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Showing papers in "International Journal of Refrigeration-revue Internationale Du Froid in 1999"


Journal ArticleDOI
TL;DR: In this paper, a 1D analysis for the prediction of ejector performance at critical-mode operation is carried out, where constant pressure mixing is assumed to occur inside the constant-area section of the ejector and the entrained flow at choking condition is analyzed.
Abstract: A 1-D analysis for the prediction of ejector performance at critical-mode operation is carried out in the present study. Constant-pressure mixing is assumed to occur inside the constant-area section of the ejector and the entrained flow at choking condition is analyzed. We also carried out an experiment using 11 ejectors and R141b as the working fluid to verify the analytical results. The test results are used to determine the coefficients, h p, h s, f p and f m defined in the 1-D model by matching the test data with the analytical results. It is shown that the1-D analysis using the empirical coefficients can accurately predict the performance of the ejectors. q 1999 Elsevier Science Ltd and IIR. All rights reserved.

854 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented a transient model for a two-bed, silica gel-water adsorption chiller and found that regardless of the initial mass distribution, the chiller was able to achieve the same cyclic-steady state within four cycles or 1800s.
Abstract: This article presents a transient model for a two-bed, silica gel-water adsorption chiller. Compared with our previous cyclic-steady-state model, we found very good agreement between our model prediction and experimental data. We found that, regardless of the initial mass distribution, the chiller was able to achieve the same cyclic-steady-state within four cycles or 1800 s. We also demonstrated that the manufacturer had empirically evolved to select a fixed switching and cycle time such that the best peak evaporator temperature suppression, and near maximum cooling capacity can be achieved by a compact design.

265 citations


Journal ArticleDOI
TL;DR: In this article, two empirical correlations from the test results of 15 ejectors are derived for the performance prediction of ejectors using R141b as the working fluid, and a method of calculation for the ejector design using the correlations is also developed.
Abstract: In the present study, two empirical correlations from the test results of 15 ejectors are derived for the performance prediction of ejectors using R141b as the working fluid. The ratio of the hypothetical throat area of the entrained flow to the nozzle throat area Ae/At, the geometric design parameter of the ejector A3/At, and the pressure ratios Pg/Pe and Pc*/Pe are used to correlate the performance of the ejector. The prediction of the entrainment ratio v using the correlations is within ^ 10% error. A method of calculation for the ejector design using the correlations is also developed. R141b is shown in the present study to be a good working fluid for an ejector. The measured v for the ejectors used in the present study can reach as high as 0.54 at Pga 0.465 MPa (848C), Pc*a 0.087 MPa (288C) and Pea 0.040 MPa (88C). For Pga 0.538 MPa (908C), Pc*a 0.101 MPa (328C) and Pea 0.040 MPa (88C), v reaches 0.45. q 1999 Elsevier Science Ltd and IIR. All rights reserved.

152 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison of thermodynamic performances of sorption systems (liquid absorption, adsorption, ammonia salts and metal hydrides) is carried out for typical applications (deep-freezing, ice making, air-conditioning and heat pumping) with either air-cooled or watercooled heat sink.
Abstract: A comparison of thermodynamic performances of sorption systems (liquid absorption, adsorption, ammonia salts and metal hydrides) is carried out for typical applications (deep-freezing, ice making, air-conditioning and heat pumping) with either air-cooled or water-cooled heat sink. The results are given in terms of cooling coefficient of performance (COP) (heating COP or coefficient of amplification (COA) for the heat pump), cooling (heating) power versus reactor volume or weight and thermodynamic efficiency. LiBr–water systems show the best results for air-conditioning except when small units are required (metal hydride systems lead to more compact units). Other systems, however, show better results for other applications (chemical reaction with ammonia salts for deep-freezing, adsorption for heat pumping).

140 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of spraying water prior to vacuum cooling on the cooling time of fresh cut daffodils and found that spraying water can not only reduce cooling time without any negative effects on vase life but also reduce weight loss.
Abstract: Vacuum cooling has been widely used as a rapid cooling method for vegetables to enhance their quality and shelf life. The extension of vacuum cooling to the floricultural industry has great potential economic advantages. In the current study, vacuum cooling of freshly cut daffodils was carried out and their cooling processes were investigated. The vase life of vacuum cooled flowers with and without cold storage was studied. The results show that vacuum cooling can significantly extend the vase life of the flowers with and without cold storage and it is a very effective pre-cooling technique for cut flowers. Spraying water prior to vacuum cooling cannot only reduce the cooling time without any negative effects on vase life, but also weight loss. The reduction of weight loss is especially beneficial to vacuum cooling of vegetables.

117 citations


Journal ArticleDOI
TL;DR: In this article, the state-of-the-art performance of double effect cycles and thermal wave cycles with heat recovery and heat regeneration is evaluated in an entropic diagram of the two types of cycles.
Abstract: In these advanced adsorption cycles vapour is internally recovered between the two adsorbers, in which temperature is either uniform or non-uniform. In the first case, the cycles use the heat recovery process (double effect cycles), in the second case they use the heat regeneration process (thermal wave cycles). The full analysis (first law and second law) of vapour recovery is developed for either type of cycle. Different possible presentations in the entropic diagram of the cycles with heat recovery and those with heat regeneration are discussed. The thermodynamic differences between the two types of cycle can then clearly be highlighted. In addition, an evaluation of the current state of art of these two technologies is briefly presented.

113 citations


Journal ArticleDOI
TL;DR: In this paper, the air-side performance of fin-and-tube heat exchangers with slit geometry was investigated and the effects of fin pitch and the number of tube row were examined.
Abstract: The airside performance of fin-and-tube heat exchangers having slit geometry is experimentally investigated in this study. A total of 12 samples were tested and compared. Effects of fin pitch and the number of tube row were examined. The test results indicated that the heat transfer performance increase with decrease of fin pitch for N=1. However, for N⩾4, the effect of fin pitch on the heat transfer performance is reversed. In addition to the effect of fin pitch, the heat transfer performance decrease with increase of the number of tube row and the friction factors are relatively independent of the number of tube row. Based on the present test results and those from previous investigations, a general correlation is proposed to describe the airside performance of the slit fin configuration, the mean deviations of the proposed heat transfer and friction correlation are 5.5 and 3.8%, respectively.

106 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of energy efficiency evaluation of cogeneration systems for combined heat, cold and power production is addressed, where the primary energy rate (PER) and comparative primary energy saving (Δqp) of designed systems are compared.
Abstract: This paper deals with the problem of energetic efficiency evaluation of cogeneration systems for combined heat, cold and power production. Cogeneration systems have a large potential for energy saving, especially when they simultaneously produce heat, cold and power as useful energy flows. Various cogeneration systems for combined heat, cold and power production are designed by means of computer simulation to minimize consumption of the primary energy. Equations of energetic efficiency of this combined cogeneration systems are presented, that relate the primary energy rate (PER) and comparative primary energy saving (Δqp) to energy parameters of designed systems. Comparison of energetic efficiency of combined cogeneration systems with contemporary conventional separate production of heat, cold and power shows a large potential for energy saving by designed combined cogeneration systems.

103 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used neural networks and expert systems to control a gas/solid sorption chilling machine, where the backpropagation learning rule and the sigmoid transfer function have been applied in feed forward, full connected, single hidden layer neural networks.
Abstract: This works focuses on using neural networks and expert systems to control a gas/solid sorption chilling machine. In such systems, the cold production changes cyclically with time due to the batchwise operation of the gas/solid reactors. The accurate simulation of the dynamic performance of the chilling machine has proven to be difficult for standard computers when using deterministic models. Additionally, some model parameters dynamically change with the reaction advancement. A new modelling approach is presented here to simulate the performance of such systems using neural networks. The backpropagation learning rule and the sigmoid transfer function have been applied in feedforward, full connected, single hidden layer neural networks. Overall control of this system is divided in three blocks: control of the machine stages, prediction of the machine performance and fault diagnosis.

93 citations


Journal ArticleDOI
TL;DR: In this paper, experimental studies on thermal stratification in chilled-water storage systems are presented, where a fibreglass storage tank in static and dynamic modes of operation is used, and the parameters varied are aspect ratio, flow rates, initial temperature difference and thickness of insulation.
Abstract: This paper presents experimental studies on thermal stratification in chilled-water storage systems. A fibreglass storage tank in static and dynamic modes of operation is used. The parameters varied are aspect ratio, flow rates, initial temperature difference and thickness of insulation. Emphasis is given to the effects of mixing at the inlet, leading to the definition of the mixing coefficient. The thermocline decay increases with the value of mixing coefficient, which is expressed as a function of Reynolds number and Richardson number.

85 citations


Journal ArticleDOI
TL;DR: In this article, pressure drop through a capillary tube is modeled in an attempt to predict the size of capillary tubes used in residential air conditioners and also to provide simple correlating equations for practicing engineers.
Abstract: In this paper, pressure drop through a capillary tube is modeled in an attempt to predict the size of capillary tubes used in residential air conditioners and also to provide simple correlating equations for practicing engineers. Stoecker's basic model was modified with the consideration of various effects due to subcooling, area contraction, different equations for viscosity and friction factor, and finally mixture effect. McAdams' equation for the two-phase viscosity and Stoecker's equation for the friction factor yielded the best results among various equations. With these equations, the modified model yielded the performance data that are comparable to those in the ASHRAE handbook. After the model was validated with experimental data for CFC12, HFC134a, HCFC22, and R407C, performance data were generated for HCFC22 and its alternatives, HFC134a, R407C, and R410A under the following conditions: condensing temperature; 40, 45, 50, 55°C, subcooling; 0, 2.5, 5°C, capillary tube diameter; 1.2–2.4 mm, mass flow rate; 5–50 g/s. These data showed that the capillary tube length varies uniformly with the changes in condensing temperature and subcooling. Finally, a regression analysis was performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and subcooling. Thus determined simple practical equations yielded a mean deviation of 2.4% for 1488 data obtained for two pure and two mixed refrigerants examined in this study.

Journal ArticleDOI
TL;DR: In this paper, a computer model of a packed tower, able to determine heat and mass transfer between air and desiccant, has been developed and a parametrical study was carried out considering the solutions H2O/LiBr and H 2O/CaCl2 to determine the optimum operative conditions.
Abstract: Chemical dehumidification of air by a liquid desiccant in a packed tower has been investigated both theoretically and experimentally for air conditioning and industrial applications. A computer model of a packed tower, able to determine heat and mass transfer between air and desiccant, has been developed and a parametrical study was carried out considering the solutions H2O/LiBr and H2O/CaCl2 to determine the optimum operative conditions. An experimental apparatus including a packed tower and a desiccant regenerator has been described together with experimental results: a set of 70 experimental runs with H2O/LiBr. Data have been reported and compared against the results of the computer code simulations.

Journal ArticleDOI
TL;DR: In this article, the authors report on the results of experimental studies on the characteristics for a falling film absorber which is made up of 24 row horizontal smooth tubes and show that while the mass transfer coefficient increases with the increase of spray density, the heat transfer coefficient is increased only in small spray density range.
Abstract: The absorber is an important component in absorption machines and its characteristics have significant effect on the overall efficiency of absorption machines. This article reports on the results of experimental studies on the characteristics for a falling film absorber which is made up of 24 row horizontal smooth tubes. It shows that while the mass transfer coefficient is increased with the increase of spray density, the heat transfer coefficient is increased only in small spray density range. There is an optimum spray density between 0.005 and 0.055 kg s −1 m −1 spray density at which the heat transfer coefficient is maximum. The heat transfer coefficient (Nusselt number), which is traditionally expressed using Reynolds number and Prandtl number, was modified taking the effect of inlet solution concentration into account. The results can be used to optimize the future design of absorption machines having a falling film absorber and using LiBr/H 2 O as working fluid.

Journal ArticleDOI
TL;DR: In this paper, the authors defined the characteristic performance curves of vapor-compression refrigeration systems as a plot between the inverse coefficient of performance (1/COP) and inverse cooling capacity ( 1/Q evap ) of the system.
Abstract: The characteristic performance curves of vapor-compression refrigeration systems are defined as a plot between the inverse coefficient of performance (1/COP) and inverse cooling capacity (1/ Q evap ) of the system. Using the actual data of a simple vapor-compression system, performance curves of the system are obtained. The curves were found to be linear and this linear relation between 1/COP and 1/ Q evap is explained in the light of various losses of the system, resulting from the irreversibilities losses due to finite rate of heat transfer in the heat exchangers and non-isentropic compression and expansion in the compressor and expansion valve of the system, respectively. A finite-time thermodynamic model which simulates the working of an actual vapor-compression system is also developed. The model is used to study the performance of a variable-speed refrigeration system in which the evaporator capacity is varied by changing the mass-flow rate of the refrigerant, while keeping the inlet chilled-water temperature as constant. The model is also used for predicting an optimum distribution of heat-exchanger areas between the evaporator and condenser for a given total heat exchanger area. In addition, the effect of subcooling and superheating on the system performance is also investigated.

Journal ArticleDOI
TL;DR: In this paper, the authors used a packed bed of inert material to store heat between the adsorption and desorption phases of a convective thermal wave cycle to achieve high efficiency and small size from a solid adaption cycle.
Abstract: The convective thermal wave is part of a patented cycle which uses heat transfer intensification to achieve both high efficiency and small size from a solid adsorption cycle. Such cycles normally suffer from low power density because of poor heat transfer through the adsorbent bed. Rather than attempting to heat the bed directly, it is possible to heat the refrigerant gas outside the bed and to circulate it through the bed in order to heat the sorbent. The high surface area of the grains leads to very effective heat transfer with only low levels of parasitic power needed for pumping. The new cycle presented here also utilises a packed bed of inert material to store heat between the adsorption and desorption phases of the cycle. The high degree of regeneration possible leads to good coefficients of performance (COPs). Thermodynamic modelling, based on measured heat transfer data, predicts a COP (for a specific carbon) of 0.90 when evaporating at 5°C and condensing at 40°C, with a generating temperature of 200°C and a modest system regenerator effectiveness of 0.8. Further improvement is possible. Experimental heat transfer measurements and cycle simulations are presented which show the potential of the concept to provide the basis of a gas-fired air conditioner in the range 10–100 kW cooling. A research project to build a 10-kW water chiller is underway. The laboratory system, which should be operational by June 1997, is described.

Journal ArticleDOI
TL;DR: In this paper, a general distributed parameter model is presented to describe both steady and dynamic behaviors of dryexpansion evaporators, and three different non-homogeneous two-phase flow models are used to evaluate the impact of different flow models on the accuracy of the simulation.
Abstract: A general distributed parameter model is presented to describe both steady and dynamic behaviors of dry-expansion evaporators. The homogeneous and three different non-homogeneous two-phase flow models are used to evaluate the impact of different flow models on the accuracy of the simulation. The experimental work was carried out on a full-scale refrigeration system with R-134a as the working fluid and without frost formation at the evaporator. Comparison between the modelling and experimental measurements shows that the drift flux flow models give satisfactory predictions. The simulation results indicate that an even air temperature distribution off the evaporator may be obtained by controlling liquid dry-out point at the two ends of the coil. The study also indicates that the counterflow configuration provides a higher heat exchange efficiency with a slower transient response compared with the cocurrent-flow configuration. A general distributed parameter model is presented to describe both steady and dynamic behaviors of dry-expansion evaporators. The homogeneous and three different non-homogeneous two-phase flow models are used to evaluate the impact of different flow models on the accuracy of the simulation. The experimental work was carried out on a full-scale refrigeration system with R-134a as the working fluid and without frost formation at the evaporator. Comparison between the modelling and experimental measurements shows that the drift flux flow models give satisfactory predictions. The simulation results indicate that an even air temperature distribution off the evaporator may be obtained by controlling liquid dry-out point at the two ends of the coil. The study also indicates that the counterflow configuration provides a higher heat exchange efficiency with a slower transient response compared with the cocurrent-flow configuration.

Journal ArticleDOI
TL;DR: In this article, three different schemes of metal hydride solid sorption devices for heat pumping and cooling applications are presented and compared based on theoretical evaluations, and key parameters obtained from experimental and simulation results from coupled metal hyddride reaction beds have been used for the theoretical evaluation.
Abstract: Three different schemes of metal hydride solid sorption devices for heat pumping and cooling applications are presented and compared based on theoretical evaluations. Key parameters obtained from experimental and simulation results from coupled metal hydride reaction beds have been used for the theoretical evaluation. The single (HS) and double stage (HD) devices show reasonable performances, but they require many moving parts. Using high performance reaction beds, e.g. a capillary tube bundle reaction bed, cycle times of about 5–10 min can be obtained with these devices. This corresponds to a specific power output of 100–200 W kg−1 (HS) or 150–300 W kg−1 (HD), referred to the total hydride inventory of the machine. The multi-hydride-thermal-wave (HW) system has a lower specific power output, but it offers significant advantages like modest hardware effort, low pumping power and a very wide operating temperature range.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the performance of a plain fin, a strip fin and combinations thereof in the fin-and-tube heat exchanger and found that a hybrid fin, plain fin at front row and strip fin at rear row, was more effective to enhance the heat transfer than that of the whole strip fin.
Abstract: This work discusses about the pressure drop and heat transfer characteristics of a plain fin, a strip fin and combinations thereof in the fin-and-tube heat exchanger. Experimental apparatus and test algorithm using scale-up model fin geometry are discussed. The present work uses the electric heaters inside of the tube as the heating source to simulate the hot water loop in the wind tunnel test. The test results of the plain and strip fins are compared with the existing correlation and experimental data. It was found that a hybrid fin, plain fin at front row and strip fin at rear row, was more effective to enhance the heat transfer than that of the whole strip fin at the same fan power.

Journal ArticleDOI
TL;DR: In this paper, the authors numerically evaluate some of the parameters involved in modeling the process of frost formation on flat cold surfaces subject to the flow of humid air and compare the results with available results in the literature.
Abstract: This paper numerically evaluates some of the parameters involved in modeling the process of frost formation on flat cold surfaces subject to the flow of humid air. The model employs one-dimensional transient formulation based upon the local volume averaging technique. The modeling process was validated by comparison with available experimental data. Numerical experiments were realized to determine the best initial values of the diffusivity, initial radius and geometry of the ice crystals. This model was applied to the known case of flow of humid air over a single flat cold plate to predict the frost temperature, density and thickness distribution along the flow direction and also the void fraction. The results were compared with available results in the literature. The model was then extended to solve the case of flow of humid air between two parallel cold plates for which there are no available results.

Journal ArticleDOI
TL;DR: In this article, a thermodynamic computer analysis of an automobile air-conditioner was carried out for the initial screening of possible mixture candidates, and refrigerant mixtures composed of HCFC22, HFC134a, HCFC142b, RE170 (dimethylether), HC290 (propane), and HC600a (iso-butane) were proposed to supplement CFC12.
Abstract: In this study, thermodynamic performance of supplementary/retrofit refrigerant mixtures for CFC12 used in existing automobile air-conditioners was examined. A thermodynamic computer analysis of an automobile air-conditioner was carried out for the initial screening of possible mixture candidates, and refrigerant mixtures composed of HCFC22, HFC134a, HCFC142b, RE170 (dimethylether), HC290 (propane), and HC600a (iso-butane) were proposed to supplement CFC12. Also a breadboard type refrigeration test facility was manufactured to verify the performance of the alternative refrigerant mixtures proposed through the computer analysis. Test results showed that HFC134a/RE170 mixture with zero ozone depletion potential is the best long term candidate to supplement CFC12. On the other hand, HCFC22/HFC134a/RE170 and HCFC22/HFC134a/HCFC142b mixtures are good only as short term supplementary/retrofit alternatives since they contain HCFC22. A hydrocarbon mixture of HC290/HC600a showed a good performance but its use in existing automobile air-conditioners should be carefully considered due to its flammability.

Journal ArticleDOI
TL;DR: In this article, the influence of mixture composition on the occurrence of pinch points is studied and it is shown that multi-component mixtures are preferable over many wide boiling binary mixtures for various applications from the point of view of pinch point and glide matching.
Abstract: In a recent study, it was shown by the authors that perfect glide matching of heat transfer fluid and the refrigerant is difficult in condensers and evaporators for many zeotropic mixtures and also that pinch points can occur in both the condensers and evaporators due to the non-linear variation of enthalpy during phase change. Also, a simple method was presented for predicting the occurrence of pinch points. In this paper, the influence of mixture composition on occurrence of pinch points is studied. From the thermodynamic analysis, it is shown that multi-component mixtures are preferable over many wide boiling binary mixtures for various applications from the point of view of pinch points and glide matching. The results are illustrated with a number of examples.

Journal ArticleDOI
TL;DR: In this article, the effect of circuitry on the performance of wavy finned condensers was investigated and a total of eight arrangements were made and tested, and the test results indicated that counter-cross flow would give better performance than other arrangements.
Abstract: An experimental study was carried out to investigate the effect of circuitry on the performance of wavy finned condensers. A total of eight arrangements were made and tested. The arrangements included six 1-circuit and two 2-circuit arrangements. For the one-circuit arrangement, the test results indicate that counter-cross flow would give better performance than other arrangements. However, heat conduction along the fins may offset the benefits of the counter-cross arrangement. This study has proposed two modifications to the counter-cross flow arrangement. For the two-circuit arrangement, a unique characteristic of “pressure gain” was observed when one circuit is completely condensed and the other is still in two-phase region.

Journal ArticleDOI
TL;DR: In this article, experimental studies are carried out on a metal hydride cooling system working with ZrMnFe/MmNi4.5Al0.5 pair.
Abstract: Experimental studies are carried out on a metal hydride cooling system working with ZrMnFe/MmNi4.5Al0.5 pair. The effects of operating parameters such as heat source, heat sink and refrigeration temperatures, and half-cycle times on the system performance are obtained. The experimental results are compared with an analytical model proposed earlier by the authors, and a satisfactory agreement is found between the two.

Journal ArticleDOI
TL;DR: In this article, a comparison of compression/absorption heat pump performance with compression heat pump (CHP) and compression heat pumps (CAHP) is performed for various heating applications and with specified investment level.
Abstract: This article concerns two main studies: a parameter study and a comparison. In the parameter study, the CAHP is focused upon. Its COP sensitivity to changes in the absorber and desorber falling-film tube length, heat exchanger area distribution, and concentration change of the solution in the absorber is studied. The relative distribution between the desorber and absorber is found to have little impact on COP. The area distributed to the solution heat exchanger and the concentration change in the absorber is found to have a large impact on COP when examined separately, but when they are studied together, and with optimized concentration change for each area distribution, the total impact is low. It is shown that the falling-film tubes should be designed to be as long as possible in order to increase the COP. The comparison involves a new procedure for comparing the performance (COP) of a compression/absorption heat pump (CAHP) with that of a compression heat pump (CHP). In the procedure local heat transfer coefficients and pressure drop are taken into account. Further, the comparison is performed for various heating applications and with specified investment level. The heating applications are typically industrial or district heating cases and are chosen to study impact of three different kinds: size of the sink and source temperature change (glide), temperature lift for a given sink and source glide and temperature level for a given sink and source glide. Ammonia/water is used as working fluid in the CAHP and isobutane in the CHP. A relevant industrial design is assumed for the CHP (including an indirect economizer coupling, suction gas heat exchanger, sub-cooler and surface enhancements in evaporator and condenser), which is not the case in previous comparisons of this type. The absorber and desorber in the CAHP are modeled as vertical falling-film tube-and-shell heat exchangers. The main results for the comparison study are: (1) the COP of the CAHP is as good as that of the CHP when the sink and source glides are 10 K; (2) when the glide of the sink and source is increased to 20 K, the CAHP has a 12% better performance than the CHP; and (3) an increased temperature lift and an increased temperature level give the CAHP a relatively worse COP. Some COP-increasing design parameters to be studied further are proposed for the CAHP.

Journal ArticleDOI
TL;DR: In this paper, an etude de l'influence des lubrifiants circulant dans les installations frigorifiques, sur les mecanismes d'ebullition ou condensation convective, ainsi que le manque de donnees fournies par les fabricants imposent l'utilisation de modeles predictifs for the determination des proprietes thermodynamiques et de transport, d'une part, des huiles de lubrification, d''une part des melanges de fr
Abstract: Resume L'etude de l'influence des lubrifiants circulant dans les installations frigorifiques, sur les mecanismes d'ebullition ou condensation convective, ainsi que le manque de donnees fournies par les fabricants imposent l'utilisation de modeles predictifs pour la determination des proprietes thermodynamiques et de transport, d'une part, des huiles de lubrification, d'autre part des melanges de frigorigenes et d'huiles Cette etude propose un recueil de correlations pour le calcul des proprietes des huiles Ensuite, une comparaison de quelques methodes disponibles dans la litterature pour determiner les proprietes de tels melanges est presentee

Journal ArticleDOI
TL;DR: In this paper, experimental analysis was performed for ammonia-water falling film absorption process in a plate heat exchanger with enhanced surfaces such as offset strip fin, and the authors examined the effects of liquid and vapor flow characteristics, inlet subcooling of the liquid flow and inlet concentration difference on heat and mass transfer performance.
Abstract: In this article, experimental analysis was performed for ammonia–water falling film absorption process in a plate heat exchanger with enhanced surfaces such as offset strip fin. This article examined the effects of liquid and vapor flow characteristics, inlet subcooling of the liquid flow and inlet concentration difference on heat and mass transfer performance. The inlet liquid concentration was selected as 5%, 10% and 15% of ammonia by mass while the inlet vapor concentration was varied from 64.7% to 79.7%. It was found that before absorption started, there was a rectification process at the top of the test section by the inlet subcooling effect. Water desorption phenomenon was found near the bottom of the test section. It was found that the lower inlet liquid temperature and the higher inlet vapor temperature, the higher Nusselt and Sherwood numbers are obtained. Nusselt and Sherwood number correlations were developed as functions of falling film Reynolds Re 1 , vapor Reynolds number Re v , inlet subcooling and inlet concentration difference with ±15% and ±20% error bands, respectively.

Journal ArticleDOI
TL;DR: In this article, les caracteristiques thermophysiques intrinseques du fluide sont etudiees soit theoriquement, soit a partir d'une analyse bibliographique.
Abstract: Resume Les contraintes environnementales, de plus en plus fortes, impliquent la mise en oeuvre des solutions nouvelles dans les operations industrielles ou tertiaires de distribution du froid. Parmi ces solutions figurent l'emploi des fluides frigoporteurs diphasiques. Le fluide etudie dans ce travail est un melange forme de glace et d’une solution aqueuse d’ethanol appele coulis de glace. Dans cette premiere partie de l'article, les caracteristiques thermophysiques intrinseques du fluide sont etudiees soit theoriquement, soit a partir d’une analyse bibliographique. On donne les variations de l’enthalpie, de la masse volumique, de la conductivite, de la capacite thermique apparente et de la viscosite du melange en fonction de la temperature (de 20 °C a − 30 °C) pour diverses valeurs de la concentration initiale de la solution en alcool. Pour les variations de l'enthalpie, une confirmation experimentale de la methode de calcul utilisee est realisee. La deuxieme partie de l’article est consacree a des etudes experimentales du comportement thermique et rheologique du coulis de glace.

Journal ArticleDOI
TL;DR: In this paper, two adsorption systems are considered: zeolite-water and activated carbon-methanol, both consisting of two ''uniform temperature'' adsorbent beds operating with internal heat recovery by a heat carrier circuit.
Abstract: Two adsorption systems are considered: zeolite–water and activated carbon–methanol, both consisting of two `uniform temperature' adsorbent beds operating with internal heat recovery by a heat carrier circuit. Regarding the zeolite–water system, the performance obtained with a new adsorbent bed, with good heat transfer properties, is compared with a traditional tube and fin exchanger embedded with zeolite pellets. The performances were calculated by using a dynamic model developed and validated previously. Results show that the system based on the new adsorber has a higher specific power and the same Coefficient of Performance. Results of simulation for adsorbers consisting of finned tube heat exchangers and utilising the activated carbon–methanol pair are also presented.

Journal ArticleDOI
TL;DR: In this paper, the condensation heat transfer coefficients (HTCs) of a plain tube, low fin tube, and Turbo-C tube were measured for the low pressure refrigerants CFC11 and HCFC123 and for the medium pressure (HFC12 and HFC134a) for all the tubes tested.
Abstract: In this study, condensation heat transfer coefficients (HTCs) of a plain tube, low fin tube, and Turbo-C tube were measured for the low pressure refrigerants CFC11 and HCFC123 and for the medium pressure refrigerants CFC12 and HFC134a. All data were taken at the vapor temperature of 39°C with a wall subcooling of 3–8°C. Test results showed that the HTCs of HFC123, an alternative for CFC11, were 8.2–19.2% lower than those of CFC11 for all the tubes tested. On the other hand, the HTCs of HFC134a, an alternative for CFC12, were 0.0–31.8% higher than those of CFC12 for all the tubes tested. For all refrigerants tested, the Turbo-C tube showed the highest HTCs among the tubes tested showing almost an 8 times increase in HTCs as compared to the plain tube. Nusselt's prediction equation yielded a 12% deviation for the plain tube data while Beatty and Katz's prediction equation yielded a 20.0% deviation for the low fin tube data.

Journal ArticleDOI
TL;DR: In this article, the basic mechanism of Marangoni convection in absorption systems was reviewed from the viewpoints of the surface tension and the interfacial tension gradients, and it was proposed that the radical-out model should be a criterion for MARM induction within the solubility limit in NH3-H2O system.
Abstract: The objectives of this paper are to obtain experimental data of surface tension and interfacial tension, and to develop a new model of Marangoni convection for the best selection of heat transfer additive in ammonia–water absorption systems. The basic mechanism of Marangoni convection in absorption systems was reviewed from the viewpoints of the surface tension and the interfacial tension gradients. Marangoni convection was successfully visualized using a shadow graphic method. The solubility limits of the additives in ammonia–water solution ranged from 500 to 3000 ppm depending on the heat transfer additives. These values are much higher than those in LiBr–H2O solution in which the solubility ranged from 70 to 400 ppm. The temperature gradient of the surface tension should not be a criterion for Marangoni convection inducement in NH3–H2O system. The concentration and temperature gradients of the interfacial tension should not be a criterion for Marangoni convection inducement in NH3–H2O system. The magnitude of the interfacial tension did not affect the occurrence of Marangoni convection either. It was found that addition of the heat transfer additive beyond the solubility limit assisted Marangoni convection occurrence, but should not be a criterion for Marangoni convection inducement. It was proposed that the radical-out model should be a criterion for Marangoni convection inducement within the solubility limit in NH3–H2O system.