A New Model for Predicting Flow Boiling Heat Transfer Coefficients in Horizontal Microfin Tubes

2016 ◽  
Author(s):  
Reem Merchant ◽  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Experimental Database ◽  
New Model ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Wide Range ◽  
Microfin Tubes

The objective of the current work is to present a new correlation for predicting heat transfer coefficients (HTCs) for flow boiling in horizontal microfin tubes. Correlations to predict HTCs have been proposed by numerous authors such as Yu et al., Thome et al., Cavallini et al., Yun et al., Chamra and Mago, Wu et al., and other researchers. The correlations proposed are semi-empirical due to the difficulties associated with modeling the physics of flow boiling in microfin tubes. The above correlations are based on smooth tube flow boiling correlations which are modified to capture the effect of the inner grooves in the microfin tubes on the boiling process. In a previous work, it has been demonstrated that no single correlation can reasonably predict the flow boiling HTCs over a wide range of operating conditions and tube geometric parameters (Merchant and Mehendale). A new model has been proposed and validated using an experimental database of 1576 points from published literature. For the full dataset, the new correlation has X30% of 67.3%, compared to Cavallini et al. and Wu et al. with X30% of 44.2% and 40.6% respectively. The performance of the new model for tube diameters less than and greater than 5 mm has also been discussed for halogenated refrigerants and CO2.

Flow Boiling of R134a and R134a/Propane Mixtures at Low Saturation Temperatures Inside a Plain Horizontal Tube

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
A. Rabah ◽  
S. Kabelac
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Azeotropic Point ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Maximum Decrease

Local heat transfer coefficients for flow boiling of pure 1,1,1,2-tetrafluoroethane (R134a) and binary mixtures of propane (R290) and R134a were measured. The experimental setup employed a vapor heated plain horizontal tube (di=10mm, do=12mm, L=500mm). The measurements covered a wide range of saturation temperatures (233≤Ts≤278K), mass fluxes (100≤ṁ≤300kg∕m2s), qualities (0≤ẋ≤1), and concentrations (0≤z̃≤0.65). In the zeotropic region of R134a/R290 mixtures, the measured local heat transfer coefficient was found to show a maximum decrease by a factor of 2 relative to that for pure R134a. At the azeotropic point (65% R290), it was found to increase by a factor of 1.2. The measured local heat transfer coefficients for both R134a and R134a/R290 were compared with a number of correlations.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with to the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Critical Analysis of the Available Ammonia Horizontal In-Tube Flow Boiling Heat Transfer Correlations for Liquid Overfeed Evaporators

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
N. Ablanque ◽  
J. Rigola ◽  
C. Oliet ◽  
J. Castro
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Boiling ◽  
Critical Examination ◽  
Data Sets ◽  
Transfer Coefficients ◽  
Experimental Database ◽  
Heat Transfer Coefficients ◽  
Tube Type ◽  
Heat Transfer Correlations

The aim of this work is to present a critical examination of both the available experimental data and the performance of the available heat transfer correlations for oil-free ammonia horizontal in-tube boiling at fin-and-tube-type air-to-refrigerant liquid overfeed evaporation conditions. First, a selection and comparison of the experimental database found in the open literature at the mentioned working conditions is presented. Subsequently, after a short description of the most relevant heat transfer correlations, and in accordance with the selected data, a detailed analysis of the performance of each correlation is carried out. Results show an important divergence between the experimental data sets and conclude that the presently available correlations show considerable discrepancies in heat transfer coefficients within the selected conditions.

Flow Boiling in a Short Narrow Gap Channel

2013 ◽  
Author(s):  
D. D. Janssen ◽  
J. M. Dixon ◽  
S. J. Young ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Small Scale ◽  
Narrow Gap ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
O 10

Heat transfer coefficients in sub-cooled flow boiling in symmetrically heated narrow gap channels are reported at power densities of 1 kW/cm3 and greater. A pair of parallel ceramic resistance heaters in a nearly adiabatic housing forms the flow passage with length-to-gap ratios of 16:1 and 34:1. Water, Novec™ 7200 and 7300 are used as the heat transfer fluids at a mass flux of 100 to 1000 kg/m2s. Reynolds numbers range from ∼200 to ∼5600, Weber numbers range from ∼0.75 to ∼173, and boiling numbers from O(10−4) to O(10−2). Flow regimes span single-phase convection to nucleate flow boiling depending on mass flux and inlet sub-cooling, and exit quality can reach 40% in some cases. Results include overall two-phase heat transfer coefficients, wall temperature, exit quality and coefficient of performance. The initiation of flow boiling demonstrates that mean heater temperatures can be maintained below 95 °C over a wide range of power density and up to and exceeding 1 kW/cm3. A super position principle is suggested as an analytical framework to estimate exit quality and heat transfer coefficients. Highly favorable coefficients of performance across the data set indicate that the pumping power penalty within the heated zone is very small. Thus convective boiling in which the mechanism is nucleate boiling appears to hold the greatest potential to increase heat transfer coefficients, especially in small scale, inter-chip cooling strategies.

The Heat Transfer Characteristics of a 16 kW Steam Driven Double Effect Absorption Chiller

2008 ◽  
Author(s):  
Hongxi Yin ◽  
David H. Archer ◽  
Ming Qu
Keyword(s):  
Heat Transfer ◽  
Double Effect ◽  
Operating Conditions ◽  
Saturated Steam ◽  
Absorption Chiller ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Computational Performance ◽  
Partial Load ◽  
Wide Range

A 16 kW (4.6 refrigerant tons) steam driven, double effect, parallel flow absorption chiller has been designed, manufactured, and installed in the Intelligent Workplace (IW) of Carnegie Mellon University (CMU). This chiller is driven by 6 bar saturated steam and uses a 57% LiBr-H2O sorbent. It is the smallest absorption chiller available in the existing market. The absorption chiller consists of five major and four minor heat transfer components. The manufacturer of the chiller has provided information on detailed configuration and dimensions of these components to support the calculation of their heat transfer areas, A’s, and the estimation of overall heat transfer coefficients, U’s. A steady state computational performance model for the chiller has been developed based on the applicable scientific and engineering principles. The model has been used to calculate all chiller internal working conditions and to analyze the experimental data over a wide range of operating conditions. Heat transfer coefficients inside and outside of the tubes making up the chiller’s heat transfer components have been estimated by published empirical correlations. The product of the overall heat transfer coefficient and the surface contact area, UA’s, for the 5 major heat transfer components have been estimated using the chiller model and measured performance data. Significant variations, 30%, in this parameter are observed under partial load, reduced flow conditions. Deviations between the experimental measurements and the model solutions have been analyzed to evaluate the model accuracy. At design operating conditions, the overall deviation is about 6%.

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