Experimental and numerical analysis of air temperature uniformity in occupied zone under stratum ventilation for heating mode

2021 ◽  
pp. 103016
Author(s):  
Junmeng Lyu ◽  
Xuan Feng ◽  
Yong Cheng ◽  
Chunhui Liao
Keyword(s):  
Numerical Analysis ◽  
Air Temperature ◽  
Temperature Uniformity ◽  
Heating Mode ◽  
Occupied Zone

Airflow pattern and performance of wall confluent jets ventilation for heating in a typical office space

2019 ◽  
Vol 29 (1) ◽  
pp. 67-83
Author(s):  
Diyi Tan ◽  
Baizhan Li ◽  
Yong Cheng ◽  
Hong Liu ◽  
Jinhua Chen
Keyword(s):  
Air Temperature ◽  
Temperature Difference ◽  
Thermal Environment ◽  
Ambient Air ◽  
Air Velocity ◽  
Text Model ◽  
Jet Velocity ◽  
Ventilation Performance ◽  
Heating Mode ◽  
Occupied Zone

To investigate an air distribution system with the potential to provide a comfortable thermal environment and efficient ventilation performance in heating mode, this study compared the numerical results of the RNG k-[Formula: see text] model, realizable k-[Formula: see text] model and SST k-ω model with experimental data obtained from a typical office with wall confluent jets ventilation (WCJV) for heating. The SST k-ω model was chosen for numerical study of WCJV. The findings showed that the WCJV performed better than mixing ventilation (MV) in the heating mode because WCJV could entrain less ambient air and maintain the jets’ momentum and energy to reach the occupied zone. The effects of supply air temperature difference (in the range of 2.00°C to 7.79°C) and supply air velocity (in the range of 2.20 m/s to 8.50 m/s) on the jet velocity profiles and ventilation performance of WCJV were also quantified. The results showed that the jet velocity profile was more sensitive to the supply air velocity than to the supply air temperature difference. Accordingly, reducing the supply air velocity might result in poorer thermal environment and air quality in the occupied zone because the warm air jets cannot spread out over the floor area. The results can be helpful in understanding WCJV used for ventilation under heating mode.

scholarly journals Temperature uniformity in the CERN CLOUD chamber

2017 ◽  
Vol 10 (12) ◽  
pp. 5075-5088 ◽  
Author(s):  
António Dias ◽  
Sebastian Ehrhart ◽  
Alexander Vogel ◽  
Christina Williamson ◽  
João Almeida ◽  
...  
Keyword(s):  
Steady State ◽  
Air Temperature ◽  
Elevated Temperatures ◽  
Trace Gases ◽  
Vertical Direction ◽  
Cloud Chamber ◽  
Temperature Uniformity ◽  
Atmospheric Conditions ◽  
Cloud Droplets ◽  
Experimental Conditions

Abstract. The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN (European Council for Nuclear Research) investigates the nucleation and growth of aerosol particles under atmospheric conditions and their activation into cloud droplets. A key feature of the CLOUD experiment is precise control of the experimental parameters. Temperature uniformity and stability in the chamber are important since many of the processes under study are sensitive to temperature and also to contaminants that can be released from the stainless steel walls by upward temperature fluctuations. The air enclosed within the 26 m3 CLOUD chamber is equipped with several arrays (strings) of high precision, fast-response thermometers to measure its temperature. Here we present a study of the air temperature uniformity inside the CLOUD chamber under various experimental conditions. Measurements were performed under calibration conditions and run conditions, which are distinguished by the flow rate of fresh air and trace gases entering the chamber at 20 and up to 210 L min−1, respectively. During steady-state calibration runs between −70 and +20 °C, the air temperature uniformity is better than ±0.06 °C in the radial direction and ±0.1 °C in the vertical direction. Larger non-uniformities are present during experimental runs, depending on the temperature control of the make-up air and trace gases (since some trace gases require elevated temperatures until injection into the chamber). The temperature stability is ±0.04 °C over periods of several hours during either calibration or steady-state run conditions. During rapid adiabatic expansions to activate cloud droplets and ice particles, the chamber walls are up to 10 °C warmer than the enclosed air. This results in temperature differences of ±1.5 °C in the vertical direction and ±1 °C in the horizontal direction, while the air returns to its equilibrium temperature with a time constant of about 200 s.

scholarly journals Experimental Investigation of Ventilation Performance of Different Air Distribution Systems in an Office Environment—Heating Mode

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1835 ◽  
Author(s):  
Arman Ameen ◽  
Mathias Cehlin ◽  
Ulf Larsson ◽  
Taghi Karimipanah
Keyword(s):  
Thermal Comfort ◽  
Distribution Systems ◽  
Cold Climate ◽  
Air Distribution ◽  
Temperature Pattern ◽  
Office Environment ◽  
Ventilation Effectiveness ◽  
Local Thermal Comfort ◽  
Heating Mode ◽  
Occupied Zone

A vital requirement for all-air ventilation systems are their functionality to operate both in cooling and heating mode. This article experimentally investigates two newly designed air distribution systems, corner impinging jet (CIJV) and hybrid displacement ventilation (HDV) in comparison against a mixing type air distribution system. These three different systems are examined and compared to one another to evaluate their performance based on local thermal comfort and ventilation effectiveness when operating in heating mode. The evaluated test room is an office environment with two workstations. One of the office walls, which has three windows, faces a cold climate chamber. The results show that CIJV and HDV perform similar to a mixing ventilation in terms of ventilation effectiveness close to the workstations. As for local thermal comfort evaluation, the results show a small advantage for CIJV in the occupied zone. Comparing C2-CIJV to C2-CMV the average draught rate (DR) in the occupied zone is 0.3% for C2-CIJV and 5.3% for C2-CMV with the highest difference reaching as high as 10% at the height of 1.7 m. The results indicate that these systems can perform as well as mixing ventilation when used in offices that require moderate heating. The results also show that downdraught from the windows greatly impacts on the overall airflow and temperature pattern in the room.

Effect of Oscillating Flow on Thermal Stratification in an Enclosure

2005 ◽  
Author(s):  
Sung Ki Kim ◽  
Seo Young Kim
Keyword(s):  
Uniform Distribution ◽  
Air Temperature ◽  
Thermal Stratification ◽  
Three Dimensional ◽  
Oscillating Flow ◽  
Temperature Uniformity ◽  
Flow Oscillation ◽  
Air Mixing ◽  
Dimensional Measurements ◽  
Specific Frequency

The present study aims at investigating the effect of oscillating flow on thermal stratification in a gas oven. To date, the fan convectors are common to reduce thermal stratification inside various types of oven. The impetus of the present study is to investigate the feasibility of flow oscillation to achieve more uniform distribution of air temperature within an oven. To produce the flow oscillation, an acoustic woofer is vertically installed on the back of a gas oven. The operating frequency of the acoustic woofer is varied from 30 to 60 Hz. Three-dimensional measurements of air temperature inside the oven are implemented to evaluate temperature uniformity. The experimental results show that the oscillating flow with a specific frequency enhances air mixing dramatically, which results in the attenuation of thermal stratification inside the oven. The actual baking of sponge cake also shows that the convector using the flow oscillation can provide better results compared to the conventional fan convectors.

Numerical Analysis on the Effect of Thermal Insulation of Closure on Fire Smoke Spread Rate in Building's Corridor

2014 ◽  
Vol 513-517 ◽  
pp. 2635-2638
Author(s):  
Xuan Wei Peng
Keyword(s):  
Numerical Analysis ◽  
Thermal Insulation ◽  
Air Temperature ◽  
Spread Rate ◽  
Smoke Flow ◽  
External Insulation ◽  
Flow Prediction ◽  
Smoke Spread ◽  
Fire Smoke ◽  
Fire Ignition

The corridor is an important way of evacuation and rescue in building fire. The fire smoke flow prediction software developed successfully was applied to simulate a building with a 28.8 meters long corridor to investigate the effect of the different thermal insulation on fire smoke spread rate. Two representative thermal insulation, external insulation and internal insulation were compared. In 3600s fire time, air temperature in the corridor of external insulation is much lower than that of internal insulation. The air temperature gap gets narrowed between the two insulation methods in the corridor with the prolongation of fire time. Temperature difference increases as the distance increase from the fire ignition place. The corridor gets unsafe of internal insulation in 7 minute since fire ignition, while about half the length of the corridor stay secure of external insulation in 10 minutes since fire ignition. That implies more available safe egress time can be gained with external insulation than internal insulation. Smoke spread rate was numerically compared based on the air temperature variation. Smoke spread rate of internal insulation is much higher than that of external insulation and the corresponding ratio is 1.732:1.

scholarly journals Prediction and Evaluation of Dynamic Variations of the Thermal Environment in an Air-Conditioned Room Using Collaborative Simulation Method

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5378
Author(s):  
Lin He ◽  
Shunan Zhao ◽  
Guowen Xu ◽  
Xin Wu ◽  
Junlong Xie ◽  
...  
Keyword(s):  
Air Temperature ◽  
Temperature Difference ◽  
Thermal Environment ◽  
Structural Parameters ◽  
Simulation Method ◽  
Outer Diameter ◽  
Control Parameters ◽  
Temperature Uniformity ◽  
Collaborative Simulation ◽  
Dynamic Variations

In this study, a collaborative simulation method is proposed to predict dynamic variations of the thermal environment in an air-conditioned room. The room thermal environment was predicted and analyzed by varying the structural and control parameters of the air conditioner considering the dynamic coupling effect. Connections and regularities were established between the applicable parameters and evaluation indices of the thermal environment. The simulation results demonstrated the interactions among the system structural parameters, control parameters, and the thermal environment. Within a certain parameter range, the evaporator structure exhibited a significant effect on temperature uniformity and vertical air temperature difference, followed by predicted mean vote (PMV) and draught rate (DR). The associated evaluation indices were sensitive to fin spacing, tube spacing, and tube outer diameter, in the same order, which were structural parameters of the evaporator. The effect of the air supply angle on the vertical air temperature difference was evident; however, its influence on the PMV, DR, and temperature uniformity did not indicate consistent variations.

Thermal Environment Analysis and Improvement on Isolated Cold Aisle Data Centers

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Lin Su ◽  
Zhilin Huang ◽  
Kaijun Dong
Keyword(s):  
Air Temperature ◽  
Data Centers ◽  
Thermal Environment ◽  
High Porosity ◽  
Temperature Uniformity ◽  
Transitional Form ◽  
Environment Analysis ◽  
Cooling Performance ◽  
Adequate Ventilation ◽  
Airflow Distribution

Abstract Isolated cold aisle airflow distribution is a transitional form from non-isolated airflow distribution to closed cold aisle airflow distribution. With the increase of the power of racks, cooling failure may happen in the layout of the isolated cold aisle. This paper presents the study on cooling performance of the racks which are improved through bottom ventilating reform and adjustment. Inlet/outlet air temperature and mass flow rate of the racks are investigated in detail under conditions of various bottom ventilated areas and various porosities of the raised floor. The characteristics of airflow distribution are contrastively analyzed through calculating indexes of the thermal environment of data centers. Results show that adequate ventilation through the bottom of the racks is good for improvement of the state of airflow distribution. There is an optimization range (0.1–0.3 m and 0.05–0.15 m, respectively) of the ventilated area at the bottom of the racks. And high porosity (above 50%) of the ventilated area can reduce the inlet and outlet temperatures of the racks and the racks in different positions have a better temperature uniformity. In conclusion, bottom ventilation of racks is a feasible plan to improve airflow distribution, and schemes of ventilated area and porosity of corresponding raised floor should be designed respectively under consideration of the layout of racks and AC.

scholarly journals Experimental comparison of local low velocity unit combined with radiant panel and diffuse ceiling ventilation systems

2020 ◽  
Vol 29 (6) ◽  
pp. 895-914 ◽  
Author(s):  
Weixin Zhao ◽  
Simo Kilpeläinen ◽  
Risto Kosonen ◽  
Juha Jokisalo
Keyword(s):  
Air Temperature ◽  
Experimental Comparison ◽  
Cooling Power ◽  
Airflow Rate ◽  
Low Velocity ◽  
Exhaust Temperature ◽  
Local Supply ◽  
Clean Air ◽  
Radiant Panel ◽  
Occupied Zone

In this study, the performance of a micro-environment system was analysed and compared with diffused ceiling ventilation. In the analysed micro-environment low velocity radiant panel system, two low velocity units and radiant panels were installed above workstations to supply directly clean air to occupants and to cover the cooling power required. With diffused ceiling ventilation, all cooling demand is covered with air and thus, the airflow rate required is higher than with low velocity radiant panel system. The varied heat gain from 40 to 80 W/m2 consists of two seated dummies, laptops, monitors and simulated solar gain. The results show that with perimeter exhaust and local supply air, 8–13% reduction of the total cooling load required is possible, in comparison to the standard mixing systems. The average exhaust temperature was 0.7–1.9°C higher than average room air temperature at the workstation. Moreover, the mean air temperature with the low velocity radiant panel system at the occupied zone was 0.6°C lower than with diffused ceiling ventilation. With low velocity radiant panel system, the air velocity was less than 0.12 m/s in the occupied zone. Also, the draught rate was less than 10%. Furthermore, the air change efficiency with the low velocity radiant panel system was over 70% which is better than 44–49% efficiency with diffused ceiling ventilation.

scholarly journals Analysis of Energy Exchange with the Ground in a Two-Chamber Vegetable Cold Store, Assuming Different Lengths of Technological Break, with the Use of a Numerical Calculation Method—A Case Study

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4970
Author(s):  
Paweł Sokołowski ◽  
Grzegorz Nawalany
Keyword(s):  
Numerical Analysis ◽  
Air Temperature ◽  
Energy Demand ◽  
Experimental Studies ◽  
Calculation Model ◽  
Energy Losses ◽  
Cold Store ◽  
Numerical Calculation Method ◽  
The Impact ◽  
Floor Temperature

The paper deals with the impact of the technological break duration during the cold storage cycle on the energy demand of the cold store for vegetables and fruit and the temperature distribution in the ground under the cold store. The studied facility was a two-chamber vegetable cold store located in southern Poland used to store carrots (Daucus carota) for nine months a year. The experiments were conducted for 12 months (01.05.2017–30.04.2018). The technological break during this period lasted three months (from 1 July 2018 to 30 September 2018). Continuous measurements (with 1-h frequency) were made in order to determine the boundary conditions for numerical analysis. The measured parameters included indoor air temperature, outdoor air temperature, ground temperature under the building and in its vicinity. There were 22 measuring points andPT100 sensors were used. The numerical analysis was based on the elementary balances method. WUFIplus® software was used as a calculation supporting tool. The numerical analysis was conducted for 14 calculation variants, with different duration of technological break. The calculation model validation was performed and the results showed a good correlation with the experimental data. The results of experimental studies and of calculations showed a significant impact of the technological break duration on the soil distribution in the ground and the building energy demand. A technological break of less than 4 weeks is the most optimal in the summer. The technological break longer than 4 weeks significantly affects the cooling energy demand in the first days of the cooling cycle and significantly extends the time necessary for the ground and the floor to reach the optimum temperature. The analysis of the floor temperature results (points A1–C1) showed that the technological break longer than four weeks causes the average floor temperature to exceed 4.0 °C. Therefore, the optimum solution is technological break lasting 7–35 days. Absence of technological break results in a decrease of energy gains from the ground by 20% relative to a three-month technological break. The impact of technological break duration was clearly seen in terms of energy losses from the cold store to the ground. In case of a 91-day technological break, the energy losses to the ground were 1289.5 kWh/a, while in case of absence of technological break this value was ninefold lower (147.5 kWh/a).

Research on Fire Behavior of a Suspended Pre-Stressed Steel Reticulated Shell with Large Span

2011 ◽  
Vol 243-249 ◽  
pp. 1223-1227
Author(s):  
Xin Tang Wang ◽  
Ming Zhou ◽  
Zhi Guo Xie ◽  
Feng Bo Yu
Keyword(s):  
Numerical Analysis ◽  
Air Temperature ◽  
Fire Behavior ◽  
Steel Structures ◽  
Large Space ◽  
Large Span ◽  
Fire Source ◽  
Air Temperatures ◽  
Lattice Shell ◽  
Key Nodes

In order to study the fire-resistance behavior of the spatial pre-stressed steel structures with large span, the model of numerical analysis of a suspended pre-stressed steel reticulated shell subjected to fire load is established with using the software Marc. Based on the model presented here, numerical analysis of thermal response and structural response of the pre-stressed steel structure are computed for the key nodes of the structure. For comparison, the air temperatures near the key nodes are also calculated based on the practical formula of large space air temperature rise. The different location of fire source is considered for analysis of response temperature, displacements and stresses of the nodes of the pre-stressed lattice shell. It is shown that the air temperatures was much higher than the response temperatures of the nodes of the lattice shell during a quite period of time after a fire takes place, and the temperature of the cable nodes are also less than the air temperature near the nodes. It is also concluded that not the cable nearest the fire source but the other cables around the cable fail to work first in the fire.

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