Heat Transfer Analysis of Falling Film Evaporation on a Horizontal Elliptical Tube

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Saeid Jani ◽  
Meysam Amini
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Transfer Coefficient ◽  
Free Surface ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Heat Transfer Analysis ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Constant Wall Temperature

Heat and mass transfer analysis of falling liquid film over a heated horizontal elliptical tube used in desalination systems are investigated. The heat transfer analysis is based on the energy integral formulation with constant wall temperature. Thermal conditions at free surface of the liquid falling film are assumed to be subcooled and saturated, and the effects of surface tension have been considered. The effects of boiling and ripple at the film free surface have been ignored. Heat transfer zoning is considered as the three distinct regions, namely, the jet impingement region, the thermal developing region, and the fully developed region. Extensive analytical study is performed on the thermal hydraulic behavior of the three above mentioned regions, and correlations for both of the film and thermal boundary layer thicknesses, as well as the local and average heat transfer coefficients, have been derived. The results show that the effects of surface tension on heat transfer coefficient is nearly negligible. Based on the presented results, it can be emphasized that the overall heat transfer coefficient increases by increasing the ellipticity of the tube, implying that the elliptical tubes possess more advantages over circular tubes in desalination systems. Comparisons of the analytical results with the existing experimental data verify the validation of the present study.

Three-Dimensional Transient Heat Conduction Equation Solution for Accurate Quantification of Heat Transfer Coefficient in Transient Liquid Crystal Experiments

2019 ◽  
Author(s):  
Shoaib Ahmed ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Conduction Model

Abstract Liquid crystal thermography and infrared thermography techniques are typically employed to measure detailed surface temperatures, where local heat transfer coefficient (HTC) values are calculated by employing suitable conduction models. One such practice, which is very popular and easy to use, is the transient liquid crystal thermography using one-dimensional semi-infinite conduction model. In these experiments, a test surface with low thermal conductivity and low thermal diffusivity (e.g. acrylic) is used where a step-change in coolant air temperature is induced and surface temperature response is recorded. An error minimization routine is then employed to guess heat transfer coefficients of each pixel, where wall temperature evolution is known through an analytical expression. The assumption that heat flow in the solid is essentially in one-dimension, often leads to errors in HTC determination and this error depends on true HTC, wall temperature evolution and HTC gradient. A representative case of array jet impingement under maximum crossflow condition has been considered here. This heat transfer enhancement concept is widely used in gas turbine leading edge and electronics cooling. Jet impingement is a popular cooling technique which results in high convective heat rates and has steep gradients in heat transfer coefficient distribution. In this paper, we have presented a procedure for solution of three-dimensional transient conduction equation using alternating direction implicit method and an error minimization routine to find accurate heat transfer coefficients at relatively lower computational cost. The HTC results obtained using 1D semi-infinite conduction model and 3D conduction model were compared and it was found that the heat transfer coefficient obtained using the 3D model was consistently higher than the conventional 1D model by 3–16%. Significant deviations, as high as 8–20% in local heat transfer at the stagnation points of the jets were observed between h1D and h3D.

Performances of falling film evaporators on whole milk and a comparison with performance on skim milk

1997 ◽  
Vol 64 (1) ◽  
pp. 57-67 ◽  
Author(s):  
R. SELWYN JEBSON ◽  
HONG CHEN
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Skim Milk ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Liquid Loading ◽  
Heat Transfer Coefficients ◽  
Whole Milk ◽  
The Heat Transfer Coefficient

The performances of falling film evaporators used in the New Zealand dairy industry for concentrating whole milk were evaluated by determining kg steam used/kg water evaporated, and the heat transfer coefficient of each pass in the evaporators. A specially written computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·0 kW/m2K, and the steam consumption from 0·10 to 0·39 kg steam/kg evaporation, depending on the number of effects. The steam consumptions for whole and skim milk were similar. The momentum of the vapours passing down the tubes, the temperature difference across the tubes, the viscosity of the feed and the liquid loading were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented, and other factors likely to have an influence on the performance are discussed. The correlation is compared with that obtained for skim milk.

Heat transfer characterization under radial jet and falling film induced rewetting

Kerntechnik ◽  
2021 ◽  
Vol 86 (5) ◽  
pp. 325-337
Author(s):  
M. Kumar ◽  
D. Mukhopadhyay
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Jet Impingement ◽  
Falling Film ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Fuel Pin

Abstract Empirical correlations are developed for rewetting velocity and maximum heat transfer coefficient during rewetting phase of single hot vertical Fuel Pin Simulator (FPS) by using radial jet impingement and falling film. Emergency Core Cooling System (ECCS) has been designed for Advance Heavy water Reactor (AHWR) to rewet the hot fuel pin under the loss of coolant accident. Coolant injection takes place from a water rod which is located at the center of the fuel bundle in form of jets to rewet hot surface of fuel pin under loss of coolant accident. This kind of design to reflood the fuel bundle is different than bottom and top spray reflooding practiced in PWR and BWR type of nuclear reactors. There are two different kinds of rewetting found during radial jet induced cooling. The first one is due to radial jet impingement and the second one is due to falling film which is below the jet impingement point. Rewetting velocity has been predicted along the length of fuel pin due to radial jet impingement cooling. Temperature of FPS has been varied from 400°C to 700°C with help of different powers supply, simulating decay heat of reactor. A variation of coolant radial jet mass flow rate is from 0.5 lpm to 1.8 lpm. It is considered during ECCS injection. It has been observed from the experiments that rewetting velocity decreases with increasing the clad surface temperature and increases with increasing the coolant mass flow rate. The rewetting velocity in falling film is found to be nearly 1.8 times higher than rewetting velocity predicted in circumferential direction. Further, it is found that maximum heat transfer coefficient increases with increasing the radial jet coolant mass flow rate. The maximum heat transfer coefficient in case of radial jet impingement is found to be nearly 1.5 times the falling film rewetting. Developed correlation predicts the maximum heat transfer coefficient with experimental data well within the error band of ±10%.

The Concept of Adiabatic Heat Transfer Coefficient and its Application to Turbomachinery

2013 ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients ◽  
Thermal Boundary Conditions ◽  
Critical Components

Typical turbomachinery flows are too complex to be predicted by analytical solutions alone. Therefore numerous correlations and test data are used in conjunction with numerical tools in order to design thermally critical components. This approach can be problematic because these correlations and data are not fully independent of the boundary conditions applied. The heat transfer coefficients obtained are not only dependent on the aerodynamics of the flow but also on the thermal boundary layer created along the surface. The adiabatic heat transfer coefficient is the only one which is independent of the thermal boundary conditions, as long as the energy equation can be considered linear with respect to the temperature. However, a proper prediction of the surface temperature cannot be obtained with the adiabatic heat transfer coefficient alone. This paper first reviews the concept of adiabatic heat transfer coefficient and its application to turbomachinery flows. Later, a concept is introduced to allow interchanging between different definitions of heat transfer coefficient and boundary conditions, i.e. constant heat flux or constant wall temperature. Finally, a typical configuration for measuring the adiabatic heat transfer coefficient on a turbine blade and the conversion to other definitions of heat transfer coefficient is presented and evaluated. It is shown that with the technique presented here even small deficiencies of some experiments can be compensated for.

Optimize the Evaporating Heat Transfer Coefficient of Refrigeration System Using Nano Fluid

2014 ◽  
Vol 592-594 ◽  
pp. 951-955 ◽  
Author(s):  
T. Coumaressin ◽  
K. Palaniradja ◽  
K. Velmurugan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Horizontal Tube ◽  
Hot Water ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Nano Fluid

Improving heat transfer characteristics in refrigeration and air conditioning systems has been intensively studied by many investigators. In the present work the effect of using CuO-R134a in the vapour compression system on the evaporating heat transfer coefficient is investigated by CFD heat transfer analysis using the FLUENT software. An experimental test rig is designed for this purpose. The test section is a horizontal tube in the tube heat exchanger made from copper. The refrigerant is evaporated inside an inner copper tube and the heat load is provided from hot water that passing in an annulus surrounding the inner tube. Heat transfer coefficients were evaluated using FLUENT for heat flux ranged from 10 to 40 kW/m2, using nanoCuO concentrations ranged from 0.05 to 1% and particle size from 15 to 70 nm. The measurements indicated that for a certain nanoconcentration as heat flux or mass flux increases the evaporating heat transfer coefficient increases and also that the evaporating heat transfer coefficient increases with increasing nanoCuO concentrations up to certain value then decreases. The obtained evaporating heat transfer coefficient result have been optimized at its maximum value for the best CuOnano particles concentration in R134a refrigerant.

A New Model for Predicting Falling Film Evaporation Heat Transfer Coefficients

2016 ◽  
Author(s):  
Apurva Baruah ◽  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Design ◽  
Falling Film ◽  
Transfer Coefficients ◽  
New Model ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Falling Film Evaporation

For falling film evaporation, the most important considerations from a thermal design standpoint are the onset of film dryout and the local heat transfer coefficients in partially and fully wet conditions. Previous methods developed for the prediction of (i) pool boiling heat transfer coefficient (HTCs), (ii) the onset of dryout, and (iii) falling film heat transfer coefficient consist of empirical, tube-specific constants which are quite difficult, if not impossible, to determine, and hence have limited utility. New methods to predict these parameters have been developed in the present study, which eliminate the special constants by incorporating dimensionless parameters that capture the effect of refrigerant properties and macro-level tube-geometry. The predictions of the new model have been found to be better than or comparable to those of the best available existing models.

Performances of falling film evaporators

1991 ◽  
Vol 58 (1) ◽  
pp. 29-38 ◽  
Author(s):  
R. Selwyn Jebson ◽  
Mani Iyer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Skim Milk ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Steam Consumption ◽  
Heat Transfer Coefficients ◽  
Whole Milk ◽  
The Heat Transfer Coefficient

SummaryThe performances of falling film evaporators used in the New Zealand dairy industry for concentrating skim milk, whole milk and buttermilk were evaluated by determining (1) the kg steam used per kg water evaporated, and (2) the heat transfer coefficient of each pass in the evaporators. A computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·2 kW/m2 per °C and the steam consumption from 0·4 to 0·09 kg steam/kg evaporation. The viscosity of the feed and the momentum of the vapours passing down the tubes were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented. Other factors likely to have an influence on the performance are discussed.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

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