Friction heat loss

The Optimal Insulation Thickness and Pipe Diameter. The principal results are embodied in Figures 7 and 8. Figure 7 shows total cost curves as functions of nominal pipe diameter for three insulation thicknesses (0 = 1.0, 3.5, and 7.0 inches). Figure 8 illustrates the piping system costs (friction, heat-loss, pipe, insulation, and total) as functions of nominal pipe diameter when the insulation thickness is optimal for that pipe diameter. 

In practice, because of friction, heat loss, and other complications, the maximum efficiency of a steam turbine is only about 40 percent. Therefore for every ton of coal used at a power plant, 0.40 ton generates electricity while the rest of it ends up warming the surroundings ... 

A typical BWR usually delivers steam at 285°C and has a condenser tenq)erature of - 25°C, hence = 0.47. Due to a less efficient energy cycle, friction, heat losses, pumps, etc., the net efficiency ( ei) of both reactor types is only about 0.32 — 0.35 (net electric output delivered to the grid divided by gross thermal output from reactor). In coal-, oil- and gas-fired power plants higher steam temperatures can be achieved, 500°C with T- 530°C and 30°C, = 0.65... 

Heating resulting from frictional heat loss could reasonably extend these lifetimes by 50 percent or more. 

A simple cooling cycle serves to illustrate the concepts. Figure 1 shows a temperature—entropy plot for an actual refrigeration cycle. Gas at state 1 enters the compressor and its pressure and temperature are increased to state 2. There is a decrease in efficiency represented by the increase in entropy from state 1 to state 2 caused by friction, heat transfer, and other losses in the compressor. From state 2 to states 3 and 4 the gas is cooled and condensed by contact with a heat sink. Losses occur here because the refrigerant temperature must always be above the heat sink temperature for heat transfer to take... 

Bernoulli s equation (Equation 2-53), which accounis for static and dynamic pressure losses (due to changes in velocity), but does not account for frictional pressure losses, energ losses due to heat transfer, or work done in an engine. 

Time, pressure, and temperature controls indicate whether the performance requirements of a molded product are being met. The time factors include the rate of injection, duration of ram pressure, time of cooling, time of piastication, and screw RPM. Pressure requirement factors relate to injection high and low pressure cycles, back pressure on the extruder screw, and pressure loss before the plastic enters the cavity which can be caused by a variety of restrictions in the mold. The temperature control factors are in the mold (cavity and core), barrel, and nozzle, as well as the melt temperature from back pressure, screw speed, frictional heat, and so on in the plasticator. 

The existence of two stable states (at given values of the operating parameters) is due to the dominant role of the gravity or friction forces at the various meniscus positions. A decrease in the gravity leads to the displacement of the meniscus toward the outlet and to a decrease in the heat losses and an increase in the liquid and vapor velocities. A decrease in the micro-channel diameter leads to a monotonic increase in the liquid and vapor velocities, whereas the dependence of the meniscus position versus d has an extremum. 

In this case all the heat flows into the rubber. If the heat is produced by friction, part of it will flow into the rubber and the other part into the track surface. Assuming a large heat capacity for both and neglecting heat losses to the sides, the amount of heat flowing into the rubber is given by... 

Generally, the efficiency of steam turbines decreases with decreasing load. The overall turbine efficiency can be represented by two components the isentropic efficiency and the mechanical efficiency. The mechanical efficiency reflects the efficiency with which the energy that is extracted from steam is transformed into useful power and accounts for mechanical frictional losses, heat losses, and so on. The mechanical efficiency is high (typically 0.95 to 0.99)6. However, the mechanical efficiency does not reflect the efficiency with which energy is extracted from steam. This is characterized by the isentropic efficiency introduced in Figure 2.1 and Equation 2.3, defined as ... 

For diabatic flow, that is, one-component flow with subcooled and saturated nucleate boiling, bubbles may exist at the wall of the tube and in the liquid boundary layer. In an investigation of steam-water flow characteristics at high pressures, Kirillov et al. (1978) showed the effects of mass flux and heat flux on the dependence of wave crest amplitude, 8f, on the steam quality, X (Fig. 3.46). The effects of mass and heat fluxes on the relative frictional pressure losses are shown in Figure 3.47. These experimental data agree quite satisfactorily with Tarasova s recommendation (Sec. 3.5.3). 

When a system involves dissipative effects such as friction caused by molecular collisions or turbulence caused by a non-uniform molecular distribution, even under adiabahc conditions, ds becomes a positive value, and then Eqs. (1.13) and (1.14) are no longer valid. However, when these physical effects are very small and heat loss from the system or heat gain by the system are also small, the system is considered to undergo an isentropic change. 

It is insol in w and moderately sol in organic solvents or monomers. Unstable at ordinary room temp and should not be stored at above 70°F (in order to avoid loss of active oxygen) and away from all sources of heat. It should not be subjected to frictional heat or grinding. 

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