Total mass flow

In a ouce-throiigh system, the feedwater entering the unit absorbs heat until it is completely couveided to steam. The total mass flow through the waterwall tubes equals the feedwater flow and, during uorm operation, the total steam flow As only steam leaves the boiler, there is no need for a steam drum. 

The above criteria are a guide for detecting potential problems with gas letdown systems and apply for the first 90 m of piping downstream of the pressure reducer under concern. Systems with only liquid flow are not considered potential problems and need not be investigated. For systems with two phase flow, use the conservative assumption of the total mass flow rate as gas. Any system exceeding these criteria should be further evaluated. 

Thus the total mass flows tn= m, + m,) differ in different cases. Water vapor flow th, is obtained by multiplying the dry air mass flow by the corresponding humidity x (Eq. 4.93). As a basic quantity in humid air mass and energy balance calculations, we use dry air mass flow m and the effect of humidity on the energy balance is noted in the enthalpy h, (Eq. 4.87). 

L/G = ratio of total mass flow of tvater and dry air in cooling tower, Ib/lb... 

When two samples of air are brought together the condition of the mixture may be arrived at arithmetically by adding the heat flow of each and dividing by the total mass flow and similarly for the moisture flow. Alternatively, plot the condition of each onto a psychrometric chart. The mixed condition lies on a straight line between the two in a position proportional to the two quantities. 

Total mass flow rates are given by the product of volumetric flow multiplied by density. Component mass flows are given by the product of volumetric flow rates multiplied by concentration. 

The conservation of energy, however, differs from that of mass in that energy can be generated (or consumed) in a chemical process. Material can change form, new molecular species can be formed by chemical reaction, but the total mass flow into a process unit must be equal to the flow out at the steady state. The same is not true of energy. The total enthalpy of the outlet streams will not equal that of the inlet streams if energy is generated or consumed in the processes such as that due to heat of reaction. 

Vapour quality, x = mass vapour/total mass flow = 0.1 /0.4 = 0.25 Viscosity of vapour = 0.0084 mNm 2s... 

G Total mass flow-rate per unit area ML-2T- ... 

We come back to derive the process transfer functions for the blending problem.9 The total mass flow balance is... 

The interfacial area a was not measured, and the quantity (Ua/V) was correlated versus the total mass flow rate. From results of this type, the general parameters given in Eqs. (30) cannot be evaluated. Therefore, the only design that can be safely performed is for the Aroclor-water system in a 3-in. pipe. 

If required by the model(s) to be used, back-up data for each entry in the matrix or table may be supplied to resolve the total mass flow into spatial cells (UTM coordinates, depth or height), temporal cells (hourly frequency distributions, diurnal cycles, seasonal subdivisions or secular trends on annual intervals) or speciation cells (by valency state of anions or by hydrocarbon structure, for example). The level of difficulty encountered by the user in supplying these data may influence the choice of model(s). 

The total mass flow rate is then 29.58(89.86) = 2658 g/sec or 2.658 kg/sec. For 1000 tubes in parallel the available cross section for flow is given by... 

R = L m The total mass flow is that of the liquid only in the mixture... 

Example 15-2 Estimate the pressure gradient (in psi/ft) for a two-phase mixture of air and water entering a horizontal 6 in. sch 40 pipe at a total mass flow rate of 6500 lbm/min at 150 psia, 60°F, with a quality (a) of 0.1 lbm air/lbm water. Compare your answers using the (a) omega (b) Lockhart-... 

For a fluid in a region of space where there is neither a source nor a sink, the total mass flow out of the region must balance the rate of decrease of the total mass in the volume. This balance means that... 

The case for evaporation of a volatile from a pool of liquid has already been considered in chapter 3. The total mass flow rate from the evaporating pool is given by Equation 3-12 ... 

The flow of gas-liquid mixtures in pipes and other items of process equipment is common and extremely important. In some cases the quality, that is the mass fraction of gas in the two-phase flow, will vary very little over a large distance. An example of this is the flow in many gas-oil pipelines. In other cases, boiling or condensation occurs and the quality may change very significantly although the total mass flow rate remains constant. 

Dengler and Addoms 8 measured heat transfer to water boiling in a 6 m tube and found that the heat flux increased steadily up the tube as the percentage of vapour increased, as shown in Figure 14.4. Where convection was predominant, the data were correlated using the ratio of the observed two-phase heat transfer coefficient (htp) to that which would be obtained had the same total mass flow been all liquid (hi) as the ordinate. As discussed in Volume 6, Chapter 12, this ratio was plotted against the reciprocal of Xtt, the parameter for two-phase turbulent flow developed by Lockhart and Martinelli(9). The liquid coefficient hL is given by ... 

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