Heat exchange characteristics, comparison

These curves provide a comparison of heat transfer rotes for plate heat exchangers and shell and tube equipment. The values given ore typical for pressure drops shown and ore based upon the thermal characteristics of the fluids. 

Weislogel MM, Lichter S (1998) Capillary flow in an interior corner. 1 Eluid Mech 373 349-378 Wu PY, Little WA (1984) Measurement of the heat transfer characteristics of gas flow a fine channels heat exchangers used for microminiature refrigerators. Cryogenics 24 415 20 Xu X, Carey VP (1990) Film evaporation from a micro-grooved surface an approximate heat transfer model and its comparison with experimental data. J Thermophys 4(4) 512-520 Yarin LP, Ekelchik LA, Hetsroni G (2002) Two-phase laminar flow in a heated micro-channels. Int J Multiphase Flow 28 1589-1616... 

The important characteristic for HHM efficiency is the alloy output, i.e. the heat capacity related to weight of hydride alloy. The value achieved for today on the average for a cycle makes 40-100 W/kg. At shortening of a cycle this value grows, but up to achievement of competitive (in comparison with other heat machines of similar type) value in 1000 W/kg [8] are necessary for increasing cardinally amount of active hydrogen, to increase effective heat conductivity of a hydride bed and to optimize operation of system a sorber-heat exchanger. Thus duration of a hill cycle is estimated 2-4 minutes. 

A comparison of the physical and mechanical properties of the two alloys is given in Table 8.17. Of particular interest for heat exchangers and condensers are the thermal conductivity and expansion characteristics. Although conductivity values for both are good, the 90-10 alloy has the higher value. This partly explains the alloy s greater pop-... 

Figure 4.12 Power (V/ ) and efficiency (Titot) characteristics of a counter-current exchanger TEG system. For comparison, the intrinsic TE efficiency (t te) without heat recirculation is reported.

Three general flow regimes may be anticipated for the flow over a flat plate shown in Fig. 12 12. First, the continuum flow region is encountered when the mean free path A is very small in comparison with a characteristic body dimension. This is the convection heat-transfer situation analyzed in preceding chapters. At lo wer gas pressures, when A L, the flow seems to slip along the surface and u 4= 0 at y = 0. This situation is appropriately called slip flow. At still lower densities, all momentum and energy exchange is the result of... 

It is unfortunate that in the published catalytic studies with heat-treated NH4-exchanged Y the catalyst substrate seems to be insufficiently characterized, and the assignment of structural details, which are most important for catalytic properties, are based on assumptions, usually drawn from comparisons with similar zeolite samples. Furthermore, the catalytic properties of zeolites which are more fully characterized usually are not reported in the literature. Consequently, comparison between catalysts prepared by different investigators is very difficult and risky since the catalytically important details depend on several chemical and structural characteristics, all of which usually are not described. As an example of this problem, the dehydroxylation of heat-treated NH4" -exchanged Y depends on the temperature, atmosphere, and time employed on activation, as well as on the Si/Al ratio, the degree of NH4" exchange 16), and the residual cations 108). 

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