Indirect Refrigeration

Aqueous solutions of propylene glycol display excellent antifree2e properties and are therefore valuable as low temperature heat-transfer fluids. For apphcations involving indirect food contact, heat-transfer fluids formulated with the USP grade product are preferred, since there could be inadvertent contact with a food product. These fluids are commonly used in the brewing and dairy industries as well as in refrigerated display cases in retail grocery stores. 

Indirect refrigeration systems are more prevalent in the chemical industiy than in the food industiy, commercial refrigeration, or comfort air-conditioning. This is even more evident in the cases where a large amount of heat is to be removed or where a low temperature level is involved. Advantage of an indirect system is centrahzation of refrigeration equipment, which is specially important for relocation of refrigeration equipment in a nonhazardous area, both for people and equipment. 

The dewpoint hygrometer detects the dewpoint temperature of air by cooling a surface in contact with the air to the dewpoint temperature. There are several ways to achieve cooling and to observe the formation of condensate on the surface. The early dewpoint hygirometers were cooled simply by applying the vaporization of ether or some other suitable liquid. Condensate formation on the surface was determined visually. Other cooling methods are to use a refrigerant flow in direct or indirect contact with the back of the surface, or to use electricity with a (thermoelectric) Peltier element. 

Cooling, indirect A cooling system in which the medium to be cooled is affected b> another medium situated between it and the refrigerating apparatus. 

Where a flooded coil is located in a liquid tank, the refrigerant level will be within the tank, making it difficult to position the level control. In such cases, a gas trap or siphon can be formed in the lower balance pipe to give an indirect level in the float chamber. Siphons or traps can also be arranged to contain a non-voIatile fluid such as oil, so that the balance pipes remain free from frost. 

This is a process mainly used in power plants for separation of solute from liquid by crystallizing the solvent. Either direct refrigeration, or indirect refrigeration can be used. The process removal efficiency is over 99.5%. 

Closed-loop systems. In closed-loop systems, groundwater abstraction is not required. Such systems can be used in poorly permeable formations, such as hard rocks or clays. Closed-loop systems may be direct circulation where the heat pump refrigerant is pumped through a closed loop installed in the ground. More frequently they utilize indirect circulation. Here, water, usually with added anti-freeze (e.g., ethylene glycol or ethanol), is circulated through a closed polyethene hose system (the collector... 

Placing the entire equipment inside the refrigerator gives only a relative advantage, because the current itself creates a rise in temperature. At low temperatures, however, conductivity is smaller, less current passes, and as an indirect result, less evaporation occurs. In practice, working at room temperature is the simplest, and the runs are longer because adsorption of protein to paper is lower at higher temperatures. Even in the oven at 36° C perfect runs can be made (Fig. 6). 

Equipment Mode 1 (Mechanical refrigeration) Mode 2 (Vapor migration based indirect free cooling) Mode 3 (Indirect free cooling by the use of heat exchanger) Mode 4 (Direct free cooling with full filtering)... 

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