Heat exchangers are an equipment targeted to the efficient transfer of heat from a hot fluid flow to a cold fluid flow, in most cases through an intermediate metallic wall and without moving parts. We here focus on the thermal analysis of heat exchangers, but proper design and use requires additional fluid-dynamic analysis (for each fluid flow), mechanical analysis (for closure and resistance), materials compatibility, and so on.

Heat losses or gains of a whole heat exchanger with the environment can be neglected in comparison with the heat flow between both fluid flows; i.e. a heat exchanger can be assumed globally adiabatic. Thermal inertia of a heat exchanger is often negligible too (except in special cases when a massive porous solid is used as intermediate medium), and steady state can be assumed, reducing the generic energy balance to:

where the total enthalpy h_t has been approximated by enthalpy (i.e. negligible mechanical energy against thermal energy), and D means output minus input.

Although heat flows from hot fluid to cold fluid by thermal conduction through the separating wall (except in direct-contact types), heat exchangers are basically heat convection equipment, since it is the convective transfer what governs its performance. Convection within a heat exchanger is always forced, and may be with or without phase change of one or both fluids. When one just relies in natural convection to the environment, like in the space-heating hot-water home radiator, or the domestic fridge back-radiator, they are termed ‘radiators’ (in spite of convection being dominant), and not heat exchangers. When a fan is used to force the flow of ambient air (or when natural or artificial wind applies, like for car radiator) the name heat exchanger is often reserved for the case where the ambient fluid is ducted. Other names are used for special cases, like ‘condenser’ for the case when one fluid flow changes from vapour to liquid, ‘vaporiser’ (or evaporator, or boiler) when a fluid changes from liquid to vapour, or the ‘cooling tower’ dealt with below. Devices with just one fluid flow (like a solar collector, a spacecraft radiator, a submerged electrical heater, or a simple pipe with heat exchange with the environment) are never named heat exchangers.

To be continued…

Image credited to heatexchangerguy.com/plate-heat-exchangers.html

Mashimpeks was established in 1995 in Moscow as an implication exportation company and has been a strategic marketing and service better half of GEA PHE Systems for 12 classes. Mashimpeks is a licensed producer of plate heat exchanger skeletons for the Russian marketplace, likewise for GEA’s high performance gasketed NT-Series. In future the company, with its staff of 120, will operate on as GEA Mashimpeks.

In the premature line of work yr Mashimpeks’ remunerations were approximately 15 million euros. The company is one of the decisive market challengers in the plate heat exchanger business enterprise in Russia. Mashimpeks has two logistics pores with assorted manufacture installations and a well-structured mesh of cut rate sales and service mercantile establishments throughout the Russian Federation with its ain installations in Novosibirsk, Yekaterinburg, Samara, St. Petersburg and Irkutsk. This warrants tight and effective after sales agreements & service for PHEs by GEA.

In Solnechnogorsk, near Moscow and in Novosibirsk in the east of the area, Mashimpeks has been bringing about figures under licence to Russian industrial criterions for all scopes of gasketed GEA dental plate heat exchangers. The plates and gaskets are rendered from Germany by GEA PHE Systems. Mashimpeks specialists then meet the units in line with client specs, and are responsible for the complete after-sales & service.

Russia is a apace extending PHE mart. And there is increasing demand specifically in the petrochemical industry, for energy-saving heat energy retrieval in the chemical industry, in power station engine room and in the refrigeration, food products and pharmaceutics sectors. This is why GEA Heat Exchangers will continue to inflate the surviving Mashimpeks service and statistical distribution network to attain yet quicker law of proximity to the client. The logistics and product locations will rest and are scheduled for expanding upon in the average full term to ensure that GEA Mashimpeks can continue to issue the PHE equipment that the clients desire just as chop chop and in line with their specific pauperisms.

Source: oilandgaseurasia.com/news/p/0/news/10933/

Hot Springs Hotel has recently taken advantage of the geothermal energy smothering the hotel property by using a heat energy substitution appendage to furnish hot water for all hotel prerequisites conceived to be a first for Fiji.

After much tanoa talanoa, (words) it was decided something must be done to tackle this wasted resource, and at the same time, reduce hotel operating costs or in this case, extinguish the gas government note, so a simple heat exchanger was contrived and built.

The concept is the reverse of its marine applications programme where sea body of water is disseminated to cool hot locomotive engines, or in aircraft where cold fuel is warmed by hot locomotive engine organizations.

The hotel water supply is heated up by being diffused through the heat exchanger sunk in a geothermic hot spot on the hotel property.

The town water supply puts down the heat exchanger at the “outside” temperature of some 25 grades and is heated up to 50 grades prior to recording the hotel reticulation organization.

The appendage is all gravity-fed, thus fending off the demand for any extra pumps.

Ian Lilo, hotel maintenance handler oversaw the whole process.

Mr Lilo sounded out the beauty about geothermal energy was that it was a 24-hour, seven-days a workweek provision. This he enounces heartbeats the challenges of solar systems which is solely utile during daytime times of day on good cheery daytimes or consistent air current for wind generators.

Source: fijitimes.com/story.aspx?id=169697

Chairman and Chief Executive Officer Guohong Zhao commented, “We continued to build on the positive momentum generated in recent quarters and ended 2010 with a very solid performance. Top-line growth, which exceeded our guidance in the fourth quarter, contributed to more than 44% increase in revenues for the full year. At the same time, our focus on optimizing both our product mix and cost structure allowed us to almost double our net income in 2010.”

“Our diverse product lines enable us to cater to a broad range of customers and end users as we capitalize on several key trends that are driving the clean technology movement in China. As China faces pressures from rapid urbanization, our heat exchanger units offer efficient and effective solutions to provide heating systems to growing populations in cities throughout China. In addition, our air-cooled exchangers enable water-deficient areas in Northern China to conserve and better utilize a very limited resource. As businesses recognize the cost effectiveness of switching to clean technology solutions and are further incentivized by government stimulus plans, our plate heat exchange (“PHE”) products are quickly gaining traction across a range of industrial sectors, including the metallurgy, petrochemical and shipbuilding industries.

“As rapid urbanization and government stimulus plans designed to support carbon reduction initiatives continue to drive demand for energy efficient platforms, our broad product portfolio, integrated solutions and excellent track record of high quality applications have well prepared us to capitalize on these favorable dynamics in 2011. Additionally, our sound balance sheet and cash position, which were further strengthened by our recent fund raising, afford us with financial flexibility to invest in our future and pursue growth opportunities.”

Please read the rest of the news here.

If you are in this industry, you will definitely know how expansive a heat exchanger can be. Unless you can fabricate your own heat exchanger, that will save your company substantially a lot. Unfortunately, many companies have to purchase it from heat exchanger manufacturer. But, one good thing took place recently. DENSO Corporation has just developed 4 units of low cost heat exchanger to support the Indian automotive market. Continue reading the news below:

Kariya (Japan) As part of its ongoing effort to develop low-cost products for emerging markets, DENSO Corporation has developed four heat exchangers for the Indian market. DENSO’s new radiator, heater core, condenser and evaporator use common, locally sourced materials and are manufactured on a single production line, which helps to significantly reduce cost.

“While maintaining our DENSO quality, we’ve succeeded in substantially lowering the cost of these products by increasing our local procurement, and by using common materials to reduce the types of materials we use by more than 70 percent,” said Akio Shikamura, senior executive director of DENSO’s Thermal Systems Business Group. “We will share the newly developed cost-reduction techniques throughout the company to improve the competitiveness of our products worldwide.”

When developing the new products, DENSO carefully assessed the needs of the Indian market to determine optimal specifications, while also using India’s locally made and widely available materials. This increased local procurement, and increased the number of common materials and components for each product.

Continue reading here.

Shell and tube heat exchangers are special type of unit operation which is needed for high-pressure applications; they are durable products, which can withstand the demands of many working environments. Their design plays a large part in ashell and tube exchanger’s ability to endure exceedingly-challenging situations. The gaskets are normally spiral wound gaskets made of stainless steel.

Shell and tube heat exchangers are made from a series of tubes, which can be made of durable material such as fluoropolymers. Fluoropolymers are highly-durable plastics such as PTFE, FEP, and PFA. Fluoropolymers, like heat exchangers, have a place in a variety of industries such as the automotive, medical, and aeronautical.

In a heat exchanger’s shell, one set of tubes contains fluid, which is either heated or cooled. Another set of tubes also contains liquid, which facilitates the heating or cooling of the primary set of tubes. A tube set is referred to as the tube bundle and can take on a variety of shapes depending on what is most conducive for the intended job.

Engineers of shell and tube heat exchangers need to consider several components of construction, among them are:

• A smaller tube diameter enables the shell and tube exchanger to be economical and compact, yet a tiny diameter can facilitate malfunction and difficulty of cleaning. Larger tubing can be instituted to eradicate potential flow and cleaning problems. Engineers must factor cost, space, and the propensity of liquids to foul when constructing a heat exchanger.
• Tube thickness is important to make sure there is room for corrosion; vibration existing in the product has resistance; and, the shell and tube exchanger can withstand pressure coming from both in and outside of its internal tubes.
• Folding or wrinkling the inner tubes increases the flow of the liquid, which facilitates the transfer of heat, producing better performance from the exchanger.
• Designers also consider the layout of the inner tubes. Tubes can be fashioned in a triangular, square, rotated square, or rotated triangular fashion. Particular, internal designs are conducive to specific jobs and the elimination of potential problems such as fouling of the liquid.
• Shell and tube heat exchangers also host baffle components. Baffles serve several purposes such as holding the tube bundles in place; making sure tubes do not sag or vibrate; and, facilitating fluid flow.

Four different types of steel used for high-temperature service:

• Carbon steels – for most usage up to 750 degrees F (400 degrees C). Carbon steels are cheaper, very strong, with highest thermal conductivity. Above 750 degrees F, their creep increases; above 950 degrees F (510 degrees C) they get oxidized too.
• Chromium-molybdenum steels – resist oxidation up to 1200 degrees F (650 degrees C). But their thermal conductivity is lower; and chromium-molybdenum steels are more expensive than carbon steels.
• Ferritic stainless steels – can be used up to 1500 degrees F (820 degrees C).  Ferritic stainless steels have higher thermal conductivity, lower thermal expansion coefficient, and less expensive than other materials for the same service. Ferritic stainless steels can resist oxidation as well as attack from sulfur- and carbon-containing flue gases. Coefficient of thermal expansion of ferritic stainless steels is lower than for austenitic stainless steels. Loose strength after a very long usage at high temperatures.
• Austenitic stainless steels – the strongest among steels for use at high temperatures and do not loose strength after very long usage at high temperatures. Austenitic stainless steels resist oxidation at high temperatures and are widely used in boilers, super-heaters, refinery services, etc., where chlorine is not present.

These are part of the steels that can be used for the manufacturing of various heat exchanger including shell and tubes, spiral heat exchanger and plate heat exchanger.

This information is credited to http://brazedplateheatexchangers.wordpress.com/2010/07/01/which-types-of-steel-can-be-used-for-high-temperature-service/

1.  Is there a phase change involved in my system?

2.  How many “zones” are involved in my system?

3.  What are the flowrates and operating pressures involved in my system?

4.  What are the physical properties of the streams involved?

5.  What are the allowable pressure drops and velocities in the exchanger?

6.  What is the heat duty of the system?

7.  What is the estimated area of the exchanger?

8.  What geometric configuration is right for my exchanger?

9.  Now that I have a geometry in mind, what is the actual overall heat transfer coefficient?

10.  What is the actual area of the exchanger using the ‘actual’ heat transfer coefficient?

11. What are the materials of Construction, ease of maintenance, cost of exchanger and overall heat integration

Think of the questions…

We’ll provide answers for it in latter posts.

There are various types of heat exchangers and the function depends very much on its dedicated applications. Among them are:

• Inter-coolers and heaters
• spiral heat exchanger
• shell and tube heat exchanger
• plate and frame heat exchanger
• Regenerators – refrigeration units
• Automobile radiators
• Milk chiller of a pasteurizing plant
• Condensers and boilers in steam plant
• Evaporators
• Oil coolers of heat engine

CLASSIFICATION
Heat exchangers may be classified according to the following main criteria:

1. Nature of heat exchanger process
2. Flow arrangement
3. Physical state of fluids
4. Geometry and construction

1. Classification based on Nature of heat exchanger process

(i) Direct contact:
Heat transfer will occurs by direct mixing of two fluids. This is preferred when the direct mixing is harmless or desirable.
Ex: cooling towers
(ii) Indirect contact:
Heat transfer will occurs through a separating wall between two fluids
Ex: Regenerators and Recuperators

2. Classification based on Flow arrangement

According to the relative directions of two fluid streams the heat exchangers are classified into the following three categories:

(i) Parallel flow or co-current flow heat exchangers
(ii) Counter-flow heat exchangers
(iii) Cross-flow heat exchangers

(i) In a parallel or co-current flow heat exchanger

As the name suggests, the two fluid streams (hot and cold) travel in the same direction. The two streams enter at one end and leave at the other end. The flow arrangement and variation of temperatures of the fluid streams in case of parallel flow heat exchangers, are shown in the below figure. It is evident from the figure that the temperature difference between the hot and cold fluids goes on decreasing from inlet to outlet.

In parallel flow, it is not possible to bring the outlet temperature of the cold fluid nearly to the inlet temperature of the hot fluid. This type of heat exchanger needs a large heat transfer area, so, it is rarely used in practice.
It is particularly useful when sudden cooling or sudden heating is required.
Examples: Oil coolers, oil heaters, water heaters etc.

(II) Counter-flow heat exchangers

In a counter-flow heat exchanger, the two fluids flow in opposite direction. The hot and cold fluids enter at the opposite ends. The flow arrangement and temperature distribution for such a heat exchanger are shown schematically in the below figure.

In this flow, it is possible to bring the outlet temperature of the cold fluid nearly to the inlet temperature of the hot fluid. This type of heat exchanger needs a small heat transfer area, so, it is widely used in practice.
Examples: Oil coolers, oil heaters, water heaters etc.

(iii) Cross-flow heat exchangers

In cross-flow heat exchangers, the two fluids (hot and cold) cross one another in space, usually at right angles. The flow arrangement and temperature distribution for such a heat exchanger are shown schematically in the below figure.

Source: enggyd.blogspot.com/2010/03/description-of-heat-exchange-equipment.html

In industry, specifically process or manufacturing plants there are other types of heat exchanger such as plate heat exchangers, spiral heat exchangers and shell and tube heat exchangers. All of these heat exchangers are special and have their dedicated purpose or function when being employed. The price, size, specification, purpose and design varies within each other.

Heat exchanger must be properly maintained in order for it to be working efficiently and effectively. Energy is being transferred from one side to the other, thus it acts like an energy saver. When the heat exchanger is no longer efficiently transferring heat, it is time for cleaning. Hence, the heat exchanger will be stopped and cleaned from scale sticking on the surface of the wall. Failing to clean the heat exchanger will result to tremendous lost of energy.