Comparative study on the performance of natural draft dry, pre-cooled and wet cooling towers

He, Suoying; Gurgenci, Hal; Guan, Zhiqiang; Hooman, Kamel; Zou, Zheng; Sun, Fengzhong

doi:10.1016/j.applthermaleng.2016.01.060

Cited by 57 publications

(17 citation statements)

References 10 publications

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“…Mass of spray water taken away by the airflow per unit time is much smaller compared to the mass flow rate of spray water. Therefore, the mass flow rate of the spray water is constant [3], which means the reduction of the water flow rate by evaporation (generally 1%-3% of the water mass flow rate) is neglected in mass balance [6,16,28]. The spray water outlet temperature is equal to the spray water inlet temperature because the heat exchange between the circulating pipe and the surroundings is negligible.…”

Section: Assumptions and Simplificationsmentioning

confidence: 99%

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

Wei

Peng

et al. 2017

Energies

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Abstract:As one of the most widely used units in water cooling systems, the closed wet cooling towers (CWCTs) have two typical counter-flow constructions, in which the spray water flows from the top to the bottom, and the moist air and cooling water flow in the opposite direction vertically (parallel) or horizontally (cross), respectively. This study aims to present a simplified calculation method for conveniently and accurately analyzing the thermal performance of the two types of counter-flow CWCTs, viz. the parallel counter-flow CWCT (PCFCWCT) and the cross counter-flow CWCT (CCFCWCT). A simplified cooling capacity model that just includes two characteristic parameters is developed. The Levenberg-Marquardt method is employed to determine the model parameters by curve fitting of experimental data. Based on the proposed model, the predicted outlet temperatures of the process water are compared with the measurements of a PCFCWCT and a CCFCWCT, respectively, reported in the literature. The results indicate that the predicted values agree well with the experimental data in previous studies. The maximum absolute errors in predicting the process water outlet temperatures are 0.20 and 0.24 • C for the PCFCWCT and CCFCWCT, respectively. These results indicate that the simplified method is reliable for performance prediction of counter-flow CWCTs. Although the flow patterns of the two towers are different, the variation trends of thermal performance are similar to each other under various operating conditions. The inlet air wet-bulb temperature, inlet cooling water temperature, air flow rate, and cooling water flow rate are crucial for determining the cooling capacity of a counter-flow CWCT, while the cooling tower effectiveness is mainly determined by the flow rates of air and cooling water. Compared with the CCFCWCT, the PCFCWCT is much more applicable in a large-scale cooling water system, and the superiority would be amplified when the scale of water distribution system increases. Without multiple iterative calculations and extensive experimental data, the simplified method could be used to effectively analyze the thermal performance of counter-flow CWCTs in operation. It is useful for optimization operation of counter-flow CWCTs such that to improve the energy efficiency of the overall cooling water system.

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Section: Assumptions and Simplificationsmentioning

confidence: 99%

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

Wei

Peng

et al. 2017

Energies

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“…Habl et al [28] explored the differences of air and water as coolant for a 50 MW solar power plant located at the south of Spain and found that by using air the electricity cost increased by around 5%. He et al [29] compared three different methods to reject excess heat from a particular cooling tower located in Australia for temperatures up to 35°C: Natural dry-air draft, pre-cooled natural dry-air draft and natural wet-air draft. It was found that the natural wet-air draft approach was capable of rejecting up 3 times more heat than the dry-air approach, but at the expense of high usage of water.…”

Section: Introductionmentioning

confidence: 99%

Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region

Fuente

Larsen

Pierobon

et al. 2017

Energy

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As Arctic sea ice coverage declines it is expected that marine traffic could increase in this northern region due to shorter routes. Navigating in the Arctic offers opportunities and challenges for waste heat recovery systems (WHRS). Lower temperatures require larger heating power on board, hence a larger demand for waste heat usage, to cover services and maintaining on board spaces temperatures. However, a lower heat rejection temperature increases the WHRS thermal efficiency. The air temperature for the Arctic route selected is colder than that of the seawater, opening the opportunity of having air as coolant. This paper explores the use of two different coolants, air and seawater, for an organic Rankine cycle (ORC) unit using the available waste heat in the scavenge air system of a container ship navigating in Arctic Circle. Using a two-step single objective optimisation process, detailed models of air and seawater heat exchangers are evaluated as the WHRS condensers. The results suggest that an ORC unit using R1233zd(E) as its working fluid coupled with seawater as its coolant is the preferable option to reduce CO 2 emissions. Using the ambient air as the coolant while a less effective option could be cheaper to install.

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“…The heat and mass transfer in the pre-cooled NDDCT is coupled with air flow through the tower while the air flow is determined by balancing the energy and draft equations through an iterative process [6]. The fixed variables during iteration are tower specifications and heat exchanger specifications, hot water flow rate, hot water inlet temperature, medium thickness and ambient humidity.…”

Section: Iterative Algorithmmentioning

confidence: 99%

“…Previous studies find that the performance of NDDCTs can be improved by wetted-medium evaporative pre-cooling when the ambient air is hot and dry [6][7][8]. The concept of wetted-medium pre-cooling of a NDDCT is illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…According to He et al [6], the pre-cooling benefit is however season dependent and the pre-cooling enhancement can go up to 46% (where the pre-cooling enhancement is defined as η enhancement =(Q pre-NDDCT -Q NDDCT )/Q NDDCT ×100%, Q is the tower heat rejection rate). What significantly affects the pre-cooling performance is the wetted medium.…”

Section: Introductionmentioning

confidence: 99%

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Selection of wetted media for pre-cooling of air entering natural draft dry cooling towers

Zhang

et al. 2017

Applied Thermal Engineering

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HighlightsFour wetted media were comparatively studied for future pre-cooling design.Characteristics of wetted media suitable for pre-cooling were summarized.Media with middle efficiencies and pressure drops are superior for pre-cooling.Cellulose7060 is most promising for pre-cooling the 120m-high NDDCT. AbstractThe performance of natural draft dry cooling towers (NDDCTs) can be improved by wetted-medium evaporative pre-cooling. However, the pre-cooling benefit is season dependent and is significantly affected by wetted media. To further investigate the effect of wetted medium type on pre-cooling performance, the current study simulates a pre-cooled NDDCT using two typical types of wetted media, i.e., film (Cellulose7060 and PVC1200) and trickle (Trickle125 and Trickle100). A MATLAB program was developed and was validated against published data. The model was then used to carry out case study of a 120m-high NDDCT pre-cooled using the selected wetted media with fixed thickness of 300mm. Both the medium performance and pre-cooled NDDCT performance were compared to recommend the characteristics of wetted media promising for evaporative pre-cooling. Simulation finds that the media with high or low cooling efficiencies and pressure drops are not promising for the studied pre-cooling case while those media with middle cooling efficiencies and pressure drops intend to produce much performance enhancement and Cellulose7060 is a representative of such kind of medium. For the 120m-high NDDCT, the wetted-medium pre-cooling can raise the heat rejection rate of the tower without pre-cooling from 45MW to 92 MW, 76 MW, 68 MW and 65MW by Cellulose7060, PVC1200, Trickle125 and Trickle100, respectively at ambient temperature of 50℃ and humidity of 20%.

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Comparative study on the performance of natural draft dry, pre-cooled and wet cooling towers

Cited by 57 publications

References 10 publications

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

Performance Analyses of Counter-Flow Closed Wet Cooling Towers Based on a Simplified Calculation Method

Selection of cooling fluid for an organic Rankine cycle unit recovering heat on a container ship sailing in the Arctic region

Selection of wetted media for pre-cooling of air entering natural draft dry cooling towers

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