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Abstract: In this study, a pulp and paper mill (PPM) in the SEKA Papermaking Plant in İzmit, Turkey, is analysed through energy and exergy balances. The plant utilises recycled waste paper for papermaking. This type of raw material input makes the process highly sophisticated. The pulping uses strictly mechanical processes, such as digestion, separation by screening and hydrocyclone, and refining. The milling, as an integrated process, provides the final operations necessary to prepare the conditions required for the end-product by stock-preparation, wiring, rolling, and drying by dewatering, pressing, and evaporation. The possibility of making the entire process more thermodynamically efficient is discussed by calculating the energy and exergy losses for all the mechanical and physical sub-processes. The study shows that the energy efficiencies for each of the mechanical and physical steps in the PPM vary between 34% and 97.4%, whereas the exergy efficiencies vary between 30.2% and 94.2%. In conclusion, based on the results from the energy and exergy flow analyses, the exergy output can be improved through more efforts directed primarily to further measurements toward more efficient energy utilisation in the PPM. [Copyright &y& Elsevier]

Abstract: The paper industry is, with about 6% of the total worldwide industrial energy use, an energy-intensive industry. The drying section is with approximately 50% the largest energy consumer in a paper mill, energy use in this section is mainly heat use. Several options to decrease heat use in conventional multi-cylinder drying sections are investigated, calculating the effect on energy use. Optimization measures include a) decreasing the amount of water evaporation by applying additives in higher consistencies and by lowering the water viscosity, b) decreasing the heat use of water evaporation by increasing the dew point temperature of the dryer and c) increasing the amount of heat recovery by using exhaust air to not only pre-heat the incoming air but also to increase process water temperatures. These could all be achieved by retrofitting and/or choosing different processing conditions in existing factories. The combined thermal heat saving potential due to the optimization actions is 1.3GJh/t paper (or 32% of the drying section’s heat use) as compared to the reference situation. [ABSTRACT FROM AUTHOR]

Abstract In the face of more and more serious energy and environmental problems, energy conservation and environmental protection have attracted more attention all over the world. Combining the advantages of high temperature heat pump (HTHP) and natural refrigerant, water vapor HTHP system can effectively recover low-grade energy and is more green and environmental friendly. This paper presents a new water vapor HTHP system with 80–90 °C waste heat recovery and 120–130 °C hot water supply. The water vapor HTHP system model is established to investigate the system performance under different working conditions. Then, the experimental study of the HTHP system with water refrigerant is carried out to validate the simulation results. The simulation results present that when the evaporation temperature is under 83–87 °C and the condensation temperature among 120–128 °C, the compressor power ranges from 46.1 to 58.1 kW and system COP ranges from 3.64 to 4.87. The comparison between simulation and experimental results show good agreement with each other, which indicates that the model established in this paper has great reliability and accuracy for water vapor HTHP system. Highlights • A new HTHP system with water refrigerant was proposed to recover industry waste heat. • A detailed model of the water vapor HTHP system was established to study the system performance. • The water vapor HTHP shows good simulation and experimental performance. • The average deviation of simulation and experimental results is about 5%. [ABSTRACT FROM AUTHOR]

Numerous metrics and indices have been proposed for the assessment of thermal perception and comfort. Commonly used indices based on the estimate of the heat flow between the human and its environment includes the well-known Fanger's method, also known as the PMV-PPD thermal comfort model. Recently this thermodynamic approach has been expanded with the application of the second law of thermodynamics. In this paper, an exergy-based analysis of the relation between the human and its environment is presented. Heat and mass flow rate due to convection, radiation, evaporation and respiration are calculated and expressed in terms of exergy loss. This value is used in the modified Fanger's thermal comfort model, where the heat balance equation is replaced by the exergy loss. The paper builds upon prior studies on determination of internal and external exergy losses by revised and newly defined formulas taking into account clothing and indoor conditions. The results quantitatively show that thermal energy load in the original Fanger's PMV model could be substituted by exergy loss and it corresponds to a certain level of subjective assessed thermal comfort level. [ABSTRACT FROM AUTHOR]

The paper presents an innovative and advanced MCC (mixture controlled combustion). The MCC model is coupled to the innovative mechanistically based 0D spray model presented in a companion paper [1] that provides inputs on fuel mass distribution. Advanced MCC model is embedded into a 2-zone combustion modeling framework. Advanced MCC predicts ROHR (Rate-Of-Heat-Release) as the combination of the premixed and two diffusion parts, which correspond to rich and lean spray region. It also calculates the amount of fuel available for premixed combustion based on the duration of the ignition delay period. In addition, it reduces the reaction rate based on the oxygen availability using mechanistic basis, based on evaporation rate and based on mechanistically determined fuel amount that has reached the walls. High level of model predictability was confirmed by good agreement between the simulated and the measured ROHR traces over very broad operating range of the engine by using fixed parameters of the advanced MCC model and the spray model. Moreover, the applied modeling framework with embedded innovative spray and advanced MCC model features HiL (Hardware-in-the-Loop) compatible computational times. [ABSTRACT FROM AUTHOR]

Abstract The present paper experimentally investigates the thermal performances of an Organic Rankine Cycle (ORC) using a self-developed single screw expander. Experiments were conducted to study the net efficiency of the ORC under different cooling water flows in different seasons. Taking the power consumed by the circulation pump, cooling water pump, cooling tower fan and lubricant oil pump into account, the experimental results showed that the maximum value of produced net power and net efficiency achieved 3.27 kW and 3.04%, respectively, obtained at a cooling water flow of 12 m3 h−1 in winter. The experimental results also reported that the shaft power and shaft efficiency of the expander increased gradually with growth of cooling water flow. Under the same evaporating temperature, the performances of the ORC system deteriorated with the increase of ambient temperature, and the net efficiency of the system in summer was decreased by more than 16.45% than that in winter. In addition, the power consumption by the cooling system was the largest factor restricting the net efficiency than the power consumption by other auxiliary machines. Therefore, reducing the power consumption by the cooling system can effectively enhance the net efficiency of the ORC system. Highlights • The net power and net efficiency of an ORC system were experimental obtained. • The power consumptions by all auxiliary machines were taken into account. • The power consumptions and influences of the cooling system on ORC were discussed. • The ORC net power and net efficiency achieved 3.27 kW and 3.04%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Building legislation along with environmental and comfort concerns are increasingly driving designers of building services and air conditioning equipment towards more energy efficient solutions. Heat pipe technology is emerging as a viable, efficient and environmentally-sound technology for applications in efficient air handling unit designs. In this paper, an experimental investigation on the thermal performance of an air-to-air heat exchanger, which utilises heat pipe technology, will be presented. The heat exchanger consisted of 7 loop heat pipes with finned evaporator and condenser sections. The heat exchanger was fully instrumented to test for the effect of the variation of heat load and the air velocity, through the heat exchanger, on the overall thermal resistance of the loops. The values of the effectiveness of the heat pipe heat exchanger are shown to vary with the air velocity as expected but the results also allow the prediction of effectiveness variation with the heat load and operating temperature (previously assumed to be constant). The results allow an interpretation of the overall thermal performance of each loop heat pipe as a function of the load and air velocity. The paper concludes with a theoretical analysis of the energy savings that would be expected when utilising the technology in a representative application. [ABSTRACT FROM AUTHOR]

The isothermal phase transition process of pure working fluids cannot effectively match the liquefied natural gas (LNG) gasification process, resulting in low efficiency of LNG cold energy power generation systems. In order to improve the temperature matching characteristics, mixed working fluids with a temperature glide during the phase change process can be adopted. In our previous study, the two-stage condensing process also effectively improved the temperature matching characteristics; thus, this paper presents a two-stage condensation combined cycle using zeotropic mixtures, and the effects of the type and number of components for mixed refrigerants on the two-stage condensing combined cycle system performance are studied. With the net power output as the objective function, the evaporation temperature, condensing temperatures, LNG expander inlet temperature, and working fluid mole fractions are optimised by the genetic algorithm. The results demonstrate that the net power output of n-C 5 H 12 is the largest among the studied pure fluids. The net power output of the binary mixed working fluid at the optimum mole fractions is obviously superior to that of pure working fluids. The system performance is improved when the hydrocarbon mixture is selected as a working fluid, and the optimum number of components is three. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical and experimental investigation on HDH evaporation system performance was performed. A fixed size HDH system was constructed, and for the purpose to obtain the optimal operating parameters, a mathematical model was proposed to investigate the effect of the operating parameters on the evaporation rate and specific steam consumption (SSC). The evaporation rate is proportional to three operating parameters. SSC decrease with the increase of heat recovery ratio (HRR) in regenerator. Moreover, the operating parameters of the system were optimized to obtain minimum SSC using the GlobalSearch algorithm. The minimum SSC is 0.338–0.398 kg per kg of evaporated water at different evaporation capacities. And the value of minimum SSC increases with an increase in the evaporation limit. Furthermore, the experimental results were compared with the optimized results, and they are in good agreement. Considering both the evaporation rate and SSC, the recommended operating parameters are: m g  = 502.53 kg/h, m l  = 3556.93 kg/h, T lie  = 83.59 °C. [ABSTRACT FROM AUTHOR]

In this paper, the mathematical models of pre-heated and internally-heated liquid desiccant regenerator are established including parallel flow, counter flow and cross flow with two kinds of different flow directions of heated water respectively. Simulation results reflect that regeneration performances of the internally-heated are about 2–4 times that of the pre-heated in most conditions, greatly depending on the ratios of flow-rate of solution to air ( m s / m a ) and water to air ( m w / m a ) respectively. The regeneration performances, when the heated-water flows counter to solution, are superior to that of heated water parallel to solution. And the regeneration performances generally increase with increases in the NTU 1 and NTU 2 while a fitted curve combining NTU 1 with NTU 2 occurs to indicate the fastest increase in regeneration performance. Although the concentration difference increases with the m s / m a reducing, the evaporation rate gets its maximum value when the ratio of mass flow-rate of solution to air is equal to 0.2. The regeneration performances increase with increasing air temperature and decreasing its moisture content as well as linearly increase with higher inlet temperature of heated-water, but decrease with increasing solution concentration. The proposed regeneration mode and flow pattern will be helpful in the design and optimization of the regenerators. [ABSTRACT FROM AUTHOR]

In this paper, a sorption thermal storage system with large concentration glide is proposed to achieve long term thermal storage with high energy storage density. The system consists of a storage subsystem and a cooling subsystem. In the charging process, the condensation of the storage subsystem is cooled by the cooling subsystem. The pressure of storage subsystem is decreased and its concentration glide is enlarged. The ammonia-water solution is chosen as working pair considering the subzero working condition. Performances of the proposed system and the conventional system are calculated and compared under heat input temperature of 90 °C. For the heating supply with temperature of 40 °C under ambient temperature of −10 °C, the proposed system obtains COP of 0.18 and energy density of 293.9 kJ/kg. The conventional system cannot deliver heat output under the same condition. For the cooling supply with temperature of -5 °C under ambient temperature of 30 °C, the proposed system obtains COP of 0.27 and energy density of 466.9 kJ/kg. Compared with the conventional system, 138% energy density enhancement and 21% COP degradation are achieved. The proposed system has higher energy density than the conventional system, especially when the heat source temperature or evaporation temperature is low. [ABSTRACT FROM AUTHOR]

NG (Natural gas) distribution pressure varies in a wide range in different applications and has significant effect on system exergy efficiency. RC (Rankine cycle) and DEC (direct expansion cycle) can utilize the cold and pressure exergies of LNG (liquefied natural gas), respectively. In this paper, SRC (single-stage RC), PTRC (parallel two-stage RC) and CTRC (cascade two-stage RC) with and without DEC are optimized by Particle Swarm Optimization and compared to obtain the optimal configurations for different NG distribution pressures. Propane, propylene, ethane and ethylene are adopted as the working fluids. The results show that the addition of DEC could increase the exergy efficiency by lifting the evaporation temperature of LNG. CTRC + DEC with propane/ethylene and CTRC + DEC with propane/ethane as the working fluid achieve the largest exergy efficiencies of 23.89% and 18.25% at NG distribution pressures of 1 MPa and 2 MPa, respectively. PTRC + DEC with propane/ethane is the optimal system with maximum exergy efficiencies of 15.18%, 13.24%, 11.7% and 10.4% at NG distribution pressures of 3, 4, 5 and 6 MPa, respectively. PTRC + DEC with ethane as the working fluid in both cycles is a generally suitable system for all NG distribution pressures with high efficiency and only one type of working fluid. [ABSTRACT FROM AUTHOR]

Crude benchmark oil prices play a crucial role in energy policy and investment management. Previous research confined itself to studying the static, uncertain, short- or long-term relationship between global benchmark oil prices, ignoring the time-varying, quantitative, dynamic nature of the relationship during various stages of oil price volatility. This paper proposes a novel approach combining grey relation analysis, optimization wavelet analysis, and Bayesian network modeling to explore the multi-period evolution of the dynamic relationship between global benchmark oil prices and regional oil spot price. We analyze the evolution of the most significant decision-making risk periods, as well as the combined strategy-making reference oil prices and the corresponding periods during various stages of volatility. Furthermore, we determine that the network evolution of the quantitative lead/lag relationship between different influences of global benchmark oil prices shows a multi-period evolution phenomenon. For policy makers and market investors, our combined model can provide decision-making periods with the lowest expected risk and decision-making target reference oil prices and corresponding weights for strategy adjustment and market arbitrage. This study provides further information regarding period weights of target reference oil prices, facilitating efforts to perform multi-agent energy policy and intertemporal market arbitrage. [ABSTRACT FROM AUTHOR]

This paper evaluates the operational advantages of using a backing material for photovoltaic modules different than the industry-standard Tedlar. Synthetic clay, composed mostly of gypsum, is investigated to be part of cells backing and has been found to provide passive cooling properties, successfully reducing the operating temperatures of tested cells from 28 °C to 10 °C. The XRD (X-Ray diffraction) and SEM (Scanning Electron Microscopy) microstructural examination, as well as porosity tests have revealed the random pore distribution of the clay and their volumetric stability at high operating temperatures, which is essential in enhancing evaporation. The characterization of IV performance of bare cells compared with ones backed by clay and aluminum revealed the structural and thermal advantages of using clay, while Nyquist plots revealed the independence of cell impedance from the mist of cooling water provided to clay medium, adding an extra 34.6% of power output when the former is compared to reference cells. [ABSTRACT FROM AUTHOR]

The ORC (organic Rankine cycle) technology has been found promising for heat recovery, but the major problem is its low efficiency, and the evaporator is a major contributor to the total irreversible losses. The heat source is segmented in two temperature ranges. The TSORC (two stage organic Rankine cycle) was put forward. The objective of this paper is to evaluate the performance enhancement of the TSORC with a reference to the ORC. The system performances (mass flow rate, evaporating temperature, VFR (volumetric flow ratio), net power output, system efficiency, and thermal conductances) for the ORC and TSORC were simulated and compared using R245fa. The objective function is the ratio of the net power output to the total thermal conductance, reflecting both the system earnings and the cost. The results show that the TSORC can enhance the net power output, and the growth rate differs with IGWT (intermediate geothermal water temperature) and GWIT (geothermal water inlet temperature) (GWIT). The TSORC exceeds the ORC and enhances the systematic performance with the GWIT. Optimal IGWT and evaporating temperatures of the TSORC maximize the net power output. The TSORC presents excellent systematic performance, which should be popularized in engineering applications. [ABSTRACT FROM AUTHOR]

In this paper we present a novel organic Rankine cycle layout, named the organic split-cycle, designed for utilization of low grade heat. The cycle is developed by implementing a simplified version of the split evaporation concept from the Kalina split-cycle in the organic Rankine cycle in order to improve the boiling process. Optimizations are carried out for eight hydrocarbon mixtures for hot fluid inlet temperatures at 120 °C and 90 °C, using a genetic algorithm to determine the cycle conditions for which the net power output is maximized. The most promising mixture is an isobutane/pentane mixture which, for the 90 °C hot fluid inlet temperature case, achieves a 14.5% higher net power output than an optimized organic Rankine cycle using the same mixture. Two parameter studies suggest that optimum conditions for the organic split-cycle are when the temperature profile allows the minimum pinch point temperature difference to be reached at two locations in the boiler. Compared to the transcritical organic Rankine cycle, the organic split-cycle improves the boiling process without an entailing increase in the boiler pressure, thus enabling an efficient low grade heat to power conversion at low boiler pressures. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to propose the integration of a hot water cooling system with a desiccant-assisted evaporative cooling system for air conditioning a data center. The feasibility of the integrated system is analyzed by a detailed energy simulation for a model data center by using TRNSYS (transient system simulation) 16 with a commercial equation solver program. The energy saving potential of the proposed system is evaluated by comparing it to a conventional air handling system with an air-side economizer serving the model data center. The results show that the proposed system saves more than 95% of the peak power demand and 84% of annual operating energy consumption with respect to the conventional air conditioning system for the data center. This advantage in energy savings is primarily obtained by the use of water-side free cooling in the hot water cooling system and the evaporative cooling effect enhanced by the liquid desiccant system in the air-side supply. Fan energy savings caused by reduced air flow in the proposed system also contributes to the reduction in operating energy. [ABSTRACT FROM AUTHOR]

This paper reports the experimental results of a single effect absorption cooling system of 3 kW of nominal cooling capacity operating with ammonia–lithium nitrate solution. The system was designed and built in the Instituto de Energías Renovables of the Universidad Nacional Autónoma de México and can be used for food conservation or air conditioning. The absorber and generator are falling film heat exchangers. The condenser, evaporator and solution heat exchanger are compact plate heat exchangers. The heat was supplied to the generator at temperatures between 85 °C and 105 °C, while the cooling water temperatures to remove the heat produced during the condensation and absorption varied between 18 °C and 36 °C. The results showed that the system can produce up to 2.7 kW of cooling capacity at heating water temperatures of 95 °C and can achieve evaporator temperatures as low as 1 °C. The experimental coefficients of performance varied between 0.45 and 0.70. Because of the developed system do not need a rectifier and reasonable good coefficients of performance were achieved, the developed system seems to be a good alternative to be used for food conservation or air conditioning. [ABSTRACT FROM AUTHOR]

This paper evaluates a one-stage technique to improve fresh water production from salty water by enhancing the evaporation and condensation. A pilot plant is designed and constructed in an arid area with 1 m 2 solar water collector area to evaluate the one-stage process. The effect of main parameters on fresh water production of the unit is studied. The results show that, the productivity, efficiency, productivity rate, and Gained Output Ratio of the desalination unit are strongly affected by the inlet hot water temperature and flow rate. Within the studied ranges, the maximum daily productivity reached to 9 l/m 2 . According to these results, fresher water production of the present system is higher than that solar humidification–dehumidification desalination system in the previous studies. The maximum daily efficiency in the desalination system is about 87%. A TDS (total dissolved solids) of fresher water is 40 ppm. Finally, the cost of distilled water per liter is $0.029. [ABSTRACT FROM AUTHOR]

The ORC (organic Rankine cycle) system is one of the most effective approaches for recovering energy from low grade heat sources like geothermal water. This paper describes the screen of fluids for geothermal ORC system. This study analyzed the influence of the working fluid properties of HC (hydro carbon) and HFC (hydro fluorine carbon) working fluids on the system performance and relates the properties to the molecular structures. HC and HFC working fluids were adopted. A theoretical ORC model was used to optimize the evaporating temperature to maximize the work output for each working fluid. The optimal working fluids are given for heat sources at 383.15 K, 403.15 K and 423.15 K. The results show that for a specific source temperature, the optimized evaporating temperatures for all the working fluids are almost the same. Based on the influence of working fluid property on system performance, two indicators are given for screening working fluids. Fluids like R32, R134a and propylene with GWP (global warming potential) value less than 1500 provide better performance than others, by extracting more energy from the heat source. [ABSTRACT FROM AUTHOR]

The purpose of the present paper is to propose a methodology for the fluid selection of an Organic Rankine Cycle for low-temperature waste heat recovery. The selection of an optimal working fluid is carried out by an optimization process, using the Genetic Algorithm. Three decision variables are considered: the working fluid, the evaporation temperature and the condensation temperature. These variables are subjected to some constraints that take into account the good operation of the heat exchangers and the expander. The defect of efficiency and the total heat exchange area per unit of power output are selected as the objective functions to be minimized. The heat recovery is made possible by a hot water source, which assumes inlet temperatures of 100 °C and 150 °C. The water mass flow rate is fixed to 1.0 kg/s. The results show that fluids with low value of critical temperature, like Novec649, RE347mcc, R245fa, optimize the defect of efficiency, whilst, in order to minimize the total heat exchange area per unit of power output, fluids with high value of thermal conductivity and latent heat of vaporization must be selected. This work offers a tool to selected an optimal working fluid, among all possible candidates, for this type of applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides an energy efficiency study of transcritical carbon dioxide systems by comparing six cycles with and without an expressor (expander–compressor), which serves as an assistant compressor or the main compressor. Several different expander–compressor arrangements in the system are investigated. The mass flow rate and compression ratio of the expander–compressor are affected by these arrangements. The COP (coefficient of performance) of STM (series model of two-stage compression transcritical CO2 cycle with an expressor as the main compressor) is found to be the highest. Although the intermediate pressure between the two compressor stages in STS (series model of two-stage compression transcritical CO2 cycle with an expressor as an assistant compressor in the second stage) cannot approach the optimum value, its COP approaches that of STM at a high evaporation temperature. PSE (parallel model of single-stage compression CO2 transcritical cycle with an expressor) and PSS (parallel model of single-stage compression CO2 transcritical cycle with an expressor and gas–liquid separator) may be feasible options for reducing the dimensions of a compressor. And the expander and compressor efficiencies are very important factors for the utilization of an expressor. [Copyright &y& Elsevier]

The present paper focuses on the experimental characterization of an open-drive scroll expander integrated into an Organic Rankine cycle using R245fa as working fluid. The expander is a commercially available air compressor that was modified to operate in expander mode. The ORC (Organic Rankine Cycle) system is designed for a nominal heat input of 20 kW and a nominal net power output of 1.8 kW. A total of 74 steady-state operating points are measured to evaluate the expander performance over a wide range of conditions. The operating parameters that are varied include the inlet pressure (from 9 to 12 bar), outlet pressure (from 1.5 to 4 bar) and rotational speed (from 2000 to 3500 rpm). The maximum isentropic efficiency and shaft power are, respectively, 75.7% and 2.1 kW. A maximum cycle efficiency of 8.5% is reached for evaporating and condensing temperatures of 97.5 °C and 26.6 °C respectively. For most of the tests, hot water is produced in the condenser and the system therefore behaves as a CHP (combined heat and power). Depending on the water temperature requirement, a power to heat ratio varying between 1.9% and 11.8% is obtained. Water over 50 °C can be produced with a power to heat ratio higher than 8%. The experimental data points are then used to generate a performance map of the expander. This performance map allows for simulation of the use of such an expander in other ORC system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a framework of thermodynamic, energy and exergy, analyses of industrial steam boilers. Mass, energy, and exergy analysis were used to develop a methodology for evaluating thermodynamic properties, energy and exergy input and output resources in industrial steam boilers. Determined methods make available an analytic procedure for the physical and chemical exergetic analysis of steam boilers for appropriate applications. The energy and exergy efficiencies obtained for the entire boiler was 69.56% and 38.57% at standard reference state temperature of 25°C for an evaporation ratio of 12. Chemical exergy of the material streams was considered to offer a more comprehensive detail on energy and exergy resource allocation and losses of the processes in a steam boiler. [Copyright &y& Elsevier]

Abstract: This paper presented the analysis on the influence of the pinch point temperature difference (PPTD) and the evaporation temperature on the performance of organic Rankine cycle (ORC) in recovering the low temperature waste heat of the flue gas. Both the net power output and the heat transfer area of the evaporator and condenser were evaluated for dry and isentropic working fluids. When the heat and cold source conditions were given, the maximum net power output and the heat transfer area were obtained. The results show that some organic working fluids cannot reach the maximum net power output to avoid the low temperature corrosion. With the increase of the PPTD of the evaporator at a given total temperature difference, the total heat transfer area decreases first and then increases, while the corresponding cost-effective performance (ratio of the net power output to total heat transfer area) displays almost the opposite variation tendency. The PPTD of the evaporator for the optimization cost-effective performance is approximately the same for different organic working fluids. Meanwhile, the isentropic working fluids show better cost-effective performance than dry working fluids. [Copyright &y& Elsevier]

Abstract: The paper presented a working fluid selection and parametric optimization using a multi-objective optimization model by simulated annealing algorithm. The screening criteria considered included heat exchanger area per unit power output (A/Wnet) and heat recovery efficiency (Ф). The independent parameters are the evaporation and condensation pressures, working fluid and cooling water velocities in tubes. A comparison of optimized results for 13 working fluids shows that boiling temperature of working fluids will greatly affect the optimal evaporating pressure. R123 is the best choice for the temperature range of 100–180°C and R141b is the optimal working fluid when the temperature higher than 180°C. When the exhaust temperature ranges from 100°C to 220°C, the optimal pinch point at evaporator is about 15°C. Economic characteristic of system decreases rapidly with heat source temperature decrease. When the heat source temperature is lower than 100°C, ORC technology is uneconomical. [Copyright &y& Elsevier]

A theoretical formula is proposed to calculate the OET (optimal evaporation temperature) of subcritical ORC (organic Rankine cycle) based on thermodynamic theory when the net power output is selected as the objective function. The OETs of 22 working fluids including wet, isentropic and dry fluids are determined under the given conditions. In order to compare the accuracy of these results, the quadratic approximation method in EES (Engineering Equation Solver) is used to optimize the net power output and the OETs are obtained by numerical simulation. The results show that the OETs calculated by the theoretical formula are consistent with the numerical simulation results. In addition, the average computational accuracy of OETs from the theoretical formula is higher than that from the simplified formula recommended by the related literature. The larger net power output will be produced when the critical temperature of working fluid approaches to the temperature of the waste heat source. According to the maximum net power output, suitable working pressure, total heat transfer capacity and expander SP (size parameter), R114, R245fa, R123, R601a, n-pentane, R141b and R113 are suited as working fluids for subcritical ORC under the given conditions in this paper. [Copyright &y& Elsevier]

Abstract: This paper provides a comparative study of the performance of cross-flow and counter-flow M-cycle heat exchangers for dew point cooling. It is recognised that evaporative cooling systems offer a low energy alternative to conventional air conditioning units. Recently emerged dew point cooling, as the renovated evaporative cooling configuration, is claimed to have much higher cooling output over the conventional evaporative modes owing to use of the M-cycle heat exchangers. Cross-flow and counter-flow heat exchangers, as the available structures for M-cycle dew point cooling processing, were theoretically and experimentally investigated to identify the difference in cooling effectiveness of both under the parallel structural/operational conditions, optimise the geometrical sizes of the exchangers and suggest their favourite operational conditions. Through development of a dedicated computer model and case-by-case experimental testing and validation, a parametric study of the cooling performance of the counter-flow and cross-flow heat exchangers was carried out. The results showed the counter-flow exchanger offered greater (around 20% higher) cooling capacity, as well as greater (15%–23% higher) dew-point and wet-bulb effectiveness when equal in physical size and under the same operating conditions. The cross-flow system, however, had a greater (10% higher) Energy Efficiency (COP). As the increased cooling effectiveness will lead to reduced air volume flow rate, smaller system size and lower cost, whilst the size and cost are the inherent barriers for use of dew point cooling as the alternation of the conventional cooling systems, the counter-flow system is considered to offer practical advantages over the cross-flow system that would aid the uptake of this low energy cooling alternative. In line with increased global demand for energy in cooling of building, largely by economic booming of emerging developing nations and recognised global warming, the research results will be of significant importance in terms of promoting deployment of the low energy dew point cooling system, helping reduction of energy use in cooling of buildings and cut of the associated carbon emission. [Copyright &y& Elsevier]

Abstract: Improving the performance of Multi Stage Flash (MSF) desalination plants is a major objective in the seawater desalination industry. Fresh water production rates from MSF plants depend on the evaporation range defined as the difference between the top brine temperature (TBT) and the bottom stage temperature. Lowering the temperature of the plant bottom stage elongates the evaporation range and increases the yield. A modified multi stage flash plant with brine mixing and cooling (MSF-MC) is presented in this paper. Part of the brine leaving the plant is mixed with fresh seawater feed then cooled to low temperature before it enters the bottom stage feed heater. This MSF-MC features several advantages such as expanded evaporation range at the conventional TBT levels, reduced feed pumping power, moderate levels of chemical treatment requirements and fixed fresh water production rates independent of seasonal seawater conditions. Operating with low feed mass fraction minimizes the cooling load and reduces the cooler size. An improvement in the yield by 1.18%–1.4% for every 1 °C reduction in the plant bottom temperature can be achieved with MSF-MC compared to conventional MSF systems. [Copyright &y& Elsevier]

Abstract: This paper deals with a numerical analysis of the evaporation of binary liquid film. The film is falling down on one plate of a vertical channel under mixed convection channel. The first plate of a vertical channel is externally submitted to a uniform heated flux q 1 while the second one (y = d) is dry and isothermal. The liquid mixture consists of water (the more volatile component) and ethylene glycol while the gas mixture has three components: dry air, water vapour and ethylene-glycol vapour. The results concern the effects of the inlet parameters in the gas and in the liquid film on the interfacial pressure, temperature and concentration profiles. The evolutions of the heat fluxes and of the water and mixture evaporation rates have been analysed. Results obtained show, in particular, that it is possible to increase the accumulated evaporation rate of water and of the liquid mixture when the inlet liquid concentration of ethylene glycol (the less volatile component) is less than 40%. This result has been explained by the fact that an increase of the inlet liquid concentration of ethylene glycol has two antagonistic effects on the accumulated evaporation rates of water and of liquid mixture. [Copyright &y& Elsevier]

Abstract: This work presents an experimental evaluation, from an energy analysis point of view, for two of the most used inter-stage systems in two-stage vapour compression cycles driven by compound compressors: the direct liquid injection and subcooler systems. The evaluation, considers the two-stage cycle with no intermediate systems as reference cycle and was performed on a plant, driven by a compound compressor using the refrigerant R404A for an evaporating temperature range of −36 to −20 °C and for a condensing temperature range of 30–47 °C. The analysis of the results shows that the inter-stage systems determine the performance of the energy parameters, which are discussed in the paper. The configuration yielding the best results was the two-stage compression cycle with subcooler, since the cooling capacity and COP values for this configuration were the highest. Conversely, the two-stage compression cycle working with direct liquid injection showed lower performance from an energy point of view, though this configuration allows a substantial reduction of the discharge temperature. [Copyright &y& Elsevier]

Abstract: This paper describes a specific thermodynamic analysis in order to efficiently match a vapour cycle to that of a stationary Internal Combustion Engine (ICE). Three different working fluids are considered to represent the main classes of fluids, with reference to the shape of the vapour lines in the T–s diagram: overhanging, nearly isoentropic and bell shaped. First a parametric analysis is conducted in order to determine optimal evaporating pressures for each fluid. After which three different cycles setups are considered: a simple cycle with the use of only engine exhaust gases as a thermal source, a simple cycle with the use of exhaust gases and engine cooling water and a regenerated cycle. A second law analysis of the cycles is performed, with reference to the available heat sources. This is done in order to determine the best fluid and cycle configuration to be employed, the main parameters of the thermodynamic cycles and the overall efficiency of the combined power system. The analysis demonstrates that a 12% increase in the overall efficiency can be achieved with respect to the engine with no bottoming; nevertheless it has been observed that the Organic Rankine Cycles (ORCs) can recover only a small fraction of the heat released by the engine through the cooling water. [Copyright &y& Elsevier]

Abstract: Desiccant evaporative systems are heat driven at moderate temperature and are usually coupled with solar collectors or with waste heat. The performance of desiccant systems is very sensitive to outside conditions and to the efficiency of the system components. In this paper the impact of these factors on the performance of two configurations of desiccant systems is investigated through simulation. First, a model of a desiccant air handling unit is briefly presented and validated experimentally. Then different efficiency combinations are studied and the critical efficiencies are derived. Finally, a comparison of the conventional and the recirculation configurations is made, based on outside conditions. [Copyright &y& Elsevier]

Air emissions from surface coating operations result from the evaporation of the organic solvents in the coatings and consist primarily of volatile organic compounds (VOCs). These VOC emissions can occur in a number of places along the production line: during atomization and application of the coating, during initial air drying of the part after it leaves the spray paint booth, and, eventually, in the bake oven.The aim of this paper is to present an innovative and sustainable process based on VOC absorption. An absorption tower is fed on the top by oil, which efficiently absorbs at low temperature the VOCs contained by the off-gas that enters the tower at its bottom. The mass ratio between oil and gas is approximately 1, so that a tray configuration results more efficiently than an alternative packed column. Saturated oil from the column is then stripped at high temperature in a vacuum system that condenses VOCs at a temperature slightly below the ambient temperature. Stripped oil is then recycled to the absorption tower. Special utilities are foreseen to reduce the water content in the gas and for energy recovery all over the plant. An industrial site located in Italy works at 14,000 Nm3/h off-gas absorbed with slightly more than 10 m3/h of oil. VOCs content in the off-gas ranges daily from 1200 to 2500 ppm; an average efficiency of approx. 90% recovery is presently obtained. A further reduction to an expected value of about 95–98% will be achieved in the next months. [Copyright &y& Elsevier]

The water injection after the compressor into the combustion air of a gas turbine and its evaporation by low-quality heat was analysed for different types of low-temperature heat sources and water-vapour contents of the pressurised air. To integrate low-quality heat—for example solar heat—into a conventional combined cycle efficiently and economically, the cycle must be changed in such a way that a maximum of low-temperature heat can be exploited. By injecting water into the compressed air, its evaporation takes place at partial pressure and therefore low-quality heat can be used. The new cycle uses only the stoichiometric air needed for the combustion. The air surplus for reducing the adiabatic temperature to the allowable gas turbine inlet temperature is substituted by water, which is injected into the compressed air and evaporated at partial pressure (i.e. at low temperature below 170 °C). After the heat recovery boiler the water-vapour content of the flue gas is recovered by partial condensation, cleaned and reused for injection. After presenting the features of the cycle, the paper concentrates on a preliminary design of the unit. Calculations were carried out for a variety of gas turbine inlet temperatures, pressure ratios and water-vapour contents. The results of the calculations are presented and the possibilities and difficulties of the low-quality heat integration will both be discussed. [Copyright &y& Elsevier]