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The brazed plate heat exchanger (BPHE) is a product of modern innovative technology. Production of BPHE started only 25 years back...

Basics of heat transfer

Heat exchangers are to best facilitate heat transfer between two or more heat transfer fluids without mixing....

Laser marking

SIA "EKO AIR" offers services of laser marking 
 
(drawing logo of the company, 1D or 2D bar code, etc.)
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Production and head office:

"Eko Air" Ltd., 30D, Miera str., Salaspils, Latvia LV-2169

 

 

 

Basics of heat transfer

Heat exchangers are to best facilitate heat transfer between two or more heat transfer fluids without mixing.

Example: one loop of the heat exchanger moves the primary hot water from the heat generation station, the other, cold sanitary water coming from the water supply company. Passing through the exchanger, sanitary water is heated from 10 to 60 °C and then supplied to the consumer.

 


Both fluid-loops may operate at different working pressures. Primary hot water can be supplied under pressure up to 16 bar, and the sanitary water system may run at 5 bar.
 
School physics taught us that fluid-flow can eitherbelaminar or turbulent . Laminar flow is rather a uniform flow, usually at low velocity. Turbulent flow is quite the opposite. This is a rough mountain river with twists , splashes and swirls . Efficient heat transfer in heat exchanger requires extremely high turbulence flow. For this purpose, heat transfer plates are embossed to form ideal corrugations to create different flow characteristics. In fact, manufacturers of heat exchangers are always looking for the ideal pattern

Also, turbulent flow minimizes the risk for fouling, scaling and clogging of the fluid channels, thus enabling longer and stable operation. The correct selection of unit design is vital.
 
EKO AIR selection software  ANeX is the tool for proper sizing and allows the customer to check the level of turbulence, besides others. The so called „Reynolds number” characterizes the turbulence and the number should be more than 500 in water to water heat transfer.

Turbulent fluid flow, thus efficient heat transfer, comes on the cost of pressure-drop. To overcome the flow-resistance you need to invest (electrical) pumping power.  You can measure it by using pressure gauges before and after the heat exchanger. Popular units are kPa or bar. Though, manufacturers know by experience common values for „maximum allowable pressure drop”.

In most cases, the customer knows the parameters for pressure drop across the heat exchanger circuits. In heat-substations, typical values range from 15 to 25 kPa. Higher allowable pressue drop may lead to more compact, less expensive heat exchangers. But the pump need to be designed accordingly. In any case, one should be cautious about pressure drop.

An increase of pressure drop during operation may indicate fouling or clogging of the heat transfer plates due to poor water quality or wrong operation of the heat exchanger (low-flow conditions). Counter actions should be taken, like controlling the flow-volumes or cleaning of the unit with special cleaning agents (CIP – cleaning in place)
 
For cost reasons and competitiveness, manufacturers aim to design heat exchangers using the smallest heat transfer area (HTA) possible to ensure the heat transfer duty. BPHE comes in different sizes and plate-corrugations (e.g. chevron types) to best meet a specific thermal duty.

The required HTA should be offered with a most compact heat exchanger. BPHE are „modular and scalable”, meaning by simply adding HT-plates you increase the HTA within the same geometric size (height x width). If the geometric size is too small, you switch to a larger size unit.

Different corrugated plates (usinf different chevron angles) are offered to best meet the different thermal duties, or customer specifications. Criteria for selection are: fluids used, temperatures in and out, allowable pressure drop and overall heat-load.
Offered chevron angles can roughly be classified into three types - H , M  and L. Type H means „High-Theta”, a chevron with a wide angle, offering a close temperature approach. This pattern provides maximum heat transfer, but creates also high pressure loss. In the model-type, H is indicated by usingthe digit 8 in the end (e.g. NB538).

Plate types M – medium theta, and L – low theta, offer more narrow angles with different heat transfer characteristics. Model types using M plates are indicated by the digit „6”, L plates are indicated by „4”.

Each thermal duty is described by a specific „theta-value”. That´s why EKO AIR even offers amixture of different plate –corrugations (e..g. LM or MH) in order to best meet YOUR specification.

Don´t you worry! the ANeX sizing program or your EKO AIR sales contact will select the most appropriate plate for your heat transfer duty!
 

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