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Before equation (eq – 1.7) can be used to determine the heat transfer area required for a given duty, an estimate of the mean temperature difference Δtm must be made. This will normally be calculated from the terminal temperature differences: the difference in the fluid temperatures at the inlet and […]

Estimation of the “true temperature difference” from the logarithmic mean temperature difference by applying a correction factor to allow for the departure from true counter-current flow: ΔT m = Ft ΔT tm                          (eq – 1.10) Where ΔT m = true temperature difference, the mean temperature difference for use in the […]

A general expression for U can be easily obtained as follows. Consider a double pipe heat exchanger in which one fluid through the inner pipe and the other fluid through the annular space between space between the two pipes. Let       L          = length of heat exchanger, m ri          = inside […]

An important parameter in the design and monitoring of heat exchangers is the overall heat transfer coefficient, U, between the two fluids. A value for U can be easily obtained by knowing the followings: Mass flow of the fluid, Specific heat of the fluid, Difference in temperature of the fluid […]

In most heat exchangers some scale formation will take place on both sides of the heat transfer surface after the heat exchanger has been in use for some time (unless scale inhibition mechanism is in place). This introduces two additional resistances in the heat flow path. Thus the total thermal […]

Steam is frequently used as heating medium. The mean temperature difference is given here:  A pure, saturated, vapour will condense at a fixed temperature, at constant pressure. For an isothermal process such as this, the simple LMTD can be used in equation 1.3; no correction factor for multiple passes is […]

In some type of heat exchanger, the temperature of both the fluids is varying and there fore logarithmic mean temperature will have to be calculated. The temperature changes of water and hot fluid may be represented graphically by the following figure. During the process the hot fluid will reject heat […]

The cold and hot fluid inlet and outlet temperature and ΔP of the fluids across the heat exchangers are very significant in determination of the health of that heat exchanger. In condensers ΔP is shown as vacuum. Any increase in ΔP or decrease in vacuum is an indication of fouling […]

Flow-rates and any change in flow-rates have different effects on Q and U values. Following are the effects: Changes Effects If hot fluid flow rate is increased     The ΔP of hot fluid across the heat exchanger will increase. The inlet P of hot fluid will increase The ΔT of hot […]

It is desirable to get a rated load or some agreed-upon load on the turbine which will be the same for each successive check and read the load, air leakage, inlet water temperature, outlet water temperature and the absolute pressure in the condenser, and convert the absolute pressure into the […]