Development of new correlations for heat transfer and friction loss of solid ring with combined square wing twisted tape inserts heat exchanger tube

ABSTRACT

An experimental analysis has been carried out for heat transfer and turbulent flow in a heat exchanger circular tube with solid ring with combined square wing twisted tape (TT) inserts. Experimentations are performed varying the solid ring with combined square wing TT insert parameters, such as changing the number of TT inserts $(N_{TT})$ from 1.0 to 4.0, ring pitch ratio $(d_R/D_T)$ from 0.5 to 2.0, wing pitch ratio $(P_W/W_T)$ from 2.0 to 3.5, wing depth ratio $(W_d/W_T)$ from 0.083 to 0.333, ring diameter ratio$(d_{iR}/d_{OR})$ from 0.831 to 0.932, and Reynolds number $\left(Re\right)$ in the range of 3,000–21,000. The experimental results show that the heat transfer is increased around 5.66 times more than the plane circular tube. The thermal hydrodynamic performance is evaluated for the optimum range of solid ring with combined square wing TT insert parameters. Statistical correlations are developed and a deviation of correlation data from the experimental data of Nusselt number and friction factor is about ± 9% and ± 6%, respectively. The correlation is helpful in prediction of the thermal performance for turbulent flow through a circular tube with solid ring with combined square wing twisted tape inserts.

KEYWORDS:

• Hydrodynamic
• solid ring
• twist ratio
• wing pitch ratio
• heat transfer

Nomenclature

$A_0$	=	Area of orifice plate, $m^2$
$C_p$	=	Specific heat capacity of air, $J/kgK$
$D_T$	=	Diameter of round pipe, $m$
$d_R$	=	Distance between rings, $m$
$d_{iR}$	=	Internal diameter of rings, $m$
$d_{oR}$	=	Outside diameter of rings, $m$
$d_{iR}/d_{OR}$	=	Ring ratio
$d_R/D_T$	=	Ring pitch ratio
$d_{TT}/W_{TT}$	=	Depth ratio
$f_{TT}$	=	Flow friction
$H_{TT}$	=	Head difference, $m$
$HET$	=	Heat exchanger tube
$K_{TT}$	=	Fluid thermal conductivity, $W/m.K$
L	=	Round pipe length, $m$
M	=	Mass stream rate of air, $kg/s$
$N_{TT}$	=	Number of twisted tapes
$N{u}_{TT}$	=	Nusselt number of solid ring with square wing inserts
ΔP	=	Pressure drop, $Pa$
$P_W$	=	Pitch between wings, $m$
$P_W/W_T$	=	Wing pitch ratio
$q_{TT}$	=	Heat flux, $\mathrm{W}$
$Q_u$	=	Heat gain, $W$
$Re$	=	Reynolds number
$R_{TT}$	=	Rayleigh number
$T_i$	=	Fluid inlet temperature, $K$
$T_m$	=	Mean temperature, $K$
$T_o$	=	Fluid outlet temperature, $K$
$TT$	=	Twisted tape
TTT	=	Typical twisted tape
$T_{TT}$	=	Total wall temperature, $K$
$T_L/W_T$	=	Twist ratio
$V_{TT}$	=	Airflow velocity, $m/s$
$W_d$	=	Wings’ depth, $m$
$W_T$	=	Width of tape, $m$
$W_d/W_T$	=	Wing depth ratio