If you require an invoice with VAT shown, please send us a request via our contact form or by email to info@alex-depot.de. We will then provide you with the invoice immediately.

We offer a 3-year warranty on our products, which covers defects in materials and workmanship. In the event of defects within the warranty period, please contact us to discuss the process for a return or exchange. You have 30 days from receipt of your order to make returns. Please contact us to obtain a return authorization and clarify further steps. Make sure the products are in their original packaging.

If a product is currently unavailable, we will do our best to get it back in stock as quickly as possible. Please let us know if you are missing a specific product and we will see if we can get it for you ahead of schedule.

Yes, we offer express shipping for an additional charge of €16.99. To use this option, please indicate that you require express shipping in the "Special Order Instructions" field in your shopping cart. We will then arrange for your order to be shipped as quickly as possible.

Yes, we offer customized plate heat exchangers designed to meet our customers' specific requirements. If you require customized solutions, please contact us with your requirements and we will be happy to help you find the right heat exchanger for your application.

The mean temperature difference of a plate heat exchanger can be calculated by several methods, depending on the type of heat exchanger and the specific conditions. A common method is the Logarithmic Mean Temperature Difference. Here is how you can calculate it:

Formula for the logarithmic mean temperature difference

LMTD = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)

variables

• LMTD: logarithmic mean temperature difference
• ΔT1: Temperature difference at one end of the heat exchanger
• ΔT2: Temperature difference at the other end of the heat exchanger

Example

• Temperature of the hot liquid at the inlet (Th): 150 °C
• Temperature of the cold liquid at the inlet (Tc): 30 °C
• Temperature of the hot liquid at the outlet (Th'): 80 °C
• Temperature of the cold liquid at the outlet (Tc'): 60 °C

1. Calculation of ΔT1 & ΔT2

ΔT1 = Th - Tc = 150 °C - 30 °C = 120 °C

ΔT2 = Th' - Tc' = 80 °C - 60 °C = 20 °C

2. Calculation of the mean temperature difference

LMTD = (120°C - 20°C) / ln(120°C / 20°C)
LMTD ≈ 55.8 °C

Q = U * A * LMTD

• Q: heat flow (W)
• U: total heat transfer coefficient (W/m²·K)
• A: Heat transfer area (m²)
• LMTD: logarithmic mean temperature difference (K)

or

Q = ṁ * cp * LMTD

• Q: heat flow (W)
• ṁ: mass flow rate (kg/s)
• cp: specific heat capacity (J/kg·K)
• LMTD: logarithmic mean temperature difference (K)

cocurrent and countercurrent principle

The transferable heat energy of a plate heat exchanger is not only determined by the size of the exchange surface and the heat transfer coefficient (k), but is also significantly influenced by the flow directions of the media involved. If both media flow in the plate heat exchanger in the same direction, this is referred to as the cocurrent principle. If they flow but in opposite directions, this is the countercurrent principle.

The flow direction has a significant influence on the average temperature difference between the media, which in turn determines the efficiency of heat transfer.

Temperature curve with the direct current principle | Temperature curve with the countercurrent principle

Theoretical consideration of the connection options of a plate heat exchanger:

In this example we assume two media with the same heat capacity and the same mass flow.

• Medium 1: 80 °C
• Medium 2: 20 °C

With the cocurrent principle, the maximum temperature that can be reached for both media would be 50 °C, which corresponds to the mixing temperature. With the countercurrent principle, however, medium 2 could reach a temperature of up to 80 °C, while medium 1 can be cooled to 20 °C.

This means that the countercurrent principle allows a larger amount of heat to be transferred using the same exchange surface area.

Finding the right plate heat exchanger doesn't have to be complicated. If you have any questions or need support, don't hesitate to contact us. We'll be happy to help you choose the right model for your needs.