In some cases, such as in cooling applications, stainless-steel micro channel porous flow plate is very critical. It requires precise approaches according to the different temperatures. This is what we refer to as high thermal length and requires specific units.
By high thermal length we mean cases with values
- Long plates, therefore more time required for liquid cooling
- Low pressure, therefore worse distribution of the liquid to cool.
Plate heat exchangers are better than shell and tube exchangers
Shell and tube heat exchangers can reach values
Scope of stainless-steel micro channel porous flow plate
It can express in two different ways: by weight or by volume. The flow units per weight are in Kg / s or kg / h the flow units per volume are in m3 / hol / min. To convert volume units to weight units, you need to multiply the volume flow by the density.
The maximum flow rate generally determines which type of heat exchanger is appropriate for a specific purpose. Moreover, alfa Laval plate heat exchangers can be common for flow rates from 0.05 kg / s to 1400kg / s. In terms of volume, this equates to 0.18 m3 / h - 5000 m3 / h in a water application.
If the flow rate exceeds these values, it will be possible to split the flow into several units in parallel.
The pressure drops in stainless-steel micro channel porous flow plate
If it is possible to increase the allowable pressure drop and accept higher pumping costs. The heat exchanger will be smaller and less expensive. As an indication, pressure drops between 20 and 200 kPa consider normal for water / water applications.
The specific heat (c ρ) is the amount of energy needed to increase 1 kg of substance by one degree centigrade. The specific heat of water at 20 ° C is 4182kJ / kg ° C or 1.0 kcal / kg ° C.
Viscosity measures the ease of flow of a liquid.
The lower the viscosity, the easier it is to slide. Viscosity express in centipoise (cP) or centistoke (cSt).
Overall heat transfer coefficient
The overall heat transfer coefficient (k) measures the resistance of the heat transfer in stainless-steel micro channel porous flow plate. Moreover, it consists of the amount of fouling, the nature of the fluids and the type of exchanger common. The overall heat transfer coefficient expresses as a W / m 2 ° C or kcal / h, m 2 ° C
Calculation method of the heat load of a heat exchanger
The heat load of a heat exchanger can calculate using the following two formulas:
Calculation of Potentiality, Theta and LMTD
P = capacity (kW)
m = mass flow (kg / s)
cρ = specific heat (kJ / kg ° C)
δt = differences between inlet and outlet temperatures on one side (° C)
k = heat exchange coefficient ( W / m 2 ° C)
A = heat exchange area (m 2 )
LMTD = logarithmic mean temperature difference
T1 = Inlet temperature - hot side
T2 = Outlet temperature - hot side
T3 = inlet temperature - cold side
T4 = Outlet temperature - cold side
LMTD in stainless-steel micro channel porous flow plate can calculate using the following formula, where ΔT1 = T1 - T4 AND Δ2 = T3 - T3
Heat transfer coefficient and design margin
The total overall heat transfer coefficient k is defined as:
The higher the K c value, the lower the R f value will be to achieve the same design margin. Each parameter of the equation can affect the choice of heat exchanger. The choice of materials generally has little effect on the efficiency, but only on the strength and corrosion properties of the unit.
In a stainless-steel micro channel porous flow plate, you can take advantage of the benefits of small differences in temperature and plate thickness between 0.3 and 0.6mm. Moreover, the alpha values
Important factors about stainless-steel micro channel porous flow plate:
- Pressure drop - The higher the allowable pressure drops, the smaller the required heat exchange surface.
- LMTD - The greater the temperature difference between the fluids, the smaller the size of the heat exchanger.
Construction materials of High-quality stainless-steel plates
High-quality stainless-steel plates are common in most heat exchangers for water / water applications. When the chloride content does not dictate the need for, less expensive stainless-steel material can be common.
Stainless-steel micro channel porous flow plate in different materials are also available for various applications. For Alfa Laval brazed plate heat exchangers, AISI 316 stainless steel is always common. For seawater and brackish water, only rarely 1 titanium (99.6% pure) should be common.
Limitations of temperature and pressure
The maximum temperature and pressure an exchanger can reach affect its cost. Moreover, as a general rule it can be said that the lower the temperatures and the maximum pressure, the lower the price will be.
The allowed fouling can express as a design margin (M) (i.e., an additional percentage of the stainless-steel micro channel porous flow plate or as a fouling factor, expressed in m 2 ° C / W or M 2 h ° C / kcal.
Higher k values
The design of the plate heat exchangers implies a turbulence, and consequently a thermal efficiency, much higher than the shell and tube exchangers. Moreover, a typical coefficient k (water / water) for a plate heat exchanger is 6000-7500 W / m 2 ° C, while a typical shell and tube exchanger returns only 2000-2500 W / m 2 ° C.
A typical R f value common for shell and tube exchangers is 1 x 10 -4 m 2 C / W. With k values
Difference in how margin is added in tube heat exchanger
In the shell and tube heat exchanger, margin is usually added by increasing the length of the tubes while maintaining the same flow in each tube.
The margin is increased by adding parallel channels, i.e. decreasing the flow per channel and thus obtaining a lower turbulence / efficiency ratio, increasing the risk of fouling. Too high fouling factor can lead to increased fouling!
Moreover, for a stainless-steel micro channel porous flow plate in water / water application, a margin of 0-15%, depending on the water quality, is generally sufficient.
