Glenn Dale, MD, United States
Glenn Dale, MD, United States

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Popli S.,Center for Environmental Energy Engineering | Popli S.,University of Maryland University College | Hwang Y.,Center for Environmental Energy Engineering | Hwang Y.,University of Maryland University College | And 2 more authors.
ASHRAE Transactions | Year: 2014

An experimental study has been conducted to evaluate the performance of three herringbone wavy-fin round tube heat exchangers (HX) working as fluid coolers in both dry and wet conditions. The effect of fin spacing and hydrophilic coating was investigated by measuring heat transfer rate and air-side pressure drop with the HX angle set at approximately 20°from vertical, which is similar to half section of a typical commercial V-shaped coil. Deluge cooling increased both HX capacity and air-side pressure drop by a factor of up to 2.78 and 2.28 respectively. Furthermore, deluge cooling achieved 2%-30% higher capacity for HXs with fin spacing 2.4 mm (0.09 in.) compared to the coil with 3 mm (0.118 in.) finspacing. Also, a hydrophilic coated HX improves HX capacity by 5%-30%, compared to a similar coil without coating. Future studies would aim at obtaining higher capacity enhancement ratios with no increase in fan power consumption. © 2014 ASHRAE.


Singh V.,Sefaira Inc. | Aute V.,Center for Environmental Energy Engineering | Radermacher R.,University of Maryland College Park
HVAC and R Research | Year: 2010

In fin-and-tube heat exchangers operating at large temperature differences (such as carbon dioxide gas coolers), the heat transfer due to fin conduction between neighboring tubes degrades the heat exchanger performance. In this paper, a validated segment-by-segment heat exchanger model capable of accounting for tube-to-tube conduction in two dimensions, as well as simulating continuous and discontinuous cut fins has been employed to study the effect of cut fins on heat exchanger performance. The effect of two separate configurations of cut fins on heat exchanger performance was studied for 36 test cases, and a heat load gain of up to 12% was shown with cut fins. Additionally, for a target heat load, fin material savings of up to 40% were shown. Further, gains of up to 20% in the inlet quality of an evaporator were shown, considering a 7.2° evaporating temperature and isenthalpic expansion. Finally, by placing constraints on the length of cuts and maximizing heat load, guidelines for location of cut fins were established. © 2010 American Society of Heating.


Al-Alili A.,The Petroleum Institute | Hwang Y.,Center for Environmental Energy Engineering | Radermacher R.,Center for Environmental Energy Engineering
Energy | Year: 2015

Removal of moisture from the air represents a considerable portion of the air conditioning load in hot and humid regions. It is a common practice to run air conditioning systems at temperatures lower than the moist air dew point temperature in order to accomplish dehumidification. Desiccant air conditioners offer a solution to meet the humidity and temperature requirements of buildings via decoupling latent and sensible loads. In this work, the performance of a new desiccant material is investigated experimentally. This desiccant material has a unique S-shape isotherm and can be regenerated using a low temperature heat source. The effects of the process air stream's temperature and humidity, the regeneration temperature, the ventilation mass flow rate, and the desiccant wheel's rotational speed on the cycle performance are investigated. ARI-humid conditions are used as a baseline. The moisture mass balance is maintained within 5% for all conducted tests. The results are presented in terms of the moisture removal rate and latent COPlat (coefficient of performance). The results show a desiccant wheel's COPlat higher than unity when it is coupled with an enthalpy wheel. © 2014 Elsevier Ltd. All rights reserved.


Al-Alili A.,The Petroleum Institute | Hwang Y.,Center for Environmental Energy Engineering | Radermacher R.,Center for Environmental Energy Engineering
International Journal of Refrigeration | Year: 2014

The removal of moisture from the supply air using conventional air conditioners (A/C) represents a considerable portion of the air conditioning load in hot and humid regions. Desiccant assisted A/Cs are used to address this issue. In this work, the performance of a hybrid A/C, which consists of a desiccant wheel, an enthalpy wheel, and a vapor compression cycle (VCC), is investigated experimentally. The effect of the process air stream's temperature and humidity, and the effect of the ventilation rate on the hybrid A/C performance are investigated. The experimental results show that the hybrid A/C is more effective than the standalone VCC in maintaining the indoor conditions within the comfort zone. The simulation of the complete hybrid solar A/C that uses a concentrating photovoltaic/thermal collector shows that a system coefficient of performance higher than unity is possible. © 2013 Elsevier Ltd and IIR. All rights reserved.

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