Creating a New Model to Predict Cooling Tower Performance and Determining Energy Saving Opportunities Through Economizer Operation

Download Creating a New Model to Predict Cooling Tower Performance and Determining Energy Saving Opportunities Through Economizer Operation PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (93 download)

DOWNLOAD NOW!


Book Synopsis Creating a New Model to Predict Cooling Tower Performance and Determining Energy Saving Opportunities Through Economizer Operation by : Pranav Yedatore Venkatesh

Download or read book Creating a New Model to Predict Cooling Tower Performance and Determining Energy Saving Opportunities Through Economizer Operation written by Pranav Yedatore Venkatesh and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooling towers form an important part of chilled water systems and perform the function of rejecting the heat to the atmosphere. These systems are often not operated optimally, and cooling towers being an integral part of the system present a significant area to study and determine possible energy saving measures. Operation of cooling towers in economizer mode in winter and variable frequency drives (VFDs) on cooling tower fans are measures that can provide considerable energy savings. The chilled water system analysis tool (CWSAT) software is developed as a primary screening tool for energy evaluation for chilled water systems and quantifies the energy usage of the various components and typical measures that can be applied to these systems to conserve energy, all while requiring minimum number of inputs to analyze component-wise energy consumption and incurred overall cost. A careful investigation of the current model in CWSAT indicates that the prediction capability of the model at lower wet bulb temperatures and at low fan power is not very accurate. A new model for accurate tower performance prediction is imperative, since economizer operation occurs at low temperatures and most cooling towers come equipped with VFDs. In this thesis, a new model to predict cooling tower performance is created to give a more accurate prediction of energy savings for a tower. Further the economic feasibility of having additional cooling tower capacity to allow for economizer cooling, in light of reduced tower capacity at lower temperatures is investigated.

Energy Performance Estimation of Cooling Towers

Download Energy Performance Estimation of Cooling Towers PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 60 pages
Book Rating : 4.:/5 (974 download)

DOWNLOAD NOW!


Book Synopsis Energy Performance Estimation of Cooling Towers by : Zilai Zhao

Download or read book Energy Performance Estimation of Cooling Towers written by Zilai Zhao and published by . This book was released on 2016 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this project is to investigate and compare the performance of cooling towers using Effectiveness-NTU model and the empirical model of cooling towers. The process of achieving the goals includes: Developed both models of the cooling tower using the Effectiveness-NTU method, and empirical method for predicting the performance at the design and off-design conditions; Stated experimental protocols and gathered data on HVAC cooling towers on campus of the University of Alabama; Used collected data to validate the models; Compared results from models with real measurements and find the limitations of models; Applied known annual weather data to estimate the performance and energy consumption of cooling tower for a whole year; Recommended the approach for the best energy and heat performance of cooling towers. As a result, the Effectiveness-NTU model provided closer results than the empirical model. All data and specifications were measured and gathered from the experiment on the cooling tower on campus. However, the air mass flow rate and the temperature of the leaving air were not always possible to gather in different cooling towers, especially industry cooling towers. Therefore, both models were designed to predict mass flow rate, and temperature of the leaving air by applying air temperature and relative humidity. Further testing is required to validate the accuracy of the models because there was a limited control over the running status of fans and the experiments were not done in wintertime with lower entering air temperature. Validation of the models on another cooling tower is also essential. Additionally, the empirical model can be improved if there is a way to reset all 27 coefficients based on different cooling towers.

HVAC Water Chillers and Cooling Towers

Download HVAC Water Chillers and Cooling Towers PDF Online Free

Author :
Publisher : CRC Press
ISBN 13 : 0824748468
Total Pages : 308 pages
Book Rating : 4.8/5 (247 download)

DOWNLOAD NOW!


Book Synopsis HVAC Water Chillers and Cooling Towers by : Herbert W. Stanford III

Download or read book HVAC Water Chillers and Cooling Towers written by Herbert W. Stanford III and published by CRC Press. This book was released on 2003-04-04 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: HVAC Water Chillers and Cooling Towers provides fundamental principles and practical techniques for the design, application, purchase, operation, and maintenance of water chillers and cooling towers. Written by a leading expert in the field, the book analyzes topics such as piping, water treatment, noise control, electrical service, and energy efficiency for optimal system and equipment performance and offers extensive checklists, troubleshooting strategies, and reference data, as well as recommended specifications for the procurement of new or replacement equipment. This reference also discusses proper installation and placement of chillers and cooling towers, start-up, and capacity.

Cooling Towers

Download Cooling Towers PDF Online Free

Author :
Publisher : Charles Nehme
ISBN 13 :
Total Pages : 26 pages
Book Rating : 4./5 ( download)

DOWNLOAD NOW!


Book Synopsis Cooling Towers by : Charles Nehme

Download or read book Cooling Towers written by Charles Nehme and published by Charles Nehme. This book was released on 2023-05-19 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Welcome to the captivating world of cooling towers, where the delicate dance between heat and temperature regulation takes center stage. Cooling towers have long been an unsung hero of various industries, quietly ensuring the smooth functioning of processes and systems that rely on efficient thermal management. Whether you are an engineer, a student, or simply someone intrigued by the inner workings of these towering structures, this book aims to provide an in-depth exploration of cooling towers and their pivotal role in our modern world. In an era marked by rapid technological advancements and the relentless pursuit of progress, the effective management of heat has become an indispensable aspect of numerous industrial operations. Cooling towers have emerged as essential tools in this endeavor, finding their place in power plants, manufacturing facilities, data centers, and countless other domains. These towering giants stand tall, resolutely undertaking the task of dissipating excess heat and maintaining optimal temperatures, thereby ensuring the smooth functioning of critical equipment. The purpose of this book is to unravel the mysteries surrounding cooling towers and offer a comprehensive understanding of their design principles, operational intricacies, and the multitude of applications they serve. Through the following chapters, we will delve into the different types of cooling towers, their underlying components, and the diverse heat transfer mechanisms that drive their operation. We will explore the fundamental principles of thermodynamics and fluid dynamics that govern their performance, and examine the factors influencing their efficiency and environmental impact. While this book strives to present a holistic overview of cooling towers, it is important to acknowledge that the field of thermal management is a dynamic and ever-evolving discipline. Advancements in technology, emerging environmental concerns, and shifting regulatory landscapes continue to shape the industry, prompting engineers and researchers to push the boundaries of efficiency, sustainability, and innovation. Thus, it is crucial to approach this subject with an open mind, recognizing that the knowledge shared here is just a snapshot in the ongoing journey of discovery. As we embark on this exploration of cooling towers, let us celebrate the spirit of ingenuity that has led to their creation and evolution. Let us marvel at the intricate designs and engineering prowess that enable these structures to operate efficiently, effectively, and often silently in the background. May this book serve as a guiding light, illuminating the fascinating world of cooling towers and inspiring further curiosity and innovation in the pursuit of optimal thermal management. I extend my deepest gratitude to the experts, engineers, and researchers whose tireless efforts have contributed to the knowledge and advancements in the field of cooling towers. Their dedication and expertise have laid the foundation for this book, and their collective wisdom continues to shape the future of thermal management. Lastly, I would like to express my appreciation to you, the reader, for embarking on this intellectual journey. I hope that this book serves as a valuable resource, igniting your passion for understanding cooling towers and empowering you to contribute to the fascinating realm of thermal management. Together, let us delve into the captivating world of cooling towers and unlock the secrets held within their towering structures.

Cooling Tower Fan Control for Energy Efficiency

Download Cooling Tower Fan Control for Energy Efficiency PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (656 download)

DOWNLOAD NOW!


Book Synopsis Cooling Tower Fan Control for Energy Efficiency by :

Download or read book Cooling Tower Fan Control for Energy Efficiency written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis evaluates the economics of alternative cooling tower capacity control methods. Annual fan electrical energy requirements are calculated for towers with single-speed, two-speed, and variable-speed fans. Fan energy requirements are determined for counter-flow and cross-flow towers designed for low initial cost and for energy efficiency. Effectiveness-NTU equations are solved to predict cooling tower performance at various fan speeds. Natural convection, which determines the cooling capacity when the fan is off, is accounted for using a mean enthalpy difference. Ambient conditions are simulated using typical meteorological year data for five locations. The results show that potential savings are not strongly dependent on the approach temperature, but do increase with increasing range in colder climates. The potential for saving is greatest for cooling towers designed for low initial cost, and is generally higher in locations where the wet-bulb temperature remains relatively constant throughout the year. Two-speed fans that can operate at half speed are generally more suitable for low-cost cooling towers. Two-speed fans that can operate at two-third speed are better for towers designed for energy efficiency and are generally better when the range exceeds 10 F.

Cooling Energy Solutions For Buildings And Cities

Download Cooling Energy Solutions For Buildings And Cities PDF Online Free

Author :
Publisher : World Scientific
ISBN 13 : 9813236981
Total Pages : 421 pages
Book Rating : 4.8/5 (132 download)

DOWNLOAD NOW!


Book Synopsis Cooling Energy Solutions For Buildings And Cities by : Mat Santamouris

Download or read book Cooling Energy Solutions For Buildings And Cities written by Mat Santamouris and published by World Scientific. This book was released on 2019-02-12 with total page 421 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the first book of its kind, this volume addresses the problem of the future cooling energy demand, the global frame defining the actual and future cooling energy consumption in the building sector. Based on the explored inputs and forecasts, a model was developed to predict the future cooling energy consumption of both the residential and commercial sector. Low energy, high-performance technological solutions for cooling energy problem in the building and city level will be presented.

Learn the ABC of Cooling Towers

Download Learn the ABC of Cooling Towers PDF Online Free

Author :
Publisher : CreateSpace
ISBN 13 : 9781505277654
Total Pages : 90 pages
Book Rating : 4.2/5 (776 download)

DOWNLOAD NOW!


Book Synopsis Learn the ABC of Cooling Towers by : A. Bhatia

Download or read book Learn the ABC of Cooling Towers written by A. Bhatia and published by CreateSpace. This book was released on 2014-11-30 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: The machines and processes of industry, as well as the air-conditioning systems for buildings generate tremendous amounts of heat, which must be continuously, dissipated if these machines and processes are to continue to operate efficiency. Water cooling is the most efficient method of dissipating heat. A cooling tower is a device used in industry to cool hot water (by partial evaporation) before reusing it as a coolant. Water directly contacts surrounding air and a very small part (1-2%) evaporate. This evaporation increases the air temperature and humidity and decreases the temperature of the water making it possible to cool below the normal air temperature. Although this heat is usually transferred to a cool, flowing volume of water, final rejection is always to the atmosphere and, invariably, is accomplished by some form of heat exchanger. The amount of cooling that you get from a cooling tower depends on the relative humidity of the air and the barometric pressure. For example, the more humid the climate the lesser will be the temperature drop and vice versa. This 6 hours Quick Book provides comprehensive information on cooling water systems and describes different types of cooling towers, their mechanical components and the problems associated with cooling water. The student must take a multiple-choice quiz consisting of thirty five (35) questions at the end of this course to obtain PDH credits. Learning Objective At the conclusion of this course, the reader will: 1)Learn different types of heat rejection systems 2)Learn the operational theory and principles of evaporative cooling tower 3)Describe the factors affecting the performance of cooling tower 4)Learn the various materials used in construction of cooling tower 5)Understand the functions of various components of cooling tower 6)Describe various control options 7)Understand the layout and installation considerations 8)Understand the water distribution mechanisms, noise and vibration issues 9)Understand the cooling tower water balance 10)Learn the importance of cooling water treatment 11)Describe the cooling tower testing requirements, various codes and standards 12)Learn by examples the equations to calculate the evaporation rate, fresh water make up and blowdown requirements

Cooling Towers

Download Cooling Towers PDF Online Free

Author :
Publisher : Butterworth-Heinemann
ISBN 13 : 1483162745
Total Pages : 207 pages
Book Rating : 4.4/5 (831 download)

DOWNLOAD NOW!


Book Synopsis Cooling Towers by : G. B. Hill

Download or read book Cooling Towers written by G. B. Hill and published by Butterworth-Heinemann. This book was released on 2013-10-22 with total page 207 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooling Towers: Principles and Practice, Third Edition, aims to provide the reader with a better understanding of the theory and practice, so that installations are correctly designed and operated. As with all branches of engineering, new technology calls for a level of technical knowledge which becomes progressively higher; this new edition seeks to ensure that the principles and practice of cooling towers are set against a background of up-to-date technology. The book is organized into three sections. Section A on cooling tower practice covers topics such as the design and operation of cooling towers; types of cooling tower; cooling tower components and construction materials; practical aspects of tower selection; industrial applications; and water quality and treatment. Section B is devoted to cooling tower theory and calculations. These include psychrometry; heat transfer theory and calculations; calculations when selecting tower size for a given duty; and the use of charts for calculation of cooling tower duties. Section C on data and tables explains the basis of the SI system of units and includes meteorological tables and data as well as data on specific heat capacity of some common substances.

A Method for Predicting the Performance of Natural Draft Cooling Towers

Download A Method for Predicting the Performance of Natural Draft Cooling Towers PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 94 pages
Book Rating : 4.3/5 (91 download)

DOWNLOAD NOW!


Book Synopsis A Method for Predicting the Performance of Natural Draft Cooling Towers by : Pacific Northwest Water Laboratory

Download or read book A Method for Predicting the Performance of Natural Draft Cooling Towers written by Pacific Northwest Water Laboratory and published by . This book was released on 1970 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Advanced Wet-dry Cooling Tower Concept Performance Prediction

Download Advanced Wet-dry Cooling Tower Concept Performance Prediction PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (699 download)

DOWNLOAD NOW!


Book Synopsis Advanced Wet-dry Cooling Tower Concept Performance Prediction by : Troxell Kimmel Snyder

Download or read book Advanced Wet-dry Cooling Tower Concept Performance Prediction written by Troxell Kimmel Snyder and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this years' work has been to test and analyze the new dry cooling tower surface previously developed. The model heat transfer test apparatus built last year has been instrumented for temperature, humidity and flow measurement and performance has been measured under a variety of operating conditions. Tower Tests showed approximately 40-50% of the total energy transfer as taking place due to evaporation. This can be compared to approximately 80 to 85% for a conventional wet cooling tower. Comparison of the model tower test results with those of a computer simulation has demonstrated the validity of that simulation and its use as a design tool. Computer predictions have been made for a full-size tower system operating at several locations. Experience with this counterflow model tower has suggested that several design problems may be avoided by blowing the cooling air horizontally through the packing section. This cross flow concept was built from the previous counterflow apparatus and included the design and fabrication of new packing plates. Instrumentation and testing of the counterflow model produced data with an average experimental error of 10%. These results were compared to the predictions of a computer model written for the cross flow configuration. In 14 test runs the predicted total heat transfer differed from the measured total heat transfer by no more than 8% with most runs coming well within 5%. With the computer analogy's validity established, it may now be used to help predict the performance of full scale wet-dry towers.

Performance Evaluation of the Braintree Electric Light Department Dry Cooling Tower

Download Performance Evaluation of the Braintree Electric Light Department Dry Cooling Tower PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 12 pages
Book Rating : 4.:/5 (2 download)

DOWNLOAD NOW!


Book Synopsis Performance Evaluation of the Braintree Electric Light Department Dry Cooling Tower by : M. D. Henderson

Download or read book Performance Evaluation of the Braintree Electric Light Department Dry Cooling Tower written by M. D. Henderson and published by . This book was released on 1981 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Advances in the Application of Passive Down-draft Evaporative Cooling Technology in the Cooling of Buildings

Download Advances in the Application of Passive Down-draft Evaporative Cooling Technology in the Cooling of Buildings PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (774 download)

DOWNLOAD NOW!


Book Synopsis Advances in the Application of Passive Down-draft Evaporative Cooling Technology in the Cooling of Buildings by : Daeho Kang

Download or read book Advances in the Application of Passive Down-draft Evaporative Cooling Technology in the Cooling of Buildings written by Daeho Kang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A passive down-draft evaporative cooling (PDEC) tower is a component that is designed to capture the wind at the top of a tower and cool the outdoor air using water evaporation. While several different types of this particular system exist, PDEC tower with spray was studied in that it is flexible, efficient, and prevalent. Sustainable feasibility has been known as the main benefit of PDEC towers, leading to significant energy savings, improvement of indoor environmental quality, and reduction of environmental cost. In contrast, PDEC towers have not been considered in some circumstances as an alternative to conventional air conditioning systems due to strong climatic dependency, insufficient cooling capacity, and huge water consumption when they could be successfully integrated. In addition, suitable methods that can resolve problems associated with PDEC towers and improve the performance of this particular system have not been presented in the literature. This study was thus designed to present the solutions that overcome these problems with PDEC towers so that they can be widely used in many types of buildings and climatic regions. Computational process modeling was carried out to understand fundamentals of down-draft evaporative cooling processes. This study developed a computational model using a commercial CFD code FLUENT, and this model was validated against experimental data. The model then explained physical phenomena occurring within the effective area of PDEC towers, so that conditions of the air were accurately predicted in different weather conditions as well as PDEC tower conditions. In addition, parametric study with this computational model defined critical factors that significantly impact the cooling performance of PDEC towers, and the importance of various factors. As a result, a practical design guide to droplet size and tower height was presented, which is applicable to most circumstances where PDEC towers could be integrated. Regression analysis using general-purpose statistical software Minitab was then followed to formulate mathematical models that provide accurate conditions of PDEC air flows. Two dependent variables, temperature and velocity, were considered. An individual sample was created by the computational model developed in this study. Correlation analysis determined independent variables that have significant relations with each dependent variable. A preliminary sampling process collected reasonable numbers of samples dealing with wide ranges of weather conditions and PDEC tower conditions. Additional samples were added using forward sampling methods so that minimum number of samples, which explain certain relations between dependent and independent variables at the lowest cost, can be appropriately determined. As a result, linear relations between dependent and independent variables were found and mathematical forms of regression equations obtained was presented. Dynamic simulations, using a whole building energy simulation program EnergyPlus, employing new mathematical models developed in this study were performed to investigate actual impacts of PDEC towers in various situations. A short-term simulation analysis demonstrated problems with current PDEC towers operation, as well as impacts to indoor thermal environment. Various alternatives to typical PDEC towers operation were analyzed, so that water flow control in conjunction with primary cooling system was determined as a reliable solution that overcomes those problems defined in this study. In addition, energy performance and various impacts to indoor thermal environment were analyzed in a long-term simulation. Consequently, PDEC towers are considered as a feasible component in various types of buildings and climates. The findings using the methods in this study demonstrate that typical PDEC towers are inefficient in energy performance and indoor thermal environment. The cooling performance of PDEC towers should thus be properly controlled to be an energy-efficient system. In addition, PDEC towers can be considered as a secondary cooling system that meets a portion of cooling loads in a space in order to accomplish low-energy goals as well as a comfortable indoor thermal environment. Furthermore, the performance of PDEC towers is strongly dependent on each critical parameter described in this study. Efforts should thus be made to find the most efficient design conditions for main parameters corresponding to the local environment. Moreover, PDEC towers are viable in various climates rather than a hot-dry climate, achieving almost the same level of energy savings with lower water consumption.

Cooling Tower Technology

Download Cooling Tower Technology PDF Online Free

Author :
Publisher : Prentice Hall
ISBN 13 : 9780133496482
Total Pages : 281 pages
Book Rating : 4.4/5 (964 download)

DOWNLOAD NOW!


Book Synopsis Cooling Tower Technology by : Robert Burger

Download or read book Cooling Tower Technology written by Robert Burger and published by Prentice Hall. This book was released on 1995 with total page 281 pages. Available in PDF, EPUB and Kindle. Book excerpt: This information-packed manual provides a compendium of successful, readily applicable techniques which you can utilize to improve the performance of any cooling tower. Authored by noted authority Robert Burger, this practical handbook covers internal elements of towers and shows you procedures for upgrading them for both energy savings and enhanced profitability of operations. This A to Z answer book covers design conditions, the relationship between CWT and WBT and the need for testing and inspection. You will learn specific methodologies to improve performance, produce colder water, and circulate a greater volume of water in the same tower. Topics include thermal performance, water distribution, water treatment, maintenance, inspection, drift elimination, and operating concepts. This reference has been updated to include an important chapter on wet bulb temperature.

Simplified Models for Assessing Heat and Mass Transfer in Evaporative Towers

Download Simplified Models for Assessing Heat and Mass Transfer in Evaporative Towers PDF Online Free

Author :
Publisher : Morgan & Claypool Publishers
ISBN 13 : 1627051929
Total Pages : 126 pages
Book Rating : 4.6/5 (27 download)

DOWNLOAD NOW!


Book Synopsis Simplified Models for Assessing Heat and Mass Transfer in Evaporative Towers by : Giulio Lorenzini

Download or read book Simplified Models for Assessing Heat and Mass Transfer in Evaporative Towers written by Giulio Lorenzini and published by Morgan & Claypool Publishers. This book was released on 2013-07-01 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this book is to supply valid and reasonable parameters in order to guide the choice of the right model of industrial evaporative tower according to operating conditions which vary depending on the particular industrial context: power plants, chemical plants, food processing plants and other industrial facilities are characterized by specific assets and requirements that have to be satisfied. Evaporative cooling is increasingly employed each time a significant water flow at a temperature which does not greatly differ from ambient temperature is needed for removing a remarkable heat load; its aim is to refrigerate a water flow through the partial evaporation of the same.

Cooling Towers

Download Cooling Towers PDF Online Free

Author :
Publisher : Butterworth-Heinemann
ISBN 13 :
Total Pages : 368 pages
Book Rating : 4.3/5 (91 download)

DOWNLOAD NOW!


Book Synopsis Cooling Towers by : Nicholas P. Cheremisinoff

Download or read book Cooling Towers written by Nicholas P. Cheremisinoff and published by Butterworth-Heinemann. This book was released on 1981 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Energy Efficiency Analysis and Modeling of a Multiple-chiller Plant for Process Industries

Download Energy Efficiency Analysis and Modeling of a Multiple-chiller Plant for Process Industries PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 622 pages
Book Rating : 4.:/5 (32 download)

DOWNLOAD NOW!


Book Synopsis Energy Efficiency Analysis and Modeling of a Multiple-chiller Plant for Process Industries by : Chinh Van Le

Download or read book Energy Efficiency Analysis and Modeling of a Multiple-chiller Plant for Process Industries written by Chinh Van Le and published by . This book was released on 2008 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Cooling Tower Environment--1974

Download Cooling Tower Environment--1974 PDF Online Free

Author :
Publisher :
ISBN 13 :
Total Pages : 660 pages
Book Rating : 4.:/5 (318 download)

DOWNLOAD NOW!


Book Synopsis Cooling Tower Environment--1974 by : Steven R. Hanna

Download or read book Cooling Tower Environment--1974 written by Steven R. Hanna and published by . This book was released on 1975 with total page 660 pages. Available in PDF, EPUB and Kindle. Book excerpt: