Closed-loop heat pump systems

A closed-loop heat pump system based on hydrides, a metal hydride super heat pump (MHSHP) system, has been investigated at JAERI with the purpose not only to... 

Bose, J. Parker, J. and McQmston, F. (198.S). DesignAIata Manual for Closed-Loop Ground-Coupled Heat Pump Systems. Atlanta American Society of Heating,... 

Most heat transfer systems are of a closed loop design that circulates a heat transfer medium between heaters and heat exchangers. Circulation pumps provide flow and regulating valves are used for process control. The heat transfer medium is usually steam, a high flash point oil, or in process plants flammable liquids and gases. Inherently steam is a safer medium to use and is preferred over other mediums. When steam supplies are unavailable high flash point oils (organic or synthetics) are sometimes used. 

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... 

Use closed-loop systems, which might be installed down-mine , or within settlement basins at a minewater treatment plant. Here the collector fluid circulates in a closed-loop and never comes into contact with the mine water. Likewise, mine water never enters the heat pump or heat exchanger elements. The problem is thus wholly averted, although there are limitations in capacity to closed-loop systems. For larger capacity operations, open systems will be preferred. Furthermore, the exterior of such closed-loop systems may become heavily fouled, necessitating periodic removal for cleaning. 

Drainback (Solar) Systems - A closed-loop solar heating system in which the heat transfer fluid in the collector loop drains into a tank or reservoir whenever the booster pump stops to protect the collector loop from freezing. 

TECs are usually integrated with thermocouples and temperature controllers to form a closed-loop system in which a fixed temperature is maintained on one side of the assembly. In designing a TEC system, there are three key parameters hot-side temperature, desired cold-side temperature, and the total heat load to be pumped over the differential temperature. If a single TEC stage cannot meet the desired temperature differential, then additional stages must be cascaded [28]. 

During plant shutdown periods, where the reactor coolant pumps are stopped, the normal residual heat removal system provides the motive force for the chemical and volume control system purification. Purification flow Ifom the normal residual heat removal system heat exchanger is routed directly through the normal chemical and volume control system purification loop. Boron changes and dissolved gas control are still possible by operating the chemical and volume control system in a semi-closed loop arrangement. 

PHENTX, SUPERPHENIX and PFR are so-called pool reactors, whereas the other three projects are loop reactors. In a pool reactor, the whole primary heat transfer system including main pumps and intermediate heat exchangers is integrated into the reactor vessel (pool), while the loop reactors have parallel primary sodium heat transfer circuits (loops) with the main heat transfer components external to the reactor vessel. The secondary heat transfer system, installed between primary system and water/steam system for safety reasons, is practically identical in both cases. It also consists of three parallel circuits. Live steam conditions and the achievable efficiency are very similar in all plants 500°C, 165 bar, 40%. These are close to the conditions of coal-fired stations. 

To reduce this loss of exergy, systems should be designed to reduce head loss and heat loss to the environment. In the case of a closed reactor coolant loop, work supplied by the pump overcomes the flow resistance in the loop. The flow resistance converts the work supplied into thermal energy which has some exergy. As a result, the lost exergy from pump work in a closed look system is difference between the work added and the exergy of heat at the same temperature. 

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