Analytical and Numerical Modeling of Solar Chimney

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Mohammad Raghib Shakeel ◽  
Jihad Al-Sadah ◽  
Esmail M. A. Mokheimer
Keyword(s):  
Flow Rate ◽  
Volume Flow Rate ◽  
Air Flow ◽  
Incident Radiation ◽  
Analytical Models ◽  
Air Flow Rate ◽  
Solar Chimney ◽  
Trombe Wall ◽  
Flow Through ◽  
Induced Flow

Solar chimney or Trombe wall has been studied numerically and analytically. Analytical results available in the literature overestimate air flow rate by 46–97%. While insulated walls are used in the experiments, there might still be loss from the chimney walls, which is not usually considered in the available analytical models. It is found that the overestimation of air flow rate can be reduced to 3–14% by including heat losses from the glass and wall side of the chimney in the analytical model. The presently developed numerical model is validated against experimental data from literature. The conditions within which the analytical solution can give good approximate results regarding the air volume flow rate have been identified and discussed. We found that the analytical method simulates solar chimneys well for gap widths of up to 0.3 m and incident radiation above 500 W/m2. The present numerical results revealed that the optimum value of chimney gap width that maximizes the induced flow through the chimney is 0.3 m.

scholarly journals Automobile Radiator’s Engineering and Analysation

2020 ◽  
Vol 9 (5) ◽  
pp. 554-558
Keyword(s):  
Flow Rate ◽  
Heat Dissipation ◽  
Cooling System ◽  
Volume Flow Rate ◽  
Air Flow ◽  
Temperature Drop ◽  
Inlet Temperature ◽  
Air Flow Rate ◽  
Air Velocity ◽  
Cooling Fan

The shape of a radiator cover is crucial either in determining the pattern of air flow or in increasing the same through the radiator core thereby increasing the thermal efficiency, thus making it a necessity to understand it. Moreover the parts circumjacent to the core namely the upper tank, lower tank, cooling fan, fins, tubes, etc promote the air flow rate. Also it is to note that the air flow rate of discharge gases from radiator core is one of the prime factors in determining the automobile cooling system. Initially factors such as temperature, pressure, air flow rate that affect the performance are obtained in order to derive out the entities of operation. One of the observations that can be made through this paper is that as the volume of the coolant increases, the rate of heat dissipation increases, also parameters like inlet temperature and volume flow rate of coolant, air velocity, temperature drop and drop in pressure of coolant are factors that contribute in radiator performance evidently.

scholarly journals Coupling Effect of Air Flow Rate and Operating Conditions on the Performance of Electric Vehicle R744 Air Conditioning System

2021 ◽  
Vol 11 (11) ◽  
pp. 4855
Author(s):  
Anci Wang ◽  
Jianmin Fang ◽  
Xiang Yin ◽  
Yulong Song ◽  
Feng Cao ◽  
...  
Keyword(s):  
Electric Vehicle ◽  
Flow Rate ◽  
Air Conditioning ◽  
Volume Flow Rate ◽  
Air Flow ◽  
Volume Flow ◽  
Air Flow Rate ◽  
Air Volume ◽  
Discharge Pressure ◽  
Air Conditioning Systems

The air flow rate on the gas cooler side is one of the key parameters affecting the performance and running safety of transcritical CO2 electric vehicle air conditioning systems. After experimentally analyzing the effects of the air volume flow rate in the gas cooler on the cycle parameters and system performance, a novel method to evaluate the optimal air flow rate was proposed. In addition, the effect of the gas cooler air volume flow rate on the key performance parameters of the system (e.g., optimal discharge pressure) was explored. Finally, the coupling effects of the compressor speed, ambient temperature and optimal air flow rate on the system performance was also exhaustively assessed. It was found that as the discharge temperature, the CO2 temperature at the gas cooler outlet and the discharge pressure did not vary more than ±2%, the corresponding gas cooler air volume flow rate was optimal. For the single-row and dual-process microchannel evaporator used in this work, the recommended value of the optimal gas cooler air volume flow rate was 2500 m3·h−1. The results could provide reference for the fan speed design of electric vehicle CO2 air conditioning systems, especially for the performance under idling model.

scholarly journals Effects on the Ventilation of a Two-Storey Building under Different Thermal Conditions

2019 ◽  
Vol 111 ◽  
pp. 02009
Author(s):  
Tim Röder ◽  
Paul Mathis ◽  
Dirk Müller
Keyword(s):  
Flow Rate ◽  
Static Pressure ◽  
Air Flow ◽  
Thermal Conditions ◽  
Volume Flow ◽  
Air Flow Rate ◽  
Static Pressure Difference ◽  
Flow Through ◽  
Flow Pressure ◽  
Storey Building

In this paper it is shown how the air flow rate of decentralized ventilation devices can be affected by a staircase of a two-storey building under different thermal conditions. Since these devices need local fans for supplying the requested volume flow, pressure loads have a significant impact on the delivered volume flow rates. Regarding this, the study comprises two analyses: First, a CFD-model is developed to simulate the ventilation air flow through a simplified staircase. By varying parameters for rooms’ temperature and ventilation direction, the hydrostatic pressure in the staircase is evaluated. The simulations – characterized by high Archimedes numbers – are successfully validated with findings from preliminary work. In a second part, the pressure conditions inside the staircase are referred to outside conditions. Consequently, a static pressure difference at the ventilation device on each storey can be observed. We found that the deliverable volume air flow rate can decrease up to 10 % from the nominal flow rate due to temperature differences between the storeys and outside. Therefore, heat recovery and ventilation effectiveness may also be impaired.

Numerical Simulation of Air Flow in BiPV-Trombe Wall

2013 ◽  
Vol 860-863 ◽  
pp. 141-145 ◽  
Author(s):  
Xiao Wei Xu ◽  
Ya Xin Su
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Rate ◽  
Air Flow ◽  
Channel Height ◽  
Air Flow Rate ◽  
Air Velocity ◽  
Trombe Wall ◽  
Multivariable Regression ◽  
Cfd Method

A novel built-in photovoltaic Trombe wall (BiPV-TW) was proposed in this paper and the air flow in a BiPV-Trombe wall was numerically simulated by CFD method. The effect of channel height on flow patterns and air velocity was analyzed. The mass flow rate of air was calculated and a dimensionless expression to calculate the air flow rate in term of a Reynolds number was correlated according to a modified Rayleigh number and the aspect ratio, H/b, which took into account both of the channel sizes and solar radiation based on a multivariable regression analysis.

scholarly journals Analisis Sudut Lempar Gabah Pada Mesin Pembersihan Gabah Dengan Media Aliran Udara

2015 ◽  
Vol 8 (1) ◽  
pp. 29-40
Author(s):  
Suhendra Suhendra ◽  
Budi Setiawan
Keyword(s):  
Bulk Density ◽  
Flow Rate ◽  
Air Flow ◽  
Prediction Equation ◽  
Cleaning Process ◽  
Air Flow Rate ◽  
Cleaning Machine ◽  
Flow Through ◽  
Grain Bulk ◽  
The Relationship

Abstrak. Penanganan pasca panen padi merupakan salah satu upaya untuk meningkatkan produksi padi, dengan semaksimal mungkin menekan kehilangan hasil panen. Salah satu faktor yang mempengaruhi kehilangan hasil panen padi adalah proses pembersihan gabah. Berdasarkan hal tersebut, diperlukan suatu upaya untuk mendapatkan proses pembersihan gabah yang optimal dengan cara menganalisis variabel yang berpengaruh pada proses pembersihan gabah. Penelitian ini bertujuan untuk menghasilkan suatu persamaan matematika untuk memprediksi besar sudut lempar gabah, mengetahui hubungan antar variabel yang mempengaruhi proses pembersihan gabah secara mekanis serta untuk mendapatkan variabel yang diperlukan dalam rancang bangun mesin pembersih gabah dengan media pembersih berupa aliran udara. Melalui pendekatan analisis dimensi diperoleh persamaan prediksi sudut lempar gabah (θ) sebagai fungsi dari bulk density gabah (ρ), diameter saluran udara (D), laju aliran udara (V), kapasitas (Kp), diameter gabah (d), kadar air gabah (α) serta jarak saluran udara dan gabah jatuh (l) yaitu :       θ = 0,0661.(ρ.d^2.V/Kp)^0,643 . (dxα/t)^0,0618Hasil validasi persamaan prediksi sudut lempar gabah menunjukkan bahwa hasil prediksi tidak berbeda nyata dengan hasil observasi sehingga persamaan prediksi yang dibuat dapat diterima. Hasil simulasi persamaan prediksi menunjukkan bahwa diameter saluran udara dan jarak saluran udara saat gabah jatuh memiliki pengaruh tetapi tidak signifikan terhadap besarnya sudut lempar gabah, sedangkan laju aliran udara dan kapasitas memiliki pengaruh yang signifikan terhadap besarnya sudut lempar gabah. Throw Angle Analysis of Grain on Grain Cleaning Machine With Air FlowAbstract. Post-harvest handling of rice is one of the efforts to increase rice production, with maximum pressing crop yield loss. One of the factors that influence the loss of the harvest is the process of cleaning of the grain. Based on this, we need an effort to obtain optimal grain cleaning process by analyzing the variables that affect in the grain cleaning process. This research aims to produce a mathematical equation to predict the large grain throwing angle, determine the relationship between the variables that affect in the mechanical cleaning process grain and to obtain the necessary variables in the design of grain cleaning machine with cleaning media in the form of air flow. Through the dimensional analysis approach derived prediction equations throwing grain angle (θ) as a function of grain bulk density (ρ), the diameter of the airways (D), the air flow rate (V), capacity (Kp), grain diameter (d), water content grain (α) and distance airways and grain fall (l), namely:θ = 0,0661.(ρ.d^2.V/Kp)^0,643 . (dxα/t)^0,0618The result of prediction equation from grain throwing angle show that prediction result is not different significant with observation result. Simulation result of prediction equation show that the diameter  of airways and distance airways when grain fall has influence but not significant on the value of  grain throwing angle, whereas the air flow rate and capacity has significant influence on the value of  grain throwing angle.

scholarly journals Model of thermal buoyancy in cavity-ventilated roof constructions

2021 ◽  
pp. 174425912098418
Author(s):  
Toivo Säwén ◽  
Martina Stockhaus ◽  
Carl-Eric Hagentoft ◽  
Nora Schjøth Bunkholt ◽  
Paula Wahlgren
Keyword(s):  
Analytical Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Air Flow ◽  
Wind Pressure ◽  
Air Flow Rate ◽  
Test Set ◽  
Air Cavity ◽  
Thermal Buoyancy ◽  
The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

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