Measured Heat Transfer Rates Research Articles

Crossflow polymeric hollow fiber heat exchanger: fiber tension effects on heat transfer and airside pressure drop

In various applications, a polymeric hollow fiber heat exchanger (PHFHE) is a competitive alternative to a conventional heat exchanger (HE). Standard empirical models for predicting the crossflow tube HE characteristics are defined for devices with rigid tubes with relatively large diameters compared to the polymeric hollow fibers with an outer diameter of around 1 mm. This study examines the impact of tension force on airside heat transfer rate and pressure drop in a crossflow PHFHE. The tension force influences the stiffness of the flexible polymeric fibers and their response to applied airflow. Two liquid–gas PHFHEs were designed and manufactured to ensure uniformity of the fibers' arrangement (inline and staggered). An experimental stand enabling the application of defined tension force in the range of 0–9000 N was designed, manufactured and placed into the calorimetric tunnel, where heat transfer rate and pressure drop measurement were performed with varying air velocity between 2 and 8 ms−1 (corresponding to Reynolds number of 240–970). Among our key findings was that the elongation of the fibers due to thermal expansion or stress relaxation has a considerable impact on the fibers' arrangement and resulting fluid flow. Moreover, the application of tension force yielded no substantial change in air pressure drop; however, it led to a notable enhancement in heat transfer rate. Specifically, under a maximal tension force of 9000 N, the heat transfer rate increased by around 11% compared to the unloaded state.

An Experimental Examination into the Efficiency of a Shell-and-Tube Heat Exchanger for an EGR Cooler

The increasing concerns over environmental pollution and stringent regulations on emission have led to the widespread adoption of exhaust gas recirculation (EGR) systems in interna combustion engines. EGR systems help reduce nitrogen oxide (NOx) emissions by recirculating a portion of exhaust gaes back into the combustion chamber. Howerver, the elevated temperature of exhaust gases poses challenges related to thermal management, necessitating the use of exhaust gas recirculation cooler. The experimental setup allows for the controlled circulation of exhaust gases and cooling fluids, thereby facilitating the measurement of heat transfer rates, pressure drops and overall thermal efficiency. These parameters encompass the inlet and outlet temperatures of both the exhaust gases and the cooling fluids flow rates for both fluids resulting pressure drops. By systematically altering these factors, the intricate, interplay between the various parameters and their inputs on the heat exchangers thermal performances are comprehensively explored. Addition, the research develops into critical aspects often overshadowed in EGR cooler studies on fouling. Overtime, the accumulation of deposits in the heat exchanger surface can led to reduced heat transfer efficiency. The outcomes of this study are instrumental for the advancement of EGR cooler technologies fostering more sustainable and environmentally friendly and automotive engines.

Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed

This study investigates the interaction between a premixed methane-air flame and particles inside a model packed bed. The opacity of the spherical packed beds to visible light poses a major barrier to the implementation of highly resolved optical diagnostics, so that no detailed experimental data were so far available for the validation of numerical simulation. Here, a two-dimensional cylindrical packed bed design is set up, which enables direct line-of-sight optical measurements without loss of spatial resolution over the fluid region between the particles. In this study, the case of cold metallic cylindrical particles (T = 377 K) relevant to start-up of a reactor is investigated using internal particle cooling, which also allows cylinder specific heat transfer rate measurements by differential temperature measurements on the coolant streams. The two dimensional assumption is first verified by measuring the inflow velocity and cylinder temperature profile along the cylinders. Chemiluminescence imaging is then performed using a telecentric lens to observe the position and geometry of the two-dimensional flame front with respect to the surrounding cylinders without loss of resolution. Simultaneously, the cylinder-specific flame to cylinder heat transfer rates and cylinder surface temperature are measured. As the flame is closely surrounded by the three cooled cylinders, intense heat transfer is observed in this region corresponding to 25 ± 2.5% of the flame thermal power. Flames were stabilised at different positions depending on inflow velocity and equivalence ratio, and a direct correlation between flame to cylinder stand-off distance and the heat transfer rate normalised to the flame thermal power was found for both top and side cylinders. Also, sidewall quenching distances to the curved cylinder surfaces were evaluated, and seem to be influenced by the presence of a warm recirculation zone behind the cylinders. This investigation provides fully resolved flame front position and heat transfer rates for a known geometry and cylinder thermal boundary conditions, and provides validation data for numerical simulations of this high flame particle coupling case.

Morphological nanolayer impact on hybrid nanofluids flow due to dispersion of polymer/CNT matrix nanocomposite material

<abstract> <p>The objective of this study is to explore the heat transfer properties and flow features of an MHD hybrid nanofluid due to the dispersion of polymer/CNT matrix nanocomposite material through orthogonal permeable disks with the impact of morphological nanolayer. Matrix nanocomposites (MNC) are high-performance materials with unique properties and design opportunities. These MNC materials are beneficial in a variety of applications, spanning from packaging to biomedical applications, due to their exceptional thermophysical properties. The present innovative study is the dispersion of polymeric/ceramic matrix nanocomposite material on magnetized hybrid nanofluids flow through the orthogonal porous coaxial disks is deliberated. Further, we also examined the numerically prominence of the permeability ($ {\mathrm{A}}_{\mathrm{*}} $) function consisting of the Permeable Reynold number associated with the expansion/contraction ratio. The morphological significant effects of these nanomaterials on flow and heat transfer characteristics are explored. The mathematical structure, as well as empirical relations for nanocomposite materials, are formulated as partial differential equations, which are then translated into ordinary differential expressions using appropriate variables. The Runge–Kutta and shooting methods are utilized to find the accurate numerical solution. Variations in skin friction coefficient and Nusselt number at the lower and upper walls of disks, as well as heat transfer rate measurements, are computed using important engineering physical factors. A comparison table and graph of effective nanolayer thermal conductivity (ENTC) and non-effective nanolayer thermal conductivity are presented. It is observed that the increment in nanolayer thickness (0.4−1.6), enhanced the ENTC and thermal phenomena. By the enhancement in hybrid nanoparticles volume fraction (2% to 6%), significant enhancement in Nusselt number is noticed. This novel work may be beneficial for nanotechnology and relevant nanocomponents.</p> </abstract>

Magnetized Tri-hybrid Nanofluids flow with binary Chemical Reaction and activation Energy through the porous Surfaces

Hybrid nanofluids are important to researchers because of their industrial applications due to their high heat transfer rates. Tri hybrid different types of nanoparticles are discussed here with Newtonian fluids under the effect of MHD. The most important chemical reaction associated with mass transfer and activation energy parameters hasbeen discussed in detail. The current research focuses on two-dimensional fluids with heat transfer enhancement flowing over a porous surface. The mathematical modeling of the problem, as well as empirical relations for nanoparticle materials, is expressed as PDEs, which are then translated into ODEs using appropriate variables. The Runge–Kutta and shooting methods are combined to solve the problems of the created coupled differential system. Variations in nanoparticle volume fraction at the lower and upper walls of porous plates, as well as heat transfer rate measurements, are computed using controlling physical factors. The impact of flow-related variables on the axial, radial, and temperature components of velocity and temperature distribution is also assessed.

Insight into Dynamic of Mono and Hybrid Nanofluids Subject to Binary Chemical Reaction, Activation Energy, and Magnetic Field through the Porous Surfaces

The mathematical modeling of the activation energy and binary chemical reaction system with six distinct types of nanoparticles, along with the magnetohydrodynamic effect, is studied in this paper. Different types of hybrid nanofluids flowing over porous surfaces with heat and mass transfer aspects are examined here. The empirical relations for nanoparticle materials associated with thermophysical properties are expressed as partial differential equations, which are then interpreted into ordinary differential expressions using appropriate variables. The initial shooting method converts the boundary condition into the initial condition with an appropriate guess and finally finds out an accurate numerical solution by using the Runge–Kutta method with numerical stability. Variations in nanoparticle volume fraction at the lower and upper walls of porous surfaces, as well as the heat transfer rate measurements, are computed using the controlling physical factors. The effects of the flow-related variables on the axial velocity, radial velocity, temperature, and concentration profile dispersion are also investigated. The Permeable Reynolds number is directly proportional to the regression parameter. The injection/suction phenomenon associated with the expanding/contracting cases, respectively, have been described with engineering parameters. The hybrid nanoparticle volume fraction (1–5%) has a significant effect on the thermal system and radial velocity.

A Real-Time Output–Loss Method for Monitoring Heat Rate for Coal-Fired Power Plants

Abstract This paper describes a real-time performance monitoring method based on PTC 4-2013 for determining instantaneous heat rates for coal-fired power plants. The calculation protocol uses a modified output–loss approach applied to a control volume that closely conforms to the boiler. The largest energy balance term is the heat transfer rate to the steam, which is known accurately in real-time when the plant employs properly calibrated instrumentation. The first-law energy balance also requires a balanced combustion equation which depends on coal composition, which is not known in real-time. A periodic or alert-driven calibration utilizes an ultimate analysis of a carefully collected coal sample and historic plant data obtained during the collection time of the coal sample. This is used to calculate correction factors for the coal mass flowrate, air preheater leakage, and CO2 and SO2 concentrations at the economizer exit derived from continuous emissions monitoring systems (CEMS) measurements performed at that location. The iterative calculations required to determine the coal composition in real-time are presented. The real-time performance algorithm exhibited significant sensitivity associated with measurements of the steam heat transfer rate, which was the dominant term in the overall boiler energy balance. Other input parameters generally yielded a much lower influence on calculated heat rate. It was concluded that for optimal accuracy of the output–loss method the steam and coal mass flowrates must be measured as accurately as possible.

The Modification of the Perforated Plate in the Fluidized-Bed Combustor to Analyze Heat Convection Rate and Temperature

Investigation of combustion temperature through experiments with a wide range of fuels, both solid and liquid, is continuously being conducted by scientists around the world, while the measurement of heat transfer rate can be analyzed when the combustion process occurs. Previous research has generally been conducted using liquefied gas, fossil fuels, and alcohol additives. Specifically, the research in this work investigated the convection heat rate and combustion temperature through the modification of the perforated plate. The experiment was conducted in the fluidized-bed combustor (FBC) fuel chamber using solid waste fuel of oil palm biomass. Measurements were performed at four different points using the HotTemp HT-306 Digital Thermometer. The results of the experiment showed that the convection heat rate in measurement one (M-I) reached 8.258 W/m2 for palm kernel shell (PKS) fuel. Meanwhile, in measurement two (M-II), the convection rate of 7.392 W/m2 was produced by oil palm midrib (OPM) fuel. The highest combustion temperature was recorded with OPM fuel (884°C) at M-I. However, the combustion temperature of the PKS combustion process is higher at 896°C but shows a less good trend than OPM. Overall, the measurement results of the three types of fuel used to modify the perforated plate applied in the FBC fuel chamber are excellent. It can be proven that the fuel is put into the combustion chamber with nothing left.

Measurement of mid-low order of magnitude of heat transfer rate using infrared thermography in rarefied flow

Based on the analysis of demand for measuring heat transfer of hypersonic vehicle at high attitude, aimed at the characteristic of mid-low order of magnitude of heat transfer rate at ground test for simulating rarefied flow, various factors of the influence on measurement accuracy of mid-low order of magnitude of heat transfer were analyzed. Firstly, the influence of model heating time on heat transfer measurement was analyzed from reducing lateral error of experiment model to controlling temperature rise of model surface, which was based on a steady heat transfer of model surface and one-dimensional and semi-infinite hypothesis. Secondly, model adiabat materials with low thermal diffusivity were put to use. Transient Plane Source Method was introduced so as to calibrate thermal physical parameter(density, specific heat ratio and thermal conductivity) of model material with high accuracy. Kinds of method, such as diffusing compensation and phase-locked method, were adopted to raise measurement accuracy of model surface emittance. Finally, when using thin-wall calorimetry to obtain model surface heat transfer rate, thermocouple was welded on the inner surface of test model to measure heat transfer rate such as MW/m2 order of magnitude, while one was done on the outer surface of model to measure that with several kW/m2 to several hundred kW/m2 by thermocouple or by infrared thermography. In order to compare these results, on the experimental condition of Mach number 12, total pressure 4.2 MPa and total temperature 700 K, heat transfer rate at different points of the double cone thin-wall model was measured by thermocouple and infrared thermography simultaneously. The results indicated that the heat transfer rate measured with infrared thermometry was approaching to that done with thermocouple on the outer surface of model, that heat transfer rate by thermocouple on the outer surface of model was greater than that by thermocouple on the inner surface of test model, and that the influence of model heating time on the measurement of heat transfer rate with different order of magnitude was different.

Casting of Ferroalloys

Casting of ferroalloys is a part of the production process that has been somewhat outdated compared to the preceding reduction and refining processing part of the manufacturing process. Layer casting and chill mold casting have been the dominant types of casting processes even if casting on cast iron plates, water-cooled copper and granulation has gained a certain, but moderate volume. Elkem took the initiative to explore a Direct Strip Casting (DSC) type of process. Measurements of heat transfer rates related to different substrate materials, introductory laboratory scale casting in order of studying material structures and properties, and full-scale experimental casting of 65 % FeSi alloy was performed. One main reason for changing the casting process is the environmental issue. The DSC method seems also to represent an economic advantage over traditional methods.

Air-cooled absorbers for extreme-ambient absorption heat pumps

• Ammonia-water air-cooled absorber modeled and tested. • Single-pressure loop and air-handling unit used for experiments. • Baseline conditions with 51.7 °C ambient air. • Good agreement between experiments and models. An investigation of air-coupled absorbers for an ammonia-water absorption system operating in extreme ambient conditions was conducted. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin absorbers for a 2.64-kW absorption chiller operated at high ambient temperatures. A single-pressure ammonia-water test facility was used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design conditions. Absorber performance was studied over a range of air temperatures and flow rates, inlet solution temperatures, and concentrated solution flow rates and concentrations. At design conditions, round-tube corrugated-fin absorbers of 394 and 551 fins per meter (FPM) demonstrated comparable performance, and measured heat transfer rates were predicted well. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

Experiments on Measurement of Heat Transfer Rate of Gas Flow Through Microchannel with Constant Wall Temperature

Experiments on Measurement of Heat Transfer Rate of Gas Flow Through Microchannel with Constant Wall Temperature

Comparison between modelled and measured heat transfer rates during the departure of a steam bubble from a solid surface

This paper presents analysis of the heat transfer attendant upon the departure of a single steam bubble during pool boiling of water at atmospheric pressure. The flow of heat from a solid surface to liquid water during and immediately after bubble lift-off has been extracted from micro-scale measurements of the spatial and temporal variation of the temperature at the solid surface beneath the bubble. The numerical procedure used to extract the heat flux from the temperature variations at the solid surface has been assessed and verified, and applied to investigate the heat transfer during the bubble departure phase, and after the eventual bubble lift-off. Results confirm that fluid motion activated by a departing bubble is the cause of heat transfer enhancement. The phenomenon can be characterised as the process of rewetting, by an advancing liquid front, of a dry portion of wall area at the base of the bubble. The portion of wall area that is affected by the observed heat transfer augmentation mechanism has been found to be that of a circle of diameter roughly equal to half the bubble departure diameter. The current measurements enabled validation of interface-capturing numerical simulation of the hydrodynamics and heat transfer of single bubble formation and departure from a surface, including conjugate heat transfer in the solid substrate. From simulation results, the spatial and temporal variation of the heat flux at the solid surface beneath the bubble has been computed and monitored during bubble departure and after the eventual bubble lift-off. Heat transfer rates at bubble departure extracted from simulation have been found in good agreement with measurements. The simulation correctly captured experimental trends and was found to give an accurate estimate of the magnitude of the flows of heat to the liquid due to the bringing of cold fluid in the vicinity of the wall caused by the bubble departure process.

Effects of Angle of Attack and Bluntness on Heating Rate Distribution of Blunt Models at Hypersonic Speeds

The effects of nose radius on stagnation and surface heat transfer rate along the surface are addressed in this research paper. Experiments are carried out in hypersonic shock tunnel, at hypersonic Mach number of 6.56 for 11.38° apex angle blunt cone with nose radius of 0.2R, base radius of R. Similarly, experiments are carried out at Mach 7.32 for 13.87° apex angle blunt cone models with nose radius of 0.18R′, base radius of R′. Test is performed at stagnation enthalpy of 1.4 and 2 MJ/kg with effective test time of 3.5 ms. Convective heat transfer measurements have been carried out on the test model at two different angles of attack, namely 0° and 5° with angle of rotation of 0°, 90°,180° with platinum thin film sensors. ANSYS-Fluent used to simulate the flow over the blunt models at different Mach numbers. The measured shock standoff distance from Schlieren visualization images compared with theory and computational fluid dynamic study for both configurations. The measured stagnation heating value is compared with theoretical value estimated using Fay-Riddell expression and numerical simulation. The measured heat transfer rate is higher for configuration 1 than configuration 2. The increases in heat transfer rate is due higher density ratio across the shock wave and the reduced shock layer thickness. The measured shock layer thickness is 2.06 mm for Mach 6.56 and 3.45 mm for Mach 7.32. The heat transfer rate is higher for Mach 6.56 as compared to Mach 7.32.

Heat transfer rate and surface pressure measurements in short duration hypersonic flow

ABSTRACTExperiments were carried out with air as the test gas to obtain the surface convective heating rate and surface pressure distribution on blunt and sharp cone models flying at hypersonic speeds. Tests were performed in a hypersonic shock tunnel at two different angles of attack: ${0}^\circ$ and ${5}^\circ$ with angles of rotation $\phi = {0}^\circ, {90}^\circ$, and ${180}^\circ$. The experiments were conducted at a stagnation enthalpy of 1.4MJ/kg, flow Mach number of 6.56 and free stream Reynolds number based on the model length of $9.1 \times {10}^{5}$. The effective test time of the shock tunnel is 3ms. The results obtained for cone model with a bluntness ratio of 0.2 were compared with sharp cone models for $\alpha ={0}^\circ$. The measured stagnation heat transfer value matched well with the theoretical value predicted by the Fay and Riddell correlation and with the CFD results.

Concentric Annular Thermosyphon for Passive Cooling System of Spent Fuel Pool

Since the Fukushima accident, safety issues about spent fuel pools(SFP) have been raised. Current cooling systems of SFP are vulnerable to an accident such as a blackout. Hence, lots of attempts to develop passive cooling systems of SFP have been made, and heat pipes can be used effectively to develop a new passive cooling system of SFP. An annular thermosyphon is similar to a conventional heat pipe except that the cross section of the pipe is annular instead of circular. The heat transfer area and heat transfer coefficient of the evaporator section of the annular thermosyphon can be increased significantly without increasing the outer diameter of a pipe. In this study, a new passive cooling system of SFP with the annular thermosyphon was designed, and experiments were conducted to optimize the thermal performance of the thermosyphon. Using R-134a as working fluid, we measured the temperatures of the evaporator section and the condenser section of the heat pipe by changing the charging ratio and the air velocity. And We measured heat transfer rate of heat pipe at the emergency cases. The result of experiments shows that the optimal charging ratio is 65%, and that heat transfer rate increases as air velocity and water temperature increases. The narrower clearance, the better thermal performance.

Experimental comparison of the heat transfer of supercritical R134a in a micro-fin tube and a smooth tube

Measured heat transfer rates of supercritical R134a were compared for flows in a horizontal micro-fin tube and in a smooth tube for mass fluxes from 100 to 700 kg m−2 s−1, heat fluxes from 10 to 70 kW m−2, and pressures from 4.26 to 5 MPa. The results showed that the micro-fin tube wall temperatures had smaller changes as the heat flux was increased than on the smooth tube. The heat transfer coefficients along the top of the smooth tube are reduced more by the buoyancy effect than in the micro-fin tube. Then, the results were used to evaluate four buoyancy criteria for horizontal flows for both the smooth tube and micro-fin tube with the GrbReb2.0ρbρwxd criterion found to give the best prediction accuracy for both types of tubes. The threshold for the onset of the buoyancy effect in the smooth tube was around 100 but was around 2000 in the micro-fin tube, which indicates that the effect of buoyancy is greatly reduced in the micro-fin tube. Comparisons of the measured heat transfer coefficients for all 5520 experimental data points showed that the heat transfer coefficient in the micro-fin tube was 1.68 times that in the smooth tube on the top and 1.59 times that in the smooth tube on the bottom.

Ferrofluids for heat transfer enhancement under an external magnetic field

Overheating of power electronic devices has become a significant issue due to their continued miniaturization and increased heat flux that needs to be dissipated. Ferrofluids (magnetic nanofluids) have been shown to have higher thermal conductivity than their base aqueous or oil based fluids due to the solid magnetic nanoparticles that make up the ferrofluid. This allows higher convective heat transfer rates and, importantly, the ability to externally effect the flow using a magnetic field. In this paper, we focus on material characterization of ferrofluids and measurement of heat transfer rates for single-phase ferrofluidic forced convective flow in microchannels. We show that heat transfer properties of the flow are enhanced with the use of ferrofluids and that the material make-up of the ferrofluid affects these properties. In this paper, we argue that generally, convective heat transfer rates for ferrofluids are increased by increasing the solid volume concentration of magnetic particles (∼0.2–0.4%). Interestingly, increasing magnetic flux was shown to decrease heat transfer enhancement. This was due to a reduction in the thermal conductivity of the bulk fluid caused by magnetic nanoparticles being drawn out of the isotropic mixture and becoming pinned to the channel wall in the region of strongest magnetic field. We show that there is good correlation between both theory and experimental visualization of this phenomenon.

Correcting energy balance error in heat exchanger data by maximum likelihood method

In this paper, the uncertainty propagation during the heat exchanger performance data analysis is examined through Monte Carlo simulations. Using the simulation tool, different methods for averaging redundant heat transfer rate measurements for heat exchangers are compared in terms of the uncertainty propagation. When compared to the popular arithmetic mean method, it is found that the weighted linear averaging method is superior for minimizing the uncertainty of the average heat transfer rate, but not necessarily resulting in a minimized uncertainty for the overall performance characteristic (i.e. UA). Also, it is found that the calculated UA values from UA-LMTD method and effectiveness-NTU method are not exactly the same when there is an energy balance error in the redundant heat transfer rates. These issues are caused by the underlying discrepancies in the measured variables during the data reduction. In the present work, a full reconciliation of all measured variables is proposed which makes adjustments to not only heat transfer rates but also other underlying measurements such as mass flow rates and temperatures. The amounts of corrections to individual variables are determined by straightforward formulas derived from a constrained, weighted least squares method. From Monte Carlo simulations, these corrections to variables are confirmed to be the most likely errors with given uncertainties and observed energy balance error. The proposed method consistently yields a minimum uncertainty for both heat transfer rate and UA, and it also produces identical results from UA-LMTD and effectiveness-NTU methods. Using sample data for an air conditioning heat exchanger, the advantage of the proposed method is demonstrated.

Hypersonic shock tunnel studies of Edney Type III and IV shock interactions

Of all the possible outcomes of the shock interaction problem, Edney Type-III and Type-IV are considered to be of great importance as they lead to high heat transfer rates on the surface in the vicinity of the interaction. The enhancement in heat transfer occurs because of shear layer attachment in Type-III interaction and impingement of supersonic jet in Type-IV interaction. In this study, unsteady nature of these interactions is studied in conventional shock tunnel at moderate enthalpy condition of 1.07 Mj/kg at flow Mach number of 5.62. A hemispherical model, 50 mm in diameter, mounted with thin film Platinum gauges is used along with a 25° wedge to serve as a shock generator. The schlieren images are captured along with the surface convective heat transfer rate measurements for the analysis of flowfield over the model during the test time. The pixel intensity scan is performed along several lines running horizontally to estimate the steadiness of the flowfield. These are correlated with the heat transfer rate measurements to understand the non-steady nature of the interaction during the small test times offered by the shock tunnel.