Question: Can Effectiveness Of Heat Exchanger Be Greater Than 1?

What is the effectiveness of heat exchanger?

The effectiveness (ϵ) of a heat exchanger is defined as the ratio of the actual heat transfer to the maximum possible heat transfer.

Qmax is the minimum of these two values i.

e.

aRajput, R.K., 2007,Engineering Thermodynamics, Laxmi Publications, New Delhi..

What is the advantage of counter flow system?

The counter-flow heat exchanger has three significant advantages over the parallel flow design. First, the more uniform temperature difference between the two fluids minimizes the thermal stresses throughout the exchanger.

What is capacity ratio of a heat exchanger?

Capacity ratio (C): It is defined as ratio of minimum to maximum capacity rate of fluids being used in a heat exchanger. as cmin = mh cph and cmax = mc cpc. The fluid with lower heat capacity rate will undergo greater change in temperature as compared to fluid with higher heat capacity rate.

How does the effectiveness change as the size of a heat exchanger changes?

With increase of the coil length, the effective heat exchange surface area increases. This leads to a higher heat transfer rate and thus the effectiveness will increase. Furthermore, as the coil diameter increases (while the shell diameter is kept constant), the gap between the coil and the shell decreases.

What is h in heat transfer?

The approximate rate of heat transfer between the bulk of the fluid inside the pipe and the pipe external surface is: where q = heat transfer rate (W) h = convective heat transfer coefficient (W/(m2·K)) t = wall thickness (m) k = wall thermal conductivity (W/m·K) A = area (m2) = difference in temperature.

Under what conditions can a counter flow heat exchanger have an effectiveness of one?

When capacity ratio is equal to one and NTU value is very large then the counter flow heat exchanger will have an effectiveness of one i.e. 100% effectiveness.

How do you calculate the number of heat exchangers on a tube?

The main basic Heat Exchanger equation is:Q = U x A x ΔTm = The log mean temperature difference ΔTm is:ΔTm = (T1 – t2) – (T2 – t1)= °F. Where:T1 = Inlet tube side fluid temperature; t2 = Outlet shell side fluid temperature;ln (T1 – t2) (T2 – t1)

Is a heat exchanger with a very large NTU say 10 necessarily a good one to buy?

For specified values of and , the value of NTU is a measure of the heat transfer surface area . … So large value of NTU in a heat exchanger is not economically justified. Therefore it is not necessarily a good one to buy.

How do you calculate the effectiveness of a heat exchanger?

If one of the fluids is undergoing a change of phase throughout the entire heat exchanger and at a constant temperature (i.e. heat capacity is infinite), the thermal efficiency is simply Eff=1-exp(-U.A/Cmin), where Cmin is the heat capacity (m x cp) for the single phase fluid, U-overall heat transfer coeffcient and A …

Why lmtd is used in heat exchanger?

The log mean temperature difference (LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. … The use of the LMTD arises, straightforwardly, from the analysis of a heat exchanger with constant flow rate and fluid thermal properties.

What is the most effective heat exchanger?

Plate exchanger is the most efficient due to turbulent flow on both sides. High heat-transfer coefficient and high turbulence due to even flow distribution are important. However, a plate heat exchanger regenerator is restricted to low viscosities. With high viscosities, a special tubular may be required.

What is the difference between double pipe and shell and tube heat exchanger?

Double pipe heat exchanger consists of two concentric pipes of different diameters. One pipe is for hot fluid and another is for cold fluid. … Shell and tube heat exchanger consists of a shell in which large number of parallel tubes are present. One fluid hot or cold flow in shell and other hot or cold flow in the tubes.

Under what conditions is the effectiveness NTU method definitely preferred over the lmtd method in heat exchanger analysis?

In heat exchanger analysis, if the fluid inlet and outlet temperatures are specified or can be determined by simple energy balance, the LMTD method can be used; but when these temperatures are not available The NTU or The Effectiveness method is used.

Why is a counter flow heat exchanger better than a parallel flow heat exchanger?

Counter flow heat exchangers are inherently more efficient than parallel flow heat exchangers because they create a more uniform temperature difference between the fluids, over the entire length of the fluid path. … For example, one fluid may make 2 passes, the other 4 passes.

What are the different types of heat exchangers?

What are the different types of heat exchanger?Parallel-flow and counter-flow heat exchanger.Finned and Unfinned tubular heat exchanger.U-tube, single pass straight and two pass straight heat exchanger.Plate-and-frame heat exchanger.Pate-fin heat exchanger.Microchannel heat exchanger.

Why do we use correction factor in heat exchanger?

It is a measure of the heat exchanger’s departure from the ideal behavior of a counter flow heat exchanger having the same terminal temperatures. … Log Mean Temperature Difference Correction Factor F is dependent on temperature effectiveness P and heat capacity rate ratio R for a given flow arrangement.

How do you calculate lmtd in heat exchanger?

by definition given above, LMTD for counter current flow = (60-50) / ln(60/50) = 10 / 0.1823 = 54.850C. For co-current heat exchanger, ΔT1 = TH1 – TC1 = 100 – 30 = 700C (At first end hot and cold fluids enter the heat exchanger.) (At the other end hot and cold fluids exit the heat exchanger.)