ME-407 Heat Transfer Project PDF

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Heat Transfer Project (Prof Eon Soo Lee)...

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ME-407-002 Heat Transfer MECHANICAL AND INDUSTRIAL ENGINEERING DEPARTMENT

AT NEW JERSEY INSTITUTE OF TECHNOLOGY

ME 407 Project: Car Engine Cooling System

by -------------AND-----------------------SECTION ____002________

Instructor: Eon Soo Lee

May 7, 2019

Engine Cooling Radiator: Performance Analysis This heat transfer project focuses on the performance analysis of the radiator used in automobiles to cool down the engine. To understand the importance of the radiator, it is necessary to understand the working of the car engine cooling system. Automobiles can have two different types of cooling systems, it can be either air cooled or liquid cooled. Most cars use liquid cooling system and therefore this project report specifically focuses on the liquid cooling system. In a liquid cooling system, a fluid usually Ethylene Glycol known as the “coolant” flows through the passages in the engine block. When this coolant flows, it absorbs heat from the engine components and make its way back to the radiator in the front of the car. In the radiator the heat transfer from the coolant to the surrounding takes place through heat transfer process, mainly convection and conduction. Since convection process is also involved, the velocity with which the air strikes the radiator becomes a crucial parameter in the cooling phenomenon through radiator fins.The cooling system of most automobiles is a combination of different parts. The main parts used in the cooling process of an automobile are listed below: ● The Radiator ● The Radiator Cooling Fans ● Pressure Cap and Reserve Tanks ● Water Pump ● Thermostat ● Bypass System ● Freeze Plugs ● Head Gaskets and Intake Manifold Gaskets ● Heater Core ● Hoses

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Car Cooling System

Radiator: The radiator provides an escape route to the heat generated in the engine components, the coolant brings the heat from different engine components to the radiator and the radiator cools it down using the air stream from outside of the car. The radiator is usually made of flattened aluminum tubes and also it has aluminum stripes that run in a zigzag pattern between the tubes. The diagram below shows the various components of a radiator.

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The core is the main part of the radiator and it consists of a large metal block with small fins , the heat is dissipated to the surrounding air from the core by means of small vents. The outlet and inlet tanks helps in moving the coolant from the hot part of engine to the radiator. It is very important to dissipate the heat to the surrounding because too much heating can cause significant damage to the engine. As the coolant flows through the tubes of the radiator, heat is transferred through the fins and tube walls to the air by conduction and convection . A major problem that the car radiators face is the thermal resistance caused by air flowing over the radiator. For a radiator to be effective the heat transfer should be maximized between the radiator and its surroundings. The diagram below shows a simple model of how the heat is dissipated to the surroundings using the radiator.

Engine Overheating Problem: A common problem that people often face is overheating of their car engines due to some issue involving the car cooling system. Overheating can happen due to a number of reasons such as low coolant levels, 3

unresponsive thermostat, leaks in the radiator, cooling fan not working etc. The goal of this project to analyse the workings of an automobile radiator and find ways to increase the performance of the radiator and thus reduce the overheating problems arising due to inefficient radiators. Solutions to Overheating Problems: Since the radiator acts as a heat exchanger, transferring excess heat from the engine to the surrounding , its performance can be increased by increasing the heat transfer rate. An increase in the heat transfer rate would mean more and more heat from the engine will be transferred to the surrounding in less time. Now there are various factors that need to be dealt with in order to increase the heat transfer rate. Following are important factors that affect the performance of an automobile radiator: ● Air and coolant flow , fin density and air inlet temperature. ● Thermal Conductivity of the coolant. ● Surface area and the size of the radiator. By performing a thermal analysis on different velocities of an automobile, important performance parameters such as the heat transfer coefficient and efficiency of the radiator can be derived. But in order to perform a thermal analysis it is important to set a list of assumptions that need to be considered. The assumptions are: ● Steady state conditions prevails. ● No thermal energy sources i.e. no heat generation in the radiator ● No phase change in the coolant flowing in the radiator ● Specific heat of coolant is constant throughout the radiator ● Uniform fluid flow throughout the radiator ● Kinetic and Potential energy changes are negligible Since the radiator tubes usually have non circular cross section, it is important to get the value of the hydraulic diameter in order to perform the thermal analysis. The following relation is used to calculate the hydraulic diameter.

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Hydraulic diameter, Dhyd =

4 Atube Ptube

…...(Eq. 1)

Where , Atube = Area of the radiator tube Ptube = Perimeter of the radiator tube. Although for the Ptube , the perimeter in contact with the coolant should be used but since the difference between the inner and the outer perimeters is so less that it is convenient to simply use the outer perimeter of the tube. Once the hydraulic has been determined, its value can now be used to find the reynolds number.

D hyd .⍴ . v μ

Reynold’s Number, Re =

…….(Eq.2)

To calculate the Nusselt number, the reynold’s number and the Prandtl number for the coolant (Ethylene Glycol) will be used Nusselt Number , Nu= 0.023 x Re0.8 x Pr0.4 Another important parameter to consider is the velocity of the air. The air travels through the radiator tubes and the fins and by means of convective heat transfer it picks up the excess heat from different engine components.

N A radiator −( ¿ ¿ tube H tube Lradiator ) Velocity of the air , Q air V air = ¿ where , Qair = Total air volumetric flow rate

Aradiator= Area of radiator Ntube = Number of tubes of radiator Htube = Height of the tube Lradiator = Length of the radiator 5

…….(Eq.3)

The reynolds number can now be calculated using the following relation, Re =

V air W fin❑ v air

…...(Eq.4)

where , Wfin = width of the fin, and v air = kinematic viscosity of the air. The flow of air can be assumed to be similar to flow of air over a flat plate given the geometry of the radiator tubes. The assumption that the flow of air is similar to flow over a flat plate also makes it necessary to assume the flow to be laminar since a flow of air over a flat plate never reaches the critical reynolds number value of 0.5 x 106. The nusselt number for a laminar flow over a flat plate will then be calculated as ,

Nu=0.664Reair1/2Prair1/3 ……. (Eq.5) And finally to calculate the convective heat transfer coefficient, the following relation will be used

hair =

Nuair k air W tube

……..(Eq.6)

where , Nuair = Nusselt number of air kair = thermal conductivity of the air Wtube = Width of the tube Since automobile radiators consists of fins , it is important to calculate the efficiency of these fins to be able to make proper judgements about the overall performance of the radiator. Although for most automobiles the fins are sinusoidal in geometry, they will be assumed to be straight for calculation purposes. The following relation is used to calculate the efficiency of a fin. Efficiency of a fin,

ηfin =

tanh(m Lc ) m Lc

Where Lc is the characteristic length of the fin.

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…….(Eq.7)

Analysis: Nusselt number of air versus the Reynold’s number of air graph. Assuming the flow of air over the radiator to be laminar, the Nu was calculated using equation no.5 and the following graph was generated for Reynold’s number of air ranging from 0 to 100000.

Heat Transfer Coefficient of Air vs The Velocity of Air Since most automobiles are driven in the range of 0 mph to 100 mph, the same range is used to generate the heat transfer coefficient vs the air velocity graph. To get the values of heat transfer coefficients at different Nu, equation no. 6 is used. Below is the generated graph.

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Conclusions: The above two generated graphs provide useful information about the factors that affect the performance of the radiator. It can be observed from the graph of Nusselt number vs the Reynold’s number that there is an increase in the value of the reynold’s number with increasing Nusselt number value.

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Abstract This heat transfer project focuses on the analysis of the radiator used in automobiles to cool down the engine. To understand the importance of the radiator, it is necessary to understand the working of the car engine cooling system. Automobiles can have two different types of cooling systems, it can be either air cooled or liquid cooled. Most cars use liquid cooling system and therefore this project report specifically focuses on the liquid cooling system. In a liquid cooling system, a fluid usually Ethylene Glycol known as the “coolant” flows through the passages in the engine block. When this coolant flows, it absorbs heat from the engine components and make its way back to the radiator in the front of the car. In the radiator the heat transfer from the coolant to the surrounding takes place through heat transfer process, mainly convection and conduction. Since convection process is also involved, the velocity with which the air strikes the radiator becomes a crucial parameter in the cooling phenomenon through radiator fins.

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Table of Contents Objectives & Team Member Roles1 Objectives2 Team Member Roles3 Problem Statement/Model Development4 Introduction5 Analysis6 Results2 Discussion3 Conclusion4 References5

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Objectives & Team Member Roles Objectives 1. Understand the principles and decisions made in designing a radiator cooling system. 2. Use the principles and methods of heat transfer which we learned in ME 407 Heat Transfer class to understand an applied application of convection cooling. 3. Understand why and what is causing overheating? 4. Design the model using Creo, SolidWorks and Flow Simulation System to fully understand the concept. 5. Do the theoretical breakdown of a cooling convection of Radiator and a stimulating study on a system that is not frequently experiential in current day to day function.

Team Member Roles

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Problem Statement/Model Development

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Introduction Radiator also known as Heat Exchanger on the purpose of controlling the heat of an engine. Radiator plays a major role in transferring the heat from the engine parts to an atmosphere its whole system and working. In the field of Automobile, it is a huge factor since it is a main components of an automotive cooling system. A radiator has an aluminum mesh and in the aluminum mesh there is a tube that runs parallel though all the way down inside the radiator. The process begins with the hot water tends to enter from one side of the aluminum mesh/radiator and flows through the tube and comes out with a cold water. Here is the whole cooling process takes place.

Figure 1: Full Schematic of the Car Cooling Process The way it works is, the air is going to be feeding through it, and aluminum fins will be attached all to the tubes. As the air passes through, it is going to cool these fins which are connected to the tubes as shown in figure 2. The cooling system of most automobiles is a combination of different parts.

Openpr.com. (2017). Increasing Number of Vehicles and Growing Average Age of Vehicles are Expected to Propel the Growth of Automotive Radiator Market in Near Future, According to Research Nester. - openPR. 13

[online] Available at: https://www.openpr.com/news/825886/Increasing-Number-of-Vehicles-and-GrowingAverage-Age-of-Vehicles-are-Expected-to-Propel-the-Growth-of-Automotive-Radiator-Market-in-Neat-FutureAccording-to-Research-Nester.html [Accessed 8 May 2019]. The main parts used in the cooling process of an automobile are listed below. But we will mostly focus on the Radiator since it is the first most important component into controlling the cooling process. o

The Radiator

o

The Radiator Cooling Fans

o

Pressure Cap and Reserve Tanks

o

Water Pump

o

Thermostat

o

Bypass System

o

Freeze Plugs

o

Head Gaskets and Intake Manifold Gaskets

o

Heater Core

o

Hoses

Figure 2: Radiator Water Tubes and Fins pitch

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Ismael, T., Yun, S. and Ulugbek, F. (2016). Radiator Heat Dissipation Performance. Journal of Electronics Cooling and Thermal Control, 06(02), pp.88-96.

Radiator: The radiator provides an escape route to the heat generated in the engine components, the coolant brings the heat from different engine components to the radiator and the radiator cools it down using the air stream from outside of the car. The radiator is usually made of flattened aluminum tubes and also it has aluminum stripes that run in a zigzag pattern between the tubes. The diagram below shows the various components of a radiator.

Figure 3: Radiator Core The core is the main part of the radiator and it consists of a large metal block with small fins, the heat is dissipated to the surrounding air from the core by means of small vents. The outlet and inlet tanks help in moving the coolant from the hot part of engine to the radiator. It is very important to dissipate the heat to the surrounding because too much heating can cause significant damage to the engine. As the coolant flows through the tubes of the radiator, heat is transferred through the fins and tube walls to the air by conduction and convection. As shown in the figure below.

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Figure 4: Heat Exchanger Core (Coolant and Air Flow)

A major problem that the car radiators face is the thermal resistance caused by air flowing over the radiator. For a radiator to be effective the heat transfer should be maximized between the radiator and its surroundings. The diagram below shows a simple model of how the heat is dissipated to the surroundings using the radiator.

Figure 5: Process of Heat Dissipated By performing a thermal analysis on different velocities of an automobile, important performance parameters such as the heat transfer coefficient and efficiency of the radiator can be derived. But in order to perform a thermal analysis it is important to set a list of assumptions that need to be considered. The assumptions are: o

Steady state conditions prevail.

o

No thermal energy sources i.e. no heat generation in the radiator

o

No phase change in the coolant flowing in the radiator

o

Specific heat of coolant is constant throughout the radiator

o

Uniform fluid flow throughout the radiator

o

Kinetic and Potential energy changes are negligible

Since the radiator tubes usually have non-circular cross section, it is important to get the value of the hydraulic diameter in order to perform the thermal analysis. The following relation is used to calculate the hydraulic diameter.

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Ismael, T., Yun, S. and Ulugbek, F. (2016). Radiator Heat Dissipation Performance. Journal of Electronics Cooling and Thermal Control, 06(02), pp.88-96.

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Work Cited https://file.scirp.org/pdf/JECTC_2016062314393531.pdf http://www.cttc.upc.edu/research/node/124 http://www.tjprc.org/publishpapers/--1465457319-1.%20IJAUERD%20-%20FOAM%20FINNED%20DOWN %20FLOW%20TYPE%20AUTOMOTIVE%20RADIATOR.pdf

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