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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

EXPERIMENTAL STUDY OF HEAT TRANSFER AND PRESSURE DROP IN A MULTISTRING BASED DIRECT CONTACT HEAT EXCHANGER

Get access (open in a dialog) DOI: 10.1615/IHTC16.nee.022112
pages 7541-7548

Abstract

Evaporative cooling in thermoelectric power plants is a single largest source of fresh water consumption. This has motivated intense research and development efforts on dry cooling solutions. Existing air cooled condensers, however, have found rather limited commercial success due in part to their high capital costs and large foot weights. One intriguing alternative is indirect cooling of steam using a novel direct-contact heat exchanger. The new heat exchanger consists of an array of low-cost and light-weight polymer strings. A nonvolatile liquid coolant flows down the strings and is cooled by a counterflowing air stream before returning to the steam condenser. We constructed a 1.6 m-tall prototype heat exchanger with as many as 112 strings to examine its heat transfer performance and associated air pressure drop. Spatial temperature distributions along the heat exchanger and gas-phase pressure drop are obtained under different combinations of the liquid flow rate, air velocity, and string pitch. A numerical model is also constructed to help interpret and validate our experimental results. We demonstrate that the local heat transfer effectiveness is governed primarily by the ratio of the liquid and air-side heat capacity rates and the gas-phase pressure drop by the air velocity and string pitch. When compared with structured packing consisting of parallel plates, the new string-based heat exchanger offers an approximately 1.5 times lower gas-phase pressure drop for the same heat exchanger effectiveness. The present work helps develop a foundation for systematical design and optimization of multi-string heat exchangers.