Heat transfer and hydraulic characteristics of micro finned tube inserted with twisted tape inserts and hybrid nanofluid (CNT/Al₂O₃)

1

ABSTRACT

This paper communicates the enhancement of heat transfer, friction characteristics and thermal performance of micro finned tube fitted with Left/Right and regular insert tape inserts using CNT and CNT/Al₂O₃ nanofluid. Two different concentrations of nanoparticles were used in the present investigation. In contrast, the CNT/Al₂O₃ nanoparticles are mixed in a weight ratio (50:50) and sonicated for about 2 hours using a bath type sonicator. The prepared nanofluids are stable for almost 48 hours without any sedimentation. Results show that the increase in nanoparticle concentration in the base fluid increases the performance index under turbulence flow regime while the Reynolds number in the range of 2000< Re<5500. Similarly, the Nusselt number and friction increase by 250% and 400%, respectively, with the maximum concentration of nanoparticle and minimum twist ratio. Results also reveal that the use of alternate arrangement increases the turbulence for maximum friction gain and improvement in the convective heat transfer coefficient.

KEYWORDS:

• Heat transfer
• friction factor
• hybrid Nanofluid
• twisted tape Inserts

Nomenclature

Al₂O₃–Aluminium oxide

A–Area (m²)

avg–Average

CNT–Carbon nano tubes

d – Diameter (m)

μ–Dynamic Viscosity

f – Friction factor

Q – Heat flux (W/m²)

Al₂O₃/CNT-Hybrid Alumina – Carbo Nano Tubes Nanofluid

i – Inlet

T_w,in–Inlet fluid temperature

LR–Left Right

LRT – Left right tape

MWCNT – Multiwall Carbon Nano Tubes

Nu – Nusselt number

Nu_plain–Nusselt number of plain tube

o – Outlet

T_w,out–Outlet fluid temperature

Pr – Prandtl number

Re – Reynolds number

C_pnf–Specific heat of nanofluid

T_s–Surface temperature

k – Thermal conductivity (W/mK)

K_nf–Thermal conductivity of nanofluid

u – Velocity (m/s)

ϕ-Volume concentration

w – Water

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the DST/SERB [SB/FTP/ETA-444/2012].