The results of theoretical studies and experiments of the developed exhaust ventilation system with direct evaporative air- cooling with using “wet mats” are given. It has shown sufficient efficiency with increasing quality of flower cutting in the summer months. The effect of moisture on the operation of this system was studied. It is established that the heat absorption capacity of air directly depends on its temperature and relative humidity. It is also determined that the temperature of leaves and flowers in summer is usually 2 ÷ 7 °C greater than the air temperature in the greenhouses. In an experimental greenhouse, according to the results of experiments, the effectiveness of the developed installation for evaporative cooling of its operation was determined.

Coupled electroelasticity theory, acoustic approximation, and two-wire transmission line theory are used to study the generation of waves by a submerged cylindrical piezoelectric transducer connected by a cable to a source of nonstationary electric signals. The problem is reduced to a system of integral Volterra equations using the Laplace transform and analytical inversion of boundary conditions. The results of calculations for different cable lengths are presented Keywords: electroelasticity, piezoelectricity, generation of nonstationary waves, two-wire line Most studies on electroelasticity and hydroelectroelasticity have been carried out for time-periodic dynamic processes [5,8]. The significance of these results does not detract from the importance of such problems in a nonstationary formulation. This is due to the wide application of piezoceramic transducers that operate in pulse modes. There was a series of studies in which such problems were formulated assuming a potential difference between conductive coatings of the transducer. In addition to periodic publications (such as [12,13]), these results are partially generalized in the monograph [1] and review [14]. Of the recent studies on nonstationary continuum mechanics, it is worthwhile to mention the papers [9,16,17]. There are hydroelectroelastic systems where the piezoelectric transducer and the generator are spaced far apart and connected by a long cable. The influence of such a wire line on the transient characteristics was analyzed in [10,11,15], where the transducer is thin-walled and its behavior is described by the theory of electroelastic shells based on the Kirchhoff-Love hypotheses [5].The present paper addresses the problem of wave generation by a thick-walled, infinitely long, cylindrical piezoelectric transducer immersed in a perfect compressible liquid. The solid conductive coatings on the inner and outer surfaces of the transducer are connected by a two-wire line with distributed parameters (cable) to a source of nonstationary electric signals. The medium inside the cylinder is vacuum. A similar problem where a transducer is excited by a signal supplied directly to its electrodes was solved in [2].The dynamic processes in the hydroelectroelastic system in question are modeled using coupled electroelasticity theory [5], acoustic approximation, and two-wire transmission line theory [3].We will use the following notation: u r is the radial displacement of the transducer; σ rr and σ θθ are the radial and circumferential components of the stress tensor; Ψ and D r are the potential and electric displacements of the electric field; C E 11 , C E 13 , and C E 33 are the elastic moduli; ρ c is density; e 33 and e 31 are the piezoelectric moduli; d 33 is a piezoelectric constant; ε 33 s is the dielectric permittivity of the material; R 1 and R 2 are the outer and inner radii of the cylinder; r is the radial coordinate; ϕ is the velocity potential of the ambient acoustic medium; p and V r are the pressure and velocity in this medium; ρ and c are its ...

No abstract

No abstract