Mixing Of Hot Air Research Articles

Numerical and experimental investigations on thermal management for data center with cold aisle containment configuration

This study proposes the container data center with the featured cold aisle containment (CAC) as effective thermal control strategy. In design, the overhead downward flow system is implemented with a heat exchanger arranged right above the data center on the air side and an evaporative water chiller on the water side to form the cooling approach. The cold airflows and hot exhausts of racks are separately transported by the contained cold and hot aisles to alleviate the problem of cold and hot air mixing. The measurements of air temperature and velocity of racks are used to validate the prediction accuracy of the computational fluid dynamics (CFD) model. The performance metrics in terms of the rack cooling index (RCI), return temperature index (RTI), supply heat index (SHI) are used to examine the design effectiveness of the proposed test data center. The simulations are then extended to assess the air distribution and thermal management at varied supply air temperatures and velocities for a large-scale data center to be built in the green energy technology demonstration site of the Shalun smart green energy science city. Overall, the calculated average PUE of 1.38 for the large-scale data center is notably less than the average PUE of 1.59 from the results of 2020 data center industry survey, indicating the potential savings of cooling energy and cost. This paper demonstrates a generalized approach as an easily adaptable, cost-effective solution for data centers to be deployed in tropical and subtropical areas.

Design and Computational Fluid Dynamics Analysis of a Novel Compact Mixing Chamber in Blast Furnace Ironmaking

Abstract Homogeneous mixing of hot air from the hot blast stove with suitable quantity of cold air in a mixing chamber is very essential to maintain uniform temperature of hot air at all tuyers of a blast furnace. Proper design of the mixing chamber is very important for stable and efficient operation of blast furnace, lower energy consumption, and lower carbon dioxide emission. Comprehensive understanding of the physics of the mixing process is very essential for efficient design of the mixing chamber. In this paper, computational fluid dynamics (CFD) simulations are conducted to analyze the mixing of hot and cold air in a tangential cold gas inlet type and in a radial cold gas inlet type mixing chambers, which are commonly used in the industry. Results show that both types of mixing chamber produce very non-homogeneous mixture of cold and hot air despite having large mixing length in the long hot blast main. Also, design of a novel compact mixing chamber is presented and CFD analysis of this mixing chamber is conducted. The new mixing chamber is found to produce almost homogeneously mixed air stream within a very short length due to very high turbulence of the intensely swirling air flow. Also, the new mixing chamber is found to save large amount of high-quality thermal energy, which is wasted in the other two designs through the wall of the long hot blast main.

Application of separated heat pipe system in data center cooling

This paper mainly studies the application of separated heat pipe system on data center cooling. Separated heat pipe system mainly consists of four parts: evaporator, condenser, vapor pipe and liquid pipe. Compared with traditional computer room air conditioning (CRAC) system, which is a kind of room level cooling, heat pipe cooling system is rack level cooling. There are mainly three advantages for separated heat pipe system, firstly, air flow organization is better for there is nearly no hot and cold air mixing, secondly, such system can use cold ambient air as heat sink in winter, thirdly, as the evaporator is placed directly inside the rack, heat generated from IT equipment will be soon absorbed by heat pipe system, thus there is nearly no local hot spots inside the rack. To describe the working condition of the system, there are mainly three parts in this paper. Firstly, operation performance in summer, winter and trans-season is tested. Secondly, as the system can use free cold ambient air to produce chilled water, the time of using free cold ambient air is tested. Finally, T-Q diagram is used to compare the heat transfer process in heat pipe system and traditional CRAC system. The results show that, IT equipment can work in a safe and reliable environment. Besides, the heat sink temperature in heat pipe system is much higher than CRAC system and there is nearly no cold and hot air mixing in heat pipe system. In summary, heat pipe system can save more electrical energy than CRAC system.

乾湿計の原理による沸点温度以上での湿度測定方法

Superheated steam/high-humidity air over boiling point temperature is used as a heating media for food heating machineries, such as steamers and ovens. However, there is no suitable humidity measuring equipment under high temperature and humidity air. Therefore, we have developed a measuring device using porous ceramics based on the principle of the psychrometer. In this study, we have developed a humidity generator of calibrate the humidity measuring device. Standard humidity is generated by mixing of hot air and superheated steam. We have verified the accuracy by comparing values in steam mole fraction measured by the calibrated dew-point instrument and by the flow meters as well as by the psycrometer using porous ceramics. We have analyzed uncertainty of the generated humidity to evaluate the reliability.

Measurement of Air Flow Rate Sensitivity to the Differential Pressure Across a Server Rack in a Data Center

Presently, air cooling is the most common method of thermal management in data centers. In a data center, multiple servers are housed in a rack, and the racks are arranged in rows to allow cold air entry from the front (cold aisle) and hot air exit from the back (hot aisle), in what is referred as hot-aisle-cold-aisle (HACA) arrangement. If the racks are kept in an open room space, the differential pressure between the front and back of the rack is zero. However, this may not be true for some scenarios, such as, in the case of cold aisle containment, where the cold aisle is physically separated from the hot data center room space to minimize cold and hot air mixing. For an under-provisioned case (total supplied tile air flow rate < total rack air flow rate) the pressure in the cold aisle (front of the rack) will be lower than the data center room space (back of the rack). For this case, the rack air flow rate will be lower than the case without the containment. In this paper, we will present a methodology to measure the rack air flow rate sensitivity to differential pressure across the rack. Here, we use perforated covers at the back of the racks, which results in higher back pressure (and lower rack air flow rate) and the corresponding sensitivity of rack air flow rate to the differential pressure is obtained. The influence of variation and nonuniformity in the server fan speed is investigated, and it is observed that with consideration of fan laws, one can obtain results for different average fan speeds with reasonable accuracy. The measured sensitivity can be used to determine the rack air flow rate with variation in the cold aisle pressure, which can then be used as a boundary condition in computational fluid dynamics (CFD)/rapid models for data center air flow modeling. The measured sensitivity can also be used to determine the change in rack air flow rate with the use of different types of front/back perforated doors at the rack. Here, the rack air flow rate is measured using an array of thermal anemometers, pressure is measured using a micromanometer, and the fan speed is measured using an optical tachometer.

FL2-2 Numerical Study on Soot Precursor of JP-8 Surrogate under Diesel Conditions Using a Two-Stage Lagrangian (TSL) Model(FL: Fuels,General Session Papers)

Fuel properties, fuel injection, fuel-air mixing, and the resulting combustion processes strongly influence the functionality and performance of diesel engines. The Single-Fuel Concept (SFC) for application of JP-8 fuel to diesel engines contains potential problems for current and advanced combustion engines. In order to maximize efficiency while limiting emissions and maintaining robust combustion for these systems when using JP-8 as a fuel, fundamental spray, ignition, and combustion properties need to be thoroughly understood and characterized. Recently, surrogate fuels have been widely studied to simulate combustion characteristics of real fuels including diesel and JP-8. In this study, the combustion and polycyclic aromatic hydrocarbon (PAH) growth characteristics of JP-8 were investigated numerically through the surrogate components and results were compared with those of n-heptane under diesel in-cylinder conditions. The reaction mechanism of JP-8 surrogate fuel was modified with addition of soot chemistry from n-heptane reaction mechanism. First, closed reactor model using CHEMKIN code was used to calculate pyrene yield as PAH indicator over a wide range of temperature and equivalence ratios for both fuels. Second, the Two-Stage Lagrangian (TSL) model capable of coupling detailed chemical kinetics with a simplified jet flow field were used to simulate high-pressure spray combustion by incorporating data on mixing or entrainment of fuel/air and flame lift-off length from published experimental data. Results indicated that closed reactor simulation showed similar yields of C_2H_2, C_6H_6, and pyrene for both fuels. However, TSL model showed that PAH region was shifted to lower equivalence ratio and higher temperature compared to closed reactor simulation due to a fact that the mixing of hot air into fuel spray would result in higher core temperature.