scholarly journals Comparative Study of the Cross-Flow Heat and Mass Exchangers for Indirect Evaporative Cooling Using Numerical Methods

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3374 ◽  
Author(s):  
Yugang Wang ◽  
Xiang Huang ◽  
Li Li
Keyword(s):  
Numerical Methods ◽  
Comparative Study ◽  
Flow Rate ◽  
Air Flow ◽  
Evaporative Cooling ◽  
Cross Flow ◽  
Air Flow Rate ◽  
Cooling Performance ◽  
Indirect Evaporative Cooling ◽  
The Cross

This paper presents a comparative study of the cross-flow regenerative heat and mass exchanger (HMX) and the conventional cross-flow HMX for indirect evaporative cooling (IEC) with numerical methods. The objective of this study is mainly to clarify the applicability of the two HMXs. The numerical model was built and validated by existing experimental data. The difference in heat and mass transfer between the two HMXs was revealed by analyzing the change of the temperature and moisture content of the air, and the influence of the main operating parameters on the cooling performance of the HMXs was analyzed. In the typical operating conditions, when the HMXs are used alone, the cooling performance of the regenerative HMX is better than that of the conventional HMX under low supply air flow rate. When the HMXs are used in the multistage evaporative cooling systems with high supply air flow rate, the conventional HMX is more suitable as the first stage of the system to pre-cool the supply air, while the regenerative HMX is more suitable as the second stage to re-cool the supply air.

scholarly journals ENHANCING THE EFFICIENCY OF INDOOR LOCAL VENTILATION USING CROSS-FLOW FANS: CASE STUDY FOR A SMOKING CABIN

2016 ◽  
Vol 21 (3) ◽  
Author(s):  
DRAGOMIRESCU ANDREI ◽  
CIOCĂNEA ADRIAN
Keyword(s):  
Flow Rate ◽  
Air Flow ◽  
Cross Flow ◽  
Flow Coefficient ◽  
Air Flow Rate ◽  
Low Velocity ◽  
Original Solution ◽  
Local Space ◽  
Local Ventilation

<p>The paper presents an original solution for increasing air quality and reducing energy consumption of the local indoor ventilation by using cross-flow fans. The solution is a combination between the local exhaust ventilation (LEV) technique from industry, negative-pressure isolation rooms used in hospitals, and air curtains (AC) used for isolating of indoor/outdoor spaces. The solution provides a high air flow rate at low velocity due to the high value of the flow coefficient of the cross flow fans and, in the same time, allows modular setup according to local space geometry. A case study is proposed regarding the isolation of a smoking area where smell and airborne particles appear. A 3D numerical simulation was performed, in which one cross-flow fan with long axial length was considered. The optimum air flow rate and flow pattern was obtained in order to isolate the local space. The results show that a new approach for reducing sick building syndrome could be addressed by providing modular and local ventilation using cross-flow fans.</p>

Experimental Feasibility Study of Radial Injection Cooling of Three-Pad Air Foil Bearings

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Suman K. Shrestha ◽  
Daejong Kim ◽  
Young Cheol Kim
Keyword(s):  
Heat Exchange ◽  
Flow Rate ◽  
High Speed ◽  
Air Flow ◽  
Air Flow Rate ◽  
Design Factor ◽  
Cooling Performance ◽  
Radial Injection ◽  
Cooling Air Flow ◽  
Cooling Air

The foil bearing (FB) is one type of hydrodynamic bearing using air or another gas as a lubricant. When FBs are designed, installed, and operated properly, they are a very cost-effective and reliable solution for oil-free turbomachinery. Because there is no mechanical contact between the rotor and its bearings, quiet operation with very low friction is possible once the rotor lifts off the bearings. However, because of the high speed of operation, thermal management is a very important design factor to consider. The most widely accepted cooling method for FBs is axial flow cooling, which uses cooling air or gas passing through heat-exchange channels formed underneath the top foil. The advantage of axial cooling is that no hardware modification is necessary to implement it, because the elastic foundation structures of the FB serve as the heat-exchange channels. Its disadvantage is that an axial temperature gradient exists on the journal shaft and bearing. In this paper, the cooling characteristics of axial cooling are compared with those of multipoint radial injection, which uses high-speed injection of cooling air onto the shaft at multiple locations. Experiments were performed on a three-pad FB 49 mm in diameter and 37.5 mm in length, at speeds of 30,000 rpm and 40,000 rpm. Injection speeds were chosen to be higher than the journal surface speed, but the total cooling air flow rate was matched to that of the axial cooling cases. Experimental results show that radial injection cooling is comparable to axial cooling at 30,000 rpm, in terms of cooling performance. Tests at 40,000 rpm reveal that the axial cooling performance reaches saturation when the pressure drop across the bearing is larger than 1000 Pa, while the cooling performance of radial injection is proportional to the cooling air flow rate and does not become saturated. Overall, multipoint radial injection is better than axial cooling at high rotor speeds.

Two-Phase Flow Visualization for a Hybrid Heat Sink

2018 ◽  
Author(s):  
Danish Rahman ◽  
Ahmad Almomani ◽  
Ibrahim Hassan ◽  
Yasser Al-Hamidi ◽  
Aziz Rahman
Keyword(s):  
Flow Rate ◽  
Slug Flow ◽  
Air Flow ◽  
Plug Flow ◽  
Cross Flow ◽  
Flow Regimes ◽  
Air Flow Rate ◽  
Two Phase ◽  
Flow Rates ◽  
Impingement Jet

This paper aimed to study two-phase flow under adiabatic conditions through the process of flow visualization. This was done through the use of a test section with a cross flow and a jet impingement (swirl jet). The flow regimes under different air-water flow rates were determined using a high-speed camera that recorded digital videos. For each of the flow rates the pressure differential between the inlet and the outlets were measured. Through the pressure drop it is proposed that the types of flow regimes may later be able to be predicted. Nine air-water flow rates were considered to collect data and generate a flow map for the impingement jet and cross flow. The major observed flow regimes within the crossflow and impingement jet followed the predicted trend with bubbly and plug flow in the former, and slug flow in the latter. It was further observed that increasing the air flow rate increased the likelihood of bubbly and plug flow in both the cross-flow and impingement jet. In the cross flow, a lower air flow rate resulted in bubbly flow while within the impingement jet, a lower air flow rate resulted in slug flow.

scholarly journals Integral Thermo-Anemometers for Average Temperature and Airflow Measurement in Ducts, at Anemostat Outlets and in Ventilation Grilles

2020 ◽  
Vol 23 (4) ◽  
pp. 14-21
Author(s):  
Oleh S. Tsakanian ◽  
◽  
Serhii V. Koshel ◽  
Keyword(s):  
Cross Section ◽  
Flow Rate ◽  
Air Flow ◽  
Hot Wire ◽  
Air Flow Rate ◽  
National Academy Of Sciences ◽  
Calibration Dependence ◽  
The Cross ◽  
And Control ◽  
Ventilation Systems

When creating ventilation systems, it is important to correctly calculate the volumes of air inflow and outflow. If an error is made in the calculation or a redistribution of air flows is required, measurements are indispensable. The existing methods for determining the air flow rate by using point measurements in the cross-section are laborious and time-consuming, and taking readings at different time points introduces a significant error into the result. A. M. Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine has developed a new hot-wire anemometer whose use greatly simplifies the measuring process. This device allows one to measure the average values of temperature and air velocity (flow rate) in the cross-section of air ducts or at the inlets and outlets of grilles and anemostats, and can be used in real time to monitor and control air flow rate and temperature in ventilation systems. The probe of the hot-wire anemometer is a metal shell with guides on which a sensitive element is laid. Its principle of operation is to change the heat transfer coefficient at different air leakage velocities. The anemometer is preliminarily calibrated in laboratory conditions at various velocities. There has been obtained a calibration dependence that can be used to measure the air flow rate at the inlets and outlets of air distribution devices and directly in the air ducts. To improve the measurement accuracy, it is necessary to provide the 90° angle of airflow leakage on the hot-wire anemometer probe. For this, special air collectors and air flow rectifiers are used.

scholarly journals ENHANCING THE EFFICIENCY OF INDOOR LOCAL VENTILATION USING CROSS-FLOW FANS: CASE STUDY FOR A SMOKING CABIN

2015 ◽  
Vol 21 (3) ◽  
pp. 28-34
Author(s):  
ANDREI DRAGOMIRESCU ◽  
ADRIAN CIOCĂNEA
Keyword(s):  
Flow Rate ◽  
Air Flow ◽  
Cross Flow ◽  
Flow Coefficient ◽  
Air Flow Rate ◽  
Low Velocity ◽  
Original Solution ◽  
Local Space ◽  
Local Ventilation

The paper presents an original solution for increasing air quality and reducing energy consumption of the local indoor ventilation by using cross-flow fans. The solution is a combination between the local exhaust ventilation (LEV) technique from industry, negative-pressure isolation rooms used in hospitals, and air curtains (AC) used for isolating of indoor/outdoor spaces. The solution provides a high air flow rate at low velocity due to the high value of the flow coefficient of the cross flow fans and, in the same time, allows modular setup according to local space geometry. A case study is proposed regarding the isolation of a smoking area where smell and airborne particles appear. A 3D numerical simulation was performed, in which one cross-flow fan with long axial length was considered. The optimum air flow rate and flow pattern was obtained in order to isolate the local space. The results show that a new approach for reducing sick building syndrome could be addressed by providing modular and local ventilation using cross-flow fans.

scholarly journals COMPUTATIONAL SIMULATION OF THE EVAPORTIVE AIR COOLING PROCESS IN A SUBWAY TUNNEL

2021 ◽  
Vol 2 (3) ◽  
pp. 115-122
Author(s):  
Elena L. Alferova
Keyword(s):  
Flow Rate ◽  
Air Flow ◽  
Computational Simulation ◽  
Evaporative Cooling ◽  
Water Flow Rate ◽  
Air Cooling ◽  
Air Flow Rate ◽  
Subway Tunnel ◽  
Pump Equipment ◽  
Metro Tunnel

The paper shows the possibility of using evaporative cooling of air by spraying water directly in the tunnel. The solution of the problem of modeling the process of removing heat excess from the air during the phase transition of water from the liquid state to the gaseous in the conditions of the metro tunnel is carried out. It is shown that using method significantly reduces the requirements for ventilation equipment in comparison with the method of removing heat surpluses only by mechanical ventilation. When using evaporative cooling method of removing heat surpluses in a subway tunnel, the maximum air flow rate of one fan will be 67.5 m/s with 104 kW power, the power of the pump equipment will be nearly 50 kW, with a water flow rate 1.5 m per hour. When removing heat surpluses only by ventilation, the air flow rate of one fan (with two fans in parallel work) will be up to 269 m/s, and the power will be 727 kW.

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