Investigational analysis of roughened solar air heater channel having W-shaped ribs with symmetrical gaps along with staggered ribs

ABSTRACT

An investigational analysis upon heat exchange and friction misfortunes was led on the roughened rectangular solar-oriented air heater channel. The counterfeit roughness as W-shaped ribs utilizing symmetrical gaps alongside staggered ribs was made using round wires on one side of the wall as it were. The scope of parameters was viewed as using Reynolds number (Re) from 4000 to 14000, relative roughness pitch (P/e) 10–14, relative gap width (g/e) 0.5–2.0, relative staggered rib length (w/e) 1.5–6.0, relative staggered pitch (p/P) 0.45–0.75, number of gaps (n) 1–4, approach angle (α) 60°, relative roughness height (e/D_h) 0.0423, duct aspect ratio (W/H) 10. Utilizing these parameters in the picked range, the far-reaching examination of the framework has been practised. The most extreme growth in Nusselt number proportion was recorded 4.10 practically equivalent to Re = 12000, P/e = 12, g/e = 1, w/e = 4.5, p/P = .65 and n = 2. THEP was likewise determined and the most extreme improvement was observed to be 3.24.

KEYWORDS:

• Solar air heater
• heat transfer
• friction factor
• staggered ribs
• W-shaped ribs
• thermo-hydraulic efficiency

Nomenclature

$A_o$	=	cross-segment region of the opening, m2
$A_p$	=	absorber plate area, m2
$C_d$	=	coefficient of discharge of orifice
$C_p$	=	specific heat of at constant pressure, J kg−1 K−1
Dh	=	hydraulic diameter, m
e	=	rib height, m
g	=	width of gap, m
H	=	duct depth, m
h	=	convective heat exchange coefficient, W m−2K
ka	=	air thermal conductivity, W m−1K
L	=	length of test section, m
$\dot{m}$	=	mass flow rate, kg s−1
P	=	rib pitch, m
p	=	staggered rib pitch, m
$Q_a$	=	heat exchange rate, W
$\mathrm{\Delta }{P}_d$	=	pressure drop crosswise over conduit test segment, N m−2
$\mathrm{\Delta }{P}_o$	=	pressure drop crosswise over orifice plate, N m−2
Tin	=	air temperature at inlet, K
Tout	=	outlet air temperature, K
$T_{mp}$	=	area weighted average plate temperature, K
$T_{mf}$	=	mean fluid temperature, K
V	=	channel air velocity, m s−1
W	=	width of channel, m
w	=	length of staggered rib, m

Dimensionless parameters

e/Dh	=	relative roughness height
f	=	friction factor of roughened surface
fs	=	friction factor of smooth surface
g/e	=	relative gap width
Nu	=	Nusselt number
Nus	=	Nusselt number of smooth surface
n	=	number of gaps
P/e	=	relative roughness pitch
p/P	=	relative staggered pitch
Pr	=	Prandtl number
Re	=	Reynolds number
THEP	=	thermo-hydraulic efficiency parameter
w/e	=	relative staggered length

Greek symbols

α	=	Approach angle for flow
β	=	proportion of hole distance across to pipe breadth
ρair,0	=	density of air at outlet temperature, kg m−3
ρair	=	density of air at mean fluid temperature, kg m−3
ϑ	=	kinematic viscosity of air, m2 s−1

Acknowledgments

The author accepts the financial support immensely in the form research stipend from MHRD, Govt. of India to carry out this work.

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Additional information

Notes on contributors

Sushant Thakur

Sushant Thakur completed his master degree in Energy Technology. And currently, he is a research scholar in Centre for Energy and Environmental Engineering, National Institute of Technology, Hamirpur, Himachal Pradesh, India.

N.S. Thakur

N.S. Thakur Thakur received his PhD from Indian Institute of Technology, Roorkee, India. his area of interests include Renewable energy, Heat transfer, thermal analysis of energy systems. He is presently a senior professor in Centre for Energy and Environmental Engineering, National Institute of Technology, Hamirpur, Himachal Pradesh, India.