家用空调器采用微细尺度强化传热技术展望

基于对我国家用空调器产品现状的分析,探讨了执行新能效标准后空调换热器采用新型强化传热技术的潜在需求。制冷剂在微细管内凝结和沸腾传热的已有研究成果显示,家用空调器采用微细尺度强化传热技术,可以使换热器趋于紧凑、高效,从而使空调器满足新能效标准的要求。     

Refrigerant R134a condensation heat transfer and pressure drop inside a small brazed plate heat exchanger

This paper presents the experimental tests on HFC-134a condensation inside a small brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated.A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20 kg/m² s. For refrigerant mass flux lower than 20 kg/m² s, the saturated vapour heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [Nusselt, W., 1916. Die oberflachenkondensation des wasserdampfes. Z. Ver. Dt. Ing. 60, 541–546, 569–575] analysis for vertical surface. For refrigerant mass flux higher than 20 kg/m² s, the saturated vapour heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. [Akers, W.W., Deans, H.A., Crosser, O.K., 1959. Condensing heat transfer within horizontal tubes. Chem. Eng. Prog. Symp. Ser. 55, 171–176] equation. In the forced convection condensation region, the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by the Webb [Webb, R.L., 1998. Convective condensation of superheated vapour. ASME J. Heat Transfer 120, 418–421] model. The heat transfer coefficients show weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.     

Influence of Thermal Flow Field of Cooling Tower on Recirculation Ratio of a Direct Air-Cooled System for a Power Plant

In order to get thermal flow field of direct air-cooled system, the hot water was supplied to the direct air-cooled condenser. The PIV experiments were carried out to get thermal flow field of a direct air-cooled system under different conditions in low velocity wind tunnel, at the same time, the recirculation ratio at cooling tower was measured, so the relationship between flow field characteristic and recirculation ratio of cooling tower can be discussed, from the results we can see that: the flow field configuration fore-and-aft cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed fore-and-aft cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle, the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration fore-and-aft cooling tower reasonably can decrease recirculation ratio under cooling tower, and heat dispel effect of ACC can also be improved.     

干冰法膨丝线CO2回收系统的改进

介绍了干冰法膨胀烟丝浸渍器和CO2回收过程中混有空气的状况,分析了回收系统设备的运行工况和性能,通过在CO2冷凝器上增设自动排气阀代替原手动阀,提高了冷凝CO2的效能,改善了设备运行工况,降低了CO2损耗。     

海水凝汽器传热管的选材与防护

对海水凝汽器传热管材料与防护各方面问题作了评述，回顾了材质的变迁历程，重点对铜合金管与钛管的腐蚀或损伤，从可靠性与经济性方面作了比较分析。     

Energy saving analysis and thermal performance evaluation of a hydrogen-enriched natural gas-fired condensing boiler

Hydrogen-enriched natural gas (HENG) has attracted widespread attention due to its lower pollutant emissions and industrial decarbonization in the past decades. HENG combustion boosts the water content in the flue gas, which is highly favorable for condensing boilers to recover additional latent heat. The energy saving and thermal performance of a condensing boiler burning HENG were evaluated at a constant heat load of 2.8 MW in this study. The variations in combustion products and boiler efficiency were investigated based on the material balance and energy conservation. The heat transfer calculations were employed to evaluate the thermal performance of boiler heating surfaces. The energy recovery performance of the condenser was assessed via a thermal design method. Results show that H₂ enrichment enhances the radiation intensity of the flame due to the incremental triatomic gases with higher emissivity in the furnace. The heat absorption ratio increases with H₂ enrichment in the radiative heating surface, while it shows a reverse tendency in the convective heating surface. The condensing boiler efficiency based on lower heating value increases from 101.83% to 110.60%, the total heat transfer rate of the condenser increases from 2.77 × 10⁵ W to 4.61 × 10⁵ W, and the total area required decreases from 46.45 m² to 42.16 m², as the H₂ enriches from 0 to 100% under the exhaust flue gas temperature of 318 K. Although the amount of recoverable heat in the exhaust flue gas increases considerably after H₂ blending, the original condenser with natural gas as the designed fuel could meet the requirements of the heat recovery for HENG without increasing the extra heating surface. When the H₂ fraction is enriched from 0 to 100%, CO₂ emission intensity drops from 6.05 × 10⁻⁸ kg J⁻¹ to 0. This work may offer some theoretical references for the application and generalization of HENG condensing boilers.