Heat transfer enhancement in pool boiling of a refrigerant fluid with wire nets structures

Abstract

Among many methods to enhance boiling heat transfer by means of porous coatings, the use of the wire nets covering the heated surface demonstrates some advantages due to its simplicity and low cost. Easiness of a wire net mounting at the heated wall allows testing many different nets and their combinations. This paper presents the experimental results on heat transfer and crisis using the dielectric refrigerant R141b pool boiling under atmospheric pressure. The analysis carried out in the present paper demonstrates that success in boiling heat transfer enhancement is provided not only by the nucleation sites density increase, but also by designing the channels in the porous structure to escape the generated vapor. Unsatisfactory results in relation to CHF value have been obtained with rather thick porous coating. In this case the problem is to provide vapor evacuation from the wall. Rather essential heat transfer coefficient and CHF increase has been observed while the porous structure has been formed with 3–7 layers of nets using wire of 0.25–0.40 mm diameter and mesh aperture of approximately 2 mm. The nets of stainless steel gave the greater effect with respect to copper, aluminium and brass. It is demonstrated that the presence of porous coatings brings about a considerable enhancement of the thermal stability of the system. An approximate model of crisis in boiling at the surface coated with metallic nets has been developed.