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Influence factors on thermal conductivity of ammonia-water nanofluids

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Journal of Central South University 2012年第6期19卷 1622-1628页

作者：杨柳杜垲张小松 School of Energy and Environment Southeast University

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,*** thermal conductivities were measured by using a KD2 Pro thermal properties *** influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index *** results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of *** the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is ***,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

关键词： binary nanofluids ammonia-water thermal conductivity size effect dispersion stability

Theoretical and experimental investigation on a liquid-gas ejector power cycle using ammonia-water

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Science China(Technological Sciences) 2013年第9期56卷 2289-2298页

作者： YUAN Han MEI Ning LI Yan YANG Shuai HU SiYuan HAN YiFang College of Engineering Ocean University of China

The purpose of this paper is to investigate a novel power cycle using low-temperature heat sources such as oceanic-thermal, biomass as well as industrial waste heat. Both a reheater and a liquid-gas ejector are used in this ammonia-water based cycle. Energy analysis and parametric analysis are performed to guide the theoretical performance and experimental investigation is done to verify the theoretical results. The results show that the generator pressure, heating source temperature and turbine outlet depressurization made by the ejector can affect the cycle performances. Besides, the experimental thermal efficiency is much lower than the theoretical one on account of the heat losses and irreversibility. Moreover, the performance of liquid-gas ejector is affected by primary flow pressure and temperature.

关键词： ammonia-water power cycle ejector efficiency

Performance analysis of ammonia-water absorption/compression combined refrigeration cycle

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Journal of Southeast University(English Edition) 2014年第1期30卷 60-67页

作者：鲍帅阳杜垲蔡星辰牛晓峰武云龙东南大学能源与环境学院南京210096 南京工业大学城市建设与安全工程学院南京211816

In view of different compressor adding ways in the ammonia-water absorption/compression combined refrigeration AWA /CCR cycle combining the Schulz state equation of the ammonia-water solution the theoretical analysis and calculations on two combination ways by adding the compressor in the high-pressure area and in the low-pressure area are conducted *** effects of several factors including the evaporation temperature Te heat-source temperature Th as well as the cooling water temperature Tw on the equivalent heat consumption in compression qCW heat consumption in absorption qG and the system coefficient of performance COP are analyzed under the two combination *** results show that the effect of the equivalent heat consumption in compression on the COP is less than that of the heat consumption in *** the compressor set in the high-pressure area uses more energy than that in the low-pressure area. Moreover the compressor in the low-pressure area is superior to that in the high-pressure area with respect to the COP. Under the given intermediate pressure there is an optimum heat-source temperature corresponding to the maximum COP of the AWA/CCR cycle.

关键词： ammonia-water absorption compression refrigeration combined refrigeration cycle coefficient of performance COP

Magnetic Field Enhancement in ammonia-water Absorption Refrigeration Systems

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Energy and Power Engineering 2014年第4期6卷 54-68页

作者： Moradeyo K. Odunfa Richard O. Fagbenle Olanrewaju M. Oyewola Olayinka S. Ohunakin Mechanical Engineering Department Covenant University Ota Nigeria Mechanical Engineering Department Obafemi Awolowo University Ile-Ife Nigeria Mechanical Engineering Department University of Ibadan Ibadan Nigeria

Absorption enhancement has been considered as an effective way of improving coefficient of performance (COP) of refrigeration systems and magnetic enhancement is one of these methods. A model of magnetic field enhancement in ammonia-water absorption systems is presented in this paper. A numerical model using finite difference scheme was developed based on the conservation equations and mass transport relationship. Macroscopic magnetic field force was introduced in the momentum equation. The model was validated using data obtained from the literature. Changes in the physical properties of ammonia solution while absorbing both in the direction of falling film and across its thickness were investigated. The magnetic field was found to have some positive effect on the ammonia-water falling film absorption. The results indicate that absorption performance enhancement increased with magnetic intensity. The COP of simple ammonia solution absorption refrigeration system increased by 1.9% and 3.6% for magnetic induction of 1.4 and 3.0 Tesla respectively.

关键词： ammonia-water Absorption Refrigeration Magnetic Field Force ammonia Solution Concentration Coefficient of Performance Finite Difference Scheme Numerical Solution

Computer Simulation of an ammonia-water Absorption Cycle for Refrigeration: Using a Distillation Tower to Replace the Generator

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Energy and Power Engineering 2020年第6期12卷 237-256页

作者： You-Im Chang Lin-Chia Wu Cherng-Chiao Wu Larry K. Jang Department of Chemical Engineering Tunghai University Taiwan Department of Chemical Engineering California State University Long Beach CA USA

By using a distillation tower as the regenerator, the coefficient of performance (COP) of the ammonia-water absorption refrigeration cycle is calculated in this work. Two types of distillation towers, namely an equilibrium-stage tower with a total condenser and a packed-bed tower with a partial condenser, are used in the cycle. From the simulation results, it is found that both types of distillation towers can successfully increase the COP of the cycle due to increased ammonia concentration in the vapor phase of the ammonia-water refrigerant. It was also found that the tower equipped with a partial condenser provides higher COP than that of the tower equipped with a total condenser. The value of COP can be further increased when the generator is replaced by the packed-bed tower in this water-ammonia absorption cycle. The effects of the mass flow rate ratio of NH3/H2O, stage number, reflux ratio and energy duty of the tower on the COP of the cycle are also studied in the present paper.

关键词： Simulation ammonia-water Absorption Refrigeration

Thermodynamic Modelling of a 10-kW ammonia-water Absorption Machine

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Journal of Energy and Power Engineering 2022年第5期16卷 213-221页

作者： Fatimata Dione Ababacar Thiam Djicknoum Diouf Amadou-Seidou Maiga Dept.of Applied Physics Faculty of Applied Sciences and TechnologyGaston Berger UniversitySaint-Louis BP 234Senegal Efficiency and Energy Systems Research Team Alioune Diop UniversityBambey BP 30Senegal

Absorption chillers are cooling units usually powered by renewable energy or waste *** performance generally depends on the temperatures of the heat source,the ambient and the medium to be *** present work deals with the thermodynamic study of a 10 kW NH3/H2O absorption machine in order to find the COP(coefficient of performance).The first and second laws of thermodynamics were used for the operating *** thermodynamic properties of the NH3/H2O mixture were determined using the EES(Engineering Equation Solver)*** results of the simulation of the machine were validated with the results of the *** validation,the program was used to simulate a 10-kW NH3/H2O absorption machine for milk conservation/cold storage in northern *** simulation results of the 10-kW ammonia-water absorption machine give an acceptable COP of 0.521 with a milk storage temperature of 4°C.

关键词： Absorption ammonia-water COP EES

Thermodynamic and Experimental Analysis of an ammonia-water Absorption Chiller

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Energy and Power Engineering 2010年第4期2卷 298-305页

作者： Dingfeng Kong Jianhua Liu Liang Zhang Hang He Zhiyun Fang 不详

A single stage ammonia-water absorption chiller with complete condensation is designed, built and tested. The apparatus is designed for a cooling capacity of 2814 W, which is obtained using electric heater as heating source. The thermodynamic models have been derived using the First and Second Laws. Calculated results are compared with experimental data. The results show that the cooling capacity of experimental apparatus is found between 1900 and 2200 W with the actual coefficient of performance (COP) between 0.32 and 0.36. The contribution of the components to internal entropy production is analyzed. It shows that the larger irreversibility is caused by spanning the largest temperature and dissipated thermal energy by heat transfer losses at the generator and evaporator. In the experimentation, the low pressure is lower than the designed value. This is a consequence of a large capacity in the falling film absorber which performs as expected. This decreases the evaporation pressure, and the evaporating temperature could be reduced to the designed value.

关键词： Absorption Chiller ammonia-water Thermodynamic Modeling Experimental Performance

Review of enhancement for ocean thermal energy conversion system

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Journal of Ocean Engineering and Science 2023年第5期8卷 533-545页

作者： Safaa Malik Abbas HendDakhelSkhaal Alhassany David Vera Francisco Jurado Department of Electrical Engineering University of Jaen23700EPS LinaresJaenSpain

Ocean thermal energy conversion(OTEC)is a renewable energy source that uses differences in ocean water temperature between warm surface and cold depth to generate *** is an essential link in the carbon neutrality chain and one of the rising sectors of the ocean *** paper provides an overview of studies on closed thermodynamic cycles and the numerous difficulties that OTEC technology faces.A description of the thermodynamic cycles incorporating mixed or pure working fluids,as well as the implications of different working fluids on cycle efficiency were also *** in condensing and evaporating temperatures induced by variations in heat resources affect the efficiency of cycles with pure working *** strategies,such as intermediate extraction regeneration and heat recovery of ammonia-depleted solution can increase the thermal efficiency with mixed working *** addition,the impact of the ejector on the cycle’s performance is ***,the efficiency-improving strate-gies are described and *** efficiency can increase using suitable working fluids and taking steps to maximize the rate of ocean thermal *** establish which approach is the most effective,different methods have been evaluated and compared under identical operating conditions.

关键词： Ocean thermal energy conversion Organic rankine cycle ammonia-water Liquid-vapor ejector Vapor-vapor ejector

Coupled Heat and Mass Transfer Analysis of NH3-H2O Falling Film Absorption on Inner Tube Surface with Low Solution Flow Rates

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Journal of Shanghai Jiaotong university(Science) 2016年第4期21卷 395-405页

作者：林芃王如竹 China Ship Development and Design Center Shanghai 201108 China Institute of Refrigeration and Cryogenics Shanghai Jiaotong University Shanghai 200240 China

NH_3-H_2O falling film absorption usually takes place with low solution flow rate in real absorption refrigeration system. An experimental study of inner vertical absorption is carried out for the consideration of air-cooling absorber. Variable working conditions are tested to evaluate the heat and mass transfer *** traditional evaluation method based on log-mean-temperature(concentration) difference is criticized for its lack of theoretical basis while simultaneous heat and mass transfer process occurs. A new method proposed by Kim and Infante Ferreira is modified to evaluate the experimental results with reasonable assumptions. The method is based on the derivation of coupled heat and mass transfer differential equations of NH_3-H_2O absorption *** analysis of the same experimental data shows that the new method realizes better consistency with smaller error, especially in heat transfer aspect. Heat and mass transfer performance is enhanced with the increase of solution Reynolds number. Sub-cooling of inlet weak solution also has positive influence on the absorption process,which should be evaluated by the new method correctly. Two correlations are developed to evaluate both Nusselt and Sherwood numbers for the design of air-cooling absorber.

关键词： falling film absorption heat and mass transfer ammonia-water