Experimental Study Of Heat Transfer Research Articles

REDUCED HEAT LOSS THROUGH WINDOW STRUCTURES

The results of theoretical and experimental studies of heat transfer through the window structures of the building are presented, the thermal characteristics of the windows are established and the level of heat loss realized through them is estimated. To determine the heat transfer resistance of two-chamber double-glazed units, numerical modeling of radiative-convective heat transfer is performed, taking into account the thermal conductivity of the gas layer between the glasses. Natural free convection of the gaseous medium in the double-glazed chambers occurs as a result of the temperature difference between the side glass surfaces of the chamber. Modeling is performed by numerically solving the system of fluid dynamics and energy equations for the air layer and glass. On the inner surfaces of the chambers, conditions of the fourth kind are set, which take into account the radiation and conductive components of the total heat flow coming from the glass surface. The results of simulation of heat transfer through double-glazed windows with ordinary glass indicate that about 60 % of heat is transferred by radiation. Therefore, an effective measure to reduce heat loss through windows is to reduce the radiation component of the total heat flow by applying a low-emissivity coating to the inner surfaces of the glass unit. This makes it possible to reduce the total heat flow (and, accordingly, heat loss to the environment) by 20–34 %, depending on the number of glass surfaces with this coating. Conducted independent experimental studies confirm the modeling results. In order to comply with the current requirements of state building regulations and to achieve the energy efficiency class of type C buildings (specific heat consumption for heating 1 sq. m of usable area is less than 75 kWh), for the climatic conditions of Kyiv, it is recommended to use double-chamber windows with two low-emission coatings with the formula of the glass unit: 4M1-10-i4M1-10-i4M1. Bibl. 22, Fig. 8.

Experimental heat transfer study of an enhanced storage medium

Phase change materials (PCMs) are suitable for storing solar energy due to their high-density energy storage and ability to operate in a wide range of temperatures. However, the lower thermophysical properties of PCMs limit their use in solar energy storage applications. Therefore, the incorporation of nanoparticles has emerged as a promising technique to enhance the storage density of PCMs.Extensive studies have been conducted on the measurement of thermophysical properties of both PCMs and nano-PCMs (PCMs with nanoparticles dispersed in them). However, there has been no comprehensive study covering the following aspects: (a) the measurement of thermophysical properties of NaNO3 (PCM) and nano-NaNO3 (nano-PCM), (b) solar energy storage of NaNO3 involving both sensible heat and latent heat in the same study, (c) the construction and implementation of an experimental rig capable of studying heat transfer in PCM and nano-PCM for solar energy storage applications (with a maximum temperature of up to 350 °C), and (d) investigating the effect of nanoparticles on large-scale solar energy storage systems. Therefore, the aim of this study is to experimentally investigate all of the aforementioned points. In order to develop and test these solar storage mediums, an experimental setup has been designed and manufactured, as mentioned earlier.Furthermore, limited studies have considered sodium nitrate salt (NaNO3) as a PCM. In this study, NaNO3 is used as the base material, and two types of materials are considered: PCM1, which consists of sodium nitrate salt (NaNO3), and PCM2, which consists of sodium nitrate salt (NaNO3) with 0.75 wt% iron oxide nanoparticles (Fe2O3) added. The experiments conducted involved both steady-state and transient conditions. The results showed that the addition of nanoparticles improved the charging and discharging by 25.6 % and 23.929 %, respectively. Moreover, the specific heat capacity and latent heat of the developed PCMs increased by 17.857 % and 9.97 %, respectively. These findings suggest that PCM2, with the presence of nanoparticles, melts and discharges energy faster compared to PCM1. Overall, this study contributes to the understanding of solar energy storage using PCMs and nano-PCMs, highlighting the potential benefits of nanoparticle incorporation in enhancing their performance.

Transient Thermal Analysis of a Double Duct Solar Roof Chimney Coupled With a Scaled Room

Abstract This research presents a detailed transient experimental and computational study of heat transfer and airflow in a scaled room linked with a double-duct vertical roof solar chimney (SC). The analysis was made in the coupled system, varying the heat flux supplied to the roof SC absorber during the day. Experimental temperature profiles were obtained at six different depths and heights, the empirical heat transfer coefficient was computed for the SC absorber, and the variation of air changes per hour was determined. A good agreement between experimental and numerical temperature profiles and average Nusselt number (Nut) is shown in the latter of average difference of 3.41%. The validated computational model was used to analyze the effect of the transient heating of the SC on temperature fields and flow patterns in the thermal system. Almost symmetrical temperature and y-velocity profiles are formed in the ducts at different hours of the day, with thermal boundary layers of about 4 mm. Correlations of the Nusselt number and air changes per hour (ACH) are provided as a function of the modified Rayleigh number.

Experimental study of refrigerant condensation heat transfer and pressure drop in horizontal tubes with full and partial coiled wire inserts (CWIs)

The condensation heat transfer coefficient (HTC) and pressure loss in the horizontal smooth and wire-inserted tubes were investigated experimentally. Three different coiled wire inserts (CWIs) of the full length of 1000 mm and partial lengths of 100 mm and 200 mm with 0.8 mm wire thickness and 9.5 mm pitch were studied. The main condenser was a heat exchanger of double pipe type with an 8 mm inner diameter for the refrigerant and an active length of 1 m cooled by water circulating in the annulus. The experiments were conducted for different refrigerant mass velocities within 90–400 kg/m2s and low vapor mass fraction (x < 0.3). The findings revealed that using 1000 mm (full-length), 200 mm, and 100 mm length CWIs improved the HTC by 95%, 40%, and 18%, respectively, over the smooth tube. The HTC per unit pressure drop was also evaluated to assess the performance of full and partial CWIs. The results showed that the HTC per unit pressure loss decreases for all tubes as the mass velocity increases. In addition, the performance of the tubes with CWIs approached that of the smooth tube at higher mass velocities. The ratios of HTC per unit pressure drop at higher mass fluxes for full-length, 200 mm, and 100 mm length CWIs to that of the smooth tube were about 0.4, 0.78, and 0.9, respectively. Although the pressure drop increased almost linearly with the partial CWI length, the HTC increased sharply for the small inserts and gradually for the larger insert lengths. The results obtained for the condensation HTC in smooth and full wire-inserted tubes were also compared with the estimations of well-known correlations in the literature. Furthermore, three new correlations were developed to predict condensation HTC in smooth tubes and tubes with full and partial CWIs. It was shown that the new correlations are more accurate than the available ones.

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Experimental Study of Natural Convection Heat Transfer in Confined Porous Media Heated From Side

Transient three-dimensional natural convection heat transfer due to the influences of heating from one side of an enclosure filled with a saturated porous media, whereas the opposite side is maintained at a constant cold temperature, and the other four sides are adiabatic, were investigated in the present work experimentally. Silica sand was used as a porous media saturated with distilled water filled in a cubic enclosure heated from the side,using six electrical controlled heaters, at constant temperatures of (60, 70, 80, 90, and 100oC). The inverse side cooled at a constant temperature of (24oC) using an aluminum heat exchanger, consisted of 15 channels feeded with constant temperature water. Eighty thermocouples were used to control the heated and cooled sides, and to measure the temperature in the entire enclosure. Experimental results showed that the heat transfer regime was mainly conduction for all Rayleigh numbers with small influence of convection for Ra=42 and greater for Ra=55. This effect increased with the angle of inclination of the enclosure. Numerical and experimental results showed a good agreement. There was a rapid increase in the temperature at the entire media at the early time, reduced gradually until the steady state condition reached. This temperature and heat transfer to and from the porous media, were increased as the Rayleigh number and/or inclination angle increased. The Nusselt number increased directly with the angle of inclination up to o θ = 45 and then decreased. Correlation equations are obtained from the experimental investigation, showed the change of the average and local Nusselt number with time, distance, Rayleigh number, and the inclination angle.

An Experimental Study of Natural Convection Heat Transfer from a Horizontal and Slightly Inclined Plate-Fin Heat Sink

An Experimental Study of Natural Convection Heat Transfer from a Horizontal and Slightly Inclined Plate-Fin Heat Sink

Experimental study of heat transfer in a rectangular cell with built-in lattice channels

We experimentally study the heat transfer and flow characteristics of thermal convection in a rectangular cell with built-in lattice channels. The working fluid used is water with a Prandtl number of 5.5, and the Rayleigh number ranges from 2.5×108 to 6.9×109. Three proposed models with different channel sizes and positions and the classical Rayleigh–Bénard convection (RBC) are studied, and the heat transfer and flow structure characteristics are analyzed using measured temperature signals. The first model included two short channels placed near the top and bottom plates, which disrupt the mixing zone and enhance heat transport. The second model involves relatively long channels positioned at the center of the cell, but far from the thermal boundary layer, resulting in a more coherent bulk flow that also enhances heat transport. For these two configurations, the heat transfer enhancement rate is approximately 20% compared to standard RBC. The third model uses long lattice channels that almost touches the top and bottom plates. This configuration results in a maximum heat transfer enhancement of about 138% due to the organized boundary layer and bulk flow induced by lattice channels. The presence of channels also results in a two-order smaller standard deviation of temperature, indicating a significant reduction in fluctuations. However, the average temperatures in the center of some channels were significantly different from the mean system temperature, suggesting the existence of cold or hot fluid flow through the channel. Our experimental results show that the inclusion of channels with appropriate lengths and positions can effectively regulate the flow near the boundary layer and in the bulk, leading to significant enhancements in heat transfer.

Experimental Study of Heat Transfer in Bundles of Wavy Pipes of a Hot-water Boiler

The possibility of intensifying heat exchange by using wavy pipes and a membrane between them is considered. It is known that heat exchange in curved pipes and channels of the coil type proceeds more intensively than in straight ones. Increasing the intensity of heat exchange and the use of double-light screens will reduce the dimensions of the boiler unit, which will improve its technical characteristics. For this purpose, experimental studies of heat transfer and resistance in bundles of wavy pipes have been carried out in two flow directions: in the plane of bending of pipes and in the plane perpendicular to the bending of pipes. So, for the flow in the direction of bending pipes, heat transfer and resistance are 9% higher than in bundles of straight pipes. And for a flow perpendicular to the bending plane of wavy pipes, the heat exchange is 13%, and the resistance is 20% higher than in bundles of straight pipes. To further increase heat transfer, it is proposed to use finning by installing membranes between wavy pipes.

Numerical and experimental study of natural convection heat transfer on flat and corrugated plates

PurposeThe purpose of this study is to numerically and experimentally investigate the natural convection heat transfer in flat plates and plates with square, trapezoidal and triangular corrugations.Design/methodology/approachThis work is an extension of the previous studies by Verderio et al. (2021a, 2021b, 2021c, 2021d, 2022a). An experimental apparatus was built to measure the plates’ temperatures during the natural convection cooling process. Several physical parameters were evaluated through the experimental methodology. Free and open-source computational tools were used to simulate the experimental conditions and to quantitatively and qualitatively evaluate the thermal plume characteristics over the plates.FindingsThe numerical results were experimentally validated with reasonable accuracy in the range of studied for the different plates. Empirical correlations of , and , with good accuracy and statistical representativeness, were obtained for the studied geometries. The convective thermal efficiency of corrugated plates (Δη), as a function of , was also experimentally studied quantitatively. In agreement with the findings of Oosthuizen and Garrett (2001), the experimental and numerical results proved that the increase in the heat exchange area of the corrugations has a greater influence on the convective exchange and the thermal efficiency than the disturbances caused in the flow (which reduce ). The plate with trapezoidal corrugations presented the highest convective thermal efficiency, followed by the plates with square and triangular corrugations. It was also proved that the thermal efficiency of corrugated plates increases with .Practical implicationsThe results demonstrate that corrugated surfaces have greater thermal efficiency than flat plates in heating and/or cooling systems by natural convection. This way, corrugated plates can reduce the dependence on auxiliary forced convection systems, with application in technological areas and Industry 4.0.Originality/valueThe empirical correlations obtained for the corrected Nusselt number and thermal efficiency for the corrugated plate geometries studied are original and unpublished, as well as the experimental validation of the developed three-dimensional numerical code.

OPERATION FEATURES OF ENVIRONMENTALLY EFFICIENT BOILER PLANTS OF MUNICIPAL THERMAL POWER ENGINEERING

The work is devoted to research on the improvement of thermal energy production technologies in gas-consuming heating boiler installations while improving their environmental performance and increasing the operation reliability. The work purpose is to study the heat and humidity modes of the air-supply ducts of boiler plants with exhaust gases recirculation systems into the blown air. The main objectives of the study are: to determine the thermal parameters of a heating boiler with a 2 MW heating capacity with a exhaust gases recirculation system mixed with blown air into its furnace space under conditions of using heat recovery technologies and without them; determination and analysis the heat and humidity parameters of this mixture in different operating modes of boiler plants. Known thermal calculation methods of boiler plants and data from our own experimental studies of heat transfer during deep cooling of boiler plant exhaust gases were used. The thermal calculation results of the heating boiler with a system for exhaust gas recirculation into its furnace space mixed with blown air are presented. The regularities of changes in the adiabatic combustion temperature and heat-humidity characteristics of the above mixture depending on the boiler heat load in different its operation modes during the heating period and the share of flue gas recirculation from 10 to 20 % were established. The research results show that the introduction of recirculation gases leads to a decrease by 150 – 250 °С of the adiabatic combustion temperature tad due to the need to consume fuel heat for heating the introduced ballast and the greater of the recirculation share s the lower the level of the indicated temperature. The research results also showed that gas recirculation causes insignificant (in the range of 0.5 – 4.7 °С) changes in the temperature of the boiler exhaust gases. Based on the data obtained, the change regularities in the heat-humidity characteristics (temperature and dew point) of the mixture of recirculated gases and air in different boiler operating modes during the heating period and under the studied recirculation shares were established. It is shown that recirculation causes condensate formation on the surfaces of air ducts in all operating modes of boiler and in some modes their icing is possible. To prevent these negative phenomena, it is necessary to apply measures to increase the temperature of the gas-air mixture by a value not less than Δtsum = 15 – 35 °С.

Experimental and theoretical study of heat and mass transfer in a continuous, vertical and coaxial pyrolysis reactor for high porosity biochar production

The development of a high porosity biochar production facility to meet an industrial need requires a detailed knowledge of the thermochemical phenomena of pyrolysis. The main challenge of this work is the production of biochar with a high porosity in large quantities, and producing a residual gas that can be used for drying biomass. Two complementary tools have been here developed and operated: a patented prototype and a designing numerical model. The model was developed in parallel with tests on the prototype and a characterisation phase of the various materials involved in the pyrolysis process in order to increase the correspondence between numerical model and experimental results. The model is used to predict, depending on the geometry chosen, the temperature in the pyrolysis zone, the heating rate and residence time corresponding to the applied biomass flow rate, as well as the biochar and gas mass yields.This study demonstrated the ability of the experimental plant to produce a high porosity biochar with a specific surface of 200m2.g-1 in the best case and a constant carbon content around 90% on dry basis due to the separation of the partial oxidation and pyrolysis zones. Following a material characterisation phase and a customisation of the parameters of the Arrhenius formalism adapted to pine bark, the numerical model shows a strong correspondence in terms of temperatures, biochar yield and thermochemical kinetics with the experimental observations from the prototype.

Experimental Investigations of Forced Convection of Nanofluids in Smooth, Horizontal, Round Tubes: A Review

A comprehensive review of published works dealing with experimental studies of forced convection heat transfer of nanofluids is presented. The survey is limited to straight, smooth, and round tubes. Moreover, only mono nanofluids exhibiting Newtonian behaviour are considered. Works on experimental research of forced convection in tubes are presented in a chronological order in the first part of the article. In this part, attention was paid to the influence of nanoparticles on the intensification of heat transfer. Information on the tested nanofluids, the measurement technique used, and the measurement range are presented in tabular form. Correlation equations proposed by individual researchers are also presented. In order to explain the controversy regarding the different influences of nanoparticles on the intensity of heat transfer during forced convection of nanofluids, the second part of the paper presents a comparison of the test results obtained by different researchers for the same nanofluid, possibly under the same thermal and flow conditions. Finally, the main conclusions are discussed.

Experimental and Numerical Study of Heat Transfer in Thin-Walled Structures Built by Direct Metal Deposition and Geometry Improvement via Laser Power Modulation

Experimental and Numerical Study of Heat Transfer in Thin-Walled Structures Built by Direct Metal Deposition and Geometry Improvement via Laser Power Modulation

Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Experimental study of dynamic combustion behavior and heat transfer of heptane pool fire with burning time under thin fuel thickness (2.0 mm–14.0 mm)

A dynamic combustion period occurs after the liquid fuel ignition, but the combustion mechanism is complicated and unclear due to dynamic heat transfer between the fuel and the substrate. This work uses a method of experimental research and theoretical analysis to study the dynamic combustion behaviour and heat transfer of pool fire with burning time (t) under thin fuel thickness (δ). Research contents include the relation of flame height (Z), burning rate (m˙), heat transfer between fuel and substrate with t, and the evolution mechanism of the output composition of total heat feedback with δ. The research found Z and m˙ increase with t until maintaining constant, whereas δ is different. Heat convection loss increases rapidly, then increases slowly, and finally keeps constant because thin-layer fuel is quickly heated. Heat radiation loss firstly surges, then fluctuates due to the combined effect of the flame shape and necking effect. Total heat loss tends from radiation to convection. The heat for heating fuel and the heat radiation reflected from the substrate are considered in the dynamic combustion stage. The fractions of heating fuel, vaporization heat, heat loss and heat reflection were calculated and studied. This work adds theoretical knowledge of fire dynamics

Porosity Effect of Polystyrene Membranes on Desalination Performance: A Combined Experimental and Numerical Heat and Mass Transfer Study in Direct Contact Membrane Distillation.

Membrane distillation (MD) is a thermal-based membrane operation with high potential for use in the treatment of aqueous streams. In this study, the linear relationship between the permeate flux and the bulk feed temperature for different electrospun polystyrene membranes is discussed. The dynamics of combined heat and mass transfer mechanisms across different membrane porosities of 77%, 89%, and 94%, each with different thicknesses, are examined. The main results for the effect of porosity with respect to the thermal efficiency and evaporation efficiency of the DCMD system are reported for electrospun polystyrene membranes. A 14.6% increase in thermal efficiency was noted for a 15% increase in membrane porosity. Meanwhile, a 15.6% rise in porosity resulted in a 5% increase in evaporation efficiency. A mathematical validation along with computational predictions is presented and interlinked with the maximum thermal and evaporation efficiencies for the surface membrane temperatures at the feed and temperature boundary regions. This work helps to further understand the interlinked correlations of the surface membrane temperatures at the feed and temperature boundary regions with respect to the change in membrane porosity.

Experimental study of natural heat transfer from finned heat exchanger fixed in variable shape of duct

The work was an experimental study of natural heat transfer from heated cylinders fixed in variable shape air duct, made from Pyrex glass. Two finned cylinders made from mild iron, outer diameter (12) mm, inner diameter (10) mm, rectangle fins dimensions (70*40) mm. The angle of two walls from the duct was changed to five angles α:(0°,3°,5°,10°,15°) with vertical to make converge shape. The cylinders were fixed inside the duct at top, centre and bottom. The cylinders were heated by supply variable power of constant heat flux (88,177,390 and 680) W/m2. The study was done with Rayleigh numbers (15x103 to 14x104). The heat was carried by free convection by atmosphere air. The results of experimental found for top location, the value of Nusselt number increased by 7.8% at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 5°, and increased by 20% at ԛ•= 680 W/ m2 when increased the value of angle from 0° to 15°.For centre location, the value of Nusselt number increased by 25 % at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 3°, and increase by 21 % at ԛ•= 680 W/ m2 when increase the value of angle from 0° to 10°.For bottom location, the value of Nusselt number increased by 35 % at ԛ•= 88 W/ m2 when increase the value of angle from 0° to 3°,and increased by 30 % at ԛ•= 680 W/ m2 when increasing the value of angle from 0° to 10°.The best location for the heat exchanger was at the bottom, and the best angle was 15°.

Experimental Study of Heat Transfer During Quenching of Steel Cylinders in Boiling Nanofluid

Current study was dedicated to explore cooling performance of TiO2 nanofluid. Preliminary tests have shown the possibility of significant improvement of emergency cooling performance by nanofluids in the case of overheated surfaces. Tests that were held during current investigation were performed with cylinders of stainless steel, which were used as an overheated surface. The temperature was recorded by a digital system of 3 type-K thermocouples. The object, preheated in a furnace to high temperatures (600–800 °C), was immersed into boiling distilled water. Usage of the set of thermocouples allows to determine heat flow in steel cylinder by its temperature distribution. The implementation of emergency cooling was to add a certain amount of nanofluid concentrate to the volume of boiling distilled water. The experiment was continued until the complete cooling of the object (up to 100 °C—the temperature of the surrounding liquid). Calculations confirmed increase of heat transfer coefficient for NF and, respectively, about 40% decrease in cooling time for NanoFluid compared to distilled water was observed. Three method of determination of heat transfer coefficient were compared.

Experimental Study of Free-Convective Heat Transfer of Single-Row Bundles of Tubes with Spiral Aluminum Fins of Different Heights in an Air Flow Intensified by an Exhaust Shaft

Experimental Study of Free-Convective Heat Transfer of Single-Row Bundles of Tubes with Spiral Aluminum Fins of Different Heights in an Air Flow Intensified by an Exhaust Shaft