低气压下板式电加热器换热性能的研究

Study of the Heat Transfer Performance of a Plate Electric Heater at Low Barometric Pressure

板式电加热器是一种常用的供热设备 ,其电热板的温度有一定的限制。随着海拔高度的增加 ,大气压力的降低会引起空气密度的减小 ,根据传热学理论的分析 ,将导致自然对流换热系数h下降 ,即电加热器的换热性能下降。按照Kreith和Gryzagoridis提出的经验公式 ,若仅考虑气压的影响 ,在唐古拉山垭口处竖平壁的自然对流换热系数h仅为海平面处的 73%。如果板式电加热器的电功率不变时 ,电热板的温度就会升高。

Plate electric heater is a common heating apparatus.The temperature of the heating plates is limited. With the increase of the altitude the decease of the ambient pressure induces the reduction of the air density. So the free convection heat transfer coefficient h , or the heat transfer performance of the plate electric heater will decrease by heat transfer analysis.According to the empirical relations of Kreith and Gryzagoridis the free convection heat transfer coefficient h at Tangula Mountain Pass is only 73% of that at the sea level for a vertical plane if only the barometric pressure variation is considered.Therefore the temperature of the heating plates will increase if the power of the electric heater is constant.The trend is verified by the experimental results in a lower air pressure tank.