Mass flow, water

The zoning of the space is based on the assumption of constant temperature, concentration, and humidity in each separate zone." - The boundaries between the zones can be vertical or horizontal. The balances for air mass flow, contaminant mass flow, water vapor mass flow, and beat flow arc determined between zones and between zone and outer boundaries. 

The calculation of the two-zone model is based on the balance equations for air mass flow, contaminant mass flow, water vapor mass flow, and heat flow of both zones. 

It s the same with mass flows. Water vapor diffuses from steam through pores onto adsorbent sites, and solvent vapor diffuses from adsorbent sites through pores to be carried away by the steam flow. Both flows are from where there is much of one kind of mass to where there is little, in aid of producing an equilibrium distribution of each material. 

Coal is fed as a paste containing 25 wt % water, and sorbent is fed diy by a lock-hopper system with pneumatic conveying. The top size of each feedstock is 3 mm in). The latent heat lost evaporating the water fed with the paste is compensated by increased gas turbine power output resulting from the increased flue-gas mass flow rate. For the 80-MWe unit, there are six coal feed points (one per 4.5 m" [48 ft"]) and four sorbent feed points (one per 6.7 m" [72 ft"]), all entering beneath the tube bank along one wall. The bed depth is... 

To remove these undesirable but unavoidable salt deposits, a signi-fieant amount (about 1 % of mass flow) of boiler feedwater at 80-90°C is periodieally injeeted. Injeetion nozzles are typieally loeated in the inlet seetion, in the return ehannels, and in the labyrinth seals on the diseharge side of nitrous gas eompressors. This periodie flushing of the eompressor with water does have eertain disadvantages ... 

Water Injection—Mid-compressor flashing is used to cool the compressed air and add mass flow to the system. 

Flow Low mass flow indicated. Mass flow error. Transmitter zero shift. Measurement is high. Measurement error. Liquid droplets in gas. Static pressure change in gas. Free water in fluid. Pulsation in flow. Non-standard pipe runs. Install demister upstream heat gas upstream of sensor. Add pressure recording pen. Mount transmitter above taps. Add process pulsation damper. Estimate limits of error. 

Technical calculations dealing with humid air are reasonable to solve with dry air mass flow rates, because these remain constant in spite of changes in the amount of water vapor in the air. For that reason a definition for enthalpy,... 

We denoted the mass of dry air in a volume V as that is, p, - w,/Vj, and the mass of water vapor in V as m, that is, pp = mp/Yp. In practical calculations we usually handle volume flow volume flow is known in the suction inlet of a fan when the operating point of the fan is defined. Volume flow q, expressing the total air flow or the combined volume flow of water vapor and dry air, is not constant in various parts of the duct, because the pressure and temperature can vary. Therefore in technical calculations dealing with humid air, materia flows are treated as mass flows. Also, while the humidity can vary, the basic quantity is dry air mass flow w,(kg d.a./s). If, for instance, we know the volume flow q,. of a fan, the dry air mass flow through the fan is... 

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). 

The air, contaminant, and water vapor mass flow elements in outer boundaries and between the zones are created by... 

Plots of efficiency against pressure ratio for the full injection EGT plant, for a maximum to minimum temperature 5, are shown in Fig. 6.9, compared with lower values of efficiency in the dry CBTX plant. There are. several points to be noted first that an increase in efficiency is worthwhile, up to 10% secondly that the total water injection is up to over 10% of the air mass flow and thirdly that the optimum pressure ratio increases to about 8, from about 5 for that of the dry cycle. 

For the IFB plant the main advantage lies in the reduction of the inlet temperature, mainly by saturating the air with a very fine spray of water droplets [13]. This, in itself, results in an increased power output, but it is evident that the water may continue to evaporate within the compressor, resulting in a lowering of the compressor delivery temperature. A remarkable result observed by Utamura is an increase of some 8% in power output for only a small water mass flow (about 1% of air mass flow). However, the compressor performance may be adversely affected as the stages become mismatched [14], even for the small water quantities injected. 

FIGURE 16.23 Inulln isolated from small (—). medium ( ) and large (A) tubers separated on P-6 (140 X 1.5 cm) flow rate 0.33 ml/min eluenf. H20(dest) + 0.002% NaNa mass detection Waters 403 R differential refractive index detector, sensitivity 8X applied sample solution volume I ml of a 20-mg/ml aqueous inulin solution. 

Example 6.4 A small water-cooled condenser uses mains water at 13°C and heats this to 24°C before it goes to waste. The evaporator duty is 4.2 kW and the motor output is 1.7 kW. What is the water mass flow ... 

This cooling effect of the evaporation of water can be applied directly to the condenser refrigerant pipes in the evaporative condenser (Eigure 6.7). The mass flow of water over the condenser tubes must be enough to ensure wetting of the tube surface, and will be of the order of 80-160 times the quantity evaporated. The mass flow of air must be sufficient to carry away the water vapour formed, and a compromise must be reached with expected variations in ambient conditions. An average figure is 0.06 kg/ (s kW). 

Example 6.5 A water tower serves a condenser rated at 880 kW and the water-circulating pump takes another 15 kW. What will be the evaporation rate, the approximate circulation rate, and the air mass flow ... 

It will be seen that the water and air mass flow rates over a cooling tower are roughly equal. 

Condensers are sized so that they can reject the system heat load under maximum conditions of air or water temperature. In colder weather, the condensing temperature will fall with that of the cooling medium and this may cause difficulties in correct operation of the plant. In particular, the pressure across the expansion valve (see also Chapter 8) may be too low to circulate the required mass flow of the refrigerant. Under such circumstances, artificial means must be used to keep the head pressure up, always remembering that the condensing pressure should be kept as low as practical for power economy. 

Example 24.1 Air circulates at the rate of 68 kg/s and is to be heated from 16°C to 34°C. Calculate the heat input and the water mass flow for an air heater coil having hot water entering at 85°C and leaving at 74°C. 

Assuming the mass flows of air and water to be equal, an approximate balance can be found. 

Example 25.3 Air enters a cooling tower at 26°C dry bulb and 20°C wet bulb. Water at the same mass flow enters at 29°C and leaves at 24°C. If the air leaves the tower at 98% saturation, what is its final condition ... 

Calculations of this sort are only of importance to the tower designer. Manufacturers application data will give the cooling range or capacity in terms of wet bulb, inlet water temperature and mass flow [16, 19]. 

The removal of heat within an enclosed space must be considered as a multi-step heat transfer process. Heat passes from the occupants or equipment to the air within the space, and from there to the refrigerant or chilled water. It follows that the temperature differences at each step are a reciprocal function of the air mass flow. Where there is a high latent heat load within the space, the relative humidity will also vary with the air flow - the variation being higher with low air flow. 

The air humidification flow diagram for material balance is shown in Figure 9.2. The mass flow rate for water into the humidification unit is ... 

Mass flow rate of cooling water = 35000 lbmh 1... 

Wall-to-bed heat-transfer coefficients were also measured by Viswanathan et al. (V6). The bed diameter was 2 in. and the media used were air, water, and quartz particles of 0.649- and 0.928-mm mean diameter. All experiments were carried out with constant bed height, whereas the amount of solid particles as well as the gas and liquid flow rates were varied. The results are presented in that paper as plots of heat-transfer coefficient versus the ratio between mass flow rate of gas and mass flow rate of liquid. The heat-transfer coefficient increased sharply to a maximum value, which was reached for relatively low gas-liquid ratios, and further increase of the ratio led to a reduction of the heat-transfer coefficient. It was also observed that the maximum value of the heat-transfer coefficient depends on the amount of solid particles in the column. Thus, for 0.928-mm particles, the maximum value of the heat-transfer coefficient obtained in experiments with 750-gm solids was approximately 40% higher than those obtained in experiments with 250- and 1250-gm solids. 

Sulphuric acid of density 1300 kg/m3 is flowing through a pipe of 50 mm, internal diameter. A thin-lipped orifice, 10 mm in diameter is fitted in the pipe and the differential pressure shown on a mercury manometer is 0.1 m. Assuming that the leads to the manometer are filled with the acid, calculate (a) the mass flow rate of acid and (b) the approximate drop in pressure caused by the orifice in kN/m2. The coefficient of discharge of the orifice may be taken as 0.61, the density of mercury as 13.550 kg/m3 and the density of the water as OHIO kg/m ... 

It is supposed that water is to be cooled at a mass rate L per unit area from a temperature 0L2 to Ql - The air will be assumed to have a temperature 6G, a humidity Jf ], and an enthalpy Hoi (which can be calculated from the temperature and humidity), at the inlet point at the bottom of the tower, and its mass flow per unit area will be taken as G. The change in the condition of the liquid and gas phases will now be followed on an enthalpy-temperature diagram (Figure 13.16). The enthalpy-temperature curve PQ for saturated air is plotted either using calculated data or from the humidity chart (Figure 13.4). The region below this line relates to unsaturated air and the region above it to supersaturated air. If it is assumed that the air in contact with the liquid surface... 

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