Showing papers in "International Journal of Air-conditioning and Refrigeration in 2013"
TL;DR: In this paper, a review of the two-stage heat pump systems for various applications is presented, including two stage cycle with intercooling, two stage with refrigerant injection and two stage cascade cycle.
Abstract: There is increasing demand for domestic and industrial refrigeration, space heating and air conditioning. Heat pump systems offer economical alternatives for recovering heat from different sources for use in these applications. As a renewable energy technology for sustainable environment, the heat pump's high efficiency and low environmental impact have already drawn a fair amount of attention all over the world. Some of these domestic and industrial applications require very low evaporating temperatures and very high condensing temperatures which induce high compressor pressure ratios beyond the practical range for single-stage heat pump cycles. These high pressure ratios also produce low coefficient of performance (COP) values and expose the compressor to high discharge temperature, low volumetric efficiency and damage. However, this challenge can be overcome by adopting two-stage heat pump cycles. In this paper, recent works on two-stage heat pump systems for various applications are reviewed. They include two-stage cycle with intercooling, two-stage cycle with refrigerant injection and two-stage cascade cycle. Research and innovative designs of systems that make use of these two-stage cycles have been able to get heat pumps to handle applications with lower and higher temperatures, while enhancing heating capacity up to 30% and COP up to 31%.
48 citations
TL;DR: In this paper, water droplets were allowed to fall freely onto hydrophobic and hydrophilic heated surfaces, and their impacts were imaged using high-speed cameras to investigate the droplet dynamics and heat transfer.
Abstract: Water droplets, 2 mm in diameter, were allowed to fall freely onto hydrophobic and hydrophilic heated surfaces, and their impacts were imaged using high-speed cameras to investigate the droplet dynamics and heat transfer. As the heating power increased, the water droplets evaporated faster, eventually hovering over the surface due to the formation of a boiling film when the Leidenfrost point (LFP) was reached. The heat transfer from the surface into the droplet was evaluated, and LFP transition phenomena were investigated using time-resolved imaging of both side and bottom views. The hydrophilic surface showed a higher heat transfer rate and a higher LFP than the hydrophobic surface did. Furthermore, the droplet dynamics revealed very different shapes depending on the surface wettability; vigorous bubble nucleation and growth was observable for the hydrophilic surface, but not the hydrophobic surface. The rebound behavior of the droplets was analyzed based on the droplet free energy, including kinetic, potential, and surface energy terms.
28 citations
TL;DR: In this article, a 5.1 mm O.D. microfin tube with 40 fins with 18° helix angle and 40° fin apex angle was used to measure heat transfer and pressure drop.
Abstract: R-410A's evaporation heat transfer and pressure drop data are provided for a 5.1 mm O.D. microfin tube having 40 fins with 18° helix angle and 40° fin apex angle. Tests were conducted for a range of quality (0.2–0.6), mass flux (260–433 kg/m2s), heat flux (10–20 kW/m2) and saturation temperature (8–12°C). Data are compared with smooth tube counterpart. It was found that both heat transfer coefficient and pressure drop increased as mass flux increased. The range of pressure drop penalty factor (1.10–1.70) was slightly smaller than that of heat transfer enhancement factor (1.39–1.79). Data are compared with available heat transfer and pressure drop correlations.
20 citations
TL;DR: The effect of desorption temperature on the performance of adsorption cooling systems driven by waste heat from fuel cells was analyzed in this article, where the authors employed activated carbon fiber (ACF) of type A-20-ethanol and RD type silica gel-water as adsorbent-refrigerant pairs.
Abstract: In the present paper, the effect of desorption temperature on the performance of adsorption cooling systems driven by waste heat from fuel cells was analyzed. The studied adsorption cooling systems employ activated carbon fiber (ACF) of type A-20–ethanol and RD type silica gel–water as adsorbent–refrigerant pairs. Two different temperature levels of waste heat from polymer electrolyte fuel cell (PEFC) and solid oxide fuel cell (SOFC) are used as the heat source of the adsorption cooling systems. The adsorption cycles consist of one pair of adsorption–desorption heat exchanger, a condenser and an evaporator. System performance in terms of specific cooling capacity (SCC) and coefficient of performance (COP) are determined and compared between the studied two systems. Results show that silica gel–water based adsorption cooling system is preferable for effective utilization of relatively lower temperature heat source. At relatively high temperature heat source, COP of ACF–ethanol based adsorption system shows better performance than that of silica gel–water based adsorption system.
16 citations
TL;DR: In this paper, the authors deal with the design and analysis of a quarter-wavelength, 10 W capacity, thermoacoustic refrigerator using short stack boundary layer approximation assumptions, and the effect of operating frequency on the performance of the refrigerator is studied using dimensional normalization technique.
Abstract: This paper deals with the design and analysis of a quarter-wavelength, 10 W capacity, thermoacoustic refrigerator using short stack boundary layer approximation assumptions. The effect of operating frequency on the performance of the refrigerator is studied using dimensional normalization technique. The variation of stack diameter with average gas pressure and cooling power is discussed. The resonator optimization is discussed and the calculation results show a 9% improvement in the coefficient of performance and 201% improvement in power density for the optimized quarter-wavelength resonator compared to published optimization studies. The optimized resonator design is tested with DeltaEC software and the results show better performance compared to past established resonator designs.
15 citations
TL;DR: In this article, an analytical investigation on the performance of adsorption-compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type, has been performed.
Abstract: An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.
15 citations
TL;DR: In this paper, phase change material (PCM) is used as latent heat thermal storage system to enhance the heat transfer of the evaporator in a household refrigerator, and the experimental results with PCM confirm that, depending on the thermal load and the types of PCM average compressor running time per cycle is reduced significantly and it is found about 2-36% as compared to without PCM.
Abstract: An experimental investigation has been carried out to know about the performance improvement of a household refrigerator using phase change material (PCM). PCMs are used as latent heat thermal storage system to enhance the heat transfer of the evaporator. PCM is located behind the five sides of the evaporator cabinet in which the evaporator coil is immersed. Water (melting point 0°C) and Eutectic solutions (melting point −5°C) are used as PCMs for this experiment at different thermal loads. Depending on the types of PCM and thermal load, around 20–27% COP improvement of the refrigeration cycle has been observed with PCM with respect to without PCM. With the increase of the quantity of PCM (0.003 to 0.00425 m3) COP increases about 6%. Between two different PCMs the COP improvement for Eutectic solution is higher than Water. The experimental results with PCM confirm that, depending on the thermal load and the types of PCM average compressor running time per cycle is reduced significantly and it is found about 2–36% as compared to without PCM.
13 citations
TL;DR: In this article, a design of moving coil loudspeaker for a 10 W cooling power thermo-acoustic refrigerator is presented, where the gas spring system for matching the frequency of the commercially available loudspeaker with the acoustic resonator tube for maximizing electro-acoustical efficiency of the loudspeaker is discussed.
Abstract: This paper presents a design of moving coil loudspeaker for a 10 W cooling power thermoacoustic refrigerator. An electrical model is presented which simulates the behavior of the loudspeaker. The gas spring system for matching the frequency of the commercially available loudspeaker with the frequency of the acoustic resonator tube for maximizing electro-acoustical efficiency of the loudspeaker is discussed. The optimum back volume for the gas spring system is found to be 59.7 cc, which is about 1.9% of the total resonator volume when the loudspeaker frequency and the acoustic resonator frequency is made equal at 400 Hz with a moving mass of 20 g. The effect of force factor Bl on loudspeaker performance is discussed. Analysis results shows that for better performance of a refrigerator, the loudspeaker should be chosen to have a large force factor and small values for electrical and mechanical resistances. The refrigerator system is tested with DeltaEC software and its results are in good agreement with an electrical model results.
13 citations
TL;DR: An off-board test bench has been developed for evaluating the performance of an automotive air conditioning system andrelations for the volumetric efficiency of the compressor and COP of the system have been developed.
Abstract: An off-board test bench has been developed for evaluating the performance of an automotive air conditioning system. The facility consists of the mechanical hardware used in an automobile along with a large number of additional sensors and a standalone control system that mimics the operations in a car. The performance of the individual components and the system has been investigated for two major independent variables of running automobiles, namely the compressor speed and the speed of the evaporator fan. Correlations for the volumetric efficiency of the compressor and COP of the system have been developed. While the refrigerant flow rate is influenced mainly by compressor speed, the COP depends on both the operating variables. The investigation also establishes that the design of the rig, the selection and placement of the sensors and the method of measurement are suitable for its further deployment under dynamic condition and for fault diagnosis.
12 citations
TL;DR: In this article, the energy performance of transcritical CO2 refrigeration and heat pump systems was evaluated from a thermodynamic point of view, using a dual expansion valve and a balance CO2 liquid receiver adjustment device, which can control high and low side pressure effectively.
Abstract: This work presents the experimental evaluation of the energy performance of transcritical CO2 refrigeration and heat pump systems. The optimal gas cooler pressures and the optimal COP have been analyzed from a thermodynamic point of view. The systems used a new dual expansion valve and a balance CO2 liquid receiver adjustment device, which can control high and low side pressure effectively. Moreover, we demonstrate the influence of the internal heat exchanger (IHX) on the systems' performances, on the basis of the analysis of the relative COP index RCOPI, the compressor power index RPCI and other parameters which can confirm the truth of. The experimental evaluation covers five evaporating levels (-10 to 10°C) and in a wide range of gas cooler pressures (75 to 120 bar). It is concluded that with the IHX system, compressor power is relatively low when the high side pressure is over 100 bar, and the evaporation temperature is below 0°C. The COP of the system without the IHX is slightly higher than the system with the IHX; it is increasing about 3% to 5%, when the evaporation temperature is over 5°C. Relative to the single expansion process, the dual expansion cycle can decrease the influence of pressure fluctuations of CO2 supercritical fluid and liquid mixture on the systems.
9 citations
TL;DR: In this paper, the heat transfer characteristics of carbon dioxide, ammonia, and hydrocarbons are reviewed, and the general trends and recommendable models of flow boiling and condensation heat transfer with carbon dioxide and ammonia are summarized.
Abstract: The existing artificial and chemical refrigerants have been phased out due to environmental concerns, and they have been replaced with environmentally friendly refrigerants. Among them, carbon dioxide, ammonia, and hydrocarbons are paid attention as next generation refrigerants, and their application has been widely expanded. Therefore, in this paper, the latest studies of flow boiling and condensation heat transfer characteristics of carbon dioxide, ammonia, and hydrocarbon are reviewed. The heat transfer characteristics of ammonia and hydrocarbon show the relatively similar trends with the conventional refrigerants compared to those of carbon dioxide. The general trends and recommendable models of flow boiling and condensation heat transfer with carbon dioxide, ammonia, and hydrocarbons are summarized.
TL;DR: In this paper, an NH3-H2O ejector-absorption refrigeration cycle and an R-152a ejector cooling cycle were employed with a renewable energy power generator to make a proposed compact power generation and triple effect ejectorabsorption cooling cycle.
Abstract: An NH3–H2O ejector-absorption refrigeration cycle, and an R-152a ejector refrigeration cycle are employed with a renewable energy power generator to make a proposed compact power generation and triple effect ejector-absorption refrigeration cycle. The exergy analysis of the cycle leads to a possible performance improvement. Approximately 71.69% of the input exergy is destructed due to irreversibilities in different components. Around 7.976% is available as the useful exergy output. The exhaust exergy lost to the environment is 20.33%, which is lower than the exhaust energy loss of 47.95%, while the useful energy output is 27.88%. The refrigerants used are of zero ODP and negligible GWP, and the CO2 emission of the exhaust gases is very small as compared to that of the fossil fuel run engine, hence, this cycle is favorable to the global environment. The results also show that the proposed cycle has significant higher energy and exergy efficiency than the earlier investigated 'triple effect refrigeration cycle' and 'the combined power and ejector-refrigeration cycle'.
TL;DR: In this paper, second law analysis has been done for the vapor compression-vapor absorption (VC-VA) cascade system, where Ammonia-water is considered as the working pair in absorption section and R407C is dealt as working fluid in VC section, for a wide range of cooling capacity by considering a variable speed reciprocating compressor.
Abstract: In this paper, second law analysis has been done for the vapor compression–vapor absorption (VC–VA) cascade system. Ammonia–water is considered as the working pair in absorption section and R407C is dealt as the working fluid in VC section. Exergy destruction or the irreversibility rate is determined in each components of VC–VA cascade system, for a wide range of cooling capacity by considering a variable speed reciprocating compressor. Further in this, Coefficient of structural bond (CSB) analysis is carried out to quantify the effect of varying the generator temperature, effectiveness of solution heat exchanger, inlet temperature of external fluids in evaporator/condenser and some other variables. Solution heat exchanger and the condenser are reported to have high CSB value, so have a great scope of improvement to reduce the irreversibility rate of the whole system.
TL;DR: In this paper, the heat transfer and pressure drop characteristic of air flow between parallel plates with concavity and convexity is grasped, and the possibility of using a fin-less heat exchanger is considered analytically.
Abstract: For an automobile air-conditioning system, performance improvement of the heat exchanger is needed to fit in the change of refrigerant and heat pump system. In this study, the heat transfer and pressure drop characteristic of air flow between parallel plates with concavity and convexity is grasped, and the possibility of using a fin-less heat exchanger is considered analytically. And it has been shown that a fin-less heat exchanger has the possibility of increasing performance compared to a conventional heat exchanger, which uses a corrugated louver fin.
TL;DR: In this article, a sine wave fin-and-tube heat exchanger with oval tubes of 0.6 aspect ratio was tested and the effect of tube row on j factor was investigated.
Abstract: Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes of 0.6 aspect ratio. Twelve samples having different fin pitches and tube rows were tested. Eight herringbone wave fin-and-tube heat exchangers having round tubes were also tested. For round tube samples, the effect of tube row on j factor is not prominent. For oval tube samples, however, the highest j factor is observed for two row configuration, whereas the lowest one is observed for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. The friction factor decreases as number of tube row increases. Comparison with round tube samples reveals that airside performance of oval fin-and-tube heat exchangers is generally superior except for one-row configuration.
TL;DR: In this article, the effect of internal condensation on the performance of a heat recovery ventilator was investigated using a plate-type sensible heat exchanger element that was designed for very humid and dusty environments such as chicken broiler houses.
Abstract: This study experimentally investigates the effect of internal condensation on the performance of a heat recovery ventilator. Experiments were performed using a plate-type sensible heat exchanger element that was designed for very humid and dusty environments such as chicken broiler houses. The results of these experiments show that the temperature efficiency considering condensation is always greater than that without considering latent heat. As outdoor temperature decreases or indoor relative humidity increases, temperature efficiency increases owing to an increase in the rate of condensation. The present polypropylene-based sensible heat exchanger element could be a solution for harsh environments because it can discharge condensate water by gravity and is resistant to moisture and other toxic gases.
TL;DR: In this paper, a dynamic model of a combined radiant floor heating (RFH) and domestic hot water supply (DHWS) system is developed and validated by using measured data gathered from an experimental test facility.
Abstract: A dynamic model of a combined radiant floor heating (RFH) and domestic hot water supply (DHWS) system is developed and validated by using measured data gathered from an experimental test facility. The validated model was used to study the dynamic responses of the system under different operating conditions. Optimal control and predictive control strategies were designed and simulated to study system performance and energy consumption. Results showed that the control strategy with the heating load prediction could save up to 12.7% energy. Also, the optimal control strategy with optimal set-points could save 8.6% energy input to the boiler and 42.9% pump energy consumption while maintaining the zone temperatures and DHWS temperatures close to their respective set-points.
TL;DR: In this paper, a number of published articles about the automotive air conditioning system, which contain the belt-driven compressors, heat exchangers, and refrigerants, were considered.
Abstract: In spite of the increase of the concern on electric vehicles (which is called green cars) and electrically driven automotive air conditioning system, the conventional automotive air conditioning system for internal combustion engines has been still investigated widely due to the realistic consideration. This paper is intended to include many automotive air conditioning system articles published in 1997 to 2013. This review, although extensive cannot include every paper; some selection is necessary. Reviewed papers herein are related to the research and development on effective design and performance improvement for the automotive air conditioning system and components, including theoretical, numerical, analytical and experimental works. Therefore, a number of published articles about the automotive air conditioning system, which contain the belt-driven compressors, heat exchangers and refrigerants, were considered. Many researches have focused on improving the efficiency of automotive air conditioning system to decrease the usage rate of the internal combustion engines.
TL;DR: In this article, the authors presented the performance and economic analysis of a simple photovoltaic powered vapor compression refrigeration system carried out on winter days in the eastern province of Saudi Arabia.
Abstract: The paper presents the performance and economic analysis of a simple photovoltaic powered vapor compression refrigeration system carried out on winter days in the eastern province of the Kingdom of Saudi Arabia. The system has a 66 W DC refrigerator, 100 W PV mono-crystalline module and a 100 Ah battery bank. The thermal loads were distributed in the refrigerator cabin using ice trays of 300 mL each for a total mass of 2.1 kg. The system performed continuously without any interruption or fault for the entire time of the experiment. The minimum time taking for complete formation of ice in the trays was 6 h and 40 min. A larger area to volume ratio, which enhances the heat transfer is created due to this load distribution pattern. A refrigeration efficiency of 60% was calculated after ice formation has been completed. At the maximum solar radiation level, the best PV efficiency and solar panel orientation efficiencies were 15.5% and 98%, respectively. It was however observed from the cost analysis that the system would not be economical without government subsidy on the system components or alleviating the current subsidy on the electricity cost in Saudi Arabia.
TL;DR: In this paper, a particle/grid hybrid method for simulating multi-scale free surfaces was used to simulate gas-liquid flow simulations in a refrigerant distribution in a distributor and a bend pipe placed in the upstream of the distributor was simulated mainly using the particle method.
Abstract: Heat exchangers with small-diameter multi-path tubes have been recently used to improve the efficiency of air conditioners. The difficulty in using tubes with small diameters and multi-paths is the nonuniformity of refrigerant distribution in refrigerant distributors, which results in lower heat-exchange efficiency. Grid methods, such as the volume of fluid method, are now widely used to simulate detailed motions of gas–liquid interfaces. A weak point of grid methods is the numerical diffusion of interfaces that occurs if the scale of interfaces becomes close to the computational grid sizes. We previously developed a particle/grid hybrid method for simulating multi-scale free surfaces. For this study, we modified the hybrid method and applied it to gas–liquid flow simulations in a distributor. The liquid film behaviors in both the distributor and a bend pipe placed in the upstream of the distributor were simulated mainly using the particle method, and gas flows were simulated using the grid method. The predicted liquid film near the outer circumference of the curvature in the bend pipe was thicker than that of near inner circumference of the curvature, which qualitatively agreed with the measurement. The simulated distribution ratio under a steady-flow condition agreed well with the measurement; the predicted distribution ratio was 0.63 and the measured distribution ratio was 0.6.
TL;DR: In this article, the authors developed and evaluated ground heat exchanger using the foundation of a building and applied it to apartment houses utility building in Osan S-apartment and G-housing in Song-Do that is 80% energy saving test bed.
Abstract: The objective of this study is to develop and evaluate ground heat exchanger using the foundation of a building. To this end, we added ground heat exchanger feature to PHC piles and evaluated its heating and cooling performance. First, we investigated the building's foundation system, pipes for heat exchanger and grouting materials. As an outcome, we designed a prototype of building-integrated geothermal system (BIGS). Second, we applied BIGS to apartment houses utility building in Osan S-apartment and G-housing in Song-Do that is 80% energy saving test bed. Third, for the performance of BIGS, we monitored heating performance during winter season in the Osan facility and cooling performance during summer season in the Song-Do facility.
TL;DR: In this paper, the heat transfer characteristics of the M20 refrigerant mixture, flowing through a fin-and-tube evaporator, experimentally studied in an appliance tested in a psychrometric test facility.
Abstract: R22 has been used as a refrigerant in residential air-conditioners and heat pumps for many decades. Even as the Montreal protocol set the phasing out of R22 due to its ODP, many alternatives to R22 are found in published literature. The M20 refrigerant mixture is one such alternative with specific advantages. This paper presents the heat transfer characteristics of the M20 refrigerant mixture, flowing through a fin-and-tube evaporator, experimentally studied in an appliance tested in a psychrometric test facility. The experimental setup consisted of a window air-conditioner fixed in a psychrometric room with instruments to measure the temperatures/pressures of the refrigerant and mass flow rate of the refrigerant as well as air. The experiment was carried out in accordance with the Bureau of Indian Standards (BIS) and American Society of Heating Refrigerating Air-Conditioning Engineers (ASHRAE) test conditions. M20 being considered as an alternative for R22, the overall heat transfer coefficient of the M20 refrigerant mixture has been evaluated, and compared with that of R22. It can be observed that the heat transfer coefficient of R22 is better than that of the M20 refrigerant mixture, for the prevailing flow conditions in the evaporator. The reduction in the overall heat transfer coefficient of the M20 refrigerant mixture as compared to R22, ranges from 7.3% to 20.7%.
SIDI1
TL;DR: In this article, the authors analyzed the impact of ventilation heat recovery with the heating and cooling potential of earth air heat exchanger in real climatic conditions in domestic buildings in the Middle Atlas region.
Abstract: In this study, we analyze the impact of ventilation heat recovery with the heating and cooling potential of earth air heat exchanger in real climatic conditions in domestic buildings in the Middle Atlas region. In our case study, we calculate the primary energy used by a domestic building built as per the conventional house design parameters required by the Moroccan regulation. We use climate data for the city of Fes in Northern Moroccan. Three system configurations were considered. The first was the mechanical extract ventilation system both with and without heat recovery. The second was the mechanical extract ventilation system with earth to air heat exchanger system (EAHEX), and the third system was the mechanical balanced ventilation system coupled with EAHEX system. Primary energy use strongly influences natural resources efficiency and the environmental impacts of energy supply activities. In this study we explore the primary energy implications of the mechanical balanced ventilation system coupled with the EAHEX system in residential buildings. The results of this study shows that the use of a balanced ventilation system, with a high efficiency instead of a mechanical extract ventilation system, decreases the final and primary energy consumption. Moreover, it decreases or increases the CO2 emission depending on the primary energy sources.
TL;DR: In this article, a new method was developed to generate ice slurry without the deposition of an ice layer on a cooled surface, which is based on freezing-point depression of the aqueous solution, which was maintained under high-pressure conditions.
Abstract: A cold thermal energy storage system has been developed for HVAC. There are many ice-based cooling systems operating around the world. Ice slurry, which is a mixture of fine ice crystals and liquid water, is utilized in ice storage systems owing to its good flowability and large latent heat of fusion. For slurry ice production techniques, there are presently a number of commercially available ice slurry generators (e.g., Supercooled slurry ice generator, Scraper type generator, and Vacuum type generator, etc.). In the present study, a new method was developed to generate ice slurry without the deposition of an ice layer on a cooled surface. The basic components of the experimental apparatus is a cooling brine circulating loop, a high pressure pump, a valve, an aqueous solution flow loop containing the test section, which is made of transparent acrylic, and the associated instrumentation. This new method is based on freezing-point depression of the aqueous solution, which is maintained under high-pressure conditions. To control the timing for solidification and to generate ice slurry, we investigated the relationships among the pressure and temperature of the aqueous solution. The freezing phenomenon of the aqueous solution in the test section was observed in detail. As a result, we developed a new ice slurry generator based on the new method that controls the pressure and temperature of the aqueous solution. Experimental results showed that the characteristics of the ice slurry generation were closely related to the pressure and initial stage temperature of the test fluid. Finally, the optimum operation condition of the ice slurry generator based on visualization experiment was discussed.
TL;DR: In this article, a slot-type premixed burner is used to completely block noises and harmful gases for the purpose of use in a household, and air supplied to a burner recovers heat from the exhaust gas in order to improve the efficiency of energy use.
Abstract: As fossil fuel has been depleted, a reasonable use of energy is required. In this regard, the cascade use of thermal energy has been proactively considered in view of available energy. For the purpose, the micro co-generation system for a household based on Stirling engine was suggested as a unit of distributed energy system. A slot-type premixed burner is used to completely block noises and harmful gases for the purpose of use in a household, and air supplied to a burner recovers heat from the exhaust gas in order to improve the efficiency of energy use. This study conducted a numerical simulation on combustion in a combustion chamber to investigate the effects that recuperation of heat from exhaust gas have on heat transfer and combustion characteristics.
TL;DR: In this paper, a thermodynamic model is proposed to analyze and assess the performance, through energy and exergy, of a cascade active magnetic regenerative (AMR) refrigerator operation a regenerative Brayton cycle This cascade refrigeration system works with GdxTb1-x alloys as magnetic materials where the composition of the alloy varies for different stages.
Abstract: In the present study, a thermodynamic model is proposed to analyze and assess the performance, through energy and exergy, of a cascade active magnetic regenerative (AMR) refrigerator operation a regenerative Brayton cycle This cascade refrigeration system works with GdxTb1–x alloys as magnetic materials where the composition of the alloy varies for different stages In this model, the heat transfer fluid considered is a water– glycol mixture (50% by weight) The refrigeration capacity, total power consumption, coefficients of performance (COP), exergy efficiency and exergy destruction rate of a cascade AMR refrigeration (AMRR) system are determined To understand the system performance more comprehensively, a parametric study is performed to investigate the effects of several important design parameters on COP and exergy efficiency of the system
TL;DR: In this paper, the authors evaluated the effect of vehicle speed on the cooling capacity and sub-cooling of condenser of automotive air conditioner and found that an increase of 16.6% in cooling capacity can be reached as the speed of vehicle was raised from 6 to 110 km h-1.
Abstract: Due to the concern in energy shortage and environmental protection, electric vehicle is considered to be a substitute for the conventional gasoline-powered vehicles due to its characteristics of high efficiency and no emission. However, the load of air conditioning causes a serious problem for electric vehicles, especially in tropical and subtropical areas. The compressor of conventional air conditioning system is driven by engine and its speed is thus coupled to vehicle speed. In electric vehicles, the compressor is driven by electric motors and compressor speed could be decoupled to vehicle speed. This mechanism provides an opportunity to improve the energy efficiency of electric vehicle since the operation of air conditioning system may be independent of vehicle speed. The purpose of this paper is to find out the electric fan operation model as vehicle speed is varied. This paper was to establish a theoretical model for the condenser of automotive air conditioner and to conduct simulation to evaluate the effect of vehicle speed on the cooling capacity and sub-cooling of condenser. Results of simulation demonstrated that vehicle with 6 km h-1 speed has the 5°C of sub-cooling at 0.0266 kg s-1 of refrigerant flow rate and the cooling capacity was 4.93 kW. In this study, an increase of 16.6% in cooling capacity can be reached as the speed of vehicle was raised from 6 to 110 km h-1 and can promote the sub-cooling to 19.5°C. It was also found that the cooling capacity of air conditioner is extremely sensitive to vehicle speed while the vehicle is running at low speed. Furthermore, increases in the vehicle speed resulted in reduction of the length of superheat region from 17.5 to 8.5 cm. Finally, a correlation among these variables and the simulated cooling capacity was obtained in this study, enabling the relevant researchers to evaluate automotive air conditioner performance under different vehicle speeds more easily.
TL;DR: In this paper, the authors developed an acceleration test method for the diaphragm gas meter and the guarantee of B10 lifetime of 3000 h in normal operation condition, where the flow rate and operation temperature were chosen as acceleration factors.
Abstract: The present study has been conducted to verify and enhance the MTBF of the diaphragm gas meter The goals of this study were the development of acceleration test method for the diaphragm gas meter and the guarantee of B10 lifetime of 3000 h in normal operation condition To develop the acceleration test method, the flow rate and the operation temperature were chosen as acceleration factors and experiments of 1000 h in four conditions are conducted The results showed that the log-normal life distribution conforms to the diaphragm gas meter life distribution and the combination of the temperature and the flow rate can have the acceleration factor of up to 348 The uncertainty of the flow rate accuracy verification is 020% and the log-normal life distribution is used
TL;DR: In this paper, the authors investigated experimentally the performance of different radiant floor cooling modules with embedded chilled water piping and found that the modular design of the radiant floor used has low heat resistance between the chilled water and the radiant cooling surface.
Abstract: This study investigates experimentally the performance of radiant floor cooling modules. Different radiant cooling modular units with embedded chilled water piping were tested for cooling performance. The effects of pipe pitch and also the effects of extended fins were tested. The results of the experiments show that the modular design of radiant floor used has low heat resistance between the chilled water and the radiant cooling surface. Mean radiant temperature was analyzed to measure the cooling comfort performance. An increase of radiant cooling surface area was found to be important for effective radiant heat exchange. Moreover, the larger the temperature difference between the radiant surface and the walls, higher rate of radiant cooling can be achieved. The cooling intensity in terms of per unit area was tested to be as high as 60 W/m2. In conclusion the radiant floor cooling modular units are effective to remove sensible heat and provide comfort cooling. In practice it can be supplemented with lower humidity outdoor air supply for the removal of latent heat.
TL;DR: In this paper, the evaporation rate of a spherical cap was analyzed and verified by experiments, and the results showed that three stages are shown in the Evaporation process, and that the rates in these three stages coincident with the theoretical conclusion.
Abstract: The evaporation of droplet on a substrate is a hot topic. Considering the droplet shape as a spherical cap, the equations about the droplet evaporation rate of the constant contact angle stage, the constant contact diameter stage and the transitional stage are theoretically analyzed and verified by experiments. The results show that three stages are shown in the evaporation process, and the evaporation rates in these three stages coincident with the theoretical conclusion. In the constant contact angle stage, the evaporation rate is proportional to the square of base radius. While in the constant contact diameter stage, the evaporation rate is proportional to the cube of base radius. The evaporation rate in the transitional stage approximates to that of the constant contact angle stage.