Heat exchangers are widely used in industry both for cooling and heating large-scale industrial processes. The type and size of heat exchanger used can be tailored to suit a process depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical composition and various other thermodynamic properties. Finnfoam Texas City Texas
In many industrial processes there is a waste of energy or a heat stream that is being exhausted, heat exchangers can be used to recover this heat and put it to use by heating a different stream in the process. This practice saves a lot of money in the industry, as the heat supplied to other streams from the heat exchangers would otherwise come from an external source that is more expensive and more harmful to the environment.
Heat exchangers are used in many industries, including:
In wastewater treatment, heat exchangers play a vital role in maintaining optimal temperatures within anaerobic digesters to promote the growth of microbes that remove pollutants. Common types of heat exchangers used in this application are the double pipe heat exchanger as well as the plate and frame heat exchanger. Finnfoam Texas City Texas
In aircraft Finn foam Texas City Texas
In commercial aircraft heat exchangers are used to take heat from the engine’s oil system to heat cold fuel. This improves fuel efficiency, as well as reduces the possibility of water entrapped in the fuel freezing in components. Finn foam Texas City Texas
Current market and forecast Finn foam Texas City Texas
Estimated at US$42.7 billion in 2012, the global demand of heat exchangers will experience robust growth of about 7.8% annually over the next years. The market value expected to reach US$57.9 billion by 2016 and to approach US$78.16 billion by 2020. Tubular heat exchangers and plate heat exchangers still the most widely applied product types. Finnfoam Texas City Texas
A model of a simple heat exchanger Finn foam Texas City Texas
A simple heat exchange might thought of as two straight pipes with fluid flow, which thermally connected. Let the pipes of equal length L, carrying fluids with heat capacity (energy per unit mass per unit change in temperature) and let the mass flow rate of the fluids through the pipes, both in the same direction, (mass per unit time), where the subscript applies to pipe 1 or pipe 2. Finn foam Texas City Texas
Temperature profiles for the pipes are and where x is the distance along the pipe. Assume a steady state, so that the temperature profiles are not functions of time. Assume also that the only transfer of heat from a small volume of fluid in one pipe is to the fluid element in the other pipe at the same position, i.e., there is no transfer of heat along a pipe due to temperature differences in that pipe. By Newton’s law of cooling the rate of change in energy of a small volume of fluid is proportional to the difference in temperatures between it and the corresponding element in the other pipe:
( this is for parallel flow in the same direction and opposite temperature gradients, but for counter-flow heat exchange countercurrent exchange the sign is Finn foam Texas City Texas opposite in the second equation in front of ) Finnfoam Texas City Texas
, where the thermal energy per unit length and γ is the thermal connection constant per unit length between the two pipes. This change in internal energy results in a change in the temperature of the fluid element. The time rate of change for the fluid element being carried along by the flow is: Finn foam Texas City Texas
where is the “thermal mass flow rate”. The differential equations governing the heat exchanger may now be written as: Finnfoam Texas City Texas
Note that, since the system is in a steady state, there are no partial derivatives of temperature with respect to time, and since there is no heat transfer along the pipe, there are no second derivatives in x as is found in the heat equation. These two coupled first-order differential equations may be solved to yield:
where , ,
(this is for parallel-flow, but for counter-flow the sign in front of is negative, so that if , for the same “thermal mass flow rate” in both opposite directions, the gradient of temperature is constant and the temperatures linear in position x with a constant difference along the exchanger, explaining why the countercurrent design countercurrent exchange is the most efficient ) Finnfoam Texas City Texas
and A and B are two as yet undetermined constants of integration. Let and be the temperatures at x=0 and let and be the temperatures at the end of the pipe at x=L. Define the average temperatures in each pipe as:
Using the solutions above, these temperatures are:Choosing any two of the temperatures above eliminates the constants of integration, letting us find the other four temperatures. We find the total energy transferred by integrating the expressions for the time rate of change of internal energy per unit length:
By the conservation of energy, the sum of the two energies zero. The Finn foam Texas City Texas quantity known as the Log mean temperature difference, and a measure of the effectiveness of the heat exchanger in transferring heat energy. Finnfoam Texas City Texas
Construction. Finn foam Texas City Texas
This ensures no mixing of the two fluids occurs. Any leakage is from the periphery cover to the atmosphere, or to a passage that contains the same fluid. . Finn foam Texas City Texas
Self-cleaning [. Finn foam Texas City Texas
Spiral heat exchangers are often used in the heating of fluids that contain solids and thus tend to foul the inside of the heat exchanger. The low-pressure droplets the SHE handle fouling more easily. The SHE uses a “self-cleaning” mechanism, whereby fouled surfaces cause a localized increase in fluid velocity, thus increasing the drag (or fluid friction) on the fouled surface, thus helping to dislodge the blockage and keep the heat exchanger clean. “The internal walls that make up the heat transfer surface often rather thick, which makes the SHE very robust, and able to last a long time in demanding environments.” They also easily cleaned, opening out like an oven where any buildup of foulant can removed by pressure washing. . Finn foam Texas City Texas
Self-cleaning water filters used to keep the system clean and running without the need to shut down or replace cartridges and bags. . Finnfoam Texas City Texas
Flow arrangements. Finn foam Texas City Texas
A comparison between the operations and effects of a concurrent and a countercurrent flow exchange system is depicted by the upper and lower diagrams respectively. In both it is assumed (and indicated) that red has a higher value (e.g. of temperature) than blue and that the property being transported in the channels therefore flows from red to blue. Note that channels are contiguous if the effective exchange is to occur (i.e. there can be no gap between the channels). . Finnfoam Texas City Texas
There are three main types of flows in a spiral heat exchanger:
Counter-current Flow: Fluids flow in opposite directions. These used for liquid-liquid, condensing and gas cooling applications. Units usually mounted vertically when condensing vapor and mounted horizontally when handling high concentrations of solids. . Finn foam Texas City Texas
Spiral Flow/Cross Flow: One fluid in spiral flow and the other in a cross flow. Spiral flow passages are welded at each side for this type of spiral heat exchanger. This type of flow suitable for handling low-density gas, which passes through the cross flow, avoiding pressure loss. It can used for liquid-liquid applications if one liquid has a considerably greater flow rate than the other. . Finn foam Texas City Texas
Distributed Vapour/Spiral flow: This design that of a condenser, andis usually mounted vertically. It designed to cater for the sub-cooling of both condensate and non-condensable. The coolant moves in a spiral and leaves via the top. Hot gases that enter leave as condensate via the bottom outlet. .Finnfoam Texas City Texas
Applications. Finn foam Texas City Texas
The Spiral heat exchanger is good for applications such as pasteurization, digester heating, heat recovery, pre-heating (see: recuperator), and effluent cooling. For sludge treatment, SHEs are generally smaller than other types of heat exchangers. These used to transfer the heat.
Selection. Finn foam Texas City Texas
Due to the many variables involved, selecting optimal heat exchangers is challenging. Hand calculations possible, but many iterations typically needed. As such, heat exchangers most often selected via computer programs, either by system designers, who typically engineers, or by equipment vendors. . Finnfoam Texas City Texas
To select an appropriate heat exchanger, the system designers (or equipment vendors) would first consider the design limitations for each heat exchanger type. Though cost is often the primary criterion, several other selection criteria are important:
High/ low-pressure limits. Finn foam Texas City Texas
Thermal performance. Finn foam Texas City Texas
Temperature ranges. Finn foam Texas City Texas
Product mix (liquid/liquid, particulates or high-solids liquid). Finn foam Texas City Texas
Pressure drops across the exchanger
Fluid flow capacity
Cleanability, maintenance and repair.Finnfoam Texas City Texas
Materials required for construction. Finn foam Texas City Texas
Ability and ease of future expansion.Finnfoam Texas City Texas
Material selection, such as copper, aluminum, carbon steel, stainless steel, nickel alloys, ceramic, polymer, and titanium. . Finn foam Texas City Texas
Small-diameter coil technologies are becoming more popular in modern air conditioning and refrigeration systems because they have better rates of heat transfer than a conventionally sized condenser and evaporator coils with round copper tubes and aluminum or copper fin that have been the standard in the HVAC industry. Small diameter coils can withstand the higher pressures required by the new generation of environmentally friendlier refrigerants. Two small diameter coil technologies are currently available for air conditioning and refrigeration products: copper microgroove and brazed aluminum microchannel. . Finnfoam Texas City Texas
Choosing the right heat exchanger (HX) requires some knowledge of the different heat exchanger types, as well as the environment where the unit must operate. Typically in the manufacturing industry, several different types of heat exchangers used for just one processor system to derive the final product. For example, a kettle HX for pre-heating, a double pipe HX for the ‘carrier’ fluid and a plate and frame HX for final cooling. With sufficient knowledge of heat exchanger types and operating requirements, an appropriate selection can made to optimise the process. . Finn foam Texas City Texas. Finn foam Texas City Texas
Nueva Orleans• Baton Rouge• Shreveport• Lafayette• Lake Charles• Kenner• Bossier City• Monroe• Alexandria• Houma• Nueva Iberia• Slidell• Ruston• Sulphur• Hammond• Natchitoches• Gretna• Chalmette• Opelousas• Zachary• Thibodaux• Pineville• Baker• Crowley• Minden• West Monroe• Morgan City• Abbeville• Bogalusa• Mandeville• Bastrop• DeRidder• Eunice• Jennings• Denham Springs• Gonzales• Harahan • Houston• San Antonio• Dallas• Austin• Fort Worth• El Paso• Arlington• Corpus Christi• Plano• Laredo• Lubbock• Garland• Irving• Amarillo• Grand Prairie• Brownsville• Pasadena• Mesquite• McKinney• McAllen• Killeen• Waco• Carrollton• Beaumont• Abilene• Frisco• Denton• Midland• Wichita Falls• Odessa• Round Rock• Richardson• Tyler• Lewisville• College Station• San Angelo• Pearland• Texas City Texas