Comparison Of Thermal Performance Research Articles

Experimental and numerical studies on heat transfer enhancement for air conditioner condensers using a wavy fin with a rectangular winglet

The air side thermal performance of wavy fins with rectangular winglets are studied using experimental and numerical methods. The following parameters are selected for investigation: the attack angle, placed location, span and length of the rectangular winglet. The results show that all parameters affect the thermal performance of the air side. The best configurations of the winglet that provide the maximum j/f(1/3) for both winglet lengths are the 3.5 mm horizontal distance, 7 mm vertical distance, 60° attack angle and 1.25 mm winglet span. Moreover, the thermal performance comparisons between the optimal design of the wavy fin with winglet and normal wavy fin are reported. Wavy fins with winglets provide a larger heat transfer coefficient, pressure drop and j/f(1/3) than those of normal wavy fins. For the j/f(1/3) comparison, wavy fins with winglets provide a j/f(1/3) greater than that of normal wavy fins by 5.4–14.6 %, with the Reynolds number ranging from 1650 to 4423.

Heat transfer enhancement due to a staggered element using liquid crystal thermography in an inclined discrete rib roughened solar air heater

In the present work, flow topology and heat transfer characteristics have been studied experimentally to visualize the Nusselt number distribution of inclined discrete rib with staggered elements inside a rectangular duct using liquid crystal thermography technique. Thermo-chromic liquid crystals act as a thermal imaging tool and used for visualizing the surface temperature distributions throughout the specified zone of a roughened surface. The experiment has been carried out with an applicable range of waft parameters, Reynolds number varied from 4000 to 12,500. The roughness pitch to rib height ratio assorted from 8 to 14, the ratio of length of staggered element to gap width as 2, relative staggered position as 0.6 and ratio of width of gap to roughness height as 1. The comparison of Nusselt number, flow friction, and thermal performance of the rectangular channel having inclined rib staggered arrangement with inclined rib without a staggered element has done. The staggered element helps to strengthen the flow by increasing the turbulence intensity in its nearby region and resulting in more heat transfer. The maximum increment in the Nusselt number and friction factor is 3.29 & 4.04, respectively, at a pitch of 10. The maximum thermo-hydraulic performance obtained as 2.06 at Reynolds number of 12,438.

Thermal performance of new ecological material integrated into residential building in semi-arid and cold climates

New concepts and ecological material called Poncebloc are investigated in this paper. This material is proposed as structural and thermal insulation for building envelope due to its excellent mechanical and thermophysical properties. For this motive, an in-situ building constructed with classical material largely used in Moroccan construction is monitored during one year and then modelized numerically using TRNSYS to perform a comparison of thermal and energy performance of two buildings one constructed with Poncebloc and the second one with classical materials and this for two types of climate semi-arid represented by Marrakech city and cold represented by Ifrane. The proposed concept is economically efficient as the results show a reduction in cooling energy needs of 66% and 97% for Marrakech and Ifrane, respectively; it also decreased the heating need by 44% and 42% for Marrakech and Ifrane respectively. Consequently, the bioclimatic building leads to a net reduction in GHG emissions of 60% and 45% for Marrakech and Ifrane, respectively, compared to the reference case.

Effect of Dimensionless Number (KN and RE) on Performance Index of Concentric Circular Micro Channel

Overall performance of any type of heat channel is largely depends upon Knudsen number and Reynolds number [1]. In present work the outcome of dimensionless number on heat transfer properties of micro channel heat exchanger [2]are investigated. CFD analysis of counter flowmicro channel was performed for both slip and no slip flow using Fluent as CFD code. Based on results obtain, pressure drop increases with increment in Reynolds number and Knudsen number. The effectiveness reduces with increment in Reynolds number. The comparison of thermal and hydrodynamics performance between slip and no slip flow for heat exchanger is investigated. The effectiveness increases with decreasing values of Reynolds number for counter flow. For higher effectiveness of the micro channel heat exchanger, Reynolds number should be less.

Thermal and Fluid Dynamic Performance Comparison of Three Nanofluids in Microchannels Using Analytical and Computational Models

The fluid dynamic and thermal performance of three nanofluids containing aluminum oxide, copper oxide, and silicon dioxide nanoparticles dispersed in 60:40 ethylene glycol and water base fluid as a coolant in a microchannel heatsink are compared here by two methods. The first is a simple analytical analysis, which is acceptable for very low nanoparticle volumetric concentration (1–2%). The second method is a rigorous three-dimensional finite volume conjugate heat transfer and fluid dynamic model based upon a constant heat flux boundary condition, which is applicable for cooling electronic chips. The fluids’ thermophysical properties employed in the modeling are based on empirically derived, temperature dependent correlations from the literature. The analytical and computational results for pressure drop and Nusselt number were in good agreement with the nanofluids showing a maximum difference of 4.1% and 2.9%, respectively. Computations cover the practical range of Reynolds number from 20 to 200 in the laminar regime. Based on equal Reynolds number, all of the nanofluids examined generate a higher convective heat transfer coefficient in the microchannel than the base fluid, while copper oxide provided the most significant increase by 21%. Based on the analyses performed for this study, nanofluids can enhance the cooling performance of the heatsink by requiring a lower pumping power to maintain the same maximum wall temperature. Aluminum oxide and copper oxide nanofluids of 2% concentration reduce the pumping power by 23% and 22%, respectively, while maintaining the same maximum wall temperature as the base fluid.

Comparison of thermal performance between green roofs and conventional roofs

The present study compares the thermal performance of two buildings, one with a conventional roof and another with a green roof. In order to achieve this, a transient mathematical model is developed which considers the heat transfer through the walls and the roof, additionally the model considers the energy balance to determine the change of the temperature inside buildings. The mathematical model needs as input data, solar radiation, ambient temperature and wind speed, which are accessible meteorological variables. The results show that green roofs reduce inside temperature fluctuations of buildings up to 14 K, compared to conventional roofs. Additionally, green roofs allow reaching the comfort temperature: the temperature inside buildings is reduced up to 12 K for warm climates as Mexico City.

Experimental characterization and thermal performance comparison of six Moroccan rocks used as filler materials in a packed bed storage system

Abstract The incorporation of thermal energy storage in concentrated solar power plants enables correcting the mismatch between energy supply and demand and therefore, makes CSP plants more dispatchable. So far, an air-rock packed bed storage system has been suggested as a cost effective technology. This option appears to be economically and technically attractive due to the use of a single tank and inexpensive filler materials. In this perspective, the purpose of this paper is to experimentally investigate the properties of several types of rocks (cipolin, hornfels, and limestone), in order to define their range of operating temperatures. The studied rocks were compared with other types of rocks namely: gneisses, quartzite, and flint. To achieve this objective, the chemical and structural compositions of rocks were identified, the most relevant thermophysical and mechanical characteristics were characterized and the effect of temperature increase on thermal capacity, diffusivity and conductivity was assessed as well. Besides, a simulation tool was developed to investigate the behavior of a packed bed storage system and compare its performance when filled with different types of rocks. Among the studied rocks, it has been concluded that gneisses are the most potential rock candidate for thermal energy storage applications with a maximum operating temperature of 550°C. This is attributed to its high thermal capacity which has the most significant impact on the thermal performance of an air-rock packed bed storage system.

A Comparison of Energy and Thermal Performance of Rooftop Greenhouses and Green Roofs in Mediterranean Climate: A Hygrothermal Assessment in WUFI

In urban areas, a considerable proportion of energy demand is allocated to buildings. Since rooftops constitute one-fourth of all urban surfaces, an increasing amount of attention is paid to achieving the most efficient shapes and component designs compatible with every climate and urban context, for rooftops of varying sizes. In this study, three types of rooftop technologies, namely insulated, green roof, and rooftop greenhouse, are evaluated for energy and thermal performance using computer simulations. Water surface exposure, absorption, and intrusion are the three important factors in the calculation of hygrothermal models that impact energy consumption and building envelope performance; however, a few studies are specifically focused on providing realistic results in multi-dimensional hygrothermal models and the assessment of the impact of moisture in roofing solutions. This paper aims at evaluating the performance of three different roofing technologies through a two-dimensional hygrothermal simulation in software WUFI. To accomplish this, a precise localized microclimate model of a complex urban context on the scale of a neighborhood was employed to evaluate the cooling and heating loads of the buildings, the impact of the water content in the green roof on the thermal behavior of the roof surface, and the feasibility of designing a building with nearly zero cooling needs. A two-story building in the city center of Bologna, Italy is modelled. Simulation results have shown that during the cooling period, the performance of the designed rooftop greenhouse is the most effective by 50% reduction in cooling loads. Besides, the impact of moisture in green roofs has been detected as a negative factor for thermal and energy performance of the building in the Mediterranean climate. The results ultimately highlighted the capability of passively-designed rooftop greenhouses to create a building with nearly zero cooling needs.

Comparison of Thermal Performance of Newly Produced Lightweight Wall and Roof Elements for Energy-efficient Buildings

Comparison of Thermal Performance of Newly Produced Lightweight Wall and Roof Elements for Energy-efficient Buildings

Interfacial performance of aramid, basalt and carbon fiber reinforced polymer bonded concrete exposed to high temperature

Externally bonding fiber reinforced polymer (FRP) is an effective approach to strengthen/retrofit concrete structures. However, little is known on bond performance of FRP-bonded concrete under high temperature, impeding the application of FRP in buildings potentially subjected to fire. In this paper, the bond performance of aramid, basalt and carbon FRP-concrete subjected to high temperature (80–300 °C) has been investigated through acoustic-laser technique, macroscale fracture tests and microscale characterization. Results have shown that the deterioration percentages of both peel and shear interface fracture toughness of aramid FRP-bonded concrete are largest under high temperature, followed by carbon FRP-bonded concrete and basalt FRP-bonded concrete. The mechanisms behind different bond performance have been revealed with variations of microscale morphology and chemical decomposition. The results and findings can provide a fair comparison of thermal susceptibility and residual bond performance of various FRP-bonded systems, and contribute to designing FRP strengthening/retrofitting systems under high temperature.

School building experimental characterization in Mediterranean climate regarding comfort, indoor air quality and energy consumption

Public school buildings represent an important share of public buildings in Europe, some of them built several decades ago. In Portugal, there are about 5800 public schools, many of them in free-running conditions, with significant thermal discomfort and without any heating strategy due to economic restrictions. This work studies the Portuguese Brandão school model (from the ‘70 s), which comprises about 100 non-refurbished basic schools. This paper suggests the passive refurbishment of these public schools with some affordable interventions, regarding the climate features and the reduced capacity to support the operating costs. A prototype classroom was prepared in a Brandão school, in Porto. The in situ experimental campaign consisted of temperature, relative humidity, CO2 concentration and energy consumption measurements. The prototype construction included the improvement of the envelope and of the technical systems. The main goals of this work are: (1) the comparison of the prototype in-service thermal performance in pre-existing conditions and the improvement after the refurbishment in free-running conditions or with some intermittent heating strategies; (2) the establishment of discomfort indexes for the assessment of the discomfort for Mediterranean temperate climate; (3) the quantification of the energy consumption vs discomfort regarding the passive refurbishment strategy and the intermittent heating strategies. When comparing the before and after refurbishment results, the mean daily discomfort indicator has decreased from 34.7 °C.hour to 25.2 °C.hour in free-running conditions and after the refurbishment has decreased from 25.2 °C.hour to 11.9 °C.hour for 3 heating hours strategy and to 2.5 °C.hour for 10 heating hours strategy. There was an expected increase of CO2 inside the classroom for the corresponding months before and after refurbishment, although the mean CO2 was below the required 1500 ppm.

Study of Mini Channel Heat Sink with Different Internal Configuration

In this paper a numerical analysis of three-dimensional laminar flow through rectangular channel heat sinks of different geometric configuration is presented and a comparison of thermal performance among the heat sinks is discussed. Liquid water was used as coolant in the aluminum made heat sink with a glass cover above it. The aspect ratio (section height to width) of rectangular channels of the mini-channel heat sink was 0.33. A heat flux of 20 W/cm2 was continuously applied at the bottom of the channel with different inlet velocity for Reynold’s number ranging from 150 to 1044. Interconnectors and obstacles at different positions and numbers inside the channel were introduced in order to enhance the thermal performance. These modifications cause secondary flow between the parallel channels and the obstacles disrupt the boundary layer formation of the flow inside the channel which leads to the increase in heat transfer rate. Finally, Nusselt number, overall thermal resistance and maximum temperature of the heat sink were calculated to compare the performances of the modified heat sinks with the conventional mini channel heat sink and it was observed that the heat sink with both interconnectors and obstacles enhanced the thermal performance more significantly than other configurations. A maximum of 36% increase in Nusselt number was observed (for Re =1044).

Visualizing the Impacts of Renewable Energy Growth in the U.S. Midcontinent

This paper presents the visualization approach for enhancing analyses of the ongoing Renewable Integration Impact (RIIA) Assessment by the Midcontinent Independent System Operator (MISO), and brings the following contributions. First, this paper details the customization of state-of-the-art, open-source visualization code to complement existing power system visualization tools and data analytic processes used in MISO. Second, this paper describes how MISO integrates this visualization tool within a novel and holistic process for studying renewable integration issues. This visualization tool provides additional insights for RIIA from multiple aspects with fine spatial-temporal granularity, including the comparison of thermal generation performance at different renewable integration scenarios, improved understanding of complex interactions between regions within MISO, the effects of transmission upgrades on curtailment reduction using optimization techniques, and the improved verification of MISO's simulation results. Lastly, we make the updated visualization code package publicly available.

Comparison of Thermal Performance for Two Types of ETFP System under Various Operation Schemes

Comparison of Thermal Performance for Two Types of ETFP System under Various Operation Schemes

Numerical investigation on the thermal performance of double glazing air flow window with integrated blinds

In this paper, double glazing air flow window with integrated blinds (IBAFW) numerically is investigated and the only winter indoor mode is considered for further assessments. To validate the CFD model, the results are compared with the experimental data found in the literature. For the thermal performance evaluation, total heat gain (qgain) which represents the heat gained by ventilation (qadv)and heat gained by the back glass (qbg) was considered. As a part of the study, effect of the structural parameters such as tilt angle of blinds, gap size and the areas of inlet and outlet vents on the thermal performance of IBAFW were studied. The results showed that by changing the blinds tilt angle from 30° to 60°, total heat gain increased approximately 132–146% in different solar radiation ranges. It is also concluded that increasing the gap size increased the total heat gain approximately 106%. However, the increase of outlet vent area effected reversely and resulted in decreasing the thermal efficiency by 127%.Additionally, thermal performance comparison between IBAFW and conventional solar ventilated window (SOLVENT) was carried out. The results showed that the IBAFW reveals approximately 330–580% higher thermal efficiency comparing to the SOLVENT systems.

Thermal performance comparison of different sun tracking configurations

Parabolic trough collector (PTC) is one of the most widespread solar concentration technologies and represents the biggest share of the CSP market; it is currently used in various applications, such as electricity generation, heat production for industrial processes, water desalination in arid regions and industrial cooling. The current paper provides a synopsis of the commonly used sun trackers and investigates the impact of various sun tracking modes on thermal performance of a parabolic trough collector. Two sun-tracking configurations, full automatic and semi-automatic, and a stationary one have numerically been investigated. The simulation results have shown that, under the system conditions (design, operating and weather), the PTC's performance depends strongly on the kind of sun tracking technique and on how this technique is exploited. Furthermore, the current study has proven that there are some optimal semi-automatic configurations that are more efficient than one-axis sun tracking systems. The comparison of the mathematical model used in this paper with the thermal profile of some experimental data available in the literature has shown a good agreement with a remarkably low relative error (2.93%).

Thermal performance comparison of recycled and clay roof tiles due heat radiation by digital holographic interferometry

It is through the recycling process that disposed waste materials could regain a new purpose on their use, take for instance the tetrapak™ packaging. This material consists of thermally joint layers of paper, aluminum and polyethylene. Once recycled, the two latter materials form a new composite named poly-aluminum which is employed to manufacture roof tiles that serve as environmental protection against solar radiation and rain. This work reports an optical nondestructive comparison study of the surface deformation in poly-aluminum and clay roof tiles exposed to heat radiation. The optical system based on a sensitive out-of-plane interferometer configuration records several image holograms from a controlled heat source that raises the temperature on the tile’s surface. The retrieved optical phase renders the tiles surface’s deformation for a temperature range of 25 degrees on a Celsius scale. The results show a greater deformation profile from the poly-aluminum tile compared with the classic clay tile. However, its thermal insulation properties are better than those of the clay roof tile.

Experimental investigation on thermal performance of plate fin heat sinks with nano PCM

In this study, electronic devices are experimentally examined to improve the thermal performance of the plate fin heat sink. It is performed on the basis of the paraffin wax used as a phase change material (PCM) filled in a heat sink plate. The aim of the study is to select the most efficient SiO2 volume fraction in paraffin wax to be filled in a heat sink with a plate finish. The SiO2 is considered to be a nano-particle and 1%, 3%, and 5% of SiO2 volume is selected for the preparation of nanoPCM. At the base of the plate fin heat sink, a constant heat source is applied. A plate fin heat sink is selected to quantify the effect of nanoPCM as a reference heat sink. The effect of thermal performance of heat sinks was examined using a different volume fraction of nanoPCM. The thermal performance comparison is carried out with and without PCM for the plate heat sink of Reynolds number 4000- 16000. In order to find the effect of PCM and variable Reynolds number, the investigation of the plate fin heat sink is examined. The results showed that the inclusion of PCM (paraffin wax and SiO2-based nanoPCM) in the heat sink plate provides better cooling performance and keeps the desired temperature. The results show that the heat sink based on PCM enriched with nanoparticles provided better thermal performance compared to the heat sink with a simple PCM. The thermal performance of the SiO2 based nanoPCM 3% volume fraction is better than 1% volume fraction and the heat sinks of the plate finish.

Numerical comparison of thermal and hydraulic performances for heat exchangers having circular and elliptic cross-section

The plain fin and circular tubes are generally used in heat exchangers of cooling systems. Numerous studies aiming at enhancing the thermal and hydraulic performances of this type of heat exchangers by changing the fin geometries are present in literature. In the present study, thermal and hydraulic performances of the heat exchangers with circular and elliptical tube have been compared using computational fluid dynamic method. Initially, the validation and comparison were done for the obtained data of the finned and circular tube design with respect to the performance results of the finned and circular tube design in the literature. The ellipticity ratios for the staggered arrangements of heat exchangers were changed within the range of b/a = 0.307–1.0. Numerical studies were performed with ANSYS-Fluent software within the range of Re = 750–2850 based on the fin spacing. As a result of the numerical validation studies, all analyses were solved by utilizing the SST k-ω turbulence model yielding closer values to the available studies similar to literature. Colburn factor j, friction factor f, JF values being the efficiency index and normalized j*, f* and JF* values were calculated and presented graphically. Moreover, temperature contours and streamline patterns were visually presented to evaluate the flow structures around the six different arrangements and to explain the physical reasons of pressure drop and heat transfer phenomena. The largest values of the Colburn factor j and the friction factor f known respectively as an indicator of heat transfer and a measure of pressure drop were obtained for the circular-tube-design ratio of b/a = 1.0 when compared to the other arrangements. According to the JF values, which is the efficiency index and the integrated outcome of heat transfer and pressure drop, the best result was obtained for the model with the diameter ratio of b/a = 0.307. Variations of the JF values for the arrangements of b/a = 0.333 and b/a = 0.307 depending on Reynolds numbers were found to be significantly close to each other. Finally, it is demonstrated that elliptical cross-section tubes with a better design in terms of lower pressure drop and less separated flow structures can be preferred in heat exchanger applications in order to provide energy saving.

Bionic hierarchy growth method for optimal design of dendritic heat transfer structure

ABSTRACTTo design an effective and easy-to-manufacture conductive heat transfer structure, a bionic hierarchy growth method inspired by a natural branch system is suggested. The heat transfer structure is assembled by heat channels which are determined by width, start point and end point. Hierarchy growth consists of successive growth of principal channel and lateral channel. Specifically, the space colonization algorithm with temperature information (SCATI) is applied to the growth of the principal channels, and the law of minimal thermal resistance is applied to control the growth of the lateral channels. The superiority of the suggested method is demonstrated by three typical design problems. In addition, design parameters including the number of principal channels and the bifurcation exponent in Murray’s law are discussed, and the results prove the reasonability of the parameter selection based on natural branch systems. Finally, the thermal performance comparison between the structure designed by constructal theory and a dendritic heat transfer structure shows experimentally the effectiveness of the suggested method.