*Article* **Experimental and Numerical Study of Heat Pipe Heat Exchanger with Individually Finned Heat Pipes**

**Grzegorz Górecki \*, Marcin Ł ˛ecki, Artur Norbert Gutkowski, Dariusz Andrzejewski, Bartosz Warwas, Michał Kowalczyk and Artur Romaniak**

> Faculty of Mechanical Engineering, Institute of Turbomachinery, Lodz University of Technology, 219/223 Wolczanska Street, 90-924 Lodz, Poland; marcin.lecki@p.lodz.pl (M.Ł.); artur.gutkowski@p.lodz.pl (A.N.G.); dariusz.a.zsp@gmail.com (D.A.); bartosz.warwas@dokt.p.lodz.pl (B.W.); michal.kowalczyk.1@dokt.p.lodz.pl (M.K.); artur.romaniak@dokt.p.lodz.pl (A.R.) **\*** Correspondence: grzegorz.gorecki@p.lodz.pl; Tel.: +48-42-631-23-20

**Abstract:** The present study is devoted to the modeling, design, and experimental study of a heat pipe heat exchanger utilized as a recuperator in small air conditioning systems (airflow <sup>≈</sup> 300–500 m3/h), comprised of individually finned heat pipes. A thermal heat pipe heat exchanger model was developed, based on available correlations. Based on the previous experimental works of authors, refrigerant R404A was recognized as the best working fluid with a 20% heat pipe filling ratio. An engineering analysis of parametric calculations performed with the aid of the computational model concluded 20 rows of finned heat pipes in the staggered arrangement as a guarantee of stable heat exchanger effectiveness ≈ 60%. The optimization of the overall cost function by the "brute-force" method has backed up the choice of the best heat exchanger parameters. The 0.05 m traversal (finned pipes in contact with each other) and 0.062 m longitudinal distance were optimized to maximize effectiveness (up to 66%) and minimize pressure drop (less than 150 Pa). The designed heat exchanger was constructed and tested on the experimental rig. The experimental data yielded a good level of agreement with the model—relative difference within 10%.

**Keywords:** heat pipe heat exchanger; wickless heat pipe; heat transfer; individually finned tubes
