PDF Optimum insulation thickness: Radial heat conduction through insulated pipe

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International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)

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ISSN (Print): 2319-3182, Volume -6, Issue-1-2, 2017 163

Optimum insulation thickness: Radial heat conduction through insulated pipe

1Puspendra Upadhyay, ²Sunil Yadav, ³Kiran D. Devade

1,2,3Indira College of Engineering and Management

Email: ¹[email protected], ²[email protected], ³[email protected] Abstract— In last few decade critical radius has gain

tremendous attention and application in thermal cylindrical and spherical heat transfer system. In order to get desired heat transfer from cylindrical and spherical system thickness of insulation play a very important role. In this experimental effect of insulation thickness and heat input is studied by using a ceramic insulation around a pipe. After performing and analyzing it can be concluded that optimum thickness lies between critical radius and thickness where heat transfer is minimum.

Index Terms—critical radius, crossover radius, insulation, heat transfer.

I. INTRODUCTION

In today’s era critical radius and crossover radius has gain tremendous attentions in thermal heat conduction through cylindrical and spherical body. The heat conducted through a planer body have a monotonically behavior with addition of insulation i.e thermal resistance keeps on increasing with addition of insulation. But thermal resistance of cylinder and sphere have a nonlinear relations with thickness of insulation. In transient thermal system thickness of insulation plays a very important role.

For example thermal insulation can be used to increase heat dissipation from a system to another system, it may be used to avoid heat lose or it may be used as a protective shield which separate two system. Heat transfer through insulation and heat transfer without insulation can be related by crossover radius.

Critical radius for cylinder and sphere is defined as thickness of insulation for which heat transfer rate will be maximum through insulation. Critical radius depends on thermal conductivity of insulation, heat transfer convection coefficient and radius of insulation.

Conduction through insulation and convection outside the insulation plays a major role in defining a critical and cross over radius [1,2]. Relation between Conduction, convection and desired radius of insulation can be define in terms of non-dimensional Biot number [1]. Sunan et al.

have used FDE method to draw relationship between steady state and transient state thermal system [4]. M.R Kulkarni have illustrated the relationship of biot number with outer radius of insulation and ratio of heat transfer through the insulation to heat transfer without insulation [3].

This experiment deals with optimizing thickness of insulation over a cylindrical pipe and to define optimum range of thickness for maximum and minimum heat transfer through the insulation at different heat inputs.

II. EXPERIMENT SETUP AND FORMULATIONS

Experimental setup consist of frame, K type thermocouple, temperature indicator, Voltmeter, Ammeter, Copper pipe, Resistive heater, main switch, ceramic tape is used as insulating material. Copper pipe having inner diameter 30mm and outer diameter 32mm is heated by resistive type rod heater which is placed inside the cavity of cupper pipe.in order to get mean temperature four equidistant thermocouple were placed on insulation surface and four equidistant thermocouple were placed on inner surface. Insulation thickness were maintain at 3mm, 6mm, 9 mm, 12mm and 15mm. Thermal conductivity of ceramic zirconium oxide is 1.7 W/mK, assumed to be constant for given range of temperature [6].

Different heat input 50Watt, 75Watt, 100Watt and 150 Watt were supplied by using resistive rod heater.

Figure 1: Schematic Diagram of Experimental Setup

Figure 2: Experimental Setup

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Thermal resistance through insulation is calculated by using

Rt=

Where Rt= thermal insulation resistance R2= Outer insulation thickness R1= Inner insulation thickness

K= Thermal conductivity of insulation L= Length of Pipe

Heat transfer through insulation is given by

Qins=

Table 1: Sample observation at 50 watt heat input Insulation

thickness ( mm)

Heat transfer without insulation

(Watt)

Heat transfer with insulation

(Watt)

3 50.90568 552.187

6 50.90568 796

9 50.90568 286

12 50.90568 342

15 50.90568 366

thickness ( mm)

Heat transfer without insulation (Watt)

(Watt)

3 71.17487 818.645

6 71.17487 1256

9 71.17487 469

12 71.17487 618

15 71.17487 613

thickness ( mm)

Heat transfer without insulation

(Watt)

3 85.26071 1188

6 85.26071 1645

9 85.26071 626

12 85.26071 656

15 85.26071 849

thickness ( mm)

Heat transfer without insulation (Watt)

(Watt)

3 106.939 1517

6 106.939 2248

9 106.939 666

12 106.939 921

15 106.939 1040

III. RESULT AND DISCUSSION

After achieving desired steady state condition temperature at various location and recorded at 50Watt, 75Waat, 100Watt and 125Watt inputs. On the basis of observed reading and calculation a graph is plot between heat ratio and radius ratio. Heat ratio is a non-dimensional term which is defined a heat transfer through insulation and heat transfer without insulation. Radius ratio is non dimensional term which is defined as ratio of thickness of insulation to maximum thickness of insulation.

Figure 3: Plot between Heat ratio and Insulation Thickness

From the above graph following points can be observed:

1. Maximum heat transfer occurs at point A which is at 5.6mm thickness of insulation.

2. Effect of heat input on critical radius can be neglected as there is no effect of higher heat input on critical radius.

3. At point B, heat transfer is minimum through insulation after which it increases due to radiation.

4. Between point A and point B, heat transfer vary from maximum to minimum.

IV. CONCLUSION

From the experiment it can be concluded that heat transfer will be maximum at 5.6mm and minimum heat transfer

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will occur at 9.54 mm. So in order to get higher and lowest heat transfer insulation thickness lies between point A and Point B i.e 6.9mm to 9.54 mm.

REFERENCES

[1] M. R. Kulkarni “Critical radius for radial heat conduction: A necessary criterion but not always sufficient,” pp. 967-979, 30 Aug 2003.

[2] Dinesh kumar Sahu, Prakash kumar sen, Gopal sahu “A Review on Thermal Insulation and Its Optimum Thickness to Reduce Heat Loss,”

IJIRST. Vol.2 issue.06 pp. ISSN (online):

2349-6010, November 2015

[3] N.B.Totala, Anant A.Paralkar,Nikhil R.Kakade, Kunal R.Kawthekar “Analysis for critical radius of

insulation for a cylinder,” vol.3, issue.9 pp. 32-38, November 2013.

[4] Sunan Huang, Jaronie Mohd Jani, Martin Leary, Aleksandar Subic “The critical and crossover radii on transient heating,” pp. 325-334, 2013.

[5] M. S. a. R. M. K. Abdul Razak.R.Kaladgi, "A Study on Critical Radius and Crossover Radius of Insulation for Various Heat Transfer Problems,"

Columbia International Publishing American Journal of Heat and Mass, vol. 3, pp. 149-156, 2014.

[6] J. B. Wachtman “Mechanical and Thermal Properties of Ceramics: Proceedings”, Issue 303, pp. 79, 1969.

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