TEMPERATURE CONTROLLER (WEEK 5)

Temperature controller

To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or thermal electric cooler as input. It compares the actual temperature to the desired control temperature, or set point, and provides an output to a control element. The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller.

This circuit can cool your heat generating electronic devices by operating a DC fan when the temperature in its vicinity increases above the preset level. Its operation is fully automatic and turns off when the temperature returns normal. It uses a small 12V DC brush fewer fans used in computers

When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor of fan. Also, the brightness of the LED will be proportional to the speed of the fan.

1.3 On/Off Control

An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the set point. For heating control, the output is on when the temperature is below the set point, and off above set point. Since the temperature crosses the set point to change the output state, the process temperature will be cycling continually, going from below set point to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an on-off differential, or “hysteresis,” is added to the controller operations. This differential requires that the temperature exceed set point by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or making fast, continual switches if the cycling above and below the set point occurs very rapidly. On-off control is usually used where a precise control is not necessary, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm. One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.

THERMOELECTRIC COOLING (WEEK 4)

Thermoelectric Cooling

Thermoelectric cooling uses the Peltier effect to create a heat flux between the junctions of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). They can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.^[1]

This technology is far less commonly applied to refrigeration than vapor-compression refrigeration is. The main advantages of a Peltier cooler (compared to a vapor-compression refrigerator) are its lack of moving parts or circulating liquid, and its small size and flexible shape (form factor). Its main disadvantage is that it cannot simultaneously have low cost and high power efficiency. Many researchers and companies are trying to develop Peltier coolers that are both cheap and efficient.

A Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a voltage is applied across the device, and as a result, a difference in temperature will build up between the two sides.^[2] When operated as a generator, one side of the device is heated to a temperature greater than the other side, and as a result, a difference in voltage will build up between the two sides. However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice-versa, due to different design and packaging requirements.

Thermoelectric junctions are generally only around 5–10% as efficient as the ideal refrigerator compared with 40–60% achieved by conventional compression cycle systems. Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature Peltier (thermoelectric) cooler performance is a function of ambient temperature, hot and cold side heat exchanger (heat sink) performance, thermal load, Peltier module (thermopile) geometry, and Peltier electrical parameters.

LITERATURE REVIEW (WEEK 3)

In 1834 Jean Peltier noted that when an electrical current is applied across the junction of two dissimilar metals, heat is removed from one of the metals and transferred to the other. This is the basis of thermoelectric refrigeration. Thermoelectric modules are constructed from a series of tiny metal cubes of dissimilar exotic metals which are physically bonded together and connected electrically. When electrical current passes through the cube junctions, heat is transferred from one metal to the other. Solid-state thermoelectric modules are capable of transferring large quantities of heat when connected to a heat absorbing device on one side and a heat dissipating device on the other. The Koolatron's internal aluminium cold plate fins absorb heat from the contents, (food and beverages), and the thermoelectric modules transfer it to heat dissipating fins under the control panel. Here, a small fan helps to disperse the heat into the air. The system is totally environmentally friendly and contains no hazardous gases, nor pipes nor coils and no compressor. The only moving part is the small 12-volt fan. Thermoelectric modules are too expensive for normal domestic and commercial applications which run only on regular household current. They are ideally suited to recreational applications because they are lightweight, compact, and insensitive to motion or tilting, have no moving parts, and can operate directly from 12-volt batteries.

Jean Peltier

Tom Mancini 

If want to do is heat or cool, using solar energy this way is probably more efficient and certainly cheaper than converting it first into electricity. "That approach ought to be comparable to photovoltaics, or a little better. Traditionally solar-powered refrigerators and vaccine coolers use a combination of solar panels and lead batteries to store energy for cloudy days and at night in the absence of sunlight to keep their contents cool. These fridges are expensive and require heavy lead-acid batteries which tend to deteriorate, especially in hot climates, or are misused for other purposes.[3][4] In addition, the batteries require maintenance, must be replaced approximately every three years, and must be disposed of as hazardous wastes possibly resulting in lead pollution.[3] These problems and the resulting higher costs have been an obstacle for the use of solar powered refrigerators in developing areas.

The use of solar energy to power refrigeration strives to minimize the negative impacts refrigerators have on the environment.^[1][2] Fishermen in the village of Maruata, which is located on the Mexican Pacific coast, have no electricity. But for the past 16 years they have been able to store their fish on ice: Seven ice makers, powered by nothing but the scorching sun, churn out a half ton of ice every day.

Solar refrigeration can also be inexpensive and it would give the electric grid much-needed relief. Electricity demand peaks on hot summer days—150 gigawatts more in summer than winter in the U.S. (A gigawatt equals on billion watts.) That's almost 1.5 times the generating capacity of all the coal-fired power plants west of the Mississippi River. Further, solar is plentiful. The solar energy hitting 54 square feet (five square meters) of land each year is the equivalent of all the electricity used by one American household, according to data from the National Renewable Energy Laboratory and Energy Information Administration, both part of the U.S. Department of Energy.

 Adam Grosser

More than a billion people lack access to electricity and refrigeration, which means they also lack access to important vaccines that need to be kept cool. Nonprofits are pouring millions into developing vaccines that don't need refrigeration, but tech venture capitalist Adam Grosser has a different idea: change the fridge.

Working with a thermodynamics team at Stanford, Grosser built a thermos-sized device that contains a refrigerant that's triggered when the device is heated and left to cool. It then acts like a powerful cold pack, turning anything from a jug to a hole in the ground into a twenty-four-hour minifridge. At roughly fifty dollars apiece, Grosser's device could potentially bring people in the developing world high-maintenance medicines -- and the simple pleasure of a cold drink on a hot day.

INTRODUCTION (WEEK 2)

Refrigerator

A refrigerator (colloquially fridge) is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Cooling is a popular food storage technique in developed countries and works by decreasing or even arresting the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs.

A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F).[1] A similar device which maintains a temperature below the freezing point of water is called a freezer. The refrigerator is a relatively modern invention among kitchen appliances. It replaced the icebox, which had been a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an icebox.

Freezer units are used in households and in industry and commerce. Most household freezers maintain temperatures from -10 to 0 °F (-23 to -18 °C), although some freezer-only units can achieve −30 °F (−34 °C), and lower. Refrigerators generally do not achieve lower than -10 °F (-23 °C), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests (resembling upright units laid on their backs). Many upright modern freezers come with an ice dispenser built into their door

Some refrigerators are now divided into four zones to store different types of food:

−18 °C (−0 °F)	Freezer
0 °C (32 °F)	Meats
5 °C (41 °F)	Refrigerator
10 °C (50 °F)	Vegetables

Table 1: Temperature

The capacity of a refrigerator is measured in either litres or cubic feet. Typically the volume of a combined refrigerator-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 liters (4.94 cubic feet) for the refrigerator, although these values are highly variable.

Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37 to 41 °F)[1] is ideal for the refrigerator compartment and −18 °C (−0 °F) for the freezer. Some refrigerators are required to be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area such as a garage.

European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers.

Temperature	Time Storage
min temperature = −6 °C (21 °F).	Maximum storage time for (pre frozen) food is 1 week
min temperature = −12 °C (10 °F).	Maximum storage time for (pre frozen) food is 1 month
min temperature = −18 °C (−0 °F).	Maximum storage time for (pre frozen) food is between 3 and 12 months depending on type (meat, vegetables, fish, etc

Table 2: Temperature And Time 

WEEK 1

Final year project briefing

  

Briefing about final year project. Its take 1 hours to explain to find a supervisor and title final year project.

In 1 week i choose supervisor Madam Zurin Zuraida Abu Baharin.

And project that i choose its potable mini fridge

PORTABLE MINI FRIDGE 

Ò  To provides facilities for people who love outdoor activities

Ò  To implement it as a backup for house refrigerator

Ò  To build mini fridge that could possibly be easily placed under desk in any other area

Ò  To use transportations mini fridge for children some favorite beverages

Submit the title FYP and supervisor before 10.8.2012