Knowledge base
In short
Pressure drop is the push a pump must give to drive liquid through the exchanger, and approach temperature is how close the outgoing liquid gets to the temperature of the other circuit. A tighter approach needs a larger or more demanding exchanger, and a lower pressure drop usually needs a larger one as well, so the two are agreed together with the engineering team.
Two terms appear in almost every plate heat exchanger enquiry and offer: pressure drop and approach temperature. Buyers often meet them for the first time on a datasheet and are not sure which way is better. This guide explains in plain words what each term means, why they pull against each other and what a buyer should say about them, without any formulas or figures.
What Pressure Drop Means
Liquid has to be pushed through the narrow passages between the plates, and every push meets resistance. The pressure drop is the loss of pressure the liquid suffers on its way through the exchanger, and it is the work the circuit pump must make up. A higher pressure drop means a bigger pump and more electricity for as long as the plant runs.
Pressure drop is therefore not a defect of the exchanger but a cost of using it. It is paid every hour of operation, which is why it belongs in the decision from the start and not only in the pump selection afterwards.
What Approach Temperature Means
The approach temperature describes how close the two liquids come to each other in temperature. A tight approach means the cooled liquid leaves almost as cold as the cooling liquid arriving on the other side. A wide approach means the exchanger is content with a larger gap.
A tight approach is valuable where every degree counts, for example when a dry cooler or radiator outside already has to work hard on a hot day. A wide approach gives a smaller, cheaper exchanger, but the plant side then runs warmer than it might have done.
Why The Two Pull Against Each Other
An exchanger can reach a tight approach with more plates, which means more surface and a larger unit, or by pushing the liquid through faster, which raises the pressure drop. It can keep the pressure drop low by giving the liquid more room, which again means a larger unit. There is no setting that delivers a tight approach, a low pressure drop and a small exchanger all at once.
The right balance depends on the job. A plant with a strong pump and an expensive cooling side may accept more pressure drop, while a plant with a weak pump or a long pipe run may not. This is why a good offer states what was assumed for each side, and why the engineering team asks about the pumps already installed.
What To Tell The Supplier
The simplest and most useful thing a buyer can do is state what is fixed and what is flexible: the temperatures the plant needs, the pressure the existing pump can spare and whether space and budget allow a larger unit. With that, the exchanger can be selected for the real circuit instead of a guess.
TECS Engineering designs and delivers plate heat exchanger solutions for engine, power plant and industrial cooling circuits; send the circuit details and the pump data, and the engineering team will answer.
In Short
- Pressure drop is the resistance the pump must overcome in the exchanger
- It is paid in pump size and electricity for as long as the plant runs
- Approach temperature is how close the two liquids come in temperature
- A tight approach needs more surface or a harder working exchanger
- Tight approach, low pressure drop and small size cannot all be had at once
- State what is fixed and what is flexible, and the unit is selected for it
What To Send With An Enquiry
- The liquids on both sides and the heat to be moved
- The temperatures the plant needs on each side
- The pressure the existing pumps can spare, if known
- The space and weight available for the unit
- Whether efficiency, size or price matters most
- Details of the dry cooler, radiator or other equipment in the circuit
Questions We Are Often Asked
What is pressure drop in a plate heat exchanger?
It is the loss of pressure the liquid suffers passing through the exchanger. The circuit pump has to make it up, so it affects pump size and running cost.
What is approach temperature?
It describes how close the two liquids come to each other in temperature. A tight approach means the cooled liquid leaves nearly as cold as the cooling liquid entering on the other side.
Is a lower pressure drop always better?
Not always. It saves pump energy, but it usually needs a larger and more costly exchanger, so the right value depends on the circuit and the budget.
Why does a tight approach cost more?
It needs more heat transfer surface or a harder working exchanger, so the unit is larger or the pressure drop is higher.
What should I tell the supplier about them?
Say what is fixed and what can give: the temperatures needed, the pressure the pumps can spare and the space available. The engineering team then selects the unit for the real circuit.
Contact Us
Send us the heat duty, the fluid temperatures and flow rates, the ambient conditions and the installation limits. We answer with a design proposal - or write to us on WhatsApp.
