为研究超临界压力下的对流传热特性,对超临界压力氟利昂R134a在内径25 mm垂直圆管中的受热上升流动传热进行了实验研究,获得压力4.5 MPa和4.7 MPa、质量流速G=400~700 kg/（m2·s）、热流密度q=30~60 k W/m2的实验数据,对换热强化...为研究超临界压力下的对流传热特性,对超临界压力氟利昂R134a在内径25 mm垂直圆管中的受热上升流动传热进行了实验研究,获得压力4.5 MPa和4.7 MPa、质量流速G=400~700 kg/（m2·s）、热流密度q=30~60 k W/m2的实验数据,对换热强化和传热恶化的规律和特性以及其影响因素进行了分析。结果发现,在拟临界区附近,超临界压力R134a出现明显的强化换热现象。在低质量流速或高热流密度下发生传热恶化,其恶化边界为q/G〉0.06 k J/kg。在特定的工况下观察到两次传热恶化：第一次发生在临近入口区域,在不同流体入口温度下均观测到恶化;第二次发生在远离入口区域,仅在一定流体焓值范围内存在。实验参数敏感性分析表明,传热强化随质量流速的增加、热流密度的减小、压力的降低而增加,而传热恶化则相反。展开更多
The article analyzes a shell and tube type condenser’s thermal performance using concepts of efficiency and effectiveness. Freon 134a is used as a coolant flowing through the shell. Water or water-based aluminum oxid...The article analyzes a shell and tube type condenser’s thermal performance using concepts of efficiency and effectiveness. Freon 134a is used as a coolant flowing through the shell. Water or water-based aluminum oxide nanoparticles are at relatively low saturation pressure in the tube. The condenser consists of 36 tubes divided into three central regions for analysis: superheated steam, saturated steam, and subcooled liquid. The three regions contain four tubes with three steps each, that is, 12 tubes. Region I, superheated steam, includes three horizontal baffles. Profiles of temperature, efficiency, and effectiveness are presented graphically for the three regions, with fixed refrigerant flow equal to 0.20 kg/s and fluid flow rate in the tube ranging from 0.05 kg/s to 0.40 kg/s. The experimental result for vapor pressure equal to 1.2 MPa and water flow equal to 0.41 kg/s was used as one of the references for the model’s physical compatibility.展开更多
文摘为研究超临界压力下的对流传热特性,对超临界压力氟利昂R134a在内径25 mm垂直圆管中的受热上升流动传热进行了实验研究,获得压力4.5 MPa和4.7 MPa、质量流速G=400~700 kg/（m2·s）、热流密度q=30~60 k W/m2的实验数据,对换热强化和传热恶化的规律和特性以及其影响因素进行了分析。结果发现,在拟临界区附近,超临界压力R134a出现明显的强化换热现象。在低质量流速或高热流密度下发生传热恶化,其恶化边界为q/G〉0.06 k J/kg。在特定的工况下观察到两次传热恶化：第一次发生在临近入口区域,在不同流体入口温度下均观测到恶化;第二次发生在远离入口区域,仅在一定流体焓值范围内存在。实验参数敏感性分析表明,传热强化随质量流速的增加、热流密度的减小、压力的降低而增加,而传热恶化则相反。
文摘The article analyzes a shell and tube type condenser’s thermal performance using concepts of efficiency and effectiveness. Freon 134a is used as a coolant flowing through the shell. Water or water-based aluminum oxide nanoparticles are at relatively low saturation pressure in the tube. The condenser consists of 36 tubes divided into three central regions for analysis: superheated steam, saturated steam, and subcooled liquid. The three regions contain four tubes with three steps each, that is, 12 tubes. Region I, superheated steam, includes three horizontal baffles. Profiles of temperature, efficiency, and effectiveness are presented graphically for the three regions, with fixed refrigerant flow equal to 0.20 kg/s and fluid flow rate in the tube ranging from 0.05 kg/s to 0.40 kg/s. The experimental result for vapor pressure equal to 1.2 MPa and water flow equal to 0.41 kg/s was used as one of the references for the model’s physical compatibility.
