Search results
Results from the WOW.Com Content Network
Precipitation fouling is a very common problem in boilers and heat exchangers operating with hard water and often results in limescale. Through changes in temperature, or solvent evaporation or degasification , the concentration of salts may exceed the saturation , leading to a precipitation of solids (usually crystals).
The number of transfer units (NTU) method is used to calculate the rate of heat transfer in heat exchangers (especially parallel flow, counter current, and cross-flow exchangers) when there is insufficient information to calculate the log mean temperature difference (LMTD).
Fluid flow simulation for a shell-and-tube style exchanger; The shell inlet is at the top rear and outlet in the foreground at the bottom Shell and tube heat exchanger. A shell-and-tube heat exchanger is a class of heat exchanger designs. [1] [2] It is the most common type of heat exchanger in oil refineries and other large chemical processes ...
Assume heat transfer [2] is occurring in a heat exchanger along an axis z, from generic coordinate A to B, between two fluids, identified as 1 and 2, whose temperatures along z are T 1 (z) and T 2 (z). The local exchanged heat flux at z is proportional to the temperature difference:
Temperature vs. heat load diagram of hot stream (H 2 O entering at 20 bar, 473.15 K, and 4 kg/s) and cold stream (R-11 entering at 18 bar, 303.15 K, and 5 kg/s) in a counter-flow heat exchanger. "Pinch" is the point of closest approach between the hot and cold streams in the T vs. H diagram.
Because heat exchangers can be configured many different ways, TEMA has standardized the nomenclature of exchanger types. [13] A letter designation is used for the front head type, shell type, and rear head type of an exchanger. For example, a fixed tubesheet exchanger with bolted removable bonnets is designated as a 'BEM' type.
For the same amount of heat exchanged, the size of the plate heat exchanger is smaller, because of the large heat transfer area afforded by the plates (the large area through which heat can travel). Increase and reduction of the heat transfer area is simple in a plate heat-exchanger, through the addition or removal of plates from the stack.
An alternative to the earth-to-air heat exchanger is the "water" to earth heat exchanger. This is typically similar to a geothermal heat pump tubing embedded horizontally in the soil (or could be a vertical sonde) to a similar depth of the earth-air heat exchanger. It uses approximately double the length of pipe of 35 mm diameter, e.g., around ...