Elsevier

Applied Thermal Engineering

Volume 124, September 2017, Pages 521-524
Applied Thermal Engineering

Adsorptive transformation of ambient heat: A new cycle

https://doi.org/10.1016/j.applthermaleng.2017.06.051Get rights and content

Highlights

  • A new adsorptive cycle for upgrading the ambient heat is suggested and analyzed.

  • Regeneration of the adsorbent is performed by dropping the vapour pressure over it.

  • The pressure drop is ensured by low ambient air temperature.

  • The regeneration is easier at colder ambient.

  • The new cycle “Heat from Cold” can be interesting for cold countries and the Arctic.

Abstract

In this communication, a new adsorptive cycle for upgrading the ambient heat is suggested and briefly analyzed. The main feature of this cycle is that regeneration of adsorbent is performed by dropping the vapour pressure over adsorbent at a constant temperature, rather than by adsorbent heating as usual. This pressure drop is ensured by low ambient air temperature and does not need the supply of energy that has commercial value. It is essential that the regeneration is easier at colder ambient. Since the useful heat that gains commercial value is obtained by means of a low ambient temperature, the new approach is called “Heat from Cold” (HeCol). It can be interesting for countries with cold climate, and especially for the Arctic zone.

Introduction

The greenhouse gases emission and global warming are one of the most important environmental concerns [1]. The world community has realized the gravity of these problems and taken initiatives to alleviate or reverse this situation. Fulfilment of these initiatives requires the replacement of fossil fuels with renewable energy sources (the Sun, wind, ambient heat – natural water basins, soil, air, etc.). These new heat sources have significantly lower temperature than that achieved by burning fossil fuels which opens a niche for applying adsorption technologies for heat transformation [2].

By now, the adsorptive heat transformation (AHT) has made spectacular progress, and several adsorptive chillers/heat pumps have already appeared in the market [3], [4]. These units are commonly driven by a temperature difference between the ambient (280–310 K) and an external heat source (330–450 K) which is used for adsorbent heating and regeneration. In this communication, we consider the possibility to use for heat upgrading the temperature difference between two natural thermostats, both being at low temperature (near 0–20 °C or below). They can be, for instance, the ambient air (TL) and a natural water reservoir (TM), like ocean, sea, river, lake and underground water. Heat from the water basin has no commercial value and is available for free. In cold countries during winter time, the T-difference between these thermostats can reach 30 °C and more, thus having a potential to produce a work.

The maximal work is determined by the second law of thermodynamics (SLT) as W = Q (1  TL/TM) [5], where Q is the amount of heat supplied from a thermostat at temperature TM, TL is the temperature of a heat sink that is the ambient air. Indeed, at TM = 2 °C = 275 K, that is a typical winter temperature of water in rivers, lakes, etc. in cold countries, and the ambient temperature TL = −30 °C (243 K) and −50 °C (223 K), the efficiency of this two temperature cycleηSLT=1-TM/TLequals 0.116 and 0.189, respectively (Fig. 1a). It seems quite encouraging, especially if keep in mind that the heat Q at TM is consumed for free. Afterwards, this work can be used to upgrade the temperature of heat taken from the water basin up to a higher level (TH) sufficient for heating, thus gaining commercial value. The SLT efficiency of such three temperature (3T) heat transformer can be determined if consider two Carnot machines [6], [7]ηSLT=(1/TL-1/TM)/(1/TL-1/TH).

The function ηSLT(TL) is calculated at various temperatures TM of the water basin under the assumption of a constant temperature lift (TH  TM) = 30 K (Fig. 1b). The estimated efficiencies are quite encouraging and demonstrate that this 3T cycle can, in principle, be of practical interest. Of course, AHT units do not produce and consume work, but operate only with heat fluxes, however, have the same thermodynamic limits as the two Carnot machines.

In this communication, a new AHT cycle driven by the temperature difference between two natural heat reservoirs is suggested for upgrading the ambient heat. Since the useful heat that gains commercial value is obtained by means a low ambient temperature, the new approach is called “Heat from Cold” (HeCol). It can be interesting for countries with cold climate, and especially for the Arctic zone.

Section snippets

Description of the new cycle

A common 3T adsorptive cycle for cooling and heat pumping operates between three thermostats with temperatures TL, TM and TH, and consists of two isosters and two isobars (Fig. 2a). The heat supplied from an external heat source at temperature TH is used for heating adsorbent and removing adsorbed refrigerant (regeneration stage). This temperature has to be at least 50–60 °C [8], but commonly it is 80–100 °C [1], [4].

The simplest 3T HeCol cycle also operates between three thermostats with

Conclusions

A new adsorptive cycle for upgrading the ambient heat is suggested and briefly analyzed. The main feature of this cycle is that regeneration of adsorbent is performed by isothermal dropping the vapour pressure over adsorbent, which is ensured by low ambient air temperature. The colder the ambient air the easier the regeneration, therefore the new approach is called “Heat from Cold” (HeCol). It can be interesting for territories with cold climate (the Northern parts of the USA, Canada, Europe

Acknowledgement

The author thanks the Russian Science Foundation for financial support of this study (grant no. 16-19-10259).

References (17)

There are more references available in the full text version of this article.

Cited by (53)

View all citing articles on Scopus
View full text