Research on the air pressure drop in plate finned tube heat exchangers

In order to establish a reliable procedure for estimation of air pressure drop, experiments on plate finned tube heat exchangers have been conducted, as well as the research on the open literature. The procedure of Kays and London was tested against the experimental data and significant level of uncertainty was found. Using own experimental data, as well as previously published data of Kays and London, new correlation for estimation of air pressure drop has been established. Statistical parameters of new correlation enable the conclusion that it can be used for wide range of Reynolds numbers.     

Experimental studies on pressure drop characteristics of cryogenic cross-counter flow coiled finned tube heat exchangers

Cross-counter flow coiled finned tube heat exchangers used in medium capacity helium liquefiers/refrigerators were developed in our lab. These heat exchangers were developed using integrated low finned tubes. Experimental studies have been performed to know the pressure drop characteristics of tube side and shell side flow of these heat exchangers. All experiments were performed at room temperature in the Reynolds number range of 3000-30,000 for tube side and 25-155 for shell side. The results of present experiments indicate that available correlations for tube side can not be used for prediction of tube side pressure drop data due to complex surface formation at inner side of tube during formation of fins over the outer surface. Results also indicate that surface roughness effect becomes more pronounced as the value of di/D_m increases. New correlations based on present experimental data are proposed for predicting the friction factors for tube side and shell side.     

A survey of correlations for heat transfer and pressure drop for evaporation and condensation in plate heat exchangers

Plate Heat Exchangers (PHEs) are used in a wide variety of applications including heating, ventilation, air-conditioning, and refrigeration. PHEs are characterized by compactness, flexible thermal sizing, close approach temperature, and enhanced heat transfer performance. Due to their desirable characteristics, they are increasingly utilized in two-phase flow applications. Detailed research on heat transfer and fluid flow characteristics in these types of exchangers is required to design and use plate heat exchangers in an optimal manner. This paper reviews the available literature on the correlations for heat transfer and pressure drop calculations for two-phase flow in PHEs as an initial process step in order to understand the current research status. Comparative evaluations for some of the existing correlations are presented in the light of their applicability to different refrigerants. Overall, there is a significant gap in the literature regarding two-phase heat transfer and fluid flow characteristics of these types of exchangers.     

齿形参数对内螺纹铜管换热及阻力性能的影响

介绍ACR内螺纹铜管齿形参数——齿条数及齿顶角对蒸发单管换热性能及阻力性能的影响。     

Effect of fin spacing on the heat transfer and pressure drop of a two-row plate fin and tube heat exchanger

The analogy between heat and mass transfer (using the naphthalene sublimation technique to measure the mass transfer coefficient) was used to investigate the heat transfer capabilities of various two-row plate fin and tube heat exchanger configurations. Average transfer coefficients were determined from measurements of the mass transferred in an analogical system consisting of a pair of naphthalene plates and an array of spacer discs. The analogical system modelled a typical heat exchanger flow passage. Special attention was given to the effect of fin spacing on heat transfer capabilities. A physical interpretation of the experimental data has been given and new conclusions have been drawn. The pressure drop of the heat exchanger configurations has also been investigated.     

Influence of irrigation density on heat transfer during condensation in finned tube bundles

The authors presented results of experimental investigations of heat transfer with film condensation of practically motionless vapor in finned tube bundles of different geometry.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 1, pp. 16–22, July, 1986.     

Experimental investigation on flow condensation heat transfer and pressure drop of R170 in a horizontal tube

Condensation heat transfer and pressure drop of R170 were studied experimentally in a horizontal tube with inner diameter of 4 mm. The tests were conducted at saturation pressures from 1 MPa to 2.5 MPa, mass fluxes from 100 kg (m²∙s)⁻¹ to 250 kg (m²∙s)⁻¹ and average heat fluxes from 55.3 kW m⁻² to 96.3 kW m⁻² over the entire vapor quality range. The effects of vapor quality, mass flux and saturation pressure on condensation heat transfer and pressure drop were examined and analyzed. The experimental data were compared with various well-known correlations of condensation heat transfer coefficient and pressure drop. The comparison results showed that Koyama et al. correlation agreed with the experimental heat transfer coefficient with a mean absolute relative deviation less than 25%, and the Yan and Lin correlation can accurately predict the experimental pressure drop with a mean absolute relative deviation less than 18%.     

Two-phase heat transfer and pressure drop of LNG during saturated flow boiling in a horizontal tube

Two-phase heat transfer and pressure drop of LNG (liquefied natural gas) have been measured in a horizontal smooth tube with an inner diameter of 8 mm. The experiments were conducted at inlet pressures from 0.3 to 0.7 MPa with a heat flux of 8–36 kW m⁻², and mass flux of 49.2–201.8 kg m⁻² s⁻¹. The effect of vapor quality, inlet pressure, heat flux and mass flux on the heat transfer characteristic are discussed. The comparisons of the experimental data with the predicted value by existing correlations are analyzed. Zou et al. (2010) correlation shows the best accuracy with 24.1% RMS deviation among them. Moreover four frictional pressure drop methods are also chosen to compare with the experimental database.     

NH3 in-tube condensation heat transfer and pressure drop in a smooth tube

This paper presents an overview of the issues and new results for in-tube condensation of ammonia in horizontal round tubes. A new empirical correlation is presented based on measured NH₃ in-tube condensation heat transfer and pressure drop by Komandiwirya et al. [Komandiwirya, H.B., Hrnjak, P.S., Newell, T.A., 2005. An experimental investigation of pressure drop and heat transfer in an in-tube condensation system of ammonia with and without miscible oil in smooth and enhanced tubes. ACRC CR-54, University of Illinois at Urbana-Champaign] in an 8.1 mm aluminum tube at a saturation temperature of 35 °C, and for a mass flux range of 20–270 kg m⁻² s⁻¹. Most correlations overpredict these measured NH₃ heat transfer coefficients, up to 300%. The reasons are attributed to difference in thermophysical properties of ammonia compared to other refrigerants used in generation and validation of the correlations. Based on the conventional correlations, thermophysical properties of ammonia, and measured heat transfer coefficients, a new correlation was developed which can predict most of the measured values within ±20%. Measured NH₃ pressure drop is shown and discussed. Two separated flow models are shown to predict the pressure drop relatively well at pressure drop higher than 1 kPa m⁻¹, while a homogeneous model yields acceptable values at pressure drop less than 1 kPa m⁻¹. The pressure drop mechanism and prediction accuracy are explained though the use of flow patterns.     

过冷段翅片管换热器的试验研究

对过冷段翅片管换热器对空气源热泵冷热水机组系统性能的影响进行试验研究。过冷段翅片管换热器通过横向导热和强制对流换热可增大制冷剂液体过冷度，制热工况下，可使系统性能系数COP提高约19％，并有效降低翅片表面结霜。     

Assessment of condensation heat transfer correlations in the modelling of fin and tube heat exchangers

This is the second paper of a series that assesses the performance of a refrigeration system model by means of cycle parameters. In this case, the condensation temperature is the parameter to study and it is focused on fin and tube condensers. It also studies the influence of the heat transfer models on the estimation of this refrigeration cycle parameter and different correlations for the heat transfer coefficients have been implemented in order to characterise the heat transfer in the heat exchangers. The flow inside the heat exchangers is considered one-dimensional as in previous works. In the cycle definition, other submodels for all the cycle component have been taken into account to complete the system of equations that characterises the behaviour of the refrigeration cycle. This global system is solved by means of a Newton–Raphson algorithm and a known technique called SEWTLE is used to model the heat exchangers. Some experimental results are employed to compare the condensation temperatures provided by the numerical procedure and to evaluate the performance of each heat transfer coefficient. These experimental results correspond to an air-to-water heat pump and are obtained by using R-22 and R-290 as refrigerants.     

Assessment of boiling heat transfer correlations in the modelling of fin and tube heat exchangers

A new way to assess the performance of refrigeration system models is presented in this paper, based on the estimation of cycle parameters, such as the evaporation temperature which will determine the validity of the method. This paper is the first of a series which will also study the influence of the heat transfer coefficient models on the estimation of the refrigeration cycle parameters. It focuses on fin and tube evaporators and includes the dehumidification process of humid air. The flow through the heat exchanger is considered to be steady and the refrigerant flow inside the tubes is considered one-dimensional. The evaporator model is discretised in cells where 1D mass, momentum and energy conservation equations are solved by using an iterative procedure called SEWTLE. This procedure is based on decoupling the calculation of the fluid flows from each other assuming that the tube temperature field is known at each fluid iteration. Special attention is paid to the correlations utilised for the evaluation of heat transfer coefficients as well as the friction factor on the air and on the refrigerant side. A comparison between calculated values and measured results is made on the basis of the evaporation temperature. The experimental results used in this work correspond to an air-to-water heat pump and have been obtained by using R-22 and R-290 as refrigerants.     

Prediction of heat transfer correlations for compact heat exchangers

Zusammenfassung In der vorliegenden Arbeit werden zwei numerische Verfahren zur Bestimmung von empirischen Gleichungen in Kreuzstrom-Wärmeübertragern mit vergrößerter Oberfläche verglichen. Bei der ersten Methode wird nur eine Gleichung für den Wärmeübergangskoeffizienten auf der Gasseite gesucht, während der Wärmeübergangskoeffizient an der inneren Oberfläche des Rohres bekannt ist und nach den Gleichungen von Dittus-Boelter oder Gnielinski berechnet wird. Bei der zweiten Methode werden gleichzeitig Gleichungen für den Wärmeübergang sowohl auf der Gasseite als auch bei der Rohrströmung ermittelt.

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The following paper compares two numerical methods for determining correlations for heat transfer coefficients in cross-flow compact heat exchangers. In the first method, only the correlation for the air-side heat transfer coefficient is determined. The heat transfer coefficient on the tube-side is calculated using the Gnielinski or Dittus-Boelter correlations. In the second method, the heat transfer correlations both on the tube and air-side are determined simultaneously in order to predict the air-side heat transfer more accurately.

     

板换换热与压降关联式遗传算法参数辨识

针对板换的换热及压降关联式适用范围窄的缺点，在分析板换传热和压力损失原理的基础上，建立板式换热器分布参数模型，借鉴已有的换热和压降关联式，并以关联式中的系数为优化辨识变量，以换热器特性参数模拟值与试验值相对偏差为优化目标函数，采用遗传算法进行优化计算，获得待辨识参数的值，得到新的换热和压降关联式，通过与已有的较高精度关联式和试验数据的比较，证明所获得的关联式具有较高的精度，通过遗传算法参数辨识获得板换换热及压降关联式是一种行之有效的关联式获取方法。     

Performance of heat transfer and pressure drop in superconducting cable former

This study was performed of the heat transfer and the pressure drop in superconducting cable former of more realistic geometry. Liquid nitrogen passes through the former for cooling. Corrugated pipes are used as formers to ensure flexibility, and the ratio of pitch and depth of corrugation p/e is less than 5, which is out of the range of normal usage. Range of the test was p/e=1–15, e/D=0.039–0.118. The heat transfer and the pressure drop were proportional to the corrugation depth, which is the same with the results reported by previous researchers. But the effect of pitch was different from the results of the range p/e>10. The heat transfer and the pressure drop had the maximum values on the range of p/e=5–10. Based on the numerical results, discussion was made on the design of superconducting cable former.     

Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators

We investigate an alternative tube-fin evaporator design (accelerated flow evaporator, AFE) in which the air-side local heat transfer coefficient is increased due to a progressive reduction of the free-flow area. For a given heat transfer rate, this enhancement is expected to partially compensate the decrease in surface area, which reduces the evaporator material cost. The air-side thermal-hydraulic behavior of nine AFEs was determined experimentally, and a calculation method that relies on j and f correlations for plain tube-fin heat exchangers and on mass and momentum balances has been proposed. The method enables the calculation of the by-pass fraction associated with the air stream through the clearance between the tube bank and the outer edge of the fins. The agreement between the model, which introduces no additional fitting parameters, and the experiments is within ±10% for all heat transfer data and ±15% for the majority of the pressure drop data.     

电冰箱用微通道冷凝器制冷剂侧传热与压降特性试验研究

建立电冰箱换热器试验台,对具有百叶窗翅片的微通道冷凝器制冷剂侧的传热和压降进行测试。结果表明:随着制冷剂质量流速的增加,冷凝器换热量、换热系数及制冷剂流动压降均增大,在冷凝压力为1.46MPa,制冷剂质量流速从90 kg/(m~2·s)增加到150 kg/(m~2·s)时,换热量、换热系数和压降分别增加63%,116%和166%;随着冷凝压力的升高,换热量增大,换热系数减小,在制冷剂质量流速为150 kg/(m~2·s)时,冷凝压力为1.46 MPa与冷凝压力为1.16 MPa相比,换热量增加12%,换热系数降低39%。     

Heat transfer and pressure drop for boiling nitrogen flowing in a horizontal tube: 2. Pressure drop

The pressure drop of boiling two-phase nitrogen flow in a smooth horizontal tube has been studied experimentally. The results show in principle the well-known dependence of the local pressure drop from the vapour quality, the mass flow rate, and the heat flux.A comparison of the measured frictional pressure drop shows a sufficient agreement with predicted values using published correlations. The accelerational pressure gradient can also be predicted taking into account a suitable void fraction relationship.     

Condensing two-phase pressure drop and heat transfer coefficient of propane in a horizontal multiport mini-channel tube: Experimental measurements

This article reports the condensing flow heat transfer coefficient and pressure drop results of propane (R290) flowing through a square section horizontal multiport mini-channel tube made of aluminium having an internal diameter of 1.16 mm and a condensing length of 259 mm. Pressure drop and two phase flow experiments were performed at saturation temperatures of 30, 40 and 50 °C. Heat flux was varied from 15.76 to 32.25 kWm⁻² and mass velocity varied from 175 to 350 kg m⁻² s⁻¹. The results show that the two-phase friction pressure gradient increases with the increase of mass velocity and vapour quality and with the decrease of saturation temperature. The heat transfer coefficients showed to increase with increases of vapour quality and mass velocity while increases of saturation temperature were observed to reduce heat transfer coefficient. The two phase frictional pressure drop correlations of Sun and Mishima and Agarwal and Garimella, and the two-phase flow heat transfer correlations of Koyama et al. and Wang et al. predicted well the experimental results.     

An experimental study on heat transfer and pressure drop characteristics of carbon dioxide during gas cooling process in a horizontal tube

The heat transfer coefficient and pressure drop during gas cooling process of CO₂ (R744) in a horizontal tube were investigated experimentally. The experiments are conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and a gas cooler (test section). The water loop consists of a variable speed pump, an isothermal tank, and a flow meter. The refrigerant, circulated by the variable-speed pump, condenses in the inner tube while water flows in the annulus. The gas cooler of tube diameter is 6000 mm in length, and it is divided into 12 subsections.The pressure drop of CO₂ in the gas cooler shows a relatively good agreement with those predicted by Blasius's correlation. The local heat transfer coefficient of CO₂ agrees well with the correlation by Bringer–Smith. However, at the region near Pseudo-critical temperature, the experiments indicate higher values than the Bringer–Smith correlation. Based on the experimental data presented in this paper, a new correlation to predict the heat transfer coefficient of supercritical CO₂ during in-tube cooling has been developed. The majority of the experimental values are within 18% of the values predicted by the new correlation.