Terms Of Temperature Reduction Research Articles

Experimental and numerical investigations on the influence of phase change materials on heat transfer reduction across the roof of a building

ABSTRACT Faced with the problems of increasing energy scarcity and ongoing environmental deterioration, phase change materials (PCM) have attracted a lot of attention recently for improving building energy performance. Utilizing the PCMs in buildings is one of the efficient approaches to reduce the heat penetration into the buildings. In this work, the thermal performance of a building equipped with PCM roof is analyzed and compared with a plain roof building. The uniqueness of this study is to analyze the effect of PCM experimentally and numerically through parametric investigation with different PCMs (HS29 and OM29), encapsulation materials (aluminum and steel) and PCM thickness. The experimental analysis shows that the PCM incorporated roof decreased the inner room temperature of the building by 2°C vis-à-vis plain roof and hence helps reduce the cooling load and enables passive cooling of the building with energy savings. A numerical analysis was carried out using COMSOL and validated with maximum and average errors of 7.43% and 4.87% respectively. The parametric investigation from the validated model indicates that the PCM OM29 is effective compared to HS29 in terms of temperature reduction. The steel encapsulating panels are observed to be better than aluminum at the peak sunshine hours while the aluminum panel is effective for the other periods. It is observed that the increase in PCM thickness augments the reduction in heat transfer while the 6 cm PCM thickness showed a higher temperature reduction by 3.6°C vis-a-vis 2 cm PCM thickness.

Design and Study of Domestic Cooling System through Roof Ventilation Assisted by Evaporative Cooling

This study shows the evaluation of the indirect evaporative cooling system beneath the roof that aims to reduce the cooling load in buildings. As the energy demand for space cooling increases over the years, the evaporative cooler that has lower energy consumption can be a green technology for space cooling compared with air-conditioning systems. An example of an evaporative roof cooling method that is commonly used is a rooftop sprinkler system. This study emphasizes the evaluation of the performances of an indirect evaporative cooler and rooftop sprinkler system in terms of temperature reduction and cooling capacity. The modelling is done by using the sol-air temperature to estimate the solar heat gain. Then, the cooling power of each system is calculated, and finally, the indoor temperature for the respective system can be determined. The finding shows that the temperature drop for the indirect evaporative cooler is 9.2°C, whereas for the rooftop sprinkler system, it is only about 4.4°C. The simulated cooling load of the indirect evaporative cooler for this test house can go up to 49.2W.

Attic ventilation and radiant heat barriers in naturally ventilated galvanized metal-Roofed buildings

ABSTRACT The study's uniqueness stems from its goal of determining the efficacy of natural attic vents and radiation heat barriers on galvanized metal roof buildings in lowering attic and indoor air temperatures for thermal comfort in a humid tropical climate, a topic that has received little attention in previous research. This was accomplished by utilizing three separate experimental situations using two tiny models of single-sloped zinc-roofed houses, each with varied attic ventilation openings and radiant heat barrier applications. The thermal conditions of the attic and occupant rooms in the ventilated test cell tended to be cooler than in the unventilated one in the first experiment, which compared a test cell with 20% ventilation apertures in the attic to another test cell without ventilation. The second experiment, which compared a test cell with 10% attic ventilation to another test cell (without attic ventilation) with radiant heat barrier application, found that the radiant heat barrier's effect on temperature reduction was generally better. The third experiment, which compared a test cell with 20% attic ventilation to a test cell without attic ventilation but with radiant heat barrier application, revealed that attic ventilation outperformed the radiant heat barrier in terms of temperature reduction.

Antipyretic Effectiveness of Oral Acetaminophen Versus Rectal Acetaminophen in Pediatric Patients With Fever.

Acetaminophen, one of the routine medicines used for temperature reduction in febrile children, is available in multiple routes of administration, including oral and rectal routes. Our objective is to compare the antipyretic effectiveness of oral acetaminophen versus rectal acetaminophen in pediatric patients with fever in terms of temperature reduction. Medline and Embase databases were searched from inception to August 2021. Cohort studies, case-control studies, experimental studies, and randomized controlled trial studies comparing oral and rectal administered acetaminophen in pediatric patients were included. Two reviewers independently extracted data. A total of 5 randomized studies (n = 362) were included in the meta-analysis. No significant difference was found between oral and rectal acetaminophen in temperature reduction at 1 hour (weighted mean difference [WMD], 0.04°C; 95% confidence interval [CI], -0.10°C to 0.19°C; P = .501) or 3 hours (WMD, -0.14°C; 95% CI, -0.37°C to 0.10°C; P = .212) after administration (WMD, -0.14°C; 95% CI, -0.37°C to 0.10°C; P = .212). Oral and rectal acetaminophen have no significant difference in antipyretic effectiveness at 1 and 3 hours after administration. If both options are available, oral acetaminophen would be preferred because of a more predictable drug level after administration. However, for febrile children with specific circumstances for whom oral acetaminophen could not be administered, rectal acetaminophen may be an alternative option for a short period of time (<48 hours).

Optically selective PDMS/AIN coatings as a passive daytime radiative cooling design

Passive radiative cooling is a natural process in which an object or surface emits thermal radiation into the cold sky to prevent it from heating up. Daytime passive cooling technology requires a selective design to reflect incoming solar radiation and simultaneously emit thermal radiation to the cold universe through the sky window 8–13 µm. In this study, we propose multilayer design of cooling device consisting of bilayer of polydimethylsiloxane foil (PDMC) and aluminum nitride (AIN) both deposed on silver coated glass. The spectral radiative properties of the proposed device are examined using the transfer matrix method. Numerical results show that our design acts as infrared optical window, as it has a high solar reflection with an average of over 96 % and strong thermal emissivity in atmospheric transparency window with an average of over 90 %. In absence of parasitic heat exchange, high cooling power of 107 W/m2 at ambient temperature with an effective temperature drop of 45 K below the ambient are obtained. The cooling effect persists even in the presence of parasitic heat exchange with temperature reduction of 17 K below the ambient. To assess the validity of this study, the performance of the multilayer design is compared with an experimental black emitter and the results indicate that our design has good properties in terms of temperature reduction. In the light of our findings, we can state that our design can fundamentally enable new methods for advancing the applications of exploiting radiative cooling.

Numerical analysis of an automobile cabin thermal management using passive phase change material

Nowadays, efforts are being made to reduce HVAC load in vehicles and maintain comfortable temperatures within the cabin, predominantly owing to extreme weather conditions, particularly during the hot summer season. Solar radiation increases heat transfer in vehicles. In addition to the greenhouse effect, it adds significantly to increasing heat content inside the vehicle's cabin, thus increasing temperature. Thus, there is a need for thermal management of automobiles, which could be achieved using utilizing latent heat storage materials, such as Phase Change Materials (PCMs). Present research focuses on computational fluid dynamics simulations for evaluating performances of four PCMs – OM 29, HS 24, Bio Q27 and CaCl2·6H2O in thermal management of vehicle’s cabin for a short duration of time (120 s). Accordingly, most appropriate PCM is selected based on the results achieved in terms of temperature reduction, difference in temperature achieved and standard comfortable temperature, and melt fraction for further analysis of cabin for a longer duration (3600 s). Results revealed that within 120 s, PCM incorporation facilitates cabin temperature reduction of approximately 7 K. Moreover, CaCl2·6H2O proved to be the most suitable amongst four PCMs studied, based on the criteria mentioned above for the given environment conditions. Hence, its performance is further explored for a period of 1 h, that resulted in reducing cabin’s peak temperature approximately by 33 K.

Evaluation of photovoltaic panels using different nano phase change material and a concise comparison: An experimental study

The cooling techniques of photovoltaic (PV) panels captured special attention due to positive impact on PV panels efficiency as continuous elevation of temperature degraded its performance. A number of studies have suggested the better prospects of air, water and phase change material (PCM) for thermal management of PV modules. The present work studies three different nanoparticle-based nano-PCMs for acceleration in performance of PV panel in terms of temperature reduction and increment of electrical efficiency. The experimental methodology was tested in the outdoor conditions of Taxila, Pakistan during winter seasons by using different concentrations (0.25 wt% and 0.5 wt%) of multiwall carbon nanotubes nanoparticles, graphene nanoplatelets and magnesium oxide nanoparticles in phase change material (PT-58). The topmost performance of PV panel is found at 0.5 wt% nanomaterial concentration in graphene nanoplatelets/PT-58 nano-PCM. The experimental results indicate that maximum temperature reduction is observed to be 9.94 °C, 6.53 °C for PV/nano-PCM at 0.5 wt% of graphene nanoplatelets/PT-58 nano-PCM and 0.25 wt% of graphene nanoplatelets/PT-58 nano-PCM respectively while it was 5.01 °C for PV/PCM with highest observation in electrical efficiency of 12.10%, 11.97% and 11.74% respectively as compared to conventional PV panel. The maximum percentage increase of electrical power was 33.07% in case of GNPs/PT-58 nano-PCM at 0.5 wt% of nanomaterial in base PCM. The graphene nanoplatelets based nano-PCM exhibited best results in terms of temperature reduction as well as electrical efficiency and higher concentration of nanoparticles indicated good results compared to low concentration in nano-PCM.

PERFORMANCE EVALUATION OF POULTRY HOUSES UNDER DIFFERENT EVAPORATIVE COOLING SYSTEMS

Poultry production occupied a major role in the agriculture industry worldwide. Poultry housing design plays a vital role in determination of the internal climatic conditions for optimum health, growth and productive performance of the poultries. The present investigation aimed to evaluate the performance of different evaporative cooling systems with environmental control of poultry houses. The effect of two different evaporative cooling systems (direct and indirect) under three water flow rates of 2, 4 and 6 l/min.m2 on poultry houses performance was evaluated in terms of temperature reduction, relative humidity, evaporative cooling efficiency, poultry weight, consumed energy and cost. Experimental results revealed that using direct evaporative cooling system with 4 l/min.m2 water flow rate and indirect evaporative cooling system with 2 l/min.m2 water flow rate provided sufficient conditions of temperature reduction (9.59 and 7.28oC), relative humidity (63.88 and 61.21%), cooling efficiency (75.67 and 83.67 %), poultry weight (2.4 and 2.3 kg) and consumed energy (1.2 and 6 kW.day) with net return (7.54 and 5.80 LE/kg), in that order. Based on previously mentioned results, it is recommended to use direct evaporative cooling system for poultry houses as it minimizes both energy and cost requirements compared to the indirect evaporative cooling system, therefore it was found to be suitable for small rural farmers.

Determination of the Effect of Green Roofs on Indoor Temperature by the Use of Simulation in a Tropical Landscape

Aims: To use a simulation base exploration to carry out 6 scenarios of green roof construction methods to determine the most efficient in improving indoor thermal comfort.&#x0D; Study Design: Simulation Design was used as the study design.&#x0D; Place and Duration of Study: The study was conducted at the Department of Horticulture – Kwame Nkrumah University of Science and Technology located at Kumasi-Ghana between 2016 and 2019.&#x0D; Methodology: A simulation experimental setup was done to run for 1 year to cover the two seasons in Ghana. Version 5.0.2 Design Builder and Energy Plus 5.8 was used to work on 6 scenarios using leaf area indexes (LAI) of 2 and 5 as well as soil depth (thickness) of (70-150 mm), 200 mm, 300 mm and 500 mm. Also a real life experiment was done at the Department of Horticulture by constructing 9 test cells and using treatments such as Portulaca grandiflora and Setcreasea purpurea to validate the results for the simulation. The time setup for the simulation was from 12.00 am to 11.59 pm.&#x0D; Results: A leaf area indexes (LAI) of 5 and soil depth of 70 mm-150 mm recorded the lowest simulated temperature ranging from 26.26°C to 29.30°C for scenario one. For scenario two, a leaf area indexes (LAI) of 5 and a soil depth of 200mm recorded the lowest significantly (P≤0.05) indoor temperature in August (26.20°C) and the highest (29.26°C) in March. In February, June and August, significant differences (P≤0.05) were achieved by leaf area indexes (LAI) 5 and soil thickness 500 mm for scenario three. January, March to July indicated significant differences (P≤0.05) between the treatments leaf area indexes (LAI) 2 and soil thickness 300 mm and leaf area indexes (LAI) 5 and soil depth of 300 mm recorded 26.32°C to 29.33°C for August and March respectively for scenario four. A soil depth of 500 mm and leaf area indexes (LAI) of 2 gave significantly (P≤0.05) low temperatures indoors all year (26.27 to 29.32°C) for scenario five and in August leaf area indexes (LAI) 5 and soil thickness of 500 mm recorded the least temperature all year for scenario six.&#x0D; Conclusion: From the exploration, a soil depth of 70 mm – 150 mm and a LAI of 5, LAI of 5 and soil depth of 200 mm and LAI of 2 and soil depth of 500 mm achieved the lowest temperature and performed better in terms of temperature reduction which will lead to thermal comfort of occupants.

A reduced-scale experiment to evaluate the thermal performance of building envelopes containing phase change material spheres

To reduce the heat transfer between outdoor and indoor environments, phase change materials (PCMs) were introduced to building envelopes. Research has shown that the position of PCMs is a key factor that influences the thermal behaviour of building envelopes containing PCMs. In the present paper, experiments were conducted to define the optimum PCM position to enhance the cooling and heating energy performance. PCMs with a melting temperature between 27 °C and 29 °C were encapsulated in spheres, arranged in an insulation layer. An electric heating film was adopted to simulate the solar radiation that was received by the outer surface of building envelopes. The thermal performance of the envelopes with PCM spheres was analysed in terms of temperature reduction and elevation, surface temperature amplitude and PCM phase transition temperature and time. With higher heating rate, the temperature reduction was higher for the PCM spheres at same positions. With same heating rate, the temperature reduction increased and then decreased when the PCM spheres moved from outdoor to indoor. The maximum temperature reduction using PCM spheres was 13.03 °C by 23.0% when the solar radiation was 200 W/m2 and the maximum temperature elevation using PCM spheres was 7.8 °C by 56.7%. The allowable thermal resistance between PCMs and outdoor environment under different heating rate was given. The PCMs are recommended to install on the inward-most layer of the wall if they can complete their melting process.

APPLYING DIRECT EVAPORATIVE COOLING SYSTEM FOR CONTROLLING ENVIRONMENTAL CONDITIONS IN RABBIT HOUSES

Heat stress is a major problem that faces rabbit’s breeders. This problem adversely affects rabbit's growth and reduces the resistance to diseases. The present research was carried out to apply and evaluate the performance of a direct evaporative pad cooling system in rabbit houses to control environmental conditions. The direct evaporative pad cooling system performance was studied as a function of change in pad thickness (10 and 15 cm), water flow rate (3, 5 and 7 L/min.m2) and rabbit stocking density with an approximate average (0.5 and 1.0 rabbit/m2). Performance evaluation of the evaporative pad cooling system was carried out in terms of temperature reduction, cooling efficiency, temperature-humidity index, daily body weight gain and mortality ratio. The experimental results clarified that values of temperature reduction (7.3 and 6.8 oC), cooling efficiency (94.92 and 90.91 %), temperature-humidity index (26.30 and 27.40 oC), daily body weight gain (38.80 and 38 g/rabbit/day) and mortality ratio (0.2 and 0.4 %) are in the optimal limits under conditions of 15 cm pad thickness and 5 L/min.m2 water flow rate for rabbit stocking densities of 0.5 and 1.0 rabbit/m2, respectively.

Thermal management of conventional PV panel using PCM with movable shutters – A numerical study

Effect of Phase Change Material (PCM) on electrical efficiency and operating temperature of PV panel is studied in this article. PCM is filled in rotatable shutters attached to the back side of PV panel. PCM filled rotatable shutters are used to ensure the complete solidification of PCM during non-sunshine hours. During sunshine hours PCM filled shutters are closed and absorb excess heat generated by PV panel. The absorbed heat is discharged by rotating the PCM filled shutters to ambient during non-sunshine hours. The modeling results revealed that conventional PV panel temperature without PCM can be as high as 64 °C that can be reduced to 42 °C using PCM filled shutters with melting temperature of 35 °C. Efficiency can be improved up to 9% during peak summer season for the PV panel working under hot humid climatic conditions. Maximum benefits of PCM in terms of temperature reduction and are observed during the summer season compared to the winter season. The study also suggested that states if the PCM melting temperature is approximately equal to the average of the maximum ambient temperature of all summer months, then maximum benefits in terms of efficiency improvement and temperature reduction can be achieved for the whole year.

Studying Temperature Variations that Occurred during Cold and Hot Rolling of AA5454-O Alloy

In this study, temperature distribution that occurred during cold and hot rolling of AA5454-O alloy has been investigated. Temperature variation taking place in the aluminium alloy that has undergone plastic deformation between the rollers during hot and cold rolling process is of major importance in terms of determining the positive and negative characteristics or features which such temperature variation adds to the formation of the internal structure of the material concerned. Temperature distribution has been measured by use of the installed laboratory equipment and respective data recorded has been presented in the form of graphic charts. Temperature distribution has varied depending on the application of hot or cold rolling process and it has been noted that variations in terms of temperature reduction took place depending on the number of roll passes. While average temperature variation has occurred as a 16°C increase in the case of cold rolling, it has been observed that such variation appeared as a 100°C decrease on the average in the case of hot rolling.

Layout-Driven Post-Placement Techniques for Temperature Reduction and Thermal Gradient Minimization

With the continuing scaling of CMOS technology, on-chip temperature and thermal-induced variations have become a major design concern. To effectively limit the high temperature in a chip equipped with a cost-effective cooling system, thermal specific approaches, besides low power techniques, are necessary at the chip design level. The high temperature in hotspots and large thermal gradients are caused by the high local power density and the nonuniform power dissipation across the chip. With the objective of reducing power density in hotspots, we propose two placement techniques that spread cells in hotspots over a larger area. Increasing the area occupied by the hotspot directly reduces its power density, leading to a reduction in peak temperature and thermal gradient. To minimize the introduced overhead in delay and dynamic power, we maintain the relative positions of the coupling cells in the new layout. We compare the proposed methods in terms of temperature reduction, timing, and area overhead to the baseline method, which enlarges the circuit area uniformly. The experimental results showed that our methods achieve a larger reduction in both peak temperature and thermal gradient than the baseline method. The baseline method, although reducing peak temperature in most cases, has little impact on thermal gradient.