The knowledge of the wettability at the interface of different liquids and solid surfaces must be replenished in steps with material science. Wettability is a critical property in technologies where the interaction of fluid and solid substances is part of the working processes. This paper provides a brief experimental study dealing with the equilibrium contact angle identification at the interface of ammonia and stainless steel plates (SS316L) at different temperatures. The method with the capillary rise at the vertical plate has been exploited and validated with the available water/SS316L test data. The contact angles in the range 10° … 27° have been identified for the temperature range [-11 … 75] 0 C with the apparent justification of wettability improvement with an increase in fluid temperature. • Contact angles of stainless steel plate (316 L) and anhydrous ammonia were identified using the capillary rise at the vertical plate approach. • The wettability of the ammonia-stainless steel interface improves substantially with the fluid temperature rising. • Contact angles of the ammonia-stainless steel interface were identified to be in the range [10 … 27] 0 for the temperatures [-11 … 75] 0 C. 

The equilibrium contact angle of ammonia-stainless steel interface

Flat-plate loop heat pipe (FLHP) is a passive two-phase heat transfer device. Comparing with traditional LHP with a cylindrical evaporator, it can be directly connected to a flat heat source without the employment of a saddle, which can effectively reduce the system thermal resistance and enhance the temperature uniformity. In this work, a stainless steel-ammonia FLHP was developed, and extensive experiments have been conducted to investigate its startup characteristics with the evaporator in the horizontal and vertical positions. Experimental results show that the FLHP exhibits excellent startup performance. It can successfully start up at a small heat load as low as 2 W with no obvious temperature overshoot. In a wide power range of 5–35 W, the FLHP generally starts up in only one situation, much simpler than the startup of a LHP with a cylindrical evaporator. For this rectangular evaporator, the heat leak from the evaporator to the compensation chamber (CC) becomes very small. As a result, the vapor can easily exit the condenser in most cases in the power range of 5–35 W, leading to a 100% utilization efficiency of the condenser and the resultant satisfactory thermal performance of the FLHP. In addition, the startup performance and the system thermal resistance of the FLHP are insensitive to the evaporator orientation, promising great application potential in future electronics cooling.

Zehui Yang

Papers

Startup characteristics of an ammonia loop heat pipe with a rectangular evaporator