Study on the heat transfer performance of heat exchange surfaces and flow channels under negative pressure

Abstract

This paper presents a theoretical analysis and simulation study on the heat transfer characteristics of heat exchange surfaces and flow channels under negative pressure. A theoretical analysis model of the air side in the heat transfer channel is established, and the dynamic and steady-state characteristics of the flow and thermal boundary layer inside the channel are derived as functions of environmental pressure variations. A CFD analysis is employed to establish a simulation model for the heat transfer process, and this model is used to simulate the field synergy of the finned tube heat exchanger under low-pressure conditions. The research results indicate that the heat transfer performance of the heat exchanger under negative pressure significantly deteriorates compared to atmospheric conditions. As the ambient pressure decreases from atmospheric pressure to −40 kPa, the heat transfer coefficient on the air side of the heat exchanger decreases by 30% to 47.7%. However, the pressure drop increases by 34.7% to 144.2%. This is closely related to changes in the properties of the cooling medium, the drastic variation of the boundary layer, and the alteration in the synergy between velocity and temperature fields in the low-pressure environment. Under the same boundary conditions such as velocity and temperature, the field synergy between the air-side velocity and temperature fields of the finned tube is higher under low pressure than under atmospheric pressure, which is attributed to the thickness variation of the flow boundary layer and thermal boundary layer caused by the decrease in environmental pressure. In addition, the attenuation of latent heat performance is mainly related to the mass transfer process and the drastic change of the concentration boundary layer under a low pressure environment.