Characteristics of R718 Thermal Systems and Possibilities for Implementation in Refrigeration / Heat Pump Systems in Buildings

Regulations for CFCs and HCFCs refrigerants phase out and HFCs and HFEs reduction and renewed interest in natural refrigerants (water R718, CO2 R744, ammonia R717, air, hydrocarbons etc.) are discussed. Thermodynamic properties of water (R718) are analyzed and benefits of applicationas well as challenges in the implementation of R718 systems are explained. Deep vacuum operating conditions and low specific volumetric cooling capacity of R718 are peculiarities that cause large and extremely large volumetric flow rates for the temperature range of refrigeration / heat pump air –conditioning applications. The required pressure ratio for a given temperature lift is high. The high value of the water isentropic exponent causes high temperature at the compressor discharge. The specifics in the R718 turbo compressors caused by that reasons are analyzed and the range of optimum application of R718 refrigeration / heat pump systems are estimated

Influence of Different Gases on the Design Point of an Industrial Axial Compressor and Deduced Aerodynamical Rematching Methodology

This paper presents a numerical investigation of the effects of compressing various gases, for example, carbon dioxide (CO2) and methane (CH4), on an eight-stage axial air compressor. Several adaptation methods are applied to achieve a similar operating point as for air. Theoretically, the operating point depends on Mach number, flow angles, Reynolds number and isentropic exponent. Numerical results show mismatch effects which arise in the parameters using a non-adapted geometry. A rematching procedure is described, including deduced speed adjustments, in order to achieve Mach number equality at compressor inlet. Only shroud modifications are performed to rematch the flow angles of the air simulation. Although Reynolds and Mach number are kept constant at compressor inlet, an inevitable deviation in downstream flow causes mismatches in efficiency and pressure ratio. Both analytical and numerical methodologies show that the scale of shroud adjustments, as well as the size of mismatch in Mach and Reynolds number, can be correlated to the isentropic gas exponent. In summary, the main impact on gas behavior in an axial air compressor is attributable to the change in isentropic exponent. Derivations of shroud adaptation and analyses of inevitable aerodynamic mismatch are therefore developed depending on the isentropic exponent.

The Effect of Isentropic Exponent on Transonic Turbine Performance

The isentropic exponent is one of the most important properties affecting gas dynamics. Nonetheless, its effect on turbine performance is not well known. This paper discusses a series of experimental and computational studies to determine the effect of isentropic exponent on the flow field within a turbine vane. Experiments are performed using a newly modified transient wind tunnel that enables annular cascade testing with a wide range of working fluids and operating conditions. For the present study, tests are undertaken using air, CO2, R134a, and argon, giving a range of isentropic exponent from 1.08 to 1.67. Measurements include detailed wall static pressures that are compared with computational simulations. Our results show that over the range of isentropic exponents tested here, the loss can vary between 20% and 35%, depending on vane exit Mach number. The results are important for future turbines operating with real-gas effects and/or those where high gas temperatures can lead to variations in the isentropic exponent.

The Effect of Isentropic Exponent on Transonic Turbine Performance

The isentropic exponent is one of the most important properties affecting gas dynamics. Nonetheless, its effect on turbine performance is not well known. The paper discusses a series of experimental and computational studies to determine the effect of isentropic exponent on the flow field within a turbine vane. Experiments are performed using a newly modified transient wind tunnel which enables annular cascade testing with a wide range of working fluids and operating conditions. For the present study tests are undertaken using air, CO2, R134a and argon, giving a range of isentropic exponent from 1.08–1.67. Measurements include detailed wall static pressures which are compared with computational simulations. Our results show that over the range of isentropic exponents tested here, the loss can vary by between 20%–35%, depending on vane exit Mach number. The results are important for future turbines operating with real-gas effects and/or those where high gas temperatures can lead to variations in isentropic exponent.

(P,ρ,T) properties of 1-octyl-3-methylimidazolium tetrafluoroborate

(p,?,T) data of 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF4] over a wide range of temperatures, from 278.15 to 413.15 K, and pressures, p, up to 140 MPa are reported with an estimated ?0.01?0.08 % experimental relative average percent deviation (APD) in the density. The measurements were performed using an Anton Paar DMA HPM vibration tube densimeter. (p,?,T) Data for [OMIM][BF4] was fitted and the parameters of the applied equation were determined as a function of pressure and temperature. After a thorough analysis of literature values and validity of the used equation of state, various thermophysical properties, such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, internal pressure, heat capacities at constant pressure and volume, speed of sound and isentropic exponent at temperatures in the range 278.15?413.15 K and pressures p up to 140 MPa were calculated.