figure 5.4.5 we can state that the temperature gradient decreases with fluctuation of Reynolds figure. It shows that the rate of heat transportation tend to acquire lower when the air speed increases as the heat soaking up from the home base is more with high air speed. This status satisfies Fourier ‘s Law of heat conductivity where heat flows down a temperature gradient.

5.5 Overall Discussion

In this subdivision, the consequences of the two design of chilling channel are being compared. The mean temperature graph ( figure 5.5.1 ) shows that the temperature for 40 channels designs are somewhat higher than the 20 channel design. It started at rather similar temperature but the alterations in 20 channels design are more drastically. This can be prove by Figure 5.5.3 below where the temperature gradient for 20 channels design scope higher than 40 channels which is in between 0.173-0.325. In the other manus, the temperature gradient for 40 channels ranges in 0.11 and 019. Last but non least, the chilling effectivity graph ( Figure 5.5.2 ) shows a large difference of per centum of the chilling. It can be said that the 20 channels design has the higher chilling effectivity where it can take to a coveted chilling channels design.

Figure 5.5.1: Average Temperature of Bipolar Plate

Figure 5.5.2: Cooling Effectiveness

Figure 5.5.3: Temperature Gradient

Chapter VI

CONCLUSION & A ; RECOMMENDATION

6.0 Introduction

In this chapter, the focal point is stress on recommendation for effectual air chilling channel design for PEMFC. Most of the simulation parametric quantities are similar, except for the recess air speed. Therefore, different consequences were obtained and the parametric quantity that contributes to the consequence was identified. Therefore, there are few recommendations in this chapter in order to better the CFD analysis of PEMPC air chilling channel.

6.1 Decision

The chief aim of this survey was to obtain the highest heat transportation rate for fuel cell utilizing air chilling application. To find the highest heat transportation efficiency, several design of chilling channel was designed.

The CFD simulation that has been carried out predicts the status at the surface of the bipolar home base. The simulation consequence aid in placing the most suited design which can replace the standard design of the chilling channel.

Based on the survey, several decisions can be drawn as follows:

The survey has achieved its nonsubjective by planing the most effectual geometry of air chilling channel design.

From the analysis the most desirable geometry design for bipolar home base of air chilling channel is the 20 channels type based on temperature distribution and heat transportation rate at the highest.

6.2 Recommendations

The survey of the PEM bipolar home base chilling channel is non merely intend for the flow field on the channel but it provides many other interesting things to be studied. After finishing this survey, several recommendations can be suggested. The recommendations are as follow:

Base size and surface size that used in this simulation was big because of the computing machine is non capable to run smaller mesh sizes. High public presentation computing machine is capable to run the simulation with smaller base size and surface size, it is because the base and surface size related in mesh size. If mesh size is finest the accurate consequence will be achieved.

The best heat transportation rate is when the mercantile establishment temperature is equal to the recess temperature. This status is difficult to accomplish and it must hold high air speed input and good design of air chilling channel. Therefore, simulation at 3.0 m/s air speed is suggested.

The consequence of simulation can be verified if there was an experimental value to be compared with the simulation value.