Arjstte 02 001

Advanced Research Journals of Science and Technology

ADVANCED RESEARCH JOURNALS OF SCIENCE AND TECHNOLOGY

(ARJST)

SECOND LAW ANALYSIS ON RALLY CAR RADIATOR

2349-9027

Boda Rahul Kishore 1, Vallem Srinivasa Rao 2, Medapati Sreenivasa Reddy 3, 1 Research Scholar,Department of Thermal Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

2 Associate Professor,Department of Mechanical Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

3 Associate Professor,Department of Mechanical Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

Abstract In the present work, Second law analysis is carried out to analyse the irreversibility in a Rally Car Radiator. The radiator with louvered fin and elliptical tube heat exchanger is used for the internal combustion engine. After providing the necessary concise information on radiator, the task is performed on minimizing entropy generation for the radiator considered. So, second law analysis explores the availability of the system and hence better performance for a radiator.

The Thermodynamic irreversibility or number of entropy generation units (Ns) indicates the amount of lost useful power, which is not available due to system irreversibilities. In a heat exchanger irreversibilities are generated due to finite temperature difference heat transfer in the fluid streams and the pressure drops along them.

From the balanced effect of water flow rate and air velocity it is observed that the value of irreversibility gradually falls down to a value and again rises towards the optimum value when mass flow rate is considered and whereas air velocity is considered the irreversibility always decreases.

*Corresponding Author: Boda Rahul Kishore , Research Scholar, Department of Thermal Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

Published: December 07, 2015 Review Type: peer reviewed Volume: II, Issue : I Citation: Boda Rahul Kishore ,Research Scholar (2015) SECOND LAW ANALYSIS ON RALLY CAR RADIATOR

HEAT EXCHANGERS Heat exchangers are systems that transfer heat between mediums. The fluids or gases in a heat exchanger can be mixed or the energy transference can go through a conductive wall that keeps them separate.

Commercial heat exchangers are found in car radiators, furnaces, refrigerators, and chemical processing systems.

Plate heat exchangers, tube heat exchangers, and regenerative heat exchangers are all different models that are appropriate for different-tasks.

Fluid flow in cross flow direction

Thermodynamically, the effectiveness for the cross flow exchanger falls in between that for the counter flow and parallel flow arrangements.

The largest structural temperature difference exists at the corner of the entering hot and cold fluids, such as point ‘a’ in Fig.

Compact cross flow heat exchangers; the two fluids flow in directions normal to each other.

Typical fluid flow arrangements and temperature variations are idealized as two-dimensional and are shown in the figures below for the inlet and outlet sections only respectively.

Temperature distribution at inlet and outlets of cross flow heat exchangers

15

Advanced Research Journals of Science and Technology

This is one of the most common flow arrangements used for PFHE, because it greatly simplifies the header design at the entrance and exit of each fluid. If the desired heat exchanger effectiveness is high, the size penalty for the cross flow exchanger may become excessive. In such case, a counter flow unit is preferred.

NEED OF COMPACT HEAT EXCHANGERS The heat transfer coefficient for gases is generally one or two orders of magnitude lower than that for water, oil and other liquids. So to minimize the size and weight of a gas-to-liquid heat exchanger, the thermal conductance on both sides of the exchanger should be approximately the same. So the heat transfer surface on the gas side needs to have much large area and be more compact than can be realized practically with the circular tubes commonly used in shell- and tube exchangers. Thus, for an approximately balanced design a compact surface is employed on the gas side of gas-to-gas, gas-to-liquid, and gas –to- phase change heat exchangers.

EXTENDED SURFACE HEAT EXCHANGERS Plate fin and tube fin are main types of extended surface heat exchangers. Plate fin type of exchangers has corrugated fins most commonly having triangular and rectangular cross sections or spacers sandwiched between parallel plates. While in tube fin heat exchanger the round and rectangulartubes are used. Fins are generally used on the outside, but they may be used on the inside of the tubes also. They are attached to the tubes by a tight mechanical fit, tension winding, adhesive bonding, soldering, brazing, welding, or extrusion.

(2) A single heat exchanger can incorporate several different process streams and the unique plate-fin construction allows these to enter/exit the exchanger at intermediate points along the exchanger length rather than just at the ends.

(3) Very close temperature approaches between streams (typically 1 to 30oC) can be accommodated leading to operational cost savings.

(4) High thermal efficiency, use of aluminum and multistream capability combine to form a compact, low –weight structure.

(5) Usually plate-fin exchangers operate at cryogenic temperatures. Therefore the exchanger is housed in an insulated ‘cold- box’ (typically carbon steel) to preserve the cold. Alternatively, a locally applied exterior insulant may be used.

(6) The versatility of plate- fin heat exchangers, coupled with the ability to manufacture them in a variety of other materials, makes them ideal for a range of process duties outside the cryogenics field.

(7) Low weight per unit transfer and possibility of heat exchange between many process streams.

RADIATOR

INTRODUCTION TO PLATE-FIN HEAT EXCHANGERS (PFHE) A plate-fin heat exchanger (PFHE) is a type of compact exchanger that consists of a stack of alternate flat plates called parting sheets and corrugated fins brazed together as a block. Streams exchange heat by flowing along the passages made by the fins between the parting sheets.

The fins serve both as a secondary heat transfer surface and mechanical support for the internal pressure between layers. Fig. gives the idea about the construction of the PFHE.

Figure showing the flow direction of water through engine and radiator

TYPES OF RADIATORS Radiator is a common term for several types of heat exchangers. Radiators can be used in automobiles, buildings, and electronics.

Basic components of plate-fin heat exchanger The core of matrix, parting sheets, and side bars is laid up by hand, clamped firmly in a jig, and then brazed into a rigid structure, either in a molten salt bath or in a vacuum furnace the result is a strong, rigid structure of extremely high volumetric heat transfer surface density.

However, the units are limited in overall size and materials of construction and cannot be cleaned mechanically.

The most common area of application is in cryogenic processing such as liquefied natural gas production, hydrogen purification and helium separation and liquefaction.

Advantages PFHE have some advantages over other forms of heat exchangers, only limited by operating fluid temperatures and pressures. These advantages are: (1) Very large heat transfer area per unit volume of heat exchanger. This surface area is composed of primary and secondary (finned) surfaces. The effective surface area is over five times greater than that of a conventional shell and tube heat exchanger. Area densities range from 850 to 1,500 m2/m3.So high thermal effectiveness can be achieved.

A typical modern automobile radiator

A Cast Iron Household Radiator

Conventional radiators: A conventional hot-water radiator consists of a sealed hollow metal container, usually flat in shape. Hot water enters at one end and rises to the top of the radiator by way of convection or by pressure from a pump elsewhere in the building.

16

Advanced Research Journals of Science and Technology

Steam: Steam has the advantage of flowing through the pipes under its own pressure without the need for pumping. For this reason, it was adopted earlier, before electric motors and pumps became available. Steam is also far easier to distribute than hot water throughout large, tall buildings like skyscrapers. However, the higher temperatures steam systems operate at make them inherently less efficient, as unwanted heat loss is inevitably greater.

Fan assisted Radiators: A more recent type of heater used in homes is the fan assisted radiator. It contains a heat exchanger fed by hot water from the heating system. A thermostatic switch senses the heat and energizes an electric fan which blows air over the heat exchanger.

LITERATURE SURVEY: 1.Maximov A modeling of the mechanical systems with dissipative processes as thermodynamic systems has been performed in this article. On the basis of the Gouy–Stodola’s theorem the entropy generation minimization method for thermodynamic optimization of these systems has been applied. The outcomes of a thermodynamic optimization of metal-forming processes and rotor brake systems have been shown. It has been proved that the generated entropy is a generalized optimization criterion for this kind of systems. The vector optimization criterion has been substituted by the generated entropy functional depending on the vector of controlling factors (process parameters).

The generated entropy plays the role of a surrogate function of a feasible scalarised function, and therefore it is not necessary to scalarize the vector optimization criterion. The optimization is reduced to generated entropy minimization. The effectiveness of the latter approach has been proved. Heat exchanger which is a physical form of the matter motion occurs because of the hysteresis of the material. As a result of hysteresis and internal friction along the contact surfaces of the individual subsystems, there is dissipation of mechanical energy—heat is generated inside and along the boundaries of the subsystems.

Entropy generation minimization (EGM) is the method of modeling and optimization of real devices that owe their imperfection to heat transfer, mass transfer, and fluid flow and other transport processes. EGM method was first described as a modeling and optimization meth EGM as a fundamental optimization approach has been implemented to processes with heat and fluid flow.

or without pressure drop constraints, respectively. Performance of the CHE is evaluated according to the conditions of the structure sizes that the GA generated, and the corresponding volume and cost are calculated. It is shown that with pressure drop constraints the optimized CHE provides about 30% lower volume or about 15% lower annual cost, while without pressure drop constraints the optimized CHE provides about 49% lower volume or about 16% lower annual cost than those presented in the literature.

CHEs own merits of compactness, small volume, low weight, high ectiveness and low cost. Plate–Fin Compact Heat Exchangers (PFCHEs) are widely used in gas–gas applications such as micro turbine, regenerators and recuperators. PFCHEs are extensively used in automobile, naval and aeronautical applications.

PFCHE has high compactness (up to 1000–2500 m2/m3) and has low weight because of the use of aluminum. The materials of plate and fin are aluminum with a thermal conductivity of 190W/(m K), density of 2790 kg/m3. Plain triangular and oset strip fins are employed on each side.

CALCULATION PROCEDURE FOR TFHE: In a conventional tube-fin heat exchanger, heat exchanger between the two fluids takes place by conduction through the tube wall. In an air-to-liquid exchanger, the heat transfer coefficient on the liquid side is generally one order of magnitude higher than on the gas side. Hence to have balanced thermal conductance on both sides for a minimum size heat exchanger, fins are used on the airside to increase surface area.

Here a tube-fin heat exchanger having flat fins is designed on the thermo dynamic basis. Fins can be plain, wave, or interrupted, and the array of tubes can have tubes of circular, oval, rectangular, or other shapes. A tube fin exchanger with flat fins has been referred to variously as a plate and tube, and tube in plate fin exchanger.

Finned tube exchanger is designed for air-to-water configuration which is known as intercooler in which hot fluids flow inside the tubes, and hot processed air is circulated outside by forced or induced draft over the extended surface. Same method can also be used for water-to-air heat exchangers is as given below.

(1) First select the surface index for the tube fin heat exchanger. Here the surface selected is 9.68-0.87. the term 9.68 represents number of fins per inch.

(2) Calculate geometrical characteristics for tube inside and tube outside parts.

(3) Second law analysis is applied to it.

The main objective of this study is to obtain a generalized model of the state of the mechanical systems with dissipative processes modelled as thermodynamic ones and also thermodynamic optimization by means of generated entropy functional minimization.

2.Wang et al: In this study a plate–fin type Compact Heat Exchanger (CHE) is considered for optimization. The optimization method uses a Genetic Algorithm (GA) to search, combine and optimize structure sizes of the CHE. The minimum total volume or/and total annual cost of the CHE are taken as objective functions in the GA, respectively.

The geometries of the fins are fixed while three shape parameters are varied for the optimization objectives with

Heat Exchanger Dimensions

17

Advanced Research Journals of Science and Technology

Tube inside geometry calculations:- (Ref.1)

Cross-sectional view of the single tube

Tubes are considered as flat and the sides are curved.

The geometrical characteristics of interest for analysis are evaluated as following.

Water is considered to pass through the tubes.

Wetted circumference for a single tube

Unit cell of the area exposed to air stream

Reviewing the external tube surface, the area can be calculated using equation E.6: (E.1) Once the wetted circumference is known for a single tube, the wetted area in a single tube can be calculated through multiplying equation E.1 by length of the tube, which in this case is 0.32m. Further, the number of tubes counted for the total heat exchanger 216. The total wetted tube area through which heat is transferred in the core is thus: Total wetted tube area (E.2) Hydraulic radius of non-circular duct

Hydraulic diameter of tubes

(E.3)

(E.4) On substituting E.3 in E.4, and using the variables defined in the fig E.1, the hydraulic diameter is found to be:

(E.5) Calculating the total wetted area exposed to the Airstream In order to calculate the total area exposed to the airstream, a unit cell fin assembly is a defined as is done for the 3 core 4mm fin pitch heat exchanger in equation E.2. In reality a radius is found on the fin where it is attached to the water tube, but due to the inconsistency of the actual radius, an angled arrangement is assumed for the purpose of this calculation.

The total wetted area exposed to the air stream in this unit cell consists of two elements: • External tube surface • Fin surface

Definition of various geometric parameters

The unit fin surface is obtained by calculating the area of four surfaces:

The total area exposed to the air stream is thus:

18

Advanced Research Journals of Science and Technology

In order to calculate the total area exposed to the air stream, the number of unit cells in the heat exchanger needs to be established. It is known that the heat exchanger consists out of 216 tubes. The number of unit cells per tube is simply obtained by dividing the fin pitch into the total length of the tube, i.e. 320mm. The resultant area exposed to the air stream for the 3 core 4mm fin pitch heat exchanger is thus:

Calculating the air stream hydraulic diameter of the air channel is done on the same principle as for the water tube. In this case, the wetted perimeter is however defined as given in equation E.11:

(E.15) Wilson Constants: These are the constant used in finding the variable ‘K’ which is used in effectiveness equation. d=0.5749 C4=0.17361

a=0.37738 C5=0.82786

To find the effectiveness first we have to find some of the terms by using the equations given below: Mass flow rate of water:

Dynamic viscosity ( ), Prandtl number ( ), Thermal conductivity of water ( ) for water are taken from data book at the inlet temperatures.

Reynolds number for water: The values like inlet temperatures, dimensions of the radiator are taken from the Refence.1.

Parameters

Values

Inlet temperature of Water Ta,1=340.13o K Inlet temperature of Airstream

Tb,1=300.37o K

Mass flow rate of air:

Table showing the Inlet temperatures of both the fluids

ANALYSIS PROCEDURE TO FIND OUT THE NUMBER OF ENTROPY GENERATION UNITS, NS To calculate the number of entropy generation units first we have to find the effectiveness of the radiator, then mass flow rates, areas, Reynolds’s number, outlet temperatures, pressure drops of both the fluids.

Later all the above values are substituted in the equation E.38 and number entropy generation units is calculated.

Finding of Effectiveness: (Ref.1)

Dynamic viscosity ( ), Prandtl number ( ), Thermal conductivity of air ( ) for air are taken from data book at the inlet temperatures.

Reynolds number for air:

19

Advanced Research Journals of Science and Technology

Finding the pressure drop on air stream side: Fanning friction factor for air stream:

On substituting the values obtained from the above equations in the equations given below fanning friction factor value is obtained.(Ref.7)

Finding of pressure drop on water side: (Ref.3) Fanning friction factor for water: The value is taken from Heat & Mass transfer data book by considering the following data,

FLOW CHART SHOWING THE STEP-BY-STEP PROCEDURE TO FIND OUT THE NUMBER OF ENTROPY GENERATION UNITS

From graph number-102 of Kays & London book, on substituting the value of St (Pr) 0.23 fanning friction factor is taken “fa�. (Ref.3) Exchanger flow stream mass velocity

Now pressure drop on water side is calculated by substituting the above data in the equation given below

20

Advanced Research Journals of Science and Technology

Balanced effect Water flow rate and Air velocity over the value of Effectiveness

From the figure of the balanced effect of water flow rate and air velocity it is observed that the effectiveness of the radiator gradually increases to a value and then falls down towards the optimum value when mass flow rate is considered and whereas air velocity is considered effectiveness always increases. Thus we can say that by increasing the velocity of air we can increase the heat transfer rate.

RESULTS: The given below are the results obtained during the second law analysis.

Effect Water flow rate and Air velocity over the value of Ns

From the above figure it can be observed that, as the velocity of air increases Ns value gradually reduce indicating improved heat transfer in the radiator. However entropy generation number increases up to some extent and then decreases. With reference to the water flow rate indicating that heat transfer has an optimum value.

Balanced effect Water flow rate and Air velocity over the value of Ns

From the figure of the balanced effect of water flow rate and air velocity it is observed that the value of irreversibility gradually falls down to a value and again rises towards the optimum value when mass flow rate is considered and whereas air velocity is considered the irreversibility always decreases.

From the above figure it can be observed that, as the velocity of air increases effectiveness value gradually increases indicating improved heat transfer in the radiator.

However effectiveness increases up to some extent and then decreases. With reference to the water flow rate indicating that heat transfer has an optimum value.

21

Advanced Research Journals of Science and Technology

CONCLUISION: Second law analysis procedure of a Rally car radiator has been performed. From the analysis the following conclusions are made, • The balanced effect of water flow rate and air velocity it is observed that the value of irreversibility gradually falls down to a value and again rises towards the optimum value when mass flow rate is considered and whereas air velocity is considered the irreversibility always decreases.

Combined influence of Water, Air with Ns value

From the figure the combined influence of the air and water with entropy generation number is shown in the form of ellipse

• The balanced effect of water flow rate and air velocity it is observed that the effectiveness of the radiator gradually increases to a value and then falls down towards the optimum value when mass flow rate is considered and whereas air velocity is considered effectiveness always increases. Thus we can say that by increasing the velocity of air we can increase the heat transfer rate.

• As the velocity of air increases Ns value gradually reduce indicating improved heat transfer in the radiator. However entropy generation number increases up to some extent and then decreases. With reference to the water flow rate indicating that heat transfer has an optimum value.

• As the velocity of air increases effectiveness value gradually increases indicating improved heat transfer in the radiator. However effectiveness increases up to some extent and then decreases. With reference to the water flow rate indicating that heat transfer has an optimum value.

Combined influence of Water, Air with Effectiveness value

From the figure the combined influence of the air and water with effectiveness is shown in the form of ellipse.

• The combined influence of the air and water with entropy generation number is shown in the form of ellipse.

• The combined influence of the air and water with effectiveness is shown in the form of ellipse.

• The response curve shows the effect of the Reynold’s number of air and water with entropy generation units of the radiator.

• The response curve shows the effect of the Reynold’s number of air and water with effectiveness of the radiator.

REFERENCES:

Surface plots of Ns vs Reynold’s number of Water and Air

The response curve showing the effect of the Reynold’s number of air and water with entropy generation units of the radiator.

1. A model to predict the effect of the radiator core and ambient conditions and the performance of the cooling system of a Rally car by Franciscus Xavierus Laubscher.

(University of Pretoria etd – Laubscher F X (2006)).

2. Fundamentals of Heat Exchanger Design by Ramesh K.Shah and Dusan P.Sekulic.[Text book] 3. Compact heat exchangers by W.M.Kay’s and A.L.London (Stanford University).

4. Heat and Mass Transfer Data Book by C.P.Kodandaram.

5. Thermodynamic optimization of cross flow plate-fin heat exchanger using a particle swarm optimization algorithm – R.V.Rao, V.K.Patel.

-International Journal of Thermal Sciences 49 (2010) 1712-1721.

Surface plot of Effectiveness vs Reynold’s number of Water and Air

6. Second law based optimization of cross flow plate-fin heat exchanger design using Genetic Algorithm by Manish Mishra, P.K.Das, Sunil Sarangi.

-Journal of Applied Thermal Engineering Vol.29, Issue

22

Advanced Research Journals of Science and Technology

14-15, Oct.2009 pp.2983-2989

Author

7. A generalized friction correlation for Louver fin geometry by Yu-Juei, Kuei-Chang Hsu, Yur-Tsai Lin, and ChiChuang Wang.

-International Journal of the Heat and Mass Transfer 43(2000) 2237-2243 8. Optimum Louver angle design for a louvered fin heat exchanger by Jiin-yuh Jang and Ying-chi Tsai.

-International Journal of the Physical Sciences Vol.6 (28), pp.6422-6438, 9th November, 2011.

9. Experimental and numerical investigation of a Louvered fin and elliptical tube compact heat exchanger by Karthik Poornachandran, Sheik Ismail Liaguat Ali Khan, Kulasekaran Narasingamurthy and Velraj Ramalingam.

Boda Rahul Kishore, Research Scholar, Department Of Thermal Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

10. Minimizing Entropy Generation for Louvered Fins in a Plate-fin Compact Heat Exchanger by Masoud Ashadi and Nasrin Dindar Mehrabani.

-Journal of Petroleum and Gas Engineering Vol.4 (2) pp.35-45, Feb 2013.

Vallem Srinivasa Rao, Associate Professor, Department Of Mechanical Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

Medapati Sreenivasa Reddy, Associate Professor , Department Of Mechanical Engineering, Aditya Engineering College, Surampalem, Andra Pradesh, India.

23