Development of Falling Film Heat Transfer Coefficient for Industrial Chemical Processes Evaporator Design

Muhammad Wakil Shahzad, Muhammad Burhan and Kim Choon Ng

A chapter in Statistical Approaches With Emphasis on Design of Experiments Applied to Chemical Processes from IntechOpen

Abstract: In falling film evaporators, the overall heat transfer coefficient is controlled by film thickness, velocity, liquid properties and the temperature differential across the film layer. This chapter presents the heat transfer behaviour for evaporative film boiling on horizontal tubes, but working at low pressures of 0.93-3.60 kPa as well as seawater salinity of 15,000-90,000 mg/l or ppm. Owing to a dearth of literature on film-boiling at these conditions, the chapter is motivated by the importance of evaporative film-boiling in the process industries. It is observed that in addition to the above-mentioned parameters, evaporative heat transfer of seawater is affected by the emergence of micro-bubbles within the thin film layer, particularly when the liquid saturation temperatures drop below 25°C (3.1 kPa). Such micro-bubbles are generated near to the tube wall surfaces, and they enhanced the heat transfer by two or more folds when compared with the predictions of conventional evaporative film-boiling. The appearance of micro-bubbles is attributed to the rapid increase in the specific volume of vapour, i.e. dv/dT, at low saturation temperature conditions. A new correlation is thus proposed in this chapter and it shows good agreement to the measured data with an experimental uncertainty less than ±8%.

Keywords: low pressure evaporation; falling film evaporation; horizontal tubes evaporators (search for similar items in EconPapers)
JEL-codes: C60 (search for similar items in EconPapers)
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Persistent link: https://EconPapers.repec.org/RePEc:ito:pchaps:114771

DOI: 10.5772/intechopen.69299

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