scholarly journals Heat Exchanger Modelling for Solar Organic Rankine Cycle

2014 ◽  
Vol 09 (1) ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Boiling ◽  
Thermal Power ◽  
Organic Rankine Cycle ◽  
Nucleate Boiling ◽  
Heat Transfer Fluid ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Tube Heat Exchanger

The paper presents work done on the development of a heat exchanger model suitable for incorporation into a low temperature solar thermal power cycle. In particular it presents the mathematical model comprising heat transfer, mass transfer, and convective heat transfer coefficients, and velocity and pressure drop correlations for single and two phase flows. The preliminary evaporator model is based on a counter flow double pipe configuration; the flow boiling process incorporates both convective and nucleate boiling. The shell side heat transfer fluid consists of ethylene glycol at 50 % concentration; the tube side fluid flow is modelled on four candidate working fluids pre-selected from previous stages of the research study. The evaporator model is implemented on the engineering equation solver platform; following on the computer simulation results a further proposal is made for conversion of the model design into a feasible shell-and-tube heat exchanger. The outputs of the model study are in the form of the rate of heat exchange, size and type of the heat exchanger, whilst ensuring that the pressure drops and fluid velocities are within acceptable limits.

scholarly journals Heat transfer rates in hot shell, cold tube inclined baffled small shell, and tube heat exchanger using CFD and experimental approach

2021 ◽  
Vol 9 (4B) ◽  
Author(s):  
Devanand D. Chillal ◽  
◽  
Uday C. Kapale ◽  
N.R. Banapurmath ◽  
T. M. Yunus Khan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Liquid Flow ◽  
Cfd Analysis ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
Shell And Tube ◽  
Cold Liquid

The work presented is an effort to realize the changes occurring for convective coefficients of heat transfer in STHX fitted with inclined baffles. Effort has been undertaken using Fluent, a commercially available CFD code ona CAD model of small STHX with inclined baffles with cold liquid flowing into the tubes and hot liquid flowing in the shell. Four sets of CFD analysis have been carried out. The hot liquid flow rate through shell compartments varied from 0.2 kg/sec to 0.8 kg/sec in steps of 0.2 kg/sec, while keeping the cold liquid flow condition in tube at 0.4 kg/sec constant. Heat transfer rates, compartment temperatures, and overall heat transfer coefficients, for cold liquid and hot liquid, were studied. The results given by the software using CFD approach were appreciable and comparatively in agreement with the results available by the experimental work, which was undertaken for the same set of inlet pressure conditions, liquid flow rates, and inlet temperatures of liquid for both hot and cold liquids. The experimental output results were also used to validate the results given by the CFD software. The results from the CFD analysis were further used to conclude the effect of baffle inclination on heat duty. The process thus followed also helped realize the effects of baffle inclination on convective heat transfer coefficient of the liquid flow through the shell in an inclined baffle shell and tube heat exchanger. The temperature plots for both cold and hot liquid were also generated for understanding the compartmental temperature distributions inclusive of the inlet and outlet compartments. The heat duty for a heat exchanger has been found to increase with the increase in baffle inclinations from zero degree to 20 degrees. Likewise, the convective heat transfer coefficients have also been found to increase with the increase in baffle inclinations.

Comparison of 30 Boiling and Condensation Correlations for Two-Phase Flows in Compact Plate-Fin Heat Exchangers

2017 ◽  
Author(s):  
Wenhai Li ◽  
Ken Alabi ◽  
Foluso Ladeinde
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase Flows ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Heat Exchanger Design ◽  
Micro Channels ◽  
Vertical Tubes

Over the years, empirical correlations have been developed for predicting saturated flow boiling [1–15] and condensation [16–30] heat transfer coefficients inside horizontal/vertical tubes or micro-channels. In the present work, we have examined 30 of these models, and modified many of them for use in compact plate-fin heat exchangers. However, the various correlations, which have been developed for pipes and ducts, have been modified in our work to make them applicable to extended fin surfaces. The various correlations have been used in a low-order, one-dimensional, finite-volume type numerical integration of the flow and heat transfer equations in heat exchangers. The NIST’s REFPROP database [31] is used to account for the large variations in the fluid thermo-physical properties during phase change. The numerical results are compared with Yara’s experimental data [32]. The validity of the various boiling and condensation models for a real plate-fin heat exchanger design is discussed. The results show that some of the modified boiling and condensation correlations can provide acceptable prediction of heat transfer coefficient for two-phase flows in compact plate-fin heat exchangers.

scholarly journals Thermal-Hydraulic Studies on the Shell-and-Tube Heat Exchanger with Minijets

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3276 ◽  
Author(s):  
Jan Wajs ◽  
Michał Bajor ◽  
Dariusz Mikielewicz
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Waste Heat ◽  
Experimental Studies ◽  
Convection Heat Transfer ◽  
Test Facility ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Shell And Tube

In this paper a patented design of a heat exchanger with minijets, with a cylindrical construction is presented. It is followed by the results of its systematic experimental investigations in the single-phase convection heat transfer mode. Based on these results, validation of selected correlations (coming from the literature) describing the Nusselt number was carried out. An assessment of the heat exchange intensification level in the described heat exchanger was done through the comparison with a shell-and-tube exchanger of a classical design. The thermal-hydraulic characteristics of both units were the subjects of comparison. They were constructed for the identical thermal conditions, i.e., volumetric flow rates of the working media and the media temperatures at the inlets to the heat exchanger. The experimental studies of both heat exchangers were conducted on the same test facility. An increase in the heat transfer coefficients values for the minijets heat exchanger was observed in comparison with the reference one, whereas the generated minijets caused greater hydraulic resistance. Experimentally confirmed intensification of heat transfer on the air side, makes the proposed minijets heat exchanger application more attractive, for the waste heat utilization systems from gas sources.

Experimental Investigation of Heat Transfer Enhancement of Shell and Tube Heat Exchanger Using SnO2-Water and Ag-Water Nanofluids

2019 ◽  
Vol 12 (4) ◽  
Author(s):  
S. V. Sridhar ◽  
R. Karuppasamy ◽  
G. D. Sivakumar
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer Coefficient ◽  
Two Phase ◽  
Tube Heat Exchanger ◽  
Shell And Tube

Abstract In this investigation, the performance of the shell and tube heat exchanger operated with tin nanoparticles-water (SnO2-W) and silver nanoparticles-water (Ag-W) nanofluids was experimentally analyzed. SnO2-W and Ag-W nanofluids were prepared without any surface medication of nanoparticles. The effects of volume concentrations of nanoparticles on thermal conductivity, viscosity, heat transfer coefficient, fiction factor, Nusselt number, and pressure drop were analyzed. The results showed that thermal conductivity of nanofluids increased by 29% and 39% while adding 0.1 wt% of SnO2 and Ag nanoparticles, respectively, due to the unique intrinsic property of the nanoparticles. Further, the convective heat transfer coefficient was enhanced because of improvement of thermal conductivity of the two phase mixture and friction factor increased due to the increases of viscosity and density of nanofluids. Moreover, Ag nanofluid showed superior pressure drop compared to SnO2 nanofluid owing to the improvement of thermophysical properties of nanofluid.

Two-Phase Pressure Drop and Boiling Heat Transfer in a Single Horizontal Microchannel

2006 ◽  
Author(s):  
Cheol Huh ◽  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Local Flow ◽  
Heat Transfer Coefficients ◽  
Phase Pressure

With a single microchannel and a series of microheaters made with MEMS technique, two-phase pressure drop and local flow boiling heat transfer were investigated using deionized water in a single horizontal rectangular microchannel. The test microchannel has a hydraulic diameter of 100 μm and length of 40 mm. A real time observation of the flow patterns with simultaneous measurement are made possible. Tests are performed for mass fluxes of 90, 169, and 267 kg/m2s and heat fluxes of from 100 to 600 kW/m2. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient are evaluated and the effects of heat flux, mass flux, and vapor qualities on flow boiling are studied. Both the evaluated experimental data are compared with existing correlations. The experimental heat transfer coefficients are nearly independent on mass flux and the vapor quality. Most of all correlations do not provide reliable heat transfer coefficients predictions with vapor quality and prediction accuracy. As for two-phase pressure drop, the measured pressure drop increases with the mass flux and heat flux. Most of all existing correlations of two-phase frictional pressure gradient do not predict the experimental data except some limited conditions.

Experimental Study on Flow Boiling Heat Transfer in an Extremely Small Tube

2006 ◽  
Author(s):  
Haruhiko Ohta ◽  
Koichi Inoue ◽  
Yuichiro Shimada
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
Small Tube

Flow boiling heat transfer in a single small tube is investigated by using FC72 as a working fluid. The heat transfer coefficients are measured in the ranges of heat flux 2–24kW/m2 and mass velocity 100–400kg/m2s under the condition of near atmospheric pressure. Test tube, made of stainless steel, has an inner diameter of 0.51mm and a heated length of 200mm. The tube is located horizontally in a vacuum chamber to reduce the heat loss and to minimize the time to obtain data regarded as that of steady state. In the single-phase region, heat transfer coefficients due to forced convection are in good agreement with the values from the conventional theories. In the saturated region, measured heat transfer characteristics are quite different depending on whether the test liquid is deaerated or not deaerated before the experiments. By using deaerated liquid, three different heat transfer regimes are observed: In the first regime, the heat transfer is dominated by nucleate boiling in low vapor quality, and the heat transfer is deteriorated or enhanced depending on the channel confinement and heat flux. In the second regime, the heat transfer is dominated by two-phase forced convection in moderate quality as is well known for the tubes of normal size. In the third regime, the heat transfer is dominated again by two-phase forced convection, but is deteriorated in high quality. One or two regimes can disappear or become unclear depending on the conditions of flow and heating. The effects of vapor quality and mass velocity on the heat transfer characteristics due to two-phase forced convection in the moderate vapor quality are clarified in the experimental ranges tested. And a reason for the gradual heat transfer deterioration observed in high quality is discussed based on the liquid-vapor behaviors inherent in small diameter tubes.

Two-Phase Pipe Quenching Correlations for Liquid Nitrogen and Liquid Hydrogen

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
S. R. Darr ◽  
J. W. Hartwig ◽  
J. Dong ◽  
H. Wang ◽  
A. K. Majumdar ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Nitrogen ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Liquid Hydrogen ◽  
Two Phase ◽  
Cryogenic Flow ◽  
Two Phase Heat Transfer

Recently, two-phase cryogenic flow boiling data in liquid nitrogen (LN2) and liquid hydrogen (LH2) were compared to the most popular two-phase correlations, as well as correlations used in two of the most widely used commercially available thermal/fluid design codes in Hartwig et al. (2016, “Assessment of Existing Two Phase Heat Transfer Coefficient and Critical Heat Flux on Cryogenic Flow Boiling Quenching Experiments,” Int. J. Heat Mass Transfer, 93, pp. 441–463). Results uncovered that the correlations performed poorly, with predictions significantly higher than the data. Disparity is primarily due to the fact that most two-phase correlations are based on room temperature fluids, and for the heating configuration, not the quenching configuration. The penalty for such poor predictive tools is higher margin, safety factor, and cost. Before control algorithms for cryogenic transfer systems can be implemented, it is first required to develop a set of low-error, fundamental two-phase heat transfer correlations that match available cryogenic data. This paper presents the background for developing a new set of quenching/chilldown correlations for cryogenic pipe flow on thin, shorter lines, including the results of an exhaustive literature review of 61 sources. New correlations are presented which are based on the consolidated database of 79,915 quenching points for a 1.27 cm diameter line, covering a wide range of inlet subcooling, mass flux, pressure, equilibrium quality, flow direction, and even gravity level. Functional forms are presented for LN2 and LH2 chilldown correlations, including film, transition, and nucleate boiling, critical heat flux, and the Leidenfrost point.

Investigation of Two Phase Heat Transfer Coefficients of Cryogenic Mixed Refrigerants

2013 ◽  
Author(s):  
Seungwhan Baek ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Two Phase Heat Transfer

Mixed Refrigerant Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multiphase and multi-component fluid in cryogenic temperature range is necessarily required in the heat exchanger design of MR-JT refrigerator, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of mixed refrigerant are measured in a microchannel heat exchanger. Printed Circuit Heat Exchanger (PCHE) has been developed as a compact microchannel heat exchanger and used in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.

Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Leyuan Yu ◽  
Aritra Sur ◽  
Dong Liu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Instabilities ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer

Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations.

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