What is the source of the transmembrane pressure difference?

The transmembrane pressure difference is defined as the pressure required to drive water through the membrane, which is the difference between the inlet water pressure and the filtration pressure. Membranes with smaller pore sizes require a higher transmembrane pressure difference; this difference is also higher when the water temperature is low, the flux is high, or contamination occurs.

The English term for transmembrane pressure difference is Trans-Membrane Pressure Drop, abbreviated as TMP

2# aliao96 What is the difference between filtration pressure and operating pressure?

The transmembrane pressure difference is the pressure difference between the feed side and the permeate side. The working principles of liquid separation membranes and gas separation membranes also differ slightly. Generally speaking, the transmembrane pressure difference depends on the operating pressure, medium, membrane material, and membrane structure. The permeability of media in different membrane materials and membrane structures varies, depending on factors such as the hydrophobicity or hydrophilicity of the membrane, its pore structure, and membrane thickness. The transmembrane pressure difference is the driving force behind the membrane separation process; increasing this pressure difference can boost the permeation flux, but it also exacerbates concentration polarization. It is therefore necessary to select the membrane material, membrane structure, membrane area, and operating pressure based on the actual conditions. All of the above factors are interrelated.

The transmembrane pressure difference is the driving force that propels the feed fluid through the membrane

The question LZ asked isn’t well phrased; there is already a pressure difference when fluid flows through a pipe, so of course the pressure difference across a membrane is even greater.

7# yqyang85 The resistance loss in a pipeline arises from the friction between the fluid and the pipe walls; in other words, is the transmembrane pressure difference (resistance loss) caused by the friction between the micrometer-scale capillaries and the fluid?

What does it mean if TMP is 0?

When discussing the transmembrane pressure difference, it is first necessary to determine whether it is a water film or an air film process. I think the transmembrane pressure difference between the water film and the air film is fundamentally different. The principle behind the separation of water films should be similar to that of filtration, which is quite intuitive – just like when using filter paper to filter liquids, pressure is needed to push the liquid through, and the pressure loss during this process is known as the transmembrane pressure drop. The main separation theory for gas films is “dissolution-diffusion”. Whether the gas film has pores depends on how it is defined ； If nanoscale tiny pores are considered to be pores, then the gas film can also be regarded as having pores ； If not, then the gas film is a dense film. Generally speaking, gas films are usually considered dense films. The process of gas permeation is first a dissolution process. It’s similar to the process of absorption; the pressure of the gas promotes the mass transfer associated with absorption. Subsequently, the gas molecules move through the support layer (which can be considered as porous channels) and are desorbed on the other side of the membrane at lower pressure; this process also involves pressure loss. My personal intuition is that the water film consists of small pieces of filter paper performing the filtering function. A gas film is absorption and desorption.

10# herozealot has a question: Our company has a small MBR treatment unit, and the process flow is as follows: MBR tank water – MBR membrane – pipeline – MBR pump – oxidation tank. A vacuum gauge has now been installed on this pipeline near the MBR pump. I would like to ask whether this vacuum gauge is used to measure the pressure difference across a membrane? How is it measured? Thank you!