Automatic Control of a 0.3 m Cryogenic Test Facility

Abstract

Studies have been undertaken to mathematically model the cryogenic wind-tunnel process, validate the model by the use of experimental data from the 0.3 m transonic cryogenic tunnel, and construct an interactive simulator of the cryogenic tunnel using the validated model. Additionally, this model has been used for designing closed-loop feedback control laws for regulation of temperature and pressure in the 0.3 m transonic cryogenic tunnel. The global mathematical model of the cryogenic tunnel that has been developed consists of coupled nonlinear differential governing equations based on an energy state concept of the physical cryogenic phenomena. Process equations and comparisons between actual and computer simulation predictions of tunnel response are given. Also included are the control laws and simulator and tunnel responses obtained using the feedback schemes for closed-loop control of temperature and pressure. These data show that the microprocessor-based proportional-integral control laws for pressure and temperature regulation have yielded very good closed-loop results. Nomenclature A -area, m 2 or percent of valve opening b = pressure loss coefficient c m = specific heat of metal, J/kg-K c p = specific heat of gas at constant pressure, J/kg-K c v = specific heat of gas at constant volume, J/kg-K D = dimensionality constant E = internal energy, J GN 2 = gaseous nitrogen K = gain LN 2 = liquid nitrogen rh = mass flow rate, kg/s M = Mach number TV = fan speed, rpm p = total pressure, atm Q = heat flow, J/s r = pressure ratio s = Laplacian mathematical operator t -time and time constant, s T = total temperature, K V = volume, m 3 W = mass, kg a. = cooling capacity of gaseous nitrogen, J/kg 0 = cooling capacity of liquid nitrogen, J/kg 0 = thermal mass, J/K T = transport time lag, s 77 = fan efficiency 7 = ratio of specific heats Subscripts a c F G L m = acoustic = tunnel circuit = fan = gas = liquid = metal