Air-side performance of a parallel-flow parallel-fin (PF2) heat exchanger in sequential frosting / Ping Zhang in International journal of refrigeration, Vol. 33 N° 6 (Septembre 2010)  

Public ISBD [article]  inInternational journal of refrigeration > Vol. 33 N° 6 (Septembre 2010) . - pp. 1118-1128 Titre : Air-side performance of a parallel-flow parallel-fin (PF2) heat exchanger in sequential frosting Titre original : Performance côté air d'un échangeur de chaleur à écoulement parallèle aux ailettes parallèles sous des conditions de givrage séquentiel Type de document : texte imprimé Auteurs : Ping Zhang, Auteur ; P. S. Hrnjak, Auteur Année de publication : 2010 Article en page(s) : pp. 1118-1128 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Heat exchanger Finned tube Parallel flow Frosting Defrosting transfer Pressure drop Performance Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The thermal-hydraulic performance in periodic frosting conditions is experimentally studied for the parallel-flow parallel-fin heat exchanger, henceforth referred to as a PF2 heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal. Typically, it takes a few frosting/defrosting cycles to come to repeatable conditions. The criterion for the initiation of defrost and a sufficiently long defrost period are determined for the test PF2 heat exchanger and test condition. The effects of blower operation on the pressure drop, frost accumulation, water retention, and capacity in time are compared under the conditions of 15 sequential frosting cycles. Pressure drop across the heat exchanger and overall heat transfer coefficient are quantified under frost conditions as functions of the air humidity and air face velocity. The performances of two types of flat-tube heat exchangers, PF2 heat exchanger and conventional parallel-flow serpentine-fin (PFSF) heat exchanger, are compared and the results obtained are presented. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000812 [article] Air-side performance of a parallel-flow parallel-fin (PF2) heat exchanger in sequential frosting = Performance côté air d'un échangeur de chaleur à écoulement parallèle aux ailettes parallèles sous des conditions de givrage séquentiel [texte imprimé] / Ping Zhang, Auteur ; P. S. Hrnjak, Auteur . - 2010 . - pp. 1118-1128. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 6 (Septembre 2010) . - pp. 1118-1128 Mots-clés : Heat exchanger Finned tube Parallel flow Frosting Defrosting transfer Pressure drop Performance Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The thermal-hydraulic performance in periodic frosting conditions is experimentally studied for the parallel-flow parallel-fin heat exchanger, henceforth referred to as a PF2 heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal. Typically, it takes a few frosting/defrosting cycles to come to repeatable conditions. The criterion for the initiation of defrost and a sufficiently long defrost period are determined for the test PF2 heat exchanger and test condition. The effects of blower operation on the pressure drop, frost accumulation, water retention, and capacity in time are compared under the conditions of 15 sequential frosting cycles. Pressure drop across the heat exchanger and overall heat transfer coefficient are quantified under frost conditions as functions of the air humidity and air face velocity. The performances of two types of flat-tube heat exchangers, PF2 heat exchanger and conventional parallel-flow serpentine-fin (PFSF) heat exchanger, are compared and the results obtained are presented. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700710000812

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Effect of some geometric parameters on performance of PF2 heat exchangers in periodic frosting / Ping Zhang in International journal of refrigeration, Vol. 33 N° 2 (Mars 2010)  

Public ISBD [article]  inInternational journal of refrigeration > Vol. 33 N° 2 (Mars 2010) . - pp. 334-346 Titre : Effect of some geometric parameters on performance of PF2 heat exchangers in periodic frosting Titre original : Impact de certains paramètres sur la performance d'échangeurs à écoulements et aux ailettes parallèles lors d'épisodes périodiques de givrage Type de document : texte imprimé Auteurs : Ping Zhang, Auteur ; P. S. Hrnjak, Auteur Année de publication : 2011 Article en page(s) : pp. 334-346 Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Heat exchanger Finned tube Experiment Performance Parameter Geometry Frosting Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The thermal performance under conditions of initial frost growth and subsequent refrosting after a defrost is experimentally studied for the parallel flow parallel fin (PF2) heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal (typically outdoor heat exchanger in heat pump operation). This paper focuses on quantification of the effects of geometry (i.e. fin pitch 12–22 fpi and louver pitch 1.4–2.8 mm) on defrost and refrost times. Eight heat exchangers differing in louver pitch and fin spacing are studied. A series of tests are conducted in search for the best geometry. The effects of geometry on heat transfer (thermal performance) and pressure drop for air face velocities of 0.9, 2, and 3 m/s are determined and used for comparison. Characteristics of initial heat transfer coefficient and pressure drop during the first frosting cycle are reported in terms of Colburn j0 factor and Fanning friction f0 factor, as a function of ReLp and geometry. The newly developed air-side correlations for PF2 heat exchangers (Colburn j0 factor and Fanning friction f0 factor) predict the test data within rms error of ±10%, and with mean deviation of 2.95% and 4.98%, respectively. The correlations are base on a very low Reynolds numbers in the range of 100–620, and 8 PF2 heat exchangers using 48 experimental data. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700709002515 [article] Effect of some geometric parameters on performance of PF2 heat exchangers in periodic frosting = Impact de certains paramètres sur la performance d'échangeurs à écoulements et aux ailettes parallèles lors d'épisodes périodiques de givrage [texte imprimé] / Ping Zhang, Auteur ; P. S. Hrnjak, Auteur . - 2011 . - pp. 334-346. Génie Mécanique Langues : Anglais (eng) in International journal of refrigeration > Vol. 33 N° 2 (Mars 2010) . - pp. 334-346 Mots-clés : Heat exchanger Finned tube Experiment Performance Parameter Geometry Frosting Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The thermal performance under conditions of initial frost growth and subsequent refrosting after a defrost is experimentally studied for the parallel flow parallel fin (PF2) heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal (typically outdoor heat exchanger in heat pump operation). This paper focuses on quantification of the effects of geometry (i.e. fin pitch 12–22 fpi and louver pitch 1.4–2.8 mm) on defrost and refrost times. Eight heat exchangers differing in louver pitch and fin spacing are studied. A series of tests are conducted in search for the best geometry. The effects of geometry on heat transfer (thermal performance) and pressure drop for air face velocities of 0.9, 2, and 3 m/s are determined and used for comparison. Characteristics of initial heat transfer coefficient and pressure drop during the first frosting cycle are reported in terms of Colburn j0 factor and Fanning friction f0 factor, as a function of ReLp and geometry. The newly developed air-side correlations for PF2 heat exchangers (Colburn j0 factor and Fanning friction f0 factor) predict the test data within rms error of ±10%, and with mean deviation of 2.95% and 4.98%, respectively. The correlations are base on a very low Reynolds numbers in the range of 100–620, and 8 PF2 heat exchangers using 48 experimental data. DEWEY : 621.5 ISSN : 0140-7007 En ligne : http://www.sciencedirect.com/science/article/pii/S0140700709002515

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Flow modes and mode transitions for falling films on flat tubes / Xiaofei Wang in Journal of heat transfer, Vol. 134 N° 2 (Fevrier 2012)  

Public ISBD [article]  inJournal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 09 p. Titre : Flow modes and mode transitions for falling films on flat tubes Type de document : texte imprimé Auteurs : Xiaofei Wang, Auteur ; P. S. Hrnjak, Auteur ; S. Elbel, Auteur Année de publication : 2012 Article en page(s) : 09 p. Note générale : Heat transfer Langues : Anglais (eng) Mots-clés : Drops External flows Film flow Flow instability visualisation Jets Laminar to turbulent transitions Liquid films Pipe Two-phase Index. décimale : 536 Chaleur. Thermodynamique Résumé : Flow mode transitions for a liquid film falling over flat tubes are studied for a wide range of conditions. Hydraulic oil, ethylene glycol, ethylene-glycol-water mixtures (at three different volume ratios), and water are used as working fluids in experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow modes are observed over a range of flow rate and tube spacing. The flow modes are more complex but similar to those manifested on round tubes, and include the sheet, sheet-jet, jet, jet-droplet, and droplet modes. However, the transitions at Ga1/4 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...] [article] Flow modes and mode transitions for falling films on flat tubes [texte imprimé] / Xiaofei Wang, Auteur ; P. S. Hrnjak, Auteur ; S. Elbel, Auteur . - 2012 . - 09 p. Heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 2 (Fevrier 2012) . - 09 p. Mots-clés : Drops External flows Film flow Flow instability visualisation Jets Laminar to turbulent transitions Liquid films Pipe Two-phase Index. décimale : 536 Chaleur. Thermodynamique Résumé : Flow mode transitions for a liquid film falling over flat tubes are studied for a wide range of conditions. Hydraulic oil, ethylene glycol, ethylene-glycol-water mixtures (at three different volume ratios), and water are used as working fluids in experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow modes are observed over a range of flow rate and tube spacing. The flow modes are more complex but similar to those manifested on round tubes, and include the sheet, sheet-jet, jet, jet-droplet, and droplet modes. However, the transitions at Ga1/4 DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000002 [...]

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