Cooling Surface Area Research Articles

The reduction of the energy demand of a hall-type object through vegetative roof constructions

The topic of the energy efficiency of buildings is still relevant, and this article focuses on one form of passively reducing their energy demands, in this case, for a hall-type structure. Hall-type structures are largely horizontal constructions, meaning that their length and width often significantly exceed their height. As a result, a larger cooled surface area of the roof is expected in comparison to the cooled surface area of the facade. While not the sole factor influencing the selection of a structure or balance calculations, it was one of the initial considerations. It is also anticipated that with a larger construction area and its opening structures, there will be a greater area available for covering with a green roof. The coverage of the building's energy facilities occupy a certain percentage of the roof construction area. The work then delves into the energy balances of the given structure under various operational conditions, based on measurements of the thermal-technical improvement of the construction, depending on its composition and coverage with a green structure. The results include balance-based energy savings achieved through the green element, as well as the percentage savings in different operational conditions.

Experimental investigation on cooling surface heat transfer behavior of a thermally activated building system in warm and humid zones

Thermally Activated Building System (TABS), is one of the alternative cooling methodology, due to the numerous advantages it provides the building industry. This system consists of encapsulated pipes within the building structure to control the surface temperature, which helps to remove the sensible heat from the indoor. The objective of this investigation is to experimentally evaluate the influence of cooling surface area and the effect of cooling water inlet flow velocities on the TABS performance in the warm and humid zone under natural ventilation, and the experimental results were compared with the conventional building (CB), which does not have any cooling arrangements. An increase in water inlet velocity from 0.35 to 1.5 m/s substantially removes the thermal energy stored in the TABS, and reduces the average indoor temperature by 3 °C. In a CB, the average heat gain of all surfaces varies from −3 W/m2 to 13 W/m2. Moreover, in all surface cooling (ASC), it varied from −2 W/m2 to 24 W/m2. This resulted in increased surface cooling, which increased the surface heat gain and indoor cooling capacity. There are no significant thermal behaviour and heat transfer variations at 1 m/s and 1.5 m/s of inlet water flow velocities.

Influence of cooling surface area on indoor air and surface heat transfer characteristics of a thermally activated building system in warm and humid zones: An Experimental study

Several alternatives have been introduced in recent years to enhance the thermal comfort levels within buildings. Thermally Activated Building Systems (TABS), one of the above alternatives, have gained interest because of the huge benefits this technology offers the building sector. This type of system consists of encapsulated pipes within the building structure to control the surface temperature. This study explores the thermal behavior of the cooling surface and fluctuations in indoor air temperature (IAT) of TABS under various cooling scenarios. Only limited number of investigations has been carried out to study the heat transfer behavior of TABS. Hence, the building indoor thermal properties such as air temperature, surface temperature and rate of heat transfer between the indoor air and inner surface of the TABS has been evaluated experimentally by enhancing the cooling surface area. Moreover the results were compared with the conventional building (no cooling provides). The thermal energy stored in the TABS is significantly removed by the increase in cooling surface area, resulting in a 2°C decrease in the average indoor air temperature. The average heat gain of all wall surfaces in the case of no cooling (WOC) ranges from −3 to 13 W/m2. The amount of heat gain on the walls was not significantly affected by only roof and floor cooling (R+F) activities. Moreover, it ranged from −2 to 24 W/m2 in all surface cooling (ASC) scenarios. As a result, there was additional surface cooling, which increased surface heat gain and indoor cooling capacity.

Sawtooth V-Trough Cavity for Low-Concentration Photovoltaic Systems Based on Small-Scale Linear Fresnel Reflectors: Optimal Design, Verification, and Construction

Ensuring the uniformity of solar irradiance distribution on photovoltaic cells is a major challenge in low-concentrating photovoltaic systems based on a small-scale linear Fresnel reflector. A novel sawtooth V-cavity design method based on an optimization algorithm to achieve uniform irradiance distribution on photovoltaic cells is presented. The reliability of the design was verified using the Monte Carlo ray-tracing method and a laser experiment. A prototype was built using 3D printing technology with a biodegradable green polymer material known as polylactic acid. The new cavity was compared to the standard V-trough cavity, keeping the cavity aperture, reflective surface area, and photovoltaic cell width constant. In addition, the focal height, number of mirrors, mirror width, and mirror spacing were also kept constant; so, the cost of the two configurations was the same from the point of view of the primary reflector system. The new design ensured the uniform distribution of solar irradiation and significantly reduced the height of the cavity. The significant decrease in the height of the proposed cavity has the following advantages: (i) a decrease in the dimensions of the fixed structure of the small-scale linear Fresnel reflector, thus reducing its cost, (ii) a significant decrease in the surface area exposed to wind loads, thus reducing the cost of the fixed structure and secondary system structures, (iii) a reduction in the difficulty of the manufacture, maintenance, and transportation of the cavity’s reflecting walls, and (iv) an increase in the cooling surface area, which increases the electrical efficiency of the photovoltaic cells.

Indoor thermal comfort analysis of TABS with untreated natural ventilation in a warm and humid climate – An experimental study

BackgroundThermally activated building systems (TABS) are the most environment-friendly and energy-efficient cooling technology. These cooling methods, which use pipe-encapsulated building surfaces to minimize the indoor cooling load, have been used in this work. The primary objective of the research is to measure the energy use, thermal comfort and the impact of cooling surface area and water inlet flow velocities on the performance of TABS with natural ventilation assistance in a warm and humid environment. MethodsExperimental studies were conducted to investigate the impact of cooling surface area and water inlet flow velocities on the performance of thermally active buildings with natural ventilation assistance. Significant findingsNatural ventilation had a significant impact on advancing and increasing the average indoor air temperature by 1.5 °C when compared to the neutral adaptive comfort band. The increase in the water inlet velocity from 0.35 to 1.5 m/s substantially removes the thermal energy stored in the TABS system by reducing the average indoor temperature by 2 °C. The predicted percentage dissatisfied (PPD) was approximately 40% of all cooled surfaces. The energy consumption for 1 m/s water inlet velocity, which provides similar thermal comfort for higher flow rates, is 1.3 kWh. Therefore, from the study, 1 m/s water inlet velocity is found to be the optimal value, where comfort and energy consumption are within an acceptable range. Hence, the operating parameters under which the building envelope is cooled would significantly impact the performance of the thermally activated building system.

A comparison of oscillating sweeping jet and steady normal jet in cooling gas turbine leading edge: Numerical analysis

Impinging jets have emerged as a prominent cooling technology in the gas turbine industry. With the addition of fluidic oscillators as heat removal devices, steady-state impinging jets can be converted to sweeping impinging jets, presenting an opportunity to improve the heat transfer performance of current impinging jets by covering a larger cooling surface area on the leading edge of a gas turbine blade. Sweeping jets are self-oscillating devices that operate based on the Coanda effect, making them self-sustaining. In this study, the flow and heat transfer performance of an array of seven steady and sweeping impinging jets were investigated using the unsteady Reynolds-averaged Navier-Stokes turbulent SST k-ω model. The sweeping jet impingement improved the heat removal performance by cooling a larger surface area of the leading edge with a constant heat flux and by improving the overall time-averaged cooling effectiveness. Compared with the steady jet case, the sweeping jet case shows an improvement in heat transfer of 12.2%. Further, the use of fluidic oscillators (sweeping jets) produced a more uniform mass flow rate distribution from all jets compared with a simple jet.

Evaluation of district heating patterns for Hungarian residential buildings: Case study of Budapest

The present study focuses on analysing the heat consumption of multifamily buildings. The study evaluates measured district heating consumption data in Budapest, Hungary. The examined 218 buildings were grouped into 11 building types based on their architectural characteristics and analysed separately. The study aims to answer the question: how the buildings' characteristics influence the energy demand of the buildings. In the buildings only the total energy consumption is measured, thus the domestic hot water energy demand was examined in the summer months, when there is no heating in the building. The domestic hot water heat loss was 37–54% of total heat consumption in the summer period. The specific total district heating consumption data [kWh/m3/day] has higher deviation in colder months. The length of heating period is 183 days in Hungary, however the average length of heating period was longer in the examined buildings and it was even longer in case of the uninsulated buildings. From the measured consumption data the energy signature curves were developed for each building type for both the insulated and uninsulated buildings separately and the results were compared and analysed in detail. The energy signature diagrams showed a significant gap between the insulated and uninsulated buildings’ total district heating consumption data in the heating period. Lines were fitted to the data and the slope of the lines fitted to uninsulated buildings’ data indicate higher decline for every building type. A separation method was also suggested to divide the data of heating and non-heating period if its term is unknown. The difference between the average slope values of the fitted lines were analysed compared to buildings’ characteristics. It aimed to examine if the consumption reduction is influenced by the buildings’ physical parameters. In conclusion, the buildings’ characteristics did not always influence the final results (e.g. domestic hot water heat loss). But uninsulated buildings tend to have longer heating periods and buildings with smaller cooling surface area per heated volume had a predominantly lower energy consumption reduction rate.

Electromagnetic Design Characterization of a Dual Rotor Axial Flux Motor for Electric Aircraft

This article presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain-oriented electrical steel, Halbach arrays, and wires with rectangular cross sections, are used to improve torque density and efficiency. A novel winding arrangement is used to mitigate interturn short-circuit faults. Rather than simply optimizing the motor by itself, this article evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of these subsystems to select the design with the system-level optimal performance. This article uses finite-element simulations to characterize tradeoffs among active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, increase the structural mass required to support the rotors, and introduce complexity to the manufacturing process. Further analysis for a selected design reveals that the power factor can be significantly improved with a minimal torque penalty via field weakening due to significant saturation in the stator teeth.

Thermal comfort of a radiant cooling system in glass fiber reinforced gypsum roof – An experimental study

• Thermal comfort is achieved in a low embodied energy building with low energy cooling. • A high supply water temperature of 20 °C provided thermal comfort in a warm climate. • Radiant cooling of all surfaces provided thermal comfort even in hot weather. • Regression equations are developed to quantify the comfort in similar structure. • Air cavities in glass fiber reinforced gypsum roofs reduce penetration of solar heat. A holistic energy conservation approach that reduces the operational and embodied energy of the building is the need of the hour. A novel system that integrates the energy-efficient thermally activated building system (TABS) with the eco-friendly glass fibre reinforced gypsum (GFRG) reduces both operational and embodied energies. This system is termed a thermally activated glass fibre reinforced gypsum (TAGFRG) system, and research publications on this novel system are scarce. TAGFRG system is in the development stage; hence, its thermal comfort performance must be investigated extensively. A good understanding of the influence of operating parameters of the TAGFRG system can help in achieving the required thermal comfort by controlling these parameters. Therefore, the influences of supply water temperature and cooling surfaces are investigated experimentally and quantified using Fanger and adaptive thermal comfort models. An experiment room (3.46 m × 3.46 m × 3.46 m) with a TAGFRG roof in a warm and humid climate is used for this study. The proposed system can achieve 90% thermal comfort throughout the day, even at a high supply water temperature of 18 and 20 °C. An increase in supply water temperature from 18 to 26 °C increases the diurnal average operative temperature from 24.1 to 26.1 °C. An increase in the cooling surface area increases the cooling output and improves thermal comfort. The average predicted percentage dissatisfied is 22% if the roof alone is cooled directly with TABS. It reduces to 6% if all surfaces are cooled. The regression equations developed can quantify the thermal comfort indices for buildings with similar conditions at various water temperatures.

Calculation of Cooling Area and Surface Area of Roll-Type Membranes of Electrobaromembrane Apparatus for Separation of Technological Solutions

Calculation of Cooling Area and Surface Area of Roll-Type Membranes of Electrobaromembrane Apparatus for Separation of Technological Solutions

Heat transfer and pressure drop of film condensation in a horizontal minitube for HFO1234yf refrigerant

This paper applies the computational fluid dynamics (CFD) simulation to study the condensate two-phase thermofluid characteristics of refrigerant HFO-1234yf flowing through horizontal straight and convergent passages for guiding the design of minitube heat exchangers. The theoretical analysis employs the volume-of-fluid (VOF) method to model the progression of film condensation process for determining the distributions of velocity, pressure, temperature, vapor volume fraction and film thickness for liquid-vapor interfacial flows. The Lee model is formulated as a user defined function to treat the phase change effect at the interface. The predictions of heat transfer coefficients and pressure drops agree reasonably well with the measured data from the referencing literature at the mass and heat fluxes of 200–800 kg/m2 s and 9.9–24.3 kW/m2 for validation of the computational model. The simulated results are presented to capture the complex two-phase flow behaviors during the film condensation progression, including the formation of interfacial ripples of annular films, wave-shaped films with elongated necking regions, shedding of liquid ligaments and breakup of these ligaments entrained into the vapor core. The VOF calculations also estimate the average heat transfer coefficient and pressure drop up to 11.3 kW/m2 K and 55.1 kPa at a mass flux of 800 kg/m2 s for the straight tube, showing similar thermal performance to refrigerant HFC-134a reported by open literature. The convergent passage essentially raises the average heat transfer coefficient and pressure drop because of more severe shear stresses over the film surface. The correlations of heat transfer coefficient and pressure drop are compared with CFD predictions for straight and convergent tubes. The performance assessment is thus conducted using the validated correlations to guide the redesign of minitube heat exchangers with HFO1234yf as an alternative refrigerant in various energy systems. Two design changes are presented using HFO1234yf refrigerant to enlarge the total surface area up to 13.49% in straight tubes or broaden the cooling surface area of only 6.4% in convergent tubes for matching the performance of R134a.

Experimental analysis on the effect of cooling surface area and flow rate for water cooled photovoltaic module

Application of water spray or water flow on the surface of photovoltaic (PV) modules is one of the techniques used to increase efficiency. Main parameter that affect the performance by this technique is water flow rate and cooling surface are. However, there is less study focus on those parameters. Thus, the objective of this paper is to investigate the effect of water-cooled surface area and water flow rate on the temperature and power output of the PV. Orifices were used to create half-cooled and fully-cooled surface area for water to flow as cooling techniques while the hand valve was used to control the flow rate of water at 120 L/h, 180 L/h and 240 L/h flowing onto the panel. A solar simulator was constructed and used to provide 600 W/m2, 1,000 W/m2, and 1,200 W/m2 irradiance for the panel. The testing methodology consists of three different experiments for each irradiance level. It was found that more cooling surface area covered could significantly reduce temperature in any irradiance level, and fully-cooled module could keep the temperature at below 40 °C eventhough the irradiance was at 1,200 W/m2. In addition, the optimum flow rate also depends on the cooling surface area. Thus, there is a unique relation between cooling surface area and optimum flow rate. Thus, further investigation is needed on this relation.

Radiative sky cooling-assisted thermoelectric cooling system for building applications

Thermoelectric cooling suffers from low energy conversion efficiency (i.e., COP) which is a major bottleneck that hurdles its wide application, especially for large-scale systems. The COP of thermoelectric cooling system can be improved by integrating with other technologies. Due to its “free” nature, radiative sky cooling technology can potentially be integrated with thermoelectric cooling to obtain much higher system COP. This study introduces a novel radiative sky cooling-assisted thermoelectric cooling (RSC-TEC) system. The system has four different working modes under different operating conditions. A case study has been conducted for a two-story residential building that has 223 m2 living zone area located in Los Angeles, USA. Sensitivity analysis is first performed to size the system parameters. It is shown that the RSC-TEC system with a 0.83 m3 cold storage tank, 32 m2 radiative cooling surface area, and 101 thermoelectric modules (Laird ZT8-12), could achieve annual cooling COP of 1.87. Further analysis showed that daytime and nighttime cooling of the radiative sky cooling subsystem contribute to 55.0% and 45.0% of annual cold generation (heat dissipation) respectively, which indicates the critical importance of daytime cooling. The RSC-TEC system demonstrates a potential solution for large-scale adoption of the thermoelectric cooling technology.

Impact of Cell Size and Format on External Short Circuit Behavior of Lithium-Ion Cells at Varying Cooling Conditions: Modeling and Simulation

A multidimensional multiphysics model is presented to describe the external short circuit behavior of lithium-ion cells of various formats and sizes at different convective cooling conditions. For this purpose, a previously published homogenized physical-chemical model of the external short circuit behavior of a small-sized lithium-ion cell was combined with an electrical and a thermal model to describe in-plane inhomogeneities in current density and heat generation rate throughout the electrodes, together with the resulting temperature distribution within the cell’s jelly roll or electrode stack. With the investigated cylindrical, prismatic, and pouch-type cell formats combined with cell capacities ranging from consumer-sized to automotive applications, a comprehensive cell design study is presented during external short circuits. The investigated surface and tab cooling strategies reveal a limited cooling capability of each cell format and size, which seems to be defined by the ratio of cooled surface area to electrode area as well as the thermal resistivity of the respective cell geometry. The simulation results show that only thin cells with a large ratio of cooling surface to electrode area can be physically maintained within an uncritical operating window of cell temperature and state of charge in case a low-resistance external short circuit is applied.

Determination of long-term permissible currents in wires of power supply systems of railways

In the standard for contact wires made from copper and its alloys, the values of long-term permissible temperatures have significantly decreased. This requires recalculation of previously valid values of long-term permissible currents. Authors considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

Selection of parameters of geometrically similar impact electromagnetic machines

The interrelation between machine volume, cooling surface area and linear dimensions of geometrically similar volumes is established for impact electromagnetic machines. Magnetic field finite-element simulation results show the electromagnetic machines volumes influence on economic indicators.

Subambient Cooling of Water: Toward Real-World Applications of Daytime Radiative Cooling

Summary Real-world applications of radiative sky cooling require thoughtful design of the system, along with clear understanding of weather effects on system performance. This work explores application of radiative sky cooling based upon a low-cost radiative cooling metamaterial that can be scalably manufactured. A radiative cooled-cold collection (RadiCold) module is developed to cool water to 10.6°C below ambient at noon under stationary conditions. The effects of different weather conditions (wind speed, precipitable water, and cloud cover) on the performance of radiative cooling have been investigated. A kilowatt (kW)-scale RadiCold system with 13.5 m2 radiative cooling surface area is then built and demonstrated to provide a maximum cooling power of 1,296 W at night, and an average cooling power of 607 W at noon (12–2 p.m.) under 952 W/m2 average solar irradiance at 26.5 L/(h⋅m2) volumetric flow rate. A building-integrated RadiCold system is proposed to provide continuous day-and-night cooling.

How to Design a Park and Its Surrounding Urban Morphology to Optimize the Spreading of Cool Air?

Green areas induce smaller increases in the air temperature than built-up areas. They can offer a solution to mitigating the urban heat island impacts during heat waves, since the cool air generated by a park is diffused into its immediate surroundings through forced or natural convection. The purpose of this study is to characterize the effect of several variables (park size, morphology of surrounding urban area, and wind speed) on the spreading of cool air. A parametric study is performed to run computational fluid dynamics simulations. The air temperature entering the computational domain was set at 35 °C, and the 2-m high surface included within the 34 °C isotherm was defined as an indicator of cool air spreading. The effects of park shape and orientation were negligible in comparison with size effects. The number of buildings was better correlated with the cooled surface area than the typical urban parameters identified in the literature (i.e., building density, aspect ratio, or mean building height). Since the number of buildings is obviously related to the number of streets, this result suggests that the greater the number of streets around a park, the wider the area that cool air spreads.

Experimental and numerical studies of helium-cooled modular divertors with multiple jets

As part of the US-Japan PHENIX program, the helium-cooled modular divertor with multiple jets (HEMJ) and a simpler “flat” variant were experimentally studied in a closed helium loop with a redesigned test chamber at coolant inlet temperatures as great as 425 °C, incident heat fluxes as great as 2.2 MW/m2 and prototypical inlet pressures of ∼10 MPa. The data were used to develop correlations for the average Nusselt number and loss coefficient for a range of mass flow rates; these correlations were used in turn to predict the thermal-hydraulic performance of a single divertor module at prototypical conditions.The experimental results suggest that a flat jet array with six holes surrounding one central hole, all of the same diameter, can provide similar average heat transfer coefficients as the HEMJ divertor, albeit with higher pumping power requirements. Because of its smaller cooled surface area, however, this design has lower maximum allowable heat fluxes compared with the HEMJ divertor. Nevertheless, the flat variant could potentially simplify manufacturing and reduce the costs required to fabricate O(106) “finger” modules.

Experimental Analysis on the Effect of Area of Surface Cooling for a Water-Cooled Photovoltaic

Water flow for a water-cooled Photovoltaic (PV) may not cover the whole surface area of PV. Thus, the objective of this paper is to experimentally observe the effect of cooling surface area for a water-cooled PV. A water-cooled PV with 30W output was tested when its surface area was 50% and 100% covered with flowing water. This condition was tested at water flow rate of 120 mL/h, and irradiace of 855 W/m2, respectively. It was found that the panel recorded a maximum temperature of 72.10°C when it is uncooled. When it is cooled temperature decreased 22.05% and 51.04% for half and full surface, respectively, and temperature also remained constant approximately at 32oC for full surface. The current remained constant as expected and effect of temperature could be seen in voltage. Voltage increases when temperate decreases, and decreases when temperature increases. As the results, the power outputs for uncooled, half surface, and full surface were 10.38W, 10.66W and 11.08W, respectively. As compared to uncooled, this shows the increment of 6.10% and 13.50% for half surface and full surface, respectively. Thus, it could be concluded that the cooling surface area has substantial effects on the performance of water-cooled PV.