Experimental studies on desalination system for ocean thermal energy utilisation

Investigation of cascade high temperature heat pump optimal design theory based on experiment supporting multi-objective optimization

This article presents a comparative thermodynamic analysis based on numerical methods for a hybrid refrigeration system suitable to operate as vapour absorption system (VA), vapour compression–absorption system (VCA) and vapour compression system (VC). The working fluid employed for the first two systems is ammonia–water and it is pure ammonia in case of the third system. The system is being powered by waste energy and conventional energy depending on the mode of operation. The effect on performance parameters like COP and exergy efficiency during all modes of operation has been evaluated by keeping the uniform parametric conditions like condenser temperature (40 °C) and evaporator temperature (5 °C) for all the modes of operation. The effect of ambient temperature on the exergy loss in each component of the different modes of operation have also been evaluated and discussed. The results obtained indicate that COP and exergy efficiency for VCA mode initially increases and then decreases whereas for VA and VC mode the COP and exergy efficiency decreases with condenser temperature. The analysis also reveals that with the variation in evaporator temperature the COP and exergy efficiency for VC mode increases whilst for VA and VCA mode the COP shows a slight increase whereas exergy efficiency decreases. The variation of exergy efficiency and exergy loss in different components with condenser and evaporator temperature shows that exergy efficiency is found to be the highest in VC mode whereas the lowest in VCA mode for both the temperature variations. The variation of compressor work and exergy loss in compressors with evaporator and condenser temperature shows that compressor work and exergy loss is lesser for VCA mode when compared to VC mode.

Küresel ısınma Dünya gündeminin ana konularından birisidir. Dolayısıyla, soğutucu akışkanların çevresel etkilerini azaltmak için birçok çalışma ve düzenleme yapılmaktadır. Çevre dostu soğutucu akışkanların kullanılması soğutucu akışkanların çevre üzerinde olumsuz etkisinin azaltılması için gereklidir. Düşük küresel ısınma potansiyeline (GWP) sahip HFC/HFO soğutucu akışkan karışımları HFC soğutucu akışkanların yerini aldığı düşünülmekte ve son zamanlarda ticari olarak üretilmektedirler. Bu çalışmada, R134a ve R513A soğutucu akışkanlarının performansları teorik olarak incelenmiştir. Ayrıca soğutucu akışkanların çevresel etki değerlendirilmesi yaşamsal döngü iklim performansına (LCCP) göre incelenmiştir. Soğutucu akışkanların enerji performansları farklı evaporatör (-15 ile 2.5 oC arasında) ve kondenser (30 ve 35 oC) sıcaklıkları için yapılmıştır. Evaportaör sıcaklığı -15 oC ve kondenser sıcaklığı 30 oC iken R134a ve R513A’nın COP değerleri sırasıyla 3.87 ve 3.77’dir. Aynı kondenser sıcaklığı için evaporatör sıcaklığı 2.5 oC olduğunda R134a ve R513A’nın COP değerleri sırasıyla 7.28 ve 7.16 olmaktadır. Dolaysıyla R134a ve R513A’nın COP değerlerinin hemen hemen benzer olduğu söylenebilir. R513A’nın GWP oranı R134a’nın yaklaşık yarısı kadardır. Dolayısıyla R513A R134a’dan %56 oranında daha az direkt emisyon (DE) değerine sahip olduğu görülmüştür. Her iki soğutucu akışkanın toplam emisyon değerinin büyük bir çoğunluğu (R134a için %94.98, R513A için %96.77) sistemin enerji tüketiminden kaynaklanmaktadır. R513A soğutucu akışkanın yanıcılık özelliğinin yoktur ayrıca doğrudan R134a ile çalışan sistemde herhangi bir değişiklik yapmadan kullanılabilir. R513A yukarıda saydığımız özelliklerden dolayı R134a’ya alternatif olarak kullanılabilir.

ABSTRACTWater scarcity increases alarmingly as the population increases. Over the years, a number of salt water desalination techniques have been proposed and reached limitations. The requirement of minimum energy is very well satisfied by an adsorption system, since it can operate with low-grade energy and waste heat exhaust from most industries. The first part of this work discusses the effect of condenser and evaporator temperatures on the performance of silica-gel adsorption cycle mathematically. The second part discusses the performance variations due to mass recovery in the two-bed adsorption system mathematically. It was found that the reduction in condenser temperature and increase in the evaporator temperature both increase the fresh water productivity and cooling capacity of a plant. A desalination plant with mass recovery assistance is superior in performance than the conventional plant. Portable water productivity of 8 m3/day/ton is achieved with the condenser temperature of 15°C and the evaporator temperature of 30°C.

The performance of an ejector as an expansion device rather than the conventional expansion valve or capillary tube in a vapor compression system is experimentally analyzed. Experiments have been conducted using 28 ejectors of different dimensions at the same condenser and evaporator temperatures, and it has been observed that for utmost performance, an optimum area ratio of the ejector is required. One of the ejector geometry has been experimented further for a wide range of condenser and evaporator temperatures. The coefficient of performance is found to be enhanced by at least 10% in comparison to the conventional vapor compression system for the considered range of condenser and evaporator temperatures and the maximum improvement in COP obtained is 12.83% at 14.3∘C evaporator temperature and 32.4∘C condenser temperature with 17.9211 ejector area ratio. The refrigerant R134a has been used as the working substance.

Experimental investigation of adsorption water desalination/cooling system using CPO-27Ni MOF

In the present work, exergy analysis method is applied to estimate exergy and exergy loss of each component, total exergy loss, dimensionless exergy loss of each component, and exergetic efficiency of vapor compression heat pump for simultaneous cooling and heating applications over a wide range of operating conditions. Varied parameters include evaporation and condensation temperatures, refrigerant type and compressor speed. Five refrigerants namely; R12, R124, R134a, R152a and R290 are used as working fluids. Evaporation temperature ranging from 0 to 10°C is used to achieve the required water supply temperature for chiller systems. Condensation temperature is varied between 50 and 80°C to cover a wide range of applications such as hot water supply, drying, cleaning ... etc. Compressor speed is changed from 750 to 3000rpm. Results showed that the change in compressor speed yields the highest influence on the refrigerant mass flow rate followed by that of evaporation temperature and then by that of the condensation temperature. This leads to that varying of compressor speed can effectively control exergy output of the heat pump. Effect of the evaporation temperature on exergy loss rate and its dimensionless exergy loss of the compressor and expansion device is essential. The exergy loss rate of the expansion device is more sensitive to the condensation temperature followed by the compressor, liquid-suction: neat exchanger, the condenser and the evaporator in that order. However, at higher condensation temperatures, the expansion device and the compressor yield about 47% and 35% of total exergy loss respectively. R290 demands the highest input exergy while R124 needs the lowest required exergy. From high useful exergy point of view, the preferable refrigerants are R290, R152a, R134a, R12 and R124 in that order. At evaporation temperature of 0°C, the maximum exergetic efficiency can be obtained by R152a followed by R12, R124, R134a and finally by R290. However, at evaporation temperature of 10°C, the maximum efficiency value of the VCHP for simultaneous cooling and heating applications is 0.54, 0.53, 0.49, 0.48 and 0.44 for R12, R152a, R124, R134a and R290 respectively. The condensation temperatures ranging from 55°C to 60°C yield the maximum exergetic efficiency for all refrigerants under investigation.

Cut-off temperature evaluation and performance comparison from energetic and exergetic perspective for NH3-H2O absorption refrigeration system

Performance characteristics of the ejector refrigeration system based on the constant area ejector flow model

Irreversibility analyses during compression process are presented for some refrigerants namely, R290, R134a, R12, R22, and R152a in a vapor compression refrigeration cycle. The effects of evaporator temperature, condenser temperature and isentropic efficiency on the irreversibility rates and exergetic efficiencies of the refrigerants under study are investigated By the means of a computer code that simulates a vapor compression cycle including subcooling and superheating. For all the refrigerants in this study, the irreversibility in the compression process decreased as the evaporator temperature and isentropic efficiency increased and it increased with the increasing values of the condenser temperatures. Exergetic efficiency of the compressor increased as the isentropic efficiency of the compressor increased while it decreased with the increasing values of evaporator temperatures. In the case of increasing evaporator and condenser temperatures, and isentropic efficiency values, R22 and R152a approximately show the same and lowest values of compressor irreversibility while R290 has the lowest values. The compressor irreversibilities and compressor exergetic efficiencies of R12 and R134a placed in the moderate range in the case of increasing evaporator and condenser temperatures, and isentropic efficiency values.

In this study, an exergy analysis of an ice production plant was carried out. The exergy formulas were written and solved based on actual plant data to point out the thermodynamics inutility. For the analysis, the necessary data are obtained from an ice production plant situated at GIDC Navsari, Gujarat, India. The plant included ammonia refrigerant vapor compression refrigeration system having 24 tonnes of ice manufacturing capacity per day, including Kirloskar-4 cylinder reciprocating compressor, shell and tube condenser, induced draft counter flow cooling tower with fill- and flooded-type evaporator. Here the effect of condenser and evaporator temperature on exergy efficiency of components, compressor work and on COP, was also discussed. It is found that the significant amount of exergy drop is happened in compressor out of numerous parts of the ice plant, and it depends on evaporating temperature, condensing temperature, and geographical conditions. To measure the exergy loss (irreversibility) of the ice production procedure, an effort was also formed. So, to get the knowledge about the potential location for the plant execution refinement, an important detail can be obtained with the help of the exergetic study and its subsidiary derivatives.

In this study, statistical methods (Taguchi, analysis of variance (ANOVA), and grey relational analysis (GRA)) are used to evaluate the impact, contribution ratios, and order of importance of parameters on the energy and exergy efficiencies of the simple organic Rankine cycle (SORC) and dual pressure organic Rankine cycle (DORC). The parameters being investigated are the working fluid (A), pinch point temperature difference of the evaporator (B) and condenser (C), degree of superheating (D), evaporator temperature (E), condenser temperature (F), turbine isentropic efficiency (G), pump isentropic efficiency (H), and low-pressure evaporator temperature (J, for DPORC only). Whereas the Taguchi method determines the optimum parameter combination for maximum system performance, ANOVA weighs the influence of individual parameters on the performance of the target function, and GRA optimizes the multi-response characteristic function. The condenser and evap-orator temperatures, pinch point temperature difference of the condenser and turbine isentropic efficiency are revealed as the major process parameters for multi-response performance characteristics of SORC, with an influence factor of 44.79%, 20.96%, 14.81% and 10.69%, respectively. While considering three different working fluids: HFE7000 (1), R245fa (2), and R141b (3), the combination A1B1C1D3E2F1G3H3 is determined as the optimum operating condition for multi-response per-formance characteristic of SORC with first- (energy) and second- (exergy) law efficiencies calculated as 18.64% and 51.69%, respectively. For DPORC, the turbine isentropic efficiency, condenser temperature, and pinch point temperature difference of the condenser and evaporator are the main process parameters for multi-response performance with 41.90%, 17.80%, 14.75%, and 10.47% impact factors, respectively. The best operating condition is obtained as A1B1C1D3E2F1G3H3J2 with first- and second-law efficiencies computed as 13.17% and 57.33%, respectively.

This paper is focused both on the thermodynamic and economic analysis of an organic Rankine cycle (ORC) based geothermal power plant. The analysis is applied to a case study of the geothermal field Recica near the city of Karlovac. Simple cycle configuration of the ORC was applied. Thermodynamic and economic performance of an ORC geothermal system using 8 working fluids: R134a, isobutane, R245fa, R601, R601a, R290, R1234yf, and R1234ze(E)], with different critical temperatures are analyzed. The thermodynamic analysis is performed on the basis of the analysis of influence of the operation conditions, such as evaporation and condensation temperatures and pressures, and evaporator and con-denser pinch point temperature difference, on the cycle characteristics such as net power output, and plant irreversibility. The economic analysis is performed on the basis of relationship between the net power output and the total cost of equipment used in the ORC. Mathematical models are defined for proposed organic Rankine geothermal power plant, and the analysis is performed by using the software package engineering equation solver. The analysis reveals that the working fluids, n-pentane and isopentane, show the best economic performances, regardless the evaporation temperatures, while the working fluid R1234yf and R290 have the best thermodynamic performances. In addition, each analyzed working fluid has its corresponding economically optimal condensation temperature (and condensation pressure). Economically optimal pinch point temperature difference of evaporator has different values, depending on the working fluid, while pinch point temperature difference of condenser has similar values for all analyzed working fluids. Analysis results demonstrate that the subcritical ORC geothermal power plant represents a promising option for electricity production application.

This study analyzed the effect of the refrigerant type selection, condenser and evaporator temperatures on thermal efficiency, network output, second-law efficiency, and exergy destruction values obtained with an advanced approach to exergy analysis. The thermal source was considered a low-temperature geothermal resource at 90°. The refrigerants R11, R123, and R245ca were used as a working fluid. The evaporator and condenser temperatures investigated were 76°, 80°, 84°, and 26°, 31°, and 36°, respectively. Firstly, the thermodynamic aspects were validated by using the literature study. Then, the L27 orthogonal array was created, and further the Taguchi method was applied to objectives. The ranking order of parameters and optimum cases were obtained by calculating signal-to-noise (S/N) ratios. Subsequently, the ANOVA method was applied, yielding satisfactory R<sup>2</sup> values and allowing for the determination of the impact ratios of the parameters. Because of the diverse nature of objectives, the contribution ratios of parameters have different values. The contribution ratio results showed that the working fluid is the most important and dominant parameter for net work output (95.1%) and endogenous (97%), avoidable (97.6%), and unavoidable (95%) exergy destructions. Alternatively, the condenser temperature is the most important parameter for thermal efficiency (66.6%), second-law efficiency (66.6%), and exogenous exergy destruction (62.2%). The results showed the rank order of the parameters and the contribution ratio values are largely compatible.

Performance and Evaluation of Aqua Ammonia Auto Air Conditioner System Using Exhaust Waste Energy