scholarly journals Assessment of the efficiency of the use of activating turbulent jets to eliminate the risk of the formation of unventilated zones in large premises

2021 ◽  
Vol 2131 (5) ◽  
pp. 052068
Author(s):  
A M Grimitlin ◽  
A S Strongin

Abstract Strict requirements for microclimate parameters are imposed on food storage premises, which are equipped with artificial cooling systems. The experience of operating the refrigerated premises revealed the following disadvantages: uneven distribution and significant fluctuations in temperature and relative humidity; periodic precipitation of condensate in low-temperature sections. Elimination of the noted disadvantages is effectively achieved by using axial fans that form a swirling air stream that induces the ambient air. Swirling jets used to intensify the process of air circulation in a room in order to eliminate unventilated zones will be called activating jets. To assess the efficiency of the application of activating turbulent jets, an integral method based on the energy balance was used. Using the example of a representative object, it is shown that the distance of the effective application of an activating turbulent jet should be calculated taking into account the influence of environmental turbulence, which is determined by the amount of energy introduced and dissipated in the room.

2017 ◽  
Vol 52 (5) ◽  
Author(s):  
A. Doroshenko ◽  
K. Shestopalov ◽  
I. Mladionov

The concept of evaporative coolers of gases and fluids on the basis of monoblock multichannel polymeric structures is presented. Different schemes of indirect evaporative coolers, in which the natural cooling limit is the dew point of the ambient air  are discussed. In such systems the cooling temperature is lower than the wet bulb temperature of the ambient air. Special attention is paid to the recondensation of water vapor for deep evaporative cooling. It is shown that for the solution of the recondensation problem it is necessary to vary the ratio of the contacting air and water flows, particularly in each stage of the multistage system. Recommendations for the deep cooling process implementation in the evaporative coolers of gases and liquids are given.


2021 ◽  
Vol 409 ◽  
pp. 158-178
Author(s):  
Abdelkader Feddal ◽  
Abbes Azzi ◽  
Ahmed Zineddine Dellil

This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 104, 10 104 and 20 104 .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.


1974 ◽  
Vol 25 (1) ◽  
pp. 69-80 ◽  
Author(s):  
R A Antonia ◽  
R W Bilger

SummaryThree analyses are presented for predicting the development of an axisymmetric turbulent jet issuing into a co-flowing external air stream. The first analysis is analogous to a method used by Patel to predict the growth of a two-dimensional jet in an external air stream. The method is found to be inadequate when the excess velocity on the axis of the jet becomes small compared with the external stream velocity. The second analysis assumes that the turbulence structure is similar at different streamwise stations but it breaks down when the advection of turbulent energy becomes comparable with the turbulent energy production. In the third approach, a two-parameter model of turbulence developed by Rodi and Spalding, which uses two differential equations for the turbulent energy and the length scale of the turbulence respectively, is found to predict closely the experimental results of Antonia and Bilger for a ratio of jet to external stream velocity of 3.0. The success of this last method emphasises the non-similar character of turbulence.


Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
Kevin M. Lyons

The aim of this investigation is to determine the effects of confinement on the stabilization of turbulent, lifted methane (CH4) jet flames. A confinement cylinder (stainless steel) separates the coflow from the ambient air and restricts excess room air from being entrained into the combustion chamber, and thus produces varying stabilization patterns. The experiments were executed using fully confined, semi-confined, and unconfined conditions, as well as by varying fuel flow rate and coflow velocity (ambient air flowing in the same direction as the fuel jet). Methane flames experience liftoff and blowout at well-known conditions for unconfined jets, however, it was determined that with semi-confined conditions the flame does not experience blowout. Instead of the conventional unconfined stabilization patterns, an intense, intermittent behavior of the flame was observed. This sporadic behavior of the flame, while under semi-confinement, was determined to be a result from the restricted oxidizer access as well as the asymmetrical boundary layer that forms due to the viewing window. While under full confinement the flame behaved in a similar method as while under no confinement (full ambient air access). The stable nature of the flame while fully confined lacked the expected change in leading edge fluctuations that normally occur in turbulent jet flames. These behaviors address the combustion chemistry (lack of oxygen), turbulent mixing, and heat release that combine to produce the observed phenomena.


1993 ◽  
Vol 115 (4) ◽  
pp. 212-219 ◽  
Author(s):  
A. A. Pesaran

We conducted experiments to quantify the effects of thermal cycling and exposure to contamination on solid desiccant materials that may be used in desiccant cooling systems. The source of contamination was cigarette smoke, which is considered one of the worst pollutants in building cooling applications. We exposed five different solid desiccants to “ambient” and “contaminated” humid air: silica gel, activated alumina, activated carbon, molecular sieves, and lithium chloride. We obtained the moisture capacity of samples as a function of exposure time. Compared to virgin desiccant samples, the capacity loss caused by thermal cycling with humid ambient air was 10 percent to 30 percent for all desiccants. The capacity loss because of combined effect of thermal cycling with “smoke-filled” humid air was between 30 percent to 70 percent. The higher losses occurred after four months of experiment time, which is equivalent to four to eight years of field operation. Using a system model and smoke degradation data on silica gel, we predicted that, for low-temperature regeneration, the loss in performance of a ventilation-cycle desiccant cooling system would be between 10 percent to 35 percent, in about eight years, with higher value under worst conditions.


Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 81 ◽  
Author(s):  
Małgorzata Fedorczak-Cisak ◽  
Katarzyna Nowak ◽  
Marcin Furtak

Improving the energy efficiency of buildings is among the most urgent social development tasks due to the scale of energy consumption in this industry. At the same time, it is essential to meet high requirements for indoor environmental quality and thermal comfort. The issue of overheating is most often analysed in summer but it also occurs in transition seasons, when the cooling systems do not operate. The paper attempts to evaluate the effectiveness of external mobile shading elements on the microclimate of rooms with large glazed areas in the transition season. Passive solutions, such as shading elements, which limit the increase of indoor temperature, do not always allow the acquisition and maintenance of comfortable solutions for the duration of the season, as demonstrated by the authors. Temporary cooling of the rooms may be necessary to maintain comfortable conditions for the users, or other solutions should be devised to improve comfort (e.g., reduction of clothing insulation characteristics). The novelty of the study consists in the analysis of comfort in a “nearly zero energy consumption” building (NZEB) during a period not analyzed by other scientists. This is a transition period during which heating/cooling systems do not operate. The research task set by the authors involved the assessment of the possibility to reduce office space overheating in the transition season (spring) by using external shading equipment in rooms with large glazed areas. An additional research task aimed at checking the extent to which user behaviour, such as reduction in clothing insulation characteristics, can improve comfort in overheated rooms. The results of the tests reveal that the difference in the ambient air temperature between a room with external venetian blinds and an identical room with no venetian blinds in the transition season, i.e., from 27 March to 6 April 2017, ranged from 12.3 to 2.1 °C. The use of a shading system (external venetian blinds positioned at an angle of 45°) reduced the number of discomfort hours by 92% (during working hours) compared to the room without external venetian blinds. A reduction in the thermal insulation of the clothes worn by people working in the room with no venetian blinds helped to reduce the number of discomfort hours by 31%.


Author(s):  
Mohammad Ahmadi Bidakhvidi ◽  
Rasoul Shirzadeh ◽  
Steve Vanlanduit

Piezoelectric vibrating fans operating at resonance are a viable cooling technology due to its easy scalability and low power consumption. This study focuses on the characterization and optimization of the thermal performance of these miniature flapping cooling systems. Different experiments in a miniature windtunnel are conducted to investigate the cooling performance of the oscillating fans. The Strouhal number is a dimensionless parameter describing wing kinematics of flying systems. The aerodynamic propulsive efficiency of these systems is high over a narrow range of Strouhal numbers. Different St numbers were obtained and investigated, by changing the flow velocity of the win-tunnel. In practical applications different St could be obtained by combining conventional axial fans with piezoelectric fans. Both the feasibility of a single fan and array of fans is studied. For a wide range of operating coditions, including distance from heat source, dynamic tip deflection and orientation, the heat transfer performance of the piezoelectric fans is characterized.


Author(s):  
Andrey Gunawan ◽  
Nicholas W. Fette ◽  
Patrick E. Phelan

Recovering waste heat from automobiles remains an inviting subject for research. Solid-state thermoelectric generators (TEGs) have been widely investigated for this purpose, but their practical application remains challenging. An alternative to TEGs are thermogalvanic cells. Temperature difference between hot and cold electrodes creates a potential difference. Once connected to a load, electrical current and power are delivered, converting heat into electricity. In this work, we investigate the feasibility of incorporating such systems into automobiles. We carry out the experiments under real-world conditions. A climate-controlled wind tunnel is built to provide equivalent conditions to the ambient air stream under the car. The demonstrated system achieved a power density on the order of mW m−2. We compare the power generated to those of TEGs currently tested by GM, Honda, BMW and Ford. Further, a simple economic estimation is calculated to assess the $ per Watt cost of future practical thermogalvanic waste heat recovery system.


1970 ◽  
Vol 1 (6) ◽  
pp. 108-111
Author(s):  
G. N. Abramovich ◽  
O. V. Yakovlevskii ◽  
I. P. Smirnova ◽  
A. N. Sekundov ◽  
S. Yu. Krasheninnikov

2021 ◽  
Vol 22 (2) ◽  
pp. 280-287
Author(s):  
Mehraj ud din Bhat ◽  
Anish C Pandey

The present study is carried out in Gwalior to know the level of pollutants viz sulphur dioxide (SO2) and nitrogen dioxide (NO2). In this study, both NO2 and SO2 were collected during different seasons, and estimation was done using chemical methods. The methods used for the determination of SO2 and NO2 in the ambient air of Gwalior was (Modified West and Geake method) and (Modified Jacob and Hochheisier). The SO2 from the air stream was absorbed in a sodium tetramer curate solution. NO2 was collected by bubbling air through a sodium hydroxide solution to form a stable solution of sodium nitrate. Meteorological parameters like temperature, relative humidity were recorded by thermometers and hygrometry during the sampling. Rainfall data was taken from Indian Meteorological Department, New Delhi, for four sampling years. The statistical analysis was carried out between the level of pollutants SO2 and NO2 measured and meteorological parameters recorded during the sampling. This study observed that pollutants were very high in winter and summer compared to monsoon and post-monsoon periods due to the heavy transport movement and favourable meteorological conditions like temperature, humidity, rainfall, and wind speed and directions.


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