4.0 – HEAT EXCHANGERS CALCULATIONS:

If you’re asking about the effect of mixing or not mixing a fluid as the fluid is passing through the heat exchanger, I believe that the reason mixing provides better performance is because a mixed fluid will transfer thermal energy, or really just the kinetic energy of the molecules at the exchanger surface, to the …

Tube Fin Heat Exchangers, also called finned coil heat exchangers, consist of tubes that pass through a dense fin stack that is mechanically supported by a mounting frame. Fluid passes through the tube coils, conducts heat to the fins and dissipates heat to air forced through the heat exchanger.

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

What is the difference between mixed and unmixed fluids in cross-flow? In a counter flow heat exchanger, the hot and cold fluids enter the heat exchanger at opposite ends and flow in opposite direction. But in case of cross flow heat exchanger, the two fluids usually move perpendicular to each other.

In (a) the cross-flow is said to be unmixed since the plate fins force the fluid to flow through a particular inter fin spacing and prevent it from moving in the transverse direction (i.e., parallel to the tubes). The cross-flow in (b) is said to be mixed since the fluid now is free to move in the transverse direction.

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.

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.

Each of the three types of heat exchangers (Parallel, Cross and Counter Flow) has advantages and disadvantages. But of the three, the counter flow heat exchanger design is the most efficient when comparing heat transfer rate per unit surface area.

One is termed a cocurrent heat exchanger, while the other is termed a countercurrent heat exchanger. In the cocurrent mode, both the hot and cold streams enter the heat exchanger at one end, and leave at the opposite end. In the countercurrent mode, the streams enter at opposite ends of the 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.

Counter Flow Heat Exchanger The diagram above shows a Shell and Tube Heat Exchanger. In the counter flow setup, the fluids are travelling along the heat exchanger in opposite directions. This distributes the heat more evenly across the heat exchanger and allows for maximum efficiency.

Heat exchangers can be designed both for heating and for cooling. While in heat exchangers a service fluid heats a process fluid without both having direct contact with each other, in electric heaters only the fluid to be heated is in the process.

Main Criteria for Heat Exchanger Sizing and Selection For a gasketed plate heat exchanger, the gaskets must be compatible with the fluids in the unit. Thermal fluid characteristics and product mix. If the heating or cooling fluid is susceptible to fouling, a corrosion resistant material may be needed. Location.

Here are 5 proven industry practices to boost heat exchanger performance and maintain process efficiency:

1. Online and Offline Cleaning.
2. Maintaining Heat Exchanger.
3. Periodic Cleaning.
4. Cleaning the PHE Manually.
5. Minimizing the Fouling Factor.
6. Analyzing and Addressing Issues in Heat Exchanger Efficiency.

A crossflow heat exchanger is designed so that the two fluids flow perpendicular to one another. This is typically utilized when one fluid is a liquid and the other is a gas, as in a car radiator in which hot water flowing left and right is cooled by air moving up or down, Bright Hub Engineering explained.

6. Which of the following is not an example of recuperators type heat exchanger? Explanation: Recuperators are not used in chemical factories. 7.

Flow arrangements There are three main types of flows in a spiral heat exchanger: Counter-current Flow: Fluids flow in opposite directions. These are used for liquid-liquid, condensing and gas cooling applications.

Cross flow filtration is when the flow is applied tangentially across the membrane surface. As feed flows across the membrane surface, filtrate passes through while concentrate accumulates at the opposite end of the membrane.

Cross flow filtration – a filtration process in which feed water flows tangentially across a membrane surface – is widely utilized in wastewater filtration. Cross filtration works by introducing feed water under pressure across the membrane surface, instead of directly onto the filter.

In technical applications crossflow microfiltration is an established process for the separation of microparticles, bacteria and emulsion droplet. The following article describes the development and the state of the art.

A crossflow turbine is designed using a large cylindrical mechanism composed of a central rotor surrounded by a “cage” of blades arranged into a water wheel shape. Water is directed onto the turbine through a nozzle that creates a flat sheet of water, and then is directed onto the blades using a guide vane.

The operation of a Pelton turbine is fairly simple. In this type of turbine, high speed jets of water emerge from the nozzles that surround the turbine. These nozzles are arranged so the water jet will hit the buckets at splitters, the center of the bucket where the water jet is divided into two streams.

The bulb turbine is a reaction turbine of Kaplan type which is used for extremely low heads. The runner of a bulb turbine may have different numbers of blades depending on the head and water flow. The bulb turbines have higher full-load efficiency and higher flow capacity as compared to Kaplan turbine.

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Power is recovered from both the hydrostatic head and from the kinetic energy of the flowing water.

Explanation: Based on heads and discharges, turbines are classified into Pelton, Francis or Kaplan. Pelton has high head and low discharge. Explanation: Based on heads and discharges, turbines are classified into Pelton, Francis or Kaplan. Kaplan has low head and high discharge.

Efficiency of Kaplan turbine is higher than Francis turbine. Kaplan turbine is more compact in cross-section and has lower rotational speed to that of Francis turbine. In Kaplan turbine, the water flows axially in and axially out while in Francis turbine it is radially in and axially out.

Kaplan turbines could technically work across a wide range of heads and flow rates, but because of other turbine types being more effective on higher heads, and because Kaplan’s are relative expensive, they are the turbine of choice for lower head sites with high flow rates.

Pelton wheel is used where a high head is available because as I said in the first point static pressure head of water is used in the Pelton wheel. Francis turbine is a mixed flow type reaction turbine where both static and dynamic pressure head of water is used. So it is used where the medium head is available.