Conclusão e auto avaliação

A paz do senhor Jesus cristo a todos, a conclusão que fica deste trabalho exposto para vocês no blog é que ainda temos muito a aprender e pesquisar para conserguir as respostas para as muitas perguntas que cercam esse assunto de geladeira movida a energia solar ou qualquer outro tipo de energia gerado em determinados processos industriais. O tema é amplo e bacana e vale apena ser estudo pelo menos conhecido.
Sobre minha auto avaliação, eu considero que a nota justa seria 8 em 10 pontos devido ao desafio exposto e por eu ter tido a coragem de querer e conseguir passar pelo menos uma pequena idéia do assunto. Não merço 10 porque cometi algumas penalizações como por exemplo teve dias que não postei no blog.
Fiquem com Deus que o senhor continue nos abençoando nessa caminhada.

nova data da apresentação

Galera, a apresentação do lactea passou para semana (7/12) que não faltem a minha apresentação. OK!
Um abraço.

sobre apresentação

Galera espero todos vocês amanhã. Um abraço.

Estudo secundário sobre bomba de calor

Graça e Paz do senhor JESUS CRISTO a todos.
Vou postar um estudo adicional aqui a respeito sobre bomba de calor do livro do Çengel. Ele está em inglês, mas dá para cada um acompanhar, isso é mais para fins de curiosidade, pois a bomba de calor é um ciclo de refrigeração operando de modo reverso.
Um abraço.

HEAT PUMP SYSTEMS

Heat pumps are generally more expensive to purchase and install than other heating systems, but they save money in the long run in some areas because they lower the heating bills. Despite their relatively higher initial costs, the popularity of heat pumps is increasing. About one-third of all single-family
homes built in the United States in the last decade are heated by heat pumps.
The most common energy source for heat pumps is atmospheric air (air-to-air systems), although water and soil are also used. The major problem with air-source systems is  frosting, which occurs in humid climates when the temperature falls below 2 to 5°C. The frost accumulation on the evaporator coils is highly undesirable since it seriously disrupts heat transfer. The coils can be defrosted, however, by reversing the heat pump cycle (running it as an air conditioner). This results in a reduction in the efficiency of the
system. Water-source systems usually use well water from depths of up to 80 m in the temperature range of 5 to 18°C, and they do not have a frosting problem. They typically have higher COPs but are more complex and require easy access to a large body of water such as underground water.
Ground-source systems are also rather involved since they require long tubing placed deep in the ground where the soil temperature is relatively constant. The COP of heat pumps usually ranges between 1.5 and 4, depending on the particular system used and the temperature of the source. A new class
of recently developed heat pumps that use variable-speed electric motor drives are at least twice as energy efficient as their predecessors.
Both the capacity and the efficiency of a heat pump fall significantly at low temperatures. Therefore, most air-source heat pumps require a supplementary heating system such as electric resistance heaters or an oil or gas furnace. Since water and soil temperatures do not fluctuate much, supplementary heating may not be required for water-source or ground-source systems. However, the heat pump system must be large enough to meet the maximum heating load.
Heat pumps and air conditioners have the same mechanical components.
Therefore, it is not economical to have two separate systems to meet the heating and cooling requirements of a building. One system can be used as a heat pump in winter and an air conditioner in summer. This is accom-
plished by adding a reversing valve to the cycle, as shown in Fig. 11–9( mostrada no livro deste autor no capítulo 11). Asa result of this modification, the condenser of the heat pump (located indoors) functions as the evaporator of the air conditioner in summer. Also, the evaporator of the heat pump (located outdoors) serves as the condenser of the air conditioner. This feature increases the competitiveness of the heat pump. Such dual-purpose units are commonly used in motels.
Heat pumps are most competitive in areas that have a large cooling load during the cooling season and a relatively small heating load during the heating season, such as in the southern parts of the United States. In these areas, the heat pump can meet the entire cooling and heating needs of residential or commercial buildings. The heat pump is least competitive in areas where the heating load is very large and the cooling load is small, such as in the northern parts of the United States.

Dica para estudo

Graça e paz do senhor Jesus cristo o nosso salvador para todos.
Pessoal eu sugiro que entrem nesses sites abaixo para vocês entenderem melhor a respeito da geladeira solar que mostrarei na apresentação, pois como é um tema em estudo, cheguei na conclusão não ser legal postar informações a respeito. Portanto não postarei nada sobre o estudo mas darei dicas de estudo como estou fazendo agora. Mas podem ficar tranquilos que vou fazer uma explicação no dia da apresentação.

http://pt.wikipedia.org/wiki/Refrigera%C3%A7%C3%A3o_por_absor%C3%A7%C3%A3o
http://www.fem.unicamp.br/~em672/Absorcao_Alan_Andre.html

Entendo mais sobre refrigeração

A Graça e paz do senhor Jesus cristo.
Na última postagem que efetuei no blog, expus um ciclo termodinâmico teórico que se encontra no livro de termodinâmica do Çengel.
Mas para melhor entendimento sobre como cada componente age na prática, quero recomendar a leitura do livro: Refrigeração e ar condicionado-Stoecker & Jones.

Por exemplo o dispositivo de expansão, na verdade é uma válvula de Expansão que pode ser: tubo capilar, válvula de expansão termostática, válvulas de bóia e entre outras. Sendo que cada uma é importante em determinada aplicação.

O Condensador e o evaporador são trocadores de calor, que podem ser de condensador carçaca tubos, condensador resfriado a ar. No caso do evaporador de expansão direta, entre outros.
No caso do compressor tem muitos fatores a serem considerados como espaço nocivo, rendimento de espaço nocivo, entre tantas coisas que não tem como eu abordar aqui.

Portanto sugiro a leitura desses itens e também da parte que fala de refrigeração por absorção.

diagramas do estudo de refrigeração

diagramas do estudo de refrigeração do livro do cengel poder ser visto no capítulo 11, nome é 
thermodynamics an engineering approach, 5ª edição, çengel.

Estudos sobre refrigeração

Graça e paz do senhor Jesus Cristo a todos do blog.

Galera vou postar um estudo sobre o assunto de refrigeração que está no livro de termodinâmica do Cengel, o problema que ele está em inglês, mas dá pra acompanhar. Um abraço e até mais.

11–3 THE IDEAL VAPOR-COMPRESSION REFRIGERATION CYCLE

Many of the impracticalities associated with the reversed Carnot cycle can be eliminated by vaporizing the refrigerant completely before it is compressed and by replacing the turbine with a throttling device, such as an
expansion valve or capillary tube. The cycle that results is called the  ideal vapor-compression refrigeration cycle, and it is shown schematically and on a T-s diagram in Fig. 11–3. The vapor-compression refrigeration cycle is the most widely used cycle for refrigerators, air-conditioning systems, and heat pumps. It consists of four processes:

1-2 Isentropic compression in a compressor
2-3 Constant-pressure heat rejection in a condenser
3-4 Throttling in an expansion device
4-1 Constant-pressure heat absorption in an evaporator

In an ideal vapor-compression refrigeration cycle, the refrigerant enters the compressor at state 1 as saturated vapor and is compressed isentropically to the condenser pressure. The temperature of the refrigerant  increases during this isentropic compression process to well above the temperature of the surrounding medium. The refrigerant then enters the condenser as superheated vapor at state 2 and leaves as saturated liquid at state 3 as a result of heat rejection to the surroundings. The temperature of the refrigerant at this state
is still above the temperature of the surroundings.
The saturated liquid refrigerant at state 3 is throttled to the evaporator pressure by passing it through an expansion valve or capillary tube. The temperature of the refrigerant drops below the temperature of the refrigerated space during this process. The refrigerant enters the evaporator at state 4 as a low-quality saturated mixture, and it completely evaporates by absorbing heat from the refrigerated space. The refrigerant leaves the evaporator as saturated vapor and reenters the compressor, completing the cycle.
In a household refrigerator, the tubes in the freezer compartment where heat is absorbed by the refrigerant serves as the evaporator. The coils behind the refrigerator, where heat is dissipated to the kitchen air, serve as the condenser (Fig. 11–4).
Remember that the area under the process curve on a  T-s diagram represents the heat transfer for internally reversible processes. The area under the process curve 4-1 represents the heat absorbed by the refrigerant in the evaporator, and the area under the process curve 2-3 represents the heat rejected in
the condenser. A rule of thumb is that the COP improves by 2 to 4 percent for each °C the evaporating temperature is raised or the condensing temperature is lowered.
Another diagram frequently used in the analysis of vapor-compression refrigeration cycles is the P-h diagram, as shown in Fig. 11–5. On this diagram, three of the four processes appear as straight lines, and the heat transfer in the condenser and the evaporator is proportional to the lengths of the
corresponding process curves.
Notice that unlike the ideal cycles discussed before, the ideal vapor-compression refrigeration cycle is not an internally reversible cycle since it involves an irreversible (throttling) process. This process is maintained in
the cycle to make it a more realistic model for the actual vapor-compression refrigeration cycle. If the throttling device were replaced by an isentropic turbine, the refrigerant would enter the evaporator at state 4' instead of state 4. As a result, the refrigeration capacity would increase (by the area under process curve 4'-4 in Fig. 11–3) and the net work input would decrease (by the amount of work output of the turbine). Replacing the expansion valve by a turbine is not practical, however, since the added benefits cannot justify the added cost and complexity.
All four components associated with the vapor-compression refrigeration cycle are steady-flow devices, and thus all four processes that make up the cycle can be analyzed as steady-flow processes. The kinetic and potential energy changes of the refrigerant are usually small relative to the work and heat transfer terms, and therefore they can be neglected. Then the steady-flow energy equation on a unit–mass basis reduces to
(qin - qout) + (win - wout)= he - hi

The condenser and the evaporator do not involve any work, and the compressor can be approximated as adiabatic. Then the COPs of refrigerators and heat pumps operating on the vapor-compression refrigeration cycle can be expressed as
COP(R) = qL/win = (h1-h4)/(h2-h1)
COP(hp)= qH/win =(h2-h3)/(h2-h1)
where a h1 = hg and h3= hf for the ideal case.
Vapor-compression refrigeration dates back to 1834 when the Englishman Jacob Perkins received a patent for a closed-cycle ice machine using ether or other volatile fluids as refrigerants. A working model of this machine was built, but it was never produced commercially. In 1850, Alexander Twining
began to design and build vapor-compression ice machines using ethyl ether, which is a commercially used refrigerant in vapor-compression systems. Initially, vapor-compression refrigeration systems were large and were mainly used for ice making, brewing, and cold storage. They lacked automatic controls and were steam-engine driven. In the 1890s, electric motor-driven smaller machines equipped with automatic controls started to replace the older units, and refrigeration systems began to appear in butcher shops and households. By 1930, the continued improvements made it possible to have vapor-compression refrigeration systems that were relatively efficient, reliable, small, and inexpensive.

Aviso importante

Graça e paz do senhor Jesus Cristo para todos.
Galera infelizmente não vai ter postagem essa semana, o motivo é porque não estou conseguindo acessar as informações do meu arquivo de memória, mas assim que resolvido o problema, volto a postar para vocês.
Até mais.

Uma breve apresentação sobre o tema refrigeração

Boa tarde a todos e não se esqueçam que Jesus cristo ama vocês!

Refrigeração é retirar calor produzido por uma substância ou um espaço proporcionando uma temperatura inferior à da vizinha(meio).

Há cinco tipos de sistemas de refrigeração, a saber:
  1-Sistemas de compressão de vapor
  2-Sistemas de absorção(caso da geladeira solar)
  3-Sistemas de compressão de gás
  4-Sistemas termoelétricos
  5-Sistemas de resfriamento evaporativo

Os sistemas de nº1 são os mais utilizados.
Os sistemas de nº2 são vantajosos quando se dispõe de uma fonte de calor baixo custo (ex.: energia solar).
Os sistemas de nº3 são utilizados para liquefação de gases.
Os sistemas de nº4 possuem baixa eficiência não utilizam fluidos refrigerantes e não possuem partes móveis.
Os sistemas de nº5 possuem baixo consumo de energia.