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Effect of the surface texture on the heat transfer coefficient in nucleate boiling of aqueous lithium bromide solution at low heat fluxes
Possible types of generators of absorption chillers are flooded pool generators. The advantages of pool generators compared to tube bundle falling-film heat exchangers appear if nucleate boiling is achieved. This demands an excess temperature of ≥14 K (25°F) between the heated wall and fluid, which limits the amount of the typical applications. One possibility to reduce the excess temperature is a mechanical or a coated treatment of the heat exchanger surface. Within this work, experiments to investigate the influence of surface properties and pressure have been carried out to achieve a greater understanding because only limited data in the literature can be found dealing with these aspects. It could be shown that the surface structure has an important impact on the sorbent-side heat transfer coefficient. With a simple treatment of the surface, a reduction of the excess temperature, and hence an increase of the heat transfer coefficient by around 20% at a pressure of 70 mbar (1.0 psi), could be achieved. Furthermore, the empiric coefficients of the equation for nucleate boiling of an aqueous lithium bromide solution under sub-atmospheric pressure have been determined.
Effect of the surface texture on the heat transfer coefficient in nucleate boiling of aqueous lithium bromide solution at low heat fluxes
Possible types of generators of absorption chillers are flooded pool generators. The advantages of pool generators compared to tube bundle falling-film heat exchangers appear if nucleate boiling is achieved. This demands an excess temperature of ≥14 K (25°F) between the heated wall and fluid, which limits the amount of the typical applications. One possibility to reduce the excess temperature is a mechanical or a coated treatment of the heat exchanger surface. Within this work, experiments to investigate the influence of surface properties and pressure have been carried out to achieve a greater understanding because only limited data in the literature can be found dealing with these aspects. It could be shown that the surface structure has an important impact on the sorbent-side heat transfer coefficient. With a simple treatment of the surface, a reduction of the excess temperature, and hence an increase of the heat transfer coefficient by around 20% at a pressure of 70 mbar (1.0 psi), could be achieved. Furthermore, the empiric coefficients of the equation for nucleate boiling of an aqueous lithium bromide solution under sub-atmospheric pressure have been determined.
Effect of the surface texture on the heat transfer coefficient in nucleate boiling of aqueous lithium bromide solution at low heat fluxes
Menhart, Florian (author) / Riepl, Manuel (author) / Natzer, Stefan (author)
Science and Technology for the Built Environment ; 21 ; 258-266
2015-04-03
9 pages
Article (Journal)
Electronic Resource
English
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