A Uniquely Finned Tube Heat Exchanger Design of a Condenser for Heavy-Duty Air Conditioning Systems (original) (raw)

This study introduces the design of a novel condenser for air conditioning systems. Enhancement of performance of the system was manifested by increasing the coe±cient of performance (COP), decreasing the pressure drop and the power consumed by the refrigerant compressor and the cooling water pump. The design consists of an adiabatic double-pipe heat exchanger with longitudinal rectangular¯ns. This model can enhance heat transfer coe±cient and expose more area per unit length. This novel design supersedes other conventional condenser designs by 4.7% higher COP, 8.2% lower water pressure drop, 4.68% lower compressor power. Two refrigerants have been examined in the study; R-134a which is used in commercial and industrial chillers and R-1234ze which has low global warming potential. A i Cross-sectional area of the inner pipe, m 2 A o Cross-sectional area of the outer pipe, m 2 A s Total heat transfer area of the heat exchanger, m 2 A sÀd Total surface area at design point, m 2 B Length of the¯n, m C Capital cost, $ C d Capital cost at design point, $ d e Hydraulic mean diameter for heat transfer, m d ef Hydraulic mean diameter for pressure drop, m d i Inner pipe diameter, m d o Outer pipe diameter, m d iÀd Inner pipe diameter at design point, m D oÀd Outer pipe diameter at design point, m E Dimensionless function E F Friction factor F Dimensionless function F Fr Froude number G Mass°ow rate per unit area, kg m À1 s À1 H Heat transfer coe±cient, W m À1 K À1 , speci¯c enthalpy, kJ kg À1 H Dimensionless function K m Thermal conductivity of carbon steel, W m À1 K À1 K R Thermal conductivity of refrigerant, W m À1 K À1 K w Thermal conductivity of water, Q m À1 K À1 L Length of heat exchanger, m _ m R Mass°ow rate of refrigerant, kg s À1 _ m w Mass°ow rate of water, kg s À1 n f Number of¯ns n fÀd Number of¯ns at design point N sNumber of heat exchangers Nu Nusselt number N d Number of heat exchangers at design point P 1 Pressure of refrigerant in the condensation and de-super heating stages, kPa P 2 Pressure of cooling water P R Total pressure drop of refrigerant in the condensation and de-super heating stages, kPa P RÀd Total pressure drop of refrigerant in the condensation and de-super heating stages at design point, kPa P w Total pressure drop of water, kPa P W Àd Total pressure drop of water at design point, kPa P wh Perimeter for the heat transfer in the outer surface of the inner pipe and the surface of the¯ns, m P wf Perimeter for pressure drop in the outer surface of the inner pipe and the surface of the¯ns plus the inner diameter of the outer pipe, m Pr Prandtl Number _ Q w Volume°ow rate of water, m 3 s À1 q′ Heat transfer rate per unit length, kW m À1 q 0 d Heat transfer rate per unit length at design point, kW m À1 R Thermal resistance, m 2 K W À1 Re Reynolds number S T Total heat transfer surface area, m 2 S base Base surface area of heat transfer per unit length, m S fin Fin surface area per unit length, m S′ Surface area per unit length of the annulus, m t i Thickness of inner pipe, m t o Thickness of outer pipe, m T Temperature, o C U o Overall heat transfer coe±cient of the system, W m À1 K À1 V Velocity, m s À1 We Weber number X Quality (dryness fraction %) Greek symbols H E±ciency E®ectiveness M Viscosity, kg m À1 s À1 P Density, kg m À3 Thickness of the¯n, m È Condensation mass°ux factor Subscripts