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.

Tuesday, November 26, 2013

Creative CV design

Inspired by my passion to programming, I have created a creative design for my CV. This was created using Microsoft office Visio: New ð Software and database ð Windows XP user interface.

Wednesday, November 13, 2013

Facing of crystal ball

In case of facing of glass balls to get crystals, for the same depth of cut, the following image shows the effect of grinding wheel diameter. The larger the diameter ratio between grinding wheel and glass ball diameter, the more flat surface is obtained. Thanks to Eng. M. Sayyed who told me this before. 

Monday, August 12, 2013

Common problems of thermocouples used in data acquision systems

Common problems of thermocouples used in data acquision systems:

The following are some points to consider in thermocouple connections in data acquision systems. These points may help in troubleshooting.

□ Open channel: always generates random large unreasonable readings. The hardware solution is to place a thermocouple free to ambient or use a jumper (when using a jumper, the reading will be the same as ambient assuming the data acquision card has a built-in Cold Junction Compensation CJC). The software solution is to detect open channels and eliminate their readings 
(software filter)

§  □ Inverted/exchanged poles of thermocouple wire in the male socket plug

§  □ Inverted/exchanged  poles of thermocouple wire in the female socket

§  □ Inverted/exchanged poles of thermocouple at the connection with the data acquision card 

§  □ Thermocouple junction is not established, wires are not welded together, or wires are not twisted on each other.

§ □ Thermocouple tip is touching a large conductive part:  a continuity tester (buzzer) is used to detect such a problem. One probe is connected to the large conductive surface and the other probe is connected to one thermocouple plug pin. If buzzer works then this means that thermocouple junction is not electrically insulated.

§ □ Thermocouple wire is in touch with a conductive part with leaking current

§  □ Thermocouple socket plug has oxidized pins, so they are not conducting

§ □ Non-smooth/unstable thermocouple readings: occur when thermocouple is placed in low thermal capacity stagnant mediums like air, and when placed in a flowing streams of fluids like water or air

§  □ Noise in readings: occur when thermocouples are placed near power sources and conductors with high and/or alternating magnetic fields. This problem appears in the single-ended thermocouple connections.

§    □ Un-calibrated system: the system should be calibrated as overall in a process called on-site calibration. Calibrating thermocouple alone is not useful because it does not take in consideration thermocouple wires, wires connections, and ambient noise.

Thursday, January 31, 2013

Comparison between contact and non-contact tachometers

Contact tachometer:

§  Used when rotor is accessible

§  It’s used in concentric mode. It’s always applied to shaft center. Shaft should have a centering hole, so the rotating element will not slip out

§  It can also be applied in tangential mode if the rotor has an external circular rim, but rpm recalculation must be conducted based on the diameter ratio between rotor and the rotating element

§  No need for rotary encoder

§  Transfers rotational motion of rotor and converts it internally to pulses

§  Measures instantaneous rpm (based on number of divisions of the internal-rotary encoder)

§  It must be parallel to the rotating shaft.

Non-contact (laser) tachometer:

§  Requires too much tuning before each measurement.

§  It’s –in most cases- supplied with a counter feature

§  It’s sensitive to distance between it and rotor.

§  It’s used for indoor use only.

§  Sensitive to reflectivity of rotor.

§  An external encoder is needed. Some models use a reflecting tape for generating pulses.

§  It can be used also with an external emitter (sender), so it will counts pulse receptions.