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Showing papers in "International Journal of Refrigeration-revue Internationale Du Froid in 2007"


Journal ArticleDOI
TL;DR: A new method by combining the model-based FDD method and the Support Vector Machine (SVM) method can help to maintain the health of the HVAC systems, reduce energy consumption and maintenance cost.
Abstract: Preventive maintenance plays a very important role in the modern Heating, Ventilation and Air Conditioning (HVAC) systems for guaranteeing the thermal comfort, energy saving and reliability. Its key is a cost-effective Fault Detection and Diagnosis (FDD) method. To achieve this goal, this paper proposes a new method by combining the model-based FDD method and the Support Vector Machine (SVM) method. A lumped-parameter model of a single zone HVAC system is developed first, and then the characteristics of three major faults, including the recirculation damper stuck, cooling coil fouling/block and supply fan speed decreasing, are investigated by computer simulation. It is found that the supply air temperature, mixed air temperature, outlet water temperature and control signal are sensitive to the faults and can be selected as the fault indicators. Based on the variations of the system states under the normal and faulty conditions of different degrees, the faults can be detected efficiently by using the residual analysis method. Furthermore, a multi-layer SVM classifier is developed, and the diagnosis results show that this classifier is effective with high accuracy. As a result, the presented Model-Based Fault Detection and Diagnosis (MBFDD) method can help to maintain the health of the HVAC systems, reduce energy consumption and maintenance cost.

212 citations


Journal ArticleDOI
TL;DR: Prospective methods for future simulation of refrigeration systems, such as noise-field simulation, simulation with knowledge engineering methodology and calculation methods for nanofluid properties, are introduced briefly.
Abstract: Simulation has been widely used for performance prediction and optimum design of refrigeration systems. A brief review on history of simulation for vapour-compression refrigeration systems is done. The models for evaporator, condenser, compressor, capillary tube and envelop structure are summarized. Some developing simulation techniques, including implicit regression and explicit calculation method for refrigerant thermodynamic properties, model-based intelligent simulation methodology and graph-theory based simulation method, are presented. Prospective methods for future simulation of refrigeration systems, such as noise-field simulation, simulation with knowledge engineering methodology and calculation methods for nanofluid properties, are introduced briefly.

185 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of the cycle is studied by means of a method introduced in previous papers which consists of assessing the goodness of a calculation method by looking at representative variables such as the evaporation or the condensation temperature depending on the case evaluated.
Abstract: This paper studies refrigeration cycles in which plate heat exchangers are used as either evaporators or condensers. The performance of the cycle is studied by means of a method introduced in previous papers which consists of assessing the goodness of a calculation method by looking at representative variables such as the evaporation or the condensation temperature depending on the case evaluated. This procedure is also used to compare several heat transfer coefficients in the refrigerant side. As in previous works the models of all the cycle components are considered together with the heat exchanger models in such a way that the system of equations they provide is solved by means of a Newton–Raphson algorithm. Calculated and measured values of the evaporation and the condensation temperatures are also compared. The experimental results correspond to the same air-to-water heat pump studied in other papers and they have been obtained by using refrigerants R-22 and R-290.

172 citations


Journal ArticleDOI
TL;DR: In this article, a comprehensive comparative parametric analysis of packed bed dehumidifiers for three commonly used desiccant materials viz. triethylene glycol, lithium chloride and calcium chloride is presented.
Abstract: Desiccant systems find applications in a very large variety of industrial and daily usage products including the new HVAC installations. An overview of liquid desiccant technology has been presented in this paper along with a compilation of experimental performance data of liquid desiccant dehumidifiers, empirical dehumidification effectiveness and mass transfer correlations in a useful and easy to read tabular format. The latest trends in this area suggest that hybrid systems are of current interest to HVAC industry, not only for high latent load applications but also for improving indoor air quality. The paper presents a comprehensive comparative parametric analysis of packed bed dehumidifiers for three commonly used desiccant materials viz. triethylene glycol, lithium chloride and calcium chloride, using empirical correlations for dehumidification effectiveness from the literature. The analysis reveals significant variations and anomalies in trends between the predictions by various correlations for the same operating conditions, and highlights the need for benchmarking the performance of desiccant dehumidifiers.

166 citations


Journal ArticleDOI
TL;DR: In this article, a rotary solid desiccant cooling system using a compound Desiccant Wheel (DW) has been developed, which can work well under a lower regeneration temperature and have a higher dehumidification capacity.
Abstract: The paper is aimed to develop a high performance rotary solid desiccant cooling system using a novel compound desiccant wheel (DW). The unique feature of the desiccant wheel is that it can work well under a lower regeneration temperature and have a higher dehumidification capacity due to the contribution of the new compound desiccant materials. Experimental results indicate that the novel desiccant wheel under practical operation can remove more moisture from the process air by about 20–40% over the desiccant wheel employing regular silica gel. A mathematical model that is used to predict the system performance has been validated with the test results. By integrating the desiccant wheel with evaporative cooling, heat recovery and heating for regeneration sections, a solid desiccant cooling system can be formed. Simulation results show that because of the use of the new compound desiccant, the desiccant cooling system can work under much lower regeneration temperature and have a relative high COP, thus low grade thermal energy resources, such as solar energy, waste heat, etc., can be efficiently utilized to drive such a cooling cycle.

154 citations


Journal ArticleDOI
TL;DR: In this article, the results of an investigation into the free cooling efficiency in a heavyweight and lightweight low energy building using a mechanical ventilation system with two latent heat thermal energy storages (LHTESs), one for cooling fresh supply air and the other for cooling the recirculated indoor air.
Abstract: This article presents the results of an investigation into the free cooling efficiency in a heavyweight and lightweight low energy building using a mechanical ventilation system with two latent heat thermal energy storages (LHTESs), one for cooling the fresh supply air and the other for cooling the re-circulated indoor air. Both LHTESs contain sphere encapsulated PCM (paraffin RT20). Using a developed and experimentally verified numerical model of the LHTES, the temperature response functions, based on the heat storage size, the air flow rates and the PCM's thermal properties, are established in the form of a Fourier series and empirical equations and used in the TRNSYS building thermal response model. Several mechanical ventilation, night cooling and free cooling operation modes were analysed and compared. It was found that the free cooling technique enables a reduction in the size of the mechanical ventilation system, provides more favourable temperatures and therefore enables better thermal comfort conditions, and in our studied case also fresh air for the occupants.

137 citations


Journal ArticleDOI
TL;DR: In this article, a two-bed, activated carbon fiber (ACF)-ethanol adsorption chiller is presented, which utilizes effectively low-temperature waste heat sources of temperature between 60 and 95°C along with a coolant at 30°C.
Abstract: This article presents the transient modelling for a two-bed, activated carbon fiber (ACF)–ethanol adsorption chiller. This innovative adsorption chiller employs pitch based ACF of type A-20 as adsorbent which is a fibrous adsorbent having the advantages of fast adsorption rate, high porosity and ease of handling when compared with granular adsorbents and powdered adsorbents. Ethanol is used as refrigerant as it has no harm to environment, it is a non-toxic substance, moreover, ethanol has comparatively higher vapor pressure even at low temperature. This innovative system utilizes effectively low-temperature waste heat sources of temperature between 60 and 95 °C along with a coolant at 30 °C. We have found that, regardless of the initial mass distribution, the ACF–ethanol adsorption chiller is able to achieve the same cyclic-steady-state within three cycles or 1890 s.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the bubble behavior during the NH 3 /H 2 O absorption process with chemical surfactant and nano-particles was analyzed and the effect of nanoparticles and surfactants on the absorption characteristics was analyzed.
Abstract: The objectives of this paper are to visualize the bubble behavior during the NH 3 /H 2 O absorption process with chemical surfactant and nano-particles and to study the effect of nano-particles and surfactants on the absorption characteristics. Binary nanofluid which means binary mixture with nano-sized particles is tested to apply nanofluid to the absorption system. Cu, CuO and Al 2 O 3 nano-particles are added into NH 3 /H 2 O solution to make the binary nanofluids, and 2-ethyl-1-hexanol, n -octanol and 2-octanol are used as the surfactants. The concentration of ammonia in the basefluid, that of nano-particles in the nanofluid, and that of surfactants in the nanofluid are considered as the key parameters. The results show that the addition of surfactants and nano-particles improves the absorption performance up to 5.32 times. It can be concluded that the addition of both surfactants and nano-particles enhances significantly the absorption performance during the ammonia bubble absorption process.

129 citations


Journal ArticleDOI
TL;DR: The development and evaluation of features and virtual sensors that form the basis of a methodology for detecting and diagnosing multiple-simultaneous faults in vapor compression air conditioning equipment are described.
Abstract: This paper describes the development and evaluation of features and virtual sensors that form the basis of a methodology for detecting and diagnosing multiple-simultaneous faults in vapor compression air conditioning equipment. The features were developed based upon a physical understanding of the system, cost considerations, and heuristics derived from experimental data and modeling results. Virtual sensors were developed in order to reduce the cost of implementation. The validity of the features and virtual sensors was evaluated using measurements from a variety of different air conditioners tested in a laboratory environment. More detailed evaluation results are presented in separate papers.

114 citations


Journal ArticleDOI
TL;DR: Gungor et al. as discussed by the authors measured heat transfer coefficients at constant wall temperature conditions, while pressure drop measurement and flow visualization are carried out at adiabatic conditions, and the results showed that the Muller-Steinhagen and Heck correlation can predict most of the measured pressure drop within the range of ±30%.
Abstract: Flow boiling heat transfer coefficient, pressure drop, and flow pattern are investigated in the horizontal smooth tube of 6.1 mm inner diameter for CO 2 , R410A, and R22. Flow boiling heat transfer coefficients are measured at the constant wall temperature conditions, while pressure drop measurement and flow visualization are carried out at adiabatic conditions. This research is performed at evaporation temperatures of −15 and −30 °C, mass flux from 100 to 400 kg m −2 s −1 , and heat flux from 5 to 15 kW m −2 for vapor qualities ranging from 0.1 to 0.8. The measured R410A heat transfer coefficients are compared to other published data. The comparison of heat transfer coefficients for CO 2 , R410A, and R22 is presented at various heat fluxes, mass fluxes, and evaporation temperatures. The difference of coefficients for each refrigerant is explained with the Gungor and Winterton [K.E. Gungor, R.H.S. Winterton, A general correlation for flow boiling in tubes and annuli, Int. J. Heat Mass Transfer 29 (1986) 351–358] correlation based on the thermophysical properties of refrigerants. The Wattelet et al. [J.P. Wattelet, J.C. Chato, B.R. Christoffersen, J.A. Gaibel, M. Ponchner, P.J. Kenny, R.L. Shimon, T.C. Villaneuva, N.L. Rhines, K.A. Sweeney, D.G. Allen, T.T. Heshberger, Heat Transfer Flow Regimes of Refrigerants in a Horizontal-tube Evaporator, ACRC TR-55, University of Illinois at Urbana-Champaign, 1994], and Gungor and Winterton [K.E. Gungor, R.H.S. Winterton, A general correlation for flow boiling in tubes and annuli, Int. J. Heat Mass Transfer 29 (1986) 351–358] correlations give the best agreement with the measured heat transfer coefficients for CO 2 and R410A. Pressure drop for CO 2 , R410A, and R22 at various mass fluxes, evaporation temperatures and qualities is presented in this paper. The Muller-Steinhagen and Heck [H. Muller-Steinhagen, K. Heck, A simple friction pressure drop correlation for two-phase flow in pipes, Chem. Eng. Process. 20 (1986) 297–308], and Friedel [L. Friedel, Improved friction pressure correlations for horizontal and vertical two-phase pipe flow, in: The European Two-Phase Flow Group Meeting, Ispra, Italy, 1979 (paper E2)] correlation can predict most of the measured pressure drop within the range of ±30%. The relation between pressure drop and properties for each refrigerant is described by applying the Muller-Steinhagen and Heck correlation. The observed two-phase flow patterns for CO 2 and R410A are presented and compared with flow pattern maps. Most of the flow patterns can be determined by the Weisman et al. [J. Weisman, D. Duncan, J. Gibson, T. Crawford, Effect of fluid properties and pipe diameter on two-phase flow patterns in horizontal lines, Int. J. Multiphase Flow 5 (1979) 437–462] flow pattern map.

106 citations


Journal ArticleDOI
TL;DR: In this paper, the experimental heat transfer coefficients and pressure drop measured during refrigerant R134a vaporization inside a small brazed plate heat exchanger (BPHE) are investigated.
Abstract: This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant R134a vaporisation inside a small brazed plate heat exchanger (BPHE): the effects of heat flux, refrigerant mass flux, saturation temperature and outlet conditions are investigated. The BPHE tested consists of 10 plates, 72 mm in width and 310 mm in length, which present a macro-scale herringbone corrugation with an inclination angle of 65° and corrugation amplitude of 2 mm. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity both to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. The experimental heat transfer coefficients are also compared with two well-known correlations for nucleate pool boiling and a correlation for frictional pressure drop is proposed.

Journal ArticleDOI
TL;DR: In this paper, the authors present a study of flow regimes, pressure drops, and heat transfer coefficients during refrigerant condensation inside a smooth, an 18° helical micro-fin, and a herringbone tube.
Abstract: This paper presents a study of flow regimes, pressure drops, and heat transfer coefficients during refrigerant condensation inside a smooth, an 18° helical micro-fin, and a herringbone tubes. Experimental work was conducted for condensing refrigerants R-22, R-407C, and R-134a at an average saturation temperature of 40 °C with mass fluxes ranging from 400 to 800 kg m −2 s −1 , and with vapour qualities ranging from 0.85 to 0.95 at condenser inlet and from 0.05 to 0.15 at condenser outlet. These test conditions represent annular and intermittent (slug and plug) flow conditions. Results showed that transition from annular flow to intermittent flow, on average for the three refrigerants, occurred at a vapour quality of 0.49 for the smooth tube, 0.29 for the helical micro-fin tube, and 0.26 for the herringbone tube. These transition vapour qualities were also reflected in the pressure gradients, with the herringbone tube having the highest pressure gradient. The pressure gradients encountered in the herringbone tube were about 79% higher than that of the smooth tube and about 27% higher than that of the helical micro-fin tube. A widely used pressure drop correlation for condensation in helical micro-fin tubes was modified for the case of the herringbone tube. The modified correlation predicted the data within a 1% error with an absolute deviation of 7%. Heat transfer enhancement factors for the herringbone tube against the smooth tube were on average 70% higher while against the helical micro-fin tube it was 40% higher. A correlation for predicting heat transfer coefficients inside a helical micro-fin tube was modified for the herringbone tube. On average the correlation predicted the data to within 4% with an average standard deviation of 8%.

Journal ArticleDOI
TL;DR: In this article, the authors examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO2, and obtained local heat transfer coefficients for heat fluxes ranging from 10 to 40 kWm−m−2, mass fluxes from 200 to 600 kgm−s−1, a saturation temperature of 10 −C, and quality up to 1.0.
Abstract: This study examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO2. The local heat transfer coefficients were obtained for heat fluxes ranging from 10 to 40 kW m−2, mass fluxes ranging from 200 to 600 kg m−2 s−1, a saturation temperature of 10 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 2000 mm. The section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. An increasing and decreasing heat transfer coefficient occurred at the lower vapor quality with increasing heat flux and mass flux. The mean heat transfer coefficient ratio of R-22:R-134a:CO2 was approximately 1.0:0.8:2.0. Laminar flow was observed in the minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in minichannels was developed with a mean deviation of 11.21%.

Journal ArticleDOI
TL;DR: In this paper, the performance of the solar-driven ejector refrigeration system with iso-butane (R600a) as the refrigerant is studied by dynamic simulation, and the effects that both the operating conditions and the solar collector types have on the system's performance are also examined.
Abstract: In this paper, the performance of the solar-driven ejector refrigeration system with iso-butane (R600a) as the refrigerant is studied. The effects that both the operating conditions and the solar collector types have on the system's performance are also examined by dynamic simulation. The TRNSYS and EES simulation tools are used to model and analyze the performance of a solar-driven ejector refrigeration system. The whole system is modelled under the TRNSYS environment, but the model of the ejector refrigeration subsystem is developed in the Engineering Equations Solver (EES) program. A solar fraction of 75% is obtained when using the evacuated tube solar collector. In the very hot environment, the system requires relatively high generator temperature, thus a flat plate solar collector is not economically competitive because the high amount of auxiliary heat needed to boost up the generator temperature. The results from the simulation indicate that an efficient ejector system can only work in a region with decent solar radiation and where a sufficiently low condenser temperature can be kept. The average yearly system thermal ratio (STR) is about 0.22, the COP of the cooling subsystem is about 0.48, and the solar collector efficiency is about 0.47 at Te 15 °C, Tc 5 °C above the ambient temperature, evacuated collector area 50 m2 and hot storage tank volume 2 m3.

Journal ArticleDOI
TL;DR: In this paper, an improved lump-parameter design model was developed to investigate the water-circulation heat recovery scheme as applied to the two-bed silica gel-water adsorption chillers.
Abstract: This article develops an improved lump-parameter design model to investigate the water-circulation heat recovery scheme as applied to the two-bed silica gel–water adsorption chillers. We demonstrate that performance predictions stemming from this improved lump-parameter formalism compare favorably with experimental results at various conditions, particularly at the industrial rated conditions. We find that the present lump-parameter formalism adequately elucidates the water-circulation heat recovery scheme as does the distributed-parameter formalism. In the studied working condition of a two-bed silica gel–water adsorption chiller, the differences in cooling capacities and coefficients of performance (or COP) by using the two different formalisms are typically less than 10%. This gives rise to a useful and rapid design tool for the industry.

Journal ArticleDOI
TL;DR: In this article, a new boiling heat transfer coefficient correlation that is based on the superposition model for CO 2 was developed with 8.41% mean deviation, which is about three times higher than that of R-134a.
Abstract: Experiments were performed on the convective boiling heat transfer in horizontal minichannels with CO 2 . The test section is made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm and with lengths of 2000 and 3000 mm, respectively, and it is uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 20–40 kW m −2 , a mass flux range of 200–600 kg m −2 s −1 , saturation temperatures of 10, 0, −5, and −10 °C and quality ranges of up to 1.0. Nucleate boiling heat transfer contribution was predominant, especially at low quality region. The reduction of heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux, mass flux and saturation temperature, and with a smaller inner tube diameter. The experimental heat transfer coefficient of CO 2 is about three times higher than that of R-134a. Laminar flow appears in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for CO 2 was developed with 8.41% mean deviation.

Journal ArticleDOI
TL;DR: In this article, the convective motion in nanofluids sets in easily as the Soret and Dufour effects and the initial concentration of nanoparticles increase, and the linear stability theory under one-fluid model was obtained.
Abstract: Thermodiffusion (Soret effect) and diffusionthermo (Dufour effect) effects on convective instabilities in nanofluids have been theoretically investigated. Thermodiffusion implies that mass diffusion is induced by thermal gradient, which is so-called the Soret effect. Diffusionthermo implies that heat transfer is induced by concentration gradient, which is so-called the Dufour effect. By using the linear stability theory under one-fluid model, a characteristic dimensionless parameter was newly obtained. From the instability analysis with given conditions, it is found that the convective motion in nanofluids sets in easily as the Soret and Dufour effects and the initial concentration of nanoparticles increase.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed several novel systems of that type, based on ammonia-water working fluid, which achieved energy and exergy efficiencies of ∼28% and 55-60%, respectively, for the base case studied (at maximum heat input temperature of 450°C).
Abstract: Refrigeration cogeneration systems which generate power alongside with cooling improve energy utilization significantly, because such systems offer a more reasonable arrangement of energy and exergy “flows” within the system, which results in lower fuel consumption as compared to the separate generation of power and cooling or heating. This paper proposes several novel systems of that type, based on ammonia–water working fluid. Importantly, general principles for integration of refrigeration and power systems to produce better energy and exergy efficiencies are summarized, based primarily on the reduction of exergy destruction. The proposed plants analyzed here operate in a fully-integrated combined cycle mode with ammonia–water Rankine cycle(s) and an ammonia refrigeration cycle, interconnected by absorption, separation and heat transfer processes. It was found that the cogeneration systems have good performance, with energy and exergy efficiencies of ∼28% and 55–60%, respectively, for the base-case studied (at maximum heat input temperature of 450 °C). That efficiency is, by itself, excellent for cogeneration cycles using heat sources at these temperatures, with the exergy efficiency comparable to that of nuclear power plants. When using exhaust heat from topping gas turbine power plants, the total plant energy efficiency can rise to the remarkable value of about 57%. The hardware proposed for use is conventional and commercially available; no hardware additional to that needed in conventional power and absorption cycles is needed.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mass flow characteristics of R22 and R410A through EEVs, and developed an empirical correlation for the prediction of mass flow rates.
Abstract: The applications of electronic expansion valves (EEVs) into multi-type heat pumps and inverter heat pumps in building air-conditioning systems have increased for comfort environmental control and energy conservation. However, test data and mass flow models of EEVs are very limited in open literature. The objectives of this study are to investigate the mass flow characteristics of R22 and R410A through EEVs and to develop an empirical correlation for the prediction of mass flow rates of R22 and R410A through EEVs. Mass flow rates through six EEVs were measured by varying the EEV opening, inlet and outlet pressures, and the subcooling. Mass flow rates of R410A were compared with those of R22 at the same test conditions. Based on the experimental data, an empirical correlation for mass flow predictions in EEVs was developed by modifying the orifice equation. The predictions of the present correlation showed good agreement with the measured data with average and standard deviations of 0.76% and 5.9%, respectively. Approximately 92% of the measured data were within ±10% of the predictions.

Journal ArticleDOI
TL;DR: In this paper, three two-phase ejectors are used as an expansion device in the refrigeration cycle, and the effects of throat diameter of the motive nozzle, on the coefficient of performance, primary mass flow rate of the refrigerant, secondary mass flow ratio of the fluid, recirculation ratio, average evaporator pressure, compressor pressure ratio, discharge temperature and cooling capacity are presented.
Abstract: This paper is a part in a series that reports on the experimental study of the performance of the two-phase ejector expansion refrigeration cycle. In the present study, three two-phase ejectors are used as an expansion device in the refrigeration cycle. The effects of throat diameter of the motive nozzle, on the coefficient of performance, primary mass flow rate of the refrigerant, secondary mass flow rate of the refrigerant, recirculation ratio, average evaporator pressure, compressor pressure ratio, discharge temperature and cooling capacity, which have never before appeared in open literature, are presented. The effects of the heat sink and heat source temperatures on the system performance are also discussed.

Journal ArticleDOI
TL;DR: In this article, an analysis was carried out to study the efficiency of annular fin when subjected to simultaneous heat and mass transfer mechanisms, and closed-form solutions for a dry-fin case presented in many text books were special cases for the solutions presented in this paper.
Abstract: An analysis was carried out to study the efficiency of annular fin when subjected to simultaneous heat and mass transfer mechanisms The temperature and humidity ratio differences are the driving forces for the heat and mass transfer, respectively Analytical solutions are obtained for the temperature distribution over the fin surface when the fin is fully wet The effect of the atmospheric pressure on the fin efficiency was also studied, in addition to fin optimum dimensions It is demonstrated that the closed-form solutions for a dry-fin case presented in many text books are special cases for the solutions presented in this paper

Journal ArticleDOI
TL;DR: Saha et al. as discussed by the authors presented a two-bed, activated carbon fiber (ACF) -ethanol adsorption chiller, which has been studied on the basis of the transient modelling developed by the same authors.
Abstract: This article presents the performance evaluation of a two-bed, activated carbon fiber (ACF)–ethanol adsorption chiller, which has been studied on the basis of the transient modelling developed by the same authors [B.B. Saha, I.I. El-Sharkawy, A. Chakraborty, S. Koyama, Study on an activated carbon fiber–ethanol adsorption chiller: Part I – system description and modelling, International Journal of Refrigeration, submitted for publication]. This innovative adsorption chiller, where pitch based ACF of type A-20 is taken as the adsorbent utilizes effectively the low-temperature waste heat sources of temperature between 60 and 95 °C along with a cooling source at ambient temperature. We have found that, regardless of the initial mass distribution, the ACF–ethanol adsorption chiller is able to achieve the same cyclic-steady-state within three half cycles or 1890 s. Simulation results show that the optimum COP values are obtained at driving source temperatures between 80 and 85 °C and makes this chiller suitable for low-temperature waste heat recovery with relatively higher performance.

Journal ArticleDOI
TL;DR: In order to improve the energy separate efficiency of vortex tubes, three innovative technologies were applied to vortex tubes in this article, including a new nozzle with equal gradient of Mach number and a new intake flow passage of nozzles with equal flow velocity.
Abstract: Vortex tube (VT) is a simple energy separating device which is compact and simple to produce and to operate. Although intensive research has been carried out in many countries over the years, the efficiency is still low. In order to improve the energy separate efficiency of vortex tubes, three innovative technologies were applied to vortex tubes. A new nozzle with equal gradient of Mach number and a new intake flow passage of nozzles with equal flow velocity were designed and developed to reduce the flow loss. A new kind of diffuser invented by us was installed for reducing friction loss of air flow energy at the end of the hot end tube of vortex tube, which can greatly improve the performance of vortex tube. The experiment results indicated that these modifications could remarkably improve the performance of vortex tube. The developed vortex tube was not only superior to the conventional vortex tube but also superior to that made by two companies in world under big cold gas mass flow ratio.

Journal ArticleDOI
TL;DR: In this paper, an analysis of the performance of well freezers, chest freezers and open fronted chilled cabinets under EN441 test conditions demonstrated that maximum temperatures in cabinets were generally in the most exposed (to ambient) areas and that minimum temperatures were located in the least exposed areas.
Abstract: An analysis of the performance of well freezers, chest freezers, frozen and chilled door cabinets (solid or glass door) and open fronted chilled cabinets under EN441 test conditions demonstrated that maximum temperatures in cabinets were generally in the most exposed (to ambient) areas and that minimum temperatures were located in the least exposed areas. Detailed positions of maximum and minimum temperature varied between cabinet types. In chest freezers 95% of the maximum temperature positions were located in the top layer and 95% of the minimum temperature positions were located in the middle layer of the cabinets. In full door frozen cabinets the maximum temperature position was in the majority of cases on the top shelf (64%) with most maximum packs being at the front of the top shelf (53%). In the chilled full door cabinets 94% of the maximum temperature packs were situated at the front of the cabinet. In open fronted cabinets the majority of maximum temperature packs (97%) were located at the front of the cabinet, the largest number (60%) being at the front of the base of the cabinet. In well cabinets the majority of maximum temperature packs (81%) were located in the top layer of the cabinet and the majority (91%) of minimum temperature packs were located in the bottom of the cabinet. Large differences in energy consumed by cabinets of similar size and temperature performance were found indicating that large reductions in energy and CO2 emissions could be achieved by selection of the most efficient cabinets. © 2006 Elsevier Ltd and IIR.

Journal ArticleDOI
TL;DR: Experiments show that the feedback controller employed is multi-input–multi-output-based and possesses a cascade structure for dealing with the fast and slow dynamics in the system.
Abstract: In this paper, feedback controller design for the air-conditioning system is addressed through systematic modeling and identification. Particularly, the physical model of the system reveals the key parameter that dictates energy efficiency, and the identification procedure produces a low-order, linear model suitable for controller design. The feedback controller employed is multi-input–multi-output-based and possesses a cascade structure for dealing with the fast and slow dynamics in the system. To determine appropriate control parameters, conditions that establish performance and stability of the cascade design are given. Experiments show that the controller can simultaneously achieve satisfactory transient response in the indoor temperature, and improve energy efficiency at steady state.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the energy saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps for hydronic heating systems.
Abstract: The objective of this study was to investigate the energy-saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps. Variable-speed capacity control is commonly used in air-to-air heat pumps, but not in ground source heat pumps for hydronic heating systems, even though the energy-saving potential may be greater for this application. A theoretical analysis indicates how the energy efficiency is influenced by variable-speed capacity control of the compressor. The analysis shows that, to take full advantage of the capacity control, care should be taken to achieve the correct relationship between refrigerant flow and heat transfer media flows. Intermittent control and variable-speed capacity control were compared by laboratory tests on two capacity-controlled heat pumps and one standard heat pump with a single-speed compressor. Test data were then used for seasonal performance factor (SPF) calculations. The SPF calculations show that despite improved performance at part load the variable-speed controlled heat pump did not improve the annual efficiency compared to the intermittently operated heat pump. This is mainly due to inverter and compressor motor efficiencies and the need for improved efficiency and control of pumps used in the heating and ground collector systems.

Journal ArticleDOI
TL;DR: In this article, in-tube evaporation heat transfer characteristics of carbon dioxide were experimentally investigated and analyzed as a function of evaporating temperature, mass flux, heat flux and tube geometry.
Abstract: Carbon dioxide among natural refrigerants has gained a considerable attention as an alternative refrigerant due to its excellent thermophysical properties. In-tube evaporation heat transfer characteristics of carbon dioxide were experimentally investigated and analyzed as a function of evaporating temperature, mass flux, heat flux and tube geometry. Heat transfer coefficient data during evaporation process of carbon dioxide were measured for 5 m long smooth and micro-fin tubes with outer diameters of 5 and 9.52 mm. The tests were conducted at mass fluxes of from 212 to 656 kg m −2 s −1 , saturation temperatures of from 0 to 20 °C and heat fluxes of from 6 to 20 kW m −2 . The difference of heat transfer characteristics between smooth and micro-fin tubes and the effect of mass flux, heat flux, and evaporation temperature on enhancement factor (EF) and penalty factor (PF) were presented. Average evaporation heat transfer coefficients for a micro-fin tube were approximately 150–200% for 9.52 mm OD tube and 170–210% for 5 mm OD tube higher than those for the smooth tube at the same test conditions. The effect of pressure drop expressed by measured penalty factor of 1.2–1.35 was smaller than that of heat transfer enhancement.

Journal ArticleDOI
TL;DR: In this article, the authors focus on the crystallization issues and control strategies in LiBr-H 2 O air-cooled absorption chillers, and propose a new methodology that allows for air cooler operation while avoiding crystallization.
Abstract: The concept of an air-cooled absorption chiller system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr–H 2 O solution then becomes the main challenge in the operation of the chiller, since the air-cooled absorber tends to operate at a higher temperature and concentration level than the water-cooled absorber due to the relative heat transfer characteristics of the coolant. This leads to crystallization of the working fluid. The paper focuses on the crystallization issues and control strategies in LiBr–H 2 O air-cooled absorption chillers. As a result a novel application opportunity is proposed for the integration of absorption chillers into cooling, heating and power (CHP) systems. This new methodology allows for air cooler operation while avoiding crystallization.

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TL;DR: In this paper, the effects of fin pitch and number of tube rows on the air-side heat transfer and friction characteristics of fin-and-tube heat exchangers with hydrophilic coating under wet conditions were analyzed.
Abstract: The airside heat transfer and friction characteristics of 14 enhanced fin-and-tube heat exchangers with hydrophilic coating under wet conditions are experimented. The effects of number of tube rows, fin pitch and inlet relative humidity on airside performance are analyzed. The test results show that the influences of the fin pitch and the number of tube rows on the friction characteristic under wet conditions are similar to that under dry surface owing to the existence of the hydrophilic coating. The Colburn j factors decrease as the fin pitch and the number of tube rows increase. For wavy fin, the Colburn j factors increase with the increase of the inlet relative humidity, but for interrupted fin, the Colburn j factors are relatively insensitive to the change of the inlet relative humidity. The friction characteristic is independent of the inlet relative humidity. Based on the test results, heat transfer and friction correlations, in terms of the Colburn j factor and Fanning f factor, are proposed to describe the airside performance of the enhanced fin geometry with hydrophilic coating under wet conditions. For wavy fin, the correlation of the Colburn j factor gives a mean deviation of 7.6%, while the correlation of Fanning f factor shows a mean deviation of 9.1%. For interrupted fin, the correlation of the Colburn j factor gives a mean deviation of 9.7%, while the correlation of Fanning f factor shows a mean deviation of 7.3%.

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TL;DR: In this paper, a performance analysis and optimization based on a new thermo-ecological optimization criterion has been carried out for refrigerators, where the ecological objective function is defined as the ratio of the cooling load to the loss rate of availability (or entropy generation rate).
Abstract: A performance analysis and optimization based on a new thermo-ecological optimization criterion has been carried out for refrigerators. The ecological objective function is defined as the ratio of the cooling load to the loss rate of availability (or entropy generation rate). The maximum of the ecological performance criterion and the corresponding optimal conditions have been derived analytically. The optimum performance parameters which maximize the objective function have been investigated and the effects of irreversibility parameters on the general and optimal performances are discussed detailed. The obtained results may provide a general theoretical tool for the ecological design of refrigerators.