Heat pipe-based radiator for low grade geothermal energy conversion in domestic space heating

Abstract

A severe technical drawback of geothermal heat pumps (GHPs) is the fact that the nominal operating temperature available for domestic space heating is typically in the region of 50°C. This is 25°C to 40°C less than conventional boiler settings used in hydronic central heating applications. As a result, GHPs are not generally ideal for direct replacement of conventional hydronic central heating systems because of the low relative distribution temperatures unless extreme measures are taken to improve the thermal insulation of the buildings. A preferable option for GHPs is underfloor heating. In terms of retrofitting existing buildings neither the reinsulating nor the underfloor heating options are attractive due to the large added cost and disruptive nature of the installation. As such, very high performance low temperature radiators that are pluggable into existing hydronic central heating systems are a major enabling technology for this sustainable energy source. In this investigation a Simulation Driven Design technique was utilized to develop a novel low water content and high thermal throughput heat pipe-based radiator. The radiator was subsequently fabricated and tested and showed an exceptionally high power density and very fast response time compared with conventional wet radiators.

Numerical modelling of the temperature distribution in a two-phase closed thermosyphon

“…As shown in Figure 1, two thermocouples, labelled as Te 1 and Te 2 were used to monitor the evaporator section and were placed 40mm and 160mm from the bottom. Another thermocouple, labelled as Ta, was positioned at the centre of the adiabatic section, while the condenser section was monitored using five, evenly spaced, thermocouples, labelled as Tc 1 to Tc 5 . These five thermocouples were also used to confirm the non-existence of non-condensable gases (NCGs) within the heat pipes throughout the conducted tests.…”

“…This is different from a wicked heat pipe, where the working fluid is returned from the condenser by capillary forces [1][2][3][4]. Heat pipes have been successfully used for waste heat energy recovery in a vast range of engineering applications, such as heating, ventilation, and air conditioning (HVAC) systems [5], ground source heat pumps [6], water heating systems [7] and electronics thermal management [8]. This is mainly because of their simple structure, special flexibility, high efficiency, good compactness, and excellent reversibility [9][10][11][12].…”

Three-dimensional CFD simulation of geyser boiling in a two-phase closed thermosyphon

“…The vapour then moves to the condenser section, where it changes phase again back to liquid, along the condenser's wall, giving up its latent heat absorbed in the evaporator section. The condensed liquid is then returned to the evaporator due to gravitational or capillary forces, according to the type of heat pipe [8,9]. Two-phase closed thermosyphons have been extensively used in many applications [10]; however, up to now, computational numerical studies on heat pipes, displaying the complex two-phase flow inside the heat pipe, are at an early stage.…”

CFD modelling of a two-phase closed thermosyphon charged with R134a and R404a

“…The vapour then moves to the condenser section where it changes phase again, back to liquid, along the condenser's wall, giving up its latent heat that it absorbed in the evaporator section. The condensed liquid is then returned to the evaporator due to gravitational or capillary forces, according to the type of heat pipe [1][2][3][4][5]. Heat pipes have been successfully used for waste heat energy recovery in a vast range of engineering applications, such as heating, ventilation, and air conditioning (HVAC) systems [2], ground source heat pumps [6], water heating systems [7] and electronics thermal management [8].…”

“…The condensed liquid is then returned to the evaporator due to gravitational or capillary forces, according to the type of heat pipe [1][2][3][4][5]. Heat pipes have been successfully used for waste heat energy recovery in a vast range of engineering applications, such as heating, ventilation, and air conditioning (HVAC) systems [2], ground source heat pumps [6], water heating systems [7] and electronics thermal management [8].The most important characteristics to consider in identifying suitable working fluids are compatibility and wettability with the heat pipe materials, good thermal stability and conductivity, high latent heat of evaporation, high surface tension and low viscosity for both liquid and vapour [9]. In typical thermosyphons, the selection of the working fluid and the shell materials is subject to the working environment and temperature under which the thermosyphon-based system will function.…”