# What is Pressure gradient: Definition and 35 Discussions

In atmospheric science, the pressure gradient (typically of air but more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure increases the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of pascals per metre (Pa/m). Mathematically, it is obtained by applying the del operator to a pressure function of position. The negative gradient of pressure is known as the force density.
In petroleum geology and the petrochemical sciences pertaining to oil wells, and more specifically within hydrostatics, pressure gradients refer to the gradient of vertical pressure in a column of fluid within a wellbore and are generally expressed in pounds per square inch per foot (psi/ft). This column of fluid is subject to the compound pressure gradient of the overlying fluids. The path and geometry of the column is totally irrelevant; only the vertical depth of the column has any relevance to the vertical pressure of any point within its column and the pressure gradient for any given true vertical depth.

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1. ### Can you use Taylor Series with mathematical objects other than points?

I was recently studying the pressure gradient force, and I found it interesting (though this may be incorrect) that you can use a Taylor expansion to pretend that the value of the internal pressure of the fluid does not matter at all, because the internal pressure forces that are a part of the...
2. ### B Variation of air density with height

Using the ideal gas equation ##PV = nRT\Rightarrow PV = \frac{m}{M} RT## where ##m,M## are the mass and molecular weights of the gas respectively. This yields ##\frac{m}{V} = \frac{PM}{RT} = \rho##, the density of the gas at a point with pressure ##P##. If only we can obtain the variation of...
3. ### Sorry, another Bernoulli equation paradox

Let's start with a horizontal tube with a constant diameter. I'm not sure if it's important, but let's assume it's frictionless. I will have some fluid flowing in this tube and if it's important, we can make the fluid incompressible, inviscid, irrotational, etc. To create a flow in the tube...
4. ### I What is the pressure gradient towards the centre of a large planet?

Given that the gravitational field falls to zero at the centre of a large body (e.g. the earth), what happens to the pressure curve? (Assuming no effects due to high temperature.) Does it ease off too? What would the curve look like and what would the formula be?
5. ### Pressure gradient causes conservative force?

Is the force that accelerates afluid betwen two points of different pressure conservative?
6. ### Why can't we use the hydrostatic pressure gradient to do work?

Is there any way to harness the hydrostatic pressure gradient to generate energy? The pressure at the surface of an ocean is atmospheric pressure.As we descend down the ocean, the pressure increases .After a point, the pressure will be very high.Why can't we use this pressure difference to do work?
7. ### Using Ideal Gas Law to Calculate Vertical Pressure Gradient

Homework Statement Consider a cylindrical parcel of air of area A and infinitesimal height dz. If this air parcel is to remain stationary, the difference between the total pressure forces exerted on its top and bottom faces must be equal to its weight. Use this information and the ideal gas...
8. ### Pressure gradient in a sphere

Have cylinder made from semipermeable material .There is positive pressure inside cylinder and negative pressure outside cylinder .How gradient of pressure will be changed if we convert from cylinder t o sphere? Thank you
9. ### Pressure gradient in wakes around a cylinder

Hi, Let's consider a cylinder of infinite length and fluid flowing "over" (I'm not sure of which words I should use, sorry) it like in the figure: Let's consider x>>D in order to neglect what's happening near the rear surface of the cylinder. Let's get rid of static pressure which doesn't...
10. ### The effect of pressure gradient across dissimilar fluids

So my question is - would a strong enough negative pressure be able to pull a gas through a liquid? I can draw a diagram if anyone needs it but I'm trying to figure out what would happen in the following situation. Imagine you had a solid pipe that formed a large U shape with one end sealed...
11. ### Pressure Gradient for Nitrous Flow

Hello everyone, I am currently working on an undergraduate club team for the Intercollegiate Rocket Engineering Competition. I am attempting to do a calculation to determine the pressure needed in a vessel leading to another pressurized combustion chamber to achieve a desired mass flow rate...
12. ### Determine the pressure gradient for suction

Hello, Im designing a product which will pump components as vacuum cleaner does. I have 2 questions: Im trying to calculate the pressure different in order to pump those metal component with : M=0.2 kg , dimensions (mm) cylinder with diameter 5.5 mm length 600mm . the formula for pressure...
13. ### Optimum shape for a pressurized structure in a pressure gradient

I came across this pie-in-the-sea concept: (Obviously, the pictured structure would be extremely susceptible to complete catastrophic failure, having no apparent internal means of water-tight seals to prevent complete implosion. Which is why you'd more logically build a city in tube-and pod...
14. ### Pressure gradient along a streamline using CV analysis

Homework Statement Use a CV analysis to show that an element of fluid along a streamline gives $\partial p/\partial x=-\rho u\partial u/\partial x$ Homework Equations $\sum F=\oint_{CS}^{ } \rho \overrightarrow{V}(\overrightarrow{V_{rel}}\cdot \overrightarrow{n})$ The Attempt at a...
15. T

### Relationship between the pressure gradient and mass flow of a gas

Hi everyone, I would like to know how to calculate the diameter of a pipe when we know the desired mass flow, the gas type, and the pressure at both end. I have these requirements : Gas : O2 Molecular weight : 0.032 [kg / mol] Desired mass flow : 0.32 [kg / s] Pressure in the gas tank : p1 =...

I simulated an incompressible turbulent flow across a tube. I managed to solve it using OpenFoam and the results seem to be right. However, I noted some vacuum pressure after the sudden expansion but can't figure out why the pressure decreases and then increases again. According to Bernoulli's...
17. ### Bernoullis & Pressure Gradient force

The more I learn about Bernoulli's the less I feel I understand it The problem statement If I had a ball (balloon) filled with fluid at pressure P being acted on by two opposing forces F+ and F- F+ being larger than F- there would be a net force accelerating the ball to the right but the...

In nature, gradient is always required for flow; whether it is temperature gradient for heat transfer or pressure difference for fluid flow. There is a case of Venturimeter in which we have throat section. After throat there is a divergent section. How could flow even happen in that adverse...

For a symmetrical wing (NACA 0012 - due to wide data avaialble) at 0 deg inclination the following Cp to x/c relationship exists: The upper and lower surfaces produce the same Cp and hence a symmetric wing with no inclination doesn't produce a result force (i'm happy with this). Now at an...
20. ### Aerodynamics vs pressure Gradient

Could someone explain the image we see below of a fully separated and stagnated flow over a wing if we were to focus on where the flows rejoin on the trailing edge we see above a fully stagnated flow DP=0 The static pressure here in the boundary layer above where the flows rejoin should be...
21. ### Exploring the Relationship between Pressure Gradient and Density in Physics

Homework Statement why the pressure gradient is = - 2ρg ? why not ρg ? Homework EquationsThe Attempt at a Solution
22. ### Corresponding Pressure gradient with flow velocity

I have some questions concerning hydraulic engineering. I'm currently working an simulating laminar flow. This laminar flow is induced by a pressure gradient. The assumed length is 1 meter, therefore the pressure gradient is equal to the actual pressure in reference with zero. What are typical...
23. ### Pressure gradient term in Navier-Stokes

Hi, I've been thinking about the Navier-Stokes equations and trying to build skill in implementing it in various situations. In a particular situation, if I have a fluid flowing down an inclined surface such that it forms a film of finite height which is smaller than the length of flow, there...
24. ### Pressure gradient across flat plate with flow is zero?

So I learned recently that pressure gradient in the flow direction for flow over a flat plate is zero. However I don't understand this, because there has to be something that sets the flow in motion in the first place, and for fluids this has to be a pressure gradient. Could someone explain why...
25. ### Fluid flow through positive pressure gradient

I am a student of 11th standard and being introduced to Bernoulli's principle made me wonder , how does flow takes place in positive pressure gradient (i.e. from low pressure region to high pressure region), in a diffuser or a diverging part of a venturi meter , since we know that flow always...
26. ### Liquid pressure gradient in zero gravity

Is there any data about such measurements? I think, there has to be a pressure gradient in a floating liquid sphere due to surface tension.
27. ### Hot Air Balloon Shape and Pressure Gradient Within the Envelope

I am interested in the math involved to calculate the ideal natural teardrop shape for a hot air balloon. I want to learn the details of what is involved to calculate this accurately. I read this https://www.physicsforums.com/showthread.php?t=658802 which was a really nice start, but it...
28. ### Pressure gradient in Jeans Lenght

All the demonstrations on Jeans instability start with: \rho g \ge \nabla P Then they substitute \nabla P with nkT/R. But from ideal gas law: PV = nkT, so P = nkT/V = nkT/R^3 (I'm not interested in proportionality factors, so let's not bother about 4/3 \pi, ecc...) Now, gradient of P, to...
29. ### Pressure Gradient in Hydrostatic Equilibrium

Homework Statement Consider an isothermal atmosphere (T = const.) over a sufficiently small range of radii, so that you can assume that the gravitation acceleration g is constant. Use the equation for the gas pressure gradient in hydrostatic equilibrium to show that the gas pressure decreases...
30. ### [Fluid mechanics] Find pressure gradient

First of all sorry my english, I'm an italian student Homework Statement The velocity field is known ux=6x+8z*cos(a*t) uy=3xz*sin(b*t)+2 uz=-6z The fluid is incompressible. I need to find the pressure gradient and the i have to determine if it's a turbulent flows, but at the moment i need...

Suppose we have fluid in a vessel (Vessel A) with inside Pressure 120 bar (achieved by a pump)… When we open the valve, the fluid starts to flow into another vessel (vessel B) that was hitherto empty... Due to the Pressure gradient, the fluid flows with a certain velocity into vessel B. But the...
32. ### Fluid Mechanics: pressure gradient of a tube bifurcation

The question is as follows: A circular tube of radius 'a' bifurcates into two tubes with equal radii 'ka', where k is a dimensionless coefficient. Derive an expression for the ratio of the pressure gradient in each bifurcated tube to that in the initial tube in terms of 'k'. I'm not sure...
33. ### Do stirling engines have a pressure gradient across the regenerator?

There is a temperature difference and we know the transition of the working fluid (from the hot chamber to the cold one) is isometric. So either there must be a pressure difference, or the number of molecules must be smaller; however, this can't be the case since eventually all the gas must move...
34. ### Temperature and pressure gradient in a gas

I have derived that, when there is a temperature difference (gradient) in a gas (consider a long tube with one end maintained at 100oC and other end maintained at 0oC), there will be a pressure gradient (something similar to Bernoulli's law). Please see the attached document or this link for...