The heat transfer performance of a micro-scale, axisymmetric, confined jet impinging on a flat surface at high Mach numbers (0.2 to 0.6) and low Reynolds numbers (419 to 1310) was computationally studied. The flow is characterized by Knudsen numbers, based on the jet radius, large enough (0.0013) to warrant slip-flow boundary conditions at the impinging surface. The effects of Mach number, compressibility, and slip-flow on heat transfer results are presented, along with the local Nusselt number distributions, and velocity and temperature fields near the impingement surface. Results for uniform wall heat flux show that the wall temperature decreases with increasing Mach number, with a local minimum at r/D = 0.7. The slip velocity also increases with Mach number with peak values also near r/D = 0.7. The resulting Nusselt number increases with increasing Mach number, and a local maximum in the Nusselt number is observed at r/D = 0.6, not at the centerline. In general, compressibility improves heat transfer due to increased fluid density near the impinging surface. Also, inclusion of slip-velocity increases the rate of heat transfer. However, the accompanying temperature-jump condition at the wall is found to reduce the local heat transfer rate. The net effect of the slip-flow boundary conditions applied in this study was an overall reduction in heat transfer.
{"title":"Simulation of Micro-Scale Jet Impingement Heat Transfer","authors":"Paul A. Boeschoten, D. Pence, J. Liburdy","doi":"10.1115/imece2000-1542","DOIUrl":"https://doi.org/10.1115/imece2000-1542","url":null,"abstract":"\u0000 The heat transfer performance of a micro-scale, axisymmetric, confined jet impinging on a flat surface at high Mach numbers (0.2 to 0.6) and low Reynolds numbers (419 to 1310) was computationally studied. The flow is characterized by Knudsen numbers, based on the jet radius, large enough (0.0013) to warrant slip-flow boundary conditions at the impinging surface. The effects of Mach number, compressibility, and slip-flow on heat transfer results are presented, along with the local Nusselt number distributions, and velocity and temperature fields near the impingement surface. Results for uniform wall heat flux show that the wall temperature decreases with increasing Mach number, with a local minimum at r/D = 0.7. The slip velocity also increases with Mach number with peak values also near r/D = 0.7. The resulting Nusselt number increases with increasing Mach number, and a local maximum in the Nusselt number is observed at r/D = 0.6, not at the centerline. In general, compressibility improves heat transfer due to increased fluid density near the impinging surface. Also, inclusion of slip-velocity increases the rate of heat transfer. However, the accompanying temperature-jump condition at the wall is found to reduce the local heat transfer rate. The net effect of the slip-flow boundary conditions applied in this study was an overall reduction in heat transfer.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"01 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127246942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work utilizes the cascade algorithm to predict the heat transfer characteristics of a one-dimensional longitudinal fin of rectangular profile in a boiling liquid. In this analysis, the geometric parameters of the fin, the temperature at the fin base and the saturation temperature of the boiling liquid are assumed. With the utilization of experimental boiling heat transfer coefficient curves, the heat flux, temperature profile, and boiling heat transfer coefficient of each point on the fin are obtained. The effectiveness of the fin in a boiling liquid is plotted for different fin thicknesses. It is found that the fin conductivity, boiling liquid, fin geometry and fin base temperature all affect the effectiveness of the fin in boiling. The effectiveness curves clearly indicate whether a fin should be used or when it is advantageous to use a fin in boiling liquid.
{"title":"Heat Transfer Characteristics for a Single Fin in a Boiling Liquid","authors":"Yingzong Bu, A. Kraus, B. Chung","doi":"10.1115/imece2000-1517","DOIUrl":"https://doi.org/10.1115/imece2000-1517","url":null,"abstract":"\u0000 This work utilizes the cascade algorithm to predict the heat transfer characteristics of a one-dimensional longitudinal fin of rectangular profile in a boiling liquid. In this analysis, the geometric parameters of the fin, the temperature at the fin base and the saturation temperature of the boiling liquid are assumed. With the utilization of experimental boiling heat transfer coefficient curves, the heat flux, temperature profile, and boiling heat transfer coefficient of each point on the fin are obtained. The effectiveness of the fin in a boiling liquid is plotted for different fin thicknesses. It is found that the fin conductivity, boiling liquid, fin geometry and fin base temperature all affect the effectiveness of the fin in boiling. The effectiveness curves clearly indicate whether a fin should be used or when it is advantageous to use a fin in boiling liquid.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123498035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study reported thermal performance of a thermally enhanced plastic ball grid array (PBGA), namely T2-BGA™ which incorporates a heat slug in package, with a foam-metal heat sink on the top of this package. Experimental measurement of junction-to-ambient thermal resistance is performed in accordance with the SEMI standards of G38-0996 and G42-0996 for thermal characterization of BGA packages. Allowable power dissipation is subject to the constraint of junction temperature (Tj) at 95°C and ambient temperature (Ta) in chassis at 35 °C under free and forced air (0 ∼ 3 m/s) conditions. Based on this constraint, allowable power dissipation of a regular PBGA with a commercial pin fin heat sink under free and 3 m/s forced air is 5.45 W and 9.17 W compared with those of T2-BGA with a foam heat sink of 6.80 W and 19.6 W respectively. This results show that T2-BGA™ with a foam heat sink offers enormous potential to high power package applications.
{"title":"Cooling of Thermal Enhanced BGA Package Using Foam Metal Heat Sinks","authors":"Jenn-Jiang Hwang, C. Chao","doi":"10.1115/imece2000-1545","DOIUrl":"https://doi.org/10.1115/imece2000-1545","url":null,"abstract":"\u0000 This study reported thermal performance of a thermally enhanced plastic ball grid array (PBGA), namely T2-BGA™ which incorporates a heat slug in package, with a foam-metal heat sink on the top of this package. Experimental measurement of junction-to-ambient thermal resistance is performed in accordance with the SEMI standards of G38-0996 and G42-0996 for thermal characterization of BGA packages. Allowable power dissipation is subject to the constraint of junction temperature (Tj) at 95°C and ambient temperature (Ta) in chassis at 35 °C under free and forced air (0 ∼ 3 m/s) conditions. Based on this constraint, allowable power dissipation of a regular PBGA with a commercial pin fin heat sink under free and 3 m/s forced air is 5.45 W and 9.17 W compared with those of T2-BGA with a foam heat sink of 6.80 W and 19.6 W respectively. This results show that T2-BGA™ with a foam heat sink offers enormous potential to high power package applications.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"457 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123639875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat sinks (or components) for electronic applications, the components are usually subjected to a peripherally non-uniform heat flux. Even if the applied heat flux is uniform in the axial direction [which is unlikely], both intuition and recent investigations have clearly shown that both the local heat flux and the eventual critical heat flux (CHF) in this three-dimensional case will differ significantly from similar quantities found in the voluminous body of data for uniformly heated tubes and flow channels. Although this latter case has been used in the past as an estimate for the former case, more study has become necessary to examine the three-dimensional temperature and heat flux distributions and related CHF. Work thus far has shown that the non-uniform peripheral heat flux condition enhances CHF in some cases. In order to avoid the excess costs associated with using electron- or ion-beams to produce the non-uniform heat flux, a new facility was developed which will allow three-dimensional conjugate heat transfer measurements and two-dimensional local subcooled flow boiling heat flux and related critical heat flux measurements. The configurations under study consist of: (1) a non-uniformly heated cylindrical-like test section with a circular coolant channel bored through the center, and (2) a monoblock which is a square cross-section parallelepiped with a circular drilled flow channel through the center line along its length. The theoretical or idealization of the cylindrical-like test section would be a circular cylinder with half (−90 degrees to +90 degrees) of its outside boundary subjected to a uniform heat flux and the remaining half insulated. For the monoblock, a uniform heat flux is applied to one of the outside surfaces and the remaining surfaces are insulated. The outside diameter of the cylindrical-like test section is 30.0 mm and its length is 200.0 mm. The monoblock square has lengths 30.0 mm. The inside diameter of the flow channel for both types of test sections is 10.0 mm. Water is the coolant. The inlet water temperature can be set at any level in the range from 26.0 °C to 130.0 °C and the exit pressure can be set at any level in the range from 0.4 MPa to 4.0 MPa. Thermocouples are placed at forty-eight locations inside the solid cylindrical-like or monoblock test section. For each of four axial stations, three thermocouples are embedded at four circumferential locations (0, 45, 135, and 180 degrees, where 0 degrees corresponds to that portion of the axis of symmetry close to the heated surface) in the wall of the test section. Finally, the mass velocity can be set at any level in the range from 0.6 to 10.0 Mg/m2s.
{"title":"A New Facility for Measurements of Three-Dimensional, Local Subcooled Flow Boiling Heat Flux and Related Critical Heat Flux","authors":"R. Boyd, P. Cofie, Qing-Yuan Li, Ali Ekhlassi","doi":"10.1115/imece2000-1522","DOIUrl":"https://doi.org/10.1115/imece2000-1522","url":null,"abstract":"\u0000 In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat sinks (or components) for electronic applications, the components are usually subjected to a peripherally non-uniform heat flux. Even if the applied heat flux is uniform in the axial direction [which is unlikely], both intuition and recent investigations have clearly shown that both the local heat flux and the eventual critical heat flux (CHF) in this three-dimensional case will differ significantly from similar quantities found in the voluminous body of data for uniformly heated tubes and flow channels. Although this latter case has been used in the past as an estimate for the former case, more study has become necessary to examine the three-dimensional temperature and heat flux distributions and related CHF. Work thus far has shown that the non-uniform peripheral heat flux condition enhances CHF in some cases.\u0000 In order to avoid the excess costs associated with using electron- or ion-beams to produce the non-uniform heat flux, a new facility was developed which will allow three-dimensional conjugate heat transfer measurements and two-dimensional local subcooled flow boiling heat flux and related critical heat flux measurements.\u0000 The configurations under study consist of: (1) a non-uniformly heated cylindrical-like test section with a circular coolant channel bored through the center, and (2) a monoblock which is a square cross-section parallelepiped with a circular drilled flow channel through the center line along its length. The theoretical or idealization of the cylindrical-like test section would be a circular cylinder with half (−90 degrees to +90 degrees) of its outside boundary subjected to a uniform heat flux and the remaining half insulated. For the monoblock, a uniform heat flux is applied to one of the outside surfaces and the remaining surfaces are insulated. The outside diameter of the cylindrical-like test section is 30.0 mm and its length is 200.0 mm. The monoblock square has lengths 30.0 mm. The inside diameter of the flow channel for both types of test sections is 10.0 mm. Water is the coolant. The inlet water temperature can be set at any level in the range from 26.0 °C to 130.0 °C and the exit pressure can be set at any level in the range from 0.4 MPa to 4.0 MPa. Thermocouples are placed at forty-eight locations inside the solid cylindrical-like or monoblock test section. For each of four axial stations, three thermocouples are embedded at four circumferential locations (0, 45, 135, and 180 degrees, where 0 degrees corresponds to that portion of the axis of symmetry close to the heated surface) in the wall of the test section. Finally, the mass velocity can be set at any level in the range from 0.6 to 10.0 Mg/m2s.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"2 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114135076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An ion-drag pump is utilized to enhance the heat transport capacity of micro heat pipes. An analytical model is developed to estimate the maximum heat transport capacity as a function of the applied electric field. The model predicts that the application of an electric field causes a four fold increase in heat transport capacity. A transient analytical model was developed to permit variation of the electric field with applied thermal load. A proportional-integral-derivative controller was used to simulate active temperature control. The feasibility of achieving active temperature control was demonstrated experimentally.
{"title":"Active Thermal Control of an Ion-Drag Pump Assisted Micro Heat Pipe","authors":"Zhiquan Yu, K. Hallinan, N. Pohlman, R. Kashani","doi":"10.1115/imece2000-1549","DOIUrl":"https://doi.org/10.1115/imece2000-1549","url":null,"abstract":"\u0000 An ion-drag pump is utilized to enhance the heat transport capacity of micro heat pipes. An analytical model is developed to estimate the maximum heat transport capacity as a function of the applied electric field. The model predicts that the application of an electric field causes a four fold increase in heat transport capacity. A transient analytical model was developed to permit variation of the electric field with applied thermal load. A proportional-integral-derivative controller was used to simulate active temperature control. The feasibility of achieving active temperature control was demonstrated experimentally.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122280237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Cavallini, Giuseppe Censi, D. Col, L. Doretti, G. Longo, L. Rossetto, C. Zilio
The high temperature glide mixture R-125/236ea at three mass compositions (28/72%, 46/54%, 63/37%) is tested during condensation against water in a tube-in-tube heat exchanger. The experimental runs to measure the heat transfer coefficients are carried out at saturation temperature ranging from 40°C to 60°C and mass velocities ranging from 100 to 750 kg/(m2 s). A gas chromatograph is used for on-line concentration measurements. By comparing the heat transfer performances of the three compositions to the condensation coefficients previously measured for the two pure components inside a smooth horizontal tube [Cavallini et al. (2000)], the dependence of the heat transfer performance on composition during condensation for a non-azeotropic mixture is investigated. The film method by Colburn and Drew (1937) is applied to predict the experimental coefficients and it is found to underestimate the heat transfer rate, with more conservative results as compared to the equilibrium method by Silver (1947), Bell and Ghaly (1973).
对三种质量组成(28/72%，46/54%，63/37%)的高温滑动混合物R-125/236ea在管中换热器中水的冷凝过程进行了测试。测量传热系数的实验运行在饱和温度范围为40°C至60°C，质量速度范围为100至750 kg/(m2 s)。气相色谱仪用于在线浓度测量。通过将三种组分的传热性能与之前在光滑水平管内测量的两种纯组分的冷凝系数进行比较[Cavallini et al.(2000)]，研究了非共沸混合物在冷凝过程中传热性能与组分的依赖关系。采用Colburn和Drew(1937)的薄膜法预测实验系数，发现它低估了传热速率，与Silver(1947)、Bell和Ghaly(1973)的平衡法相比，结果更为保守。
{"title":"Analysis and Prediction of Condensation Heat Transfer of the Zeotropic Mixture R-125/236ea","authors":"A. Cavallini, Giuseppe Censi, D. Col, L. Doretti, G. Longo, L. Rossetto, C. Zilio","doi":"10.1115/imece2000-1511","DOIUrl":"https://doi.org/10.1115/imece2000-1511","url":null,"abstract":"\u0000 The high temperature glide mixture R-125/236ea at three mass compositions (28/72%, 46/54%, 63/37%) is tested during condensation against water in a tube-in-tube heat exchanger. The experimental runs to measure the heat transfer coefficients are carried out at saturation temperature ranging from 40°C to 60°C and mass velocities ranging from 100 to 750 kg/(m2 s). A gas chromatograph is used for on-line concentration measurements. By comparing the heat transfer performances of the three compositions to the condensation coefficients previously measured for the two pure components inside a smooth horizontal tube [Cavallini et al. (2000)], the dependence of the heat transfer performance on composition during condensation for a non-azeotropic mixture is investigated.\u0000 The film method by Colburn and Drew (1937) is applied to predict the experimental coefficients and it is found to underestimate the heat transfer rate, with more conservative results as compared to the equilibrium method by Silver (1947), Bell and Ghaly (1973).","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"38 12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125734790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent studies have experimentally and theoretically examined the rate of salt deposition by natural convection on a cylinder heated above the solubility temperature corresponding to the concentration of salt in the surrounding solution at conditions typical of the Supercritical Water Oxidation (SCWO) process (Hodes et al., 2000A; Hodes, 1998). The total deposition rate of salt on the cylinder is the sum of the rates of deposition at the salt layer-solution interface (SLSI) formed on the cylinder and within the porous salt layer. The rate of deposition at the SLSI can not be accurately computed without determining whether or not salt nucleates homogeneously in the adjacent (natural convective) boundary layer. A methodology to determine whether or not homogeneous nucleation in the boundary layer is possible is presented here. This is accomplished by computing the temperature and concentration profiles in the boundary layer under the assumption that homogeneous nucleation does not occur. If, under this assumption, supersaturation does not occur, homogeneous nucleation is impossible. If supersaturation is present, homogeneous nucleation may or may not occur depending on the amount of metastability the solution can tolerate. It is shown that the Lewis number is the critical property in determining whether or not homogeneous nucleation is possible and a simple formula is developed to predict the Lewis number below which homogeneous nucleation is impossible for a given solubility boundary and set of operating conditions.
{"title":"On the Potential for Homogeneous Nucleation in Aqueous Salt Solutions at Elevated Temperatures and Pressures","authors":"Kenneth A. Smith, M. Hodes, P. Griffith","doi":"10.1115/imece2000-1514","DOIUrl":"https://doi.org/10.1115/imece2000-1514","url":null,"abstract":"\u0000 Recent studies have experimentally and theoretically examined the rate of salt deposition by natural convection on a cylinder heated above the solubility temperature corresponding to the concentration of salt in the surrounding solution at conditions typical of the Supercritical Water Oxidation (SCWO) process (Hodes et al., 2000A; Hodes, 1998). The total deposition rate of salt on the cylinder is the sum of the rates of deposition at the salt layer-solution interface (SLSI) formed on the cylinder and within the porous salt layer. The rate of deposition at the SLSI can not be accurately computed without determining whether or not salt nucleates homogeneously in the adjacent (natural convective) boundary layer. A methodology to determine whether or not homogeneous nucleation in the boundary layer is possible is presented here. This is accomplished by computing the temperature and concentration profiles in the boundary layer under the assumption that homogeneous nucleation does not occur. If, under this assumption, supersaturation does not occur, homogeneous nucleation is impossible. If supersaturation is present, homogeneous nucleation may or may not occur depending on the amount of metastability the solution can tolerate. It is shown that the Lewis number is the critical property in determining whether or not homogeneous nucleation is possible and a simple formula is developed to predict the Lewis number below which homogeneous nucleation is impossible for a given solubility boundary and set of operating conditions.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131375276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A theoretical model for steady state two-phase vertical upward flow in cylindrical channels is presented. A comparison of the results of this model for a circular channel as well as a reformulated rectangular channel model is partially made with experimental data in the literature. It shows that in general the model predicts the flow characteristics somewhat better in the bubbly regime than the slug flow indicating the need to look further into some of the constitutive relationships used to close the model in this regime.
{"title":"A Fully Developed Two-Phase Flow Model in Vertical Channels for Bubbly and Slug Flow Regimes","authors":"S. Moujaes, E. Sleight","doi":"10.1115/imece2000-1524","DOIUrl":"https://doi.org/10.1115/imece2000-1524","url":null,"abstract":"\u0000 A theoretical model for steady state two-phase vertical upward flow in cylindrical channels is presented. A comparison of the results of this model for a circular channel as well as a reformulated rectangular channel model is partially made with experimental data in the literature. It shows that in general the model predicts the flow characteristics somewhat better in the bubbly regime than the slug flow indicating the need to look further into some of the constitutive relationships used to close the model in this regime.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126823198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work an experimental study of spray cooling using monodispersed droplet sprays impinging on a flat and heated surface is reported. The aim of the work was to formulate an empirical model describing the heat flux (HF) for the nucleate boiling regime. Monodispersed water droplets with a known diameter and velocity, produced by a droplet generator, were directed toward a heated surface and the heat transfer was registered using a data acquisition system. The resulting high heat flux was investigated as function of the droplets’ diameter and velocity, mass flow rate, ambient pressure, subcooling degree and surface roughness. The resulting matrix of variables investigated in the experiments included; mass flux rate (340 < ṁ″ < 750 kg/m2s), subcooling degree (25 < Tsub < 78 °C), ambient pressure (1 < P < 1.8 bar), and surface roughness (79 < Rt < 5 μm). A generalized correlation was developed for the dimensionless HF as function of the dimensionless mass flow rate, temperature, surface roughness and pressure, along with the Jacob number. The form of the correlation is q ˙ ″ ρ V h f g = 0.245 ( Ja ) 1.038 ( Δ T sub Δ T sat ) 0.491 ( ρ σ m ˙ μ 3 ) 0.133 ( R t D ) 0.0213 ( P P 0 ) 0.291 having a confidence level greater than 95%, the differences between predicted and experimental HF were less than ±19%.
本文报道了单分散液滴溅射在平面加热表面的喷雾冷却实验研究。这项工作的目的是制定一个经验模型描述热通量(HF)的核沸腾状态。液滴发生器产生已知直径和速度的单分散水滴，将其导向受热表面，并使用数据采集系统记录传热过程。研究了液滴直径和速度、质量流量、环境压力、过冷度和表面粗糙度对高热流密度的影响。实验中研究的变量的结果矩阵包括:质量通量(340 <″< 750 kg/m2s)、过冷度(25 < Tsub < 78°C)、环境压力(1 < P < 1.8 bar)和表面粗糙度(79 < Rt < 5 μm)。建立了无因次HF与无因次质量流量、温度、表面粗糙度和压力以及Jacob数的广义相关关系。相关形式为q˙″ρ V h f g = 0.245 (Ja) 1.038 (Δ T sub Δ T sat) 0.491 (ρ σ m˙μ 3) 0.133 (R T D) 0.0213 (P P 0) 0.291，置信水平大于95%，预测HF与实验HF的差异小于±19%。
{"title":"A Heat Flux Correlation for Spray Cooling in the Nucleate Boiling Regime","authors":"E. Cabrera, J. E. González","doi":"10.1115/imece2000-1513","DOIUrl":"https://doi.org/10.1115/imece2000-1513","url":null,"abstract":"\u0000 In this work an experimental study of spray cooling using monodispersed droplet sprays impinging on a flat and heated surface is reported. The aim of the work was to formulate an empirical model describing the heat flux (HF) for the nucleate boiling regime. Monodispersed water droplets with a known diameter and velocity, produced by a droplet generator, were directed toward a heated surface and the heat transfer was registered using a data acquisition system. The resulting high heat flux was investigated as function of the droplets’ diameter and velocity, mass flow rate, ambient pressure, subcooling degree and surface roughness. The resulting matrix of variables investigated in the experiments included; mass flux rate (340 < ṁ″ < 750 kg/m2s), subcooling degree (25 < Tsub < 78 °C), ambient pressure (1 < P < 1.8 bar), and surface roughness (79 < Rt < 5 μm). A generalized correlation was developed for the dimensionless HF as function of the dimensionless mass flow rate, temperature, surface roughness and pressure, along with the Jacob number. The form of the correlation is q ˙ ″ ρ V h f g = 0.245 ( Ja ) 1.038 ( Δ T sub Δ T sat ) 0.491 ( ρ σ m ˙ μ 3 ) 0.133 ( R t D ) 0.0213 ( P P 0 ) 0.291 having a confidence level greater than 95%, the differences between predicted and experimental HF were less than ±19%.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131031199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alternative refrigerant R-134a is considered to be ozone-friendly and a potential candidate for replacing the refrigerant CFC-12 in refrigeration and air-conditioning applications. This paper presents the experimental investigation of condensation heat transfer characteristics of superheated R-134a vapor flowing inside helicoidal pipes with the cooling water flowing through the annular helicoidal passage in a counter-flow direction. The heat transfer experiment was performed for R-134a mass flow flux ranging from 100 to 420 kg/m2s with the superheat of the inlet vapor of 2.8°C and 8.3°C, respectively. The cooling water flow Reynolds Rew ranges from 1500 to 12000. The Nusselt numbers were experimentally determined for a helicoidal pipe with the helix axis of vertical direction. The correlations for Nusselt numbers are developed based on the experimental results, which can be used as a reference in the design of helicoidal pipe condensers.
{"title":"Experimental Investigation of Condensation Heat Transfer of Refrigerant R-134A in Helicoidal Pipes","authors":"J. T. Han, C. Lin, M. Ebadian","doi":"10.1115/imece2000-1510","DOIUrl":"https://doi.org/10.1115/imece2000-1510","url":null,"abstract":"\u0000 Alternative refrigerant R-134a is considered to be ozone-friendly and a potential candidate for replacing the refrigerant CFC-12 in refrigeration and air-conditioning applications. This paper presents the experimental investigation of condensation heat transfer characteristics of superheated R-134a vapor flowing inside helicoidal pipes with the cooling water flowing through the annular helicoidal passage in a counter-flow direction. The heat transfer experiment was performed for R-134a mass flow flux ranging from 100 to 420 kg/m2s with the superheat of the inlet vapor of 2.8°C and 8.3°C, respectively. The cooling water flow Reynolds Rew ranges from 1500 to 12000. The Nusselt numbers were experimentally determined for a helicoidal pipe with the helix axis of vertical direction. The correlations for Nusselt numbers are developed based on the experimental results, which can be used as a reference in the design of helicoidal pipe condensers.","PeriodicalId":120929,"journal":{"name":"Heat Transfer: Volume 4","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121862483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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