Brazed plate heat exchangers, copper or nickel?

14/06/2019

Brazed plate exchangers are a particular kind of plate heat exchangers that can be employed in applications with high pressures and a wider range of temperatures. This is due to the peculiar manufacturing process involved, that gives brazed plate heat exchangers a high mechanical resistance: plates in this kind of exchangers are made of cold-pressed stainless steel, and during the assembly of the heat exchanger the plates are piled in top one of each other with cold-pressed foils of copper or nickel between them.

The plate heat exchangers is then placed in a vacuum furnace where, at high melting temperatures respectively for the copper or nickel, the two metals melt, flowing for capillarity in the contact points welding them. All the brazed plate exchangers are checked with hydraulic pressure test, ensuring there are no pressure drops and to eliminate the defective ones.

When is better to choose copper vs. nickel? The selection must consider two factors, the need to work with corrosive fluids and the pressure level involved in the application. Copper is indeed an excellent material, but it is not compatible with steam containing amine and ammonia, being corrosive on the metal and leading in a short time to leaks and pressure drops.

A copper brazed plate exchanger on the contrary can stand pressures up to 30 bar and more, while a nickel brazed exchanger offer lower working pressure limits, 15 bar for a standard version and up to 25 bar for special versions. On the other hand, nickel is corrosion resistant to aggressive fluids that can cause corrosion to copper.

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Dimple jacket exchangers in a seaport

07/06/2019

We have developed last year an application for the dissipation of the heat produced by heat pumps, using TCOIL dimple jacket exchangers immersed in the Lake of Como. After less than a year, we are working on a new similar application that is now transferring us from the lake environment to the sea.

The solution employing TCOIL dimple jacket heat exchangers is indeed perfectly suitable for another customer, who requires the cooling/heating of water serving heat pumps in a seaport in the Italian Liguria region, using the presence of sea water. The customer at the present employs traditional plate heat exchangers, that due to the presence of sand and an inefficient filtration system used to get often clogged, leading to conditioning/heating problems of the connected equipments.

The solution developed and designed by Tempco consists in two batteries of TCOIL exchangers immersed in the waters of the seaport, manufactured using chloride resistant materials, I.e. SAF 2507 (duplex), avoiding corrosion issues with the dimple jacket exchangers operating in continuous contact with the sea water.

The installation is planned for July 2019, just in time to the start of the summer season. On a second step, we will also supply the customer further additional heat exchangers, for the revamping and energy consumption optimization of the plants.

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Fouling factor in heat exchangers

31/05/2019

More about heat exchangers, and in particular let’s face the topic of fouling factor in heat exchangers. This is a relevant topic in order to ensure the proper thermal transfer efficiency in exchangers, as I’m often asked about it. Fluids flowing inside heat exchangers can indeed contain particles that lay down in sediments in the long term, sticking on heat transfer surfaces and lowering the exchanger’s thermal efficiency.

The fouling factor is a sizing up coefficient to be applied while engineering a heat exchanger. In fact, a higher margin must be accounted in the sizing of a heat exchanger, counteracting the fouling on heat transfer surfaces due to the settling of fouling particles.

The evaluation of the coefficient relies on the kind of flowing movements involved in the heat exchangers, impacting the quantity of particles that can buildup on thermal transfer surfaces. The fouling factor then varies depending on the kind of heat exchanger, being different for a shell & tube exchanger or a plate heat exchanger. The effective fouling factor values for a plate heat exchanger are ten times lower than the ones applicable to shell & tube heat exchangers, because fluids in a plate heat exchanger have a much more turbulent flow.

A turbulent flow of the fluid within plate heat exchangers allows to drag the particles that have the potential to settle on heat transfer surfaces, thus requiring a lower oversizing coefficient of the exchanger. Another reason is represented by the construction of the kind of heat exchanger itself: a shell & tube exchanger, once it’s manufactured, cannot be expanded, while a plate heat exchanger allows to vary and increase the number of plates, boosting its thermal transfer efficiency in case of fouling fluids or different operating conditions compared to design parameters.

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Heat recovery in food delivery

24/05/2019

Increase the standard of food delivery to taste the food fragrant as it comes out of the restaurant, employing an oven that recovers the waste heat from the engine of a scooter using a heat exchanger. That’s the really smart idea of the Italian start-up Hotbox, developed upon the know-how of a team of aerospace and industrial automation engineers, including the founder and ceo Anthony Byron Prada. The Hotbox start-up realized a heat recovery solution for food delivery that allows to keep the food warm and crunchy, with the catchy slogan ‘Taste the food, not the journey’.

Hotbox consists in a robust structure housing a heat exchanger, an air recirculating system and a de-humidifier, and it allows to keep the food warm at a temperature of 85° C, and crunchy thanks to the removal of the humidity, for over 40 minutes.

The solution employs the HotAir and SteamFree technology, removing the excess of humidity that gathers during the delivery, keeping the food warm and dry as if it was just coming out of the kitchen. The solution is ideal for restaurants and the many food delivery companies that are growing everywhere in the world, such as lobo, Deliveroo, Just Eat and Uber Eats.

The technology that leverages the waste heat of the engine in scooters is already compatible with three cargo scooter models among the most employed on the market (Kymco Agility Carry 50/125, Peugeot Tweet Pro 125, Sym Symphony Cargo 125), and it will be soon adapted to many other vehicles.

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Functioning of a chiller

17/05/2019

We’ve already talked about heat pumps in a video in our Tempco Youtube channel, maybe skipping a step. That’s why I’m dedicating a new tutorial to the functioning of a chiller (english subtitles available), responding to many requests I’ve received.

Let’s start saying that we all have a chiller in our own homes: a refrigerator is indeed a chiller, working on the same physical principles. The explanation of the thermal cycle of a chiller can be commonly found in many sources on the web, involving cycles of compression, expansion, evaporation and condensation. I wanted better to underline an essential concept, being the fact that a chiller is not a ‘cold maker’, but it simply removes heat, using a refrigerant gas, or freon, as fluid thermal vector.

The refrigerant enters the environment to be cooled through a compressor, and passing through an evaporator, that is a heat exchanger, the gas evaporates. To achieve the status change from liquid to vapor, the gas absorbs thermal energy, heating up, cooling down as a consequence the environment’s temperature.

The gas reaches then the external condenser, another heat exchanger, where it cools down condensing and returning to a liquid state, dissipating the heat into the external ambient. The complete thermal cycle is then accomplished as a simple heat transfer cycle, from an environment to be cooled toward an outdoor space.

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Thermoregulation in recovery and refining of precious metals

10/05/2019

The treatment of precious metals is a very interesting and challenging field for thermoregulation applications. Recently, we’ve supplied a couple of thermoregulating units expressly developed for a customer specialized in the recovery and refining of precious metals. These last two thermoregulating units supplied joined the approx. 12 machines installed at the customer’s facility through the years, working on reactors employed in the refining process of precious metals.

The two new thermoregulating units are the result of the longtime experience of the previous installments and of the co-engineering with the customer, that requires in its production process very extreme and reliable equipments, ensuring continuous operations with pressurized water at the constant temperature of 135° C.

This peculiar need required the implementation of specific components, such as a Grundfos pump with special liquid-cooled seal. The thermoregulating units work with brazed plate heat exchangers in impact version for high pulsating pressures, specifically engineered for employ with steam and pressurized water. Modulating control valves and on/off pneumatic valves have also been installed, equipped with metallic actuators in order to stand extreme thermal stresses.

The units finally have a flowmeter monitoring the flow rate, a crucial factor to ensure the thermal exchange efficiency in the reactors. Pipings are all made of stainless steel, with flanged connections (and welded wherever they’re not flanged) and spyrometallic gaskets resistant to high temperatures.

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Fluid’s mixing in plate heat exchangers

03/05/2019

Many times I’m asked if fluids can mix in a plate heat exchanger. As I’m explaining in the new video tutorial on our Tempco YouTube channel (please turns on English subtitles), the only way it can happen is when a plate break occurs, due to corrosion of the plates’ material or cracking.

Further cases are avoided by the intelligent design of the gaskets in a heat exchanger. Fluids cannot mix indeed due to the break of a gasket, because gaskets in plate heat exchangers always offer a double protection.

Gaskets of a plate heat exchanger offer protection all along the perimeter of a plate and also in the nozzle area, where the liquid flows from a plate to another. Here, there is a double gasket, and in addition it offers a sort of drain toward the outside, so that in case one part of the gasket breaks there will be a leakage of liquid on the external side of the heat exchanger, alerting that something’s wrong is happening. Is then sufficient to stop the exchanger from operating and extract the two plates where the drop was detected, then close again the exchanger and re-starting the plant.

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Thermoregulation for electric vehicles test benches

26/04/2019

Electrification in the automotive industry is preparing a huge revolution in the mobility sector. The switch from the combustion engine to the new electric powertrain will bring several main transformations, leading to the request of new thermoregulation and cooling systems for test bench for electric engines to come.

2018 Chevrolet Bolt EV

Although a mass adoption of electric vehicles is still a far scenario – experts are expecting it to become a mass phenomenon in 10, maybe 20 years -, electric vehicles are already a reality on the market. There are still many aspects to be improved, such as the excessive weight of the battery pack and the insufficient recharge infrastructure, not developed enough to satisfy the power need of a large quantity of electric cars. In addition, if we try to imagine a future when everyone is plugging his electric car by night to the recharging station in his own home garage, there will be a serious problem to manage the high peak power demand. Here, IoT, connected cars and artificial intelligence will be strategic to develop new smart systems for the electrical grid management.

In addition, the rate of energy coming from renewable sources is still so poor, amounting to 17,1% in Italy of total power generation. The target of a sustainable mobility and decarbonization would be unattended if the energy employed to satisfy the demand of a mass fleet of electric cars comes from traditional and not renewable power sources.

Many leading automotive manufacturers in the meanwhile have already announced that they won’t be producing endothermic vehicles anymore within the next 5-10 years, and within the next 2-3 years every automotive manufacturer is planning to have electric car models for each of its offering segments. Thermoregulation and cooling applications for automotive test bench is an important application field also for Tempco, so that the transition toward a new electric powertrain will involve the development of new concepts of innovative test bench for electric engines, as it’s actually already happening.

Finally, the value chain of the battery pack industry is worth a mention. This industry involves a series of steps: European enterprises have the know-how to cover the production phase going from the battery pack to the control system, while there is a dangerous gap in skills and know-how on the first step, involving the processing of the activated mineral for the realization of cathode and anode and the production of electrodes and cells. This industrial sector is actually dominated by LG, Samsung and Sony, and by a few others eastern-Asia area manufacturers. On this purpose, Europe already launched some pilot projects, and a first call for interest was also launched in Italy, and ended last February, inviting all the potential suppliers to submit their interest to take part in the industrial value chain of electric cars.

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Piping connections in plate heat exchangers

19/04/2019

A frequently asked question from our customers in Tempco is referred to the possibility of swapping the connections of pipings in plate heat exchangers. That’s the topic I’m discussing in the new tutorial on our Tempco Youtube channel (please turn on english subtitles). In the majority of cases, the answer is Yes, it is possible, but there are also some exceptions so that is always better to ask for it in advance.

The request regards usually the possibility of reversing the direction of the flows, or to swap connections between the primary and secondary circuit. Plate heat exchangers generally have symmetrical hydraulic circuits, so that’s why it is usually possible to reverse the directions of the flows, that typically travel in countercurrent within the exchanger, and also to invert the connections between primary and secondary circuit. In both cases, the thermal transfer efficiency of the heat exchanger is not affected in a sensible way.

Anyway, is always better to ask in advance, because there are some applications with circuits that are not symmetrical, or with draining requirements. This is the case of steam, which must always enters the heat exchanger from above, so that condensation can go to the bottom in order to be completely drained from the exchanger. When using steam, it is then possible to swap primary and secondary circuit, but the direction of the flows cannot be reversed.

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Fibreglass in cooling towers

10/04/2019

The selection of technical solutions and the choice of materials in the construction of Cooling towers are guided by several factors, and principally according to the kind of water with which the plant is gonna operate. In addition to steel, another frequent choice is the fibreglass, offering a series of advantages that are clearly explained in this article.

Despite of a higher cost, due for example to the investments required in manufacturing equipments and dedicated moulds, fibreglass is the preferred choice of many manufacturers of open and closed circuit cooling towers for the realization of both components and structural profiles. The main quality of fibreglass is certainly the fact that, in constant presence of water, it does not oxides and is corrosion resistant, a main problem with chemically aggressive water, it is not affected by weather conditions and is therefore maintenance-free. Fibreglass in addition is lightweight compared to steel and metal sheets, and can be simply repaired in case of accidents returning to as new conditions.

The construction technique of the moulded components employs successive layering of glass fabric, called ‘mat’, which is then soaked in resin. Following the catalyzation, the resin and the mat layers are fused into one body, giving structural robustness and a uniform surface. A special orientation of the glass fibres can be engineered in order to better withstand and distribute static and dynamic loads.

Structural profiles are manufactured using a pultrusion (pull+extrusion) process with a dedicated die, employing a catalysed resin mixture blended with a continuous-filament fibreglass, ensuring mechanical and structural resistance.

The pieces are then coated with a UV-resistant gelcoat providing external protection, while the inside is waterproofed by applying a gelcoat with a paraffin additive aimed to prevents osmosis.

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TEMPCO researches and develops systems and solutions for cooling, heating, control temperature and heat exchange in different industrial processes.