CFD Simulation and Experimental Data for a Fixed Heat Load Natural Draft Air-Cooled Heat Exchanger With Cold Inflow Mitigation

2015 ◽  
Author(s):  
Christopher C. M. Chu ◽  
Md. Mizanur Rahman ◽  
Sivakumar Kumaresan
Keyword(s):  
Experimental Data ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Heat Load ◽  
Cfd Simulation ◽  
Air Flow ◽  
Wire Mesh ◽  
Outlet Temperature ◽  
Air Mass ◽  
Natural Draft

CFD simulation was carried out to corroborate experimental data at fixed heat load of nominally 2.3kW from a natural draft heat exchanger of face dimensions of 0.75m × 0.75m, with or without mitigation of the cold inflow at the chimney exit, where mitigation by installing wire mesh on top of the chimney has been shown by the experiments to enhance air flow rate. A chimney model was simulated at fixed heat loads in a still surrounding at ambient temperature of 30 degree Celsius and atmospheric pressure for two modes: Mode 1 and Mode 0 for with and without a flow resistor (wire mesh) respectively at the top exit. It was found that the simulation could reproduce most of the trends of the experimental data, but had a tendency to magnify the detrimental effects of cold inflow and exaggerate the remedial action of wire mesh in preventing cold inflow, as reflected by the ratio of Mode 1 to Mode 0 air mass flowrate by a factor of up to 2.36, compared to 1.50 in the experimental data. In both simulation and experiment, the average air flow rates obtained at chimney heights of 0.35m, 0.65m, 0.95m and 1.25m, showed progressive increase of air mass flow rate for all cases. Both experimental and simulated heat gain in Mode 0 were more or less constant until the highest chimney height where they showed apparent breakout upwards, whereas in Mode 1 the experimental heat gains gently reduced to a plateau while the simulated heat gains hovered at around 2.3kW. The back calculated values of Mode 0 experimental outlet temperature at between 140 to 240°C raises concern of hotspot in some electronic components by the ineffectiveness of chimney systems without cold inflow mitigation. Further experiments of similar scale with steadier control of heat flux and heating temperature, and simulating with other turbulence models in transient mode will improve understanding in both Mode 0 and Mode 1 of operation.

CRAC Heat Exchanger Response to Step Change in Chilled Water Flowrate

2009 ◽  
Author(s):  
Shawn P. Shields ◽  
Yogendra K. Joshi ◽  
Michael Patterson ◽  
Michael Meakins
Keyword(s):  
Experimental Data ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Data Center ◽  
Temperature Response ◽  
Step Change ◽  
Outlet Temperature ◽  
Power Failure ◽  
Air Supply ◽  
Chilled Water

This paper presents experimental data showing the response of a computer room air conditioning unit (CRAC) to chilled water (CHW) pump restart. The data are offered to improve and develop modeling of cooling equipment restart events following data center power failure. There are estimates that power failures will increase and limits on availability will affect data center operations at more than 90 percent of all companies over the next five years. Because providing backup power to cooling equipment increases data center first cost, it is important to have accurate models for cooling events and processes following power failure that help predict server inlet temperatures during the transient phase caused by a power failure. Since power density of computing equipment continues to rise, the temperature rise of air within the data center has been predicted to rise more quickly to an unacceptable level, increasing concern. Accurate models of CRAC response to pump restart can aid in data center cooling design, backup power infrastructure provisioning, and even compute equipment selection by predicting the air supply temperature after the generator provides power to the chilled water pump. Previous transient models include zonal models with large time scales and CFD/HT models with boundary conditions developed for steady state. These models can be improved by comparison with experimental data. The experiment consists of measuring the response of the CRAC heat exchanger to the step change in CHW flow rate upon pump restart. Inlet and outlet temperatures of both CHW and air were measured, as well CHW flow rate. A point measurement of air at the CRAC fan outlet was also taken to verify that airflow remained relatively constant. Outlet temperatures from the CRAC follow a first order response curve; it is found that the CRAC under consideration has fan outlet temperature time constant of 10 seconds. A delay of 20 seconds is observed between the fan outlet temperature response and the CHW return temperature response.

scholarly journals Thermal Evaluation of a Double-Pass Unglazed Solar Air Heater with Perforated Plate and Wire Mesh Layers

2020 ◽  
Vol 12 (9) ◽  
pp. 3619
Author(s):  
Afaq Jasim Mahmood
Keyword(s):  
Flow Rate ◽  
Thermal Efficiency ◽  
Air Flow ◽  
Wire Mesh ◽  
Inlet Temperature ◽  
Solar Air Heater ◽  
Outlet Temperature ◽  
Air Flow Rate ◽  
Double Pass ◽  
Air Heater

In this study, an experimental outdoor investigation of the thermal efficiency and outlet air temperature was conducted on an unglazed, double-pass, solar air heater with a perforated absorber plate and packing wire mesh layers as a supplemental absorbent area. This was done to observe their effects on the thermal performance of the solar air heater. The double-pass collector was constructed with a bed height of 0.05 m, and a collection area of 1.5 m2. The height of the upper channel was fixed at 0.015 m to improve the thermal efficiency, and the outlet temperature at air flow rates between 0.003 and 0.018 kg/s. The collector was mounted with a slope of 42° facing south, to maximize the intensity of solar irradiance during winter. The effects of the air flow rate, ambient temperature, inlet temperature, outlet temperature, and solar intensity were experimentally investigated. The results showed that thermal efficiency could be improved by increasing the air flow rate, where the highest thermal efficiency achieved was 86% at 0.018 kg/s. However, the temperature difference was increased to a maximum value of 38.6 °C, when the air flow rate was decreased to 0.003 kg/s. Furthermore, the results demonstrated a significant improvement in the thermal efficiency and outlet temperature; and when compared with previous research, the experimental results and the predictions for the outlet temperature using the theoretical model agreed.

scholarly journals Analysis of Heat Transfer Characteristics of a Heat Exchanger Based on a Lattice Filling

Coatings ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1089
Author(s):  
Xuhui Lai ◽  
Caihua Wang ◽  
Dongjian Peng ◽  
Huanqing Yang ◽  
Zhengying Wei
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Relative Density ◽  
Flow Rate ◽  
Heat Load ◽  
Lattice Structure ◽  
Unit Cell ◽  
Liquid Oxygen ◽  
Outlet Temperature ◽  
Parameterized Model

In response to the heat load requirements of the high-thrust liquid rocket engine, a light-weight lattice structure is used to fill traditional a heat exchanger. A parameterized model library of the lattice structure is established, and the relative density of the lattice structure is adjusted by changing the unit cell structure parameters to obtain different filling structures. A comprehensive comparison of heat exchangers with different filling structures performed in terms of weight, heat transfer efficiency, and turbulence intensity. Using the finite difference method, the numerical calculation of the non-steady heat–fluid–solid coupling conjugate heat transfer of the eight-lattice structure is performed, and the dynamic heat transfer process between the lattice structure and liquid oxygen is simulated using the VOF model and the SST k-ω model. The results show that the pressure of the fluid in the heat exchanger increases with increasing relative density, leading to a high outlet temperature and greatly increasing the outlet velocity. The support trusses close to the wall obviously hinder the flow of liquid oxygen, resulting in a sudden change in the flow rate behind the support trusses, driving the high-temperature fluid at the bottom to move upwards. The direction of the support trusses and the unit cell porosity have a greater impact on the liquid oxygen flow rate, which in turn affects the flow and heat transfer performance of the heat exchanger. In consideration of the heat load requirements of the heat exchanger, star-type lattices are used to fill the heat exchanger. When the flow is fully developed, the volume ratio of the heated fluid is 85.60%, and the outlet temperature is 390 K, which meets the design requirements.

scholarly journals Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 4
Author(s):  
Dillon Alexander Wilson ◽  
Kul Pun ◽  
Poo Balan Ganesan ◽  
Faik Hamad
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Air Flow ◽  
Bubble Diameter ◽  
Diameter Ratio ◽  
Experimental Measurements ◽  
Cfd Model ◽  
Flow Rates ◽  
Throat Diameter

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study.

scholarly journals Experimental Investigation on Improvement of Wet Cooling Tower Efficiency with Diverse Packing Compaction Using ANN-PSO Algorithm

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 167
Author(s):  
Hasan Alimoradi ◽  
Madjid Soltani ◽  
Pooriya Shahali ◽  
Farshad Moradi Kashkooli ◽  
Razieh Larizadeh ◽  
...  
Keyword(s):  
Neural Network ◽  
Water Temperature ◽  
Water Flow ◽  
Flow Rate ◽  
Cooling Tower ◽  
Air Flow ◽  
Water Flow Rate ◽  
Pso Algorithm ◽  
Outlet Temperature ◽  
Air Flow Rate

In this study, a numerical and empirical scheme for increasing cooling tower performance is developed by combining the particle swarm optimization (PSO) algorithm with a neural network and considering the packing’s compaction as an effective factor for higher accuracies. An experimental setup is used to analyze the effects of packing compaction on the performance. The neural network is optimized by the PSO algorithm in order to predict the precise temperature difference, efficiency, and outlet temperature, which are functions of air flow rate, water flow rate, inlet water temperature, inlet air temperature, inlet air relative humidity, and packing compaction. The effects of water flow rate, air flow rate, inlet water temperature, and packing compaction on the performance are examined. A new empirical model for the cooling tower performance and efficiency is also developed. Finally, the optimized performance conditions of the cooling tower are obtained by the presented correlations. The results reveal that cooling tower efficiency is increased by increasing the air flow rate, water flow rate, and packing compaction.

scholarly journals Experimental study on the performance of flat air collector with reticulated endothermic body

2020 ◽  
Vol 165 ◽  
pp. 01025
Author(s):  
Liang Hong ◽  
Han Zhiguo ◽  
Wang Jing ◽  
Duli Kunjiang ◽  
Li Zhiyong
Keyword(s):  
Experimental Study ◽  
Flow Rate ◽  
Temperature Difference ◽  
Collection Efficiency ◽  
Air Flow ◽  
Wire Mesh ◽  
Pore Density ◽  
Air Flow Rate ◽  
Flow Temperature ◽  
Mesh Density

Because the flat air collector is simple in structure, reliable in operation, and resistant to cold and frost, it is more suitable for applications such as building heating. This paper presents a flat air collector with a mesh heat sink, and analyzes the effects of air flow, temperature difference between inlet and outlet, and wire mesh density on the heat collection efficiency of the collector. The results show that when the pore density is fixed, the heat collection efficiency increases with the increase of air flow rate, which is 10% higher than that of natural convection when the air flow rate is maximum; when the air flow rate is fixed, the heat collection efficiency increases with the increase of the pore density and the temperature difference between the inlet and outlet, which can be increased by 10% -20%.

Raised Floor Hybrid Cooled Data Center: Effect on Rack Inlet Air Temperatures When In Row Cooling Units are Installed Between the Racks

2015 ◽  
Author(s):  
Tianyi Gao ◽  
James Geer ◽  
Russell Tipton ◽  
Bruce Murray ◽  
Bahgat G. Sammakia ◽  
...  
Keyword(s):  
Flow Rate ◽  
Data Center ◽  
Heat Load ◽  
Data Centers ◽  
Cooling System ◽  
Air Flow ◽  
Inlet Temperature ◽  
Air Flow Rate ◽  
Air Temperatures ◽  
Cooling Unit

The heat dissipated by high performance IT equipment such as servers and switches in data centers is increasing rapidly, which makes the thermal management even more challenging. IT equipment is typically designed to operate at a rack inlet air temperature ranging between 10 °C and 35 °C. The newest published environmental standards for operating IT equipment proposed by ASHARE specify a long term recommended dry bulb IT air inlet temperature range as 18°C to 27°C. In terms of the short term specification, the largest allowable inlet temperature range to operate at is between 5°C and 45°C. Failure in maintaining these specifications will lead to significantly detrimental impacts to the performance and reliability of these electronic devices. Thus, understanding the cooling system is of paramount importance for the design and operation of data centers. In this paper, a hybrid cooling system is numerically modeled and investigated. The numerical modeling is conducted using a commercial computational fluid dynamics (CFD) code. The hybrid cooling strategy is specified by mounting the in row cooling units between the server racks to assist the raised floor air cooling. The effect of several input variables, including rack heat load and heat density, rack air flow rate, in row cooling unit operating cooling fluid flow rate and temperature, in row coil effectiveness, centralized cooling unit supply air flow rate, non-uniformity in rack heat load, and raised floor height are studied parametrically. Their detailed effects on the rack inlet air temperatures and the in row cooler performance are presented. The modeling results and corresponding analyses are used to develop general installation and operation guidance for the in row cooler strategy of a data center.

CFD Simulation of Propane Thermal Cracking Furnace and Reactor: A Case Study

2016 ◽  
Vol 15 (3) ◽  
Author(s):  
Hossein Mohammad Ghasemi ◽  
Neda Gilani ◽  
Jafar Towfighi Daryan
Keyword(s):  
Skin Temperature ◽  
Flow Rate ◽  
Cfd Simulation ◽  
Outlet Temperature ◽  
Propane Conversion ◽  
Temperature Profiles ◽  
Fuel Flow Rate ◽  
Fuel Flow ◽  
Fuel Rate ◽  
Propylene Yield

Abstract In the present work, a different new arrangement of side-wall burners of an industrial furnace with varying fuel flow rate was studied by three-dimensional CFD simulation. Tube skin temperature and heat flux profiles were obtained by solving mass, momentum and energy equations of the furnace by Ansys Fluent software. A reasonable fuel flow rate ($$\dot m$$=0.0695 kg/s) was assigned and effect of different ratio of this rate (0.25$$\dot m$$, 0.5$$\dot m$$, 2$$\dot m$$, 4$$\dot m$$) was investigated on reactor tube skin temperature profiles. Heat and temperature non-uniform distribution was observed by proposed arrangement. It was found that proper range for fuel rate was 0.5$$\dot m$$ to 2$$\dot m$$. Temperature profiles were used in one dimensional plug flow reactor model equations to consider fuel rate variations on reactor performance. By the proposed burner arrangement, Propane conversion and Ethylene yield obtained 6.25 % and 7.2 % more than the base case. Furthermore coil outlet temperature (COT) decreased about 7 °C. Also, feed flowrate was taken as an effective parameter on reactor process under no coke formation condition. Results showed that by increasing fuel rate, outlet Propylene yield decreased, while, process gas temperature, pressure drop, process severity (propane conversion) and Ethylene yield increased along the reactor tube i. e. for 0.5$$\dot m$$ to 2$$\dot m$$ at 0.8 kg/s reactor flowrate, Propylene yield decreased 15.95 % and reached to zero, whereas Ethylene yield increased 16.5 %. Also, in any fuel rate, by increasing reactor feed flowrate, even though the reactor coil outlet temperature decreased, the desired product yields increased. At 0.95 kg/s reactor flowrate, maximum Ethylene yield was obtained about 45.5 % at 1$$\dot m$$ kg/s; while, Propylene yield production at 0.5$$\dot m$$ kg/s fuel rate was 22.41 %.

scholarly journals Numerical Study on Non-Uniform Temperature Distribution and Thermal Performance of Plate Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8280
Author(s):  
Jeonggyun Ham ◽  
Gonghee Lee ◽  
Dong-wook Oh ◽  
Honghyun Cho
Keyword(s):  
Heat Exchanger ◽  
Temperature Distribution ◽  
Flow Velocity ◽  
Mass Flow ◽  
Flow Rate ◽  
Temperature Difference ◽  
Plate Heat Exchanger ◽  
Outlet Temperature ◽  
Uniform Temperature ◽  
Plate Heat

In this study, computational fluid dynamics (CFD) analysis was performed to investigate the cause of the thermal stratification in the channel and the temperature non-uniformity of the plate heat exchanger. The flow velocity maldistribution of the channel and the merging parts caused temperature non-uniformity in the channel width direction. The non-uniformity of flow velocity and temperature in the channel is shown in Section 1 > Section 3 > Section 2 from the heat exchanger. The non-uniform temperature distribution in the channel caused channel stratification and non-uniform outlet temperature. Stratification occurred at the channel near the merging due to the flow rate non-uniformity in the channel. In particular, as the mass flow rate increased from 0.03 to 0.12 kg/s and the effectiveness increased from 0.436 to 0.615, the cold-side stratified volume decreased from 4.06 to 3.7 cm3, and the temperature difference between the stratified area and the outlet decreased from 1.21 K to 0.61 K. The increase in mass flow and the decrease in temperature difference between the cold and hot sides alleviated the non-uniformity of the outlet temperature due to the increase in effectiveness. Besides, as the inlet temperature difference between the cold and the hot side increases, the temperature non-uniformity at the outlet port is poor due to the increase in the stratified region at the channel, and the distance to obtain a uniform temperature in the outlet pipe increases as the temperature at the hot side increases.

scholarly journals Thermal Performance and Energy Saving Analysis of Indoor Air–Water Heat Exchanger Based on Micro Heat Pipe Array for Data Center

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 393 ◽  
Author(s):  
Heran Jing ◽  
Zhenhua Quan ◽  
Yaohua Zhao ◽  
Lincheng Wang ◽  
Ruyang Ren ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Energy Saving ◽  
Heat Pipe ◽  
Flow Rate ◽  
Data Center ◽  
Data Centers ◽  
Air Flow ◽  
Air Flow Rate ◽  
Cold Energy

According to the temperature regulations and high energy consumption of air conditioning (AC) system in data centers (DCs), natural cold energy becomes the focus of energy saving in data center in winter and transition season. A new type of air–water heat exchanger (AWHE) for the indoor side of DCs was designed to use natural cold energy in order to reduce the power consumption of AC. The AWHE applied micro-heat pipe arrays (MHPAs) with serrated fins on its surface to enhance heat transfer. The performance of MHPA-AWHE for different inlet water temperatures, water and air flow rates was investigated, respectively. The results showed that the maximum efficiency of the heat exchanger was 81.4% by using the effectiveness number of transfer units (ε-NTU) method. When the max air flow rate was 3000 m3/h and the water inlet temperature was 5 °C, the maximum heat transfer rate was 9.29 kW. The maximum pressure drop of the air side and water side were 339.8 Pa and 8.86 kPa, respectively. The comprehensive evaluation index j/f1/2 of the MHPA-AWHE increased by 10.8% compared to the plate–fin heat exchanger with louvered fins. The energy saving characteristics of an example DCs in Beijing was analyzed, and when the air flow rate was 2500 m3/h and the number of MHPA-AWHE modules was five, the minimum payback period of the MHPA-AWHE system was 2.3 years, which was the shortest and the most economical recorded. The maximum comprehensive energy efficiency ratio (EER) of the system after the transformation was 21.8, the electric power reduced by 28.3% compared to the system before the transformation, and the control strategy was carried out. The comprehensive performance provides a reference for MHPA-AWHE application in data centers.

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