Energy Requirements for Pumping

ENERGY REQUIREMENTS FOR PUMPING Mechanical Energy Balance Eqnation 

The energy required to pump a liquid food through a pipe line can be calculated from the mechanical eneigy balance (MEB) equation. The MEB equation can be used to analyze pipe flow systems. For the steady-state flow of an incompressible fluid, the MEB can be written as follows (Brodkey, 1%7)  

The velocities at the entrance and exit of the system can be calculated from the respective diameters of the tanks or pipes and the volumetric flow rate of the food. The energy loss term E/ consists of losses due to friction in pipe and that due to friction in valves and fittings  

Because many fluid foods are non-Newtonian in nature, estimation of fiiction losses (pressure drop) for these fluids in straight pipes and in fittings is of interest. One can estimate the fnction losses in straight pipes and tubes from the magnitude of the Fanning fnction factor,/, defined as  

For fluids that can be described by the power law (Equation 2.3), the generalized Reynolds number (GRe) can be calculated from the equation  

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In this procedure, increasing the supply temperature is considered to reduce the investment cost for the distribution system and electrical energy required for pumping stations. However, this change increases heat losses in the distribution network. 

The operation of an electrodialysis unit requires one or more pumps to circulate the diluate, the concentrate, and the electrode rinse solution through the stack. The energy required for pumping these solutions is determined by the volumes of the solutions to be pumped and the pressure drop. It can be expressed by ... 

V. The total voltage across the sixty-cell stack is 140-170 V with a cell current of 1200-1400 A, The energy consumption is 500 kWh ton although the energy required for pumping must, in this process, be high. 

In an experimental study of a small air-lift pump(6), (25 mm. diameter and 13.8 m overall height) the results were expressed by plotting the efficiency of the pump, defined as the useful work done on the water divided by the energy required for isothermal compression of the air, to a basis of energy input in the air. In each case, the curve was found to rise sharply to a maximum and then to fall off more gradually. Typical results are shown in Figure 8.37. 

The power required for pumping will be given by the product of the volumetric flowrate and the pressure difference between the pump outlet and the discharge end of the pipeline. Taking note of the fluctuating nature of the flow, it is necessary to consider the energy transferred to the fluid over a small time interval and to integrate over the cycle to obtain the mean value of the power. 

The efficiency of centrifugal pumps depends on their size. The values given in Figure 10.62 can be used to estimate the power and energy requirements for preliminary design purpose. The efficiency of reciprocating pumps is usually around 90 per cent. 

These methods of solute transfer usually rely on a relatively low intracellular concentration of the solute of interest, so that it will readily diffuse into the cell down the electrochemical gradient (as in the case of ion channels). Alternatively, the solute may be moved into the cell using chemical energy derived from another solute moved in the same direction (co-transport) or opposite direction (countertransport) on the carrier protein (symporters and antiporters respectively). The transfer of the second solute is in turn dependent on an inward electrochemical gradient. Ultimately, these gradients are established by primary, energy-requiring solute pumps (e.g. ATPases), which, on most epithelia, are located on the basolateral/serosal membrane (see Section 5.2 for discussion of ATPases). 

At low gas velocities, the bed of particles is practically a packed bed, and the pressure drop is proportional to the superficial velocity. As the gas velocity is increased, a point is reached at which the bed behavior changes from fixed particles to suspended particles. The superficial velocity required to first suspend the bed particles is known as minimum fluidization velocity (umf). The minimum fluidization velocity sets the lower limit of possible operating velocities and the approximate pressure drop can be used to approximate pumping energy requirements. For agglomeration process in the fluid-bed processor, air velocity required is normally five to six times the minimum fluidization velocity. 

Figure 12.4 Mechanism of action of Na+/K+symport inhibitors (thiazides) on the distal convoluted tubule. As in the other parts of the nephron, Na+movement is powered by the energy-requiring sodium pump (P) in the basolateral membrane which exchanges intracellular Na+for K-i-in the extracellular fluid (ECF). The transport of Na-rand Cl- into the cell from the filtrate against the prevailing electrochemical gradient is facilitated by the symporter (S). The Na-Hons are then transported by the pump mechanism described above and the Cl- ions diffuse passively Into the ECF through ion channels in the basolateral membrane. Thiazide diuretics inhibit the symporter by disabling the Cl- binding site with the loss of Na-rand Cl- in the urine.

Marking Results — Infrared Disk. The 835 nm laser beam was obtained from a dye laser which was pumped by a pulsed nitrogen laser. The energy of the laser pulse was varied as before. The marking threshold was determined (19) with respect to the threshold energy required for marking of a 150 A tellurium film on a polymethylmethacrylate substrate (a commonly-used benchmark system) under identical conditions. 

An H+ electrochemical gradient (ApH+) provides the energy required for active transport of all classical neurotransmitters into synaptic vesicles. The Mg2+-dependent vacuolar-type H+-ATPase (V-ATPase) that produces this gradient resides on internal membranes of the secretory pathway, in particular endosomes and lysosomes (vacuole in yeast) as well as secretory vesicles (Figure 3). In terms of both structure and function, this pump resembles the F-type ATPases of bacteria, mitochondria and chloroplasts, and differs from the P-type ATPases expressed at the plasma membrane of mammalian cells (e.g., the Na+/K+-, gastric H+/K+-and muscle Ca2+-ATPases) (Forgac, 1989 Nelson, 1992). The vacuolar and F0F1... 

An important aspect of each flow sheet is the use of heat pump loops to recover heat and use it at higher temperatures. For a relatively small electrical input, substantial amounts of process heat can be recovered and reused within the section. Table 3 summarises the section energy requirements for both the CEA and GA flow sheets. 

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