Sunday, December 29, 2013

Liquid droplet surface tension calculator-simulator

For those who are interested to compute water droplet shape on a horizontal surface at different contact angles, this is what is the post about.

The method simply is to assume that we have originally a spherical water droplet (in air) of certain radius. Then we are going to assume that this droplet will take the shape of a truncated sphere of new radius when it is in contact with a horizontal surface. Simply, the volume of the original sphere is the same as the volume of the truncated sphere.

I used the following system of equations:

Since the equations used can't be solved by separation of variables, so it easy to solve it using Newton-Raphson method which is an iterative method. For this reason, I used Engineering Equation Solver EES for solving the system of equations.

The following are the variable information (see the initial guess values and the variable limits which are useful to make the system convergent)

So, now, you can easily simulate a water droplet at any value of contact angle (see image below).

Saturday, December 21, 2013

Trick for downloading long videos from Youtube using IDMan

For those who are using Internet Download Manager IDMan for downloading videos from YouTube or other video streaming sites, this is a useful trick to consider when using IDMan.

By default, IDMan is using 8 connections for downloading any file (higher number of connections means higher download speed), so assuming we have a file of 80 Mbytes, IDMan will split the downloaded file into 8 equal-sized files of 10 Mbytes in its temporary directory (these files have no extension recognizable by the system). These temporary files are downloaded in parallel not in series. You can simply know the temporary directory from (IDMan menu bar - Downloads - Options - Save to - temporary directory).

After download completion IDMan will join these files to output a single file with its original extension in the location you specified. IDMan has a special file joiner that you can't join these files yourself.

Assuming you are downloading a video of 800 Mbytes from a site that does not support resuming download, and you reached a download percentage of 99% and then you lost the connection and hence you can't get the downloaded file, how will you feel about this?!!!

The trick now, is to set number of connections -before downloading- used by IDMan to 1 connection ( IDMan menu bar - Downloads - Options - Connection - Def. Max. No. connections - 1). Therefore, when you download a file it will be downloaded into a single file in the temporary directory (with no recognizable extension also), but you can copy this file to any other directory (say your desktop) during the download and set the extension to (for example .mp4). 

Now you can play the video during downloading.

This trick is also useful for those who have limit download quota and want to preview video during download. So they will not duplicate downloaded quota for a single file.

Friday, December 20, 2013

Waste area in HAWT

This is just a useful tip to consider when calculating the Performance Coefficient CP of Horizontal Axis Wind Turbine HAWT that a lot of people don't take in consideration. 

This tip I introduced in our wind turbine graduation project in 2010 which was "Helical Savonius wind turbine". This point will reduce the CP value declared by HAWTs manufacturers as they calculate based on the swept area, while the rectangular area is the real area occupied by the turbine. This rectangular area can be more useful in VAWTs.

Microcontroller ZIF socket

This is just a useful image I made when I was learning micro-controller.

Saturday, December 14, 2013

Bank receipt trick

In this post I am going to talk about a very interesting thing I discovered myself. Supermarkets, shops, and ATM machines are using thermal paper rolls which are used with thermal printers, so they don't have to refill ink. They only need to refill paper roll which is equivalent to paper and ink. 

The receipt roll has 2 faces: the first face (front face) on which transaction is printed is a "heat sensitive face", and the back face is just a normal face. The heat sensitive face looks glossy a little bit and has a smooth touch, while the back face has a rough touch.

When a spot is heated  in the heat-sensitive paper; its color is changing from white to black (normally when temperature exceeds 70 degrees Celsius) . So.., this is the first way to check if a receipt is fake or not (for those who have companies and want to check receipts). 

The other trick that the banks implement is that when the receipt is heated, the transaction data will disappear and a water mark will appear. This is really so tricky that you can't cheat a bank or make a fake transaction receipt. 

The following picture is an ATM receipt before applying heat and after applying heat using an electric iron. Make sure that the electric iron is ironing the back face and try to make a gentle rotational movement to distribute heat.

Friday, December 13, 2013

Thermoelectric cooler (Peltier) control methods

A combination of the following control methods can be used, but it depends on the application. Some points like reliability of components used, temperature precision, and safety should be taken in consideration.

Saturday, December 7, 2013

Smart phone microscope

Nowadays, everyone of us has a smart phone which has a high resolution camera!!!! . Using my smart phone Samsung Galaxy S3 Mini which has a 5 MP camera, and a concentrating lens of a Chinese (made in China) red laser pointer which does not cost more than 2 Egyptian pounds; I got a microscope with 100x magnification (calibrated on a ruler and measured using Microsoft office Visio 2007).

The flash light helps for the non-transparent samples. Which is really nice with this phone that the flash light is so close to the camera and this is helpful because the new lens array has a focal distance of around 1 cm where it is difficult to apply any light source within this distance between the cell phone and the sample. 

One of the drawbacks of this method is that the image captured tends to have a spherical distortion. Also, due to the flash light position; one side of the image (near to the flash) will have more light than the other side.

The idea is very interesting and turns your cell phone to portable microscope. You will discover a lot of things you didn't see before (invisible worlds)!!!! 

This is a sample of foam film used in the packing of an old Gigabyte motherboard.