The Conductance Ratio Method for Off-Design Heat Exchanger Modeling and its Impact on an sCO2 Recompression Cycle

2017 ◽  
Author(s):  
Francesco Crespi ◽  
David Sánchez ◽  
Kevin Hoopes ◽  
Brian Choi ◽  
Nicole Kuek
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Ratio Method ◽  
Limited Information ◽  
Transfer Coefficients ◽  
Design Performance ◽  
Conductance Ratio ◽  
The Impact

This paper presents a method to evaluate the off-design performance of a heat exchanger without specifying detailed heat exchanger geometry. Presently, off-design heat exchanger performance evaluation is often done by assuming one of the terms in a lumped volume approach is constant (such as UA, temperature difference, ε etc.) or by producing a draft heat exchanger geometry to evaluate the local heat transfer coefficients in off-design operation. As opposed to these approaches, the method presented in this paper manages to accurately predict off-design heat exchanger performance with very limited information. The method relies on a single parameter beyond the design operating conditions, namely the conductance ratio which is the product of heat transfer coefficient and area on both sides of the heat exchanger. The method is particularly powerful as it allows for the exploration of different off-design scenarios for a given on-design operating point. The paper presents a theoretical introduction of the method along with a validation using data provided by BMPC and Alfa Laval for different types of heat exchangers and working fluids, including supercritical CO2. The method is then used to model the off-design performance of a simple recuperated sCO2 cycle, showing its ability to capture the off-design performance of a heat exchanger without specifying its detailed geometry and the impact of conductance ratio on off-design cycle performance.

Thermal–Hydraulic Performance Analysis of a Convergent Double Pipe Heat Exchanger

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Ahmed T. Al-Sammarraie ◽  
Kambiz Vafai
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Hydraulic Performance ◽  
Operating Conditions ◽  
Contraction Ratio ◽  
Wide Range ◽  
Prandtl Numbers ◽  
Double Pipe ◽  
The Impact ◽  
Pipe Heat

The present investigation proposes an innovative convergent double pipe heat exchanger (C-DPHE). A two-dimensional (2D) axisymmetric heat transfer model with counterflow is employed to analyze the thermal and hydraulic performance of this configuration numerically. The impact of convergence in the flow direction, using a wide range of contraction ratio (Cr), is explored. The effect of Reynolds and Prandtl numbers on the flow and heat transfer is addressed, as well. The model results were validated with available data from the literature, and an excellent agreement has been confirmed. In general, the findings of the present study indicate that increasing the contraction ratio increases heat transfer and pressure drop in the C-DPHE. Moreover, this configuration has a prominent and sustainable performance, compared to a conventional double pipe heat exchanger (DPHE), with an enhancement in heat transfer rate up to 32% and performance factor (PF) higher than one. Another appealing merit for the C-DPHE is that it is quite effective and functional at low Reynolds and high Prandtl numbers, respectively, since no high-operating pumping power is required. Further, the optimal operating conditions can be established utilizing the comprehensive information provided in this work.

scholarly journals Performance Evaluation of Wire Cloth Micro Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 715 ◽  
Author(s):  
Hannes Fugmann ◽  
Sebastian Martens ◽  
Richard Balzer ◽  
Martin Brenner ◽  
Lena Schnabel ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Fluid Dynamic ◽  
Relative Difference ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Hydraulic Simulation ◽  
Pressure Drops ◽  
Wire Cloth ◽  
Good Agreement

The purpose of this study is to validate a thermal-hydraulic simulation model for a new type of heat exchanger for mass, volume, and coolant/refrigerant charge reduction. The new heat exchanger consists of tubes with diameters in the range of 1 m m and wires in the range of 100 m , woven together to form a 200 × 200 × 80 m m 3 wire cloth heat exchanger. Performance of the heat exchanger has been experimentally evaluated using water as inner and air as outer heat transfer medium. A computational thermal and fluid dynamic model has been implemented in OpenFOAM®. The model allows variation of geometry and operating conditions. The validation of the model is based on one single geometry with an opaque fabric and air-side velocities between 1 and 7 m / s . The simulated and measured pressure drops are found to be in good agreement with a relative difference of less than 16%. For the investigated cases, the effective heat transfer coefficients are in very good agreement (less than 5%) when adapting the contact resistance between tubes and wires. The numerical model describes the fluid flow and heat transfer of the tested heat exchanger with adequate precision and can be used for future wire cloth heat exchanger dimensioning for a variety of applications.

The Impact of Base Metal on the Thermal-Hydraulic Performance of Metal Foam Heat Exchanger for Cooling and Dehumidification Applications

2017 ◽  
Author(s):  
Kashif Nawaz ◽  
Anthony M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Base Metal ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Metal Foam ◽  
Operating Conditions ◽  
Copper Metal ◽  
The Impact

In the wake of utilization of novel materials in various thermal applications open cell metal foams have received attention due to their inherent properties such as large surface area to volume ratio and higher thermal conductivity. Additionally, complex tetradecahedron structure promotes mixing and makes them a good candidate for heat transfer applications. In this paper, a relative comparison has been made between the thermal-hydraulic performance of aluminum and copper metal foam heat exchangers with the same geometry under dry and wet operating conditions. Heat exchanger consisting of round tube with annular layer of metal foam have been considered. Experiments have been conducted using a closed-loop wind tunnel to measure the heat transfer performance and pressure drop. The impact of base metal (aluminum and copper) on the heat transfer rate has been evaluated at varying air flow rates and upstream relative humidity. It has been found that due to similar geometry (flow depth, face area, pore size) both aluminum and copper foam samples have comparable pressure drop under dry conditions. However, the pressure gradient was noticeably different for two samples under wet operating conditions. An obvious difference in heat transfer rate for aluminum and copper metal foam heat exchangers was observed under both dry and wet operating conditions. The findings have been explained in terms of the impact of the thermal conductivity of base metal and condensate retention.

Heat Transfer From Combustion Gases to a Single Row of Closely Spaced Tubes in a Swirl Crossflow Stirling Engine Heater

1982 ◽  
Vol 104 (1) ◽  
pp. 55-61 ◽  
Author(s):  
C. P. Bankston ◽  
L. H. Back
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Stirling Engine ◽  
Operating Conditions ◽  
Experimental Program ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Single Row ◽  
Transfer Characteristics

This paper describes an experimental program to determine the heat-transfer characteristics of a combustor and heat-exchanger system in a hybrid solar receiver which utilizes a Stirling engine. The system consists of a swirl combustor with a crossflow heat exchanger composed of a single row of 48 closely spaced curved tubes. In the present study, heat-transfer characteristics of the combustor/heat-exchanger system without a Stirling engine have been studied over a range of operating conditions and output levels using water as the working fluid. Non-dimensional heat-transfer coefficients based on total heat transfer have been obtained and are compared with available literature data. The results show significantly enhanced heat transfer for the present geometry and test conditions. Also, heat transfer along the length of the tubes is found to vary, the effect depending upon test condition.

A Numerical Model to Investigate Evaporative Condensers Behaviour at Tube Scale

2014 ◽  
Author(s):  
Maria Fiorentino ◽  
Giuseppe Starace
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Numerical Model ◽  
Transfer Coefficient ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Multiphase Model ◽  
Transfer Coefficients ◽  
Single Tube ◽  
Water Vaporization

Evaporative condensers operate at lower temperatures and with a higher efficiency compared to air condensers, as heat rejection is limited by air wet bulb temperature and mainly caused by water vaporization. This reduces the compressor pressure-lift and improves refrigeration cycle performance. Due to complex phenomena of heat and mass transfer on the tube bundles, modeling the evaporative condensers is a hard task and fine grids in numerical simulations are requested to reach acceptable results. A two-dimensional steady state numerical model at the single tube scale has been developed in Ansys-Fluent (release- 14.5), adopting the VOF multiphase model. Moist air has been treated as a mixture of air and water vapor species, while water vaporization and latent heat have been modeled with a C++ User Defined Function. The tube wall temperature has been assumed constant. The aim of this work is to describe the developed numerical model and to validate it by comparing results obtained at different operating conditions with empirical relationships found in the literature in terms of combined and overall heat transfer coefficients. Combined heat transfer coefficient variation along the tube surface has been analyzed, observing that the heat transfer coefficient is higher in the impingement zone, becomes approximately uniform and rises approaching the trailing edge. Moisture content distributions at different sections through the heat exchanger have been examined in detail as well. This study will be the basis to investigate the performance of the whole condenser taking into account the real evolution of the operating conditions of each single tube in the bundle, whatever its arrangement.

Heat Transfer Characteristics of a Blade Trailing Edge With Pressure Side Bleed Extraction

2013 ◽  
Author(s):  
H. Saxer-Felici ◽  
S. Naik ◽  
M. Gritsch
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Cooling System ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Heat Transfer Coefficients ◽  
The Impact

This paper investigates the heat transfer and pressure loss characteristic in the internal cooling system of the trailing edge of a gas turbine blade. The geometrical profile of the blade trailing edge and the operating conditions considered are representative of that normally found in a heavy-duty gas turbine. The trailing edge geometry consists of two radial passages with inclined turbulators which are connected with a bend. The trailing edge section consists of pins rows and a flow ejection cut-out slot. The impact of a cross-over hole in the web connecting the serpentine passages is also investigated. Both numerical and experimental studies were conducted at several passage Reynolds numbers ranging from 104 to 106. Experiments were conducted in a Perspex model at atmospheric conditions. The internal heat transfer coefficients were measured via the transient liquid crystal method and the pressure drop was measured via pressure taps. The impact of blade rotation on the heat transfer and pressure drop was also assessed numerically. Comparison of the measured and predicted heat transfer coefficients and pressure drops shows a good agreement for several flow conditions. The three-dimensional flow field in the passage and in the downstream pin banks was well captured numerically, with and without coolant injection via cross-over hole.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

scholarly journals Numerical simulation of variable thermal conductivity on 3D flow of nanofluid over a stretching sheet

2020 ◽  
Vol 9 (1) ◽  
pp. 233-243 ◽  
Author(s):  
Nainaru Tarakaramu ◽  
P.V. Satya Narayana ◽  
Bhumarapu Venkateswarlu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Stretching Sheet ◽  
Three Dimensional ◽  
Variable Thermal Conductivity ◽  
Normal Velocity ◽  
Transfer Coefficients ◽  
Similarity Transformations ◽  
Frictional Coefficients ◽  
The Impact

AbstractThe present investigation deals with the steady three-dimensional flow and heat transfer of nanofluids due to stretching sheet in the presence of magnetic field and heat source. Three types of water based nanoparticles namely, copper (Cu), aluminium oxide (Al2O3), and titanium dioxide (TiO2) are considered in this study. The temperature dependent variable thermal conductivity and thermal radiation has been introduced in the energy equation. Using suitable similarity transformations the dimensional non-linear expressions are converted into dimensionless system and are then solved numerically by Runge-Kutta-Fehlberg scheme along with well-known shooting technique. The impact of various flow parameters on axial and transverse velocities, temperature, surface frictional coefficients and rate of heat transfer coefficients are visualized both in qualitative and quantitative manners in the vicinity of stretching sheet. The results reviled that the temperature and velocity of the fluid rise with increasing values of variable thermal conductivity parameter. Also, the temperature and normal velocity of the fluid in case of Cu-water nanoparticles is more than that of Al2O3- water nanofluid. On the other hand, the axial velocity of the fluid in case of Al2O3- water nanofluid is more than that of TiO2nanoparticles. In addition, the current outcomes are matched with the previously published consequences and initiate to be a good contract as a limiting sense.

Sign in / Sign up

Export Citation Format

Share Document