Simple model and control strategy of earth-to-air heat exchangers
The worldwide energy situation forces industrialized countries to reduce their energy consumption, especially in the building sector, which makes up a high proportion of the total consumption. Techniques such as earth-to-air heat exchangers must therefore be developed and managed to meet this challenge. Yet earth-to-air heat exchangers provide better performance when linked to efficient control strategies.
Analytical characterisation of amplitude dampening and phase-shifting in air/soil heat-exchangers
This article presents the complete analytical solution for the heat diffusion of a cylindrical air/soil heat-exchanger with adiabatic or isothermal boundary condition, submitted to constant airflow with harmonic temperature signal at input. It will be shown that, depending on its thickness, the soil layer will induce either one of two kinds of amplitude-dampening and phase-shifting regimes of the periodic input signal. In particular, for a thin layer submitted to adiabatic boundary condition, it is possible to completely phase-shift the periodic input while barely dampening its amplitude, a phenomenon apparently unexploited up to now, which might give rise to interesting energy handling techniques. Analytical results are validated against a finite-difference numerical simulation model as well as against an experimental setup.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.