Three-dimensional simulation and experimental validation of solar air heater having sinusoidal rib

ABSTRACT

A new geometry of roughness in the sinusoidal form has been investigated computationally using Computational Fluid Dynamics (CFD) software for examining the influence of roughness on heat transfer and fluid friction in solar air heater and results obtained have been compared with experimental results. The simulated results for smooth solar air heater are compared with Dittus-Boelter equation for heat transfer and Blasius equation for fluid friction. The deviation of simulated results are found to be 7.55% and 16.91%, respectively. In order to validate the simulated results experimental test rig was fabricated and experiments were carried out for the same set of parameters used in the simulation. The experimental results indicate that for the roughened absorber plate having a sinusoidal rib, the variation in heat transfer is within 9% from that of simulated results and for fluid friction, deviation is within 4%. The optimal value of thermohydraulic performance (THP) is obtained 2.05 for roughness pitch (P) = 10 mm and Reynolds number (Re) = 4000, where enhancement ratio of Nusselt number (Nu_r/Nu_s) and friction factor (ƒ_r/ƒ_s) are 2.48 and 1.76, respectively. The experimental value of THP is found to be within 6.77% of the value indicated by CFD analysis. The results are also compared with the triangular and square rib and found that the optimal THP of the proposed rib is 20.06% and 33.31% more.

KEYWORDS:

• Sinusoidal
• three-dimensional simulation
• thermohydraulic performance
• solar air heater
• optimal

Nomenclature

${\mathrm{T}}_{\mathrm{o}\mathrm{u}\mathrm{t}}$	=	Temperature of air at Outlet (K)
${\mathrm{T}}_{\mathrm{i}\mathrm{n}}$	=	Temperature of air at inlet (K)
${\mathrm{T}}_{\mathrm{m}}$	=	Mean fluid temperature (K)
${\mathrm{T}}_{\mathrm{w}}$	=	Average temperature of the absorber plate (K)
h	=	Convective heat transfer coefficient (W/m2 K)
${\mathrm{A}}_{\mathrm{p}}$	=	Area of absorber plate (m2)
$P_f$	=	Prandtl number of air
$P_{f_t}$	=	Turbulent Prandtl number
ṁ	=	Mass flow rate of air (kg/s)
Nur /Nus	=	Nusselt number enhancement ratio
ƒr /ƒs	=	Friction factor enhancement ratio
ɳ	=	Thermohydraulic performance
ƒ	=	Friction factor
Abbreviation	=
THP	=	Thermohydraulic performance
SAH	=	Solar air heater
Re	=	Reynolds number
Nu	=	Nusselt number
3D	=	Three dimensional
Subscript	=
$i$	=	X Component
$j$	=	Y Component
r	=	Roughness
$out$	=	Outlet
s	=	Smooth
$in$	=	Inlet
m	=	Arithmetic mean
w	=	Wall surface
t	=	Turbulent
h	=	Hydraulic

Additional information

Notes on contributors

Sudhir Kumar

Sudhir Kumar is presently Research scholar in the department of Mechanical Engineering, National institute of technology, Patna. He obtained M. Tech (Mechanical Engineering) degree with specialization in Thermal Turbo Machinery from National Institute of Technology, Patna in 2015.

Suresh Kant Verma

Suresh Kant Verma is presently Professor in the department of Mechanical Engineering, National Institute of Technology, Patna. He obtained B.Sc (Engg.), M.Sc (Engg.) and Ph.D (Engg.) degree from Ranchi University, Ranchi. His area of interest is Heat Power Engg., Solar energy, Stirling Engine, Computational Fluid Dynamics.