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Boiling heat transfer of ammonia in vertical smooth mini channels: Experimental results and predictions
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-9902-2087
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2012 (English)In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 54, 13-21 p.Article in journal (Refereed) Published
Abstract [en]

In this article, flow boiling heat transfer results of ammonia in mini channels are reported. Experiments have been performed to investigate heat transfer in circular vertical mini channels made of stainless steel (AISI 316) with internal diameters of 1.70 mm and 1.224 mm and a uniformly heated length of 245 mm. The test conditions are: mass flux ranging from 100 to 500 kg/m2s, heat flux ranging from 15 to 355 kW/m2 and saturation temperatures of 23 °C, 33 °C and 43 °C. The effects of mass flux, heat flux, vapour quality, saturation temperature and internal diameter on heat transfer coefficients are explored in detail. The local heat transfer coefficients of ammonia with 1.70 mm tube at all vapour qualities and at lower vapour qualities with 1.224 mm tube, are more or less independent of mass flux and vapour quality and are a function of heat flux while the local heat transfer coefficients with 1.224 mm tube at higher vapour qualities are function of mass flux and vapour quality and independent of heat flux. The heat transfer coefficient is observed to be higher for lower internal diameter tube. The heat transfer coefficient is higher for higher saturation temperature at lower vapour qualities and no effect of saturation temperature is observed at higher vapour qualities for both test sections. The experimental data is compared with well known correlations and among them, the Cooper’s [1] correlation gave best predictions if all data points are included.

Place, publisher, year, edition, pages
2012. Vol. 54, 13-21 p.
Keyword [en]
Flow boiling, Ammonia, Heat transfer, Experimental study
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-80602DOI: 10.1016/j.ijthermalsci.2011.09.012ISI: 000300761400002Scopus ID: 2-s2.0-84856336840OAI: oai:DiVA.org:kth-80602DiVA: diva2:496521
Note
QC 20120210Available from: 2012-02-10 Created: 2012-02-10 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Flow boiling of ammonia and propane in mini channels
Open this publication in new window or tab >>Flow boiling of ammonia and propane in mini channels
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The environmental concerns in recent times have grown especially after signing Montreal protocol. In the last ten years, researchers have focussed mainly on understanding the boiling and condensation phenomena of HFC refrigerants in minichannels. As global warming concerns are growing day by day, due to high global warming potential, HFCs are not the ultimate option. In the near future, HFCs will probably be replaced by environmentally friendly refrigerants. Therefore, to find the potential replacements of HFCs and also to get a deeper understanding of the boiling phenomena in minichannels, more and more fluids having low GWP (Global Warming Potential) and ODP (Ozone Depletion Potential) should be tested. Recent efforts to protect the environment have led to a growing interest for natural refrigerants. However in the literature, flow boiling data of natural refrigerants in minichannels are scarce.

To meet the environmental concerns and to understand the behaviour of natural refrigerants in minichannels and the performance compared to HFCs, flow boiling experiments in single circular vertical minichannels of internal diameters of 1.70 and 1.224 mm were performed using ammonia and propane as working fluids.

Flow boiling heat transfer results of ammonia and propane with 1.70 mm channel showed that the heat transfer coefficient was a function of heat flux and the effect of mass flux was insignificant. The heat transfer coefficient of ammonia in 1.224 mm was dependent on heat flux at low vapour qualities then a clear dependence of the heat transfer coefficient on the mass flux was observed at higher vapour qualities. The heat transfer results of ammonia and propane were compared with well known correlations and among them Cooper (1989) correlation in case of ammonia and Liu and Winterton (1991) and Cooper (1984) pool boiling correlations in case of propane best predicted the experimental heat transfer data.

Results of the two phase pressure drop studies of ammonia and propane showed that the two phase pressure drop increased with the increase of mass flux, with the increase of heat flux and with the decrease of saturation temperature. The comparison of the two phase pressure drop experimental data with well known predicting models showed that none of the correlations predicted the ammonia data well and that Müller Steinhagen and Heck (1986) was well in agreement with the propane data.

Dryout of propane in 1.70 mm and 1.224 mm internal diameter channels was also investigated. Dryout heat flux was observed to increase with the increase of mass flux, with the decrease of vapour quality and with the increase of internal diameter. The effect of saturation temperature on the dryout heat flux was insignificant. The experimental dryout data were compared with macro and micro scale correlations and among them Bowring (1972) and Callizo et al. (2010a) gave best predictions.

The heat transfer and pressure drop results of ammonia and propane and dryout results of propane were compared with R134a data taken on the same test rig by Owhaib (2007) and Ali (2010). The comparison of heat transfer showed that the heat transfer coefficient was a function of heat flux and the effect of mass flux was insignificant in all tested conditions except ammonia in 1.224 mm tube where the heat transfer coefficient was dependent on heat flux at lower vapour qualities and a clear dependence of mass flux was observed at higher vapour qualities. The heat transfer data of ammonia, propane and R134a were compared with correlations and among them Cooper (1989) correlation gave best predictions. The comparison of pressure drop results showed that the two phase pressure drop of all fluids was increased with the increase of mass flux, with the increase of heat flux and with the decrease of saturation temperature. At equal heat flux and mass flux, the two phase pressure drop of ammonia was increased with the decrease of internal diameter but the diametric effects of R134a were unclear. Müller Steinhagen and Heck (1986) and Zhang and Webb (2001) best predicted the experimental data of two phase pressure drop of ammonia, propane and R134a among the correlations considered for comparison. The dryout data of propane were also compared with dryout data of R134a and it was observed that the dryout heat flux of propane and R134a increased with the increase of mass flux, with the decrease of vapour quality and with the increase of internal diameter. The effect of saturation temperature on the dryout heat flux of propane and R134a was insignificant. The correlation of Bowring (1972) for conventional channels and the microscale correlation of Callizo et al. (2010a) were among the correlations which gave best predictions of experimental data of dryout.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 107 p.
Series
Trita-REFR, ISSN 1102-0245 ; 12:01
Keyword
Flow Boiling, Mini channels, Global Warming Potential, Ammonia, Propane, R134a, HFC, Two-phase, Heat Transfer, Pressure Drop, Dry out.
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-80331 (URN)978-91-7501-264-3 (ISBN)
Public defence
2012-02-27, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120210Available from: 2012-02-10 Created: 2012-02-09 Last updated: 2012-02-10Bibliographically approved

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