4 replies to this topic

[Busani]

Good day Everyone

Am an electrical-instrumentation trained all-round individual working for a company (Botswana) that specialises in a wide range of instrumentation/process control activities.We are also involved in laboratory equipment services,repairs and supply. Most of our supplies are imported , which is not a problem because of the sophistication of some equipments and its sometimes cheaper to do so. However my goal is to at least avoid importing even the most basic of laboratory equipments, for example water bath,incubators and ovens.In as much as advanced models are being manufactured nowadays, my research has shown that for cost purposes,local laboratories still utilises the the basic types. (Basic- meaning-ones that utilise a simple digital PID controlled heating element..For this reason, am appealing for help from anyone on the design considerations for me to be able to manufacture what, believe it or not,is going to be the first locally manufactured water bath. Ready made specifications would be appreciated, though i would want to jump any step involved.The following info might help;

-Prototype Volume= 15ltrs

-Controller= PID

-Sensor= Pt100

-Heater = SSR controller immersionn type

-With agitator motor

My main problems are generating a workable diagram for the water bath (blue print) to become the basis of all future version (especially for the vessel/shell itself), is there any international standard regulations/guidelines concerning the venture that i want to undertake.

Please assist in any way possible and i hope i was clear with my request.Thanks in advance

Busani

[kkala]

My main problems are generating a workable diagram for the water bath (blue print) to become the basis of all future version (especially for the vessel/shell itself), is there any international standard regulations/guidelines concerning the venture that i want to undertake.
Does this "blue print" concerns the "integrated circuit" of the water bath heating and its controls (something like PC motherboard)? If so, I believe an electronic specialist could advise on criteria and regulations.
A lab specialist (probably Chemical Engineer, but mainly Chemist) could advise on dimensions and special requirements, which seem to be dependent on the intended use, as you can see by googling "lab water bath". A variety of water baths can be seen there, of capacities from 5 to 19.5 liters. Contrary to my experience as student, very few are still made of glass (or of transparent plastic). Plastic or metals (aluminium, stainless steel) seem to be the common material now.
Not having specific lab experience, I cannot offer some useful information. I wish you would succeed in making this piece of lab equipment.

Edited by kkala, 10 June 2011 - 03:04 PM.

[Adam_K]

As kkala said, it would be best to ask an electronic specialist on the circuitry and control philosophy behind the water bath. You could also try contacting vendors for general design information and possibly schematics.

In terms of general design ideas, I might be able to help you out - I'm a chemical engineering and science (chemistry major) student with plenty of analytical lab experience. I also helped develop the quality control program for the Victorian Desalination Project, part of which involved selecting the correct laboratory equipment for the site. For a specific design, I'd really need to know the purpose of the bath, but here are some general considerations:

Temperature range and accuracy: the temperature range is generally from 0 to 100 degrees, with accuracy up to 1/10 of a degree Celcius. I would recommend digital control as it's user friendly, though analogue is likely cheaper - in that case you'd probably want coarse and fine temperature adjustment.

Size, shape, materials: kkala was completely right that transparent glass is uncommon, and that metal and plastic are more useful. The casing should be made of a robust material, cost considerations can come in here as well as the maximum operating temperature; plastic is fine so long as it is durable, though metal is more common. You would then need an insulator between the casing and internal section (the actual water bath), which is generally made of metal. Ensure you have enough insulation to prevent the external surfaces of the bath from getting hot to prevent user injury.
The shape becomes important in determining the load on the heater, the main consideration being the loss of heat from the water/air surface; a larger area and smaller depth will allow for a greater number of vessels to be heated, but increases the energy load. A rectangular face is common. Also consider a cover - nearly fully closed (with some allowance for steam release) and partial closure with free access to the sample vessel for a reduced energy load.

Heating system - you've got the right idea by using a heater/agitator combination, just make sure that the heater will be able to provide excess energy above the maximum operating temperature (say 10% above). Also, a few simple fluid mechanics calculations and later testing various locations within the bath would determine the presence of dead zones, creating hot and cold spots. All you want here is a uniform temperature system and the ability to quickly reach the desired temperature (5-10 mins), without excessive agitation.

Control system - I assume you have much more knowledge on the control of heating systems, so you'd understand the basic type of controller and tuning constants required. The main consideration is controlling temperature to within the desired accuracy and precision, as the external temperature shouldn't change much. I'd also recommend a display of both the set temperature and actual temperature.

Good luck!

Adam

[Busani]

As kkala said, it would be best to ask an electronic specialist on the circuitry and control philosophy behind the water bath. You could also try contacting vendors for general design information and possibly schematics.

In terms of general design ideas, I might be able to help you out - I'm a chemical engineering and science (chemistry major) student with plenty of analytical lab experience. I also helped develop the quality control program for the Victorian Desalination Project, part of which involved selecting the correct laboratory equipment for the site. For a specific design, I'd really need to know the purpose of the bath, but here are some general considerations:

Temperature range and accuracy: the temperature range is generally from 0 to 100 degrees, with accuracy up to 1/10 of a degree Celcius. I would recommend digital control as it's user friendly, though analogue is likely cheaper - in that case you'd probably want coarse and fine temperature adjustment.

Size, shape, materials: kkala was completely right that transparent glass is uncommon, and that metal and plastic are more useful. The casing should be made of a robust material, cost considerations can come in here as well as the maximum operating temperature; plastic is fine so long as it is durable, though metal is more common. You would then need an insulator between the casing and internal section (the actual water bath), which is generally made of metal. Ensure you have enough insulation to prevent the external surfaces of the bath from getting hot to prevent user injury.
The shape becomes important in determining the load on the heater, the main consideration being the loss of heat from the water/air surface; a larger area and smaller depth will allow for a greater number of vessels to be heated, but increases the energy load. A rectangular face is common. Also consider a cover - nearly fully closed (with some allowance for steam release) and partial closure with free access to the sample vessel for a reduced energy load.

Heating system - you've got the right idea by using a heater/agitator combination, just make sure that the heater will be able to provide excess energy above the maximum operating temperature (say 10% above). Also, a few simple fluid mechanics calculations and later testing various locations within the bath would determine the presence of dead zones, creating hot and cold spots. All you want here is a uniform temperature system and the ability to quickly reach the desired temperature (5-10 mins), without excessive agitation.

Control system - I assume you have much more knowledge on the control of heating systems, so you'd understand the basic type of controller and tuning constants required. The main consideration is controlling temperature to within the desired accuracy and precision, as the external temperature shouldn't change much. I'd also recommend a display of both the set temperature and actual temperature.

Good luck!

Adam

Hie Adam;

Thanks very much for the information. I apologise for late reply and the fact that i was not really specific in my information request. Am glad and comforted because some of what you have mentioned is what i had in mind but due to lack of design experience i thought there must be a better track..The Control system wont be a problem to me as i have instrumentation expereince and has configured a great deal of 2 value-digital display controllers and therefore i had these in mind. I have also repaired/refurbished,calibrated,validated (with chamber temperature mapping etc) a number of temperature controlled lab instruments (water baths,incubators,ovens---as well as autoclave) and due to their "genaral simplicity" (excl. autoclaves in this case), i was motivated to design and manufacture these and thus a desk top water bath became my starting point.. Once again thanks Adam for the information,esp the surface area/depth ratio amongst everything,now i know am in the right track and the day that i manage to see the dream come true, you will know about it.


Busani

[cnaren]

Hi Busani :

Here is an old patent which may be useful as a starting reference.
Good Luck.

Naren

My main problems are generating a workable diagram for the water bath (blue print) to become the basis of all future version (especially for the vessel/shell itself), is there any international standard regulations/guidelines concerning the venture that i want to undertake.

Please assist in any way possible and i hope i was clear with my request.Thanks in advance

Busani

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