Performance enhancement of heat exchanger coolers with evaporative cooling

Air or water cooled heat exchangers (HX) are typically utilized as condensers or coolers for air-conditioning, refrigeration or process cooling applications in both commercial and industrial sector. However, air cooled heat exchanger performance degrades considerably with rise in ambient air temperature and water cooled coolers require considerable pumping power, a cooling tower and may consume a significant amount of water which may come from fresh water sources. Evaporative cooling offers a unique solution to this problem, where a small amount of wetting water evaporates on HX surface to boost performance in high ambient air temperature conditions. In this study, several evaporative cooling technologies were applied to three wavy-fin HXs to quantify capacity enhancement ratio (CER) and air-side pressure drop penalty ratio (PRΔPa) compared to respective dry case baseline values. Effect of varying wetting water flow rate, air velocity, fin spacing, hydrophilic coatings, spray orientation and inlet air temperature and relative humidity was investigated on hybrid heat exchanger performance. Several new performance comparison parameters were defined to compare different evaporative cooling approaches. Deluge cooling achieved overall highest CER but at a PRΔPa that was similar in magnitude to the CER. This limitation was found to be inherent to the nature of wetting water distribution method itself. Although front spray cooling tests indicated PRΔPa~1, front spray evaporative cooling technology was found to have up to 23-75 % lower CER at 60-100% lower PRΔPa compared to deluge cooling. In order to understand the wetting behavior a novel visualization method was proposed and implemented, which consisted of borescope assisted flow mapping of water distribution within the HX core as a function of air velocities and wetting water flow rates. It was found that up to 85% of HX volume remained dry during front spray cooling which accounted for lower capacity enhancement and deluge cooling forms non-uniform and thick water film which causes bridging and increased PRΔPa, A larger component level testing with HX size similar to commercial units allowed to identify constraints of different evaporative cooling methods, which would not be possible if tests were performed at a smaller segment or fin level. A novel spray cooling technology utilizing internal jet spray cooling within HX volume was both proposed and implemented and a provisional patent # 61/782,825 was obtained. Compared to front spray cooling at a given spray rate, internal spray cooling could either achieve up to 35% higher HX cooler capacity, or obtain same HX cooler capacity at approximately three times lower air-side pressure drop. Alternatively, at same air-side pressure drop wetting water savings of up to 68-97% are achieved. Internal spraying combines advantages of conventional technologies and overcomes the drawbacks, by getting CER of approx. 3.8, without film carryover and at PRΔPa=1, while getting maximum wetting uniformity. Intermittent cooling combined with internal spraying could reduce water consumption as evaporative cooling sustains though the brief period when spray is turned off. Thus, potential for significant energy and water savings, targeted cooling, and retrofit design offers significant commercialization opportunity for future hybrid evaporative coolers. Discussions are underway for the inclusion of this technology into product line up of a leading HX manufacturing company

Immediate placement of dental implants in non vascularised iliac graft after resection of anterior mandible : A case report

This case report presents a combination of surgical and prosthetic rehabilitation applied to a case in postsurgical reconstructed mandible. We report a patient suffering from desmoplastic ameloblastoma of mandible, who underwent Enbloc resection and reconstruction with iliac bone graft with simultaneous placement of dental implant in anterior mandible. Two dental implants were placed at both ends of the graft. At five years follow up, favourable osseointegration with healthy peri-implant tissue was reported

Visualization of Evaporatively Cooled Heat Exchanger Wetted Fin Area

At high ambient temperature, the air cooled HX capacity can be boosted by using evaporation of a water film applied directly on the heat exchanger surface in deluge, spray, or mist cooling mode. In order to accurately determine evaporatively cooled HX capacity, it is critical to know the portion of fin area wetted. However, wetting inherently is a highly non-uniform phenomenon dependent on the method of application, evaporation rate and air velocity. Furthermore, for typical optimized air cooled HXs the fin geometry is often complex and spacing narrow. This study presents a novel method to quantify HX wetted fin area through enhanced visualization in HX depth and sectional flow rate measurement. Flow maps for deluge and front spray cooling are presented at varying inlet air velocities and wetting water flow rates. This study confirms that a significant portion of HX remains dry which contributes to low experimentally obtained HX heat transfer rates, irrespective of wetting method even under moderate to high wetting water flow rates. Furthermore, it highlights the need for developing HX wetting technologies that ensure uniform wetting at lowest wetting flow rates

Amélioration de l'efficacité de turbines à gaz dans l'industrie gazière en utilisant des réfrigérateurs à absorption actionnés par de la chaleur résiduelle

Les climats chauds, accentués par le réchauffement climatique, réduisent l'efficacité énergétique des installations industrielles qui utilisent des turbines à gaz pour la production d'électricité, telles que les usines de transformation du gaz naturel (UTGNs). Un dispositif de récupération de la chaleur des gaz d'échappement de turbines par des réfrigérateurs d'absorption de bromure de lithium (H2O-LiBr) de simple effet, est thermo-économiquement évalué pour le refroidissement de l'air d'admission de turbines à gaz. La performance du système proposé, intégré dans une UTGN au Moyen-Orient, est comparée à celle des refroidisseurs évaporatifs conventionnels et des réfrigérateurs à compression de vapeur. Dans des conditions climatiques extrêmes représentant l'été dans le golfe Persique, trois réfrigérateurs d'absorption activés par la vapeur produite en récupérant 17 MW de chaleur d'échappement de turbines à gaz, pourraient fournir 12,3 MW de refroidissement et réduire la température d'admission de l'air à 10°C. Dans les mêmes conditions ambiantes, des refroidisseurs évaporatifs fourniraient une capacité de refroidissement de seulement 2,3 MW, et consommeraient 0,8 kg/s d'eau déminéralisée. Des réfrigérateurs à compression de vapeur exigeraient 2,7 MW d'énergie électrique supplémentaire pour fournir la même quantité de refroidissement que les réfrigérateurs d'absorption. L'électricité supplémentaire produite due au refroidissement d'air d'admission par réfrigération d'absorption est de 5264 MWh par an, comparé à 1774 MWh pour le refroidissement par évaporation. Le dispositif proposé permettrait non seulement de remplir les charges de refroidissement de l'air d'admission de turbine à gaz tout au long de l'année, mais fournirait également du refroidissement pour d'autre procédés de traitement du gaz naturel durant les périodes de charge hors pointe. La période d’amortissement économique du dispositif proposé varie de 1,3 à 3,4 ans sur la base des prix locaux actuels et futurs de l’eau et de l’électricité. La stratégie proposée réduirait la consommation de gaz naturel pour la production d'électricité dans les UTGNs au Moyen-Orient, permettant de réserver la production de gaz pour l’exportation, tout en réduisant les coûts de production et les émissions associées

Enhancement of Round Tube and Flat Tube-Louver Fin Heat Exchanger Performance Using Deluge Water Cooling

An experimental study has been conducted to evaluate the performance of a compact round-tube louver-fin condenser, each with frontal areas of 0.25 m2 in both dry and wet conditions. Deluge water cooling is achieved by incorporating a perforated bottom plate-type water distributor on top of the round tube heat exchanger. Water is used as a refrigerant, and enters the heat exchanger tubes at 35°C temperature. Ambient air and deluge cooling water are both maintained at 22°C temperature. Heat exchanger capacity and air-side pressure drop are measured with the heat exchanger angle set at 0° and 21° from vertical, with a frontal air velocity of 1.4 m/s and 3.5 m/s without deluge water cooling, and a frontal air velocity of 1.4 m/s with deluge water cooling. For both heat exchangers, the capacity was significantly enhanced with the use of deluge water cooling and with the heat exchanger angle set at 21° from vertical