Tube Bundle Evaporators with LGWP Refrigerant R1234ze(E)

AbstractWith new low-GWP HFO refrigerants, the heat transfer performances and methods for decreasing system refrigerant inventory are receiving increasing interest. In shell-and-tube heat exchangers, refrigerant distribution via pressurized liquid spray has the potential for high heat transfer performance while reducing refrigerant charge. However, no published studies have investigated LGWP refrigerants with spray evaporation on tube bundles. A test apparatus was constructed to measure the shell-side heat transfer coefficients of R1234ze(E) on bundles of tubes with two different enhanced-surface types and in two different bundle geometries at various refrigerant saturation temperatures. The results showed strong dependence on refrigerant properties, tube heat flux, enhanced-surface type, bundle geometry, and refrigerant inlet subcooling. The bundle heat transfer coefficients of R1234ze(E) were similar to that of R134a in the same test setup, usually within ±15% for similar conditions. In both cases, they first increased with the heat flux until a local maximum value was achieved. A localized dryout of the tubes at the bottom of the bundle penalized the overall bundle heat transfer coefficient at very high heat flux. For the condensing surface, bundle heat transfer coefficients rarely exceeded 10 kW/m2-K, whereas values in excess of 30 kW/m2-K were sometimes seen for the evaporating surface.Keywords: LGWP refrigerantsspray evaporationenhanced surfacestube bundlesSubject classification codes: include these here if the journal requires themDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also.