Must be environment friendly. Among several available refrigerants the most promising one are ammonia, methanol, water which have relatively high latent heat values and also presents good performances. The most commonly used pairs are zeolite- water, zeolite-methanol, silica gel- water, carbon — methanol and activated carbon — ammonia. Also zeolite crystals are eternal i. The refrigeration apparatus consists of two chambers, a pressure gauge, a refrigerating chamber, a vacuum pump which is run by pedaling , valves and connecting pipes.
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Pedal powered refrigerator 1. VIth Sem, Mechanical - 1 1. Nishant Prakash 2. Shubham Shukla 3. Abhishek Raj 4.
Pramod Kumar Team Guide :- Dr. REFRIGERATOR- A refrigerator colloquially fridge is a popular 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 the external environment so that the inside of fridge is cooled to a temperature below the ambient temperature of the room.
The lower temperature reduces the reproduction rate of bacteria, so the refrigerator reduces the rate of spoilage. Terms Used Zeolite : These are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts.
These occur naturally but are also produced industrially on a large scale. Adsorption : Adsorption is the adhesion of atoms, ions, or dissolved solid to a surface. This process creates a film of the Adsorbate on the surface of adsorbent.
It is a surface based process. It is driven by cohesive forces such as Van-der-wall forces, hydrogen bonding, electrostatic forces, etc. There are two types of Adsorption processes- 1. Physical Adsorption - It is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption.
In physical adsorption, the individuality of the adsorbate and the adsorbent are preserved. Chemical Adsorption - Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbant surface.
Adsorption is nearly always an exothermic process. Desorption : It is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption that is, either adsorption or absorption.
Desorption is nearly always an Endothermic Process. Adsorbate : It is the material that has been or is capable of being adsorbed. The Adsorbate is used as the refrigerant for our purpose.
Refrigerant : A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again.
Adsorbent : It is the material that has or is capable of adsorbing the Adsorbate. Drawbacks of the conventional Refrigeration Systems : This system is popular and advantageous due to its high coefficient of performance, small size and low weight but the system comes with certain disadvantages :- 1.
High Energy consumption as the compressor compresses the vapour in the cycle. Dependency on the power grid. FACT : According to the latest NASA investigation, the holes in the ozonosphere over the two poles currently occupy approximately 28,, km2, up from approximately 24,, km2 in Adsorption Cycle : A basic adsorption cycle consists of four steps : 1. Heating and pressurization 2.
Desorption and condensation 3. Cooling and depressurization 4. Adsorption and evaporation 8. Refrigerants and Adsorbents : There are several combinations of Refrigerants and Adsorbents available and each possess certain merits and demerits thus resulting in varying performances.
Choice of adsorbent : While selecting adsorbent, the most important features that must be taken care of are : 1. High adsorption and desorption capacity thus improving cooling characteristics. Good thermal conductivity, to shorten cycle time 4.
Nontoxic and non-corrosive 5. Chemically and physically compatible with chosen refrigerant 6. Must be cost effective and should be available in plenty. The most commonly used adsorbents are activated carbon, zeolite and silica gel. Choice of Refrigerant: The refrigerants must satisfy the following requisites for an effective performance : 1.
For better adsorption, molecular size should be small. High latent heat per unit volume. High thermal conductivity. Good thermal stability. Low viscosity. Must be environment friendly. Among several available refrigerants the most promising one are ammonia, methanol, water which have relatively high latent heat values and also presents good performances.
The most commonly used pairs are zeolite- water, zeolite-methanol, silica gel- water, carbon — methanol and activated carbon — ammonia. Also zeolite crystals are eternal i. This is also known as the Adsorber.
It adsorbs the vapor coming from the evaporator chamber. It consists of the evaporator chamber during the adsorption stage and the condenser during the desorption stage. Refrigerator Body : The Refrigerator body is a thermally insulated compartment. The evaporator is located at the top inside the cooling chamber.
Warmer air around the evaporator stays in this upper region. The air only cools down in the cooling phase, when it falls to the bottom of the cooling chamber. Simplified diagram of apparatus Working of the Refrigeration Apparatus : The system operates in two stages- 1. The Adsorption Stage : In the adsorption process, the valves V2 and V3 are opened, and the vacuum pump is used to extract all the air from the Zeolite cylinder and create complete vacuum inside it.
The valve V2 is then closed and the evaporator is then connected to the vacuum pump by opening valves V1 and V3. The pressure inside the evaporator is lowered such that Adsorbate starts boiling at room temperature. The valve V3 is then closed and the Zeolite chamber and evaporator are connected by opening the valves V1 and V2. As a result of heat loss from the refrigerating chamber, its temperature starts to fall.
The Desorption Stage : As soon as the Zeolite becomes saturated and is incapable of adsorbing more adsorbate, the Zeolite container is heated such that the Zeolite loses adsorbate and it gets collected in the condenser. The heat may be provided by using Solar energy making it completely eco-friendly and very less dependent on electricity.
Regeneration of zeolite occurs by heating the zeolite container opening the valves V1 and V2 such that the water lost by the zeolite reaches back to the condenser. Adsorption and Desorption Phenomenon using water as Adsorbate Hence, solar energy can be utilized for regeneration. Results — 1. After minutes of pedaling, the valve connecting the Evaporator chamber and the Zeolite Chamber are opened. The refrigeration effect could be produced for about a day.
Using a twin bed system, the theoretical COP increases to about 0. Advantages of Zeolite Adsorption Refrigeration Systems : 1. The risk of global warming and ozone depletion is completely eliminated. This offers increased mobility and independency from power grid using solar energy for regeneration. Reduced Cost — Low initial cost as well as zero running cost.
Inexpensive and easy to manufacture, since simple equipments and components are used. Applications of Zeolite Adsorption Refrigeration systems : 1. Can be used in rural areas where Electricity Supply is scarce or not available. Can be used in the medical field for storage of vaccines and medicines.
Can be used by mobile ice-cream sellers instead of conventional ice-boxes they use. This technology suits for the transport of food and other perishables.
Can be coupled with crankshaft of cars and the required heat for regeneration can be obtained from the exhaust gases of the IC engine. References : 1. Omisanya, C. Folayan, S. Aku and S. References continued : 5. Understanding Pedal Power on www.
Pedal-Powered (Vacuum) Zeolite Refrigerator
The drop in methanol vapor pressure causes methanol to boil. To do this, methanol must capture the heat of a system the inside of the refrigerator. After only about 10 minutes of pedaling, the valve to the vacuum pump can be turned off, and the line of zeolite vessel open. The zeolite then absorbs the vapor produced by the boiling of the methanol and for the liquid methanol to remain in equilibrium with the vapor phase; It should continue boiling for up to one day. In general, constant temperatures of Celsius can be reached for 1 day with only 10min pedaling. Now this is a real way to freshen up for cheap. Even ice cubes can be made and one advantage of this system is that the hotter it is outside, the colder it can be generated.
Pedal-Powered (Vacuum) Zeolite Refrigerator
Victor Papanek described this in his book Design for the real world: Quote: At Cal Arts one of my graduate students, Jim Hennessey, and I were more concerned as to how Third World people could keep part of their perishables fresh for a week or two, starting now. We developed a hand-cranked, modular produce cooler. There is a baseboard unit that includes a tyre pump, a heat exchanger, a pump, pump valves, and a metering valve, as well as a hand crank. This is surmounted by a 50 cm. It forces hot pressurised air through a heat exchange which returns the air to near-ambient temperature. The air is then metered back into the cooler, where, as it expands, it produces a temperature drop. Other modular cubes can be added.