Experimental analysis of wet gas-liquid water mixture within the tank of water in glass evacuated tube solar water heater

ABSTRACT

In this investigation, thermal performance characteristics of passive solar water heater with vacuum tube were experimentally studied by using the mixture of wet gas and liquid water. Five different outlet locations of the tank were used to produce five different proportions of wet gas-liquid water mixtures. Experimental results were proposed in the way of water temperature, gas temperature, thermal stratification number, temperature distribution zone and a correlation for thermal efficiency through wet gas proportion. It was concluded that the wet gas-liquid water mixture at a wet gas proportion of 70% ameliorates the water temperature and thermal stratification number by respectively 13.7°C and 10.33 times compared to the mixture at a wet gas proportion of 10%. For different wet gas-liquid water mixtures, temperature distribution zone shows a quadratic parabola. The correlation for thermal efficiency through different proportions of mixtures presents the regularity of linear regression equation. Also, the average R² and average Root Mean Square Error (RMSE) of regression analysis correlation are calculated as 0.936 and 0.375, respectively. The novelty of this work is evaluating the effect of different proportions of wet gas-liquid water mixture on the thermal performance and thermal stratification of passive vacuum tube solar water heater, and develop a correlation for thermal efficiency through different proportions of mixture.

KEYWORDS:

• Thermal performance characteristics
• passive solar water heater
• wet gas-liquid water mixture
• different proportions
• thermal stratification

Nomenclature

Ah	=	top half of collector area [m2]
Atank	=	surface area of the tank [m2]
Cpg	=	specific heat of wet gas [J/kgK]
Cpw	=	specific heat of water [J/kgK]
D	=	inner diameter of the water storage tank [mm]
ΔEheater	=	variation of thermal energy of solar water heater [J]
Fo	=	Fourier number
hht-tank	=	heat transfer coefficient of the tank[W.m−2.K−1]
H	=	height from storage tank top [mm]
I	=	solar radiation intensity [W.m−2]
mw	=	mass of water within the solar water heater [kg]
P	=	instrument error
QE-heater	=	useful energy of solar water heater [J]
Qh	=	input energy [J]
Qht-tank	=	radiant heat from the tank [J]
ST	=	thermal stratification number
Δt	=	timescale [s]
Tave	=	average temperature within the tank [K]
Ti	=	ambient temperature [K]
Tg1	=	initial wet gas temperature of tank [K]
Tg2	=	final wet gas temperature of tank [K]
Ts	=	tank shell temperature [K]
Tw1	=	initial water temperature of solar water heater[K]
Tw2	=	final water temperature of solar water heater[K]
Tmax	=	maximum water temperature within tank [K]
Tmin	=	minimum water temperature within tank [K]
t	=	time[s]
ttot	=	total solar radiation time[s]
u	=	uncertainty
Vn	=	nominal volume of storage tank [m3]
x	=	proportion of the wet gas
ε	=	emissivity
η	=	thermal efficiency [%]
ρg	=	density of the wet gas [kg/m3]
σ	=	Boltzmann constant [W.m−2K−4]
τ	=	dimensionless solar radiation time τ=t/ttot

Acknowledgment

This paper is supported by the Major Science and Technology Project of the Xinjiang Production and Construction Corps (No.2018AA003).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the Major Science and Technology Project of the Xinjiang Production and Construction Corps [No.2018AA003].