Preliminary assessment of parabolic solar trough-driven ammonia-water absorption cooling system for Beirut

ABSTRACT

The demand for electric power has been increasing due to the increase in population and the development of the cities. Therefore, there is a need to avoid processes that use large amounts of electric power. Ammonia-water absorption systems run by replacing the electric compressor by a thermal-driven unit, for cooling or refrigeration. In this study, Beirut weather conditions are used to estimate the required heat input available from a 42 m² parabolic trough concentrating solar collector system that supplies heat to an ammonia refrigeration cycle. The highest COP attained was 0.65 at an evaporator temperature of −5°C. The required storage tank volume was found to be 2.6 m³ at the maximum available energy in July. The absorption system is seen to be capable of operating all day and night using solar energy in June and July.

KEYWORDS:

• Ammonia
• absorption
• refrigeration
• solar
• heat and mass transfer
• heat exchangers
• Beirut

Nomenclature

$A_{ap}$	=	Aperture area of the collector (L*W) (aaaaaaaa)
$E_{density}$	=	Energy storage density of the used material in the tank (kWh/m3)
$F^{\prime }$	=	Collector efficiency factor
$h_l$	=	Specific enthalpy in liquid phase (kJ/kg)
$h_g$	=	Specific enthalpy in gas phase (kJ/kg)
$v$	=	Specific volume of the ammonia–water solution (m3/kg)
${\dot{Q}}_E$	=	Heat rate absorbed by the evaporator (kW).
${\dot{Q}}_c$	=	Heat rate rejected by the condenser (kW).
${\dot{Q}}_G$	=	Heat rate absorbed by the generator (kW).
${\dot{Q}}_A$	=	Heat rate rejected by the absorber (kW).
${\dot{m}}_{ss}$	=	Strong solution mass flow rate (kg/s).
${\dot{m}}_{ws}$	=	Weak solution mass flow rate (kg/s).
$\epsilon$	=	Heat exchanger effectiveness.
${\dot{Q}}_u$	=	Solar useful heat gain (kW).
${\dot{Q}}_{sol}$	=	Total rate of solar radiation incident on the parabolic collector aperture
$U_L$	=	Overall collector heat loss coefficient (W/m2 ◦C)
$T_f$	=	Fluid temperature in collector
$T_{air}$	=	Air ambient temperature
x	=	Ammonia mole fraction in the liquid phase
$x_m$	=	Ammonia mass fraction in the liquid phase
y	=	Ammonia mole fraction in the gas phase
${\eta }_{op}$	=	Optical efficiency of collector system