我的記事簿: 2月 2018

2018年2月22日星期四

熱量公式

H=ms\Delta T\,\!

H：熱量 ( kcal )
m：物質 ( 氣體：Nm^3 )
s：比熱 ( kcal / ( Nm^3*℃ )
△T：溫差 ( ℃ )

透過比熱容，便可計算某質量的熱能使用。例如一次實驗中，四千克重的水的溫度原先是25攝氏度，經過加熱後，溫度為45攝氏度。假如要求取使用了多少能量的話，首先要知道水的比熱容，若水的比熱容是4200的話，透過以上公式計算，便可得出：

H=4\times 4200\times (45-25)\,\!

=336000J\,\!

即是使用了336000焦耳熱能。

資料來源點我

Selective Catalytic Reduction (SCR) of NO by NH3 in a Fixed‐bed Reacto

資料來源點我

資料改為可編輯檔是便於Google翻譯

1. Introduction

Fossil fuels have been main sources for energy in terms of combustion, where chemical energy in fuels is converted into thermal and mechanical energies. When air reacts with fuels at high temperature, NOx representing NO, NO2, N2O, N2O5 and etc is unavoidable due to the reaction between oxygen and nitrogen in air [1, 2]. NOx is toxic as itself as well as a precursor of acid rain, so its regulation has been becoming more stringent all over the countries. There has been much interest in reducing NOx from engines in terms of fuel injection strategies [3], exhaust gas recirculation [4] and catalytic reactions [5], among which selective catalytic reduction (SCR) has been successfully applied in stationary applications such as boilers and power plants [6]. Although there are many reducing agents suggested, gaseous ammonia shows the best performance for this reaction [7]:

4NH3 + 4NO + O2 → 4N2 + 6H2O (1.1)

Although the equation (1.1) is a major pathway for NO in the presence of O2, the equation (1.2) is also important when NO2 is high in the mixture of NO and NO2 [8].

4NH3 + 2NO + 2NO2 → 4N2 + 6H2O (1.2)

There have been many catalysts developed for the SCR reaction [9, 10], among which a V2O5/TiO2 catalyst has been widely used in commercial applications [10]. Although the equation (1.1) is an overall reaction for SCR, many elementary steps are involved during the reaction between NO and NH3 [11]. Since NO is reacted with NH3 on catalysts, its detailed reaction mechanism has been of great interest in order to develop kinetic models of SCR depending upon catalysts [12 – 14]. According to many studies, it is accepted that NO is reacted via the Langmuir‐Hinshelwood mechanism in V2O5‐WO3/TiO2 catalysts [13], where gaseous NO and NH3 are adsorbed on the catalysts and adsorbed NO and NH3 are reacted on the surface.

There have been many researches for modeling of ammonia‐SCR systems [15 ‐ 19]. As evidenced by experiments, oxygen concentration in the exhaust gases is crucial for the SCR. Therefore, some kinetic models took into account the oxygen concentration [18, 19]. However, Chae et al. only considered NO and NH3 concentrations for their model although oxygen effect was already employed in their model [16]. Another important parameter in the SCR model is whether NH3 is oxidized by reacting oxygen as shown in the equation (1.3) [17, 18]. Since this reaction is active at high temperature over 400o C, it is observed that NO removal activity decreases over this temperature because NH3 which needs for NO reaction is converted into NO.

4NH3 + 5O2 → 4NO + 6H2O (1.3)

In this study, the reaction between NO and NH3 was simulated in COMSOL using fundamental mass and momentum equations. The model was studied if it is appropriate to describe SCR reaction, which has been experimentally proven.

1. Governing Equations

There are two governing equations employed in this model; one is a mass equation, and the other is a momentum equation. Although there is a heat evolved during the reaction of NO and NH3, an energy equation was not considered because it is very small due to small amounts of two reactants. The equation (2.1) indicates a mass equation in an advective flow.

where c is a concentration, D is a diffusion coefficient, R is a chemical reaction, and v is a velocity which is a vector form. Since the mass equation is assumed at a steady state, the 1st term is canceled out and finally the equation becomes the equation (2.2)

For a momentum equation, the incompressible Navier‐Stokes equation in a laminar flow was employed as shown in the equation (2.3) and (2.4)

未完 !!

2018年2月18日星期日

Excel 跨欄置中快捷鍵編寫

自訂Excel 跨欄置中快速鍵

1.點擊-索引標籤>開發人員>程式碼>Visual Basic；如下圖；

2.跳出Microsaft Visual Basi視窗，點擊-索引標籤>插入>模組；如下圖；

3.在工作區中輸入

Sub 跨欄置中()

' 快速鍵: Ctrl+d

With Selection

.HorizontalAlignment = xlCenter

.VerticalAlignment = xlCenter

.WrapText = False

.Orientation = 0

.AddIndent = False

.IndentLevel = 0

.ShrinkToFit = False

.ReadingOrder = xlContext

.MergeCells = False

End With

Selection.Merge

End Sub

如下圖：

.4. 點擊-索引標籤>檢視>Microsoft Excel 或索引標籤下的Excel 圖示或 Alt+F11；如下圖；

5.視窗跳至Excel -點擊-索引標籤>開發人員>程式碼>巨集；如下圖；

6.跳出巨集視窗，點擊選項；如下圖示：

7.輸入欲設定的快捷鍵，並按確定；如下圖：( 注意：不要與原Excel快捷鍵相衝突 )

8.視窗跳回巨集視窗，點擊執行；如下圖示：

9.框選合併範圍；按 Ctrl + d；如下圖示：

10.合併成功且置中；如下圖示：

11.新設置的快捷鍵並不會自動傳到每一個Excel檔案內，所以需另存新檔(樣板檔)。

參考：Excel 跨欄置中有沒有快捷鍵呢?

12.可以跨欄置中，當然可以跨欄靠左與跨欄靠右

跨欄靠左 >>

Sub 跨欄靠左()
' 快速鍵: Ctrl+s
'
With Selection
.HorizontalAlignment = xlLeft
.VerticalAlignment = xlCenter
.WrapText = False
.Orientation = 0
.AddIndent = False
.IndentLevel = 0
.ShrinkToFit = False
.ReadingOrder = xlContext
.MergeCells = False
End With
Selection.Merge
End Sub

跨欄靠右 >>

Sub 跨欄靠右()
' 快速鍵: Ctrl+s
'
With Selection
.HorizontalAlignment = xlRight
.VerticalAlignment = xlCenter
.WrapText = False
.Orientation = 0
.AddIndent = False
.IndentLevel = 0
.ShrinkToFit = False
.ReadingOrder = xlContext
.MergeCells = False
End With
Selection.Merge
End Sub