Solar Cooling for Mediterranean Region as a Crop Storage Technology

The Mediterranean region is a major supplier of fruits and vegetables to Europe. Fruit harvesting continues the year round, including certain fruits to be harvested from September to June. The follow up of the specific temperature and humidity storage conditions becomes significantly energy intensive that adversely affects the energy balance of exporters, especially when the producing country is run out of affordable energy sources. In order to reduce the energy costs during the crop storage and avoid the crop wastage, the solar ejector cooling systems were introduced. These systems developed recently, are fully autonomous, does not contain mechanically moving parts, reliable and durable in performance. In addition, the new type of thermopump with high energy and performance characteristics was elaborated and tested within the ejector cooling system, driven by the imitated low-grade heat. The results of theoretical and experimental study of the thermopump and the ejector refrigeration system were described in the study along with factors that affect the system's efficiency. The crop storages operating regimes were reviewed during the storage season for the selected products. Temperature ranges defined for systems with constant area ratio ejector at COP values remains stable. Cold accumulators or duplicate conventional systems, applied during the night were considered as backup systems, supporting a non-stop operation

Experiments and Simulations of Burner and Pool Fires in Underventilated Compartments

In the conditions where the oxygen supply into the fire compartment is insufficient to maintain steady combustion (underventilated fires), the flame becomes essentially transient and can be thrown out of the ventilation opening. In this paper, experimental and computational studies on burner and pool compartment fires with limited ventilation in a small-scale fire box with a single rectangular ventilation opening are presented. Temperature-time curves as well as video recordings demonstrating the flame ejection are obtained for four opening geometries to measure the time to flame ejection. Results of burner and pool fire experiments are presented in non-dimensional form as the dependence of induction period on the global equivalence ratio. Large Eddy Simulations, LES, of underventilated fires are carried out and compared with the experiments

Solar Cooling Technologies Using Ejector Refrigeration System

The continuous search for the effective cold generation methods resulted in the creation of thermally driven ejector refrigeration systems (ERS). Producing cold at various temperatures, the ERS serves to save electric energy and reduce greenhouse gas emissions. The theoretical analysis of the ejector cycles carried out for various ERS has proved its capability to generate the cold at +12°C to –40°C, reaching the COP values at 0.7 to 0.1 respectively. The combined cycles of water conversion, heat and cold production appear to be especially effective

Conceptual design of binary/multicomponent fluid ejector refrigeration systems

Low energy efficiency and limitations of cooling temperatures in the ejector refrigeration systems (ERSs) are major obstacles for its widespread use. The application of binary or multicomponent fluids may prove to be one of the successful ways to increase the ERS performance by 30–50%. Zeotropic mixtures, which have unlimited solubility and evaporate at specified pressures and varying temperatures, are considered as possible candidates to be applied in a binary-fluid ERS (BERS). An ideal candidate working fluid should exhibit high molecular weight, low latent heat of evaporation, high normal boiling temperature and high compressibility factor. A refrigerant fluid should have low molecular weight, high latent heat of evaporation, low boiling point and compressibility factor. BERS pursues simultaneous achievement of two main goals: increase in system's efficiency and take the condensation point up to 45–50°C at fixed coefficient of performance, i.e. employ atmospheric condenser in ERS. This article presents schematic diagrams of a multicomponent-fluid ERS; its cascade principle based on BERS enables to produce cold at several temperature ramps, using renewable or low-grade heat sources. Research outcomes from this article can improve the effective application of ejector technology

Estimation of in-situ compositions in lean gas condensate reservoirs

There is a high degree of complexity in both fluid flow and phase-behavior of gas condensate reservoirs during the depletion period due to retrograde condensation. Natural depletion in gas condensate reservoirs results in low condensate recoveries at surface due to in-situ condensation and accumulation of condensate in the reservoir especially in vicinity of wellbore. During reservoir depletion, the overall composition of reservoir fluid varies and becomes different from initial reservoir composition as pressure decline to values less than dew-point pressure. In-situ gas and condensate composition in the reservoir are changing accordingly. This paper develops a novel approach to obtain initial gas condensate reservoir composition from gas and liquid compositions taken from separator tests during several depletion stages. Based on the composition of mixed sample and initial reservoir composition, a set of novel correlations is developed for estimating initial gas condensate reservoir composition. The generalized reduced gradient (GRG) algorithm of iteration was used to tune the constant and exponents of the correlation based on available field data. The convergence criteria were to minimize the value of the squared sum, SS, of the difference between the real data and the estimated one

Turbulent diffusion combustion under conditions of limited ventilation: flame projection through an opening

Development of turbulent diffuse flame in a compartment with a vertical opening is studied experimentally and numerically. Flame projection through the opening observed under conditions of limited natural‐convective ventilation is considered. The measurements are performed in a laboratory box designed for compartment‐fire simulation. The critical (minimum) flow rate of the fuel sufficient for flame projection is determined, as well as the delay between fuel ignition and flame projection with subsequent establishment of external combustion. Dimensionless variables for processing experimental data are proposed. A generic empirical dependence of the dimensionless time of flame projection on the dimensionless flow rate of the fuel is obtained for various opening sizes, burner positions, and box sizes. The dimensionless critical flow rate of the fuel obtained is in agreement with the previously published measurements performed for gaseous and condensed fuels. Unsteady stages of flame evolution before the projection and scenarios of flame projection through the opening are identified and analyzed. A three‐dimensional numerical model is developed for calculating turbulent diffusion combustion in a compartment with an opening. The model takes into account the conjugate radiative‐convective heat transfer on solid surfaces and the thermal conductivity of the wall and floor materials. The experimentally observed stages of flame development, flame projection through the opening, and stabilization of external combustion are reproduced in numerical calculations. The numerical values of flame‐projection time are in good agreement with the measurement results and proposed empirical relation