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This paper presents a comparison of three surface condenser connection setups on the cooling water side. Four connections were considered, namely serial, mixed and two parallel ones. The analysis was conducted based on the calculated heat balances of proposed power unit for nominal and not nominal parameters for tested connections. Thermodynamic justification for the use of more complex configuration was verified. The exhaust steam pressure calculation was presented. Three methods of computing the heat transfer coefficient based on characteristic numbers, namely the Heat Exchange Institute (HEI) method, and the American Society of Mechanical Engineers (ASME) standard, were used. Calculation results were validated with the real data. The most accurate model was indicated and used in heat balance calculations. The assumptions and simplifications for the calculations are discussed. Examples of the calculation results are presented. [ABSTRACT FROM AUTHOR]

Pure drinking water sources are continuously decreasing day by day in the world and in contrast requirement is continuously increasing. Solar still is a device, which converts the saline water into pure form at a lower cost and is useful in the remote areas. But its less productivity and low efficiency is a significant issue to use it as potable water provider. Solar still productivity can be increased by using flat plate collectors, fins, evacuated tubes, different absorbing, and nanomaterials, but the major problem on its productivity is heat loss from glass cover to the ambient. Condenser reduces the temperature of the water vapor and maintain the condensation to enhance the productivity. This review shows different modification in the design of condenser attached with solar still to enhance the yield. At last the future work on the condenser is also discussed here. [ABSTRACT FROM AUTHOR]

The asymptotic formula is obtained for the capacity of a generalized condenser when parts of its plates contract to prescribed points. In contrast to the previous studies of capacity, we consider condensers with variable potential levels and establish the third term of the asymptotics. [ABSTRACT FROM AUTHOR]

• Novel mathematical model to predict the heat transfer rate of skin condensers. • Experimental validation with eigth hot-wall condenser designs. • Adhesive tape has the strongest impact on the heat exchanger performance. This paper comes out with an investigation of the thermal performance of skin-type hot-wall condensers for household refrigeration applications. Eight different hot-wall condensers were manufactured and installed in identical refrigerators. The condenser samples were constructed by varying the following design parameters: (i) adhesive tape (aluminum or polyethylene), (ii) tube O.D. (4.00 or 4.76 mm), (iii) total length (10 or 11.5 m) and (iv) condenser positioning. The refrigerators were placed inside a climate-controlled chamber and tested in steady-state conditions. A mathematical model that takes into account the heat transfer not only to the surroundings but also to the refrigerated compartments was also put forward. The model predictions were compared to the experimental data when deviations within the ±10% bounds were achieved. It was found that the adhesive tape thermal conductivity and the tube-outer sheet contact area have the strongest impact on the condenser performance. It was also found that the polyethylene tape increases the condensing pressure, due to its low thermal conductivity and thus to the smaller useful heat transfer area. It was thus concluded that the refrigerator foaming process must be carried out with an extreme care to avoid any negative impact on the tube-outer sheet contact resistance. Finally, it was noted that the heat transfer to the refrigerated compartments is directly affected by the condenser positioning and the thermal insulation thickness. [ABSTRACT FROM AUTHOR]

Desiccant coated heat exchangers (DCHEs), utilizing an inner cooling source to remove sorption heat, are promising alternatives for evaporators and condensers (DCEs/DCCs) in vapor compression (VC) heat pumps. A mathematical model is necessary to facilitate the design, analysis and performance prediction of the component and the relevant systems. In this study, a three-dimensional model of DCEs/DCCs is proposed, accounting for the two-phase phenomena, the periodical switchover, the solid-side resistance, the fluid transport in multiple directions and the coupled heat and mass transfer. Study reveals that, high latent load (inlet humidity) reduces the sensible heat handling capacity of the DCEs, while the dehumidification capacity is almost independent of its sensible heat load. DCEs possess a satisfying effect of dehumidification above the dew point, thus it is unnecessary to employ low evaporation temperature. Meanwhile, the adsorption-desorption temperature difference of 30°C seems to be the optimal value for the commonly adopted evaporation temperatures (10°C-20°C). For a specific coating thickness, there is a critical switchover period where the best performance of dehumidification is obtained. Switchover period shorter than the critical time should be avoided, and elongating the switchover cycle helps balance the ability of the system to handle the sensible and latent heat loads at the same time. [ABSTRACT FROM AUTHOR]

In the present work, a new thermosyphon active solar still is presented and experimentally investigated. To propose a simple and reliable alternative for remote regions, evacuated tube solar collectors were used to adsorb solar energy, and an enhanced condenser was employed to increase the rate of distillate production. Taking advantage of a special design, in addition to the collector, water could be poured into the basin and/or condenser. Accordingly, four possible conditions of performance were studied in this work; BECE: empty basin empty condenser, BFCE: filled basin empty condenser, BECF: empty basin filled condenser, BFCF: filled basin filled condenser. Analysis of the results showed the BECE, BFCE, BECF and BFCF cases produced 10.22, 11.86, 15.25 and 16.98 kg/(m2. day) of distillate, respectively. Consequently, it was concluded that filling the condenser effectively decreased the condenser temperature (increased temperature difference between basin and condenser), and caused 46% increase of distillate production. However, filling the basin (increasing evaporation area) enhanced the distillate production by only 14%. In overall, filling both of the basin and condenser simultaneously increased distillate production around 66%. In addition, it was revealed that the efficiencies of BECE, BFCE, BECF and BFCF cases, were 28.2, 34.7, 43.9 and 49.9%, respectively. Image 1 • A new thermosyphon active solar still was presented and investigated. • Enhanced condenser increased distillate production by 46%. • Increasing evaporation surface increased distillate production by 14%. • Production of optimized device increased 66% and reached 16.98 kg/(m2. day). • The temperature of enhanced condenser was around ambient temperature. [ABSTRACT FROM AUTHOR]

Making use of two different analytical–numerical methods for capacity computation, we obtain matching to a very high precision numerical values for capacities of a wide family of planar condensers. These two methods are based respectively on the use of the Lauricella function (Bezrodnykh and Vlasov, 2002; Bezrodnykh, 2016 [64,65]) and Riemann theta functions (Bogatyrëv, 2012; Grigoriev, 2013; Bogatyrëv and Grigor'ev, 2017; Bogatyrëv and Grigor'ev, 2018). We apply these results to benchmark the performance of numerical algorithms, which are based on adaptive h p -finite element method (Hakula et al. 2011, 2013, 2018) and boundary integral method (Tsuji, 1959; Jaswon and Symm, 1977; Albrecht and Collatz, 1980). [ABSTRACT FROM AUTHOR]

Summary: In terms of reducing the environmental pollution caused by effluent water from typical condensers and the water dependency of small modular reactors, indirect dry air‐cooled condensers (IDACs) are being considered an ultimate heat sink. While the performance of air‐cooled heat exchangers has been investigated thoroughly for decades, evaluations of the condenser performance rely primarily on empirical data. Thus, a method for precisely determining the performance of the IDAC under various environmental and thermal‐hydraulic conditions has not yet been understood. The objective of this study is to experimentally investigate the critical parameter that initiates the deterioration of the condenser performance by varying the cooling duty and water velocity. The investigation is also extended to a parametric study of the air‐cooling conditions using a best‐estimate thermal hydraulic analysis code called multi‐dimensional analysis of reactor safety (MARS‐KS) to suggest a method for designing an IDAC system. Results showed that, for a given cooling duty and water velocity, the condenser exhibited an insufficient performance above a certain cooling water temperature. The temperature was defined as the pressure transition temperature (PTT) that initiates the increase in pressure inside the condenser. The calculation results of MARS‐KS were analysed based on the PTT and was used to suggest methods for designing an appropriate IDAC for the cooling duty and environmental conditions of given target site. [ABSTRACT FROM AUTHOR]

The thermal design of an industrial shell-and-tube condenser requires the use of heat transfer coefficients, usually obtained from tables or correlations. Willing to develop a numerical model for design purposes, the present authors noticed the surprising diversity of correlations for the shellside heat transfer coefficient in the case of pure vapour condensation outside of horizontal smooth tubes. In order to shed light on this specific topic, a bibliographic study was therefore initiated. This comprehensive review is meant to provide the designers with means to understand how each correlation was obtained, from the assumptions to the resolution method. Thus two main phenomena are well accounted for in this paper: vapour shear stress and condensate inundation. Indeed, the review lists the most important contributions to this field and details their interconnections. Consequently, the present authors conclude this paper with their recommendations. [ABSTRACT FROM AUTHOR]

The prediction of freshwater production from the condenser of an agricultural seawater greenhouse is important for designing the greenhouse process. Two models, namely, Artificial Neural Network and multilinear regression (denoted as ANN and RA, respectively), were developed and tested to predict the freshwater production rate considering ambient solar intensity, condenser inlet moist-air temperature, humidity ratio and mass flowrate, and inlet coolant temperature. Statistical analysis indicated that all parameters significantly affected the prediction (p < 0.05). The accuracy of the ANN and RA models was then compared to two models previously developed by Yetilmezsoy and Abdul-Wahab and Al-Ismaili et al. (denoted as Yetilmezsoy model and Al-Ismaili model, respectively). The ANN model showed the best prediction when seven statistical criteria were considered. The Pearson correlations for ANN, RA, Yetilmezsoy, and Al-Ismaili models were observed as 1.00, 0.98, 0.88, and 0.96, respectively, while mean absolute percentage errors (MAPE) were 17.84, 79.72, 63.24, and 80.50%, respectively. Hence it could be recommended to use ANN model for the prediction of freshwater production rate, however other three simple models could also be used with lower accuracy in the cases of unavailability of the ANN model. [ABSTRACT FROM AUTHOR]

Highlights • Influence of the inlet vapour superheating in the condenser performance. • Opposite effect between the convective coefficient and the temperature difference. • Comparison between experimental data and a numerical model. • Influence of the condensing superheating zone included in the numerical model. Abstract In this investigation the influence of the degree of superheating at the inlet of a R134a condenser on its performance is studied. The degree of superheating is controlled by liquid injection from the condenser outlet by a membrane pump. The physical phenomena of influence are a reduction in the mean temperature difference and an increment in the overall heat transfer coefficient. An experimental rig has been built and a number of operating conditions tested as a function of the compressor capacity, evaporator power and the degree of inlet superheating. A numerical model has been developed for the experimental setup, the result of which has been compared with the experimental data. Additionally, the model has been used to understand the evolution of the heat transfer inside the condenser. It has been concluded that the overall condenser efficiency may slightly increase at high evaporator loads and high compressor capacities. [ABSTRACT FROM AUTHOR]

Seawater greenhouses (SWGH) utilize seawater or saline/brackish groundwater for cooling the microclimate and providing freshwater for irrigation through a humidification-dehumidification desalination process. The overall effectiveness of the SWGH greatly depends on the effectiveness of its condenser. The present study provides a good review on the available simulation models of the SWGH condenser and proposes a multiple linear regression model to predict the dehumidification rate of the condenser in the Oman SWGH. Four climatic and operational input variables were considered, including solar irradiance, inlet moist air temperature, inlet humidity ratio, and inlet air mass flow rate. The results showed that the model accurately predicts the dehumidification rate when compared against experimental values [a mean predictive error (PE) = −0.127 kg/h and root mean square error (RMSE) = 4.691 kg/h]. The model also outperformed some other model in several accuracy indicators such as PE, mean absolute predictive error, RMSE, R2, index of agreement and fractional variance. [ABSTRACT FROM AUTHOR]

The number of air-conditioning (AC) applications where natural refrigerants are used has grown in the past few years, mainly due to their favorable thermodynamic characteristics. Hence, a numerical investigation based on the second law of thermodynamics and Seasonal Energy Efficiency Ratio (SEER) for R-290/POE ISO 22 condensers is performed, where the impact of the transversal number of tubes, fin density and length of the finned tube is evaluated for three types of fins (plain, wavy and louver). Thermodynamic properties were generated via the departure function approach using the Peng–Robinson equation of state. The influence of the POE ISO 22 concentration is also accounted for in the heat transfer and pressure drop calculations. Depending on the available heat transfer area, plain or louver fins are more indicated to enhance the AC performance enhancement. For a fixed cooling capacity, points of maximum second law efficiency are achieved when the transversal number of tubes and tube length are varied. [ABSTRACT FROM AUTHOR]

For the simulation of condensers in a nuclear power plant, in general two approaches can be used, the lumped parameter model and the numerical method. The lumped parameter method is simple and rapid thus widely used in real-time simulations. The numerical method can provide more detailed information and achieve higher accuracy in comparison with the lumped model, but increases implementation complexity and computational cost. In real-time simulations of nuclear power plants, to solve the problem of uneven distribution of thermal parameters in condensers, which is not feasible for the lumped parameter method, a new method for the simulation of condensers was proposed in this research. The method divides the shell side and tube side of the condenser to different zones, and apply the lumped parameter method in each zone. The mass flow between zones in the model are calculated as flow nets. A posteriori testing has been conducted for the proposed model, thermal parameters in each zone are simulated and the results are verified with experimental benchmark data from an actual condenser. The comparison confirms that the proposed method is highly accurate not only in different steady state operations, the responses of each zone in dynamic-state operations are consistent with theoretical analyses as well. Unlike previous works, the model made it possible to get the distributions of thermal parameters in a condenser through real-time simulations on the actual working processes. [ABSTRACT FROM AUTHOR]

In view of a good thermal performance of the multi-louvered fin arrays, it is intended to introduce the special fin structure into the design of condensers for high power electricity converter cooling on the CRH (China Railway High-speed) trains in order to improve the security of normal running for the high-speed trains. The geometrical size of the multi-louvered fin arrays needed for the high power condensers is relatively larger than that of the conventional louvered fin arrays and the flow state within the large size multi-louvered fin arrays is different as well, with the Reynolds numbers based on the louver pitch over the range of 2850–11,000 in the present study. Flow and heat transfer characteristics of the large size multi-louvered fin arrays with various structural parameters are numerically simulated using Large Eddy Simulation (LES). More reasonable parameters correlated with the thermal-hydraulic performance of the large size multi-louvered fin arrays are identified compared to the conventional characteristic parameters employed in the published work. Finally, improved correlations for the Fanning friction f factor and the Colburn- j factor representing the flow and heat transfer characteristics, respectively, are put forward in terms of the identified parameters with special interval bounds for the condenser design of high power electronic cooling. [ABSTRACT FROM AUTHOR]

In the present study, numerical simulation of refrigeration cycle incorporated with a PCM heat exchanger is carried out. To this end, the refrigeration cycle without PCM has been simulated and then, the performance coefficients of the refrigerator in either with and without PCM are evaluated. The PCM heat exchanger is located in the refrigeration cycle, at a location after the condenser and before the expansion valve. The utilised PCM is N-Octadecane with fusion temperature of 27.5 °C. The simulation of heat exchanger is based on computational fluid dynamics (CFD) in which the flow inside the pipe is considered one-dimensional in the axial extension and PCM surrounding it, is considered two dimensional. Numerical simulation is carried out using MATLAB software. Simulation results show that utilizing PCM in refrigeration cycle of a refrigerator causes an improvement in the convection procedure and results a 9.58% increase in performance coefficient of refrigerator. [ABSTRACT FROM AUTHOR]

This paper presents an experimental work to study the effect of the condenser and the medium of saline water types on the performance of the solar still. Single slope solar still facing the south is used in this work. Also, four types of the condenser are tested: (i) glass, (ii) aluminum plate, (iii) aluminum heat sink with pin fins, and (iv) aluminum plate covered with an umbrella. Moreover, four mediums of the saline water inside the basin are examined: (i) only saline water in the basin, (II) Layers of black steel fibers in the basin, (iii) saturated sand with saline water, and (iv) mixture of sand and black steel fibers saturated with saline water. The solar still of only glass walls and only saline water in the basin is taken as a reference case. The performance of the other cases is referred to the reference case. The results indicate that using heat sink condenser increases the temperature of the saline water. Also, it increases the temperature difference between the condenser and the saline water relative to using glass condenser. Also, using a glass condenser with black steel fibers inside the water basin increases the daily productivity of freshwater by 35%. Using the heat sink condenser increases the daily productivity from 31% in the case of using only saline water to 52% in the case of using black steel fibers in the basin. Using an umbrella of 20 cm wide at the top of the aluminum plate condenser decreases the daily productivity by 26%. Increasing the umbrella wide to 40 cm decreases the daily productivity by 31%. [ABSTRACT FROM AUTHOR]

This work presents a modified solar still with pin fins absorber and external condenser. An experimental comparative study is carried out between the modified solar still with pin fins absorber and condenser, still with pin fins absorber and conventional still. This experimental study is conducted to evaluate the thermal behavior (evolutions of absorber and glass temperatures) and the water production performance of the modified solar still with pin fins absorber and condenser compared to other designs. All experiments are carried out under the meteorological conditions of the region of Gafsa-Tunisia during the days 01/26/2016, 01/27/2016 and 01/29/2016. Experimental results are presented, quantified and discussed to show the utility of the proposed modified solar still. [ABSTRACT FROM AUTHOR]

An example of assessment of condenser casing strength taking account of extending the casing life 30 years beyond the design life is discussed. [ABSTRACT FROM AUTHOR]

The paper describes the impact of non-condensable gas (NCG) on heat transfer in a steam turbine condenser (STC) and modelling of the steam ejector pump system (SEPS) by controlling the gas extraction rate through extraction tubes. The ideal connection points for the NCG extraction from the STC are identified by analysing the impact of the NCG on the heat transfer and measuring the existing system at a thermal power plant in Slovenia. A simulation model is designed using the Matlab software and Simulink, Neural Net Work, Fuzzy Logic and Curve Fitting Toolboxes, to control gas extraction rate through extraction tubes of the gas pumped from the STC, thus optimising the operation of the steam ejector pump system (SEPS). The gas extraction rate from the STC is controlled in the extraction tubes by pumping only the NCG to the maximum extent. The SEPS is optimised by selecting a Laval nozzle of appropriate size to reduce the steam for the operation of the SEPS, whereby the amount of the extracted NCG is maintained. As the SEPS motive steam is produced in a boiler, the consumption of coal for the production of the SEPS motive steam is reduced as well as the greenhouse gas environmental pollution. [ABSTRACT FROM AUTHOR]

The heat transfer performance variations of condensers that are caused by non-uniform distributions of air flows are investigated using a numerical simulation method. A heat exchanger designed for the outdoor unit of a heat pump system is selected and represented using a numerical model. A non-uniform profile of the air velocity is constructed through measuring the air velocity at various locations on the outdoor unit. Numerical analyses are conducted for various refrigerant circuits and air flow conditions. The results demonstrate that the heat transfer capacity is reduced depending on the air flow rate and the refrigerant circuit configuration. It is also demonstrated that the capacity reduction rate is increased as the average air velocity decreases. [ABSTRACT FROM AUTHOR]

Fin-tube heat exchangers are widely used in air-source heat pumps and air-conditioners. Because these heat exchangers are comprised of a number of tubes, there are innumerable ways of organizing the refrigerant circuitry. It is important to determine the number of refrigerant circuits because the circuitry significantly influences the performance of the heat exchangers. A method for determining the optimum number of circuits is proposed in this work. This method is applied to determine the optimum number of circuits for a fin-tube condenser. The performance analyses of fin-tube condensers with various circuit configurations demonstrates that the new method is useful in determining the number of circuits required in a heat exchanger. [ABSTRACT FROM AUTHOR]

Access to potable water to the people is narrowing down day after day all over the world. Most of the human diseases are caused by polluted or non-purified water resources. Water purification without affecting the ecosystem is the necessity of the hour. Solar distillation is one of the water purification techniques producing ultrapure distilled water. Solar still distillation systems offer sustainable tools for freshwater production. Numerous environmental and operational parameters attribute to optimize the still design. Different designs were tested by researchers to improve the productivity of solar still. In their experimentations, the solar still integrated with external or internal condenser is deemed to be effective and efficient design. In this detailed survey, we are seeking to introduce, explain and discuss the status of different solar stills integrated with different condensers arrangements. [ABSTRACT FROM AUTHOR]

This paper presents a performance analysis of air-cooled chillers with evaporatively cooled condenser in 3 different cities of Turkey with the help of meteorological data provided from the Turkish State Meteorological Service (TSMS). The aim of the study is to determine the effects of evaporative cooling on inlet air of the condenser unit under various humidity and temperature conditions, and therefore on cooling performance (COP) of the air conditioning system. Considering the summer season between June and September for 4 months, it is assumed that the cooling requirements are provided by the direct expansion air-conditioners and the condenser inlet air is cooled by evaporative cooler with 70% effectiveness. The results show that after the evaporative cooling the highest COP increase of the chillers is occurred in most arid city as 40.5%, while the lowest increase was in the most humid city as 15.5%. This improvement increased the cooling capacity by 14.3% and 5.56%, correspondingly. In addition, the mean electrical consumption is considerably decreased as 9.97%, 15.49% and 6.97% for 3 different cities. The highest water consumption was around 5 tons per day for 10 hours of operation and 1400 m3/min mean air flow rate. [ABSTRACT FROM AUTHOR]

This paper tackles an optimization approach in order to boost the fresh water production of a new design of a solar still which is located at Sfax engineering national school in Tunisia. This optimization approach is based upon the above mentioned design's improvement by coupling the conventional solar still into at a condenser, solar air and water collector and humidifier. This new concept of a distiller solar still using humidification- dehumidification processes (HD) is exploited for the desalination purpose. As a result of this work, the humidification- dehumidification processes have an essential effect in improving the solar still performance. Performance has been predicted theoretically in terms of water and inner glass cover temperatures, the inlet temperature of air and water of the new concept of distiller on water condensation rate and fresh water production. A general model based on heat and mass transfers in each component of the unit has been developed in steady dynamic regime. The developed model is used, simulating the HD system, to investigate the influence of the meteorological and operating parameters on the system productivity. The obtained set of ordinary differential equations has been converted to a set of algebraic system of equations by the functional approximation method of orthogonal collocation. The developed model is used to simulate the HD system in order to investigate the steady state behavior of each component of the unit and the entire system exposed to a variation of the entrance parameters and meteorological conditions. The obtained results were compared with those of other studies and the comparison gives a good validity of the present results. [ABSTRACT FROM AUTHOR]

Condensation heat transfer of R134a which flowed in the inner tube and cooling water which flowed in the annulus were experimentally investigated inside a smooth tube-in-tube heat exchanger in author’s previous studies. In this current work, the investigational setup consists of a 0.5 m long double tube and the inner tube is made up of smooth copper tubing of 9.52 mm outer diameter and 8.1 mm inner diameter. The experiments are carried out for the mass flux range of 260-515 kg m - 2 s - 1 and the heat flux range of 11.3-55.3 kW m - 2 and also at a mean saturation temperature interval of 40-50 °C. The mean heat transfer coefficient of R134a is found through executing an energy equivalence predicated on the energy flow from the test section. The predictability of actual correlations in open sources proposed for two-phase annular flow are tested by using authors’ experimental database. Alterations of vapor quality and saturation temperature difference with calculated condensation heat transfer coefficients are also shown according to different condensing temperatures and mass fluxes. Moreover, the independency of annular flow heat transfer empirical equations from tube orientation and the overall practicality for a vertical tube is validated. [ABSTRACT FROM AUTHOR]

This study evaluates the influence of latent heat storage elements on the condenser temperature of a commercial household refrigerator. In order to determine the power consumption and the temperature distribution, a standard wire-and-tube condenser is equipped with different heat storage elements (containing water, paraffin or copolymer compound). The results indicate that particularly the application of phase change materials (PCM) lowers the condenser temperature, which leads to a significantly reduced power consumption. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study about the effect of condenser subcooling on the performance of an air conditioning system operating with R134a and R1234yf, under the same operating conditions. For both refrigerants, it has been shown that the COP undergoes a maximum as a consequence of the trade-off between increasing refrigerating effect and increasing specific compression work. At a given operating condition, the system COP increased up to 18% for R1234yf and 9% for R134a. These results confirmed the trends obtained from a previous theoretical analysis, demonstrating that a system operating with R1234yf can benefit more from the condenser subcooling than that with R134a. The experimental results also showed that the presence of an internal heat exchanger significantly reduces the COP increase due to condenser subcooling, since both improvements compete towards reducing the throttling losses. Besides the interference between IHX and condenser subcooling, the use of both simultaneously still yields a more efficient air conditioning system, especially for R1234yf. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study about the effect of condenser subcooling on the performance of vapor-compression systems. It is shown that, as condenser subcooling increases, the COP reaches a maximum as a result of a trade-off between increasing refrigerating effect and specific compression work. The thermodynamic properties associated with the relative increase in refrigerating effect, i.e. liquid specific heat and latent heat of vaporization, are dominant to determine the maximum COP improvement with condenser subcooling. Refrigerants with large latent heat of vaporization tend to benefit less from condenser subcooling. For an air conditioning system, results indicate that the R1234yf (+8.4%) would benefit the most from condenser subcooling in comparison to R410A (7.0%), R134a (5.9%) and R717 (2.7%) due to its smaller latent heat of vaporization. On the other hand, the value of COP maximizing subcooling does not seem to be a strong function of thermodynamic properties. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a thermodynamic cycle for the production of electrical power in the 2-5 kW range, suitable for all types of thermally propelled vehicles. The sensible heat recovered from the exhaust gases feeds the energy recovery system, which is able to produce sufficient power to sustain the air conditioning system or other auxiliaries. The working fluids R134a and R245fa have been used in the ORC system, and the systems are simulated by CAMEL-ProTM software. The cycles are generated starting from the same heat source: the exhaust gas of a typical 2.0 L Diesel engine (or from a small size turbine engine). The design of the condenser has been performed to obtain a very compact component, evaluating the heat exchanger tube and fins type design. Through empirical formulas, the area of heat exchange, the heat required to exchange and the pressure drop in the element have been calculated. A commercial software package is used to build the model of the condenser, then a thermal and mechanical analysis and a CFD analysis are realized to estimate the heat exchange. Finally the evaluations, the possible future studies and possible improvements of the system are shown. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mathematical model of the heat pump plate condenser is nonlinear, steady-state, and lumped. [•] Numerical procedure Newton–Taylor linearization and Gauss elimination method. [•] Variables: water inlet temperature, pressure drop, c. pump power, and condenser surface. [•] Condenser performance as a function of c. pump power, pressure drop, and condenser surface. [•] Graphics of the condenser performance in two- and three-dimensional. [Copyright &y& Elsevier]

Corrosion and scaling of heat exchanger is a severe problem in oil refinery industries. In this paper, the corrosion mechanisms of tubes in the condenser at the top of the benzene tower have been investigated by elemental analyzer, optical microscopy, and scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. It is concluded that corrosion occurred outside the tube due to a trace amount of acidic water containing chloride ion which condensed on the surface of tubes. Then the condensed acidic water led to electrochemical corrosion during heat exchanging process in the condenser at the top of the tower. Chloride ion plays a very important role in the tube corrosion. The most important point is that chloride ion could cause the depassivation of material. Moreover, chloride ion is easily absorbed onto the surface of tubes due to the negative charge. Later, the corrosion of tubes is accelerated due to ion migration if the concentration of chloride ion increases. In addition, the loose scales of corrosion product also accelerate the electrochemical corrosion since it makes the acidic aqueous solution easier to stay and concentrate on the tube surface. [ABSTRACT FROM AUTHOR]

In this paper, an experimental study on the nature of the effects of condenser fouling on some performance characteristics and properties of a simple vapor compression system is presented. This is performed by gradually blocking the condenser air passage and measuring the change in condenser pressure, superheat temperature at the compressor exit, compressor power consumption and COP. The room temperature is kept at approximately 21 °C while the ambient temperature is at 31.6 °C with R22 as the cycle refrigerant. The variation in the above-mentioned quantities is found to be logarithmic in nature and this is connected to heat exchanger theory for phase change processes. Comparison with other works is also done and a consistent behavior is concluded for both properties as well as performance parameters. [ABSTRACT FROM AUTHOR]

Abstract: An experimental and numerical study has been carried out on the improvement of the energy performance of a refrigerating machine using a water spray upstream of the condenser. The experimental setup is based on a reversible heat pump used in cooling mode. The spray has been simply added upstream from the heat pump in order to investigate the possible performance improvements on a real machine, leaving its own control system free to adapt itself. Condensation temperature and pressure data have been measured on the refrigerating fluid side, while temperature and humidity have been measured on the air upstream and downstream the condenser. A complete model has been developed, combining a thermodynamic model for the system and heat transfer models on the air and refrigerating fluid sides. Comparisons have been carried out. Results show that water spraying upstream of the condenser may increase the global COP of the system (refrigerating machine plus spraying system) up to 28.9% for relatively hot and dry air conditions (relative humidity 19,7% and temperature 308 K). [Copyright &y& Elsevier]

The aim of the present research is the development of a computational tool for investigating condensation processes and equipment with particular attention to freeze-dryers. These condensers in fact are usually operated at very low pressures, making it difficult to experimentally acquire quantitative knowledge of all the variables involved. Mathematical modelling and CFD (Computational Fluid Dynamics) simulations are used here to achieve a better comprehension of the flow dynamics and of the process of ice condensation and deposition in the condenser, in order to evaluate condenser efficiency and gain deeper insights of the process to be used for the improvement of its design. Both a complete laboratory-scale freeze-drying apparatus and an industrial-scale condenser have been investigated in this work, modelling the process of water vapour deposition. Different operating conditions have been considered and the influence exerted by the inert gas as well as other parameters has been investigated. [ABSTRACT FROM AUTHOR]

The catalytic isotopic exchange module for hydrogen isotopes is described as a integrated system in the TRF of ICIT Ramnicu Valcea. Optimal functioning of the TRF states that for the cryogenic distillation column, gas input must have a controlled relative humidity and temperature. The catalytic exchange column can run for different input parameters of gas flow, liquid flow and temperature working regime. In situation of variable working temperature or inadequate thermostatic condition for the isotopic exchange column, demanded input parameters for the cryogenic distillation column must be obtain through different methods. One of the easiest and safety system equilibration methods requires the variation of refrigeration power of the condenser unit by the refrigeration agent flow variation. Changes in the refrigeration unit equilibrated the outlet temperature of the gas through the molsieve adsorber unit at certain values. Experimental data were obtained for different working regimes of the condenser unit installed in the catalyzed isotopic exchange system. The condensed liquid volume per time unit and the relative humidity at the condenser outlet were measured and reported in this paper. By controlling of the described parameters, considering also technical system design data and catalyst proprieties, for optimal isotopic column runs a thermic regime can be calculated and obtained. [ABSTRACT FROM AUTHOR]

Abstract: Air-conditioning (AC) system consumes high energy and releases waste-heat. In the present study, we propose a method to improve its performance and minimize waste-heat by replacing existing air-cooled condenser by an evaporation and transpiration, evapo-transpiration, condenser. The improvement is confirmed by performing experiment for a conventional air-cooled AC system and a water-cooled AC system. Condenser temperature in the air-cooled system is higher than outdoor-temperature by 5–10 °C, while it is −5 to 5 °C in case of the testing system. From simulation results, saving energy consumption is expected to reach up to 30% in summer with the testing system. Based on these results, an evapo-transpiration heat-exchanger was developed as a new condenser. Heat-transfer coefficient of the testing heat-exchanger is at least 4 times higher than that of air-cooled condenser. Even hot fluid is used inside copper-tubing, its outlet-air temperature is as nearly as outdoor temperature. [Copyright &y& Elsevier]

Abstract: The optimum design of a condenser is significant in an organic Rankine cycle to achieve higher waste heat utilization efficiency. Based on the mathematical model of a condenser using plate heat exchanger (PHE), some key geometric parameters on the total heat transfer surface area and pressure drop of the condenser are examined. In order to obtain geometric parameters of a plate heat exchanger, a multi-objective optimization of the condenser in organic Rankine cycle is conducted to achieve the optimal geometry design. The total heat transfer surface area and pressure drop are selected as two objective functions to minimize both total heat transfer surface area and pressure drop under the constant heat transfer rate and LMTD conditions. The plate width, plate length and plant distance are selected as the decision variables. Non-dominated sorting generic algorithm-II (NSGA-II) which is an effective multi-objective optimization method is employed to solve this multi-objective optimization design of PHE. The results show that an increase in channel distance or plate width increases the total heat transfer surface area and decreases pressure drop in the condenser. It is noted that the plate length of PHE has a positive effect on the optimization design of PHE. By multi-objective optimization design of the PHE, a Pareto optimal point curve is obtained, which shows that a decrease in total heat transfer surface area of a condenser can increase the pressure drop through the condenser. [Copyright &y& Elsevier]

Abstract: This paper assesses the thermo-hydraulic design approach introduced in a previous publication (Hermes, 2012) for condensers and evaporators aimed at minimum entropy generation. An algebraic model which expresses the dimensionless rate of entropy generation as a function of the number of transfer units, the fluid properties, the thermal-hydraulic characteristics, and the operating conditions is derived. Case studies are carried out with different heat exchanger configurations for small-capacity refrigeration applications. The theoretical analysis led to the conclusion that a high effectiveness heat exchanger does not necessarily provide the best thermal-hydraulic design for condenser and evaporator coils, when the rates of entropy generation due to heat transfer and fluid friction are of the same order of magnitude. The analysis also indicated that a high aspect ratio heat exchanger produces a lower amount of entropy than a low aspect ratio one. [Copyright &y& Elsevier]

Abstract: Bio-oil from fast pyrolysis of biomass consists of hundreds of compounds with a wide range of molecular weights. These include both volatile and non-volatile compounds and viscous oligomers, which complicates recovery of the liquid product from vapors and aerosols generated during pyrolysis. We have developed a bio-oil recovery system that overcomes the fouling problems that commonly occur in conventional condensers, allowing recovery of stage fractions (SF) of bio-oil with distinctive chemical and physical properties. The concept has been evaluated in an 8kg/h process development unit (PDU) consisting of a fluidized bed pyrolyzer, hot cyclones, and a series of condensers and electrostatic precipitators (ESPs) that recover five stage fractions. Red oak was pyrolyzed in the PDU and the resulting stage fractions of bio-oil analyzed for moisture, modified acid number (MAN), water insoluble content, solids content, higher heating value (HHV), kinematic viscosity and chemical composition. [Copyright &y& Elsevier]

It was analyzed the behavior of the cryogenic distillation column at the influence of an external factor. So, it was considered the non steady state for the column when exist a variation in the control system from the cooling circuit of the cryogenic distillation plant, which determine the fluctuation of the hydrogen level from the cryogenic distillation column condenser. The column has H height and NT theoretical stages, with the feed stream bicompound mixture of tritium and deuterium. The mathematical model for the simulation of the process is based on the equations of balance on the column, for the stages and for the condenser. The results were represented in specific diagrams and plots. Each parameter can offer information about the behavior of the distillation column operated at total reflux with sinusoidal oscillation of the liquid level in condenser. [ABSTRACT FROM AUTHOR]

Abstract: Flow condensation pressure drop characteristics of R410A–oil mixture inside small diameter (5.0 mm and 4.0 mm O.D.) horizontal microfin tubes were investigated experimentally covering nominal oil concentrations from 0% to 5%. The research results indicate that, comparing with the frictional pressure drop of pure R410A, the frictional pressure drop of R410A–oil mixture may decrease by maximum of 18% when the vapor quality is lower than 0.6, and increase by maximum of 13% when the vapor quality is higher than 0.6. A new frictional pressure drop correlation for R410A–oil mixture flow condensation inside microfin tubes is developed based on the refrigerant–oil mixture properties, and can agree with 94% of the experimental data within a deviation of −30% to +30%. [Copyright &y& Elsevier]

Abstract: This paper presents an advanced switched modeling approach for vapor compression cycle (VCC) systems used in Air Conditioning and Refrigeration. Building upon recent work (), a complete dynamic VCC model is presented that is able to describe the severe transient behaviors in heat exchangers (condenser/evaporator), while maintaining the moving-boundary framework, under compressor shut-down and start-up operations. The heat exchanger models retain a constant structure, but accommodate different model representations. Novel switching schemes between different representations and pseudo-state variables are introduced to accommodate the transitions of dynamic states in heat exchangers while keeping track of the vapor and liquid refrigerant zones during the stop–start transients. Two model validation studies on an experimental system show that the complete dynamic model developed in Matlab/Simulink can well predict the system dynamics in shut-down and start-up transients. [Copyright &y& Elsevier]

This work is a theoretical study that is related to the efficient use of heat pipes designed for cooling of computers. Refrigeration fluid absorbs heat from the heat source (Central Processing Unit - from CPU). The vaporizing fluid in the evaporator moves towards the condenser and condenses the cycle is completed. In this study, the designed cooling system with heat pipes mainly consists of a copper block located at CPU surface, six pieces circular channels inside block, and the heat pipes working are independent from each other. NH3, R-22 and R-134a were chosen as refrigeration fluids. Five different film temperatures were used for each fluid. It was determined that the most efficient cooling of CPU can be obtained with R-22. [ABSTRACT FROM AUTHOR]

Abstract: We describe the design and operation of a system for xenon liquefaction in which the condenser is separated from the liquid storage vessel. The condenser is cooled by a pulse tube cryocooler, while the vessel is cooled only by the liquid xenon itself. This arrangement facilitates liquid particle detector research by allowing easy access to the upper and lower flanges of the vessel. We find that an external xenon gas pump is useful for increasing the rate at which cooling power is delivered to the vessel, and we present measurements of the power and efficiency of the apparatus. [Copyright &y& Elsevier]

Abstract: This paper reports on the experimental research conducted to study the condensation of ammonia on smooth and integral-fin (32fpi) titanium tubes of 19.05mm outer diameter. Experiments were carried out at saturation temperatures of 30, 35, 40 and 45°C and wall subcoolings from 1 to 8°C. The results show that the condensation coefficients on the smooth tubes are well predicted by the Nusselt theory with an average error of +0.66% and within a deviation between −6.6% and +8.3%. The enhancement factors provided by the integral-fin tubes range from 0.77 to 1.22. The low enhancement factors are due to the high condensate retention between fins, which brings about flooded fractions of the tube perimeter from 62.9% to 73.2%, and the low thermal conductivity of titanium. The Briggs and Rose [1994. Effect of fin efficiency on a model for condensation heat transfer on a horizontal, integral-fin tube. Int. J. Heat Mass Transfer 37, 457–463.] model, which accounts for the conduction in the fins, predicts the experimental data with a mean overestimation of 20%. The analysis of the partial thermal resistances in the overall heat transfer process points out the convenience of enhancing the outside ammonia condensation when high water velocities are considered inside the tubes. [Copyright &y& Elsevier]

Abstract: Attention is drawn, to the fact that, while four different correlations for condensation in microchannels are in fair agreement for the case of R134a (on which the empirical constants in the correlations are predominately based) they differ markedly when applied to other fluids such as ammonia. A wholly theoretical model is compared with the correlations for both R134a and ammonia. [Copyright &y& Elsevier]

Abstract: Microchannel (or mini-channel) heat exchangers are drawing more attention because of the potential cost reduction and the lower refrigerant charge. Serpentine microchannel heat exchangers are even more compact because of the minimized headers. Using the serpentine microchannel condenser, some thermodynamically good but flammable refrigerants like R-290 (Propane) can be extended to more applications. To well size the serpentine microchannel condensers, a distributed-parameter model has been developed in this paper. Airside maldistribution is taken into account. Model validation shows good agreement with the experimental data. The predictions on the heating capacity and the pressure drop fall into ±10% error band. Further analysis shows the impact of the pass number and the airside maldistribution on the condenser performance. [Copyright &y& Elsevier]

Abstract: A passive solar still with separate condenser has been modeled and its performance evaluated. The system has one basin (basin 1) in the evaporation chamber and two other basins (2 and 3) in the condenser chamber, with a glass cover over the evaporator basin and an opaque condensing cover over basin 3. Basins 1, 2 and 3 yield the first, second and third effects respectively. The top part of the condensing cover is shielded from solar radiation to keep the cover relatively cool. Water vapor from the first effect condenses under the glass cover while the remainder of it flows into the condenser, by purging and diffusion, and condenses under the liner of basin 2. The performance of the system is evaluated and compared with that of a conventional solar still under the same meteorological conditions. Results show that the distillate productivity of the present still is 62% higher than that of the conventional type. Purging is the most significant mode of vapor transfer from the evaporator into the condenser chamber. The first, second and third effects contribute 60, 22 and 18% of the total distillate yield respectively. It is also found that the productivity of the solar still with separate condenser is sensitive to the absorptance of the liner of basin 1, and the mass of water in basins 1 and 2. The mass of water in basin 3 and wind speed have marginal effect on distillate production. Other results are presented and discussed in detail. [Copyright &y& Elsevier]