Proceedings of ICAPP 2015 May 03-06, 2015 - Nice (France)

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Heat Transfer and Pressure Drop Tests in NANO for Fusion-Fission Hybrid System

Jubair Ahmed Shamim1, Palash Kumar Bhowmik1, Kune Y. Suh1 1Department of Nuclear Engineering, Seoul National University

1 Gwanak Gu, Gwanak Ro, Seoul 151-744, ROK. Tel: +82-2-875-8912, Fax: +82-2-882-8912, Email:kysuh@snu.ac.kr

Abstract – Experiments were performed in the so-called NANO (Numerics Applied Nanofluid Operation) rod bundle to study convective heat transfer and the effects of grid spacer on flow restriction under fully developed single phase turbulent flow condition. The pressurized water reactor (PWR) conditions were considered while designing the NANO test loop using water as coolant spanning the Reynolds numbers from 7,463 to 20,904. A total of nine cartridge type heater rods were installed in the 3×3 square array NANO bundle which resembles a typical PWR spent fuel assembly in the fusion-fission hybrid blanket. The Nusselt numbers for a wide range of flow inlet velocity and input power were obtained and compared against the well-known correlations available in the literature. The results revealed that, while the convective heat transfer coefficient increased with increasing Reynolds number, none of the correlations abled to predict the convective heat transfer coefficient for the NANO geometry precisely. In case of pressure drop, the measured values were within 5-18% of predictions depending on the Reynolds number. The deviations were elucidated quantitatively and a new heat transfer correlation is proposed for this NANO specific rod bundle.

I. INTRODUCTION Heat transfer and fluid flow (conjugately termed as

thermal-hydraulics) are two pivotal aspects that must be taken into account while converting nuclear energy into thermal energy by extraction of heat from the nuclear fuel elements. Thermal-hydraulics in rod-bundle geometry is regarded as one of the five key avenues (other disciplines may be identified as neutron physics, structural mechanics, radioprotection, and reliability including statistics) essential for further amelioration of Nuclear Power Plant (NPP) design and Nuclear Reactor Safety (NRS) technologies.1

A major part of designing a nuclear reactor core

involves the quantification of the optimal flow of coolant and distribution of pressure drop across the core. While higher coolant flow rates will lead to better heat transfer coefficients and higher CHF limits, it will also result in larger pressure drops across the core, hence larger demand of pumping powers as well as larger dynamic loads on the core components. Thus, the role of the hydrodynamic and thermal-hydraulic core analysis is to find proper working conditions that assure both safe and economical operation of the nuclear power plant. Suh and Todreas2 experimentally investigated the effects of lateral drag changes caused by alteration of flow structure due to presence of wire-wrapped spacers for a

triangular-array rod assemblies in liquid-metal fast breeder reactor and correlated the transverse pressure drop data throughout the laminar and turbulent flow regimes. The correlation is in the form of a correction parameter applicable to the friction factor-Reynolds number relationship for the corresponding bare rod bundle. DeStordeur3 experimentally evaluated the pressure drop characteristics of a variety of spacer grids in rod-bundle geometry and correlated results in terms of a drag co-efficient (Cs) which is a function of the Reynolds number for a given spacer or grid type. Rehme4 later investigated the pressure drop for a hexagonal fuel rod bundle and on the basis of tests of several grids; he opined that the effect of the ratio of projected frontal area of the spacer to the unrestricted flow area away from the grid or spacer is of more paramount importance than was indicated by DeStordeur. Chun and Oh5 and Cigarini and Dalle Donne6 further improved Rehme’s correlation by incorporating effects of mixing devices in conjunction with grid spacers.

Makhmalbaf7 experimentally studied the convective heat transfer coefficient around a vertical hexagonal rod bundle (7 vertical rods in a hexagonal tube with a featuring 1.4 cm tube hydraulic diameter) for a vast fluid mean velocity (3800<Re<40,000) and proposed a new correlation proprietary for that specific geometry.

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Despite numerous available literatures, the authors felt that no appropriate correlations has been presented yet that is entirely satisfactory to calculate heat transfer to, and pressure drop across, the coolant flowing through rod-bundle assemblies like NANO. Therefore, the present experiment has been undertaken with a view to investigate the forced convection heat transfer and pressure drop for up flow in presence of grid spacers in a 3×3 vertical square array rod-bundle which resembles PWR conditions having water as coolant.

II. EXPERIMENTATION & INSTRUMENTATION The NANO apparatus has been constructed to measure

heat transfer to and pressure drop and across a 3×3 square array rod assembly with a pitch-to-diameter (P/D) ratio 1.286 and hydraulic diameter (Dh) 0.010288 m. While Fig.1 illustrates the schematic of NANO loop, Fig.2 depicts the layout of test facility that has been constructed at Seoul National University, ROK. The system consists of a test section, a plate type heat exchanger (OLAER PWO K Series), a water reservoir, a centrifugal pump (Wilo MHi403EM), flow control vales & stainless steel piping (pipe mat: A269 TP 316L). A total of 9 cartridge type heaters are installed in a 3×3 square array fashion which is a mimic of PWR-like fuel rod bundle. From the pump the coolant (water) enters to the plenum connected to the lower part of the vertical test section. The plenum is an empty space upstream of the heated rod bundle which houses a specially designed inlet flow distributor to suppress non-uniformity of the flow generated by pipe fittings. The flow rate is measured by an electromagnetic flow meter (Toshiba LF400, ±0.5% Accuracy) at downstream of the pump. Pressure drop along the test section is measured by two identical pressure transducers (Allsenser P601, ±0.25% FSO Accuracy) at inlet and outlet. K-type thermocouples are used to measure coolant bulk temperature and central heater rod surface temperature distribution.

A collecting tank is installed at the upper end of the test

section to abate the flow fluctuations. The overall temperature of the fluid can be controlled by changing heater current input. Locations of form loss in test geometry are exactly same as shown in Fig.3.8 Annexure-A summarizes the specification of the heater assembly region where projected frontal areas of the inlet flow distributor and grid spacers have been computed using CAD program. The bundle hydraulic diameter (Dh) is evaluated as follows:

(1)

where, x is the side of square duct (42.8 mm) and D is the heater rod diameter (9.8 mm).

Fig. 1. NANO schematic diagram.

Fig. 2. Overall layout of NANO test facility.

III. TEST PROCEDURE

In this study, pressure drop for isothermal flow conditions are obtained by controlling the coolant flow rate. Pressurized water is used as working fluid. The data are obtained by carrying out following procedure:

All control valves (except Drain Valve) are kept fully

opened and water is supplied through Main Tank (upper left in Fig.1) until the loop is filled up. Air within the loop is collected in the accumulator tank located above the heater assembly.

2 294 44 9h

x DD

x D

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After that control valve at the top of the pressure damping tank is fully closed and additional water is added in order to raise the system pressure to its maximum value without running pump (a maximum inlet pressure of 3.8 Bar can be obtained in this way without pump).

Then water supply is stopped to make it a closed loop

and pump is turned on. During experiment bypass valve is kept fully closed to achieve highest flow velocity at inlet.

After the cold circulation is fully established within the loop, then heater is turned on. Heater temperature can be controlled by using a power controller. After few minutes, secondary system coolant (water) is provided through an external heat exchanger.

Desired flow rate can be obtained by adjusting opening fraction of control valve located at the downstream of pump. Steady state condition is obtained by adjusting the flow rate of secondary system coolant.

Pressure drop across the test section is recorded by means of digital differential pressure transducers located at inlet and outlet of test section. During the experiment, the mass flow rate, pressure and

the coolant temperature data are monitored using data acquisition system named National Instruments SCXI with Lab VIEW Signal Express 2009, sample picture of which is shown in Fig.4.

Fig. 3. Form loss locations in NANO apparatus.8

Fig. 4. Temperature monitoring of NANO apparatus with Lab VIWE Signal Express 2009.

IV. HEAT TRANSFER ANALYSIS

One central parameter required to quantify heat transfer characteristics in single phase forced-convection turbulent flow regime is heat flux q (W/m2), which can be defined in terms of total heat input Q (W) into flow channel, dia D (m) and heated length l (m) of heater rods as follows since there are nine heater rods heated circumferentially:

(2)

The total heat input Q is assumed as uniform axially and

azimuthally since the thickness of heater rods is constant throughout the heated length and it can be obtained either with the product Q1 of input current I (Ampere) and voltage V (Volt) applied to heater rods or with the product Q2 of coolant flow rate 푚̇ (kg/s), coolant temperature increase ΔTb (K) over the flow channel and specific heat of coolant Cp (J/kg.K) and can be expressed as follows:

(3)

Q2 =푚̇ Cp ∆Tb (4)

To validate the estimation of Q, values of Q1 and Q2

obtained using Eq. (3) and (4) is plotted in Fig.5. Since there is fairly good agreement between Q1 and Q2 as shown in Fig.5, any of these two values can provide precise estimation of Q. In this study, values obtained by Eq. (4) is used as Q for further calculations.

To compute Nu under single phase forced-convection

turbulent flow regime numerous correlations available in literature can be implemented subject to geometry of fluid flow walls and fluid mean velocity (Reynolds number). Among those, the most frequently applied correlations are Dittus-Boelter, Sieder-Tate & Silberberg-Huber as expressed through Eq. (5) to (7) respectively.

9

Qq

Dl

1Q V I

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(5)

(6)

(7)

Use of the above correlations to estimate Nu is justified

when the fluid flow sections does not vary significantly from circular. Such channels may include square, rectangular (not too far from square), and probably equilateral or nearly equilateral triangles.

In case of fully turbulent flow along rod bundles, values

of Nu may remarkably deviate from the circular geometry due to geometric non-uniformity of the subchannels that creates substantial variation of Nu azimuthally. Apart from that for a given subchannel in a finite rod bundle, the effect of turbulence may affect adjacent subchannels differently depending on the location of subchannels with respect to the duct boundaries. Thus, the value of Nu is a function of position within the bundle.9

Therefore, for rod bundles, the Nusselt numbers for

fully developed conditions (Nu∞) is expressed as a product of (Nu∞)c.t. for a circular tube multiplied by a correction factor ψ as stated in Eq. (8):

(8)

where, (Nu∞)c.t. is usually given by Dittus-Boelter

equation unless otherwise stated.

For a square array and specifically for water with 1.1≤ P/D ≤1.3, Weisman10 has defined as follows:

(9)

and (10) Eq. (5) to (8) can be condensed in a simplified form as

shown in Eq. (11):

(11)

The values of constant coefficients i.e. a, β & b of Eq. (11) for different correlations are tabulated in Table I.

TABLE I

Constant Coefficients of Frequently Applied Correlations

Correlation Name a β b Dittus-Boelter 0.023 0.8 0.4 Sieder-Tate 0.027 0.8 0.333 Silberberg-Huber Weisman (P/D 1.286)

0.016 0.030

0.85 0.8

0.3 0.333

If it is assumed that Prandtl number Pr does not change during experiment, the following equation can be substituted in place of Eq. (11):

(12)

where, (13)

Again, Eq. (12) can be written in the following form

using logarithmic function:

(14) The above equation is equivalent to a first degree

polynomial (i.e. y=ax+b). Now, if we re-evaluate Nu and Re according to our experimental condition and plot Eq. (14), we can obtain the modified values of coefficient α and β for NANO rod-bundle assembly.

The experimental values of Nu can be obtained using

following equation based on hydraulic diameter Dh (m) of the flow channel and thermal conductivity k (W/m.K), at coolant bulk temperature:

(15)

Where, h is the convective heat transfer coefficient for

fully developed turbulent flow and it can be estimated using following equation:

(16)

where, TW and Tb are central heater rod wall surface temperature and mean bulk fluid temperature respectively.

In our present study, the experimental Nu is computed

using Eq. (15) and (16) and values thus obtained is compared (in Table II) with the Nu obtained by most renowned correlations as presented through Eq. (5) to (8) for a wide range of Re ranging from 10,082 to 20,904. Variations of experimental Nu with Re for central heater rod is plotted in Fig.6. Finally, using logarithmic function as shown in Eq. (14), Nu obtained by experiment and different correlations are plotted against inlet Re in Fig.7 and by fitting a curve featuring first degree polynomial the values of coefficient α and β in Eq. (14) are modified for NANO test apparatus. The new values of α and β for experiment and different correlations are presented in Table III. A similar study was carried out by Makhmalbaf7 for a vertical hexagonal rod bundle with 7 vertical rods in a hexagonal tube featuring 1.4 cm tube hydraulic diameter and the results of NANO experiment have been compared with that of Makhmalbaf7 in Table IV.

The analogy shows that Nu obtained by NANO

experiment significantly varies from those obtained by different correlations for same inlet Re. The correlations used in this study predicts Nu based on only two

0.8 0.40.023Re PrNu 0.14

0.8 0.3330.027 Re PrW

Nu

0.85 0.30.016 Re PrNu ReNu

Prba

ln ln ln ReNu

hh DNu

k

W b

qh

T T

. .c t

Nu Nu

0.8 0.333

. .0.023 Re Pr

c tNu

1.826 1.0430PD

Re PrbNu a

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dimensionless parameters namely inlet Reynolds number and Prandtl number. But in reality, more complex phenomenon such as geometry of coolant flow channel, velocity & temperature gradient of coolant, contact time between heater rod and coolant, heated length of heater rod, heater capacity, heat loss through insulation, precision of sensing device e.g. thermocouples, pressure transducers, flow meters etc. may directly affects the value of Nusselt number and convective heat transfer coefficient.

One pivotal reason behind low Nu obtained by NANO

experiment may be slow sensing capacity of thermocouples to rapid temperature change used in NANO apparatus. Moreover, due to high flow velocity inside the flow channel, the contact time between coolant and heater rod was short and hence experimental ∆T between inlet and outlet temperature of coolant was not so high. Therefore, the total heat input as well as experimental Nu as computed by Eq. (4) and (15) respectively, also became small compared to predictions made by different correlations.

Apart from that, although spacer grids are originally designed to maintain proper geometrical configurations of the rod bundle, it also plays a significant role on heat transfer enhancement by disrupting and re-establishing the thermal boundary layers. Spacer grids may have various special geometrical features to promote turbulence such as mixing vanes of different configurations. For example, while the split vanes may deflect the upward flow to mix between neighboring subchannels, the swirl vanes are designed to generate a pronounced swirling flow within subchannel. Another innovative design is twisted vanes having two mixing vanes at the upper ends of the interconnections between straps which are bent in opposite directions at the top slope of the triangular base to generate a cross flow between subchannels as well as swirling flow in the subchannel by regulating flow simultaneously to the fuel rod and to the gap region. Due to high cost and complexity of manufacturing, grid spacers used in NANO rod bundle are very simple in design having no mixing vanes, which in turn failed to promote turbulence as well as heat transfer rate from heater rod to coolant and hence, it is assumed as another key reason behind low Nu obtained by experiment.

TABLE II

Comparison of Nu Obtained by Experiment and Correlations

Inlet Re Nusselt Number NANO

Exp. Dittus-Boelter

Sieder-Tate

Silberberg-Huber

Weisman

10082.71 13173.32 17111.90 20904.95

15.14 20.45 22.69 25.64

63.90 79.14 97.57 114.51

70.89 87.79 108.23 127.03

57.52 72.20 90.18 106.91

76.01 94.13 116.05 136.20

TABLE III

Modified Constant Coefficients for Experiment and Different Correlations

Correlation Name α β NANO Experiment Dittus-Boelter Sieder-Tate Silberberg-Huber Weisman

0.026617 0.040055 0.044431 0.022740 0.047643

0.69 0.8 0.8 0.85 0.8

TABLE IV

Comparison of Modified Constant Coefficients with Hexagonal Rod Bundle Experiment by Makhmalbaf7

Correlation Name

NANO Experiment (Square Rod

Bundle)

Makhmalbaf’s Experiment

(Hexagonal Rod Bundle) α β α β

Experiment Dittus-Boelter Sieder-Tate Silberberg-Huber

0.026617

0.040055

0.044431

0.022740

0.69

0.8

0.8

0.85

0.03337

0.0309

0.0345

0.0187

0.8112

0.8

0.8

0.875

Fig. 5. Comparison of heat input by electric power Q1 with enthalpy increase of coolant Q2.

Fig. 6. Comparison of Nu obtained by NANO experiment and different correlations

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Fig. 7. Plot of Nu against inlet Re using logarithmic function for NANO experiment and different correlations.

V. PRESSURE DROP RESULTS

The pressure drop across the NANO rod bundle assembly is experimentally measured by means of two digital differential pressure transducers (one at inlet of test section & another at outlet of test section as shown in Fig.2) for single phase turbulent flow. The pressure loss in the complex configuration of commercial spacers arises from several hydrodynamic effects included in the flow. The spacer is used to fix the rods in the bundle. The velocity and temperature distributions redeveloped due to the blockage of the flow cross section downstream of the spacer.

The Total Pressure drop for the test section of this study

is mainly aroused from the presence of inlet flow distributor, grid spacers, frictional loss along the piping of the test section, due to presence of various pipe fittings such as 900elbows, 1800 flow dividers etc., presence of sudden enlargement and contraction in the path of coolant flow & due to the effect of gravity. Hence, the theoretical pressure drop (∆P=Pin – Pout) can be expressed as follows:

(17)

In the above equation, pressure drop due to spacer grids

& inlet flow divider has been calculated using the following correlation of Rehme: 10

(18)

where, Cv is modified drag coefficient, Vv is average bundle fluid velocity, Av is unrestricted flow area away from the grid or spacer and As is projected frontal area of the spacer. The drag coefficient (Cv) is a function of average bundle, unrestricted area Reynolds number. In this study

value of Cv is taken as 9.5 (at Re =104) as indicated by Rehme’s data for square arrays.10

The frictional pressure drop has been calculated by

using the following equation:

(19)

where, f is the average friction factor depends on the

channel geometry and flow velocity. In case of turbulent flow, Rehme10 proposed a method

to obtain the friction factor for subchannels in actual geometry. Cheng and Todreas11 fitted results of this method with polynomial of Eq. (20) as presented below:12

(20)

for turbulent flow,

(21)

The above correlation can be used to obtain friction factor in square array subchannel if the coefficients a, b1 and b2 are evaluated using Table 9-3 as documented by Todreas & Kazimi.12

To obtain friction factor for circular piping of the

NANO apparatus, Mc Adams and Blasius correlations have been used as presented in Eq. (22) and Eq. (23) respectively:

Mc Adams (for 30,000 ≤ Re ≤106):

(22)

Blasius (for Re ≤ 30,000):

(23)

Pressure drop due to gravity and form loss due to presence of abrupt change in flow directions and sudden expansion/contraction have been estimated by using Eq. (24) and (25) respectively:

(24)

(25)

Comparison of experimental pressure drop with that of

estimated for different inlet Re has been tabulated in Table V and plotted in Fig.8. Percentage of estimated pressure drop caused by different components present in NANO apparatus is shown in Fig.9.

The results demonstrates that estimated pressure drop

falls within 5% to 18% of the experimental pressure drop

Estimated SpacerGrid Friction Gravity FormP P P P P

22

2V S

SpacerGrid V

V

P CV A

A

2

2Friction

h

P fL V

D

2/

1 21 1fiTP PC a b bD D

/

0.18/Re

fiT

iT

iT

Cf

0.20.184 Ref

0.25

0.316Re

f

cosGravityP g Z 2

2Form formP kV

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depending on inlet velocity. Note that as the flow velocity is decreased, effect of grid spacers on pressure drop is also lessened and effect of gravity starts to prevail (Fig.9) which is logical as the test section is vertical. In case of the lowest inlet Re, pressure drop due to the effect of gravity is almost 69% of the total pressure drop. It is extremely difficult to establish a pressure loss coefficient correlation of general validity for grid spacers because of variation and complexity of the grid spacer geometry.

VI. CONCLUSION

The present study has been carried out on 3×3 square

array vertical rod bundle housed in a square shell with single phase turbulent flow covering a range of Re from 7,463 to 20,904 and mass flow rate (kg/sec) from 0.60 to 1.33. During analysis of convective heat transfer, the applicability of well-known correlations from literature has been verified for NANO rod bundle and finally a new correlation with modified values of constant coefficients (α and β as documented in Table III) has been proposed which is proprietary of NANO apparatus. It has been observed that due to change in channel geometry and pitch to diameter ratio, these constant coefficients also changes, hence for greater accuracy it is necessary to modify these coefficients based on experiments when a new rod bundle is constructed.

In case of pressure drop, it is observed that deviation

between experimental and estimated pressure drop lies within acceptable range which indicates that NANO apparatus is capable of measuring pressure drop as well as pumping power requirement satisfactorily.

Despite the primary objective of this experiment is to

investigate the thermal-hydraulic capabilities of alumina nanofluids (Al2O3) in terms of heat transfer and pressure drop, only pure water data are presented in this paper since the experiment using different volume concentrations of alumina nanofluid as coolant is still underway.

Fig. 8. Plot of experimental and estimated pressure drop against inlet Re.

Fig. 9. Percentage of estimated pressure drop caused by different components of NANO apparatus.

TABLE V

Comparison of Experimental and Estimated Pressure Drop

Inlet Re ∆P (Bar) (Experiment)

∆P (Bar) (Estimated)

Deviation (%)

7463.18 10082.71 13173.32 17111.90 20904.95

0.38 0.50 0.63 0.80 0.93

0.35 0.44 0.54 0.66 0.76

5.87 12.12 14.35 17.56 18.30

ACKNOWLEDGMENTS This work was supported by the National Research

Foundation of Korea (NRF) grant funded by the Korean Government (MSIP) (No. 2008-0061900) and partly supported by the Brain Korea 21 Plus Project (No. 21A20130012821).

NOMENCLATURE Cv Drag Coefficient - ∆P Pressure Drop Bar ρ Density kg/m3 V Flow Velocity m/s hf Head Loss m f Friction Factor - L Length of Flow Channel m l Heated Length of Heater Rod m

Dh Hydraulic Diameter m g Gravity Constant m/s2 μ Dynamic Viscosity of Water N s/m2

∆Z Changes in Elevation between flow inlet and outlet of test section

m

cosα Angle with the vertical in the direction of flow.

Degree

Re Reynolds Number -

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Nu Nusselt Number - Pr Prandtl Number - Pe Peclet Number - Gr Grashof Number - μb Fluid Viscosity at Fluid Bulk

Temperature N s/m2

μw Fluid Viscosity at Pipe Wall Temperature

N s/m2

h Convective Heat Transfer Coefficient W/m2.K k Thermal Conductivity of Water W/m.K

Cp Specific Heat of Water J/kg.K Tb Bulk Temperature of Water K Tw Surface Temperature of Heater Rod K P Rod Pitch m D Rod Diameter m Q Total Heat Input W q Heat Flux W/m2 푚̇ Mass Flow Rate kg/sec x Side of Square Duct m Av Unrestricted Flow Area Away from

the Grid or Spacer m2

As Projected Frontal Area of the Spacer. m2 Vv Average Bundle Fluid Velocity m/s

Kform Form Loss Coefficient -

REFERENCES

1. F. D’AURIA, “Perspectives in System Thermal-Hydraulics,” Nuclear Engineering and Technology, 44, 8, 855-870 (2012).

2. K. Y. SUH and N. E. Todreas, “An Experimental Correlation of Cross Flow Pressure Drop for Triangular Array Wire Wrapped Rod Assemblies,” Nucl. Technol, 76, 229 (1987).

3. A. M. DESTORDEUR, “Drag Coefficients for Fuel Elements Spacers,” Nucleonics, 19, 6, 74 (1961).

4. K. REHME, “Simple Method of Predicting Friction Factors of Turbulent Flow in Non-circular Channels,” Int. J. Heat Mass Transfer, 16, 933 (1973).

5. T. H. CHUN and D. S. Oh, “A Pressure Drop Model for Spacer Grids With and Without Flow Mixing Vanes,” J. Nucl. Sci. Technol., 35, 508-510 (1998).

6. M. CIGARINI and M. Dalle Donne, “Thermohydraulic Optimization of Homogeneous and Heterogeneous Advanced Pressurized Reactors,” Nucl. Technol. 80, 107-132 (1998).

7. M. H. M. MAKHMALBAF, “Experimental Study on Convective Heat Transfer Coefficient around a Vertical Hexagonal Rod Bundle,” Heat Mass Transfer, 48, 1023-1029 (2012).

8. H.M. SON and K.Y. Suh, “Automated Scoping Methodology for Liquid Metal Natural Circulation

Small Reactor,” Nuclear Engineering and Design, 274, 129-145 (2014).

9. N. E. TODREAS and M. S. Kazimi, Nuclear Systems I: Thermal Hydraulic Fundamentals, page 442-451, Hemisphere Publishing Corporation, USA (1990).

10. K. REHME, “Pressure Drop Correlations for Fuel Elements Spacers,” Nucl. Technol., 17:15 (1973).

11. S.K. CHENG and N.E. Todreas, “Hydrodynamic Models and Correlations for Wire-wrapped LMFBR Bundles and Subchannel Friction Factors and Mixing Parameters,” Nucl. Eng. Design, 92:227 (1985).

12. N. E. TODREAS and M. S. Kazimi, Nuclear Systems I: Thermal Hydraulic Fundamentals, page 384-386, Hemisphere Publishing Corporation, USA (1990).

ANNEXURE A

Specification of Heater Assembly Region

Description Unit Value Number of Heater Rods Nos. 9 Configuration - Square Array (3×3) Heater Rod’s Diameter mm 9.8 Heater Rod’s Length mm 2150 Heated Length mm 2000 Rod Pitch mm 12.6 Pitch to Diameter - 1.286 Grid Spacer Height mm 30 Grid Spacer Frontal Area mm2 920.25 Vertical Spacing between Grid Spacers

mm 600

Inlet Distributor Thickness

mm 5

Inlet Distributor Frontal Area

mm2 1241.887