Gas-dynamic losses in high-speed hermetic compressors for shipboard air-conditioning systems and methods for their reduction

Abstract

The results of research gas dynamical performances of valving knots and gas ducts of high-turning hermetic compressors of marine air conditions were presented. The numerical values of resistance coefficients of valving knots and ducts, the values of gas velocities in it and dependence this performances from operating condition of compressor were conducted. Purpose. Investigation of the gas-dynamic characteristics in the suction and discharge valve assemblies and in the corresponding gas-flow passages of high-turning reciprocating freon compressors is of particular importance for identifying ways to reduce energy losses. Method. The gas-dynamic characteristics were investigated by simulating the working medium: instead of refrigerant, the valve assemblies and channels were blown through with compressed air. The modelling was approximate because the adiabatic exponents of air and the refrigerant are not identical. During testing, the gas-flow regime was maintained according to the Reynolds criterion Rec, referred to the cylinder cross-sectional area; that is, the cylinder diameter dc was taken as the determining dimension, since for a given design the geometrical ratios in the valve assembly depend only on the cylinder diameter. The suction path of the compressor under study included the channels between the rotor and stator of the electric motor and the longitudinal grooves used for welding the stator stack; the channel in the crankcase block leading to the suction cavity of the cylinder head; the ports in the valve plate; and the suction valve. The space between the compressor casing and the compressor itself was not considered because losses in this part of the suction path are small. The discharge path of the compressor consisted of the channels in the valve plate; the discharge valve with its buffer plate and lift limiter; the discharge cavity of the cylinder head, connected by a short pipe to the receiver; the receiver, which served as the compressor muffler; and the discharge tube up to the outlet connection. Such configurations of the suction and discharge paths are typical of most marine hermetic compressors. Results. The experimental results showed that, for the considered class of high-speed compressors, the value of ζv for annular valves lies within the range 2.4–4.2, which is approximately 1.5–2 times higher than the values recommended in the literature for annular valves of reciprocating refrigeration compressors. As a result of the tests carried out with air and with refrigerant, the values of the resistance coefficient ζp forthe compressor gas passages were obtained: 3.6 for the discharge path and 4.5 for the suction path Scientific novelty. Using the obtained values of ζp and the recommended gas velocities in passage elements, the crosssections of the discharge tube and the suction ports in the valve plate were calculated. The calculation showed that the cross-section of the flow channels in the electric motor was reduced and that the resistance of the suction path increased. The flow cross-sections of the channels in the electric motor can be increased by 15–20 %, and, as a consequence, compressor power consumption can be reduced by approximately 2 %, by widening the grooves used for welding the stator stack. Practical importance. The study results were used in the development and refinement of new hermetic compressors with shaft rotational speeds of 50 s-1 and 66.7 s-1 for marine air conditioners.