Heat-exchanger efficiency

Heat exchanger efficiency, dimensionless. = Mass flow rate (tube or cold side), Ib/hr. = Mass flow rate (shell or hot side), Ib/hr. 

Figure 2.32 Heat exchanger efficiency as a function of the thermal conductivity of the wall, taken from 125. ...

The heat exchanger efficiency s is the heat transferred from one stream to the other compared with the maximum heat available. 

The temperature gap (AT) between the two flows is chosen as the controlling parameter it determines both the enthalpy feed and the Carnot efficiency of the thermoelectric element. The value of AT is related to the heat exchanger efficiency Tiexc or e-NTU (normal thermal unit), the ratio of the heat exchanged to the total exchangeable heat. This relationship comes from the definition of e-NTU for the exchanger efficiency and, in this specific case, it has the following form [16] ... 

F Heat exchanger efficiency factor Dimensionless Tf Incremental federal income %... 

Smoke (carbon) formation, which apparently is due to incomplete combustion of portions of the fuel-air mixture (i.e., rich combustion), also can pose a serious public relations problem at civilian airports and, by radiant-heat transfer from incandescent carbon particles, can shorten the endurance life of combustion-chamber liners and adjacent parts (0). Smoke would also constitute a serious problem in the case of automotive gas turbines, because accumulation of carbon and other nonvolatile fuel components on the intricate passages of the heat exchanger could reduce turbine and heat-exchanger efficiency by reducing heat-transfer rate and increasing the pressure drop across the... 

At Pd loadings of > 5 wt.%, 80-90% hydrogen conversion was found for a synthetic anode effluent containing 6.7% hydrogen and 3.35% oxygen. The heat exchanging efficiency of the bench-scale evaporator increased linearly with the aspect ratio of the vapor channels and reached 92% at an aspect ratio of 18. 

Another area to consider is heat exchanger efficiency. The concept of efficiency is to compare the actual performance of a piece of equipment with the ideal performance (i.e., the maximum potential heat transfer). The maximum heat transfer possible is established by the stream that has the minimum heat capacity. That is the minimum value for the product of stream mass flowrate and specific heat. This stream would, for maximum heat transfer, leave the exchanger at the inlet temperature of the other stream. In terms of the hot stream, the efficiency can be stated as ... 

These furnaces are good candidates for full oxy/fuel. Recuperative heat exchanger efficiencies are much lower than with regenerative furnaces, and therefore fuel savings can help to drive the conversion. Also, recuperative furnaces operate in a continuous and steady firing mode of operation similar to oxy/fuel furnaces. 

Crittenden, B.D., 1984, Chemical reaction fouling in fouling and heat exchanger efficiency. Inst. Chem. Engrs. Course, University of Leeds, 78. 

Veale, M.A., 1984, Control of deposits in cooling water systems, in Fouling and Heat Exchanger Efficiency. Continuing Education Course. Instn. Chem. Engrs., University of Leeds. 

Hydrogen is an ideal fuel for gas turbines. Due to its rapid mixing with air, a smaller combustion chamber is sufficient and the efficiency is higher compared with conventional fuels. Gas turbines modified for liquid hydrogen operation yield an up to 10 % higher thermal efficiency and output compared with fossil-fueled turbines. For systems with advanced heat exchange, efficiencies of more than 50 % are estimated to be achievable. The remainder-free combustion is stable and favorable for lifetime and maintenance. Of disadvantage is NOX production. No particular difficulties are expected for a conversion of a stationary gas turbine to H2 fuel [51]. 

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