Increase In Evaporator Temperature Research Articles

Experimental study on heat transfer of horizontal-tube falling-film flow in deviated columnar mode

Column flow is the most widely used flow pattern in horizontal-tube falling-film evaporators. Ideally, the liquid column is in the center plane of horizontal tube. In the actual falling-film evaporator, the installation deviation of nozzles, the steam sweep, as well as the disturbance caused by flash evaporation make the liquid column deviate from the center plane. The heat transfer characteristics of deviated columnar flow and its influencing factors were experimentally studied and analyzed in this paper. The results are as follows: The vertex of heat transfer coefficient curve shifts to the negative angle interval as the deviation distance increases. Meanwhile, the maximum value decreases with the increase of liquid column deviation distance. The heat transfer coefficients in the negative angle interval are greater than those at corresponding position in the positive angle interval. The heat transfer coefficients increase with the increase of evaporation temperature, spray density, and tube spacing, respectively.

Theoretical comparison analysis of R134a, R1234yf, R452A and R454C refrigerants used in automobile, trailer and commercial and industrial cooling systems

The increasing environmental disasters in recent years are caused by the release of artificial substances into the environment. The majority of artificial-containing emissions originate from petrochemical products. It also contributes to artificially containing refrigerants used in cooling systems. Artificial refrigerants have contributed greatly to the depletion of the ozone layer and subsequently to global warming. Research on new refrigerants as an alternative to refrigerants that contribute to every environmental disaster is of great importance. In this study, theoretical performance comparisons were made between R1234yf, which is an alternative to R134a refrigerant used in automobile air conditioning systems, and R452A, R454C refrigerants, which are used as alternative refrigerants in industrial, commercial and trailer cooling systems. Performance analyses were carried out according to different condenser and evaporator temperatures. Analysis results are given depending on condenser/evaporator pressure ratio, mass flow rate, compressor power, cooling effect coefficient (COP) and compressor outlet temperature. According to the study results, it was observed that the COP value increased with the increase in evaporator temperature, while the compressor inlet-outlet pressure ratio, refrigerant flow rate, compressor power and refrigerant compressor outlet temperature decreased. It was observed that the refrigerant with the highest compressor power and mass flow rate was R452A, followed by R1234yf, R454C and R134a, respectively. R134a was found to have an average of approximately 5.4%, 8.6% and 0.6% higher COP than R1234yf, R452A and R454C, respectively.

Thermodynamic Analysis of Comprehensive Performance of Carbon Dioxide(R744) and Its Mixture With Ethane(R170) Used in Refrigeration and Heating System at Low Evaporation Temperature

Abstract In this paper, the system performance of R744 and R744/R170 mixed refrigerants used in a single-stage compression transcritical cycle at low evaporation temperature was studied by simulation method, and the effect of evaporation temperature, outlet temperature of gas cooler, R170 ratio on coefficient of performance (COP), discharge temperature, optimal pressure, and compression ratio were analyzed. The results show that Popt increases and decreases with the increase of outlet temperature and evaporation temperature of gas cooler and increases first and then decreases with the increase of R170 proportion. In the heating system, the maximum and minimum Popt of R744/R170 (25/75) were 1.35 MPa, 3.6 MPa, and 2.6 MPa and 1.23 MPa, 2.93 MPa, and 1.87 MPa lower than that of R170 (0%, 22.4%, and 50%); compared to pure R744, the system pressure of the mixed R744/R170 is lower. The COPe and COPh increase with the increase of evaporation temperature and decrease with the increase of outlet temperature of the gas cooler. With the increase of R170 proportion, they first decrease and then increase; the maximum COPe and COPh of R744 were 22.4%, 29.6%, and 21.2% and 10.3%, 13.8%, and 10.8% higher than those of R170 at 22.4%, 50% and 75%, respectively.

Dynamic critical diameter of an oscillating heat pipe in vertical orientation

Generally, the oscillating heat pipe (OHP) diameter should be kept below a specific critical size. As a result, the working fluid forms a vapor-liquid slug train under the capillary action, producing a gas-spring-mass mechanical vibration system. Determining the critical diameter is essential for the OHP to form this slug train. A conventional critical diameter model only considers the surface tension and gravity. However, the vapor bubble flow in the liquid slug plays a key role in forming this essential slug train. Even if the hydraulic diameter of an OHP is much larger than the conventional critical diameter, the OHP can still function. The dynamic flow significantly affects the formation of the vapor-liquid slug-train. Therefore, a semi-empirical model was developed considering the effects of the dynamic flow and the heat input, filling ratio, and working fluid. The concept of dynamic critical diameter (DCD) was proposed. The model shows that the OHP DCD increases when the heat input increases for a given evaporator temperature. In addition, the model can predict that the OHP DCD decreases when the evaporator temperature increases.

Performance Analysis of Using Hydrocarbon Mixed Refrigerant R32-R290 as an Alternative to R410A in Reducing the GWP Value of Household Split Air Conditioners

An experiment conducted on the mixed refrigerant R32-R290, which is used in household air conditioners, is aimed at reducing the global warming potential and improving the environmental CO2 quality. This mixed refrigerant has a lower GWP and density than the refrigerant R410A. This research was conducted to determine the effect of the increased mass charge of R290 as a mixed refrigerant on the performance of split air conditioner. Three percentage compositions of 20%/80%, 25%/75%, and 30%/70% were applied as a change to R410A in household air conditioners. For the testing equipment condition, the air inlet evaporator and condenser temperatures were 17°C (300 K) and 35°C (308 K), respectively. In the first performance test, refrigerant mass charge of 100% (340 g) was employed. In the second test, mass charge of 40% (136 g), 50% (170 g), and 60% (204 g) were utilized for mixed refrigerant R32-R290. Compared to the performance of R410A, the experimental results for the mixed refrigerant indicated a 0.5% increase in the air outlet evaporator temperature, a 1% decrease in the air condenser outlet, a 29.7% increase in the average COP, a 12.9% decrease in the electrical power consumption from 545.12 W to 474.7 W, a 9.1% increase in the average exergy destruction average from 401.5 W to 441.6 W, and a 19.7% increase in the average exergy efficiency from 24.2 W to 30.1 W.

Preliminary design and optimization of a solar-driven combined cooling and power system for a data center

Aiming at the demand of reducing cost, increasing efficiency and green low-carbon development in data center, a novel solar-driven combined cooling and power system is constructed by coupling supercritical power cycle with transcritical refrigeration cycle. The heliostat field is designed, and the models on thermal, economic, environmental and comprehensive performances are established. On this basis, system performances under design conditions are studied, and the system parameters are analyzed. Thereafter, optimal system performances at typical days in four seasons are compared based on genetic algorithm. The results indicate that: under design conditions, the system energy and exergy efficiencies are 29.47% and 16.21% respectively. The total system capital cost is $1.2576 × 108. The carbon emissions are reduced by 257,420 kg per day. The comprehensive performance evaluation index (CPEI) can reach up to 47.63%. CPEI increases with the increase of turbine inlet pressure. With the increase of high-pressure compressor (HPC) inlet pressure and evaporation temperature, CPEI increases first and then decreases. Furthermore, CPEI shows a continuous downward trend as the load rate of data center increases. The system performances at autumn equinox and spring equinox are more similar, while those at summer solstice and winter solstice are quite different from those of spring equinox.

Ejector and Vapor Injection Enhanced Novel Compression-Absorption Cascade Refrigeration Systems: A Thermodynamic Parametric and Refrigerant Analysis

This study investigates the performance of two novel compression absorption cascade refrigeration systems, the Ejector Compression Absorption Cycle (ECAC) and Ejector Injection Compression Absorption Cycle (EICAC), in comparison to traditional system. In these cascaded systems, the absorption cycle (top cycle) is modified by adding a refrigerant hear exchanger (RHX) which provides higher mass flow of refrigerant to increase the COP. The simple vapor compression cycle (bottom cycle) performance is enhanced by incorporating the ejector and Vapor Injection technologies. A systematic analysis is accomplished to establish the optimal operating conditions for performance enhancement, taking into account of ejector parameters and the effect of different environmentally friendly refrigerants by the energy and exergy method. The findings demonstrate that both ECAC and EICAC systems can achieve near 15 % and 6 % higher COP, respectively, compared to conventional cascade system when using the R41-LiBr/H2O refrigerant pair under different working conditions. Maximum exergy efficiency is found to be achieved at around 73 °C, with ECAC and EICAC showing higher exergy efficiency of near 20 % and 10 %, respectively than the conventional system. The analysis also reveals that while the COP of all layouts augments linearly with increasing evaporator temperature, the exergy efficiency decreases at different rates, making the cascade systems more efficient for low-temperature applications. The LiBr/H2O refrigerant pair demonstrates superior COP and exergy efficiency as HTC refrigerant, while R161, R290, and R1270 perform better as low-temperature refrigerants for both ECAC and EICAC from both energetic and exergetic perspectives. The results of this detailed theoretical thermodynamic analysis provide a comprehensive understanding of the performance of ECAC and EICAC systems and offer valuable insights for further improvement and optimization.

"AN ATTEMPT TO IMPROVE ENERGY EFFICIENCY OF VAPOUR COMPRESSION REFRIGERATION ON SYSTEMS WORKING WITH R134a"

"Refrigeration is an industry of high importance in our modern times. It plays also a key role in maritime transport of perishables, where vapour compression refrigeration systems are dominant. These energy systems are indispensable, but they should be wise exploited because their high energy necessity. One of the frequent refrigerant chemical adopted in this system is the hydrofluorocarbon R134a. This refrigerant came to substitute traditional refrigerants, such as chlorofluorocarbons or hydro chlorofluorocarbons – substances being under environmental regulations. In this study, it is approached a single stage vapour compression refrigeration system working with R134a. The aim is to find the conditions in which this system is more energy efficient. In this respect, based on the laws of thermodynamics, are obtained information on Coefficient of Performance and energy destruction trends – when the evaporator temperature increases. Our results indicate that, although the analysis based on the first law of thermodynamics reveals that the performance of the system is higher for high evaporator temperatures, the energy destructions in this system increase together with the evaporator temperature increase. "

Experimental investigation on the heat transfer performance of falling film with deionized water on horizontal tubes

Taking deionized water as working fluid, an experimental study was conducted to investigate the heat transfer characteristics of falling film evaporation outside horizontal aluminum tube with inner diameters of 10 mm and 14 mm. The effect of spray density, heat transfer temperature, evaporation temperature, tube diameter, outlet vapor quality and degree of undercooling on overall heat transfer coefficient outside the tube was analyzed. The results show that the overall heat transfer coefficient increases with increasing evaporation temperature and tube diameter while decreases with increasing heat transfer temperature difference and outlet vapor quality. On other hand, the overall heat transfer coefficient increases with increasing spray density firstly, then decreases slightly. The effect of outlet vapor quality can be neglect.

Experimental investigation on the thermal characteristics of ultrathin vapour chamber with in-plane bending

• Probing the effects of in-plane bending on the UTVCs. • Systematic exploration of the heat transfer mechanism behind the in-plane bending effects. • A model to predicting the maximum heat transfer capacity and thermal resistance with given in- plane bending conditions was established. Although many works have been published on designing ultrathin vapour chambers (UTVCs), but no one has analyzed the effect of in-plane bending on the thermal characteristics of UTVCs. However, UTVCs often need to be designed into in-plane bending shapes to meet the limited and strict application space in portable electronic devices. Therefore, this work makes grate efforts to ascertaining the effect of in-plane bending on the thermal characteristics of UTVCs with thicknesses below 0.6 mm. UTVCs with four bending angles (0°/45°/90°/135°) and three bending radii (R10/R15/R20) were fabricated based on brazing, and the effects of filling rate and bending on the thermal characteristics of UTVC were investigated. The results show that the optimal filling rate of UTVC was 100%, the large bending angle and small bending radius lead to the increase of evaporation temperature and thermal resistance. The maximum heat transfer capacity of UTVC decreases by more than 27% when the bending angle change from 0° to 135°. In addition, a model for predicting maximum heat transfer capacity and thermal resistance was developed. The variation trend of predicted value was the same as experimental value, and the minimum error less than 3%.

Experimental study on horizontal tube falling film evaporation in geothermal powered organic Rankine cycle generation

Geothermal energy has become one of the indispensable renewable energy in the energy development in the 21st century, and it is also one of the most realistic and competitive energy. The orc power generation test system with low temperature heat source (60 ∼ 90 °C) is designed, and the key component horizontal tube falling film evaporator is designed. The experimental results show that the heat transfer coefficient increases with the increase of evaporation temperature in the range of 40 ∼ 65 °C. The experimental results show that when the spray density is in the range of 0.010 ∼ 0.025 kg/m K, the heat transfer coefficient increases with the increase of spray density. The experimental results show that when the hot water mass flow rate is in the range of 0.06 ∼ 0.18 kg/s, the heat transfer coefficient increases with the increase of hot water mass flow rate.

ABSORPTION COOLING SYSTEM UTILIZING DIESEL ENGINE EXHAUST HEAT

The global industrial development, the increasing demand for energy, the limited availability of resources for the future generations of fossil fuels, and the prevention of environmental damage caused by their burning have led to public concern. Increasing energy consumption by buildings has led the wider global attention to its social, environmental, and economic implications. In this study, the emission gases from diesel engines have been utilized to drive a single effect absorption cooling system. In this study, water and lithium bromide mixture is used as a working fluid in absorption cooling system to benefit from waste heat from diesel engine that it may reach 190°C. This system mostly require only waste heat as the energy source to function properly. It has several advantages such as lower required electricity compared with vapor compression system, and it uses safer refrigerant. Engineering Equation Solver EES was executed to analyze the performance of this system, and to study the effects of the temperature of the generator, the absorber, the condenser and the evaporator on the performance of the system and on the cooling capacity. The cycle simulation is based on the operating temperature ranges and fixed parameters which includes: Evaporating temperature within a range of 5-20 °C, generator temperature within a range of 90-120°C, condenser temperature ranges from 25 to 38°C, absorber temperature range from 25 to 34°C, effectiveness of heat exchanger range from 0.64 to 0.8, strong solution flow rate 0.05 to 1.5 kg/s. The Coefficient of Performance COP of the system, based on these inputs, reaches about 0.76 and the cooling capacity reaches to 14 kW. It is found that when the generator temperature is increased, the COP is decreased. This is because the increase in generator temperature lowers LiBr-water concentration. Also, the temperature increase of the generator increases the cooling capacity. The increase in the absorber temperature reduces the COP as well as the cooling capacity. This is due to a decrease in the concentration of the solution. The absorption rate could be raised by increasing the solution concentration. The higher the concentration, the greater the absorption rate. The COP and cooling capacity improves when the evaporator temperature increases. The increase in effectiveness of heat exchangers causes an increase of system COP.

Numerical simulation of heat pump drying system for paper exhaust hood

Abstract In view of the present situation that the exhaust waste heat of the hot air hood in the paper drying section is too much and the environment is not friendly, a closed heat pump drying system model applied to the exhaust air hood is proposed and established. Effects of evaporation temperature and condensation temperature on supply air temperature, supply air moisture content, system performance coefficient (COP) and dehumidification energy consumption ratio (SMER) were studied. Results show that with the increase of condensation temperature, the supply air temperature is unchanged, and the moisture content of the supply air increase, while the COP and SMER of the system show a downward trend. The moisture content of supply air decrease with the increase of evaporation temperature, while the supply air temperature, COP and SMER all show an upward trend. Therefore, in order to improve the drying characteristics and improve the performance of the heat pump system, the condensation temperature can be reduced and the evaporation temperature can be increased.

Research on the Influence of High-Low Pressure-Volume Ratio and Discharge Pressure on the Heating Performance of Transcritical CO2 Single- Machine Two-Stage Compression Heat Pump Water Heater

Background: In order to reduce global carbon emissions, a cross-critical CO2 singlemachine two-stage compression system was proposed. Due to the characteristics of cooling on the high-pressure side of the cross-critical cycle and bipolar compression on the single-stage, the discharge pressure and the high-low pressure volume ratio have a great influence on its heating performance. Objective: The purpose of this paper is to explore the influence of high-low pressure-volume ratio and discharge pressure on the heating performance of the system, so as to obtain the optimal operating conditions of the system. Methods: By constructing theoretical calculation formula of discharge pressure, high-low pressurevolume ratio and intermediate pressure, combined with experiments. Results: Under certain working conditions, with the increase of the volume ratio of high-low pressure, the intermediate pressure increases, the heating capacity of the system increases due to the increase of the discharge temperature and the increase of the heat exchange temperature difference on the hot water side, while the heating performance coefficient decreases slowly because the rate of the increase of the power consumption of the compressor is greater than the rate of the increase of heating capacity. With the increase of discharge pressure, the increasing rate of CO2 discharge temperature will gradually decrease at the high-pressure side, so the heating capacity of the system increases rapidly first and then tends to slow down, and the heating performance coefficient increases first and then decreases. There is an optimal value, that is, when the evaporation temperature is -20 °C, the maximum heating capacity can reach 3 kW. The system heat production performance coefficient has an optimal value of 3.29, and the optimal discharge pressure is 8.5 MPa. The optimal discharge pressure will increase with the increase of evaporation temperature. Conclusion: The selection of reasonable high-low pressure volume ratio and the control of discharge pressure can effectively improve the heating performance of cross-critical CO2 single-machine twostage compression heat pump water heater.

Experimental evaluation of vortex tube and its application in a novel trigenerative compressed air energy storage system

With the increasing penetration of volatile renewable energy sources into the energy market, the importance of energy storage systems is becoming more and more significant. Compressed air energy storage (CAES) technology has attracted a lot of attention in recent years due to its significant advantages such as high reliability with few physical and environmental constraints. A novel CAES system combining vortex tube for combined cooling, heating and power supply is proposed in this paper. Firstly, the feasibility of vortex tube application in CAES system is verified by experiment. The performance of the vortex tube under different working conditions is summarized and the relative error of the modified vortex tube model is less than 1.12%. Based on the above, the thermodynamic model of the proposed CAES system incorporating vortex tubes is established. The performance evaluation and parametric analysis of the described system are presented. It is found that the System power efficiency (PSE), System energy efficiency (SENE) and exergy efficiency reach 8.300%, 98.264% and 22.495%, respectively, under the design parameters. The PSE and SENE of the system are both enhanced with the increase of evaporation temperature and hot gas temperature.

Enhancing the efficiency of a steam jet ejector chiller for chilled ceiling

• Steam jet ejector chillers (SJECs) can be suitable for buildings with high solar gains. • SJEC was combined with radiant chilled ceiling instead of convective cooling terminal. • Increasing evaporation temperature by using chilled ceiling improved COP. • This allows lower generation temperature resulting in smaller solar collector areas. Steam jet ejector chillers (SJECs) can be a suitable cooling technology in buildings where solar heat gains constitute a significant part of the cooling load. In this study, an SJEC was combined with a radiant chilled ceiling (CC) instead of traditionally used convective cooling terminals in an effort to increase the coefficient of performance (COP) by increasing the supply water temperature to the terminal ( T water,sup ) and thus the evaporation temperature. Experiments were used to verify a mathematical model of SJEC. The model was combined with T water,sup obtained from heat transfer calculations in three types of CC performed by a verified software. The COP of the ejector cooling system was 0.25 and 0.38 for R718 (water) and R1233zd, respectively, at a generation temperature of 130 °C and T water,sup of 7 °C, assuming a fancoil. Increasing T water,sup to 9 °C, which was considered to be the lowest T water,sup theoretically possible for CC involving pipes underneath the surface, improved COP by up to 14% while providing a maximum cooling capacity of about 80 W per m 2 of room area. Further increasing T water,sup to 15 °C improved the COP by 50% compared to the fancoil, while covering cooling loads of at least 40 W per m 2 . The estimated reduction in generation temperatures due to increased COP was up to 12% ( T water,sup = 9 °C) and 37% ( T water,sup = 15 °C). This means a lower energy input needed for the cooling machine, which allows a smaller solar collector area.

Unjuk Kerja Evaporator Pada Mesin Pendingin Dengan Siklus Adsorpsi Menggunakan Energi Surya

Energy needs in Indonesia continue to increase every year. The largest use ofenergy is in the industrial sector, where its needs reach 42.12% of the totalnational energy needs. To save energy, energy saving measures are needed in theindustrial sector so that the increase in energy demand can be restrained. So weconducted research on the performance of the evaporator in a refrigerationmachine with an adsorption cycle using solar energy. The purpose of this studywas to determine the working process of the evaporator with activated carbonrefrigeration and to determine the efficiency of the evaporator in the activatedcarbon pair adsorption refrigeration system. This research was conducted byobserving and recording the evaporator temperature of the refrigeration machineevery hour. The results of the research in three days of testing, namely, on the firstday the highest evaporator temperature increase was at 16.00 o'clock, which was33.2oC and the lowest evaporator temperature was at 07.00 o'clock, which was 25.1 oC. On the second day, the highest increase in evaporator temperature was at 16.00, which was 32.2oC and the lowest evaporator temperature was at 07.00, which was 23.8 oC. On the third day, the highest increase in evaporator temperature was at 36.4 oC and the lowest evaporator temperature was at 06.00,which was 24.5 oC.Kata kunci: Adsorption, evaporator, temperature

Geothermal energy-based combined cooling heating and power system

This paper studied the geothermal energy-based combined cycle for power cooling and heating purposes. The power system consists of a double flash power cycle, whereas the LiBr-H2O refrigeration absorption cycle is used for the cooling effect. The exhausted geothermal energy from the separator is further utilized for hot water to domestic application in this system. Under the condition of 200°C geothermal water temperature, the overall efficiency of the cycle is coming out 73%, which shows that the heat lost is very less, i.e., maximum heat is utilized in this cycle. The steam turbine work is 759.24 KW, whereas the COP of vapor absorption refrigeration is 0.685, and the leading coefficient of performance of the process is 0.85 working on optimal conditions. The COP of the system increases with an increase in generator temperature, but with an increase in evaporator and condenser temperature, vapor absorption cycle performance decreases.

Experimental Analyses of Moderately High-Temperature Heat Pump Systems with R245fa and R1233zd(E)

With the limited production and use of R245fa, environmentally friendly refrigerant has attracted the attention of researchers. Due to the similar thermal characteristics, R1233zd(E) is considered to be an ideal substitute for R245fa in heat pump systems. In this study, the performance and economic analysis of heat pump systems with R245fa and R1233zd(E) as refrigerants are carried out. The results show that the total cost of R1233zd(E) system is more than 10% higher than that of R245fa system under the same heating load. With the increase of condensation temperature, the heating capacity of both systems decreases, and with the increase of evaporation temperature, the heating capacity increases. The variation trend of coefficient of performance (COP) of the two systems is similar to that of heating capacity. Under the same operating conditions, the COP of R1233zd(E) system is 19.2% higher than that of R245fa system, and the volumetric heat capacity of R1233zd(E) is 9.0%–13.9% lower than that of R245fa. The economic analysis results show that the investment cost of R1233zd(E) system is low under the same heat load.

Evaluation of structural and optical properties of TeO2 nano and micro structures grown on glass and silicon substrates using thermal evaporation method

A facile evaporation method is employed to synthesize different morphologies of TeO2 using Te powder as the source material, and glass and silicon as the growth substrates. The morphological, structural, and optical properties of the obtained TeO2 products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and ultraviolet–visible (UV–vis) analyses. The morphology change of TeO2 structures is investigated by changing the evaporation temperature and substrate type. The diameters of nanowires and microrods grown on the Si substrate through this method are in the range of 50–460 nm, while the lengths of these products are several tens of micrometers. For the glass substrate, the morphology of TeO2 products is a mixture of nano- and micro-sheets. The high-temperature process facilitates the thickening of the sheets, nanowires, and nanorods. The presented energy dispersive X-ray of the TeO2 products confirms the formation of TeO2. The variation of the absorption of TeO2, coated on glass and Si substrates, with evaporation temperature is investigated. The band gap of the samples is calculated using UV–vis spectra; the results show a reduction in the band gap with increasing evaporation temperature. Furthermore, Raman analysis is performed in the present study.