Tube bundle evaporators with LGWP refrigerant R1234ze(E)

Abstract

With 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.

Acknowledgments

The authors would like to extend a special thanks to ASHRAE, the members of Technical Committee 1.3, and especially the industry expert ASHRAE members who served on the Project Management Subcommittee for RP-1800.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was based on part of the work conducted for research project RP-1800 sponsored by ASHRAE and monitored by Technical Committee 1.3.

Notes on contributors

Joshua Rothe

Joshua Rothe, PhD, Student Member ASHRAE, is a Postdoctoral Associate. Jerin Robins Ebanesar, MS, Student Member ASHRAE, is a Graduate Research Assistant. Lorenzo Cremaschi, PhD, Full Member ASHRAE, is a Professor of Mechanical Engineering and the Director of Undergraduate Research.