Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Investigation of Vapor Ejectors in Heat Driven Ejector Refrigeration Systems
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Refrigeration systems, air-conditioning units and heat pumps have been recognized as indispensable machines in human life, and are used for e.g. food storage, provision of thermal comfort. These machines are dominated by the vapor compression refrigeration system and consume a large percentage of world-wide electricity output. Moreover, CO2 emissions related to the heating and cooling processes contribute significantly to the total amount of CO2 emission from energy use. The ejector refrigeration system (ERS) has been considered as a quite interesting system that can be driven by sustainable and renewable thermal energy, like solar energy, and low-grade waste heat, consequently, reducing the electricity use. The system has some other remarkable merits, such as being simple and reliable, having low initial and running cost with long lifetime, and providing the possibility of using environmentally-friendly refrigerants, which make it very attractive. The ERS has received extensive attention theoretically and experimentally.

This thesis describes in-depth investigations of vapor ejectors in the ERS to discover more details. An ejector model is proposed to determine the system performance and obtain the required area ratio of the ejector by introducing three ejector efficiencies. Based on this ejector model, the characteristics of the vapor ejector and the ERS are investigated from different perspectives.

The working fluid significantly influences the ejector behavior and system performance as well as the ejector design. No perfect working fluid that satisfies all the criteria of the ERS can be found. The performance of nine refrigerants has been parametrically compared in the ERS. Based on the slope of the vapor saturation curve in a T-s diagram, the working fluids can be divided into three categories: wet, dry and isentropic. A wet fluid has a negative slope of the vapor saturation curve in the T-s diagram. An isentropic expansion process from a saturated vapor state will make the state after the expansion to fall inside the liquid-vapor area of the T-s diagram which will result in droplet formation. Generally, an isentropic expansion for a dry fluid will not occur inside the liquid-vapor area, and consequently no droplets will form. An isentropic fluid has a vertical slope of the vapor saturation curve in the T-s diagram and an isentropic expansion process will hence follow the vapor saturation curve in the T-s diagram, ideally without any droplet formation. However, when the saturation condition is close to the critical point, it is possible that the isentropic expansion process of a dry fluid and an isentropic fluid occurs inside the liquid-vapor area of the T-s diagram, resulting in formation of droplets. In order to avoid droplet formation during the expansion, a minimum required superheat of the primary flow has been introduced before the nozzle inlet. Results show that the dry fluids have generally better performance than the wet fluids and the isentropic fluid. Hence the thesis mostly focuses on the features of vapor ejectors and the ERS using dry fluids.

Exergy analysis has been proven to be very useful to identify the location, magnitude, and sources of exergy destruction and exergy loss, and to determine the possibilities of system performance improvement. This method is applied to the ejector and the ERS. The ejector parameters are closely interacting. The operating condition and the ejector area ratio have a great impact on the ejector overall efficiency and system COP. The ejector efficiencies are sensitive to the operating conditions, and they significantly influence the system performance. A so-called advanced exergy analysis is adopted to quantify the interactions among the ERS components and to evaluate the realistic potential of improvement. The results indicate that, at the studied operating condition, the ejector should have the highest priority to be improved, followed by the condenser, and then the generator.

Thermoeconomics, which combines the thermodynamic analysis and economic principles, is applied to reveal new terms of interest of the ERS. The economic costs of the brine side fluids (fluids that supply heat to the generator and evaporator and remove heat from the condenser) play very essential roles in the thermoeconomic optimization of the ERS. Depending on different economic conditions, the system improvement from a thermodynamic point of view could be quite different from the thermoeconomic optimization. The ERS is economically sound when using free heat sources and heat sink.

An ejector test bench has been built to test the entrainment ratio of different ejectors. Although the experiments do not achieve the desired results, they could still be discussed. The insignificant effect of the superheat of the secondary flow found in the theoretical study is validated. The assumption of neglecting the velocities at the ejector inlets and outlet are confirmed. The quantification of the ejector efficiencies shows that they largely depend on the operating conditions and the ejector dimensions. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xii, 96 p.
Series
TRITA-REFR, ISSN 1102-0245 ; 14:04
Keyword [en]
vEjector Refrigeration System, Ejector, Efficiency, Performance, Exergy Analysis, Experiment.
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-156070ISBN: 978-91-7595-387-8 (print)OAI: oai:DiVA.org:kth-156070DiVA: diva2:764519
Public defence
2014-12-16, K2, Teknikringen 28, KTH, Stockholm, 12:00 (English)
Opponent
Supervisors
Note

QC 20141102

Available from: 2014-12-02 Created: 2014-11-19 Last updated: 2014-12-02Bibliographically approved
List of papers
1. Investigation of ejectors in refrigeration system: Optimum performance evaluation and ejector area ratios perspectives
Open this publication in new window or tab >>Investigation of ejectors in refrigeration system: Optimum performance evaluation and ejector area ratios perspectives
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, no 1-2, 182-191 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an ejector model to determine the optimum performance as well as obtaining the design area ratio of an ejector in a refrigeration system. Working fluid properties and auxiliary dynamic equations are used to model the processes in the ejector. The normal compression shock in the mixing chamber is considered. Experimental data from literature are used to validate the model, and the agreement with the model at optimum operating conditions is very good. The deviation between the model and the experimental data at non-optimum conditions is slightly larger. A study of working conditions for refrigerants R123 and R141b indicates that the condenser temperature has more influence than the generator and evaporator temperatures on the area ratio and the entrainment ratio in the ejector. Furthermore, area ratios need to keep up the pace with the variation of entrainment ratio as operating conditions are changed. A variable-geometry ejector seems a very promising alternative to ensure that the ejector refrigeration system operates at its optimum conditions. Ejector efficiencies play a very important role in the present model, and the influence of the efficiencies on the ejector performance is investigated. This ejector model may be used for parametric analysis and optimum performance evaluation as well as ejector design.

Keyword
Area ratio, Ejector, Entrainment ratio, Optimum performance, Refrigeration system
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-140794 (URN)10.1016/j.applthermaleng.2013.12.034 (DOI)000333777000019 ()2-s2.0-84891786583 (Scopus ID)
Note

QC 20140203

Available from: 2014-02-03 Created: 2014-01-31 Last updated: 2017-12-06Bibliographically approved
2. Screening of working fluids for the ejector refrigeration system
Open this publication in new window or tab >>Screening of working fluids for the ejector refrigeration system
2014 (English)In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 47, 1-14 p.Article in journal (Refereed) Published
Abstract [en]

For an ejector refrigeration system, the working fluid significantly influences the ejector behavior and system performance as well as ejector design. There are three categories of working fluids: wet fluids, dry fluids and isentropic fluids. Four wet fluids (R134a, R152a, R290 and R430A), four dry fluids (R245fa, R600, R600a and R1234ze) and one isentropic fluid (R436B) are selected in the paper. Special consideration is paid to the superheat of the ejector primary flow. This superheat is needed not only for wet fluids, but also for dry fluids and isentropic fluids at some cases, to eliminate droplets inside the ejector. A minimum superheat is found, and it is dependent on the used working fluid and the operating temperatures as well as the ejector nozzle efficiency. The comparison among these nine candidates indicates that R600 is a good candidate for the ejector refrigeration system due to a relatively high COP and its low environmental impact.

Keyword
Efficiency, Ejector, Performance, Refrigeration, Working fluids
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-156069 (URN)10.1016/j.ijrefrig.2014.07.016 (DOI)000347593400002 ()2-s2.0-84908316810 (Scopus ID)
Note

QC 20141202

Available from: 2014-11-19 Created: 2014-11-19 Last updated: 2017-12-05Bibliographically approved
3. Parametric analysis of ejector working characteristics in the refrigeration system
Open this publication in new window or tab >>Parametric analysis of ejector working characteristics in the refrigeration system
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 69, no 1-2, 130-142 p.Article in journal (Refereed) Published
Abstract [en]

A detailed investigation of ejector working characteristics in terms of refrigeration efficiency, ejector entrainment ratio, and irreversibilities in each ejector component (nozzle, mixing chamber and diffuser) is carried out by using R141b, R245fa and R600a as the working fluids. The aim of this paper is to generalize the interactions and relationships of various ejector parameters to get better understanding of the ejector working characteristics in the refrigeration system. External and internal ejector parameters are studied separately. The operating conditions and ejector component efficiencies have significant influence on the ejector behavior, and different refrigerants perform distinctively different in the ejector refrigeration system. However, effects of superheat of the three working fluids are negligible. The irreversibility related to the shock process dominates in the diffuser and plays an important role in the ejector performance. Further attention is paid on an analysis of quantifying the ejector component efficiencies based on published test data. Correlations are established to estimate the ejector efficiency and to show how ejector parameters interact.

Keyword
Ejector refrigeration, COP, Entrainment ratio, Irreversibility, Efficiency
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-148601 (URN)10.1016/j.applthermaleng.2014.04.047 (DOI)000338613200014 ()2-s2.0-84900842692 (Scopus ID)
Note

QC 20140812

Available from: 2014-08-12 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved
4. Conventional and advanced exergyanalysis of an ejector refrigeration system
Open this publication in new window or tab >>Conventional and advanced exergyanalysis of an ejector refrigeration system
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-156778 (URN)
Note

QS 2014

Available from: 2014-12-02 Created: 2014-12-02 Last updated: 2014-12-02Bibliographically approved
5. Thermoeconomic optimization of an ejector refrigeration system working with isobutane
Open this publication in new window or tab >>Thermoeconomic optimization of an ejector refrigeration system working with isobutane
2014 (English)In: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants: Natural Refrigerants and Environmental Protection, GL 2014, 2014, 286-294 p.Conference paper, Published paper (Refereed)
Abstract [en]

Thermoeconomics is a new branch of thermodynamics and consists of exergy analysis, economic modeling and thermoeconomic analysis on an energy conversion system. In this study, thermoeconomic concepts are applied to an ejector refrigeration system (ERS) that uses natural refrigerant R600a as the working fluid and has 100 kW cooling capacity. The system is investigated from thermodynamic and thermoeconomic perspectives. To optimize such a system, the objective function is defined as the sum of the costs of brine side fluids, electricity, and costs related to capital investment and operation and maintenance expense. The pinch point temperatures in the three heat changers are considered as the decision variables, with two different economic scenarios imposed to the system. An iteration technique is employed to minimize the objective function. It shows that the optimized objective function is reduced by 8.1% and 7.5% respectively compared to the non-optimized cases for the two scenarios.

Keyword
Ejector refrigeration system; Exergy; Thermoeconomic; Optimization
National Category
Engineering and Technology Energy Engineering
Identifiers
urn:nbn:se:kth:diva-156065 (URN)000352781600031 ()2-s2.0-84932187693 (Scopus ID)9782362150043 (ISBN)
Conference
11th IIR Gustav Lorentzen Conference on Natural Refrigerants, GL 2014; Shangri-La Hotel78 Beishan RoadHangzhou; China; 31 August 2014 through 2 September 2014
Note

QC 20141202

Available from: 2014-11-19 Created: 2014-11-19 Last updated: 2015-08-07Bibliographically approved

Open Access in DiVA

Thesis(1718 kB)2641 downloads
File information
File name FULLTEXT02.pdfFile size 1718 kBChecksum SHA-512
0bc43857e1a55a3eedfa34658191e8f7fee515ef259e7ce92fadb0f4a85ad1d25d17e31531eb3592517e1cc1173c93c87b8ec981c5c88d0cab82a02aa8155788
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Chen, Jianyong
By organisation
Applied Thermodynamics and Refrigeration
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 2641 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 564 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf