Étude économique des foyers domestiques par la technique d’ébullition de l’eau : cas du Bénin

Les foyers font partie de la vie courante. Chaque ménage en utilise pour la cuisson de ses repas. Dans les pays en développement, la plupart des populations utilisent surtout des foyers à combustibles ligneux. Les effets négatifs sur l’environnement sont aujourd’hui bien connus : poches de désertification, érosion des sols, changements climatiques, etc. Ces effets peuvent se mesurer à la consommation de ces foyers, laquelle dépend de la taille de la famille, des habitudes de repas et aussi du type de foyer utilisé. La présente étude, en utilisant la technique d’ébullition de l’eau, montre l’influence du type de foyer sur les performances, ainsi que l’économie qu’on peut atteindre avec les différents foyers. Les foyers à combustibles fossiles ont les meilleures performances économiques, mais le coût très bas des combustibles ligneux leur donne un avantage.Mots-clés : foyers, combustibles, performances, économie d’énergie, environnement

Thermal Response Measurement and Performance Evaluation of Borehole Heat Exchangers: A Case Study in Kazakhstan

The purpose of the present work was to determine the thermal performance of borehole heat exchangers, considering the influences of their geometric configurations and the thermophysical properties of the soil, grout and pipe wall material. A three-dimensional model was developed for the heat and mass transfer in soil (a porous medium) and grout, together with one-dimensional conductive heat transfer through the pipe walls and one-dimensional convective heat transfer of the heat transfer fluid circulating in the pipes. An algorithm was developed to solve the mathematical equations of the model. The COMSOL Multiphysics software was used to implement the algorithm and perform the numerical simulations. An apparatus was designed, installed and tested to implement the thermal response test (TRT) method. Two wells of depth 50 m were drilled in the Almaty region in Kazakhstan. Gravel and till/loam were mainly found, which are in accordance with the stratigraphic map of the local geological data. In each well, two borehole heat exchangers were installed, which were an integral part of the ground source heat pump. The TRT measurements were conducted using one borehole heat exchanger in one well and the data were obtained. The present TRT data were found to be in good agreement with those available in literature. The numerical results of the model agreed well with the present TRT data, with the root-mean-square-deviation within 0.184 °C. The TRT data, together with the predictions of the line-source analytical model, were utilized to determine the soil thermal conductivity (λg = 2.35 W/m K) and the thermal resistance of the borehole heat exchanger from the heat transfer fluid to the soil (Rb = 0.20 m K/W). The model was then used to predict the efficiencies of the borehole heat exchangers with various geometric configurations and dimensions. The simulation results show that the spiral borehole heat exchanger extracts the highest amount of heat, followed by the multi-tube, double U-type parallel, double U-type cross and single U-type. It is also found that the spiral configuration can save 34.6% drilling depth compared with the conventional single U-type one, suggesting that the spiral configuration is the best one in terms of the depth and the maximum heat extracted. The simulation results showed that (i) more heat was extracted with a higher thermal conductivity of grout material, in the range of 0.5–3.3 W/m K; (ii) the extracted heat remained unchanged for a thermal conductivity of pipe material higher than 2.0 W/m K (experiments in the range of 0.24–0.42 W/m K); (iii) the extracted heat remained unchanged for a volumetric flow rate of water higher than 1.0 m3/h (experimental flow rate 0.6 m3/h); and (iv) the heat extracted by the borehole heat exchanger increased with an increase in the thermal conductivity of the soil (experiments in the range of 0.4–6.0 W/m K). The numerical tool developed, the TRT data and simulation results obtained from the present work are of great value for design and optimization of borehole heat exchangers as well as studying other important factors such as the heat transfer performance during charging/discharging, freezing factor and thermal interference

Experimental and Theoretical Investigations of a Ground Source Heat Pump System for Water and Space Heating Applications in Kazakhstan

The ground source heat pump heating system is considered as one of the best solutions for the transition towards green heating under the continental climate conditions like Kazakhstan. In this paper, experimental and theoretical investigations were carried out to develop a ground source heat pump-based heating system under the weather conditions in Kazakhstan and to evaluate its thermodynamic performance. The water-to-water heat pump heating system, integrated with a ground source heat exchanger and used refrigerant R134a, was designed to provide hot water to meet the requirements for space heating. The predicted values of the coefficient of performance and the experimental results were found to be in good agreement within 6.2%. The thermodynamic performance of the system was also assessed using various environment-friendly refrigerants, such as R152a, R450A, R513A, R1234yf and R1234ze, as potential replacements for R134a. Although R152a is found to be a good alternative for R134a in terms of coefficient of performance and total equivalent warming impact, its flammability hinders its application. The heating system using refrigerants R450A, R513A, R1234yf and R1234ze shows 2–3% lower coefficient of performance than that of R134a. The highest exergy destruction is found to be attributed to the compressor, followed by the expansion valve, evaporator, and condenser. Considering their low flammability and low environmental impact, R450A, R513A, R1234yf and R1234ze are identified as valuable replacements for R134a

Thermodynamics of Energy Systems and Processes: A Review and Perspectives

Thermodynamics is a relatively recent physical science that was born with calorimetry and thermometry experiments: so heat remains the central concept in relation with other forms of energy. The coupling between various forms is essential and related to conversion processes. The first conversion process that was analyzed was the thermomechanical one, at the time of Carnot. Equilibrium Thermodynamics was fruitful in connection with the efficiency concept, to qualify engines. But since that time, mass and heat transfers studies have been strongly developed (thermokinetics), as well as second law aspects of thermodynamics. It results new appraisal for energy systems and processes, relevant of a true thermodynamics approach. This was initiated by Onsager at the beginning of the 20th century, by analyzing the relation between fluxes and forces (gradients) from a general, but linear point of view. More recently, it was developed through a lumped analysis for systems by Chambadal and Novikov in 1957. It was rediscovered in 1975, by Curzon and Ahlborn. And since this work, a lot of books and publications have been proposed in the literature. A review of them is proposed here, on the basis of a synthesis due to the lack of place. The author’s works are analysed and compared to the literature too. It results some original remarks and proposal relative to the obtained results: Comparison of entropy ratio method to entropy flux method, Comparison of endoreversible case to irreversible case, Comparison of adiabatic and non adiabatic systems, Comparison of constrained and non constrained systems. Main consequences of these comparisons are given, and future perspectives evoked on the main systems categories (engines; reverse machines; other eventual configurations).Conclusion is that FDOT (Finite Dimensions Thermodynamics) appears as a promising tool to be enlarged in the future

Variability and induction of cytochrome P450 monooxygenases in human liver samples and hepatocytes : analysis using LC-MS/MS cocktail-assay and RNA-interference

Die Variabilität der Expression und Funktion der P450 Enzyme (CYPs) ist eine der Ursachen dafür, dass bei gleicher Dosierung eines Medikaments Intensität und Dauer von Wirkungen und Nebenwirkungen von Patient zu Patient unterschiedlich sein können. Diese interindividuelle Variabilität der Enzyme lässt sich heute noch nicht lückenlos erklären. Prinzipiell können biologische Faktoren (z.B. Alter, Geschlecht, Hormonstatus), Umweltfaktoren (Ernährung, Rauchen, Arzneimittelinteraktionen) sowie genetische Faktoren, z.B. Polymorphismen, Enzymfunktionen beeinflussen. Um dieser Problematik nachgehen zu können und auf Aktivitätsebene relativ schnell und einfach Unterschiede nachzuweisen, wurde ein LC-MS/MS basierter P450 Cocktail-Assay zur Quantifizierung der sieben wichtigsten Enzymaktivitäten für den Arzneistoffwechsel entwickelt und in humanen Hepatozyten etabliert. Am Beispiel der Arzneistoffgruppe der HMG-CoA Reduktasehemmer (Statine) wurden Untersuchungen der Cytochrom P450 Enzyme durch zeitabhängige Enzyminduktionsprofile mittels Cocktail-Assay und mRNA-Expression gemessen. Das CYP2C8 wurde als neues, von Statinen stark induziertes P450 Enzym identifiziert. Es wurde eine bis zu 20-fache Zunahme der Aktivität durch Atorvastatin und eine ~10-fache Zunahme durch Simvastatin- und Lovastatinbehandlung nachgewiesen. Die Enzyme CYP3A4, CYP2B6 und CYP2C9 zeigten geringere, aber auch deutliche Aktivitätssteigerungen durch die Behandlung mit Atorvastatin und Simvastatin (4 bis 11-fach). Lovastatin und Rosuvastatin hatten geringere Effekte. Die Expression der mRNA entsprach weitestgehend den Beobachtungen der Aktivitäten, wobei jedoch die Auswirkungen dynamischer und drastischer mit wesentlich höheren Induktionsleveln ausfielen. Die Ergebnisse deuten auf einen stärkeren Einfluss der Behandlung mit Statinen auf P450 Expression und Aktivität hin, als bisher angenommen. Dies könnte besonders für die Co-Medikation mit anderen über CYP2C8 metabolisierten Arzneistoffen von entscheidender Bedeutung sein. Aufgrund von Korrelationsanalysen der P450 Enzymaktivitäten zu ihrem spezifischen Proteingehalt in humanen Leberproben (Leberbank am IKP) wurden unterschiedliche Ergebnisse hinsichtlich der Funktion einzelner CYP-Enzyme beobachtet. Manche CYP-Enzyme, wie z.B. CYP3A4 mit der Hydroxylierung von Atorvastatin oder CYP1A2 mit der Bildung von Acetaminophen zeigten sehr gute Korrelationen. Andere Enzyme wie z.B. CYP2C9 mit dem spezifischen Substrat Diclofenac, korrelierten wesentlich schlechter. Diese Unterschiede könnten neben biologischen Faktoren und Umwelteinflüssen mit Variabilität in den Enzymen NADPH:P450 Oxidoreduktase (POR), Cytochrom b5 oder den beiden Progesteronrezeptor-Membrankomponenten PGRMC1 und PGRMC2 zusammenhängen. Denn als potentielle Elektronendonatoren der CYP-Enzyme wären diese maßgeblich am Metabolismus von Xenobiotika beteiligt. Zur Untersuchung, welchen Einfluss die Elektronendonator-Proteine auf die Aktivität der CYP-Enzyme haben, wurde die Technik einer lentiviral basierten RNA-Interferenz (RNAi) für diese Gene in primären humanen Hepatozyten entwickelt und die P450 Aktivitäten mittels Cocktail-Assay nach dem »Knock-Down« dieser Gene bestimmt. Für die P450 Reduktase wurde ein erfolgreiches »Gene Silencing« von durchschnittlich 85% auf mRNA-Ebene erzielt. Die Expression von Cytochrom b5 wurde um 51% reduziert, PGRMC1 um ca. 30%. Für PGRMC2 konnte bisher kein signifikanter »Knock-Down« nachgewiesen werden. Nach dem »Silencing« der Reduktase wurde für die P450 Enzymaktivitäten nach 4 Tagen durchschnittlich ein leichter Rückgang von ca. 10-30% beobachtet. Nach einer Zeitdauer von 7 Tagen wurde für das CYP3A4 im Vergleich zur Kontrolle nur noch eine Restaktivität von ungefähr 5% detektiert. Für die beiden anderen potentiellen Elektronendonatoren Cytochrom b5 und PGRMC1 wurde entsprechend eine um 85% bzw. 75% reduzierte CYP3A4 Aktivität nachgewiesen. Diese ersten Ergebnisse sprechen deutlich für eine Interaktion der Enzyme POR, Cytochrom b5 und PGRMC1 mit den Arzneistoff metabolisierenden P450 Enzymen.The variability of the expression and function of the P450 enzymes (CYPs) is a cause for having different intensities and lengths of effects as well as side effects when patients are given the same dosage of medication. Up to this day, one cannot allover explain this inter individual variability of expression and activity of the enzymes. In general, there are several factors that may affect the variability, including biological factors (such us age, gender, hormonal status), environmental factors (such as nutrition, smoking, medication) as well as genetic factors like polymorphisms In order to solve this problem and to analyze relatively easy and fast activity differences, we developed an LC-MS/MS based P450 activity cocktail assay to quantify and detect simultaneously the seven most important CYPs as judged by their roles in the metabolism of clinically used drugs. The assay was established for use in in human hepatocytes as well as in recombinant and microsomal enzymes. We used the newly developed model-substrate cocktail assay to analyze the time-dependent induction of seven drug metabolizing cytochrome P450 activities as response to treatment of primary human hepatocytes with different statins. The strongest induction was observed for amodiaquine N-desalkylation of CYP2C8, which was induced up to 20-fold by atorvastatin and approximately 10-fold by simvastatin and lovastatin. Enzymes CYP3A4, CYP2B6 and 2C9 showed lower, but also significant induction after treatment with atorvastatin and simvastatin (4-11-fold). lovastatin and rosuvastatin demonstrated minor effects. Quantitative RT-PCR confirmed corresponding changes on the mRNA level with even more dramatic induction up to almost 100-fold. These data suggest a broader inducing effect of statins on cytochrome P450 expression and activity than previously known, thus further emphasizing their drug-drug interaction potential, especially for CYP2C8. Based on correlation analysis with P450 enzyme activity to their specific protein amount in human liver samples (liverbank IKP) were different functional results observed. Enzymes like CYP3A4 with atorvastatin hydroxylation or CYP1A2 with formation of acetaminophen showed very good correlations. Others like i.e. CYP2C9 with specific substrate diclofenac correlated much lower. Besides biological and environmental factors could these differences based on variability of the enzymes NADPH:P450 oxidoreductase (POR), cytochrome b5 or the two progesterone receptor-membrane components PGRMC1 and PGRMC2. After all, they would take active part in the metabolism of the xenobiotica as possible electron donors of the CYP enzymes. In order to analyze what kind of influence these proteins have on CYP enzyme activity, we developed a lentiviral based RNA-interference (RNAi) method in human hepatocytes and determined P450 activity with cocktail-assay after knocking down these genes. For the P450 reductase, we achieved a successful gene silencing of about 85% on mRNA level. The expression of cytochrome b5 was reduced by 51%, PGRMC1 about 30%. So far, it has not been possible to prove a significant knock down of PGRMC2. After silencing of reductase, an average light decline of about 10-30% of P450 enzyme activities was observed after 4 days. After a period of 7 days, a rest activity of CYP3A4 of only about 5% was detected. For both other potential electron donators cytochrome b5 and PGRMC1 was a reduced activity of 85% and 75% determined. These first results indicate a clear interaction of the enzymes POR, cytochrome b5 and PGRMC1 with the drug metabolizing enzymes