Thermal design of air cooled condenser of a solar adsorption refrigerator

The objective of this paper is to study the design of a condenser of a solar adsorption refrigerator which will be tested in the region of Biskra (Algeria). The LMTD (log mean temperature difference) method is used to calculate the size of the condenser applying experimental data obtained from the literature. For this purpose, a calculation code has been developed to determine the total heat transfer area of the heat exchanger. Therefore, we present a comparison between calculated and experimental results obtained from the literature. This comparison allowed the validation of the calculation method by applying the same experimental conditions. The discussion of the results indicates that we cannot use the ambient air in free convection mode as a cooling fluid if its temperature exceeds 30°C. This problem presents the greatest obstacle especially in the Saharan regions, such as in Biskra, where the average ambient air temperature during the summer exceeds 35°C. As a solution, we propose in this article the improvement of the heat transfer by the air-forced convection mode. Thus, it is established that the use of the air fan can extend the operating temperature limits of the condenser above 35°C

Optimizing Parabolic Through Collectors for Solar Stills: A 2D CFD Parametric Analysis

The thermal efficiency of parabolic trough collectors (PTCs) is influenced by various parameters, including length, diameter, and mass flow rate. This study employs 2D steady-state Computational Fluid Dynamics (CFD) simulations to investigate heat transfer within PTCs and enhance their performance. Exploring diverse PTC designs, involving variations in length (L = 0.5 to 3 m) and diameter (D = 10 to 60 mm), sourced from existing research to optimize desalination system applications. The investigation covers both laminar and turbulent regimes with fully developed flows, examining the effects of Reynolds number and mass flow rate. The results highlight that collector diameter has the most pronounced impact on thermal efficiency, followed by mass flow rate, while the effect of length can be neglected in comparison. A 50% diameter increase leads to over a 60% rise in efficiency for both laminar and turbulent cases, whereas a 60% decrease in mass flow rate corresponds to a 50% enhancement and a 60% improvement in efficiency for both regimes. These findings suggest that an optimal PTC design should prioritize a smaller diameter and lower mass flow rate, with length being of secondary importance and application-specific considerations also playing a pivotal role

Feasibility of solar adsorption air-conditioning in the region of Biskra: Reflection on the government support for electricity bills

In this paper, the feasibility of solar adsorption air conditioning system in the region of Biskra (Algeria) is studied. The main objective is to give a reflection on the current government support for electricity bills. A comparison between three air conditioning systems was made by taking into account economic and environmental constraints: classical mono-split system (A), classical centralized air conditioning chiller (B) and solar adsorption system (C). In the context of the current government support for electricity bills, results show that system A is actually the best choice from the total investment costs, electrical consumption and maintenance point of view. This is observed even with the gain of the electrical consumption obtained in the case of solar adsorption air conditioner (C). From an environmental point of view, the system (C) is more advantageous than the classical systems (A) & (B) especially for its use of the solar energy, its low electrical consumption, low CO2 emissions and low heat rejected to the outside. It can be concluded that the current state policy do not encourage the transition to the use of air conditioning systems operate by renewable energies. Thus, the redirection of the current support for electricity bills to the support of the investment cost of the solar adsorption air conditioner (C) will make it more competitive in the Algerian market. In this case, system (C) can replace, in the long-term, the system (A) used actually

Applicability of solar desiccant cooling systems in Algerian Sahara: Experimental investigation of flat plate collectors

The increasing interest in the development of solar cooling technologies to their various economic and impressive environmental benefits, conducted us to study the feasibility of solar desiccant cooling systems in Algerian Sahara, particularly in the region of Biskra. Thus, we present in this paper, the results of an experimental investigation of solar flat plate collectors (FPCs) to test and estimate their heat regeneration capacity for solid desiccant cooling applications. The applicability of both Pennington and Dunkle cycles taking into account the effects of some parameters such as outdoor humidity and temperature and hot air temperature required to regenerate the desiccant wheel have been studied. From the psychrometric analysis, it was found that the Dunkle cycle is suitable in warm and semiarid climate. In addition, this study has allowed us to show that the temperature achieved by the flat plate solar air heaters in a large band of air flow rate can satisfy the energy needs for the dehumidification in desiccant cooling systems. Hot water produced by the solar water heaters and the stored one are in the operating temperature gap of the system (50-80 °C)

Numerical simulation of convective heat losses in a helical tube of a cylindrical solar receiver

In this paper, natural convection heat losses in a cylindrical solar receiver are investigated numerically. The study is conducted using three helical tube diameters: 12mm, 16mm and 25mm. The diameter of the receiver is 0.3 m with an aspect ratio equal to one and three aperture ratios of 1, 0.75 and 0.5. In each case, the receiver tube inside the cylindrical cavity is modelled by a helical spiral similar to those of real systems. The simulations are performed for three inlet temperatures (of 50, 75 and 100°C) and four receiver tilt angles (of 0, 30, 60 and 900) with a constant mass flow rate of 0.0885 kg/s. The effects of some parameters such as receiver size, boundary conditions, tube diameter, receiver tilt, inlet temperature and opening ratio on convective heat losses and outlet temperature are presented in form of graphs. It has been found that the convective heat losses are reduced by using the adiabatic boundary condition imposed on the half-circumference of the tube. Thus, increasing the helical tube diameter causes an increasing in the convective heat losses. The increasing of the fluid temperature and the opening ratio are found proportional to the increasing of convective heat losses

Experimental study of solar adsorption refrigeration device

This work presents an experimental study of a solar adsorption refrigeration device using activated carbon AC-35 /methanol as working pair. The studied device is designed, realized and tested in the Development of Solar Equipment Unit, UDES, Tipaza (Algeria). The adsorption and desorption tests, carried out on the experimental device, were conducted inside the laboratory using a halogen lamp as an energy source instead the sun. The lamp is installed perpendicularly to the surface of the tubular adsorber to test four radiation levels: 800, 820, 1000 and 1020 W/m². A calculation code is developed, using the Dubinin-Astakhov mathematical model, to evaluate the thermodynamic coefficient of performance, COPth, of the experimental device. Thus, a parametric study is presented to examine the influence of the construction material and the weight of the adsorber on the COPth, the amount of cold produced in the evaporator, Qf, and the total heat supplied to the system, Qc

Contribution à l’étude du transfert thermique dans les échangeurs de chaleur des machines frigorifiques à adsorption.

L’objectif de cette thèse est de proposer des solutions techniques pour adapter les réfrigérateurs et les installations de climatisation solaires à adsorption aux régions chaudes. Dans ces régions, le dysfonctionnement des échangeurs de chaleur de refroidissement (condenseur à air et tour de refroidissement) est assez fréquent notamment durant les périodes caniculaires. Pour surmonter ce problème, nous avons proposé quatre solutions basées sur le couplage de la tour de refroidissement (ou le condenseur) avec : (i) un ventilateur assurant la convection forcée d’air, (ii) un système de refroidissement par pulvérisation d’eau, (iii) un échangeur géothermal eau / sol et (iv) un échangeur géothermal air / sol. Cette dernière solution présente un système innovant breveté en 2014 sous l’appellation Aéro-refroidisseur géothermal GAC « Géothermal Air Cooler ». Une étude d’applicabilité de chaque solution dans la région de Biskra a été présentée en donnant chaque fois les spécificités techniques et les limites de fonctionnement. Par ailleurs, beaucoup de méthodes de calcul et de dimensionnement des condenseurs à air, tour de refroidissement et des échangeurs géothermiques ont été détaillées et validées avec des résultats de la littérature. On note qu’un modèle original a été développé et validé pour la prédiction de la température du sol et l’estimation de la distance minimale entre les tubes de l’échangeur géothermal. En fin, nous pensons que les systèmes frigorifiques à adsorption peuvent être installés dans les régions chaudes en les couplant à l’une des quatre solutions proposées dans la présente thèse

Screening for Pseudomonas and Bacillus antagonistic rhizobacteria strains for the biocontrol of Fusarium wilt of chickpea

The aim of this work is to study the ability of several isolates belonging to Rhizobacteria (Pseudomonas and Bacillus) collected from several chickpea growing areas in Algeria, to control the mycelium growth of Fusarium oxysporum f. sp. ciceris. Interesting isolates were characterized for their morphological characteristics, physiological and biochemical activities as potential bio-control agent. Fungal inhibition tests were performed using plate assay and each isolate were tested for the production of protease, cyanide hydrogen, indole acetic acid, antifungal volatile and extracellular compound. According to API 50 CH, we are able to identify six Bacillus species (B. subtilis, B. circulans, B. lentus, B. aneurinilyticus, B. firmus, B. licheniformis; and with API 20NE test we have identified three Pseudomonas species (P. aeruginosa, P. luteola, P. fluorescens). The ability of bacterial isolates was varied in production of Protease, Gelatinase, Amylase, Cellulase, Acid Indole acetic, Lipase, Catalase and Cyanid Hydrogen. This is traduced in different rate of inhibition growth due to various extracellular compounds, where B61 (Bacillus aneurinilyticus) and P39 (Pseudomonas luteola) and P70 (Pseudomonas fluorescens) were the most efficient with 77 and 55.5% respectively, while B39 (Bacillus firmus) and P41 (Pseudomonas luteola) were the most efficient by volatile compounds with 70.5 and 77.5% respectively. Our results indicate that these bacteria isolates can be used in the biocontrol of Fusarium oxysporum f. sp. ciceris

Thermal design of Earth-to-Air Heat Exchanger: Performance analysis of new transient semi-analytical model for short period of continuous operation

This paper concerns the thermal design of Earth-to-Air Heat Exchanger (EAHE). The paper presents new transient semi-analytical models to estimate i) the disturbed soil thermal resistance of EAHE pipe as a function of duration of operation and ii) thermal performance of EAHE operating under transient conditions. The main aim of this study is to evaluate the parameter choices of this new model for short period of continuous operation of the system (less than 70 h). The results show that time discretization steps of 15 min and 1 h present and lead to appreciable results compared to the experiments. Therefore, the variation of the layer length step of the buried pipe does not alter simulation results. In terms of precision of the soil temperature profile, refined solutions were obtained by the decreasing of the disturbed soil radius and the increasing the number of roots of Bessel's functions. Furthermore, the effect of the variation of surrounding soil radius is discussed for short period of continuous operation of the system. The time step of 1 h and the interval of the surrounding soil radius of 0.4 m–1.1 m are found accurate for good results with a reasonable computational time